Pseudotsuga menziesii var. glauca



INTRODUCTORY

SPECIES: Pseudotsuga menziesii var. glauca
AUTHORSHIP AND CITATION:
Steinberg, Peter D. 2002. Pseudotsuga menziesii var. glauca. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

FEIS ABBREVIATION:
PSEMENG
PSEMEN

SYNONYMS:
Pseudotsuga menziesii var. glauca (Beissn.) Franco [120]
Pseudotsuga menziesii var. glauca (Mayr) Franco [90]

NRCS PLANT CODE [259]:
PSMEG

COMMON NAMES:
Rocky Mountain Douglas-fir
inland Douglas-fir
interior Douglas-fir [116]

TAXONOMY:
The currently accepted scientific name of Douglas-fir is Pseudotsuga menziesii (Mirbel) Franco (Pinaceae) [90,138,267]. This FEIS summary focuses Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Mayr) [138,267]. Coast Douglas-fir (Pseudotsuga menziesii var. menziesii) is the other recognized variety [120,138,267]. Intermediate forms and "clinal variation" in some characteristics exist where the varieties' ranges overlap [197]. There is also much variation within Rocky Mountain Douglas-fir [53], but analyses of variation in volatile leaf oils [222] and at enzyme loci have shown that splitting of varieties is in accord with the species' phylogeny. However, 1 population in Mexico did not cluster with either variety in the genetic analysis at enzyme loci [156].

Information presented in this species summary pertains to Rocky Mountain Douglas-fir, and the variety will be referred to by its full common name. When information pertains to the species as a whole, the common name Douglas-fir is used.

LIFE FORM:
Tree

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
No entry


DISTRIBUTION AND OCCURRENCE

SPECIES: Pseudotsuga menziesii var. glauca
GENERAL DISTRIBUTION:
Rocky Mountain Douglas-fir is native to the inland mountains of the Pacific Northwest and the Rocky Mountains from central British Columbia south to northern and central Mexico [119,138,267]. Its range is fairly continuous from central British Columbia south through eastern Washington and eastern Oregon to central Idaho, western Wyoming, and western Montana; it is restricted to mountain topography in Utah, Nevada, Colorado, New Mexico, Arizona, and northern and central Mexico [115]. Populations of Rocky Mountain Douglas-fir are very isolated in Texas, Coahuila, Nuevo Leon, Zacatecas, Durango, Chihuahua, and Sonora [117]. The Flora of North America provides a distributional map of Rocky Mountain Douglas-fir [90].

Coast Douglas-fir occurs naturally in British Columbia (generally west of the Continental Divide [53]), western Washington, western Oregon, California, and western Nevada [138].

ECOSYSTEMS [97]:
FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES22 Western white pine
FRES23 Fir-spruce
FRES24 Hemlock-Sitka spruce
FRES25 Larch
FRES26 Lodgepole pine
FRES29 Sagebrush
FRES34 Chaparral-mountain shrub
FRES35 Pinyon-juniper
FRES36 Mountain grasslands
FRES37 Mountain meadows

STATES:

AZ CO ID MT WY NM
NV OR TX UT WA
AB BC
MEXICO

BLM PHYSIOGRAPHIC REGIONS [38]:
5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range
8 Northern Rocky Mountains
9 Middle Rocky Mountains
10 Wyoming Basin
11 Southern Rocky Mountains
12 Colorado Plateau
13 Rocky Mountain Piedmont
16 Upper Missouri Basin and Broken Lands

KUCHLER [152] PLANT ASSOCIATIONS:
K002 Cedar-hemlock-Douglas-fir forest
K011 Western ponderosa forest
K012 Douglas-fir forest
K013 Cedar-hemlock-pine forest
K014 Grand fir-Douglas-fir forest
K015 Western spruce-fir forest
K016 Eastern ponderosa forest
K018 Pine-Douglas-fir forest
K019 Arizona pine forest
K020 Spruce-fir-Douglas-fir forest
K021 Southwestern spruce-fir forest
K022 Great Basin pine forest
K023 Juniper-pinyon woodland
K031 Oak-juniper woodland
K032 Transition between K031 (oak-juniper woodland) and K037 (mountain-mahogany-oak scrub)
K038 Great Basin sagebrush
K055 Sagebrush steppe

SAF COVER TYPES [80]:
205 Mountain hemlock
206 Engelmann spruce-subalpine fir
210 Interior Douglas-fir
211 White fir
212 Western larch
213 Grand fir
215 Western white pine
216 Blue spruce
217 Aspen
218 Lodgepole pine
219 Limber pine
220 Rocky Mountain juniper
222 Black cottonwood-willow
224 Western hemlock
227 Western redcedar-western hemlock
228 Western redcedar
235 Cottonwood-willow
237 Interior ponderosa pine
252 Paper birch

SRM (RANGELAND) COVER TYPES [242]:
101 Bluebunch wheatgrass
102 Idaho fescue
103 Green fescue
104 Antelope bitterbrush-bluebunch wheatgrass
105 Antelope bitterbrush-Idaho fescue
107 Western juniper/big sagebrush/bluebunch wheatgrass
110 Ponderosa pine-grassland
302 Bluebunch wheatgrass-Sandberg bluegrass
303 Bluebunch wheatgrass-western wheatgrass
304 Idaho fescue-bluebunch wheatgrass
305 Idaho fescue-Richardson needlegrass
306 Idaho fescue-slender wheatgrass
309 Idaho fescue-western wheatgrass
311 Rough fescue-bluebunch wheatgrass
312 Rough fescue-Idaho fescue
313 Tufted hairgrass-sedge
314 Big sagebrush-bluebunch wheatgrass
315 Big sagebrush-Idaho fescue
316 Big sagebrush-rough fescue
317 Bitterbrush-bluebunch wheatgrass
318 Bitterbrush-Idaho fescue
319 Bitterbrush-rough fescue
320 Black sagebrush-bluebunch wheatgrass
321 Black sagebrush-Idaho fescue
322 Curlleaf mountain-mahogany-bluebunch wheatgrass
323 Shrubby cinquefoil-rough fescue
324 Threetip sagebrush-Idaho fescue
401 Basin big sagebrush
402 Mountain big sagebrush
403 Wyoming big sagebrush
404 Threetip sagebrush
405 Black sagebrush
406 Low sagebrush
409 Tall forb
411 Aspen woodland
413 Gambel oak
415 Curlleaf mountain-mahogany
416 True mountain-mahogany
418 Bigtooth maple
419 Bittercherry
420 Snowbrush
421 Chokecherry-serviceberry-rose
422 Riparian
503 Arizona chaparral
504 Juniper-pinyon pine woodland
509 Transition between oak-juniper woodland and mahogany-oak association
612 Sagebrush-grass

HABITAT TYPES AND PLANT COMMUNITIES:
Rocky Mountain Douglas-fir/ponderosa pine (Pinus ponderosa) forests cover about 20 million acres (8 million ha) in Montana, Idaho, and Washington; western larch (Larix occidentalis)-Rocky Mountain Douglas-fir stands cover approximately 3.5 million acres in northern Washington, Idaho, and Montana [170]. Plant communities in which Rocky Mountain Douglas-fir are described below by region.

British Columbia: In the Similkameen Valley, British Columbia, Rocky Mountain Douglas-fir/bluebunch wheatgrass (Pseudoroegneria spicata) community types occur on southeast- and west-facing aspects between 1,600 and 3,300 feet (500 and 1,000 m); Pacific ponderosa pine (Pinus ponderosa var. ponderosa) is usually present and the dominant shrub is Saskatoon serviceberry (Amelanchier alnifolia). Rocky Mountain Douglas-fir/Idaho fescue (Festuca idahoensis) habitats occur between 1,970 and 2,950 feet (600 to 900 m); here Pacific ponderosa pine is usually dominant with Saskatoon serviceberry and bitter cherry (Prunus emarginata) in the understory. Rocky Mountain Douglas-fir/pinegrass (Calamagrostis rubescens) habitats are located approximately between 2,950 and 4,430 feet (900 to 1,350 m); Pacific ponderosa pine, Rocky Mountain lodgepole pine (Pinus contorta var. latifolia), and quaking aspen (Populus tremuloides) are seral species often present throughout stand development. Common understory associates are baldhip rose (Rosa gymnocarpa), white spirea (Spiraea betulifolia), and kinnikinnick (Arctostaphylos uva-ursi) [176]. Douglas-fir (the variety not specified) is reportedly less common in the sub-boreal hybrid spruce-Rocky Mountain lodgepole pine zone in British Columbia than it is in the rest of its range [208].

Alberta: Rocky Mountain Douglas-fir is common in foothills and lower mountain slopes in Alberta as far north as the Bow River (approximately 51° N latitude); north of the Bow River Rocky Mountain Douglas-fir stands occur only sporadically. Open (5-20% canopy cover), fire-maintained stands are common in this elevation zone. The Rocky Mountain Douglas-fir/common juniper (Juniperus communis) community type is very common on warm aspects; kinnikinnick is usually also present. Other less common community types are Rocky Mountain Douglas-fir/russet buffaloberry (Shepherdia canadensis), Rocky Mountain Douglas-fir/white spirea, Rocky Mountain Douglas-fir/prickly rose (Rosa acicularis), and Rocky Mountain Douglas-fir/Rocky Mountain juniper (Juniperus scopulorum). Open-growing Rocky Mountain Douglas-fir, Pacific ponderosa pine stands occur on south or west aspects in Kootenay National Park, with an understory of bluebunch wheatgrass, spreading dogbane (Apocynum androsaemifolium), rubber rabbitbrush (Chrysothamnus nauseosus), and Saskatoon serviceberry. Closed-canopy Rocky Mountain Douglas-fir forests are generally characterized by either ninebark (Physocarpus spp.) or boreal wildrye (Leymus innovatus) dominate the understory.  Other species in these stands are white spirea, Rocky Mountain maple (Acer glabrum), western meadowrue (Thalictrum occidentale), showy aster (Aster conspicuus), Oregon-grape (Mahonia repens), russet buffaloberry, common juniper, Saskatoon serviceberry, prickly rose, Virginia strawberry (Fragaria virginiana), common yarrow (Achillea millefolium), and kinnikinnick [2].

Montana: Pfister and others [206] describe 15 Rocky Mountain Douglas-fir habitat types in Montana.  Bunchgrasses, including Idaho fescue, rough fescue (Festuca altaica), and bluebunch wheatgrass are indicative of the 3 driest Rocky Mountain Douglas-fir types, which often occur in a mosaic with similar Pacific ponderosa pine types. The other 12 Rocky Mountain Douglas-fir habitat types in Montana are indicated by ninebark (Physocarpus malvaceus), big huckleberry (Vaccinium membranaceum), twinflower (Linnaea borealis), common snowberry (Symphoricarpos albus), pinegrass, elk sedge (Carex geyeri), white spirea, kinnikinnick, common juniper, heartleaf arnica (Arnica cordifolia), and mountain snowberry (Symphoricarpos oreophilus) [206]. 

Rocky Mountain Douglas-fir/ninebark, Rocky Mountain Douglas-fir/big huckleberry, subalpine fir (Abies lasiocarpa)/beargrass (Xerophyllum tenax), and subalpine fir/fool's huckleberry (Menziesia ferruginea) habitat types make up "more than half the forested landscape in west-central Montana" [142]. In the Rocky Mountain Douglas-fir/ninebark habitat type, Pacific ponderosa pine, Rocky Mountain lodgepole pine, and western larch are frequently overstory components; the shrub layer is dense and composed of ninebark, oceanspray (Holodiscus discolor), white spirea, and common snowberry (Symphoricarpos albus). Herbaceous species include starry Solomon's-seal (Maianthemum stellatum), western meadowrue, heartleaf arnica, and elk sedge [206]. In the Rocky Mountain Douglas-fir/big huckleberry type the overstory has a similar composition; abundant understory species include those listed for the Rocky Mountain Douglas-fir/ninebark type as well as beargrass, white spirea, and kinnikinnick. Rocky Mountain Douglas-fir is a minor seral species in the subalpine fir/beargrass habitat type; Rocky Mountain lodgepole pine and subalpine fir are climax; Engelmann spruce and whitebark pine (Pinus albicaulis) are minor seral species as well [257]. In the subalpine fir/fool's huckleberry habitat type subalpine fir and, to a lesser extent, Engelmann spruce are climax; Rocky Mountain lodgepole pine, Rocky Mountain Douglas-fir, and western larch are long-persisting seral species. Understory species present are alders (Alnus spp.), huckleberries (Vaccinium spp.), and beargrass [206].

In southwestern Montana and Idaho Rocky Mountain Douglas-fir has increased on mountain big sagebrush (Artemisia tridentata ssp. vaseyana) communities. These sites are generally classified as the Rocky Mountain Douglas-fir/pinegrass-rough fescue phase [19,20]. 

On the west side of Glacier National Park and in other wet areas of the state, Rocky Mountain Douglas-fir, western larch, western white pine (Pinus monticola), and Rocky Mountain lodgepole pine are seral to western redcedar (Thuja plicata) and western hemlock (Tsuga heterophylla) [104]. Important understory species in these western hemlock and western redcedar communities are oak fern (Gymnocarpium dryopteris), wild ginger (Asarum caudatum), fool's huckleberry, queencup beadlily (Clintonia uniflora), drops-of-gold (Disporum hookeri), threeleaf foamflower (Tiarella trifoliata), and violets (Viola spp.) [64]. Fireweed (Epilobium angustifolium), Scouler's willow (Salix scouleriana), thimbleberry (Rubus parviflorus), Saskatoon serviceberry, Rocky Mountain maple, and ceanothus (Ceanothus spp.) are important early seral understory species in these communities [206].

In the Sweetgrass Hills near the Alberta border, Rocky Mountain Douglas-fir grows with hybrid spruce (Picea glauca × P. engelmannii), Rocky Mountain maple, Saskatoon serviceberry, Oregon-grape, prince's pine (Chimaphila umbellata), common juniper, russet buffaloberry, and white spirea; forbs present include twin arnica (Arnica sororia), rock clematis (Clematis columbiana), summer coralroot (Corallorhiza maculata), Virginia strawberry, northern bedstraw (Galium boreale), Richardson's geranium (Geranium richardsonii), Davis' stickseed (Hackelia deflexa), spearleaf stonecrop (Sedum lanceolatum), starry Solomon's-seal, and western meadowrue [255].

Idaho: Between 2,300 and 4,500 feet (700 to 1,400 m) in the northern part of the state Rocky Mountain Douglas-fir habitat types are common, with the understory indicator species including common snowberry, big huckleberry, dwarf huckleberry, white spirea, pinegrass, elk sedge, Idaho fescue, and bluebunch wheatgrass. The more ubiquitous understory associates are Idaho fescue, rough fescue, beargrass, Saskatoon serviceberry, baldhip rose, Oregon-grape, and elk sedge. Common tree associates are Pacific ponderosa pine, western larch, and Rocky Mountain lodgepole pine. Rocky Mountain Douglas-fir is well-represented in subalpine fir climax stands where they occur below approximately 6,000 feet (1,800 m); other trees commonly present include Engelmann spruce, western larch, Rocky Mountain lodgepole pine, western white pine, and grand fir. Understory species in these stands are queencup beadlily, threeleaf foamflower, Idaho goldthread (Coptis occidentalis), western meadowrue, fool's huckleberry, and huckleberries. On moist sites between 1,500 and 6,300 feet (460 to 1,920 m) grand fir is climax, and Rocky Mountain Douglas-fir is seral in most types. Forbs, grasses, and shrubs are a mix of those listed for subalpine fir and Rocky Mountain Douglas-fir climax types [64]. On the Clearwater National Forest, grand fir/Oregon boxwood (Paxistima myrsinites) or grand fir/fool's huckleberry habitat types occur on north slopes and Rocky Mountain Douglas-fir/ninebark on drier aspects [30]. Rocky Mountain Douglas-fir is a major seral species in western hemlock-western redcedar stands with species compositions much like those described above for Montana [64].

In eastern Idaho (and western Wyoming) Rocky Mountain Douglas-fir habitat types listed above are present as well as Rocky Mountain Douglas-fir/Rocky Mountain maple, Rocky Mountain Douglas-fir/mountain ninebark (Physocarpus monogynus), Rocky Mountain Douglas-fir/sweetcicely (Osmorhiza berteroi), and Rocky Mountain Douglas-fir/ heartleaf arnica. The Rocky Mountain Douglas-fir habitat types occur at higher elevations in this part of the state, approximately between 5,400 and 7,500 feet (1,600 to 2,300 m) [247]. These are generally drier than similar types in northern Idaho; limber pine (Pinus flexilis) and quaking aspen are present in some communities [249]. Occasionally Rocky Mountain Douglas-fir is a minor component of whitebark pine stands [247]. Rocky Mountain Douglas-fir, with hybrid spruce and Rocky Mountain lodgepole pine, is present in many subalpine fir types of eastern Idaho (and western Wyoming). Understory species include Utah honeysuckle (Lonicera utahensis), huckleberries, thimbleberry, red baneberry (Actaea rubra), ninebark, woodland strawberry (Fragaria vesca), Oregon boxwood, Saskatoon serviceberry, twinflower, russet buffaloberry, roses (Rosa spp.), and beargrass [247]. 

In central Idaho Rocky Mountain Douglas-fir is particularly widespread, occurring in lower middle elevation sites adjacent to steppe vegetation as well as in open-canopy lower timberline stands with limber pine. Western larch is not as common in this part of the state. Many of the stands are savannah-like. Grand fir-Rocky Mountain Douglas-fir types like those above also occur in this part of the state [249].

Washington: In the Okanogan National Forest of north-central Washington, Rocky Mountain Douglas-fir occurs in open Pacific ponderosa pine/beardless wheatgrass (Pseudoroegneria spicata ssp. inermis) communities; other Rocky Mountain Douglas-fir habitat types are indicated by antelope bitterbrush (Purshia tridentata), kinnikinnick, pinegrass, huckleberries, common snowberry, mountain snowberry, Oregon boxwood, and ninebark. Rocky Mountain Douglas-fir is seral in subalpine fir habitat types with the important understory species including huckleberries, twinflower, Oregon boxwood, pinegrass, and Cascade azalea (Rhododendron albiflorum); it is also present in Engelmann spruce/horsetail (Equisetum spp.) and whitebark pine/pinegrass habitat types. Most Douglas-fir habitat types occur between 2,500 and 4,500 feet (760 to 1,400 m) but in some cases as low as 1,500 feet (460 m) and as high as 6,000 feet (1,800 m) [269]. On the east side of the Cascades in Gifford Pinchot National Forest, Rocky Mountain Douglas-fir, on dry sites, grows in nearly pure stands; shrub species present include vine maple (Acer circinatum), California hazel (Corylus cornuta var. californica), creeping snowberry (Symphoricarpos mollis), Saskatoon serviceberry, and redstem ceanothus (Ceanothus sanguineus). Forbs, grasses and sedges include longpod stitchwort (Minuartia macrocarpa), broadleaf starflower (Trientalis borealis ssp. latifolia), white hawkweed (Hieracium albiflorum), western fescue (Festuca occidentalis), and Columbia brome (Bromus vulgaris). On wetter sites in this area grand fir is almost always climax with Rocky Mountain Douglas-fir a subdominant seral species. Shrubs in these communities are oceanspray, vine maple, creeping snowberry, California hazel, dwarf Oregon-grape (Berberis nervosa), Pacific dogwood (Cornus nuttallii), thimbleberry, or huckleberries; pinegrass and elk sedge are common herbaceous species [258]. 

Wyoming: Adjacent to grasslands in the Yellowstone National Park area, Rocky Mountain Douglas-fir occurs in many-aged (up to 500 years) stands classified as Rocky Mountain Douglas-fir/common snowberry or Rocky Mountain Douglas-fir/pinegrass habitat types [32]. In the Bighorn Mountains Rocky Mountain Douglas-fir grows with subalpine fir with the following understory species: whitestem gooseberry (Ribes inerme var. klamathense), common juniper, mountain snowberry, spike fescue (Leucopoa kingii), bluegrasses (Poa spp.), heartleaf arnica, northern bedstraw, oxford ragwort (Senecio streptanthifolius), starry Solomon's-seal, Oregon-grape, prickly rose, sheep fescue (Festuca ovina), weedy milkvetch (Astragalus miser), silvery lupine (Lupinus argenteus), Pacific anemone (Anemone multifida), arrowleaf balsamroot (Balsamorhiza sagittata), rock clematis (Clematis columbiana var. tenuiloba), fernleaf biscuitroot (Lomatium dissectum), and mountain ninebark. Rocky Mountain Douglas-fir has invaded big sagebrush grasslands in the Bighorn Mountains, much as it has in Idaho and Montana [122]. Rocky Mountain Douglas-fir is sometimes present as a seral component (often minor) in some whitebark pine communities [257].

Colorado: Riparian woodlands in the mountains of western Colorado are dominated by white fir (Abies concolor), Colorado blue spruce (Picea pungens), quaking aspen, ponderosa pine, narrowleaf cottonwood (Populus angustifolia), and Rocky Mountain Douglas-fir [29]. Mixed conifer stands are generally above 8,000 feet in Arizona, New Mexico, and southwestern Colorado [84]. Rocky Mountain Douglas-fir is occasionally present in dry Rocky Mountain juniper communities that are classified as Rocky Mountain Douglas-fir/Ross' sedge (Carex rossii), Rocky Mountain Douglas-fir/elk sedge, Rocky Mountain Douglas-fir/ninebark, or Rocky Mountain Douglas-fir/fivepetal cliffbush (Jamesia americana). Associated species in these communities include common juniper, mountain ninebark, western yarrow (Achillea millefolium var. occidentalis), bluebell bellflower (Campanula rotundifolia), brittle bladder-fern (Cystopterus fragilis), Laguna mountain alumroot (Heuchera bracteata), cutleaf anemone (Pulsatilla ludoviciana), diamondleaf saxifrage (Saxifraga rhombiodea), Oregon boxwood, Woods' rose (Rosa woodsii), mountain snowberry, elk sedge, Dore's needlegrass (Achnatherum nelsonii ssp. dorei), western pearlyeverlasting (Anaphalis margaritacea), flexile milkvetch (Astragalus flexuosus), clematis (Clematis spp.), northern bedstraw, and cliffbush. Rocky Mountain Douglas-fir is an occasional seral component of interior ponderosa pine community types wherein true mountain-mahogany (Cercocarpus montanus), antelope bitterbrush, mountain muhly (Muhlenbergia montana), Ross' sedge, and spike fescue (Festuca kingii) are dominant understory species. Rocky Mountain Douglas-fir is occasionally present in limber pine/common juniper and lodgepole pine/russet buffaloberry habitat types [118]. On the Routt and White River National Forest of northwestern Colorado the Rocky Mountain Douglas-fir/Oregon boxwood habitat type is common and Rocky Mountain Douglas-fir is also in Rocky Mountain lodgepole pine habitat types that have been fire protected. Shrubs in the Rocky Mountain lodgepole pine communities include Rocky Mountain maple, Saskatoon serviceberry, mountain snowberry, and dwarf bilberry (Vaccinium myrtillus); herbs present are heartleaf arnica, Engelmann's aster (Aster engelmannii), fireweed, aspen peavine (Lathyrus lanszwertii var. leucanthus), and sweetroot (Osmorhiza spp.) [123,124].

Utah: Rocky Mountain Douglas-fir forms pure, even-aged stands on moist north-facing slopes between 5,000 and 8,000 feet (1,500 to 2,400 m) [130]. More frequently it grows in white fir, quaking aspen, and Engelmann spruce-subalpine fir habitats in Utah [267]. Common understory associates where Rocky Mountain Douglas-fir is a climax in Utah (generally between 7,000 and 9,700 feet (2,190 to 2,960 m)) include junipers (Juniperus spp.), Oregon boxwood, sagebrush (Artemisia spp.), ninebark, curlleaf mountain-mahogany (Cercocarpus ledifolius), greenleaf manzanita (Arctostaphylos patula), mountain-mahogany, Gambel oak (Quercus gambelii), Oregon-grape, and mountain snowberry [172,273]. Between 6,200 and 9,200 feet (1,890 to 2,800 m) white fir gradually becomes dominant, though Rocky Mountain Douglas-fir and interior ponderosa pine are both present on most sites (the sites are too dry for Engelmann spruce or subalpine fir); major understory associates are those listed above as well as common juniper [172,273]. Rocky Mountain Douglas-fir, with quaking aspen, interior ponderosa pine, subalpine fir, white fir, and Engelmann spruce, is a common component of blue spruce climax habitat types that occur between 7,600 and 9,000 feet (2,320 to 2,740 m) [172,273]. Indicator understory species are field horsetail (Equisetum arvense) on moist sites, common juniper and Oregon-grape on drier sites. On dry southwest exposures between 9,000 and 10,200 feet (2,740 and 3,100 m) Rocky Mountain Douglas-fir is sometimes present in open-growing limber pine-Great Basin bristlecone pine (Pinus longaeva) stands; understory vegetation is highly variable and includes the shrubs listed above. Herbaceous species in upper elevation Rocky Mountain Douglas-fir communities include elk sedge, Ross' sedge, mutton grass (Poa fendleriana), Fendler's meadowrue (Thalicturm fendleri), starry Solomon's-seal, fleabane (Erigeron spp.), arrowleaf balsamroot, bottlebrush squirreltail (Elymus elymoides), fringed brome (Bromus ciliatus), common yarrow, and sticky geranium (Geranium viscosissimum) [172,273]. In the Wasatch and Bear Ranges, Rocky Mountain Douglas-fir commonly grows with quaking aspen and Saskatoon serviceberry between 6,000 and 7,580 feet (1,830 and 2,390 m). Quaking aspen and Rocky Mountain Douglas-fir in the Uinta Range occur with common juniper; understory species (in both) include common yarrow, elk sedge, blue wildrye (Elymus glaucus), and slender wheatgrass (Elymus trachycaulus ssp. trachycaulus) [188]. Rocky Mountain Douglas-fir grows along perennial streams in Zion National Park with boxelder (Acer negundo), bigtooth maple (A. grandidentatum), velvet ash (Fraxinus velutina), Fremont cottonwood (Populus fremontii), and Gambel oak [106].

Nevada: In Great Basin National Park Rocky Mountain Douglas-fir occurs with white fir, interior ponderosa pine, willows (Salix spp.), mountain snowberry, and Oregon-grape along streams [244]. 

Arizona and New Mexico: Rocky Mountain Douglas-fir-white fir stands cover a large area in the Huachuca, Rincon, Santa Rita, Santa Catalina, Chiricahua, Graham, Santa Teresa, Winchester, and Galiruo mountains. Rocky Mountain Douglas-fir and Arizona pine (Pinus ponderosa var. arizonica) are present in nearly all white fir habitat types of the area; New Mexico locust (Robinia neomexicana) is sometimes present [10,41]. In the cool and/or moist habitats, blue spruce and Engelmann spruce also occur; in drier, warmer types, limber pine, southwestern white pine (Pinus strobiformis) co-occur [10]. Understory species in the cool/moist habitats include maples (Acer spp.), Saskatoon serviceberry, Arizona walnut (Juglans major), canyon live oak (Quercus chrysolepis), silverleaf oak (Q. hypoleucoides), Gambel oak, common chokecherry (Prunus virginiana), currants (Ribes spp.), fringed brome, prairie Junegrass (Koeleria macrantha), and mutton grass [10,41]. Understory species on warm and/or dry white fir habitat types include kinnikinnick, Gambel oak, mountain snowberry, Arizona fescue (Festuca arizonica), muhly (Muhlenbergia spp.), blackberry (Rubus spp.), and Ross' sedge [10].

Rocky Mountain Douglas-fir and/or white fir are co-climax in all of the blue spruce habitat types of the region; limber pine is present on the warm, dry sites; ponderosa pine, southwestern white pine, and quaking aspen are associates on various sites. Engelmann spruce, subalpine fir, and narrowleaf cottonwood are present on cool/moist sites. On warm, dry sites understory species include kinnikinnick, common juniper, fescues (Festuca spp.), and Oregon boxwood. Understory species on warm moist sites include red-osier dogwood (Cornus sericea), Oregon-grape, Oregon boxwood, dryspike sedge (Carex foenea), northern bedstraw, Richardson's geranium, starry Solomon's-seal, fringed brome, and fescues. On cool moist sites Fendler's meadowrue, fringed brome, muhly, rockspirea (Holodiscus dumosus), Canadian white violet (Viola canadensis), bracken fern (Pteridium aquilinum), and Richardson's geranium are also present [10].

Rocky Mountain Douglas-fir occurs in all subalpine fir habitat types except the subalpine fir/mountain bluebells (Mertensia ciliata) type, which occurs on cool, wet sites. On warm, moist sites Engelmann spruce, white fir and quaking aspen also occur, with Rocky Mountain maple, Oregon-grape, common snowberry, and fringed brome in the understory. On relatively warm, dry sites southwestern white pine is also present; understory species include rockspirea, common juniper, mountain snowberry, Richardson's geranium, and Oregon boxwood. On cool dry sites with southwestern white pine, understory species include fivepetal cliffbush, orange gooseberry (Ribes pinetorum), blue elderberry (Sambucus melanocarpa), sidebells wintergreen (Orthilla secunda), fringed brome, Richardson's geranium, starry Solomon's-seal, dwarf huckleberry, and Rocky Mountain maple [10].

In Engelmann spruce habitat types of the region Rocky Mountain Douglas-fir is a common co-dominant. On relatively cool, moist sites where Rocky Mountain Douglas-fir is present co-occurring species include white fir, quaking aspen, subalpine fir, blue spruce, and occasionally Arizona pine and southwestern white pine. The understory in these communities includes Rocky Mountain maple, fringed brome, Porter's licoriceroot (Ligusticum porteri), and starry Solomon's-seal. On drier Engelmann spruce sites subalpine fir, Rocky Mountain Douglas-fir, and quaking aspen occur with Rocky Mountain maple, fivepetal cliffbush, currants, roses, and huckleberries in the understory [10]. 

In the Sangre de Cristo Mountains of northern New Mexico, Rocky Mountain bristlecone pine (Pinus aristata) is a co-climax with Rocky Mountain Douglas-fir on relatively warm, dry sites; understory species include Arizona fescue, prairie Junegrass, and mountain muhly. In high elevation limber pine/kinnikinnick habitat types Rocky Mountain Douglas-fir is a common component [10].

Arizona pine communities may be nearly pure with Rocky Mountain Douglas-fir as only a minor climax; in these communities kinnikinnick, Gambel oak, Arizona fescue, mountain muhly, Heller's sedge (Carex heliophila), and Ross' sedge are the understory. More commonly, southwestern white pine, Rocky Mountain Douglas-fir, and, to a lesser extent, limber pine are co-dominant with junipers, wavyleaf oak (Q. × pauciloba), gray oak (Q. grisea), Arizona threeawn (Aristida arizonica), bluestem (Andropogon spp.), grama (Bouteloua spp.), pine muhly (M. dubia), longtongue muhly (M. longiligula), screwleaf muhly (M. virescens), mountain muhly, Louisiana sagebrush (Artemisia ludoviciana), Oregon-grape, Arizona fescue, bluegrass, sedges (Carex spp.), Wooton's ragwort (Senecio wootonii), and goldenrod (Solidago spp.) [10].

Texas: In the Guadalupe Mountains of New Mexico and far western Texas, Rocky Mountain Douglas-fir grows with interior ponderosa pine, Colorado pinyon (Pinus edulis), southwestern white pine, chinkapin oak (Quercus muehlenbergii), Pursh's buckthorn (Frangula purshiana), quaking aspen, and mountain snowberry [49]. In the Chisos Mountains of the Big Bend area, Rocky Mountain Douglas-fir grows with Arizona cypress (Cupressus arizonica), Arizona pine, Mexican pine (Pinus cembroides), bigtooth maple, alligator juniper (Juniperus deppeana), drooping juniper (J. flaccida), Pinchot juniper (J. pinchotii), Graves' oak (Quercus gravesii), and gray oak [76,182]. 

Mexico: In the Sierra Madre Occidental in Durango and Chihuahua Rocky Mountain Douglas-fir grows with Arizona pine, piņo blanco (P. ayachuite), Durango pine (P. durangensis), Apache pine (P. engelmannii), Chihuahuan pine (P. leiophylla var. chihuahuana), piņo triste (P. luholtzi), madrones (Arbutus spp.), and junipers [92,93]. Rocky Mountain Douglas-fir also occurs in isolated populations in Coahuila, Nuevo Leon, Zacatecas, and Sonora [117].

Classification systems describing plant communities in which Rocky Mountain Douglas-fir is a dominant species are listed below:

Alberta [2]
Arizona [10,89,189]
British Columbia [2]
Colorado [73,118,123,124]
Idaho [64,247,249]
Montana [206]
New Mexico [10,73,89]
Oregon [63,132]
Utah [172,188,273]
Washington [269]
Wyoming [247]

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Pseudotsuga menziesii var. glauca
GENERAL BOTANICAL CHARACTERISTICS:
Rocky Mountain Douglas-fir is a coniferous, evergreen tree. Open-growing trees often have branches over the length of the bole, while trees in dense stands lack lower limbs. The bark on saplings is photosynthetically active, smooth, and covered with resin blisters; mature individuals have thick, deeply-furrowed, corky bark [44,88,107,130,267]. At about age 40 (in the northern Rockies), bark becomes thick and corky [44,107]. Bark thickness in the northern Rockies is about 1 inch (2.5 cm) on 12-inch (30 cm) diameter trees, and 2.5 inches (6 cm) on 24-inch (60 cm) diameter trees [1]. Monserud [184] found that bark thickness (both layers) is equal to 13% of diameter in northern Idaho and northwestern Montana, and in the eastern Cascade Range, bark thickness is equal to 0.0704+(0.1176*diameter).  Rocky Mountain Douglas-fir mature cones are 1.6 to 2.8 inches (4 to 7 cm) long [120]. Male strobili are approximately 0.8 inch (2 cm) long and females 1.2 inches (3 cm) [53]. Needles are 0.6 to 1.4 inch (15-35 mm) long [267]. Rocky Mountain Douglas-fir grows 100 to 130 feet (30 to 42 m) high [120] (occasionally up to 160 feet (48 m) [53]). Diameter seldom exceeds 5 feet (152 cm) [53,115]. The Flora of North America [90] provides morphological descriptions and identification keys for Rocky Mountain and coast Douglas-firs.

The oldest accurately-dated Rocky Mountain Douglas-fir, 930 years old, is on the El Malpais National Monument in New Mexico. This longevity is apparently an anomaly; growing on a relatively barren lava field has protected it from fire, animals, and humans [125]. Growth typically slows dramatically between 90 and 140 years of age [185].

Rocky Mountain Douglas-fir grows much more slowly than coast Douglas-fir [115] and is also more cold tolerant [53]. Its presence in variable habitats is due to genetic differentiation rather than ecological amplitude. Races with respect to tolerance of different environmental conditions are easily detected [53,156,157,213]. Differences in cold-hardiness have been observed between northern Idaho populations and northwestern Montana populations of Rocky Mountain Douglas-fir [212].

Roots: Root morphology is variable, but when unimpeded, a taproot forms within several years. "Platelike" root morphologies occur where growth is impeded. The most prominent lateral roots begin in the 1st or 2nd year of growth. Most roots in surface soil are "long ropelike laterals of secondary and tertiary origin." Fine root production is episodic in response to changing environmental conditions; average lifespan of fine roots is usually between several days and several weeks [53]. Rocky Mountain Douglas-fir in Colorado that were 22 to 24 feet (6.7 to 7.3 m) tall and 60 to 80 years old had root systems that extended 2.7 to 5 feet (0.82 to 1.52 m) vertically and 10 to 21 feet (3 to 6.4 m) laterally [39]. In a 27 to 53 inch- (69 to 135 cm) deep soil taproots were 50% of final depth in 3 to 5 years and 90% in 6 to 8 years [53]. Richardson [218] reported root growth rates averaging 2.9 inches (7.4 cm), ranging from 1.1 to 6 inches (2.8- 15.3 cm), per year in Rocky Mountain Douglas-fir near Merritt, British Columbia; rates were lower than others had reported because soil water and texture were highly variable and coarse fragments limited growing space.

Rocky Mountain Douglas-fir is ectomycorrhizal [110] and sometimes ectendomycorrhizal; 2,000 fungal associates have been reported. Colonization is not inoculum-limited except in nursery conditions [53].

RAUNKIAER [210] LIFE FORM:
Phanerophyte

REGENERATION PROCESSES:
Breeding system: Rocky Mountain Douglas-fir is monoecious [53].

Pollination: Pollen cones are typically restricted to or more abundant on lower branches. Pollen cones develop over 1 year and wind-dispersed pollen is released for several weeks in the spring [11].

Seed production: Douglas-fir (both varieties) produces abundant crops of seed approximately every 2 to 11 years. Seed is produced annually except for "about 1 year in any 4- to 5-year period" [197]. Age at first reproduction is 12 to 15 years (both varieties). The magnitude of the cone crop is affected by the number of primordia that develop rather than by the number formed. Accordingly, the current year's crop is in large part influenced by the abortion rate of the previous year's primordia. However, even with low rates of primordia abortion, frost and insect infestation can reduce cone production [53]. Finley [87] reported estimates of the size of Rocky Mountain Douglas-fir's cone crop: in Washington and Oregon the number of cones per tree averaged 1,126 and ranged from 151 to 6,000; in British Columbia the average was 1,300 with a range of 1,000 to 4,000. Each cone contains 20 to 30 seeds [197].

Seed dispersal: Douglas-fir has winged seeds that are dispersed primarily by wind and gravity [197]. Rocky Mountain Douglas-fir seeds are disseminated about twice as far as seeds of ponderosa pine [228]. In western Montana clearcuts, Rocky Mountain Douglas-fir seeds were dispersed up to 800 feet (244 m) uphill from their source, but seedfall between 600 and 800 feet (183-244 m) was only 7% of that found in uncut stands [237]. Other studies determined that seedfall in clearcuts beyond 265 feet (80 m) from seed trees was about 3% of seedfall in uncut stands where seed trees are in close proximity [117]. According to Burns and Honkala [53] well-stocked stands have resulted from seedfall from sources 0.6 to 1.2 miles (1 to 2 km) distant, but most Douglas-fir seeds fall within 330 feet (100 m) of their source [53]. Small amounts of seeds are dispersed by mice, chipmunks, and squirrels [115,239]. Clark's nutcrackers also disperse Rocky Mountain Douglas-fir seeds. Unretrieved seeds in Clark's nutcracker caches may have a better change of establishment than wind-dispersed seed [155,256].

Seed banking: Consumption of seed by birds, mammals, and insects reduces natural regeneration of Rocky-Mountain Douglas-fir [53]. Caching of cones by red squirrels, and consumption by chipmunks, mice, voles, and birds reduces seed quantity considerably [115,239]. Between seedfall and germination, much seed is consumed by white-footed deer mice, creeping voles, chipmunks, shrews, birds, juncos, varied thrush, blue and ruffed grouse, and song sparrows [53]. Insect consumption of seed is discussed in the "Management Considerations" section of this species summary.

Germination: Most germination occurs within 150 days of seedfall, but seeds remain viable for 1 or occasionally 2 years [53]. Light exposure and, even more importantly, stratification affect the germination rate of Rocky Mountain Douglas-fir seeds [156]. In northwestern Montana, seed "soundness" averaged 39% to 43% during good seed crop years but was only 11% during poor years [237]. Average germinative capacity of Rocky Mountain Douglas-fir seed (collected in north-central Colorado) ranged from 68 to 94% under various controlled stratification periods and germination temperatures [197]. Poor seed crop years are characterized by low seed viability, possibly because of high frequency of self-fertilization [53].

Seedling establishment/growth: Coast Douglas-fir exhibits a strong preference for moist mineral soil, while Rocky Mountain Douglas-fir establishes in mineral soil and organic seedbeds less than 2 inches (5 cm) thick [53,227,228]. In western larch-Rocky Mountain Douglas-fir forests in Montana, however, natural stocking of Rocky Mountain Douglas-fir in clearcuts following site preparation was higher on undisturbed litter than on exposed surfaces [112,230]. See the 'Fire Effects' section of this summary for information on interactions of fire and seedling establishment. Bai and others [26], using constructed seedbeds with 6 treatments on seedling emergence and growth, showed that Rocky Mountain Douglas-fir germinated best in manure and fescue litter and worst in Rocky Mountain Douglas-fir litter; means and standard errors are given below:

Seed source and seedbed type Emergence (%) Emergence rate (%/day) Mortality (%) Longevity (days) Length (cm) Weight (mg/seedling)
Seed source 1

Mineral soil

48.4 (7.6) 3.23 (0.47) 49.5 (5.8) 31.5 (1.7) 12.5 (1.2) 19.5 (2.5)

Douglas-fir

12.5 (2.8) 0.29 (0.07 61.9 (13.2) 15.9 (4.0) 10.5 (1.0) 13.7 (2.6)

Ponderosa pine

55.6 (2.6) 2.28 (0.29) 58.5 (10.6) 26.8 (2.7) 10.3 (0.9) 17.1 (1.0)

Sagebrush

41.3 (5.9) 1.31 (0.22) 37.3 (4.7) 11.9 (2.0) 8.2 (0.6) 17.1 (1.5)

Fescue

75.9 (4.3) 3.19 (0.22) 43.1 (7.2) 26.8 (2.1) 10.5 (0.4) 17.5 (1.8)

Manure

82.2 (2.3) 4.62 (0.23) 29.3 (4.7) 35.6 (5.2) 12.4 (0.3) 20.0 (0.7)
Seed source 2

Mineral soil

47.8 (4.1) 3.12 (0.29) 50.1 (5.6) 29.4 (3.0) 12.4 (0.8) 19.0 (1.3)

Douglas-fir

6.6 (2.1) 0.14 (0.04) 87.5 (6.6)  14.0 (3.3) 8.6 (0.4) 12.7 (3.0)

Ponderosa pine

59.1 (2.6) 2.42 (0.15) 60.0 (5.6) 24.7 (2.2) 10.1 (0.7) 15.8 (0.8)

Sagebrush

31.6 (7.0) 1.04 (0.21) 57.8 (10.2) 16.5 (2.0) 7.9 (0.9) 11.4 (2.1)

Fescue

77.2 (2.1) 3.50 (0.16) 47.6 (3.8) 27.2 (2.3) 9.7 (0.4) 15.9 (0.7)

Manure

84.6 (2.4) 5.15 (0.17) 34.7 (5.8) 32.6 (2.0) 11.8 (0.6) 18.8 (0.4)

Seedling growth during the 1st year of establishment is slow. Seedlings are dormant from the onset of drought in summer until the following spring [53]. Seedling survival is best under partial shade in relatively dry habitats [151,227]. Establishment of Rocky Mountain Douglas-fir requires shade on southern aspects, particularly in the southern portion of its range; existing vegetation ameliorates drought and temperature extremes [53,134,229]. Coffman [62] observed survival of planted Rocky Mountain Douglas-fir in varying amounts of brush in south-central New Mexico; with brush at least 5 feet (1.5 m) away survival was 38.5%, with brush 2 to 5 (0.6 to 1.5 m) feet away survival was 47.7%, with brush 0 to 2 feet away (0 to 0.6 m) survival was 56.0%, and 66.5% of those planted under brush canopy survived (percentages are average 3-month survival for all aspects). On mesic or wet sites existing vegetation may be more inhibitive than facultative. Coast Douglas-fir grows best with weed control as competitive shading limits growth [53]. Kidd [148] observed strong negative effects of grass competition on the height, diameter and lateral leader length of Rocky Mountain Douglas-fir in a clearcut in a moist western redcedar habitat type in Idaho. Where competitive effects are predominant it is usually where grasses or sedges are rhizomatous and extract water from the same soil that Rocky Mountain Douglas-fir does [206,243].

In a clearcut in eastern Arizona at 9,100 feet (2,774 m), 6-year-old Rocky Mountain Douglas-fir averaged 21.3 inches (54 cm) tall, with a standard deviation of 9.7 inches (24.6 cm). On the same site Rocky Mountain Douglas-fir roots averaged 3.1 inches (7.9 cm) in height after the 1st growing season and averaged 7 inches (17.6 cm) tall after 5 growing seasons [133]. A study of survival and growth of seedlings planted after various types of site preparation showed that growth at post-treatment year 3 was significantly (p<0.1) less on dozer-scarified plots than on untreated control, broadcast burned, or burned pile plots [178]. On dry lower quality sites, growth of Rocky Mountain Douglas-fir is often best when seedlings have root systems and ectomycorrhizal root tips located in decaying wood or humic layers [101].

Growth is extremely slow past age 200 years, but growth rates favorably respond to thinning (mechanically or by fire) at any age [53,115]. Younger trees' growth rates are more responsive to release from competition; in central Idaho, Rocky Mountain Douglas-fir shorter than 20 feet (6 m) at time of release had higher growth rates than those taller than 20 feet  (6 m) at release [168].

Asexual regeneration: Rocky Mountain Douglas-fir does not reproduce asexually under natural conditions [53]. Cuttings for regeneration purposes have had only limited success; only trees less than 10 years old have produced cuttings that could establish. Also, cuttings that do establish generally exhibit a trailing growth habit before growing upward [117].

SITE CHARACTERISTICS:
Rocky Mountain Douglas-fir grows on a variety of sites across its wide geographic range [64,117,249]. It grows at lower elevations adjacent to and within bunchgrass communities and is also found in upper elevation subalpine forests.  It tends to be most abundant in low and middle elevation forests, where it grows over a wide range of aspects, slopes, landforms, and soils [64,73,249].

Soils: Rocky Mountain Douglas-fir grows on a wide variety of soils and parent materials. Substrates may be of igneous, sedimentary, or metamorphic origin. In some areas, particularly near the Great Plains, Rocky Mountain Douglas-fir is more common on basic parent materials such as limestone, andesite, and basalt [80,247]. In southern and central Utah, Rocky Mountain Douglas-fir shows a strong affinity for soils derived from sandstone and limestone, and often occurs on sites with shallow, rocky soils and a large amount of bare ground [277]. In the Sangre de Cristo Range, Colorado, acidic soils on north-facing slopes are dominated by Rocky Mountain lodgepole pine and/or Rocky Mountain Douglas-fir; more basic soils on southern aspects are dominated by quaking aspen or white fir [12]. In the Gros Ventre Mountains and other areas in northwestern Wyoming and Montana, pure stands of Rocky Mountain Douglas-fir develop on calcareous substrates [159].

Elevation: Rocky Mountain Douglas-fir grows "mostly" at elevations between 1,800 and 8,000 feet (550-2,440 m) in the northern part of its range [53]. In British Columbia, Douglas-fir (both varieties) grows from sea level to 2,500 feet (762 m); in Washington and Oregon it grows generally between sea level and 5,000 feet (1,520 m) (locally higher). Mesic ponderosa pine vegetation types with Rocky Mountain Douglas-fir invading generally are between 4,000 and 5,000 feet (1,219 to 1,524 m) [31]. In the central Rocky Mountains, Rocky Mountain Douglas-fir grows best between 6,000 and 8,000 feet (1,830 to 2,590 m), and between 8,000 and 9,500 feet (2,440 to 2,900 m) in the southern Rocky Mountains. Rocky Mountain Douglas-fir may grow as low as 5,100 feet (1,550 m) in canyons in central Arizona, or as high as 10,700 feet (3,262 m) on Mount Graham in southeastern Arizona [53]. In Utah Rocky Mountain Douglas-fir grows between 5,000 and 10,000 feet (1,525 to 3,050 m) [267].

Water table: Under laboratory control Rocky Mountain Douglas-fir seedlings survived non-aerated submersion for 3 days (75% survival) and 7 days (23% survival); none survived 10 days [174].

SUCCESSIONAL STATUS:
Rocky Mountain Douglas-fir is a shade-tolerant climax species in dry to moist lower and middle elevation forests but is (relatively) shade intolerant in wetter forests [64,117]. In the absence of disturbance it tends to replace interior ponderosa pine, Rocky Mountain lodgepole pine, and western larch in the northern Rockies [3,24,206]; interior ponderosa pine, Rocky Mountain lodgepole pine, limber pine, and quaking aspen in the central Rockies [24,172]; and ponderosa pine, southwestern white pine, quaking aspen, and Gambel oak in the southern Rockies [73,183].  On moist sites west of the Continental Divide western redcedar, western hemlock, spruces, and true firs replace Rocky Mountain Douglas-fir [115]. It is often a persistent seral species in grand fir and subalpine fir habitat types in the northern Rockies, in subalpine fir habitat types in the central Rockies, and in white fir habitat types in the southern Rockies [73,206,249,277].

Rocky Mountain Douglas-fir is successional to ponderosa pine and Rocky Mountain lodgepole pine but, in the absence of major disturbance, the longer-lived ponderosa pine is codominant longer than Rocky Mountain lodgepole pine [3]. Rocky Mountain Douglas-fir has invaded and increased on big sagebrush-grasslands because of decreased fire frequency, climate change, and grazing pressure [19,54]. The species has also expanded into grasslands and meadows of the southwestern United States; approximately 55% of high elevation meadows in the Jemez Mountains of northern New Mexico have been invaded by conifers since the early part of the century [68]. Rocky Mountain Douglas-fir is successional to quaking aspen and has, with other shade tolerant conifers, invaded quaking aspen stands where fire exclusion has reduced clonal reproduction [141]. Rocky Mountain Douglas-fir has also increased in open long-needled pine forests (Arizona pine, piņo blanco, Durango pine, Apache pine, Chihuahua pine, and piņo triste) in Durango and Chihuahua, Mexico [93].

The historic "ponderosa pine savannah" was, particularly in the central and northern Rocky Mountains, part of a mosaic of differing densities and species proportions resulting from temporal and spatial variability in fire regimes and climatic patterns [68,140]. Fire suppression favors increased Rocky Mountain Douglas-fir because it is less fire resistant and slower growing than ponderosa pine when juvenile [228]. In the northern part of Rocky Mountain Douglas-fir's range, in eastern Washington and Oregon, prior to settlement the mosaic of stand types was not generally observable within a 15,000 acre area. There still existed a variety of stand densities in the northern Rockies and eastern Cascade Range, but disturbance was generally larger scale [131]. Ponderosa pine forests were also heavily logged, usually by high-grading, creating higher-density and more even-aged stands, and thus making them more susceptible to increased insect and disease frequency [23].

Rocky Mountain Douglas-fir invasion and increased density on sagebrush grasslands and ponderosa pine stands have resulted from changes in fire regimes, climatic variation, selective logging, and interactions thereof over the last 100 to 150 years [26,140,228,250,252]. Today, some sagebrush communities have sapling-sized (0.8 to 5.1 inches (2 to 13 cm) in diameter) Rocky Mountain Douglas-fir mixed with the former community. On other sites, slightly older stands (7.2 to 11.8 inches (18 to 30 cm) diameter) exist, grass cover is much reduced, and remains of big sagebrush are the only evidence of the former community. In the Galena Study Area, near Butte, Montana, forested area has increased from 48% in 1878 to 75% in 1984 (of 40 reference sites) [20].

In Glacier National Park, as in other areas at the wet/cool extreme of its former range, ponderosa pine is "not reproducing," and mesic shade-tolerant conifers are replacing it. There has been a concomitant increase in fuel loading and likelihood of stand-replacing fire [164]. See the "Fire Ecology" and "Fire Effects" sections of this species summary for more information on fire's influence on succession.

Hartwell and others [109] observed forest compositional changes in 3 elevation ranges in the Bitterroot Mountains (Bass and Blodgett creeks of western Montana), showing a large increase in Rocky Mountain Douglas-fir's relative basal area in the "ponderosa pine zone;" in other zones it either decreased or was relatively constant. Their results are presented below:

Species Change in forest composition (% basal area) between 4,500 and 5,800 feet Change in forest composition (% basal area) between 5,800 and 6,900 feet Change in forest composition (% basal area) between 6,900 and 7,500 feet
1900 1995 1900 1995 1900 1995
Rocky Mountain Douglas-fir 19% 55% 24% 24% 10% 4%
Ponderosa pine 52% 26% 3% 1% ---- ----

SEASONAL DEVELOPMENT:
Meiosis and pollen development occur in late February and March, and cones typically open in April. Pollination occurs in early April, and fertilization in early June. Seed cones enlarge from March until July, and seed development continues until late August. Seed is shed in September [11].

Vegetative bud and lateral bud growth initiate in late March or April following increased enzymatic activity in March [53]. Vegetative bud burst is in late May, shoot elongation occurs in April through mid-July. Male and female cone bud primordia are present at vegetative bud break but are non-differentiable from primordia of vegetative buds until April or May [11,53]. Timing of Rocky Mountain Douglas-fir phenological events can vary greatly depending on weather, elevation, and latitude. Yearly weather variations can greatly alter timing of seedfall at a single location because cones open and release seeds as they dry [197].

Phenology of Rocky Mountain Douglas-fir in northern Idaho, western Montana, and Yellowstone Park was described as follows [232]:

 

East of continental divide (Montana and Yellowstone National Park)

West of continental divide (northern Idaho and western Montana)

Date of occurrence

Date of occurrence

Earliest Latest Average Earliest Latest Average
Bark slips March 3 May 31 May 3 March 15 June 12 May 2
Shoots start April 25 July 1 May 31 April 5 June 29 May 17
Buds burst May 10 June 22 June 5 March 27 June 19 May 23
Pollen released April 15 July 3 May 30 April 20 July 2 May 31
Pollen ends May 2 July 25 June 13 May 1 July 15 June 14
Shoots end July 1 Sept 21 July 30 June 11 Oct 21 Aug 10
Bark sticks July 6 Oct 1 Aug 16 May 20 Oct 2 Aug 12
Winter buds formed June 11 Sept 15 Aug 1 June 16 Oct 7 Aug 19
Cones full size July 11 Sept 15 Aug 13 June 10 Sept 16 Aug 6
Cones open July 26 Oct 14 Aug 25 Aug 22 Oct 5 Sept 13

FIRE ECOLOGY

SPECIES: Pseudotsuga menziesii var. glauca
FIRE ECOLOGY OR ADAPTATIONS:
Fire adaptations: In the pole and sapling stages Rocky Mountain Douglas-fir is susceptible to fire damage as bark is thin, photosynthetic, and resin-filled [67]. Trees develop fire-resistant bark in about 40 years on moist sites in the northern Rockies [88]. The thickness of the bark layers is about 12% to 13% of bole diameter in the northern Rockies [184]. Mature trees can survive moderately severe surface fires because the lower bole is covered by thick, corky bark that insulates the cambium from heat damage [1,3,88]. Fire scars are characterized by resin deposits that may increase the size of the scar in subsequent fires [44]. Rocky Mountain Douglas-fir usually forms obvious fire scars and can survive several centuries after injury, making the history of understory fire easily studied [19]. Rocky Mountain Douglas-fir is killed by crown damage; fine twigs and buds are particularly susceptible [137]. Fire resistance offered by thick bark is often offset by low-growing branches which may be retained even when shaded out and no longer green [67,88,161]. Trees that host Douglas-fir dwarf mistletoe (Arceuthobium douglasii) often accumulate dense brooms that increase likelihood of charring of the bole or torching [268].

Mature Rocky Mountain Douglas-fir is generally more fire resistant than spruces, true firs, lodgepole pine, western hemlock, western redcedar, and western white pine and slightly less fire resistant than ponderosa pine and western larch [107,265]. Rocky Mountain Douglas-fir is, however, slower growing and much less fire resistant than ponderosa pine or western larch in  sapling and pole stages [137,228,264]. High fire frequency reduces the  dominance of Rocky Mountain Douglas-fir relative to western larch and ponderosa pine because of the species' differential rates of growth and susceptibility to fire [16,88,159,228]. During pre-settlement times frequent fire often maintained ponderosa pine rather than Rocky Mountain Douglas-fir on drier sites, as Rocky Mountain Douglas-fir did not reach fire resistant size before the next fire [19]. On more mesic sites western larch was dominant as its bark is more fire resistant than ponderosa pine's and its deciduous habit allows it to recover from crown scorch more easily [228]. On moist sites Rocky Mountain Douglas-fir growth is rapid enough that some reach fire-resistant size before the next fire, allowing open stands to develop. In some grasslands and savannas, fire restricted Rocky Mountain Douglas-fir to rocky microsites with sparse herbaceous fuels. Fire suppression has allowed Rocky Mountain Douglas-fir to spread from these fire-safe sites and form extensive pole-sized stands in mountain grasslands [19].

Rocky Mountain Douglas-fir relies on wind-dispersed seeds to colonize burned areas where trees have been killed. Mineral soil exposed by burning provides a good seedbed. Seedling establishment begins a few years after fire and is restricted to within a few hundred yards of seed trees adjacent to the fire or relatively undamaged by the fire [237]. On xeric sites, Rocky Mountain Douglas-fir establishment is more successful in shade. On wet sites with thick litter layers, fire can aid establishment by reducing litter layer thickness. Oswald and others [195] observed that prescribed fire (in October) favored Rocky Mountain Douglas-fir establishment on a western redcedar/queencup beadlily habitat type by reducing the thickness of litter layers. Means are presented below. Different letters indicate means significantly different at p<0.05:

Treatment and litter depth Germination (%) Mean survival (%, 1 year) Mean height (3 yr, cm) Mean diameter (3 yr, cm)
Burned 0-1 cm 59.3a 35.5a 7.6a 0.38b
Unburned 0-1 cm 44.9b 32.8a 4.8b 0.32c
Burned 2-4 cm 41.9b 18.9b 6.9a 0.40b
Unburned 2-4 cm 6.4d 3.4c 4.9b 0.49a
Burned >4 cm 23.1c 8.1c 5.5b 0.41b
Unburned >4 cm 9.5d 3.8c 3.6b 0.31c

Fire regimes: Fire regimes in moist Rocky Mountain Douglas-fir habitat types are mixed, ranging from low to moderate severity surface fires at relatively frequent intervals (7 to 20 years) to severe crown fires at long intervals (50 to 400 years) [149]. In some areas, large fires burn at several intensities, changing with shifts in stand structure, fuel loads, topography, and weather [16]. The result is a mosaic of burn patterns. Intense crown fires or repeat fires generally favor seral associates such as quaking aspen or Rocky Mountain lodgepole pine. In the Bob Marshall Wilderness in Montana, Rocky Mountain Douglas-fir-dominated sites were converted to Rocky Mountain lodgepole pine by 3 fires at 30- to 40-year intervals. Another site in the same area was converted from a Rocky Mountain Douglas-fir-western larch forest to a forest dominated by Rocky Mountain lodgepole pine as a result of a single severe fire [94].

Northwest: Where Pacific ponderosa pine and western larch were present in open stands, mean fire return interval was 5 to 30 years. Old-growth western larch stands where Pacific ponderosa pine was not present commonly have had either mixed severity fires at 30- to 75-year intervals or stand replacing fires at mean intervals of 120 to 350 years [24]. In 1900, the ponderosa pine savanna covered about 40 million acres (16 million ha) in the United States. The stand structure persists in dry areas; in more mesic areas, Rocky Mountain Douglas-fir has or is replacing it [23]. Prior to 1900, dry Douglas-fir habitat types in the northern Rocky Mountains experienced low- to moderate-severity surface fires at less than 30-year intervals [16,206]. Where Pacific ponderosa pine is a major associate, fires at 10-year intervals were common [161]. These frequent surface fires maintained relatively open stands of Rocky Mountain Douglas-fir or, more frequently, seral stands of Pacific ponderosa pine since ponderosa pine saplings are more fire-resistant than Rocky Mountain Douglas-fir saplings [16,88,159]. Fire suppression has resulted in long fire-free periods that have allowed Rocky Mountain Douglas-fir to establish. In some areas, dense Rocky Mountain Douglas-fir thickets have formed, providing continuous ladder fuels to the crown of overstory trees. Thus, fire exclusion has increased the potential for severe, stand-replacing fires. Fire maintains ponderosa pine  on drier sites; on more mesic middle-elevation sites western larch may dominate because it can overcome crown scorch by growing a new crop of needles [228]. Stein [250] speculated that climate change over the last century has limited ponderosa pine regeneration at northern latitudes and upper elevations and in the Southwest (see below). Fires prevented Rocky Mountain Douglas-fir or grand fir from replacing ponderosa pine [23]. 

At the upper end of the Rocky Mountain Douglas-fir/pinegrass habitat type (ponderosa pine phase) in Montana, fires were mixed, sometimes spreading to crowns and occurring at an interval of 26 to 50 years, creating a many-aged structure. Conversely, moist sites on the Flathead National Forest allowed the development of even-aged classes; disturbances such as bark beetle epidemics and fire likely interacted to create the stand type. Many stands are intermediates between these 2 types. There were long fire-free periods before 1900: 41 to 97 years were the maximum fire-free intervals studied by Arno [23] in relatively moist Rocky Mountain Douglas-fir habitats of western Montana. This probably allowed some Rocky Mountain Douglas-fir development [23]. On dry Rocky Mountain Douglas-fir habitat types where limber pine is seral, limber pine (most commonly) establishes in the shade of Rocky Mountain Douglas-fir; fire when stands are young favors either grassland or an open stand of Rocky Mountain Douglas-fir [67].

Central Rocky Mountains: Fire was not as frequent as in the southern Rockies and because of this it sometimes resulted in patchy stand replacement fire in and a mixed fire regime (with mean intervals of 50 years of longer). Variable forest structure was also created by postfire regeneration in the crown fire areas. Postfire regeneration was episodic and controlled primarily by climatic factors (i. e. several age groups were in a single crown fire area). Logging has reduced the variability in ages. In central Colorado there is no evidence of high frequency surface fires as is seen in the interior ponderosa pine/bunchgrass types of the southern part of the range [140]. Fire suppression has allowed the development of dense, Rocky Mountain Douglas-fir sapling thickets and increased risk of stand replacement fire [183]. Frequent fire prevented Rocky Mountain Douglas-fir and white fir from replacing ponderosa pine. Surface fires have been excluded for about 60 to 90 years in these stands, increasing the likelihood of stand-replacing fire [23].

Southwest: A warmer, drier climate interacting with fire suppression has led to the decline of ponderosa pine/Arizona pine regeneration in the Southwest.  Swetnam and Baisan [252] state that in the southwestern United States fires in the ponderosa pine zone, in which Rocky Mountain Douglas-fir is a major component, generally occurred after several wetter years that allowed fuel accumulation, while fires in mixed conifer stands were generally not preceded by wet years but rather by extreme drought. In the Sacramento Mountains of New Mexico, mean fire interval in the ponderosa pine zone range from 3 to 11 years and 4 to 14 years in mixed conifer types; fire occurrence on these sites (since the 1500s) was correlated with Palmer drought severity indices and influenced by El-Nino southern oscillation climate patterns [47]. In the southern Rockies, frequent 8-10 year surface fires in dry Douglas-fir habitat types maintained seral stands of ponderosa pine and/or southwestern white pine [140,183].

Alberta: In the lower subalpine zone (below 6,890 feet (2,100 m) on north aspects and 5900 feet (1,800 m) on others) of Kananaskis Provincial Park near Calgary, Rocky Mountain Douglas-fir and limber pine are present on drier areas that had mean fire intervals of 90 years between 1712 and 1920. Fires were generally large, greater than 2,500 acres (>1000 ha), and were "medium to high intensity" [113].

British Columbia: Mean fire interval in the Rocky Mountain Douglas-fir biogeoclimatic zone was 92.5 years over the last "200 to 600+" years. For the same general zone the estimated average fire size was 312 acres (125 ha), with a maximum of 12,500 acres (5,000 ha) [51]. In ponderosa pine/bunchgrass types in north Kamloops, mean fire interval was 7 years "before the suppression era"; in similar communities in southern Kamloops mean fire interval was 10 years (ranging from 3 to 42 years).  In the driest Rocky Mountain Douglas-fir communities in Kamloops mean fire interval was also 10 years, ranging from 2 to 32 years [163].

Eastern Washington and eastern Oregon: In the Okanogan Highlands, approximately in the Rocky Mountain Douglas-fir and grand fir zones, mean moderate severity (moderate meaning generally surface fire with some areas of crown fire) fire interval was 22 years, with a range of 12 to 52 years. Moderate fires generally occurred after long fire-free periods with herbaceous growth and fuel accumulation. Where low-severity fire is more common western larch, Pacific ponderosa pine, and, to a lesser degree, Rocky Mountain Douglas-fir are favored over grand fir because of grand fir's canopy's proximity to the ground [5]. Western larch occurs in Rocky Mountain Douglas-fir communities that have experienced moderate- to high-severity fire that expose mineral soil and increase light penetration [3]. In the Blue Mountains fire return intervals (historically) ranged from 3 to 30 years in ponderosa pine stands. These stands now support Rocky Mountain Douglas-fir 6-12 inches (15 to 30 cm) in diameter as a result of fire exclusion [6]. Estimates for the "historic" fire return interval in eastern Washington in the Rocky Mountain Douglas-fir habitat type series include 7 to 11 years and 8 to 18 years [4]. Fires were generally large-scale, sometimes greater than 15,000 acres (6,000 ha), with variable intensities [5,131]. In the Blue Mountains of eastern Oregon and extreme southeastern Washington, fires in the Rocky Mountain Douglas-fir series are now moderate or high-severity because of fuel accumulation [4].

In the grand fir habitat type series (generally mixed conifer composition) mean fire interval was about 47 years, ranging from 25 to 100 years [3,4]. Fires in this type were variable but "moderate" severity [5]. At slightly higher elevations where grand fir and Rocky Mountain Douglas-fir are codominant, fire return intervals varied form 10 to 25 years with low-severity fire. In these forest types low-severity surface fires occurred as well as stand-replacing fires; these created openings for Rocky Mountain lodgepole pine or western larch [6].

Idaho: Northern aspects in Idaho are more likely to experience stand-replacing fires than northern aspects in Montana, because they are generally dominated by western hemlock, western redcedar, or grand fir rather than Rocky Mountain Douglas-fir [15]. On the Clearwater National Forest near Pierce, Idaho, fires in Rocky Mountain Douglas-fir stands on relatively warm aspects and grand fir-Rocky Mountain Douglas-fir stands on cool aspects were large and often severe, with few surviving overstory trees. The middle elevation mixed-conifer forests on south and west aspects have the highest fire severity in the area [30]. Arno and Davis [18] report that in stands (between 2,500 and 5,000 feet) now dominated by western hemlock and western redcedar in the Salmon-Challis National-Priest River Experimental forests, mean fire return intervals historically ranged from 50 to 150 years. Western hemlock and western redcedar are dominant on these sites where fire has been excluded. Pre-1900 forests included these climax species mixed with western white pine, western larch, Rocky Mountain Douglas-fir, grand fir, Rocky Mountain lodgepole pine, paper birch, Engelmann spruce, and Pacific ponderosa pine with the climax species. In some western white pine forests of northern Idaho, however, Rocky Mountain Douglas-fir and grand fir have increased as a result of white pine blister rust and drought. In these stands, bark beetles and root diseases in Rocky Mountain Douglas-fir have increased concomitantly [55]. Frequencies of stand-replacing and understory fires in different Rocky Mountain Douglas-fir communities of the Selway Bitterroot Wilderness Area are listed below [45]:

Forest type Elevation range (m) Aspects

Dates of earliest and latest fires

Fire intervals

Severity

Stand replacing

Understory and mixed

Earliest Latest mean number mean number
Pacific ponderosa pine/Rocky Mountain Douglas-fir 366 to 1,365 SW, S, SE 1528 1934 ---- ---- 22 127 nonlethal
Shrubfield/conifer 750 W 1880 1934 54 1 ---- ---- lethal
Rocky Mountain Douglas-fir/grand fir 1,250 to 1,798 NE, SW, W, NW 1580 1919 119 13 ---- ---- lethal and mixed
Engelmann spruce-Rocky Mountain Douglas-fir-subalpine fir 1,481 to 1,999 N, NE, NW 1589 1919 166 9 ---- ---- lethal

In dry areas of Idaho, Rocky Mountain Douglas-fir has invaded grasslands as a result of decreasing fire frequency, climate change, and grazing pressure [19,26,54]. This was observed on big sagebrush grasslands in the Lemhi Mountains of Idaho [54] and in southwestern Montana; on these sites Rocky Mountain Douglas-fir is successional to big sagebrush. Mean fire intervals were 35 to 40 years in 1910, but have been less frequent since [19].

Montana: Recently (1900 until late 1970s) in western larch/ Rocky Mountain Douglas-fir stands of Washington, Idaho, and Montana, fire intervals have been approximately 25 to 75 years-- generally longer than historic fire intervals  [170]. Accumulation of Rocky Mountain Douglas-fir has increased fire danger in ponderosa pine habitats [15]. In lower-elevation foothill Rocky Mountain Douglas-fir stands in Bighorn Canyon National Recreation Area, southeastern Montana, fire regime was mixed. Mean return interval for surface fire was 7 years and canopy fire mean interval was 31 years (since approximately 1630) [270]. In southwestern Montana, on Rocky Mountain Douglas-fir/ pinegrass habitat types, fire intervals ranged from 22 to 58 years (mean=41, n=6). In Rocky Mountain Douglas-fir/Idaho fescue habitat types, mean fire intervals ranged from 31 to 60, with a mean of 45 years. The sites had been dominated by big sagebrush, but because no fires had occurred since 1902, Rocky Mountain Douglas-fir was able to invade [19].

On 3 study sites in the Bitterroot National Forest in Montana, the Rocky Mountain Douglas-fir/bluebunch wheatgrass habitat type was dominated by Pacific ponderosa pine before 1900. Mean fire intervals were 6 years, ranging from 2 to 20 years; 11 years, ranging from 2 to 18 years; and 10 years, ranging from 2 to 18 years. At the same sites, in the Rocky Mountain Douglas-fir/ninebark habitat type (which supported ponderosa pine, Rocky Mountain Douglas-fir, Rocky Mountain lodgepole pine, and western larch before 1900), historic mean fire intervals were 7 years, ranging from 2 to 28 years; 16 years, ranging from 4 to 29; and 19 years, ranging from 2 to 28 years. Grand fir habitat types in the Bitterroot Mountains, in which western larch, Rocky Mountain lodgepole pine, and  Rocky Mountain Douglas-fir had been dominant (western larch is now sole dominant), had a mean fire interval of 17 years, ranging from 3 to 32 years [22]. On wetter grand fir mixed-conifer types, fire return interval is estimated to be 17 years in western Montana with stand-replacing fire occurring approximately every 100 to 200 years [3]. Fire intervals in Rocky Mountain Douglas-fir communities are listed below [24]:

Sample area, plot Habitat type  Aspect, slope inclination Site moisture

Old growth composition

Historic (1600-1900) mean (range) fire intervals in years Stand replacement fires detected
Ponderosa pine Western larch
Bitterroot 1,2,3 Rocky Mountain Douglas-fir/pinegrass SW, >40% Very dry present absent 49 (19 to 97) No
Lolo 1,2 Rocky Mountain Douglas-fir/pinegrass SW, >40% Very dry present absent 32 (17 to 47) No
Lolo 3 Rocky Mountain Douglas-fir/big huckleberry and pinegrass SW, >40% Moderately dry present absent 26 (7 to 51) No
Lolo 4 Rocky Mountain Douglas-fir/big huckleberry WNW, >40% Moderate present present 27 (17 to 35) Yes
Flathead 1 Rocky Mountain Douglas-fir/dwarf huckleberry Flat Moderate present absent 31 (8 to 66) Yes
Flathead 2 Rocky Mountain Douglas-fir/dwarf huckleberry Flat Moderate present present 25 to 30 Yes
Bitterroot 4 Grand fir/twinflower E, gentle Moderately moist present absent 13 (5 to 41) No
Lolo 5 Subalpine fir/queencup beadlily Flat Moist absent present 24 (9 to 42) No

In Glacier National Park, 8 sites studied in Rocky Mountain lodgepole pine, western larch, Pacific ponderosa pine, and Rocky Mountain Douglas-fir communities had mean fire intervals between 28 and 52 years (fire intervals ranged from 4 to 70 on one site to 16 to 113 years on another). Where Rocky Mountain lodgepole pine was present, stand-replacing fires had occurred at intervals between 79 and 147 years [34]. In Coram Experimental Forest subalpine fir habitat types Rocky Mountain Douglas-fir is a co-climax; before 1910 Rocky Mountain lodgepole pine was dominant but is not currently prominent because of decreased fire frequency. Fire intervals prior to 1910 for these stands are described below [69]:

Landscape position Elevation Mean (range) fire intervals
Valleys 1,000 to 1,140 m >117 years, ranging from 21 to 175 years
Montane slopes 1,200 to 1,650 m 121 years, ranging from 6 to 173 years
Lower subalpine slopes 1,575 to 1,800 m 146 years, ranging from 47 to 132 years
Upper subalpine slopes 1,800 to 1,910 m longer than 146 years, ranging from 47 to at least 175 years

Wyoming: In northwestern Wyoming cool, dry Rocky Mountain Douglas-fir likely burned every 50 to 100 years; fires were generally "thinning" surface fires. Adjacent big sagebrush communities' fire return intervals were probably shorter historically. Rocky Mountain Douglas-fir stands with seral quaking aspen burned approximately every 25 to 100 years [43]. For low-elevation sites where limber pine is seral, fire return interval was estimated at 50 to 100 years for the Yellowstone area [67]. Near Andesite Mountain in Yellowstone National Park, Rocky Mountain Douglas-fir/common snowberry and Rocky Mountain Douglas-fir/pinegrass habitat types occur in many-aged (up to 500 years) stands adjacent to grasslands. This table summarizes 3 such stands' fire histories [32]:

Elevation (m) Max age (years) Time period studied Number of fires Interval range (years) Current interval (yr) Mean fire interval
2,066 259 1766-1870 4 17-44 121 35
2,096 506 1534-1988 11 14-110 3 45
2,243 367 1756-1940 3 70-114 51 92

Utah: A survey of fire histories in Bryce Canyon National Park showed that interior ponderosa pine savannas and mixed-conifer forests (of which Rocky Mountain Douglas-fir was a major component) burned "at least once every decade and probably more often" [48]. In mixed-conifer communities in Bryce Canyon National Park there has been a decrease in fire frequency from a mean return interval of 7.5 years to 45 years since 1900; there has been a concomitant increase in white fir and Rocky Mountain Douglas-fir as well as a 200% increase in fuel accumulation. In dry Rocky Mountain Douglas-fir communities where interior ponderosa pine is potentially dominant, a fire return interval of greater than 50 years favors Rocky Mountain Douglas-fir; after 50 years fires have generally been stand-replacing [44,67]. Cooler and/or wetter Rocky Mountain Douglas-fir/Rocky Mountain lodgepole pine stands have more variable fire regimes [44]. Cool and dry Rocky Mountain Douglas-fir habitat types in central and southern Utah do not experience frequent, low-severity surface fires characteristic of the northern Rockies. These habitats are drier and typically have discontinuous ground fuels and poor grass cover that hamper fire spread [277].

Colorado: Fire regimes in Rocky Mountain Douglas-fir/interior ponderosa forest types below 8,200 feet (2,500 m) were historically likely "mixed and variable" with fires historically larger than 3.6 square miles (10 km2) occurring 50 to 60 years apart; stands were not even-aged on a landscape scale [140].  "Passive" crown fire (where crown fire occurs in a stand but does not spread to adjacent ones) was more common than "active" crown fire (where crown fire occurs and spreads from a stand) which, if it occurred, was usually very localized and confined to younger stands. When crown fire occurred it created openings. Tree recruitment thereafter was episodic and influenced by moisture [139]. Kaufman and others [139] modeled stand conditions prior to fire exclusion in the mid-elevation forests of Cheesman Lake: interior ponderosa pine (pure) patches were 35-50% of area (not as much on north slopes), interior ponderosa pine/Rocky Mountain Douglas-fir (>10% Douglas-fir canopy cover, 20% of trees are Douglas-fir) patches were 20-30% of the area, and 25% were very open (<10% canopy cover).  The fire regime and tree recruitment patterns that create this variable forest structure were [139]:

Process Mean interval (years with standard errors) Range (years)
Fires >5 km2 in 35 km2 landscape between 1496 and 1880 42.7 (12.7) 27-65
Fires in 0.5 to 2 km2 areas, 1496 to 1880 50.0 (17.2) 29-83
Tree recruitment, 1588 to 1885 45.3 (23.5) 18-82

New Mexico: In most vegetation types supporting Rocky Mountain Douglas-fir, fire is more frequent and regular (and thus lower severity) in the southern Rockies than in the central and northern Rockies. Swetnam and Baisan [252] summarize mean fire intervals in New Mexico forests between 1700-1900 as follows:

Region Stand type Mean fire interval (years with ranges)
Southeastern New Mexico Mixed conifer 9.16 (2-38), 6 (1-21)
Arizona pine/ mixed conifer 2.98 (1-15),12.29 (1-31), 7.42 (1-21), 2.93 (1-15)
Arizona pine 3.47 (1-10), 4.51 (1-18), 4.54 (1-9), 5.35 (1-16), 5.52 (1-23), 5.9 (2-19), 7.38 (1-33), 11.25 (2-33), 4.85 (1-21)
Arizona pine, pinyon, juniper, oak  6.27 (1-34)
East-central New Mexico (near Arizona border) Interior ponderosa pine  13.14 (1-30), 5.63 (1-12), 5.33 (1-12), 9.32 (1-25), 12 (2-31), 16.5 (3-55), 7.3 (2-21), 8.96 (2-30), 5.86 (1-17)
Interior ponderosa pine, pinyon, juniper  9.1 (2-22)
Central New Mexico (Santa Fe area) Arizona pine, pinyon, juniper  8.26 (1-25)
Mixed conifer 25.17 (1-89), 4.54 (1-12), 15.75 (1-33), 12 (3-32)
Interior ponderosa pine, mixed conifer  6.79 (1-24
4.75 (1-17)
Interior ponderosa pine 8 (1-24), 9.45 (1-21), 19.5 (4-52), 6.21 (1-21), 10.05 (2-29)
9.45 (1-21), 5.84 (1-24), 17.1 (1-46)
5.59 (1-13), 7.8 (1-28), 14.36 (4-28), 5.57 (1-12)

Arizona: Surface fires have been quite frequent in most Rocky Mountain Douglas-fir communities in Arizona. The Arizona ponderosa pine stands had fire return intervals of 2 to 10 years. A mixed conifer stand in the White Mountains burned at 22 year intervals (small fires occurred between) prior to 1900. In the Rincon Mountains there were approximately 80 fires between 1937 and 1986 in mixed-conifer stands (Rocky Mountain Douglas-fir and white fir) between 7,940 and 8,760 feet (2420 and 2670 m). Mean fire return interval for the mixed-conifer zone was 9.9 years: where fire was more frequent in this zone, quaking aspen was dominant [27].  In 2 Apache pine, Chihuahua pine, Arizona pine, Rocky Mountain Douglas-fir communities in the Chiricahua Mountains, mean fire interval between 1637 and 1876 was 3 to 4 years [136]. A site in the Chiricahua Mountains with Rocky Mountain Douglas-fir dominant and lesser amounts of southwestern white pine, interior ponderosa pine, white fir, and quaking aspen had a mean fire interval of 3 years between 1700 and 1900. Most fires occurred in late winter or spring; the documentary record of the area suggests that many were set by Native Americans [234]. Swetnam and Baisan [252] offer an extensive fire history record for sites throughout Arizona and New Mexico.

Texas: In mixed-conifer stands composed of interior ponderosa pine, southwestern white pine, Rocky Mountain Douglas-fir, and Colorado pinyon in the Guadalupe Mountains, mean fire return interval was 4.7 years, with a maximum of 30 years, probably result of livestock grazing. Most fires were low severity surface fires [7]. In the Chisos Mountains in the Big Bend area, Rocky Mountain Douglas-fir grows with Arizona cypress, interior ponderosa pine, Mexican pinyon, bigtooth maple, junipers, gray oak, and Graves' oak; the communities have a mean fire return interval of 70 years (between 1770 and 1940) but its range is "wide" [182]. 

Mexico: Open structure, mixed-conifer forests (Durango-fir, Arizona pine, piņo blanco, Durango pine, Apache pine, Chihuahua pine, piņo triste, madrone, and junipers) in Durango and Chihuahua, Mexico have had an increase in Rocky Mountain Douglas-fir with fire exclusion in most areas [93]. In some areas, however, such as northern Sonora and northwestern Durango, frequent fires (mean interval of 4 years) occurred into the 1970s [91]. In the 7,000-ha La Michilia Biosphere Reserve, between 1779 and 1945, fire return intervals ranged from 2 to 37 years with a mean of 9.77 years; most fires burnt over 60% of the 7,000-ha area. Highest fire frequency was in low-elevation forests rather than mixed conifer sites. Here fire exclusion has reduced fire frequency for 30 to 50 years resulting in increased fuel loading, increased density of young trees, and increased density of less fire resistant fir and Rocky Mountain Douglas-fir [93].

Fire regimes for plant communities and ecosystems in which Rocky Mountain Douglas-fir occurs are summarized below. Where this table provides information on plant communities described above, the text is generally more location-specific and more precise than the table. For further information regarding fire regimes and fire ecology of these ecosystems, see the 'Fire Ecology and Adaptation' section of the FEIS species summary for the plant community or ecosystem dominants listed below.

Community or Ecosystem Dominant Species Fire Return Interval Range (years)
grand fir Abies grandis 35-200 [17]
sagebrush steppe Artemisia tridentata/Pseudoroegneria spicata 20-70 [201]
mountain big sagebrush Artemisia tridentata var. vaseyana 15-40 [19,52,180]
Wyoming big sagebrush Artemisia tridentata var. wyomingensis 10-70 (40**) [260,272]
Arizona cypress Cupressus arizonica < 35 to 200 
western juniper Juniperus occidentalis 20-70 
Rocky Mountain juniper Juniperus scopulorum < 35 [201]
western larch Larix occidentalis 25-100 
Engelmann spruce-subalpine fir Picea engelmannii-Abies lasiocarpa 35 to > 200 
blue spruce* Picea pungens 35-200 [17]
Rocky Mountain lodgepole pine* Pinus contorta var. latifolia 25-300+ [16,221,226]
western white pine* Pinus monticola 50-200 
Pacific ponderosa pine* Pinus ponderosa var. ponderosa 1-47 
interior ponderosa pine* Pinus ponderosa var. scopulorum 2-10 
Arizona pine Pinus ponderosa var. arizonica 2-10 [17]
quaking aspen (west of the Great Plains) Populus tremuloides 7-120 [17,102,177]
mountain grasslands Pseudoroegneria spicata 3-40 (10**) [16,17]
Rocky Mountain Douglas-fir* Pseudotsuga menziesii var. glauca 25-100 [17,19,23]
western redcedar-western hemlock Thuja plicata-Tsuga heterophylla > 200 
mountain hemlock* Tsuga mertensiana 35 to > 200 [17]
*fire return interval varies widely; trends in variation are noted in the species summary
**mean

POSTFIRE REGENERATION STRATEGY [251]:
Initial off-site colonizer (off-site, initial community)
Secondary colonizer (on-site or off-site seed sources)

FIRE EFFECTS

SPECIES: Pseudotsuga menziesii var. glauca
IMMEDIATE FIRE EFFECT ON PLANT:
Fire mortality in Rocky Mountain Douglas-fir can occur via cambial damage, root damage, or crown scorch [3,107,226]. These damage indices may be highly variable across the landscape, and root damage is difficult to quantify [107,204]. Thus causal determination is limited because, by necessity, most mortality predictions or studies are based on aboveground characteristics [107,204]. In addition, postfire insect infestation of individual trees is correlated with bark and crown damage parameters [13]. An investigation of fire caused mortality in eastern Idaho and Yellowstone National Park encountered extensive variability in mortality and damage parameters: statistically, crown scorch was the best predictor of postfire mortality, but it explained very little variation (r=-.028, p<0.01) [204]. Agee [3] states that in Montana, Wyoming, and Idaho Rocky Mountain Douglas-fir is most commonly killed by crown destruction in fire and mortality is a function of both crown scorch and postfire insect damage [3].  Generally Rocky Mountain Douglas fir with greater than 60% crown scorch do not survive [193]. However, on Lubrecht Experimental Forest, mortality of Rocky Mountain Douglas-fir 8 years after a "light" surface fire in a Rocky Mountain Douglas-fir stand was best predicted by the number of quadrants of the bole with dead cambium. Secondarily, crown volume scorch was a better predictor than height of lethal scorch [226].  Shallow lateral roots can be damaged if the organic layer burns [226], but this type of damage is seldom quantified or included in mortality models [107].

The effects of fire on Rocky Mountain Douglas-fir vary with fire severity and tree size. Seedlings are most susceptible to fire damage but can live through 122 degrees Fahrenheit (50 °C) for 1 hour, 140 degrees Fahrenheit (60 °C) for  1 minute, and 158 degrees Fahrenheit  (70 °C) for 1 second [223,224]. Saplings are often killed by surface fires because their thin bark offers little protection from damage [4,265]. Photosynthetically active bark, resin blisters, closely spaced flammable needles, and thin twigs and bud scales are additional characteristics that  make saplings more vulnerable to all fires [44,88,107]. Surface fires intense enough to kill saplings by girdling them often also scorch the entire crown [271]. 

Chance of survival generally increases with tree size [4,107]. Because larger trees have thicker bark and larger crowns, they can withstand proportionally greater bole and crown damage than small trees. Following a low- to moderate-severity surface fire in an open mixed-conifer stand in Colorado, 64 out of 103 Rocky Mountain Douglas-fir trees died within 2 years. Live trees averaged 9.5 inches (24 cm) in diameter and 32 feet (9.8 m) in height, while fire-killed trees averaged 5.6 inches (14.3 cm) in diameter and 22.6 feet (6.9 m) in height [271]. Fire resistant bark develops by about age 40, but branching habit and stand density can offset this fire resistance. If branches grow (or are dead and retained) along the entire bole, as is common when the tree is open-grown, fire can climb into the crown [44,107]. If regeneration is dense and crowns overlap, the potential for canopy fire is even greater [107]. In the Yellowstone fires of 1988 Rocky Mountain Douglas-fir types had little stand replacing fire even though many fires started. Most fires started prior to curing of surface fuels: the fuel arrangement did not allow crown fire to start but carried surface fire in adjacent stands [216].  

Fuel type and arrangement, and related fire behavior, vary greatly in dry Douglas-fir habitat types. Where surface fuels are discontinuous, many trees survive burning [268]. If there are heavy fuel accumulations around bases of trees, severe cambial damage can occur from surface fires that otherwise burn primarily in the litter. Trees infested with Douglas-fir dwarf mistletoe, rust fungi (Chrysomyxa or Melampsorella), and/or needle cast fungus (Elytroderma deformans) commonly have suppressed growth and large accumulations of dead, fallen "brooms" around their base [9,198]. The branches of the brooms have a higher than normal proportion of compression wood, decreasing their susceptibility to decay and increasing the length of time that they are a fire hazard [9]. When ignited, this fine debris burns hot, girdling the bole and/or providing a fuel ladder to torch the crown [15,268].  Trees with brooms may increase fire spotting [9]. 

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
There have been a number of models to predict succession, fuel consumption, or mortality in forests that include Rocky Mountain Douglas-fir; these include CLIMACS, NONAME, and FIRESUM [3,46]. A model of mortality was developed by Ryan [223] for Rocky Mountain Douglas-fir and Pacific ponderosa pine on Lolo National Forest, Montana. Peterson and Ryan [205] modeled fire mortality in Rocky Mountain Douglas-fir for the northern Rocky Mountains for trees 15.5 m tall with diameter of 20 cm; time to cambial kill was 3.2 minutes in late summer. For a 40 cm diameter, 24.4 m tall tree, critical time to cambial kill was 13.4 minutes for the same conditions. The critical time for seedling mortality at any temperature has been modeled with the following equation (where T is temperature C°, and t is time in minutes): T= 59.44- 2.291 log e t [223]. The FIRESUM (FIRE SUccession Model) was applied to a Rocky Mountain Douglas-fir/ninebark habitat type of western Montana. With a 10-year fire return interval, predicted fireline intensities were approximately 50 to 100 kW/m; with a 20 year return interval, predicted fireline intensities were 80 to 150 kW/m; predicted fireline intensities with a 50 year return interval were 300 to 1,200 kW/m [143]. Cambial and root damage or postfire insect damage may be partial causes of the inability of crown scorch-based models to consistently accurately predict mortality [107]. 

PLANT RESPONSE TO FIRE:
Indirect postfire mortality: Douglas-fir beetle, wood borers, Douglas-fir tussock moth and western spruce budworm cause significant postfire mortality, particularly as some insect populations have increased as a result of fire suppression [5,209]. Small-scale outbreaks of Douglas-fir engraver beetles sometimes occur after "light ground fires," and root rot interacting with fire damage may also cause mortality [3,107,119,226].  On sites surveyed in Yellowstone National Park after 1988, postfire mortality was 31.7%: 18.5% from fire, 12.6% from interaction of fire, bark beetle, and wood borer, and 0.6% unidentified [209]. Postfire bark beetle infestation occurs when the phloem is not too damaged (hardened or scorched) as this condition inhibits feeding [72,129,225]. Thus the highest probability of significant postfire outbreak is in stands where most vegetation is scorched but few trunks are blackened. Bark beetles must utilize injured trees before the phloem becomes too dry for feeding [72]. Bark beetles usually used larger fire-injured trees [225]. After the Yellowstone fires of 1988 Douglas-fir beetle infestation was highest in the trees where the percentage of basal circumference killed by fire was highest [72,225]; 77% of Rocky Mountain Douglas-fir with bark beetle infestations were at least 50% girdled by fire [13]. Infestation was also more common in trees with "ample green phloem and less than 75% crown scorch" [72,225]. After a large stand-replacement fire on Shoshone National Forest, Wyoming Pasek and others [199] noted that most areas of large-diameter Douglas-fir adjacent to burned areas "likely were infested" by Douglas-fir beetle in 1990. In another postfire study in Yellowstone 83% of dead Rocky Mountain Douglas-fir were infested with wood borers and Douglas-fir beetles; 34% of living trees were infested [225]. Bark beetle populations in fire-injured trees in Yellowstone caused increased infestation of residual trees that were not fire-injured [72]. The most severely damaged trees were generally utilized in the 1st year; in following years trees with less severe damage were utilized [72,225]. Cumulative percentages of insect infestation and mortality for 4 postfire years (n=125) [225]:

 

Year

1989 1990 1991 1992
Infested 24% 62% 76% 79%
Dead 12% 37% 52% 77%

Postfire growth: Though thinning via fire can increase growth of residual trees, radial growth can be greatly reduced for up to 4 years following fire [3]. At Lubrecht Experimental Forest, western Montana, in a Rocky Mountain Douglas-fir/big huckleberry habitat type, Rocky Mountain Douglas-fir had similar growth on sites that had prescribed understory fire and those that did not [215]. On sites on the Salmon-Challis National Forest of central Idaho, Bitterroot National Forest, and Yellowstone National Park, 75% of Rocky Mountain Douglas-fir trees showed a decline in mean basal area increment over the 1st 4 postfire years (wildfires with no description given). In Rocky Mountain lodgepole pine/Rocky Mountain Douglas-fir mixed stands, postfire growth always declined when crown scorch exceeded 50% in Rocky Mountain Douglas-fir.  At these sites surviving burned Rocky Mountain Douglas-fir had the following characteristics (n=135) [204]:

  Mean Standard deviation Minimum Maximum
Diameter (cm) 35.9 15.1 13.9 109.0
Height (m) 18.1 15.1 9.0 47.0
Bark thickness (cm) 1.9 0.8 0.3 4.7
Scorch height (m) 9.7 4.8 2.5 23.0
Crown scorch (%) 40.1 26.8 0 100
Basal scorch (%) 84.0 27.5 0 100
Bark char (cm) upslope 1.00 0.78 0 5.40
Bark char (cm) downslope 0.60 0.60 0 2.10
Bark char ratio 0.45 0.31 0 1.50

Rocky Mountain Douglas-fir seedling establishment following fire is dependent on the spacing and number of surviving seed trees. Following large, stand-replacing fires, Rocky Mountain Douglas-fir seedling establishment is slow. Seedlings are restricted to the burn edge or near surviving trees within the main burn [66]. Germination of artificially sown seed was about 60% on burned seedbeds but only 10% on unburned duff [42]. On logged sites Rocky Mountain Douglas-fir establishes after slash burning, particularly where Douglas-fir is a seral species, such as in grand fir or subalpine fir habitat types, on north- and east-facing slopes [71,236]. On dry, south- and west-facing slopes some shade is often needed for seedlings to survive [112]. Many tree associates are more dependent on mineral soil for seedling establishment than Douglas-fir is. Thus burning may increase the percentage of associates such as Pacific ponderosa pine, Rocky Mountain lodgepole pine, and western larch [71].

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
In the Blue Mountains of northeastern Oregon, thinning or burning modified stand structure and tree species composition slightly in closed-canopy Rocky Mountain Douglas-fir and Pacific ponderosa pine/Rocky Mountain Douglas-fir stands in the stem exclusion stage. Stands were dominated by large (≥21 inches (53 cm) in diameter), 70- to 100-year-old, even-aged Rocky Mountain Douglas-firs and Pacific ponderosa pines, with smaller Rocky Mountain Douglas-firs that had regenerated after extensive partial cutting. Thinning removed 4- to 10-inch (10-25 cm) diameter Douglas-firs and ponderosa pines, while burning reduced the number of small-diameter Douglas-firs and killed Douglas-fir seedlings. Thin-and-burn treatments resulted in greatest reduction in basal area, reaching the targeted goal of 16.0 m˛/ha. Thin-and-burn treatments were also most successful in reducing conifer seedling density. All treatments caused minor changes in understory vegetation. The authors suggested that repeated treatments were needed in 10 to 15 years to bring stand structure and composition more in line with historical conditions. They comment that one set of treatments is not likely to mitigate nearly 80 years of fire exclusion and fuel accumulation in low-elevation, dry forests.  For further information on the effects of thinning and burning treatments on Rocky Mountain Douglas-fir and 48 other species, see the Research Project Summary of Youngblood and others' [274] study.

For further information on Rocky Mountain Douglas-fir response to fire, see the following Fire Studies:

FIRE MANAGEMENT CONSIDERATIONS:
Prescribed burning: Prescribed fire can be used for reducing fuel loadings, understory conifer reduction, or when thinning is impractical or in conflict with other uses [108]. The likelihood of ladder fuels allowing ponderosa pine mortality raises concerns about wildlife habitat and biodiversity [23]. Fire management can increase the variety of stand types and densities and reduce risk of severe fire [15]. Prescribed burning has been used to limit invasion of Rocky Mountain Douglas-fir in bunchgrass habitat types [103], and for site preparation, fuel reduction, and habitat improvement in increasingly crowded forests of the Intermountain West [149]. Low-severity surface fires generally lessen fuel loading, stimulate shrub and herbaceous growth, kill saplings, and increase plant-available nutrients in soil [21]. 

A first step to reducing  Rocky Mountain Douglas-fir cover on sites that were historically open savannas often is a "low thinning" treatment. This process mechanically removes some understory  Rocky Mountain Douglas-fir as well as suppressed members of the overstory and thus reduces the likelihood of canopy fire destroying desired overstory trees [21]. When burning understory in ponderosa pine-western larch-grand fir forests, Rocky Mountain Douglas-fir leave trees should be larger than 16 inches (40 cm) in diameter when fuels exceed 30 tons/acre (73 t/ha). Heavy fuels within 6 feet (1.8 m) of the base of leave trees should be removed [107]. Damage to desired Pacific ponderosa pine, western larch, or Rocky Mountain Douglas-fir can be minimized by moving fuel from bases of trees or prescribing fire under moist conditions [107,108]. Late summer and fall fires damage Rocky Mountain Douglas-fir foliage less than spring fires; accordingly, fires designed to eliminate encroaching saplings are often prescribed in the spring, weather permitting [203]. Predicted mortality, fuel reduction, and smoke production in a Pacific ponderosa pine-Douglas-fir stand in the Bitterroot National Forest, Montana during hypothetical low-severity prescribed fire and severe wildfire are as follows [215]:

Fuel consumption (tons per acre) Prescribed understory fire Wildfire

Duff

2.0 5.1

Small woody (0-3" diameter)

3.5 3.5

Large woody (3"+)

3.7 4.1

Canopy fuels

1.0 5.4

Particulate matter (less than 10 microns) emission (pounds per acre)

271 450

Tree mortality (%) all species by diameter

   

0-4"

91 96

4.1-8"

63 96

8.1-12"

40 79

12.1-16"

27 88

16.1"

23 80

Fuel reduction: In ponderosa pine/Rocky Mountain Douglas-fir stands, fire severity can be controlled by selecting burn conditions/days that eliminate most fine fuels but do not burn large fuels or all duff [108]. Complete duff consumption can allow excessive erosion and is thus usually avoided. Robichaud and others [220] burned a mixed western hemlock, grand fir, western white pine, western larch, and Rocky Mountain Douglas-fir stand with relatively moist conditions in late April. This reduced fuel loading and fire hazard and improved regeneration conditions by removing 50% of litter and only 22% of humus while protecting mineral soil from erosion [220]. An experimental burn in the Bitterroot National Forest provides an example of conditions that allow fuel reduction while protecting soil from erosion: fine fuel moisture was 9%, duff moisture was 50%, large woody fuel moisture was 90%; 65% of litter and "small woody fuels" was consumed and duff was reduced 20% [108]. In western larch-Rocky Mountain Douglas-fir forests in western Montana, broadcast burning in clearcuts or in standing timber can be controlled and practical when small diameter fuel (less than 4 inches (10 cm)) moisture content is between 10 and 17% [194]. Norum [193] offers "when to burn" guidelines that include the combined effects of moisture content and dead fuel loading for minimizing crown fire risk in western larch Rocky Mountain Douglas-fir stands. Fresh, cured coniferous logging slash is generally very flammable because of its loose arrangement and high percentage of needles and twigs. Flammability decreases with time, particularly as needles are compacted by winter snow. In experimental burns with 32.5 tons of slash per acre (80 t/ha) and relative humidities of 52 to 70%, the rate of fireline spread in fresh, cured Rocky Mountain Douglas-fir logging slash was 20.7 seconds/foot, while the rate of spread in 1-year-old slash was 70 seconds/foot [81]. 

Insect outbreaks: The duration and intensity, but not the frequency, of western spruce budworm epidemics have increased since 1910 [14]. Douglas-fir beetle populations and Douglas-fir dwarf mistletoe infestation have also increased [5,8]. Insect epidemics, though "naturally occurring," have been exacerbated by the presence of other insect or disease outbreaks, past high-grading timber extraction, and fire exclusion [5]. Low thinning and surface fire prescriptions that favor ponderosa pine will likely reduce the frequency and/or duration of insect outbreaks [14]. Douglas-fir dwarf mistletoe is controlled by fire [14,276]. Alexander and Hawksworth [9] state that high-severity fire controls Douglas-fir dwarf mistletoe because canopy elimination "sanitizes" the areas and trees recolonize burned sites faster than the parasite. 

Invasion of grasslands and fire: To control Rocky Mountain Douglas-fir invasion of sagebrush-bunchgrass communities, spring fires are best to kill young Rocky Mountain Douglas-fir [103,203]; the primary disadvantage to spring burning is that sometimes fuels do not dry sufficiently during this short period [103].  Gruell and others [103] provide much information on prescription specifics for sagebrush-grasslands at different degrees of  Rocky Mountain Douglas-fir invasion. Grazing can reduce fire danger by reducing fuels, and this decrease in fire frequency is in part responsible for Rocky Mountain Douglas-fir's invasion of these communities [19,54]. Fire and grazing history greatly influence the fuel buildup. In northern Idaho, Rocky Mountain Douglas-fir was more susceptible to fire damage in stands subjected to years of livestock grazing than in ungrazed stands [264]. Ungrazed stands remained open and parklike, and had a nearly continuous distribution of small fuels that carried fire well. Prescribed fires had flame lengths up to 36 inches (91 cm), but spread rapidly and only scorched the lower crowns of large trees. On grazed sites open stands were converted to dense pole stands with sparse understories and numerous sapling thickets. These stands had a greater accumulation of duff and large woody fuels that contributed little to fire spread. This resulted in a less intense but slow-spreading fire that was more damaging to trees, probably because of the long residence time [203]. Heavy grazing, however, can have the opposite effect in some cases; if unpalatable species become more dominant, probability of fire increases [278]. Published guides outline prescribed burning objectives and techniques for killing invading Rocky Mountain Douglas-fir in bunchgrass habitat types [103].

Soils: Effects of fire on soil nitrogen are variable [135]. Use of "cool" prescribed fire in moist conditions in a 250-year-old Rocky Mountain Douglas-fir, western larch, subalpine fir, Engelmann spruce stand resulted in a temporary increase in available nitrogen [135]. In 1976, Debyle [70] found that soil nitrogen decreased after prescribed fire in a clearcut Rocky Mountain Douglas-fir-western larch site; Jurgensen and others [135] stated that this was the result of the fire's high severity and surface fuel consumption. It is important to note that even where available nitrogen decreases, nitrogen fixation and other inputs compensate for this over the development of the stand [135]. Harvey and others [110] found that broadcast burning of slash (rather than "intensive removal") significantly (p<0.05) reduced the number of active ectomycorrhizal tips per tree. They suggest that when site preparation is used for natural or planted regeneration, organic layers that are less disturbed benefit the ectomycorrhizal symbiosis and nutrient uptake.

FIRE CASE STUDIES:

SPECIES: Pseudotsuga menziesii var. glauca

1st CASE STUDY:
FIRE CASE STUDY CITATION:
Crane, Marti, compiler. 1991. Prescribed fire in a western larch/Rocky Mountain Douglas-fir stand on the Lubrecht Experimental Forest, western Montana. In: Pseudotsuga menziesii var. glauca. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [ ].

REFERENCES:
Norum, Rodney A. 1975. Characteristics and effects of understory fires in western larch/Douglas-fir stands. Missoula, MT: University of Montana. 155 p. Dissertation. [191].

Norum, Rodney A. 1976. Fire intensity-fuel reduction relationships associated with understory burning in larch/Douglas-fir stands. In: Proceedings: Montana Tall Timbers fire ecology conference and fire and land management symposium; 1974 October 8-10; Missoula, MT. No. 14. Tallahassee, FL: Tall Timbers Research Station: 559-572. [192].

Norum, Rodney A. 1977. Preliminary guidelines for prescribed burning under standing timber in western larch/Douglas-fir forests. Res. Note INT-229. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 15 p. [193].

Reinhardt, Elizabeth D.; Ryan, Kevin C. 1988. Eight-year tree growth following prescribed underburning in a western Montana Douglas-fir/western larch stand. Res. Note INT-387. Ogden, UT: U.S. Department of Agriculture, Forest Service. 6 p. [214].

Ryan, Kevin C.; Peterson, David L.; Reinhardt, Elizabeth D. 1988. Modeling long-term fire-caused mortality of Douglas-fir. Forest Science. 34(1): 190-199. [226].

Stark, Nellie M. 1977. Fire and nutrient cycling in a Douglas-fir/larch forest. Ecology. 58: 16-30. [246].

Stark, N.; Steele, R. 1977. Nutrient content of forest shrubs following burning. American Journal of Botany. 64(10): 1218-1224. [245].

SEASON/SEVERITY CLASSIFICATION:
Spring and fall/low to moderately-severe

STUDY LOCATION:
The study site is the University of Montana's Lubrecht Experimental Forest located 41 miles (66 km) east of Missoula, Montana in the Garnet Mountains (north half of Section 3, T. 13 N, R. 15 W, Principal Meridian, Montana).

PREFIRE VEGETATIVE COMMUNITY:
Study plots were in a Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca)/big huckleberry (Vaccinium membranaceum) habitat type, kinnikinnick (Arctostaphylos uva-ursi) phase as described by Pfister and others [206]. Overstory trees ranged in age from 50 to 300 years; average diameter was 8.6 inches (22 cm). This stand was not vigorous and was composed primarily of Rocky Mountain Douglas-fir and western larch (Larix occidentalis) with small amounts of Rocky Mountain lodgepole pine (Pinus contorta var. latifolia) and Pacific ponderosa pine (P. ponderosa var. ponderosa). The largest, high-quality trees had been selectively logged about 50 years prior to the study. Subsequently an uneven understory of dense Rocky Mountain Douglas-fir had developed. There were a large number of widely spaced, large diameter western larch stumps indicating preharvest structure. In addition to conifers and kinnikinnick, huckleberries (Vaccinium spp.), white spirea (Spiraea betulifolia), and heartleaf arnica (Arnica cordifolia) were common in the understory [191,226].

TARGET SPECIES PHENOLOGICAL STATE:
About half of the fires occurred between May and early June after bud burst and shoot elongation initiation; the rest occurred in September and October when growth rates were probably very low and cones had already opened.

SITE DESCRIPTION:
The site is located at about 4,800 feet (1,464 m) with east to northeast exposures and slopes of 15 to 45% [214,226]. The area has warm summers and cold winters with annual precipitation of about 18 inches (470 mm), most of which falls as winter snow. Soils in the area are thin, poorly developed, sandy loams in the Holloway Series. They formed in residuum weathered from quartzite, argillite and, on these sites, contain sufficient rock to be considered talus slopes. Calcium and phosphate are limited in these soils. The site had a substantial complex fuel load including many dead small trees in understory thickets. Total dead fuel loadings ranged from 5.5 to 50 tons per acre (12.3-112.1 t/ha) [226]. 

FIRE DESCRIPTION:
Nine plots were burned in May to early July, and 11 were burned during September to mid-October with the objectives of developing techniques for controlled burning to reduce fuel accumulation and stand density [214,226]. Out of the 20 test plots broadcast burned during 1973, 9 were burned from early May to the 1st of July. The rest were burned from early September to mid-October. The average dead fuel moisture contents ranged from 8.5 to 35% and wind speeds were from 0 to 15 miles per hour (0-24 km/hr). Most plots were ignited in strips. Fire intensity on each strip was allowed to drop before the next strip was ignited. Maximum fire intensities ranged from 100 kW/m2 to 900 100 kW/m2. The herbaceous moisture content, weight of woody shrubs, weight of herbaceous material and duff moisture were variable across the landscape and were important factors in fire behavior in these stands [226]. Over 100 fire parameters were measured. 

FIRE EFFECTS ON TARGET SPECIES:
Diameter, height, average height of needle scorch, and percentage of the prefire crown volume scorched were measured on 166 burned Rocky Mountain Douglas-fir trees a few weeks after the fires. Four cambium samples per tree were taken at breast height in the spring of 1974 and tested for living tissue. In 1981 the trees were revisited, and 83 (50%) were dead. Fifty-three percent of the dead trees had been burned in spring fires and the other 47% in fall fires. Approximately 22% of the trees appeared to have died in 1974, 20% in 1975, and the other 8% during the next 6 years. Seven percent of the dead trees had no measured crown or bole damage. Mean measurements of the affected trees are organized by their 1981 status and the fire season in which they were burned and are presented below [226]:

 

Dead

Alive

Spring  Fall Spring  Fall
Diameter (inches (cm)) 6.9 (17.4) 7.3 (18.5) 8.9 (22.6) 9.5 (24.0)
Tree height (feet (m)) 42.3 (12.9) 45.9 (14.0) 51.8 (15.8) 49.8 (15.2)
Scorch height (feet (m)) 25.0 (7.6) 24.2 (7.4) 22.1 (6.7) 17.7 (3.4)
Crown volume scorched (%) 48.5 27.7 17.4 3.4
Cambial damage (number of quadrants of bole with dead cambium) 3.0 2.2 0.6 0.3

The number of dead cambium samples was the best predictor of mortality. The percentage crown scorch was a better predictor than scorch height and can be used along with tree diameter to form easily applicable models [226]. 

Three years after the fires the average cover of Rocky Mountain Douglas-fir seedlings was 0.1% on unburned plots; 0.03% on moderately burned (variable damage to shrubs and duff layer) plots; 0.17 percent on severely burned (mineral soil exposed) plots; and no seedlings established on "lightly burned" (minimal damage to shrubs and duff layer) plots [245]. Nutrient analyses of prefire and postfire soil, soil water, and some plants are described in Stark [226] and Stark and Steele [227].

Eight years after the fires, analysis of Rocky Mountain Douglas-fir radial area growth was performed [226]. Rocky Mountain Douglas-fir's relative radial increment on burned plots was about equal to that on unburned plots in the 1st year and slightly greater on burned plots thereafter. Rocky Mountain Douglas-fir's response was less positive than that of western larch. The relative radial increment of Rocky Mountain Douglas-fir trees on burned plots was greater than that of trees on unburned plots but not statistically (p>0.05) significant [214]. The average unadjusted radial growth increment of Rocky Mountain Douglas-fir trees on burned and unburned plots for the first 8 years after treatment is given below:

Year

Burned

Unburned

inches cm inches cm
1 0.021 0.053 0.021 0.054
2 0.026 0.066 0.025 0.063
3 0.03 0.075 0.031 0.079
4 0.024 0.061 0.021 0.054
5 0.024 0.062 0.023 0.059
6 0.024 0.060 0.020 0.052
7 0.024 0.061 0.019 0.049
8 0.032 0.082 0.030 0.076

FIRE MANAGEMENT IMPLICATIONS:
Underburning in similar western larch/Rocky Mountain Douglas-fir forests is feasible from a control perspective and useful for fuels reduction and thinning. After 8 years 50% of trees were dead; the best predictor of mortality was bole damage which may be at least partially controlled in prescribed fire settings. Within the range of fuel loadings in this study, fires were most manageable and still effective when the moisture content of 0- to 1-inch (0-2.5 cm) dead fuels was around 15%. Strip ignition helped overcome control and ignition problems caused by discontinuous concentrations of heavy fuels. Underburning required attention to the form, moisture status, and amount of living vegetation [226]. Detailed prescriptions for underburning are given in Norum [193].


2nd CASE STUDY:
FIRE CASE STUDY CITATION:
Crane, Marti, compiler. 1991. Prescribed fire and wildfire in a western larch/Rocky Mountain Douglas-fir stand on Miller Creek-Newman Ridge, western Montana. In: Pseudotsuga menziesii var. glauca. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [ ].

REFERENCES:
Beaufait, William R.; Hardy, Charles E.; Fischer, William C. 1977 []. Broadcast burning in larch-fir clearcuts: The Miller Creek-Newman Ridge study. Res. Pap. INT-175. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 53 p. [35].

DeByle, Norbert V. 1981. Clearcutting and fire in the larch/Douglas-fir forests of western Montana--a multifaceted research summary. Gen. Tech. Rep. INT-99. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 73 p. [71].

Shearer, Raymond C. 1975. Seedbed characteristics in western larch forests after prescribed burning. Res. Pap. INT-167. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 26 p. [235].

Shearer, Raymond C. 1976. Early establishment of conifers following prescribed broadcast burning in western larch/Douglas-fir forests. In: Proceedings, Tall Timbers fire ecology conference and fire and land management symposium; 1974 October 8-10; Missoula, MT. No. 14. Tallahassee, FL: Tall Timbers Research Station: 481-500. [236].

Shearer, Raymond C. 1982. Establishment and growth of natural and planted conifers 10 years after clearcutting and burning in a Montana larch forest. In: Baumgartner, David M., ed. Site preparation and fuels management of steep terrain: Proceedings of a symposium; 1982 February 16-16; Spokane, WA. Pullman, WA: Washington State University, Cooperative Extension: 149-157. [238].

Shearer, Raymond C. 1984. Effects of prescribed burning and wildfire on regeneration in a larch forest in northwest Montana. In: New forests for a changing world: Proceedings, Society of American Foresters convention; 1983 October 16-20; Portland, OR. Washington, DC: Society of American Foresters: 266-270. [239].

Shearer, Raymond C. 1989. Fire effects on natural conifer regeneration in western Montana. In: Baumgartner, David M.; Breuer, David W.; Zamora, Benjamin A.; [], compilers. Prescribed fire in the Intermountain region: Symposium proceedings; 1986 March 3-5; Spokane, WA. Pullman, WA: Washington State University, Cooperative Extension: 19-33. [241].

SEASON/SEVERITY CLASSIFICATION:
May through October/low to very severe

STUDY LOCATION:
Two study locations were used. The 1st contained 641 acres in the Miller Creek and Martin Creek drainages of the Flathead National Forest of northwestern Montana. This is referred to as the Miller Creek area. The 2nd location consisted of 526 acres on Newman Ridge located between Two Mile Creek and Ward Creek on the Lolo National Forest near the border of western Montana and Idaho.

PREFIRE VEGETATIVE COMMUNITY:
Most of Miller Creek was considered to be in 1 of 3 phases of the subalpine fir (Abies lasiocarpa)/queencup beadlily (Clintonia uniflora) habitat type. The fool's huckleberry (Menziesia ferruginea) phase was found on higher middle and upper north- and east-facing slopes. The beargrass (Xerophyllum tenax) phase was on drier south and west aspects and the queencup beadlily phase on most other sites. Stream bottoms belonged to the western redcedar (Thuja plicata)/queencup beadlily habitat type. The dominant conifers were Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca), western larch (Larix occidentalis), and Engelmann spruce (Picea engelmannii) with some Rocky Mountain lodgepole pine, grand fir (Abies grandis), and subalpine fir. The western larch/Rocky Mountain Douglas-fir cover type occupied over 50% of the area [35].

On Newman Ridge 7 habitat types were identified. The warmest and driest was the Rocky Mountain Douglas-fir/ninebark (Physocarpus malvaceus) habitat type on convex southwest slopes. Other habitat types included grand fir/queencup beadlily on concave east, northwest, and protected south-facing slopes; grand fir/beargrass on upper west-facing slopes; western redcedar/queencup beadlily habitat type, fool's huckleberry phase on concave north- and northeast-facing slopes; Douglas-fir/big huckleberry habitat type beargrass phase on upper south-facing slopes; subalpine fir/queencup beadlily habitat type, fool's huckleberry phase on north slopes along the ridge; and subalpine fir/beargrass habitat type, big huckleberry phase on south slopes near the ridge. Dominant conifers were Rocky Mountain Douglas-fir, larch and Rocky Mountain lodgepole pine with some Pacific ponderosa pine, grand fir, subalpine fir, western white pine (Pinus monticola), Engelmann spruce and western redcedar. The composition of prefire stands at Newman Ridge included 34% Rocky Mountain Douglas-fir [71].

TARGET SPECIES PHENOLOGICAL STATE:
Fires were prescribed in May through October affecting Rocky Mountain Douglas-fir individuals in a variety of phenological states.

SITE DESCRIPTION:
Elevation at Miller Creek ranges from 4,200 to 5,000 feet (1,280-1,524 m) with slopes averaging 24% and ranging from 9 to 35%. Soils are Andic Cryoboralfs that developed in glacial till from the argillites and quartzites of the Wallace (Belt) formation. Average precipitation is about 25 inches (640 mm) annually; approximately two-thirds falls as snow during the long cool winter. Elevation at Newman Ridge ranges from 4,400 to 5,400 feet (1,341-1,646 m) with slopes averaging 55% and ranging from 44 to 76%. Soils are Andic Cryochrepts that have developed in place or in colluvium from argillites and quartzites of the Belt formation. There is a surface loess deposit containing ash from the Mt. Mazama and Glacier Peak volcanic eruptions at both sites. Deposits are 0.5 to 2.5 inches (1-6 cm) thick at Miller Creek and 2 to 3 inches (5-8 cm) thick at Newman Ridge. Average precipitation is nearly 40 inches (1,020 mm) at Newman Ridge, of which 2/3rds falls as snow [35]. 

Sixty 10-acre (4-ha) treatment units were established at Miller Creek, and 16 units, ranging in size from 20 to 58 acres (8-24 ha), were established at Newman Ridge. The sites faced in various aspects with equal representation. The units were clearcut, slashed and burned. Fuel loads after clearcutting and before fire, excluding duff, ranged from 60 to 165 tons per acre (135-370 t/ha). Mean fuel loads are described below [35]:

Fuel class

Miller Creek fuel consumption

Newman Ridge fuel consumption

Prefire (tons/acre) Quantity burned (tons/acre) Percentage consumed Prefire (tons/acre) Quantity burned (tons/acre) Percentage consumed
needles 1.54 1.54 100 1.56 1.56 100
Duff (0 to 1 cm) 1.29 1.12 87 1.14 1.05 92
Duff (1-10 cm) 9.84 6.78 69 12.1 10.62 88
Duff (> 10 cm) 101.27 59.6 60 93.5 51.66 55
Total 113.94 69.04 61 108.29 64.89 60

FIRE DESCRIPTION:
Fires were prescribed as an assessment of site preparation and conifer regeneration techniques in western Montana. At both Miller Creek and Newman Ridge fires were prescribed on various plots throughout the year from May to October over 3 years [35]. Slash fuels were allowed to cure for an average of 9 months before burning (2 to 18 months range). Fuel moisture of 0 to 0.4 inch (0-1 cm) branchwood ranged from 5 to 21%. Burning patterns and fire severity varied among the plots burned. After broadcast burns at Miller Creek, 75% of the fuels less than 3.9 inches (10 cm) burned and 60% of the larger fuels burned. At Newman Ridge 89% of the fuels less than 3.9 inches (10 cm) burned and 55% of the larger fuels burned. Greater surface soil heating occurred at Newman Ridge than at Miller Creek because the duff layer was shallower and water content of both duff and soil was lower. The average duff reduction ranged from 36 to 70% at Miller Creek and 44 to 99% at Newman Ridge. In 1967 a wildfire burned 5 units that had been clearcut and 4 units that were uncut at Miller Creek. Average duff reduction from the wildfire was 93% with a range of 84 to 100% [35,71]. 

FIRE EFFECTS ON TARGET SPECIES:
Mortality of Rocky Mountain Douglas-fir was not assessed, but rather the usefulness of prescribed fire for site preparation and regeneration. The 1967 wildfire consumed most of the duff. Other fires were spotty and exposed some mineral soil. Fewer Rocky Mountain Douglas-fir seedlings established on unburned duff than on mineral soil. Unburned duff continued to decrease for several years, exposing bare soil on areas where the fire had left charred duff. The reasons for this decrease may include increased decomposition stimulated by warmer surface temperature during May and June where adequate moisture was present; redistribution by precipitation, runoff or wind; and oxidation. In addition to natural seeding, seeds were sown in 1967 on test plots and bare root seedlings were planted on Newman Ridge from 1970 through 1975 and on four clearcuts at Miller Creek from 1970 through 1973. Postfire seed dispersal into the clearcuts from Rocky Mountain Douglas-fir in the timber around clearcut areas was good. Over half of the seed dispersed into clearcuts at Newman Ridge was Rocky Mountain Douglas-fir. The best seed year was 1971 when 39% of the Rocky Mountain Douglas-fir seed dispersed at Newman Ridge was sound, compared with an average of 11% in other years [35,194]. The cumulative average number of sound seed of Douglas-fir from 1969 through 1974 on eight clearcuts on Newman Ridge by distance was 21,700 seeds/acre within 200 feet (61 m) of clearcut edge, 10,300 between 200 and 400 feet (61 to 122 m), 4,200 between 400 and 600 feet (122 to 183 m), and 8,400 between 600 and 800 feet (183 to 244 m) [71].

Germination of Rocky Mountain Douglas-fir began at snowmelt or soon after and was greater on mineral soil than on unburned duff more than 0.5 inch (13 mm). Seed and seedling losses were caused by rodents, drought, frost heaving, high temperatures at the soil surface and migrating juncos that ate emerging seedlings in 1968. Drought was the leading cause of mortality on south-facing slopes and second highest on other aspects. In 1978 at Miller Creek, stocking of Rocky Mountain Douglas-fir seedlings averaged 32% on burned units and 8% on unburned clearcuts. By 1984 at Miller Creek, stocking of established seedlings of Rocky Mountain Douglas-fir averaged 61% on burned units and 6% on unburned clearcuts. In 1979 at Newman Ridge, stocking of established Rocky Mountain Douglas-fir seedlings averaged 34% (range was 7% to 63%) on burned clearcuts. Aspect had a profound effect on seedling establishment: natural regeneration was lowest on south-facing slopes. The average number of established (>6 inches (15.2 cm) in height) Rocky Mountain Douglas-fir seedlings in 1984 on 37 burned units at Miller Creek and on 7 burned clearcuts at Newman Ridge by aspect was [241]:

  North East South  West
Miller Creek  

#/acre

764 746 652 1,118

#/ha

1,888 1,843 1,611 2,783
Newman Ridge  

#/acre

884 289 129 523

#/ha

2,184 714 319 1,292

Although the original stocking of Rocky Mountain Douglas-fir was less than its stocking in the original stand, new seedlings have continued to establish and stocking is becoming larger in many clearcuts. By 1984 at Miller Creek, Rocky Mountain Douglas-fir seedlings were 26% of all natural regeneration. The same year at Newman Ridge, Rocky Mountain Douglas-fir seedlings were dominant at 56% of all natural regeneration. The number of young seedlings suggests that this dominance will continue. Rocky Mountain Douglas-fir seedlings are shorter than western larch and Rocky Mountain lodgepole pine seedlings but similar in size to Engelmann spruce and taller than grand fir or subalpine fir. At Miller Creek in 1978, Douglas-fir seedlings averaged 1.8 feet (0.5 m) with a range of 6.4 to 0.5 feet (2.0-0.2 m) while at Newman Ridge in 1979, the tallest Rocky Mountain Douglas-fir seedlings averaged 2.1 feet (0.6 m). At Miller Creek regeneration varied significantly by habitat type and phase. More than twice as many Rocky Mountain Douglas-fir seedlings and saplings were growing on the western redcedar/queencup beadlily habitat type as on the queencup beadlily phase of the subalpine fir/queencup beadlily habitat type. There were 470 to 527 more stems per acre (1,161-1,302 more/ha) on the queencup beadlily phase of the subalpine fir/queencup beadlily type than on the fool's huckleberry or beargrass phases. At Newman Ridge more Douglas-fir regeneration grew on the western redcedar/queencup beadlily habitat type with the poorest Rocky Mountain Douglas-fir regeneration on the 2 Rocky Mountain Douglas-fir habitat types [241].

FIRE MANAGEMENT IMPLICATIONS:
The study demonstrates the value of prescribed fire for site preparation and Rocky Mountain Douglas-fir regeneration. During late spring and early summer, duff is usually wet and fires do not expose much mineral soil. Late summer or early fall fires are more effective at removing duff and exposing mineral soil. However, if precipitation occurs, fuels and duff need to dry for several days. At Newman Ridge, moderate severity fires removed most of the duff and prepared an adequate seedbed. At Miller Creek, the same severity fire exposed less mineral soil because the duff was thicker and wetter. Habitat type and site conditions alter the amount of duff removal needed. On mesic habitat types hot fires that expose a high proportion of mineral soil, followed by good seed years, led to overstocking. On steeper slopes with drier conditions, such as at Newman Ridge, residual duff layers have more adverse impact on the survival of seedlings. While Rocky Mountain Douglas-fir establishment during early postfire years was best on fire-exposed, mineral soil, Rocky Mountain Douglas-fir benefited least of the conifers from exposure of mineral soil. The hardest areas to regenerate at either location were the Rocky Mountain Douglas-fir habitat types at Newman Ridge. These sites were the driest areas in this study. Seed dispersal should be taken into account when deciding the time of fall fires. In a good seed year, dispersed seed could be destroyed by fires after early September at lower elevations and a few weeks later at higher elevations [35,71].

MANAGEMENT CONSIDERATIONS

SPECIES: Pseudotsuga menziesii var. glauca
WOOD PRODUCTS VALUE:
Rocky Mountain Douglas-fir is a valuable timber tree. The wood is exceptionally strong and is used for structural timber as well as poles, plywood, pulp, dimensional lumber, plywood, railroad ties, mine timbers, log cabins, posts and poles, fencing, and firewood [146,197]. Other uses listed include "machine-stress-rated lumber," finger-jointed studs, glued-laminated beams, pallets, furniture, cabinets, doors, and window frames [100].

IMPORTANCE TO LIVESTOCK AND WILDLIFE:
Livestock: Rocky Mountain Douglas-fir is poor livestock browse [78]. Rocky Mountain Douglas-fir stands have variable forage productivity; the bunchgrass habitat types, particularly the rough fescue type, are relatively productive. Generally, forage production is greatest in early succession and decreases with stand development and canopy closure. Steep topography limits livestock use in many stands [206]. Forage production in Rocky Mountain Douglas-fir habitats is as follows [132]:

Habitat type Forage production (mean with range) (pounds (dry)/ acre)
Rocky Mountain Douglas-fir/ pinegrass 300 (170-550)
Rocky Mountain Douglas-fir/ Rocky Mountain maple 150 (100-310)
Rocky Mountain Douglas-fir/mallow ninebark 275 (115-900)
Rocky Mountain Douglas-fir/ white spiraea 315 (100-500)
Rocky Mountain Douglas-fir/ common snowberry 330 (50-630)
Rocky Mountain Douglas-fir/ mountain snowberry 150 (100-300)

Big game: In general, big game use is greatest in early to mid-successional Rocky Mountain Douglas-fir stands because valuable shrub forage species' cover is reduced by shading in late successional stands [206]. Elk browsing (or lack thereof) can greatly influence shrub development in Rocky Mountain Douglas-fir stands [127].  In spring and winter (in British Columbia, Idaho, and Montana) elk use south- and southwest-facing Rocky Mountain Douglas-fir and Pacific ponderosa pine stands, particularly when shrubs and/or grasses are productive [40,206,249]. In summer, elk generally are found at higher elevations (outside the Rocky Mountain Douglas-fir and Pacific ponderosa pine zones). During fall elk use stands of Rocky Mountain lodgepole pine, subalpine fir, western larch, or grand fir with high canopy cover (>75%) [40]. Elk use of Rocky Mountain Douglas-fir is generally low if preferred species are present [95,153,154]. In parts of Yellowstone National Park elk browsing is so pervasive that young Rocky Mountain Douglas-fir are stunted at 3 to 4.5 feet (1-1.5 m) in height, with live branches trailing very close to the ground, and branches on the upper 2/3rds of the tree dead [147].

Low-elevation and south-facing open-structure Rocky Mountain Douglas-fir types are often important winter range for white-tailed and mule deer [206,249]. In a Rocky Mountain Douglas-fir/ninebark community in the Selway Bitterroot Wilderness of Idaho, white-tailed deer preferred sites that had short average distance to cover; mule deer used more open areas. White-tailed deer preferred unburned  habitat in these communities except in February when they preferred unburned Rocky Mountain Douglas-fir bunchgrass communities. Mule deer more frequently used burned portions of ninebark and bunchgrass communities [145]. Mule deer in north-central Washington showed a preference for Rocky Mountain Douglas-fir dominated conifer forests; these had an availability of 0.5% but a summer use of 9.5% and winter use of 12.0% [59]. Big game typically browse Rocky Mountain Douglas-fir in the winter or early spring when other preferred forage is lacking. Mule deer browse it more than elk do [95,153,154].

Moose winter in low-elevation Rocky Mountain Douglas-fir types in areas where willow thickets, the preferred winter habitat, are lacking; in such areas Rocky Mountain Douglas-fir is an important moose food [99]. Rocky Mountain Douglas-fir may make up a small (up to 2%) portion of bighorn sheep winter diets [144].

Small mammals: Chipmunks, mice, voles, and shrews eat large quantities of conifer seeds from the forest floor [105], and clipped cones are a staple and major part of storage of red squirrels. These animals store a large amount of Rocky Mountain Douglas-fir cones or seeds [87,105]. In the Blue Mountains of Oregon, American martens frequently use "brooms" created by rust fungi and Douglas-fir dwarf mistletoe (43%), cavities in trees (23%), and burrows in snow or hollow logs (23%) for resting sites. American marten commonly den in hollow logs. The removal of trees with brooms and other management practices aimed at reducing fuels may negatively impact marten habitat [50].

Birds: Numerous species of songbirds extract seeds from Douglas-fir cones or forage for seeds on the ground. The most common are the Clark's nutcracker, black-capped chickadee, mountain chickadee, boreal chickadee, red-breasted nuthatch, pygmy nuthatch, red-winged crossbill, white-winged crossbill, dark-eyed junco, and pine siskin [105,151,239]. Migrating flocks of dark-eyed juncos may decimate seeds and freshly germinated seedlings [151,239]. Approximately 26 species of birds feed on western spruce budworm associated with Rocky Mountain Douglas-fir [68]. Woodpeckers commonly feed in the bark of Rocky Mountain Douglas-fir [175]. Blue grouse forage on needles and buds in winter [56,169]; they and other birds rely heavily on Rocky Mountain Douglas-fir communities for cover (see below).

PALATABILITY:
The palatability of Rocky Mountain Douglas-fir to livestock is low [78]. Most livestock avoid it, but occasionally domestic sheep browse young plants [263]. Palatability to wildlife species has been rated as follows [78]:

  Colorado Montana Utah Wyoming
Pronghorn ----- ----- poor poor
Elk poor poor fair good
Mule deer poor fair fair fair
White-tailed deer ----- poor ----- fair
Small mammals fair fair good good
Small nongame birds ----- good good good
Upland game birds ----- good good good
Waterfowl ----- ----- poor poor

NUTRITIONAL VALUE:
Douglas-fir browse is not highly nutritious. Its energy and protein value are rated as fair [78]. Twig and foliage protein content in British Columbia varied between 6 and 7% throughout the year [65].

COVER VALUE:
Nongame birds: In montane forests of Colorado, Rocky Mountain Douglas-fir snags are commonly used by cavity-nesting birds [217]. Numerous species of song birds nest in Douglas-fir foliage. In central Idaho, the Rocky Mountain Douglas-fir/pinegrass and Rocky Mountain Douglas-fir/white spirea habitat types are important to nesting Steller's jays, pine siskins, western tanagers, red-breasted nuthatches, and Cooper's hawks [249]. In Montana, pileated woodpeckers prefer western larch, Pacific ponderosa pine, black cottonwood (Populus trichocarpa), and quaking aspen over Rocky Mountain Douglas-fir for nesting [175].

Game birds: Blue grouse use open, dense, and intermediate density Rocky Mountain Douglas-fir stands (pure stands or with subalpine fir, Engelmann spruce, lodgepole pine, limber pine, Rocky Mountain juniper, or quaking aspen) [56]. However, males heavily use thickets of younger Rocky Mountain Douglas-fir (average about 5 inches (12.5 cm) in diameter) that have high density (up to 1,200 trees per acre) [171]. In northeastern Utah, blue grouse were observed to prefer Rocky Mountain Douglas-fir trees for roosts during the day and subalpine fir at night [202]. Pekins and others [202] suggest that management strategies "perpetuate large trees within Douglas-fir-subalpine fir habitat in areas occupied by blue grouse." Merriam's turkeys use tall, high-canopy coverage Rocky Mountain Douglas-fir for roosts [262]. Wakeling and Rodgers [262] suggest that logging should avoid known roosts and retain 20.2 m/ha of basal area.

Raptors: Flammulated owls most commonly use old growth Rocky Mountain Douglas-fir with or without ponderosa pine because these forests have a higher insect diversity and availability, open structure, and cavities for nesting [126]. Old growth that occurs in a landscape of closed canopy forest with little habitat variety are not used as much as old growth when it occurs in complex landscape with openings and dense thickets. Where old growth occurs in forests that are predominantly closed-canopy, prescribed surface fire may augment habitat, but surface fire applied over a large area without leaving thickets probably decreases habitat quality [166]. In the River of No Return Wilderness in central Idaho, boreal owls use mixed conifer stands (39%), spruce-fir stands (25%), Rocky Mountain Douglas-fir (18%), and quaking aspen stands (18%) for breeding territories [114]. Mexican spotted owls in the San Mateo Mountains of New Mexico showed a preference for greater density of large Rocky Mountain Douglas-fir, southwestern white pine, and Gambel oak. Canopy disturbance, through stand-replacing fire or logging, may have a negative impact on Mexican spotted owl habitat [121]. Sharp-shinned hawks, great-horned owls, and Cooper's hawks also nest and/or roost in Rocky Mountain Douglas-fir [186,207].

Rocky Mountain Douglas-fir habitat types provide excellent hiding and thermal cover for deer, elk, and bighorn sheep [64]. Dittberner and Olsen [78] rate Rocky Mountain Douglas-fir cover value as "good" for mule deer, white-tailed deer, small mammals, small nongame birds, and upland game birds in Colorado, Montana, Utah, and Wyoming.

VALUE FOR REHABILITATION OF DISTURBED SITES:
Rocky Mountain Douglas-fir is planted for erosion control, particularly after fire [241]. Genetic variability in seed sources maximizes successful establishment. Same-site collection is useful; "supertree" seed will likely increase incidence of disease [157]. Also, planting low-elevation seed at high elevations can increase risk of frost damage [228]. Rehfeldt [211] recommended that in the northern Rockies, seed be used within 300 feet (91 m) of its source at elevations below 4,600 feet (1,400 m), within 410 feet (125 m) at elevations between 4,600 and 6,550 feet (1,400-2,000 m), and to within 650 feet (170 m) at elevations above 6,550 feet (2,000 m). Myers and Howe [190] successfully propagated Rocky Mountain Douglas-fir cuttings using hormone treatment and nursery rooting

Kilns are preferable for drying cones but air-drying also works. When dry, cones may be kept for 3 or 4 months without affecting viability. A seed extraction process includes tumbling dry cones, removing scales and debris, removing seed wings, and winnowing away hollow seeds and debris. Seed sowing for nurseries is most commonly done in spring; fall sowing allows stratification but also increases losses to birds and rodents. Stratification in nurseries is commonly done at 33 to 41 degrees Fahrenheit (1 to 5 °C) for 21 to 60 days [197]. More recently, Wells [266] recommended 39 degrees Fahrenheit (4 °C) for 17 weeks in a controlled environment for stratification (or 20 weeks post hard frost in Moscow, Idaho climate). In many potential Rocky Mountain Douglas-fir sites growth and survival are potentially limited by competition for water from rhizomatous grasses [206,243].

OTHER USES:
Douglas-fir is used in landscaping and for mountain windbreaks and is a popular Christmas tree [263].

OTHER MANAGEMENT CONSIDERATIONS:
Silviculture: Mixed-conifer and ponderosa pine forests have increased in density because of fire exclusion and selective (high-grade) logging of ponderosa pine [23,85]. Silvicultural methods used to regenerate Rocky Mountain Douglas-fir vary depending on site and stand conditions [228,231,233]. Clearcutting has been widely used in mature stands and to salvage stands damaged by insects or Douglas-fir dwarf mistletoe. Where Rocky Mountain Douglas-fir occurs with ponderosa pine or Rocky Mountain lodgepole pine, shelterwood or group selection methods are used. Where the above-mentioned stands have much dwarf mistletoe infestation clearcutting with fire or mechanical preparation is used. On sites with moisture supporting grand fir or western larch with Rocky Mountain lodgepole pine, ponderosa pine, and Rocky Mountain Douglas-fir shelterwood, clearcutting, or seed-tree methods are used, with shelterwood most commonly used for even-aged stands, clearcutting for disease or insect-infested stands, and seed-tree for favoring western larch on north aspects [228]. Filip [85,86] speculated that harvesting of root rot-infested (Armillaria spp., Heterobasidion annosum, and Leptographium wageneri var. ponderosum) trees increased infection of adjacent trees, particularly true firs, when site preparation is not done.

Carlson and Wulf [58] have outlined silvicultural strategies to reduce Rocky Mountain Douglas-fir susceptibility to spruce budworm. Steele and Geier-Hayes [248] recommend a stand density below 120 ft2/acre (27.5 m2/ha) to protect pure stands of Rocky Mountain Douglas-fir from extensive bark beetle infestation.

Insect damage: Insects associated with Rocky Mountain Douglas-fir include defoliators such as Douglas-fir tussock moth and western spruce budworm; bark beetles and pinhole borers like Douglas-fir engraver beetles, Douglas-fir beetle, and ambrosia beetles (Playpus spp., Gnathotrichus spp., Trypodendron spp.); and Cooley spruce gall aphids (Adelges cooleyi) [5]. Western conifer seed bug (Leptoglossus occidentalis), Douglas-fir seed chalcid (Megastigmus spermotrophus), Douglas-fir cone moth (Barbara colfaxiana), fir coneworm (Dioryctria abietivorella), ponderosa pine coneworm (Dioryctria aurenticella), and western spruce budworm consume seed [119,179]. Insect outbreaks can be widespread and pervasive. In the Blue Mountains of Oregon in 1990, 53% of U.S. Forest Service land had "visible insect-caused defoliation and mortality," with western spruce budworm causing injury and mortality on 41% of the land [98]. Douglas-fir beetle, wood borers, Douglas-fir tussock moth, and spruce budworm have increased as a result of fire suppression [5,209].

Western spruce budworm larvae feed on foliage and immature cones; in Montana in Rocky Mountain Douglas fir- pinegrass habitats, cone production was consistently much higher in lightly defoliated (0-37.5%) trees than heavily defoliated (>62.5%) trees [60]. Chrisman and others [60] suggest that cone production is reduced by direct feeding  as well as indirect defoliation effects. Dewey [74]  studied the effects of western spruce budworm on Rocky Mountain Douglas-fir cones from near Frenchtown, Montana; approximately 10% of cones from 1 season had "obvious symptoms" of insect damage.  In 4 stands near Missoula, Montana, Rocky Mountain Douglas-fir seed production was reduced ( in 1980 and 1982) approximately 33% because of insect feeding. In 1981 cone production was very low because 2nd- and 3rd-stage western spruce budworm larvae fed on ovulate buds in 1979 [240]. 

Western spruce budworm and Douglas-fir tussock moth infestations occur with periodicity (though sometimes highly variable) and can result in severe defoliation and seed supply reduction that limit survival and recruitment [228]. Between 1690 and 1989, western spruce budworm outbreaks in northern New Mexico occurred every 20 to 33 years, with durations averaging 11 years [69]. In the Blue Mountains between 1700 and 1991, "regional" scale western spruce budworm outbreaks occurred every 21 to 53 years with reduced radial growth occurring for 13 to 17 years with each outbreak. The outbreaks increased in frequency and severity in the 1900s (up to 80% mortality has occurred in some stands) [254]. Carlson and others [57] argue that outbreaks are not truly cyclical; in addition to abiotic factors, western spruce budworm starvation (towards end of outbreak), parasites and predators, and interactions thereof can influence population dynamics [57]. Lynch and Swetnam [165] analyzed western spruce budworm outbreaks in stands ranging from 98 to 694 years old; outbreaks were not confined to any age class, "nor did outbreaks appear to start in older stands." They did state, however, that outbreaks more persistent in older stands [165]. Western spruce budworm outbreaks occur in Montana, Idaho, Oregon, Washington, and southern portions of British Columbia and Alberta; frequency of outbreaks increases with decreasing precipitation and is highest in southwestern Montana and central Idaho [58,82].

Douglas-fir dwarf mistletoe: Douglas-fir dwarf mistletoe can substantially affect forest structure by causing stunted growth, reduced seed production, and mortality [37]. Mortality of infected trees is low but growth is considerably retarded [228]. Trees that host Douglas-fir dwarf mistletoe grow dense "broom" branches that increase risk of fire damage [268]. Other dwarf mistletoe-induced morphologies that increase fire severity include mortality, spike-tops, slower growth, and resin-filled stem cankers. Dwarf mistletoe-infested Rocky Mountain Douglas-fir commonly have suppressed growth and a higher than normal proportion of compression wood, decreasing their susceptibility to decay [9]. Bennetts and others [37] "suggest that in areas where management goals are not strictly focused on timber production, control of dwarf mistletoe may not be justified, practical, or even desirable... dwarf mistletoes may have positive influence on wildlife habitat."

Disease: Agee and Edmonds [5] list the disease causing parasites of Rocky Mountain Douglas-fir as root rots like Phellinus root rot (Phellinus weirii) and Armillaria root disease (Armillaria ostoyae, other Armilllaria spp.); heart rots and decays like white pocket rot (Phellinus pini), velvet top fungus (Haeolus schweinitzii), sulphur fungus (Laetoporus sulphureus), and Quinine conk (Fomitopsis officinialis) [5]. Armillaria ostoyae infects conifers most readily and is prevalent in the Northwest. It is usually saprophytic but can be pathogenic; inocula remain viable for up to 50 years [86].

"Broom" branch morphologies are caused by not only Douglas-fir dwarf mistletoe but also by rust fungi (Chrysomyxa or Melampsorella) and needle cast fungus (Elytroderma deformans) [9,198,198]. Rocky Mountain Douglas-fir is susceptible to Annosus root disease; it is a significant cause of mortality in Montana, Idaho, and Utah. Mortality may occur directly via root damage or indirectly via increased susceptibility to bark beetles. Mortality is patchy, indicative of the spread of the fungal hyphae in soil [196].

Several pathogens can be active at a small scale [196]. There are interactive effects within a stand or even on a single tree; for example, Armillaria ostayae and Phellinus weirii co-occur within small areas in northern Idaho [196]. Annosus root disease and Armillaria are often closely associated [196].

Wildlife: Ponderosa pine stands that have been invaded by Rocky Mountain Douglas-fir have been treated with shelterwood cuts in combination with prescribed surface fire, which augments big game habitat by increasing forage production and shrub vigor. In mixed-conifer stands timber harvest can improve browse for elk and deer, particularly if fire afterwards stimulates aspen regeneration [200]. Though postharvest fire reduces the cover of shrubs initially, within several years the loss may be over-compensated in growth [25].  For cavity- nester habitat in Rocky Mountain Douglas-fir/ western larch/Pacific ponderosa pine forests, McClelland [175] recommends the following: in a 1,000 acre area 50 to 100 acres of old-growth is should be preserved in scattered patches, other logs and snags should be retained as is possible, and collection of large trees for firewood should be reduced [175]. Ganey [96] contends that snag density criteria set for management goals may be unreachable: in northern Arizona, 6.7% and 16.7% of logged plots in interior ponderosa pine and mixed- conifer stands, respectively, met regional Forest Service standards for large snag retention. Among unlogged sites only 30% and 32% of interior ponderosa pine and mixed- conifer stands met the same standards.

Livestock: Grazing generally reduces grass competition, favoring increasing density of ponderosa pine-Rocky Mountain Douglas-fir forests. Increased density favors Rocky Mountain Douglas-fir over ponderosa pine. Grazing decreases likelihood of fire in the short term by reducing surface fuels [36], but increases likelihood of stand-replacing fire in the long term as stands become denser. Near Moscow, Idaho, increased grazing favored Rocky Mountain Douglas-fir increase in a Rocky Mountain Douglas-fir/ninebark habitat type. This resulted in "overstocking" and subsequent "stagnation" and increased probability of fire [275]. There is controversy over the effects of grazing on Rocky Mountain Douglas-fir establishment on formerly sagebrush-dominated grasslands [54]. Butler [54] observed that "moderate" grazing probably reduced light competition, increasing the growth of Rocky Mountain Douglas-fir seedlings that were already present, but "heavy" grazing, particularly after fire, reduces establishment in openings. Butler [54] also stated that periods of Rocky Mountain Douglas-fir invasion in meadows in the Lemhi Mountains of Idaho were correlated with cooler climate periods, specifically snowmelt timing from meadows.

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