Rubus parviflorus


Table of Contents


INTRODUCTORY

SPECIES: Rubus parviflorus
Photo © Dave Powell, USDA Forest Service, Bugwood.org

AUTHORSHIP AND CITATION:
Gucker, Corey. 2012. Rubus parviflorus. 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:
RUBPAR

COMMON NAMES:
thimbleberry
western thimbleberry

TAXONOMY:
The scientific name of thimbleberry is Rubus parviflorus Nutt. (Rosaceae) [117,239]. Thimbleberry is part of the Anoplobatus, or flowering raspberry, subgenus [248]. There are 2 thimbleberry varieties:

Rubus parviflorus Nutt. var. parviflorus [117,239]
Rubus parviflorus Nutt. var. velutinus (Hook. & Arn.) Greene [117,171]

Hybrids:
Thimbleberry may hybridize with purpleflowering raspberry (R. odoratus), evergreen blackberry (R. laciniatus), and red raspberry (R. idaeus) where distributions overlap [113,232]. Hybrids are frequently sterile [113].

SYNONYMS:
Rubus parviflorus var. bifarius Farw. [231]
Rubus parviflorus var. grandiflorus Farw. [107,231]
Rubus parviflorus var. heteradenius Fern.
Rubus parviflorus var. hypomalacus Fern. [231]

For Rubus parviflorus Nutt. var. parviflorus (the variety):
Rubacer parviflorum (Nutt.) Rydb. [236,237]

LIFE FORM:
Shrub

DISTRIBUTION AND OCCURRENCE

SPECIES: Rubus parviflorus
GENERAL DISTRIBUTION:
Map courtesy of USDA, NRCS. 2012. The PLANTS Database. National Plant Data Team, Greensboro, NC. (2012, 11 July).

In North America, thimbleberry occupies a discontinuous range. It is a widespread native throughout most of western North America, with disjunct populations to the east in the Black Hills of South Dakota and even farther east in the Great Lakes region [209,232]. Thimbleberry populations are large and widely distributed in western Canada and small and narrowly distributed in eastern Canada [17]. Thimbleberry ranges from Alaska to northern Mexico along the Pacific Coast and is particularly common in the understory of humid Pacific Northwest forests (review [199]).

Distribution of thimbleberry is narrower and more discontinuous than the above map suggests. In Alaska, thimbleberry occurs only in the coastal regions in the extreme southeastern part of the state [229], but in California, it occurs as far south as San Diego County [171]. In Nevada, thimbleberry occurs only in the northwestern counties of Washoe, Carson City, and Douglas [118]. In New Mexico and Arizona, thimbleberry is restricted to their common border, occurring primarily in western New Mexico [29] and eastern Arizona [25]. In Ontario, thimbleberry is restricted to the shores of Lake Superior and Lake Huron [205]. Thimbleberry's distribution is thought to be driven by avoidance of aridity. When site conditions were compared in areas with thimbleberry, without thimbleberry, and where thimbleberry was exceptionally abundant, thimbleberry was most common at cool moist sites [64].

Rubus parviflorus var. velutinus occurs only in California; distribution of Rubus parviflorus var. parviflorus includes all of the regions described and mapped above [226].

States and provinces:
United States: AK, AZ, CA, CO, IA, ID, IL, MA, MI, MN, MT, NM, NV, OR, SD, UT, WA, WI, WY
Canada: AB, BC, ON [226]
Mexico [199]

SITE CHARACTERISTICS AND PLANT COMMUNITIES:
Site characteristics: Thimbleberry is most common in mesic forests and riparian areas [99,100,134,236]. In subboreal conifer-hardwood forests in the Great Lakes region, thimbleberry was absent from dry sites but occurred with 4% frequency on dry-mesic, 18% on mesic, 4% on wet-mesic, and 3% on wet sites. Balsam fir (Abies balsamea) and sugar maple (Acer saccharum) dominated the mesic sites [149]. In arid habitats and ecosystems, thimbleberry is typically restricted to riparian sites (e.g., [78,209,239]).

Thimbleberry is most typical of upper floodplain sites with limited flooding or lower sites with rapidly draining soils. Along riparian sites in 2nd-growth forests in the central Cascade Range of Washington, importance value for thimbleberry was 20 on low floodplains, 24 on high floodplains, 4 on terraces, and 0 on hilltops. Generally low floodplains were inundated at least every 2 years; high floodplains were inundated less frequently but at less than 50-year intervals. Terraces were above the 100-year flood stage. (Importance values were the sum of relative cover and relative frequency divided by 2 [230]). In northwestern Oregon, thimbleberry occurred at 0 to 3 feet (1 m) above the high water line of streams on shallow cobbly silts or sands and at 2 to 10 feet (0.6-3 m) above the high water line of rivers on deep, gravelly sands [151].On 144 riparian plots in the Lake Tahoe Basin near the California-Nevada border, thimbleberry was most commonly associated with highly sinuous streams in wide valleys and rare along V-shaped, high-gradient streams [157].

Climate: Thimbleberry occurs in areas with a variety of climates. In western Oregon, thimbleberry is common in coastal regions generally free of frost, and in Wisconsin and northern Michigan, it is common at sites with prolonged freezing winter temperatures and abundant snow [248]. In Washington's Gifford Pinchot National Forest, grand fir (Abies grandis)/thimbleberry forests occurred on cool moist sites with substantial snow packs. However, thimbleberry was a poor site indicator species because it was also found—although rarely as a dominant and often confined to stream sides and seeps—in warm, moderately dry grand fir forests, warm, moist western redcedar (Thuja plicata) forests, and hot, dry, low-elevation Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) forests [222]. In British Columbia, thimbleberry occurred in areas with boreal, temperate, and mesothermal climates, but its occurrence generally increased with increasing elevation and increasing continentality [126]. It appears sensitive to extremely cold winters, short growing seasons, and extreme summer moisture stress, and it grows best in moist to wet conditions (review by [81]). However, thimbleberry is also consistently found in interior Douglas-fir communities in British Columbia's Kamloops Forest Region, where the climate is warm and dry, growing seasons are relatively long, and moisture deficits are common [138].

Elevation: Thimbleberry's elevation ranges are described only for its western range. Low elevations are occupied in the northern part of the Pacific Northwest Coast [88,102,181]. Elevations from sea level to subalpine zones are occupied in the southern part of the Coast [181], and elevations above 4,000 feet (1,200 m) are occupied in the Southwest [146,239]. In areas of western Oregon north of Douglas County, thimbleberry occurred in the subalpine zone but was most common at low elevations [222]. In the Siskiyou Mountains of Oregon and California, frequency of thimbleberry was greatest at the 1,500- to 2,500-foot (460-760 m) and 4,500- to 5,500-foot (1,400-1,700 m) elevational ranges [240]. In the western redcedar-western hemlock (Tsuga heterophylla) zone of northern Idaho, thimbleberry's probability of occurrence was greater at low elevations than high elevations, but thimbleberry height growth was greater at high elevations than low elevations [111].

Local elevation ranges for thimbleberry reported in the United States and Canada
Arizona 7,000-10,700 feet (2,100-3,200 m) [25,120]
California <8,200 feet (2,500 m) [100,171]
Colorado 7,000-10,000 feet (2,000-3,000 m) [97]
Nevada

4,900-8,200 feet (1,500-2,500 m) [118]

New Mexico

7,000-10,000 feet (2,000-3,000 m) [29,146]

Utah 4,700-9,000 feet (1,400-2,700 m) [239]
British Columbia sea level-4,000 feet (1,200 m) [81]

Soils: Thimbleberry grows best in moist, nutrient-rich soils with good drainage but tolerates a wide range of soil conditions. It occupies sites where nutrient levels range from moderate to high and moisture conditions range from relatively dry to wet. Generally, plants are much smaller on dry than moist sites and in poorly drained than rapidly drained soils (review by [81]). In Canada, thimbleberry is considered a nitrophytic shrub (that is, an indicator of nitrogen-rich soils). It is most common in seepage habitats with fresh soils that receive well aerated water. Thimbleberry also grows on wetter and drier sites but typically with reduced size and cover [185]. In coastal British Columbia, thimbleberry is an indicator of nitrogen-rich soils and friable forest floors [126]. In redwood (Sequoia sempervirens) communities of coastal northern California, thimbleberry occupied sites where nutrient levels were moderate and moisture was high [235].

Moderately deep and coarsely textured soils are common in thimbleberry habitats. On the Siuslaw National Forest, Oregon, the western sword fern (Polystichum munitum)-thimbleberry community type was common at sites where soils were typically 12 to 18 inches (30-46 cm) deep and parent materials were primarily basaltic. Cover and frequency of thimbleberry was much lower at sites where soils were very shallow [49]. In the Tillamook burn area of Oregon, the red alder (Alnus rubra)/thimbleberry community type occurred at sites where gravel made up more than 75% of the total soil volume, and the thimbleberry/broadleaf starflower (Trientalis borealis subsp. latifolia) community occurred at sites where basalt gravel made up more than 80% of the total soil volume [14].

Thimbleberry grows on serpentine and other ultramafic soils but may grow better or be more common on soils with lower levels of toxic metals. In the Cascade Range in Washington, thimbleberry was dominant on the east side but less common in the west or central regions. East side habitats had larger ranges in soil pH and organic matter than habitats in the west and central regions. Thimbleberry was most common at mesic, low-elevation sites on nonserpentine sandstone soils [52] but also occurred on serpentine soils, although largely restricted to wet, shady, cool sites. Sandstone soils were less extreme than serpentine soils with respect to moisture and pH [53]. In greenhouse studies, thimbleberry showed no ecotypic growth response to ultramafic soils. Thimbleberry plants and/or seeds collected from both ultramafic and nonultramafic soil sites grew in ultramafic soils [132].

Plant communities: Throughout its range, thimbleberry occurs in shrublands, riparian vegetation, and in deciduous, coniferous, and mixed forests. It can occur in dense, almost pure patches or as scattered individuals [225]. In the plant community descriptions below, those community and habitat types where thimbleberry was recognized as dominant are presented in bold font. See the Fire Regime Table for a list of plant communities in which thimbleberry may occur and information on the fire regimes associated with those communities.

Shrublands: In the Pacific Northwest, thimbleberry was often dominant in shrublands occurring at ecotones between prairie and forest communities and in early-seral communities following forest disturbances. Thimbleberry was common in coastal shrublands found on cool, low-elevation (<1,200 feet (370 m)) sites between grasslands and forests from Washington to California [16]. These ecotone communities were commonly referred to as coastal headland or islet shrubland communities in Oregon [16,68]. Common associates included salal (Gaultheria shallon), evergreen huckleberry (Vaccinium ovatum), and salmonberry (Rubus spectabilis) [30]. In California, common associates included coyote bush (Baccharis pilularis), blueblossom (Ceanothus thyrsiflorus) and California coffeeberry (Rhamnus californica), and the canopy height reached 15 to 20 feet (5-6 m) tall [16]. The thimbleberry/fireweed (Chamerion angustifolium) mountain meadow community type was most common at elevations below 4,900 feet (1,500 m) in Oregon and Washington [69]. In the western North Cascade Range in Washington, the subalpine thimbleberry/fireweed community type occurred on mesic, well-drained soils on steep south slopes and avalanche tracts. The community type was species rich, with up to 70 species, and it occasionally occupied large areas with vertical distances of 1 to 1.5 miles (1.6-2.4 km) and elevational ranges of 2,000 feet (600 m) [57,58]. On Monument Peak in the western Cascade Range of Oregon, thimbleberry was typical in shrubland ecotones between Douglas-fir and western hemlock forests and rock-fell communities where grasses and forbs occur sporadically in rocky outcrops. Thimbleberry shrublands also occurred at the margins and in clearings within very dense noble fir (Abies procera) forests and were especially common in clearings in Pacific silver fir (A. amabilis)-western hemlock forests [6].

Several thimbleberry communities are recognized in early forest succession. In the Oregon's Tillamook burn area, old-growth Douglas-fir forests burned 3 times in 12 years, and thimbleberry was important in seral communities including the red alder (Alnus rubra)/thimbleberry shrubland on steep north-facing slopes with gravelly soils between 800 and 1,200 feet (240-370 m) and the thimbleberry/broadleaf starflower shrubland on upper slopes and ridgetops with gravelly soils above 1,800 feet (550 m) [14]. On the Siuslaw National Forest, the western sword fern-thimbleberry ecotone community was common between headland prairies and Sitka spruce (Picea sitchensis)-western hemlock forests at sites where soils were primarily of basaltic origin and typically 12 to 18 inches (30-46 cm) deep. The young Sitka spruce in the western sword fern-thimbleberry community suggests the community could represent an early stage of forest succession [49]. In southeastern Alaska, thimbleberry occurred in meadows or in logged areas within western hemlock, Sitka spruce, and western redcedar forests where soil pH generally measured 6 to 7 [220]. In the Nez Perce and Clearwater National Forests of northern Idaho, a Rocky Mountain maple (Acer glabrum)-thimbleberry community often dominated 15 to 20 years after clearcutting and burning in the moist grand fir/wild ginger (Asarum caudatum) habitat type [77]. A thimbleberry shrubland type occurs in Michigan and Ontario. The shrubland occupies gentle to moderate slopes at fairly low elevations (620-750 feet (190-230 m)) and typically appears following burning or clearing. Thimbleberry shrublands are uncommon, which might mean they are rapidly replaced as forest succession progresses [221].

Riparian and wetland vegetation: From southeastern Alaska south to California and east to the Great Lakes, thimbleberry is described in riparian and wetland areas including streambanks [191,220], wet to moist seepage areas [10], and lakeshores [221].

Thimbleberry is recognized as a dominant in several riparian communities. In coastal British Columbia, a Sitka spruce-red alder (Alnus rubra)/thimbleberry community was recognized within the floodplain spruce association on sandy, mesic sites in the Kimsquit River Valley [15]. Although thimbleberry occurred in nearly all biogeoclimatic zones in British Columbia, it was most common on fluvial sites within the western hemlock coastal zone [81]. In northwestern Oregon, the thimbleberry/vanilla-leaf (Achlys triphylla) community was common in shallow, cobbly, streamside silts or sands at 0 to 3 feet (1 m) above the normal high water line. Thimbleberry frequency was 100% in red alder/common snowberry (Symphoricarpos albus)-salmonberry communities in deep, very gravelly, streamside sands occurring 2 to 10 feet (0.6-3 m) above the high water line of the Salmon River [151]. On western slopes of the Sierra Nevada, thimbleberry was an indicator species for white fir (Abies concolor)-dominated riparian vegetation [98]. After surveying 144 riparian plots in the Lake Tahoe Basin near the California-Nevada border, researchers determined that thimbleberry was characteristic of currant-blackberry (Ribes-Rubus spp.) communities, which were associated with wide areas of riparian vegetation along highly sinuous rivers. Currant-blackberry vegetation was least common along V-shaped, high-gradient streams [157].

Forests and woodlands: Thimbleberry is a common understory species in a variety of deciduous, coniferous, and mixed-forest types throughout its range. It may be more abundant beneath partially open canopies or in recently disturbed forests but often persists in mature and closed-canopy forests as well [20,38].

Pacific Northwest: Common overstory associates in thimbleberry habitats in the Pacific Northwest include hemlock (Tsuga spp.), western redcedar, grand fir, Douglas-fir, and red alder [54,181,190]. Although cover and size of thimbleberry may be greatest in partially open to open stands, it also occurs in the closed canopy of young deciduous and mature coniferous forests [20,38,81,190]. In coastal southeastern Alaska, thimbleberry was common in Sitka spruce-western hemlock forests and in Sitka alder (Alnus viridis subsp. sinuata) thickets [229]. In British Columbia, it occurred in nearly all biogeoclimatic zones but was uncommon in extremely cold boreal forests or exceedingly dry ponderosa pine or Douglas-fir forests. Coastal western hemlock, subboreal spruce (Picea spp.), interior western redcedar-western hemlock, montane spruce, and Engelmann spruce-subalpine fir (P. engelmannii-Abies lasiocarpa) forests on base-rich sites with subhygric to hygric, well-aerated soils were common thimbleberry habitats [38]. On the Gifford Pinchot National Forest, thimbleberry was an understory dominant in grand fir/thimbleberry/drops-of-gold (Prosartes hookeri var. hookeri) forest types on cool, moist sites receiving substantial snowfall [222]. In the central Cascade Range in Washington, importance of thimbleberry increased from west to east, and thimbleberry was a dominant in the following eastside communities:

Although thimbleberry occurred in all plant associations recognized from the western to eastern parts of Washington's Columbia River Gorge, it was most widespread and had the greatest cover in cool, moist Douglas-fir and western redcedar forests. Thimbleberry was restricted to ravine or riparian sites in more eastern parts of the gorge dominated by ponderosa pine, Oregon white oak (Quercus garryana), manzanita (Arctostaphylos spp.), big sagebrush (Artemisia tridentata), or cheatgrass (Bromus tectorum) [243]. In the Blue Mountains of Oregon, a quaking aspen (Populus tremuloides)/thimbleberry-western bracken fern-starry Solomon's-seal (Pteridium aquilinum-Smilacina stellata) community type occurred on moist sites above the Imnaha River. This type was considered seral to grand fir forests [218]. In northeastern Oregon and southeastern Washington, thimbleberry was a major species within the ponderosa pine zone at 4,900- to 6,600-foot (1,500-2,000 m) sites receiving 25 to 45 inches (640-1,100 mm) of annual precipitation [33].

Interior Northwest: Thimbleberry communities and associates in the Interior West are similar to and nearly as diverse as those described in the Pacific Northwest. In Waterton Lakes National Park in Alberta, white spruce (Picea glauca)/thimbleberry montane forest types occupied hygric to mesic sites [1]. Thimbleberry was also reported as an understory species in montane Douglas-fir forests and quaking aspen woodlands in southwestern Alberta [166]. Thimbleberry was widespread in northern Idaho and occurred with 90% frequency in western redcedar/menziesia (Menziesia ferruginea)/wild ginger habitat types [178] and 80% of stands in the western redcedar-western hemlock zone [48]. In central Idaho, thimbleberry occurred in early-seral to late-seral grand fir/Rocky Mountain maple habitat types [207] and was characteristic of late-seral Douglas-fir habitat types [208]. In Montana's Glacier National Park and Whitefish Mountains, thimbleberry dominated the understory of Engelmann spruce-subalpine fir forests [47]. Quaking aspen woodlands were common thimbleberry habitat in South Dakota, Wyoming, and Colorado. Quaking aspen/thimbleberry communities occurred at 5,600 feet (1,700 m) on limestone soils in the Black Hills of South Dakota [198] and Wyoming [36].

California and Southwest: Thimbleberry was often described in redwood stands in California [142], quaking aspen woodlands in Nevada, Utah, and Colorado [118,170,194], and subalpine fir forests in Arizona and New Mexico [66]. A redwood-Sitka spruce/thimbleberry vegetation association was described at the Headwaters Forest Reserve in central Humboldt County (Jimersson and Jones 2000 cited in [143]). In giant sequoia (Sequoiadendron giganteum) groves of the Sierra Nevada, thimbleberry development was best in riparian areas, but thimbleberry was not restricted to them. In terms of canopy cover, white fir was the dominant trees species within the groves. Giant sequoias contributed less than 5% canopy cover but occupied the largest basal area [191]. In redwood/red alder/salmonberry communities in northwestern California, thimbleberry cover was low (3%) but frequency was high (90%) [142]. Throughout California, as far south as San Diego County, thimbleberry can be found in canyons and canopy openings in mixed-conifer and white fir forests below 7,900 feet (2,400 m) [39].

Intermountain West: In the Intermountain West, the quaking aspen/thimbleberry community type occurred at fairly high-elevation sites (8,000-9,300 feet (2,400-2,800 m)), and although not especially common, the type occupied large areas within Bridger-Teton, Caribou-Targhee, Wasatch-Cache, and Uinta National Forests [170]. On the western side of the Rocky Mountains in central Colorado, thimbleberry occurred in quaking aspen groves on gentle slopes and narrowleaf cottonwood (Populus angustifolia) groves in valleys and canyons [194]. The subalpine fir/dwarf bilberry (Vaccinium myrtillus)-thimbleberry habitat type occurred at cool moist sites on steep north slopes at elevations of 8,800-9,800 feet (2,700-3,000 m) in the San Juan Mountains of southern Colorado and northern New Mexico [56]. The subalpine fir (Abies lasiocarpa var. lasiocarpa)/thimbleberry forest type occurred at high-elevation sites in central and southern Arizona and southern New Mexico [169,216]. The subalpine fir/thimbleberry habitat occurred on cobbly soils on moist, protected, west, north, or east slopes with minimal growing-season water stress [137,162].

Great Lakes: Thimbleberry occurs in subboreal forests, northern hardwood forests, and mixed forests in the Great Lakes region. In Wisconsin, thimbleberry's presence was greater in subboreal forests than other plant communities [46]. However, thimbleberry was also found beneath the "dense shadows" of yellow birch (Betula alleghaniensis), eastern hemlock (Tsuga canadensis), maples (Acer spp.), and American beech (Fagus grandifolia) (Chamberlin 1877 cited in [45]). On the Apostle Islands, the maximum frequency of thimbleberry was 40% in stands dominated by sugar maple, paper birch (B. papyrifera), or northern red oak (Q. rubra) [19]. In Michigan, thimbleberry thickets were common in northern hardwood forests and moist mixed-forest communities and especially common at forest or woodland borders and clearings near the Great Lakes [232]. On the Keweenaw Peninsula of northern Michigan, thimbleberry was the only shrub species found in all 4 upland balsam fir-white spruce and balsam fir-white spruce-hardwood (sugar maple dominated) stands. When sites ranging from wet-mesic to dry-mesic were compared, thimbleberry was most frequent on mesic sites [149,150].

Thimbleberry was also found in several other Great Lakes forest types. These types, their distribution, and site characteristics are briefly described in the table below.

Thimbleberry was noted as the most common or abundant short shrub in the following forests and woodlands near the Great Lakes [221]:

Forest or woodland type Region Site characteristics
Eastern white pine (Pinus strobus)-quaking aspen/beaked hazelnut (Corylus cornuta subsp. cornuta) forest n MN, n WI, n MI, and nw ON on dry-mesic to mesic, rapidly drained fine sands to loams
Northern whitecedar (Thuja occidentalis)/balsam fir-mountain maple (A. spicatum) n MN, n WI, n MI, and nw ON on gentle to steep slopes, 620-910 feet (190-280 m), on calcareous sandy loams
Northern whitecedar-yellow birch forest n MN, n WI, n MI, and ON on poorly drained, lowland, organic soils and gentle to somewhat steep northern slopes; soils typically acidic sandy clays with thin litter layer
White spruce-balsam fir-quaking aspen/mixed herbs forest* n MN, n MI, n WI, and nw ON up to 1,300 feet (400 m), on deep, well drained to rapidly drained but moist, fine-textured, mineral soils
White spruce/poverty oatgrass (Danthonia spicata) forest with paper birch MI and ON at up to 1,250 feet (380 m), on well drained to rapidly drained sandy or sandy loam organics
Paper birch/bush-honeysuckle (Diervilla lonicera) woodland with balsam fir n MN, n MI, and ON on gentle to steep slopes, 620-864 feet (190-260 m), on coarse loams or sandy loams; noncalcareous mineral soil, which can be very shallow (6 inches (<15 cm)) in ON
Quaking aspen-balsam poplar (Populus balsamifera)-mixed-hardwoods lowland forest n WI, MI, and ON on deep, fresh to moist, well to poorly drained soils, often fine-textured and of lacustrine origin
Quaking aspen-paper birch woodlands with balsam fir and white spruce n MN, n MI, n WI, and ON on deep, well drained to rapidly drained mineral soils, usually loams but can be clays, silts, or sands
Quaking aspen-paper birch/sugar maple-mixed-hardwoods woodland n MN, w upper MI, n WI, and nw ON on rich mesic sites with clay or silt loams
Yellow birch woodland with sugar maple and white spruce n MI and ON at 630-780 feet (190-240 m), on moderately well drained to rapidly drained sandy loams
*Thimbleberry is indicator species for open forest variant type.

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Rubus parviflorus
Photo © Rob Routledge, Sault College, Bugwood.org

GENERAL BOTANICAL CHARACTERISTICS:
Botanical description: This description covers characteristics that may be relevant to fire ecology and is not meant for identification. Keys for identification are available (e.g., [75,100,107,239]).

Thimbleberry grows as an erect, multibranched, leafy deciduous shrub that may reach 10 feet (3 m) tall [205,229,231]. Size and distinguishing characteristics relating to leaves, glands, and pubescence can be highly variable [25,107,171,176]. In Arizona, thimbleberry shrubs in the Pinaleno and Chiricahua mountains were low growing and "merely suffrutescent", but shrubs found on more favorable growing sites grew as shrubs up to 7 feet (2 m) tall [120]. In California, thimbleberry shrubs found near the coast are much hairier than those from more inland sites [100]. Thimbleberry stems and leaves are thornless [205,239]. Stems range from 2 to 15 mm in diameter [100,209] and are typically biennial. In west-central British Columbia, the majority of stems lived 2 years but some lived 3 years and produced large lateral branches [81]. Thimbleberry produces alternate, simple, maple-shaped leaves with 3- to 7-pointed lobes [107,181]. Leaves generally measure up to 8 inches (20 cm) long and wide and have irregularly serrate margins [181,205,209]. Leaf petioles are typically just slightly shorter than leaf blades [99,229]. Thimbleberry flowers and fruits develop on 2nd-year stems [81]. Flowers are often large (up to 2 inches (5 cm) across) [181,205] and occur in clusters of 2 to 10 at the branch ends [29,205,239]. Fruits are thick, firm, raspberry drupelets [146,205,231].

Thimbleberry often forms clumps or dense thickets [205] through an "extensive network" of rhizomes [181]. On 1-year-old clearcuts in Oregon's Coast Ranges, thimbleberry shrubs had rhizomes that averaged 79 inches (201 cm) long and 14.4 buds per 3 feet (1 m) of rhizome length. Roots of thimbleberry seedlings measured 16 to 20 inches (40-50 cm) long [148]. About 13 to 15 months after the eruption of Mount St Helens, thimbleberry shrubs excavated from sites with 2 to 8 inches (5-20 cm) of volcanic ash had a maximum root length of 3 inches (8 cm) and extensive rhizome development [9].

Raunkiaer [182] life form:
Phanerophyte
Geophyte

SEASONAL DEVELOPMENT:
Throughout thimbleberry's range, the timing of flower production does not vary much, but aside from flowering dates, little phenological information was available for thimbleberry. In coastal southeastern Alaska and in the Southwest region, typical flowering and fruiting dates were the same, June to July and August to September, respectively [229,231]. Typical flowering dates were slightly earlier (May to July) in the Great Lakes region [75]. Throughout thimbleberry's range, flowering dates as early as March and as late as August or September were reported [39,81,120]. A detailed study of thimbleberry phenology conducted for a 10-year period in northern Idaho and Montana found that the earliest flowers appeared on 9 May; the latest flowers appeared on 11 August; the earliest ripe fruits appeared on 30 June; the latest ripe fruits appeared on 3 September; and the earliest date for fruit drop was 15 July [196].

REGENERATION PROCESSES:
Thimbleberry reproduces sexually by seed [123,148] and asexually from rhizomes and rhizome fragments [38]. Thimbleberry regenerates from rhizomes following stem damage or top-kill, and rhizome growth is important to the development of thimbleberry thickets and large clones [18,38,81].

Pollination and breeding system: Thimbleberry flowers are perfect [209,239] but self-incompatible ([122],Williams and Darrow 1940 cited in [71]). Flowers produced by species within the Rubus genus produce large quantities of nectar to attract pollinators [248].

Seed production: Although a review reports that good thimbleberry seed crops are produced almost every year [199], flower and seed production can be rare in the Great Lakes [75] and at high-elevation sites (review by [81]).

Thimbleberry seed production appeared prolific based on single-fruit seed counts from the Pacific Northwest. In old-growth temperate rainforests on Vancouver Island, British Columbia, thimbleberry fruits averaged 125.9 seeds [28]. In grand fir forests of southeastern Washington, thimbleberry fruits averaged 73.7 seeds [180], and in western Oregon, fruits averaged 190 seeds (review [248]).

Photo © Mary Ellen (Mel) Harte, Bugwood.org

Seed dispersal: Thimbleberry seeds are dispersed by birds and mammals (review [81]). In old-growth forest on Vancouver Island, researchers evaluated seed dispersal by frugivorous birds. A little more than half of the observations of thimbleberry dispersal were of American robins, 23% were of northwestern crows, and 22% were of Swainson's thrushes. Thimbleberry fruits averaged 1.9 days on the parent plant before being removed by birds [27]. Thimbleberry shrubs were visited by birds more frequently than abundance would suggest [28]. Thimbleberry seeds were recovered from bird droppings collected in the summer from the University of British Columbia campus [152]. A study using poultry suggested that thimbleberry seeds may be destroyed in the digestive process; however, the researcher noted that because domestic chickens were bred for efficient digestion, passage of seeds by domestic chickens could be different from that of wild birds [148]. Fruits that are not removed fall near the parent plant.

Two studies show evidence of thimbleberry seed rain. In old-growth forests on Vancouver Island, slightly more thimbleberry seeds were trapped in the understory of the forest than at the edge of the forest, probably because of the greater density of plants in the forest understory (P<0.05) [26]. At a University of Columbia Research Forest, thimbleberry seeds were trapped in clearcuts but not undisturbed mixed-conifer forest stands, and in clearcuts seeds were only trapped in 1 of 3 years of sampling in the clearcut. The aboveground frequency of thimbleberry was 89.1% in the clearcut and 2.3% in the undisturbed forest [125].

Seed banking: Thimbleberry seed is likely long-lived in the soil seed bank; viable, buried seed is often found on sites with little or no thimbleberry cover [133,163]. Generally, soil-stored seed abundance decreases with increasing depth of burial [130,163]. Seed bank density is often lower in disturbed than undisturbed sites, even when aboveground abundance of thimbleberry is the opposite [96,125,206].

Although reviews report that thimbleberry seeds persist a "long time" in the soil [81] and seeds of Rubus spp. may remain viable for decades or up to a century or more in the soil because of deep dormancy [248], the only research illustrating such longevity is from a study using seed that had been in dry, cold storage (39-41 °F (4-5 °C)) for 26 years. Germination in the greenhouse averaged 22% [32]. Field studies verify short-term viability of buried thimbleberry seed: In field burial experiments on clearcut and burned sites in Oregon's Coast Ranges, viability of seed in the soil decreased sharply in the 1st year but more slowly in 2nd and 3rd years. Thimbleberry seeds from the soil had greater viability than those on the soil surface [148].

Thimbleberry seeds are generally found in the litter, duff, and mineral soil layers [124,164]; abundance of seed is often less in the lower mineral soil layers than in the upper soil, duff, and litter layers. In a dense mixed-conifer forest adjacent to the Dworshak Reservoir in northern Idaho, 84 thimbleberry seeds/m² emerged from soil samples collected from undisturbed sites where aboveground thimbleberry cover averaged only 1% [163]. On the Payette and Boise National Forests of west-central Idaho, thimbleberry seeds were common in soil samples collected from grand fir and Douglas-fir forests. Thimbleberry seed occurred in 25 of 48 sampled plots, and in 14 of the 25 plots with soil-stored thimbleberry seed, thimbleberry shrubs were not present in the aboveground vegetation. In 1 plot, the nearest thimbleberry shrub was 330 feet (100 m) away. A little more than 75% of the total thimbleberry seed bank occurred in the top 2 inches (5 cm) of soil. Viability of the thimbleberry seeds from upper layer was 16% and from lower layer (2-4 inches (5-10 cm)) was 6% [130].

Burial experiments conducted on thimbleberry seeds collected in British Columbia showed that seeds collected from the litter or duff layers were more sensitive to burial than seeds collected from mineral soil layers [152,153].
Depth of burial 1-2 cm 3 cm
Germination of seeds recovered from litter or duff layers ~5% 0%
Germination of seeds recovered from mineral soil layers ~30% ~20%

In southwestern British Columbia, comparisons of early-seral communities and adjacent midseral forests revealed that thimbleberry's seed bank occupied a deeper soil profile in the midseral forests than in the early-seral communities. Thimbleberry seeds were rare at the driest sites dominated by Douglas-fir and much more common in moist forests dominated by western hemlock and wet forests dominated by western redcedar and red alder. Soil samples were collected in late March and stored in cold, dark conditions until May, when emergence was monitored in the greenhouse and outdoors. Emergence outdoors was 88% of the emergence that occurred in the greenhouse [152,153].

Distribution of thimbleberry seed in the soil profile as related to seral condition and moisture [153]
Seral condition Early-seral forest plots Midseral forest plots
Site condition Dry* Moist* Dry Less dry Moist* Wet
Litter and duff layer 5 150 2 154 94 50
0-5 cm of mineral soil 15 84 4 84 12 123
5-10 cm of mineral soil 0 0 2 24 12 83
*Thimbleberry was present in aboveground vegetation within the plots from which soil was sampled.

Thimbleberry seeds were absent or rare on the disturbed sites in the studies described below, even though abundant seedlings have been observed on disturbed sites (see Seedling establishment and Plant response to fire).

According to a study in upper Michigan, increased light availability in canopy openings probably does not reduce the thimbleberry seed bank. In old-growth northern hardwood-eastern hemlock, significantly more thimbleberry seedlings emerged from soils collected from plots in canopy gaps than in intact forest sites (P<0.01). Thimbleberry did not occur in the aboveground vegetation of either plot type [161].

Studies that compared thimbleberry seed banks on recently disturbed and relatively undisturbed sites report that seed is generally restricted to or most abundant on undisturbed or less recently disturbed sites. At the University of British Columbia Research Forest, thimbleberry did not emerge from soil samples collected in recently clearcut (<20 years since disturbance) mixed-conifer forest, although the aboveground frequency of thimbleberry was 89.1%. Thimbleberry emergence was 63.7 seedlings/m² from soil collected in unlogged forests where its aboveground frequency was 2.3%. The researcher speculated that larger seed banks in undisturbed forests suggest long-lived thimbleberry seed and long-term seed inputs [125]. Along 3rd- and 5th-order streams on the western slope of the Cascade Range in Oregon, thimbleberry emerged from soil samples collected from higher-elevation, vegetated gravel bars but not from nonvegetated gravel bars within the active stream channel. Thimbleberry was not common in the aboveground vegetation at any study site, and emergence ranged from 0 to 3 seedlings/m² [96]. In the dry-cool subzone of interior Douglas-fir forests in south-central British Columbia, thimbleberry did not emerge from soil samples collected from logged and burned sites 1 year prior to soil sampling. Some emergence occurred from soil collected in undisturbed stands [206].

Although thimbleberry seedlings have been observed within the 1st postfire year on burned sites [82,123], thimbleberry seed may be sensitive to long-duration heating. Thimbleberry emerged from untreated soil samples (13 emergents/m²) but not from soil samples heated for an hour at oven temperatures of 120 °F to 300 °F (50-150 °C). Soil samples were collected in the subalpine fir/big huckleberry (Vaccinium membranaceum) habitat type, where thimbleberry occurred in the aboveground vegetation [31].

Germination: Thimbleberry seed viability is considered moderate, and maximum germination of 62% has been reported [81]. Seeds germinate best after cold stratification [106], and mineral soil is a better germination substrate than duff or litter [152]. Plant propagation studies conducted in British Columbia found that thimbleberry seeds soaked in water for 24 hours and chilled at 36 °F (2 °C) for 4 to 5 months germinated best [106]. In germination tests of thimbleberry seeds collected near the University of British Columbia campus, thimbleberry germination was significantly better for seeds in or on mineral soil than for seeds in or on duff and litter layers (P<0.05). Germination was relatively insensitive to light, occurring at shade levels ranging from 0% to 90% [152].

In Oregon, thimbleberry germination was greater in a growth chamber (22%) than in the field (up to 7.4%). Field sites were clearcut and burned stands in Oregon's Coast Ranges [148]. When germination and growth of thimbleberry were compared on pure alluvial sands, pure reservoir sediments, and a mixture of these sediments, germination and cover of thimbleberry were considerably greater on sand and mixed sediments than on reservoir sediments [158].

Seedling establishment: Thimbleberry seedling emergence and establishment may be encouraged on disturbed sites. Thimbleberry germination may be best in mineral soil [152], and thimbleberry seedlings have been observed on burned sites in the first year following fire [81,123]. However, available studies (as of 2012) did not investigate other factors such as climatic conditions and light and moisture availability, which are likely important to thimbleberry seedling establishment and survival.

After reviewing available literature and information from researchers and field practitioners in the Pacific Northwest, Coates and Haeussler [35] reported that soil disturbance stimulates germination of soil-stored thimbleberry seed and provides a seed bed suitable for the establishment of freshly deposited thimbleberry seeds. When seeds were sown on clearcut and burned sites in Oregon's Coast Ranges, emergence averaged 7% to 7.4% in the 1st year after seeding and 0 to 4.2% in the 2nd year after seedling. No seedlings survived 3 years [148].

Plant growth: When researchers compared the growth of rooted cuttings and seedlings of thimbleberry over 3 years, they found that the relative growth rate for seedlings exceeded that of rooted cuttings, which might mean that seedlings could reach the size of similar-aged sprouts within a few years. The researcher planted thimbleberry seeds and cuttings on a clearcut and burned field site in the Oregon Coast Ranges [148].

Although cover of thimbleberry was reduced by repeated cutting, shrubs persisted through 3 consecutive years of cutting to a 2-inch (5 cm) height in logged sites within the interior western redcedar-western hemlock zone in southern British Columbia. Thimbleberry cover averaged 39.3% on untreated plots. In spring-cut plots, thimbleberry cover averaged 13.4 % in the 4th year after cutting. In summer-cut plots, thimbleberry cover averaged 39.6% in the 4th year after cutting [37].

Vegetative regeneration: Thimbleberry is strongly rhizomatous. Rhizome growth is important to increasing the size and density of thimbleberry clones as well as regeneration of shrubs following top-kill or movement of rhizome fragments ([18,38], review by [81]). Thimbleberry clones may live up to 45 years [176]. Postfire sprouting from rhizomes also occurs; this topic is discussed in Plant response to fire.

SUCCESSIONAL STATUS:
Thimbleberry is typically present throughout all stages of forest succession, but abundance is often greater in earlier than later stages of succession. Similarly, thimbleberry occupies open sites and occurs beneath closed canopies, but abundance is typically greater in sun than shade. It occurs in recently disturbed and old-growth stands, but abundance is generally greater in young than old stands.

In the Pacific Northwest, where thimbleberry is most widespread, populations are described in early-seral to climax forest communities. In northern British Columbia, thimbleberry increases in abundance following disturbance and persists in young, seral, and mature forests on very wet to moist sites in the subboreal spruce zone [20]. In central Idaho, thimbleberry occurs in the shrub layer of early-seral to climax grand fir habitat types. It is described as spreading rapidly and forming large patches in forest openings and persisting beneath forest canopies [73,207]. When floristic and structural changes were monitored in the first 40 years following logging in western hemlock habitat types in northern Idaho, thimbleberry was considered most vulnerable to successional replacement in the late-seral stages of succession [245]. Thimbleberry was sometimes dominant in very early succession but remained in plant communities as short-lived and shade-intolerant shrub species were replaced. It easily colonized canopy openings through vegetative growth and often continued to dominate as conifers developed a closed canopy [246].

Shade relationships: Generally, cover and size of thimbleberry is greater in open stands or canopy gaps than beneath heavily shading canopies. In British Columbia, thimbleberry abundance was typically greatest in open to partially open conditions, but shrubs persisted in the understory of closed-canopy young deciduous and mature conifer forests [20,38,81]. On Monument Peak in the western Cascade Range of Oregon, thimbleberry was common in the ecotones between western hemlock and Douglas-fir forests and treeless rocky outcrop communities and was especially abundant in clearings in Pacific silver fir-western hemlock forests [6]. On the Olympic Peninsula, thimbleberry was characteristic of forest-prairie ecotones but was rare or absent in prairie plots dominated by western bracken fern and forest plots dominated by western hemlock [139]. In riparian forests along mountain streams in western Oregon and northern California, thimbleberry was significantly more frequent in gap than forest plots (P=0.001). Gap sizes ranged from 130 feet² (12 m²) to more than 21,500 feet² (2,000 m²). Thimbleberry occurred in 56 of 240 gap plots and 33 of 240 forest plots [195]. In 5- to 38-year-old stands in the western redcedar-western hemlock zone of northern Idaho, thimbleberry height growth decreased with increasing basal area of trees [111].

Thimbleberry abundance can increase substantially with canopy removal. In coastal British Columbia, thimbleberry is generally most common in open-canopy and early-seral forests that exist after cutting or burning [126]. In a review of literature and information from researchers and field practitioners in the Pacific Northwest, thimbleberry cover and frequency were reported to increase by a factor of 2 to 3 after overstory removal [35]. In clearcut, thinned, and undisturbed coniferous forests in the Siskiyou Mountains of southwestern Oregon, thimbleberry cover reached a maximum of 5% where light levels were less than 10% of full light conditions; a maximum of 25% at 11% to 60% of full light; and a maximum of 75% at over 60% full light [63]. When undisturbed, logged, and logged-and-burned stands within the western redcedar-western hemlock zone of northern Idaho were compared, frequency of thimbleberry was significantly greater in stands where tree canopy cover was less than 40% than in stands where canopy cover was more than 40% (P<0.05). Cover of thimbleberry was significantly greater under canopy cover of less than 25% than under canopy cover of more than 40% (P<0.05) [167]. Thimbleberry cover in stands with little overstory canopy development was often more than 10 times that in stands where canopy cover exceeded 55% [168]. Thimbleberry abundance changes associated with logging and fire are discussed more in Logging and burning.

Forest succession: Although generally present throughout all stages of forest succession, thimbleberry is most characteristic or common in early-seral forest communities [11,69,127,140]. In British Columbia, thimbleberry was recognized as a dominant in preclimax forest types such as the interior spruce-lodgepole pine (Picea × lutzii-Pinus contorta)-shrub community, which over time is replaced by subalpine fir-spruce or hemlock climax forest types, or a quaking aspen-paper birch-red-osier dogwood (Cornus sericea) community, which slowly develops into a climax conifer forest type [83]. When recently logged to old-growth stands were evaluated in the western hemlock zone in southwestern British Columbia, thimbleberry was most frequent in the initial and regeneration stages of development. In initial-stage forests, trees were absent or less than 5 years old. At the regeneration stage, a tree canopy existed but had not yet closed [127]. In western Oregon, the early-seral thimbleberry/starflower (Trientalis spp.) community develops into a climax western hemlock/vine maple (Acer circinatum)/salal community on dry sites, and the early-seral red alder/thimbleberry community develops into a climax western hemlock/western sword fern-sorrel (Oxalis oregona) forest type on wet sites [69]. In redwood forests in northern California, thimbleberry was an indicator species for the initial postlogging stage of forest succession, where tree ages averaged 10.2 years old [140].

Typically, thimbleberry abundance decreases as tree canopy and basal area increase and is greater in young than old-growth stands [11,79,82,116]. In the Douglas-fir-western hemlock zone, thimbleberry abundance was greater in young (35-79 years old) and mature (80-195 years old) stands than in old-growth (200-730 year olds) stands in the Cascade Range of southern Washington, but in Oregon, thimbleberry abundance was similar in young, mature, and old-growth stands within the Douglas-fir-western hemlock zone in the Coast and Cascade ranges [190]. In Douglas-fir forests in the Siskiyou Mountains, thimbleberry was a strong indicator species for young stands (14-39 years old), in which percentage of open canopy was greatest (16.9-75.9%) [116]. In grand fir forests in Montana's Swan Valley, thimbleberry occurred in young (30-90 years) to old (>150 years) and wet to dry stands, but cover was 3% to 5% greater in young than old stands [8,11]. In the western redcedar-western hemlock zone in Glacier National Park, the frequency of thimbleberry was 4% in pioneer forests dominated by lodgepole pines less than 50 years old, 20% in mature forests dominated by lodgepole pine and western larch (Larix occidentalis), and lowest (2% or less) in late-seral to climax forests dominated by western hemlock and western redcedar. Tree canopy density generally increased as forest succession progressed [79,80].

Disturbance tolerance: Thimbleberry can be found on severely and/or frequently disturbed sites. In British Columbia, it survived 3 consecutive years of cutting near ground level [37]. About 4 months after the eruption of Mount St Helens in Washington, thimbleberry was found within the "devastation" area, which included areas impacted by blowdown, scorching, debris flows, pyroclastic flows, and/or mud flows [156]. In the first year after eruption, thimbleberry occurred with low frequency in several mud flow areas where a combination of snow melt, ice, rocks, sand, and mud had moved rapidly down the Muddy River [87]. On a winter debris flow that deposited about 35,310 feet³ (1,000 m³) of material along a 390-foot (120 m) stretch of valley floor in the western hemlock zone in the central Coast Ranges of Oregon, thimbleberry cover was 9% in the 1st postdisturbance year and 25% in 9th postdisturbance year [177]. On floodplains of the Tahsish and Artlish rivers on Vancouver Island, thimbleberry's frequency was 80% in pioneer vegetation establishing on newly formed gravel bars. Thimbleberry was not found in young seral or mature climax vegetation. Time since last disturbance was not reported for seral or climax vegetation [34]. However, when succession was studied on sand dunes along a 150-mile (240 km) stretch of the Oregon coastline, thimbleberry occurred only in the near climax western hemlock-shrub community type [133].

Browsing: Most studies found greater abundance of thimbleberry on protected sites than sites exposed to browsing by wildlife. In clearcut forests in Oregon's Umatilla National Forest, thimbleberry cover was least on unprotected sites. Ten years after construction of exclosures and 11 years after forest clearing (clearcut or clearcut and burned), thimbleberry cover averaged 0.2% on unprotected, burned plots; 1.5% on unprotected, unburned plots; 2.6% on protected, burned plots; and 3.4% on protected, unburned plots. Exclosures protected the plots from elk, white-tailed deer, and mule deer; there were no livestock in the study area [60]. In logged Douglas-fir forests in the southern Oregon Coast Ranges, thimbleberry cover was significantly (P<0.01) greater in exclosures protected from elk browsing than in areas outside the exclosures [219]. Density of thimbleberry was greater inside than outside a wildlife exclosure in place for 13 to 17 years in the western redcedar-Oregon boxwood habitat type along the upper part of the Dworshak Reservoir in northern Idaho. There were 0.67 thimbleberry stems/m² inside and 0.05 stems/m² outside of the exclosures [5].

In boreal forests in Isle Royale National Park, Michigan, studies comparing thimbleberry abundance in long-term exclosures and moose-browsed sites reported conflicting results. In one study, thimbleberry biomass was significantly greater (P<0.05) in browsed areas (0.3 Mg/ha) than in protected areas (0 Mg/ha). Exclosures were constructed 37 to 39 years before the study, and the density of trees was significantly greater in exclosures than browsed areas (P<0.05). Researchers suggested that shading by trees may have reduced shrub biomass more than browsing by moose [154]. In another study, density of thimbleberry was often greater inside exclosures than on browsed sites. Exclosures were constructed in 1949 or 1950, but thimbleberry was absent from exclosures and browsed plots visited in 1949 and 1966. In 1982, the density of thimbleberry was greater in exclosures than browsed plots at 3 sites. At another site, however, the density of thimbleberry was nearly equal for exclosures and browsed plots [186].

Logging and burning: Thimbleberry abundance often increases in forests following thinning or removal of the overstory canopy. Some studies suggest that thimbleberry increases on clearcuts limit or slow conifer regeneration, while one study suggests that thimbleberry may provide safe sites for conifer seedlings. On clearcuts, thimbleberry can monopolize light, space, and nutrients through the production of a dense canopy of large leaves, an extensive network of rhizomes, and large quantities of litter, all of which can suppress establishment and survival of conifer seedlings, especially on moist sites where thimbleberry growth is typically best (review [81]). However, on especially exposed sites within a clearcut, light to moderate thimbleberry cover may shade conifer seedlings and alleviate heat or moisture stress (review [82]). In the Pacific Northwest, thimbleberry may negatively impact western hemlock regeneration. Thimbleberry sprouts often reach 1 to 2 feet (0.3-0.6 m) tall in the first growing season after overstory canopy removal, while western hemlock seedlings may only reach 1 inch (2.5 cm) tall in their first year [193]. By June immediately following overstory removal, dense thimbleberry canopies can reduce the photosynthetically active radiation that reaches conifer seedlings by 50% to 100% [176]. In the montane spruce zone of southern interior British Columbia, experimental and observational field studies were conducted to evaluate lodgepole pine seedling and sapling growth in Sitka alder-dominated clearcuts. In experimental stands, cover of thimbleberry explained 16% of the variation in available light and accounted for 24% of the variation in available moisture in September. Consistently, thimbleberry had a positive effect on the soil water potential at 12- to 18-inch (30-45 cm) depths. In unmanipulated 10-year old clearcuts, lodgepole pine seedlings were larger at sites dominated by lodgepole pine and pinegrass (Calamagrostis rubescens) than at sites dominated by Sitka alder, thimbleberry, and big huckleberry [201].

In a couple of studies, cover of thimbleberry did not impact conifer regeneration negatively. In coastal tree plantations in Oregon, survival and natural reproduction of conifers was low at creek bottom sites dominated by dense thickets of thimbleberry, salmonberry, and salal, but survival and natural reproduction of conifers was considered good on upland sites, where thimbleberry was also common [192]. Thimbleberry was rated as a "highly efficient" nurse species for establishment of lodgepole pine, ponderosa pine, Douglas-fir, Engelmann spruce, and grand fir seedlings in 5-year-old clearcuts in a grand fir/big huckleberry habitat type in west-central Idaho [72]. In the grand fir/Rocky Mountain maple habitat type of central Idaho, thimbleberry was also a "highly efficient" nurse for western larch and Engelmann spruce but was less efficient for Douglas-fir and grand fir seedlings [74].

The majority of studies from thinned or clearcut forests reported at least short-term increases in thimbleberry abundance (e.g., [59,90,197]); onset and duration of the increases varied, however, and in a few cases, thimbleberry did not increase after overstory canopy removal. On the Nez Perce and Clearwater National Forests of northern Idaho, Rocky Mountain maple/thimbleberry communities often dominate 15 to 20 years after logging and broadcast burning in grand fir/wild ginger habitat types [77]. At the H.J. Andrews Experimental Forest in the western Cascade Range in Oregon, the cover and frequency of thimbleberry increased in each of the 5 years following clearcutting and slash burning in old-growth Douglas-fir stands. In undisturbed old-growth stands, thimbleberry cover and frequency were 0.1% and 1.6%, respectively, and by the 5th postdisturbance year in clearcut and burned stands, cover and frequency were 2% and 23%, respectively [59]. Two studies indicate decreases in thimbleberry after logging and fire. At the Cascade Experimental Forest in western Oregon, thimbleberry occurred on 2 fewer microplots 17 years after thinning in western hemlock stands and 4 fewer microplots after thinning in Sitka spruce stands compared to prethinning forest surveys. Thinning operations included light to extreme tree density reductions [3]. On 1- to 2-year-old clearcut and slash burned Douglas-fir stands in Oregon's Coast Ranges, thimbleberry was "extremely rare". Frequency of thimbleberry in undisturbed stands was 5% to 49% [42].

Several studies compared thimbleberry abundance along a chronosequence since logging, where logging was often followed by broadcast or slash burning. Generally, thimbleberry abundance peaked sometime between 5 and 20 years after disturbance. On clearcut and burned Douglas-fir forest sites on the western slope of Oregon's Cascade Range that were monitored for 21 years, thimbleberry cover was lowest in the first 4 postdisturbance years and greatest in the last 6 postdisturbance years [86]. Along a 2- to 40-year chronosequence in clearcut and broadcast burned western hemlock-Douglas-fir forests in the H.J. Andrews Experimental Forest, thimbleberry cover averaged less than 2% in 2- to 5-year-old stands, 6% to 17% in 10-to 30-year-old stands, and less than 1% in 40-year-old stands. Tree canopies closed within 40 years of disturbance. Thimbleberry was rare in 450-year-old stands [197]. In northern Idaho, thimbleberry cover was greatest in 11- to 15-year-old stands when 5- to 25-year-old clearcuts in the western redcedar/western hemlock zone were evaluated. Thimbleberry cover averaged 16.7% on 11- to 15-year-old and was less than 8.5% on younger and older stands [110]. Thimbleberry cover was greatest in 8-year-old stands when 1- to 23-year-old clearcut and burned sites were compared in a grand fir/Oregon boxwood habitat type in north-central Idaho. Thimbleberry cover was less than 0.5% in the first 8 postfire years and 0.1% in near climax stands. It averaged 8.8% in 12-year-old stands and 1.1% in 23-year-old stands [247].

Logging and logging and burning compared: In the few studies that compared thimbleberry abundance on logged-and-burned and logged-but-unburned plots, abundance was generally greater on logged-and-burned sites [51,168], but differences in study design make direct comparisons difficult [89,92]. In western larch-Douglas-fir forests in western Montana, thimbleberry cover was often several times greater after than before broadcast burning in clearcuts [51]. When undisturbed, logged-but-unburned, and logged-and-burned sites were compared in the western redcedar-western hemlock zone in northern Idaho, thimbleberry cover was much greater on disturbed than undisturbed sites, but cover was similar over similarly-aged logged-but-unburned and logged-and-burned sites [242]. However, in Douglas-fir forests in Oregon's southern Coast Ranges, thimbleberry cover was similar on clearcut and burned sites 13 to 16 years after disturbance, but thimbleberry appeared earlier in the postdisturbance succession on logged-but-unburned sites than on logged-and-burned sites [219].

Case studies: Multiple studies in British Columbia monitored changes in thimbleberry cover following logging and slash burning in the subboreal spruce zone. In all studies, thimbleberry cover was much lower on clearcuts before than after slash burning. In the Mackenzie Forest District, thimbleberry cover on unburned clearcuts was 1%. Cover increased to 8.8% in the 1st year after slash burning in the clearcuts, due in small part to seedling establishment. Slash burns in the clearcuts were low to moderate severity and consumed 22% of the duff and litter layer. Thimbleberry cover was greatest in the 5th year after burning (21.6%), and although cover was lower in the 10th postfire year (13.8%), thimbleberry remained the most abundant understory shrub species. Decreases in thimbleberry cover coincided with increases in the size of interior spruce seedlings planted in the area [90]. In the Prince George Forest District, thimbleberry cover on unburned clearcuts was 6.6%, and cover increased to 15% within 1 year of slash burning in the clearcuts. There was some postfire establishment from on-site buried seed. Thimbleberry cover was similar in the 2nd and 3rd postfire years (16.5-17.2%), increased to 20.3% in the 5th postfire year, and then decreased to 12.5% in the 10th postfire year, but in all postfire sampling, thimbleberry was the most abundant understory shrub. Slash fires consumed 32% of total woody fuels, most of which was less than 3 inches (7 cm) in diameter. Duff consumption was 40% to 45%, and only 3% of mineral soil was exposed [89]. Additional studies at several sites in the Prince George Forest District reported similar findings. However, postfire increases in thimbleberry cover were most substantial at the Brink site, where slash burning occurred in August when the forest floor was very dry. The August fire consumed about 50% of total woody fuels and exposed a substantial amount of mineral soil. Slash fires at the Haggen Creek and Francis Lake sites were moderate severity and exposed only minimal amounts of mineral soil. At Haggen Creek, thimbleberry sprouted and established from seed in the 1st postfire year. Decreases in thimbleberry cover corresponded with establishment and increases in abundance of fireweed. At the Brink site, the researcher reported that the high postfire cover of thimbleberry was not adversely affecting the growth of planted interior spruce seedlings [92]. Thimbleberry was typically less than 3 feet (1 m) tall in the disturbed areas. On dry sites, thimbleberry was generally even shorter [93].

Thimbleberry cover (%) after clearcutting and slash burning at several boreal forest sites in British Columbia's Prince George Forest District [92]
Time since fire (years) Prefire 1 2 3 5 10
Haggen Creek P* 28.8 13.7 13.9 ----** ----
Francis Lake P 11.7 6.5 12.5 16.2 10.5
Brink P 56.7 36.7 45 58.3 40
*Present, but cover not measured. **No data.

FIRE EFFECTS AND MANAGEMENT

SPECIES: Rubus parviflorus
FIRE EFFECTS: Immediate fire effect on plant: Most fires only top-kill thimbleberry shrubs [103,119]. Mortality is likely restricted to sites where high temperatures penetrate deep into the mineral soil layer [210].

Postfire regeneration strategy [214]:
Rhizomatous shrub, rhizome in soil
Ground residual colonizer (on site, initial community)
Secondary colonizer (on- or off-site seed sources)

Fire adaptations and plant response to fire:

Fire adaptations: Thimbleberry sprouts from surviving rhizomes and often emerges from soil-stored seed on burned sites [200,215]. Recovery following fire is generally rapid (review by [65]).

Plant response to fire: Generally, thimbleberry reaches or exceeds prefire abundance soon after fire [119] through postfire sprouting [43,128] and seedling establishment [91,123,165]. Recovery may be delayed if high fire temperatures penetrate deeply into the soil. After reviewing the literature and information from researchers and field practitioners in the Pacific region of North America, researchers concluded that postfire recovery of thimbleberry can be delayed after severe fires or fires on mesic or coarsely-textured sites where high temperatures reach roots and rhizomes [35].

High survival rates and abundant postfire sprouts are common for thimbleberry on burned sites. Thimbleberry sprouts were "prolific" in the first year following an early June fire in the Whatcom Creek area of Bellingham, Washington. The fire, caused by a pipeline explosion, produced flame heights of 148 feet (45 m) but burned out after about 15 minutes given the wet spring conditions in the conifer and riparian forests [67]. Thimbleberry survival was 100% following late August and early September wildfires that burned riparian vegetation along creeks in the northern Sierra Nevada. The burn pattern was patchy, with sites experiencing moderate- to high-severity fire [128]. Thimbleberry sprouted "immediately" after a fire at wet, cool sites in British Columbia's subboreal spruce zone (review by [82]). On moist, productive sites within the coastal western hemlock zone near Vancouver, thimbleberry was abundant in the first postfire year and remained abundant for at least the next 4 years [81]. In paper birch and quaking aspen stands of Isle Royale National Park, a dense thimbleberry understory is possible within the first years after fires that top-kill all trees but burn little of the humus layer [40].

Although thimbleberry survival through postfire sprouts is common, 2 studies suggest that mortality or at least delayed postfire sprouting are also possible. In white fir-mixed-conifer forests in Sequoia National Park, California, first-year fire effects were evaluated in plots with fuel loads ranging from light (0.1 kg fine woody fuel/m², all 10-hour fuels removed) to heavy (~10 kg dry woody fuel/m²). The prescribed fire burned on 10 October. Thimbleberry was present in the study area before the fire but not in the first postfire year [187]. In Montana, thimbleberry was reportedly killed by a deep burning fire [210]. However, it is unclear how long postfire effects were monitored, and several other studies from the same and nearby areas report thimbleberry survival and establishment after severe fires (see Fire severity).

Thimbleberry seedling establishment is also common on burned sites. Seedlings emerged "immediately" after fire in British Columbia's subboreal spruce zone (review by [82]), in the first postfire year following a mid-July wildfire in Pattee Canyon near Missoula, Montana [123], and within 2 years of slash burning in a clearcut Engelmann spruce-subalpine fir forest in British Columbia's Headwaters Forest District [91].

Although seedlings are often found on recently burned sites, thimbleberry seed may be sensitive to long-duration heating. From soil collected in a subalpine fir/big huckleberry habitat type in Yellowstone National Park, thimbleberry emerged (13 emergents/m²) from unheated samples but not from samples that were heated for an hour at oven temperatures of 120 °F to 300 °F (50-150 °C) [31].

Some studies suggest that growth rate and fruit production of thimbleberry may be stimulated by fire. Thimbleberry growth averaged 0.25 inch (0.6 cm)/day in the first 60 days after an early May prescribed fire in seral shrublands in northern Idaho's western redcedar/western hemlock zone. Maximum surface soil temperatures were less than 250 °F (120 °C) for 51% of pyrometers and less than 150 °F (70 °C) for 26% of pyrometers. Observations in the burned area suggested that thimbleberry was "benefited by the higher intensity burning treatments" [103]. Historical accounts indicate that Indians in the Willamette Valley burned patches of Rubus spp. in forest openings to encourage fruit production in the first postfire growing season [24].

In early postfire succession, thimbleberry abundance is often greater 5 to 15 years after fire than 1 to 4 years after fire. A wildfire burned a 2nd-growth Douglas-fir/ninebark forest in Pattee Canyon near Missoula, Montana. The rapidly spreading crown fire occurred in mid-July. Thimbleberry produced fruit in the 1st postfire year. Its cover averaged 10.2% in the 1st postfire year, 13.8% in the 2nd postfire year, and 15.5% in the 5th postfire year [43,44]. Following a severe wildfire in the grand fir/queencup beadlily habitat type adjacent to the North Fork of the John Day River in Oregon, thimbleberry cover increased substantially from the 1st postfire year (1%) to the 5th postfire year (10%). The burned area was part of the Ryder Creek Fire that burned a total of 14,650 acres (5,930 ha) between 13 August and 1 December 1987. All overstory and understory trees were killed [114]. In mixed montane forests in Glacier National Park, cover of thimbleberry was generally less as time since fire exceeded 4 years. Thimbleberry cover after crown fires averaged 1.4% on 1-year-old, 2.4% on 4-year-old, 0.21% on 6-year-old, and 0.24% on 14-year-old burned sites [155]. Because site conditions likely varied among the burned areas, fire may not have been the major factor affecting thimbleberry abundance or presence.

The following Research Project Summary provides information on prescribed fire use and postfire response of plant community species including thimbleberry:
Vegetation response to restoration treatments in ponderosa pine-Douglas-fir forests of western Montana

Hamilton's Research Papers (Hamilton 2006a, Hamilton 2006b) also provide information on prescribed fire and postfire response of thimbleberry and other plant species.

Fire severity: Although some researchers suggest that when high temperatures penetrate deeply into the soil, thimbleberry may be killed or at least have delayed regeneration [187,210], several other studies indicate that thimbleberry generally tolerates severe fires [141,184,213]. Thimbleberry often dominated early succession (first 15 postfire years) following severe fires in lodgepole pine forests on the Bitterroot National Forest, Montana, and in western redcedar-western hemlock forests on the Kaniksu National Forest, Idaho. Fires typically burned late in the summer at the peak of the dry season, consumed most of the tree canopy, and exposed mineral soil [141]. Stickney [211] classified thimbleberry as a pioneer shrub on burned sites, because it was often more frequent after than before fire. In several areas, thimbleberry cover on burned sites was several times that of prefire cover and in a couple of areas, thimbleberry became a dominant species within 9 years of burning [211]. In those areas where thimbleberry seedling establishment occurred, Stickney [212] indicated that seedlings emerged from soil-stored seed. Thimbleberry sprouts and seedlings were observed as early as 1 year following the severe Sundance Fire in August 1967, which burned within the western redcedar-western hemlock zone in the Pack River Valley, northern Idaho. The Sundance Fire killed all conifers, consumed all aboveground understory vegetation, and exposed mineral soil. Within 10 years, thimbleberry occurred on 15 of 18 burned study sites and had a high cover level of 15% [213]. Thimbleberry was present within 5 years of spring and fall prescribed fires in mixed-conifer logging slash on the Fernan Ranger District in northern Idaho. On the burned sites, average duff consumption ranged from 0.8 to 1.3 inches (2-3.3 cm), and mineral soil exposure averages ranged from 57% to 73% [184].

Thimbleberry sprouts and seedlings emerged within 2 years of a prescribed fire in a clearcut mixed-conifer stand adjacent the Dworshak Reservoir in northern Idaho. In the burned area, the density of thimbleberry seedlings was less than 0.1/m², and cover of sprouts was 7.7%. In uncut forests, thimbleberry cover was 1% [163]. Frequency of thimbleberry seedlings was only slightly greater on low-severity (0.33) than high-severity (0.25) burned sites, and significant differences in postfire establishment with burn severity were not detected. Cover of thimbleberry sprouts averaged 9% on low-severity and 6% on high-severity burned sites 2 years after the fire. All sprouts emerged in the 1st postfire year. On high-severity burned sites, most organic matter and woody fuels less than 3 inches (7.5 cm) in diameter were consumed. On low-severity burned sites, little mineral soil was exposed, and some woody fuels less than 1 inch (2.5 cm) in diameter remained [164,165]. When older low- and high-severity burned clearcuts were compared, burn severity did not affect thimbleberry abundance significantly, but time since fire did (P=0.08). Cover was greatest on 3- to 5-year-old burns [164,165].

Frequency (%) of thimbleberry on low-severity and high-severity burned sites over time on a northern Idaho clearcut* [164,165]
Time since fire (years) 1 2 3 4 5 15
Low severity 83 80 80 59 56 98
High severity 61 76 78 75 53 100
*Cover of thimbleberry was less than 10% in the first 5 postfire years and about 30% to 40% in 15th postfire year.

When prefire abundance was compared with postfire abundance following prescribed fires in ponderosa pine shelter units at the Priest River Experimental Forest in northern Idaho, thimbleberry cover was relatively unchanged by a fire that burned in moist conditions but was greater than prefire levels after a fire that burned during dry conditions. Fires occurred in sites that were selectively logged, maintaining a predominantly ponderosa pine overstory of 40 to 80 basal feet²/acre. The fire that burned during moist conditions occurred on 1 June, when air temperatures were 69 to 76 °F (21-24 °C), relative humidity was 43% to 50%, and wind speeds were 1 to 8 miles (2-4 km)/hour. The fire that burned during dry conditions occurred in mid-September, when air temperatures were 54 to 77 °F (12-25 °C), relative humidity was 39% to 66%, and wind speeds were 1 to 5 miles (1-2 km)/hour. At the time of burning, duff moisture content was nearly twice as great on moist than dry sites, and woody fuel moisture was about 10% to 15% greater on moist than dry sites. Mineral soil exposure was 10% on the moist site and 38% on the dry site. Woody fuel consumption was 24% on the moist site and 57% on the dry site [202].

Cover (%) of thimbleberry before and after broadcast burning of thinned ponderosa pine forests in northern Idaho [202]
  Unburned Moist burn Dry burn
Prefire (1 year after logging) 4.2 1.3 1.2
Postfire (1 year after fire) 4.5 1.5 2.6

In the southern Cascade Range, California, thimbleberry density and frequency increased after fire regardless of season or fuel consumption, but increases were more substantial after high-consumption than moderate-consumption fires. Prescribed fires burned in early spring, late spring, or early fall in forests dominated by Jeffrey pine (Pinus jeffreyi), Douglas-fir, and incense-cedar (Calocedrus decurrens) [119]. More information about this study is available in the Research Project Summary [70] of the study by Kauffman and Martin [119]; information from the Quincy site applies to thimbleberry.

There were no discernible patterns in changes of thimbleberry abundance after the first 6 to 9 years of succession in Montana forests that were logged and then broadcast burned after slash was distributed as an even fuel bed. Thimbleberry responses ranged from decreased cover on one site to 5% increases on others [210].

While thimbleberry abundance is rarely reduced when fire follows logging, it may be reduced when logging follows fire. In Douglas-fir-hardwood forests on the Klamath National Forest, northwestern California, thimbleberry only occurred on burned sites that were not salvage logged following a surface wildfire. Thimbleberry was absent from old-growth forests but averaged 3.5% cover in the 14th postfire year in areas free of salvage logging [95]. For more information on succession as it relates to thimbleberry abundance on logged and burned sites, see Logging and burning.

FUELS AND FIRE REGIMES: Fuels: The fuel characteristics of thimbleberry were not specifically described in the available literature (2012), but fuel structures of riparian habitats may differ from those in upland habitats. In the Cummings Creek Wilderness in Oregon's Coast Ranges, average tree basal area and stand density were almost twice as great on hillsides as in riparian areas. However, volume of downed wood, shrub cover, and basal area of hardwood trees was greater in riparian areas than on hillsides. About the same number of trees survived a large, stand-replacing fire in 1849 in riparian areas as on hillsides, but Douglas-fir-dominated stands on the drier hillsides were often younger than Sitka spruce-dominated stands in the wetter riparian areas, suggesting that reburning was more likely on hillsides than in riparian areas [241].

Some studies suggest that shrublands or open forests with abundant thimbleberry in the understory may experience frequent fire. In the western redcedar-western hemlock zone of northern Idaho, where thimbleberry is common, shrublands dominate for decades after some fires. Postfire fuel accumulation is often substantial as snags fall and shrubs and conifers regenerate. The resulting shrublands can support fast-moving, intense reburns [200].

Fire regimes: Descriptions of past fire frequencies and fire severities from thimbleberry's forest and riparian habitats came almost exclusively from the western United States, although one study reports fire history from a small area of Minnesota. Even with only a portion of thimbleberry's range represented, fire history studies indicate that thimbleberry occurs in vegetation types where the fire frequency ranges from frequent to infrequent and fire behavior ranges from low-severity surface fires to high-severity crown fires.

Fire use by Indians has likely affected vegetation patterns and historic fire frequencies throughout thimbleberry's range but was rarely discussed in much detail. In south-central Washington, early accounts of the Kilikitat territories described "sharply defined borders" around prairies and shrublands occurring within woodland and forest communities. Researchers thought these patterns suggested regular burning from the peripheries into the centers of prairies and shrublands. Maintenance of early-seral communities provided high levels of berry and grass production [174]. Analysis of charcoal and pollen sediments from the Lake of the Clouds and surrounding areas in the Boundary Waters Canoe Area provided a 1,000-year fire record, which very likely included fire use by Indians. Intervals between fires ranged from 10 to 100 years or more. Thimbleberry occurred in the immediate vicinity of Lake of Clouds and surrounding areas where mixed forests dominated by jack pine (Pinus banksiana) occurred [217].

Forest communities: Fire regimes are described for a variety of upland forest communities in the Pacific Northwest and California. In these studies, fire-return intervals ranged from 50 to 200 years and generally were longest in the most mesic forest types.

On Desolation Peak in the northern Cascade Range of Washington, average fire-return intervals ranged from 52 years in ponderosa pine-Douglas-fir forests to 137 years in Douglas-fir-western hemlock and mountain hemlock-Pacific silver fir forests. Fires burned on Desolation Peak about every 15 years. They were more common or largest from 1800 to 1899. The fire rotation interval for the 8,600-acre (3,500 ha) study area was 100 years from 1573 to 1985. It was 100 years from 1600 to 1699; 208 years from 1700 to 1799; 60 years from 1800 to 1899; and 103 years from 1900 to 1985. Frequency of thimbleberry was 24% in Douglas-fir-grand fir forests where the fire-return interval averaged 93 years; 60% in Douglas-fir-Pacific silver fir forests where the fire-return interval averaged 108 years; and 25% in lodgepole pine-subalpine fir forests where the fire-return interval averaged 109 years [2].

The average fire-return interval was 85 years for a 53-mile² (1,375 km²) study area in Douglas-fir-western hemlock forests in the central Oregon Coast Ranges. Researchers reconstructed the fire history from more than 4,000 stumps at 178 sites. Fire size averaged 37 miles² (97 km²) and ranged from 7 to 210 miles² (18-544 km²), and there were 27 fire episodes in 516 years. (Fires recorded during the same year from at least 3 sites were considered fire episodes.) The fire rotation interval was 271 years. About 0.5% of the study area burned each year, and fires were typically mixed severity. Just 6 of the 27 fire episodes were considered stand-replacing in more than 50% of the sites. Average fire size was smaller (25 miles² (66 km²)) and fire rotation intervals were less (452 years) before European settlement (1478-1845) than after European settlement (1846-1909), when fire size averaged 74 miles² (192 km²) and fire rotation was 78 years. During the fire suppression era (after 1910), the fire rotation interval was 335 years. The researcher indicated that the fire history reconstruction methods used may have missed fires smaller than 4 miles² (10 km²) and underestimated the size of very large fires [109].

Fire history studies in Idaho and California suggest that topography and moisture can affect fire frequency and severity. In the Priest Lake region of northern Idaho, the average fire-return interval was 50 to 150 years on low to midslopes in western hemlock/Oregon boxwood and western redcedar/Oregon boxwood forests. Fire severity was highly variable, ranging from stand-replacing fires to surface fires that left even thin-barked overstory trees undamaged. Stands on sheltered, north-facing slopes burned less severely than stands on wind-exposed, southwestern slopes. In western redcedar/lady fern (Athyrium spp.) and western redcedar/devils-club (Oplopanax horridus) habitat types growing near streams or at seepage sites, the average fire-return interval exceeded 200 years, and fires were generally low severity [12]. In redwood forests in northern coastal California, mesic sites near the coast experienced surface fires at 250- to 500-year intervals. The most xeric, interior sites burned at intervals as short as 50 years. Intermediate sites burned every 100 to 200 years [228]. In mixed-conifer forests in the Sacramento River watershed in the Klamath Mountains, the median fire-return intervals at 2 north-facing sites were 31 and 36 years and ranged from 9 to 71 years before1850. On 2 south-facing sites, median fire-return intervals were 26 and 52 years and ranged from 7 to 65 years. Researchers indicated that burning conditions, fire size, and fire patterns changed with fire exclusion in the 1900s. During the suppression era, horizontal and vertical fuel loads increased, fire size decreased, and fire uniformity increased. A more uniform spatial pattern occurs because all but the most severe fires are generally contained, and only large fires burning during severe conditions escape suppression [203].

Riparian communities: In Oregon and California, fires that burned in wide areas of riparian vegetation along large rivers were less severe than those that burned along small rivers with narrow riparian zones. Two riparian sites were evaluated 2 to 4 years after the Biscuit Fire in southwestern Oregon and after the B and B complex fires in west-central Oregon. Within the riparian zone burned by the Biscuit Fire, fire severity, as determined by basal area mortality and degree of exposure of mineral soil, was significantly greater (P<0.05) along small streams than along large streams. The riparian plant communities along small streams closely resembled that of adjacent upland communities, whereas riparian plant communities along large streams had a much larger hardwood tree component than adjacent uplands. For riparian sites burned in the B and B complex fire, fire severity was more closely tied to plant association than stream size. Basal area mortality was significantly greater in ponderosa pine forests than in mixed-conifer forests, but mineral soil exposure was greater in mixed-conifer than ponderosa forests [85]. On the Plumas National Forest in the northern Sierra Nevada, fire was more severe along Fourth Water Creek—where riparian zones were wide and flat—than along Third Water Creek, where riparian zones were narrow and steep. Fire pattern and severity were evaluated 1 year after the Lookout wildfire burned in late August and early September. Fires burned to the water's edge less often on Third Water than Fourth Water Creek, suggesting that width of the riparian zone was negatively correlated with the extent of riparian area burned. About half of transects along Fourth Water Creek burned with moderate to high severity and had some crowning behavior. Third Water Creek burned primarily in low- to moderate-severity surface fires, but these fires did result in some mortality of understory vegetation [128].

Riparian and upland communities compared: In the studies that compared fire frequency and fire behavior in riparian and upland sites, fire frequency and fire behavior were often similar. Sometimes stream size, extent of riparian vegetation, or vegetation type were better predictors of fire behavior and fire frequency than slope position or distance from the river. In Oregon, comparisons of riparian and upland sites burned by the Biscuit Fire and by the B and B complex fire revealed that fire severity differences between upland and riparian sites depended on which measure of fire severity was used. At both burned sites, percent crown scorch and basal area mortality (indicators of overstory fire severity) were not significantly different for riparian and upland sites, but percentage of exposed mineral soil and char heights (indicators of understory fire severity) were significantly lower (P<0.01) for riparian than upland sites. Regression analyses suggested that upland fire severity was the strongest predictor of basal area mortality in riparian areas. Within the Biscuit Fire perimeter, overstory fire severity was greater in riparian areas with dense small trees, and understory fire severity was greater in areas with higher basal area of hardwoods, but this same pattern was not observed within the B and B complex fire perimeter. Within the B and B complex, overstory fire severity was significantly greater (P<0.05) in relatively dry riparian areas dominated by ponderosa pine than in relatively wet riparian areas dominated by a mix of conifers. In both areas, basal area mortality was less along large than small streams, and fires were generally less severe along low-gradient than high-gradient streams [84].

Fire-return intervals were not very different for riparian and upland areas from 36 sites in the northern Sierra Nevada. Study sites were located in forests where low- and mixed-severity fires were historically frequent (<30-year fire-return intervals). The fire-return intervals for riparian areas ranged from 8.4 to 42.3 years when all fire scars were used in estimations (liberal method) and ranged from 10 to 86.5 years when scars on 2 or more trees were required for estimations (conservative method). At uplands sites, the fire-return intervals were 6.1 to 58 years using the liberal estimation method and 10 to 56.3 years using the conservative method. The fire history record included dates from 1387 to 2005. Riparian and upland sites burned primarily in the late summer or early fall dormant seasons. Fire-return intervals for riparian and upland sites were significantly (P<0.1) different in only 25% of sites sampled. Fire-return intervals were shorter in the relatively deeper, narrower riparian zones. Fire-return intervals increased as abundance of pines (Pinus spp.) increased in upland and riparian vegetation. At 3 sites, the fire-return interval was significantly (P<0.1) shorter for riparian than upland sites, suggesting that riparian zones may occasionally act as corridors for fire spread. At most sites there were no significant differences between the fire-return intervals before or after 1850, and at 4 sites, fire-return intervals were significantly shorter after than before 1850 [227].

See the Fire Regime Table for further information on fire regimes of vegetation communities in which thimbleberry may occur.

FIRE MANAGEMENT CONSIDERATIONS:
The use of prescribed fire to specifically manage thimbleberry was not discussed in the available literature (2012). Periodic low- to high-severity fires in riparian areas would not likely affect the survival and persistence of thimbleberry (see Plant response to fire).

Fire in riparian areas can lead to increases in stream temperatures, suggesting that fire timing and its potential effect on aquatic organisms be considered when planning prescribed fire in the riparian zone. On Idaho's Payette National Forest, water temperatures were compared for 1st- and 2nd-order streams (3-10 feet (1-3 m) wide) in burned and unburned catchments. The wildfire burned in September and stream temperatures were monitored for a year, beginning about 10 months after the fire. In late summer and early fall, the daily maximum temperatures were greater for burned 62.4 °F (16.9 °C) than unburned 57.2 °F (14 °C) streams. The greatest difference between burned and unburned streams was captured in the daily temperature fluctuation, which was 2 to 3 times greater for burned than unburned streams. Researchers reported that a 3.6 to 5.4 °F (2-3 °C) increase in stream temperature can result in changes in the size at maturity, timing of emergence, and sex ratios for many aquatic organisms [189].

MANAGEMENT CONSIDERATIONS

SPECIES: Rubus parviflorus
FEDERAL LEGAL STATUS:
None

OTHER STATUS:
Information on state- and province-level protection status of plants in the United States and Canada is available at NatureServe.

IMPORTANCE TO WILDLIFE AND LIVESTOCK:
Thimbleberry is an important food source for ungulates in the West and small mammals and birds throughout its range [82,88,185].

Elk and deer: Use of thimbleberry by elk, white-tailed deer, and mule deer can be substantial in western North America. Use may be heaviest in recently burned or logged areas, where thimbleberry is often abundant. Although thimbleberry was not generally considered preferred big game forage in northern Idaho, elk, white-tailed deer, and mule deer readily browsed thimbleberry on burned sites, especially 1-year-old burned sites in the western redcedar/Oregon boxwood habitat type [13]. On the west side of the Cascade Range in the Pacific Northwest, thimbleberry was considered a principal browse species for elk, white-tailed deer, and mule deer [160]. It was important summer elk browse in Douglas-fir forests in the southern Coast Ranges in Oregon. In logged areas, cover of thimbleberry was significantly (P<0.01) greater in exclosures protected from elk browsing than in unprotected areas [219]. In northern Idaho, thimbleberry is considered to have only intermediate palatability for elk, but in the summer, its leaves were consumed a "fair" amount by elk on the Selway Game Preserve. Because of thimbleberry's abundance in that area, it was considered an important component of elk diets [244]. Based on 2 years of fecal analyses in the White Mountains of Arizona, thimbleberry made up 19.5% of female, 11.5% of male, and 11.3% of elk calf diets in the spring and 8.1% of female and male and 2.2% of calf diets in the summer [234]. In coastal forests on southern Vancouver Island, thimbleberry leaves were rated as having low to moderate importance as a mule deer summer food [41]. In Oregon, thimbleberry was a preferred mule deer food and typically eaten most in summer and early fall [61,147,159]. About 10 years after a fire in the Tillamook burn area, mule deer use of thimbleberry was "extensive" [101]. In the upper Selway River drainage of east-central Idaho, mule deer did not feed on thimbleberry between January and May, but in July, thimbleberry frequency in mule deer diets was 100% [121]. When captive mule deer were offered fresh thimbleberry forage collected from parts of northern Utah, they avoided it from 31 May to 20 June but preferred it from 1 August to 22 August [204].

Moose: Thimbleberry was important summer browse for moose near Jackson Hole, Wyoming [105] but was browsed little by moose in Isle Royale National Park, Michigan [115,179]. Thimbleberry buds were eaten in some areas of the Park in early May when moose populations were near peak levels, but in the majority of areas, thimbleberry was not browsed at all [131,172].

Bears: Several sources indicate that bears feed on thimbleberry fruits and shoots [50,82,188]. In northeastern Minnesota, thimbleberry is listed as a major food source for American black bears [188].

Small mammals: In the reviewed literature (as of 2012), a variety of small mammals were found to feed on thimbleberry fruits, but the true variety and extent of thimbleberry use by small mammals is not likely captured in this short discussion. Squirrels, chipmunks, woodrats, voles, mice, and American martens [82] have all fed on thimbleberry. In Oregon, Townsend's chipmunks, Pacific jumping mice, and deer mice ate thimbleberry fruits in the summer and fall, and dusky-footed woodrats fed on thimbleberry leaves [147]. Along the Oregon Coast from Coos to Tillamook counties, white-footed voles trapped in the red alder/salmonberry habitat type had little thimbleberry in their diets from February to March and none from June to August, but they had 14% in November diets [233]. In Glacier National Park, American marten scat was collected for 6 years, and Rubus spp. seeds were found in scat collected in the summer of all years. The greatest amount of Rubus spp. seed in scat was 12.6% [238]. In northern Minnesota, thimbleberry was recovered from 11% of the stomachs and 12% of the cheek pouches of least chipmunks captured in September. As many as 190 Rubus spp. seeds were recovered from one stomach and about 400 from a single cheek pouch [4].

Birds: A variety of birds feed on thimbleberry fruits; however, this discussion likely represents only a small sample of the true variety and extent of the use of thimbleberry by North American birds. A review reports that thimbleberry fruits can make up 10% to 25% of upland game bird diets [145]. On Vancouver Island, thimbleberry fruits were taken by American robins, northwestern crows, and Swainson's thrushes [27]. In northern California, thimbleberry fruits were a major food source for band-tailed pigeons from mid-May to mid-June [76,104]. In redwood forests, researchers observed at least one instance of varied thrushes feeding on thimbleberry [21].

Palatability and nutritional value: As browse, thimbleberry appears most palatable from late spring to early fall, given its high rates of use at this time [61,147,219,234]. In Washington, palatability of thimbleberry browse is considered fair for domestic sheep, birds, and small mammals but poor for cattle and horses. Energy and protein values for thimbleberry fruits and browse are considered low [129]. Analyses indicate that thimbleberry nutritional content is sufficient for moose, but in Isle Royale National Park, moose almost never feed on thimbleberry, possibly because of thimbleberry's tannin and cardiac glycoside contents [22]. In controlled feeding trials, yellow-pine chipmunks consumed more thimbleberry than cedar waxwings. The preference ranking of thimbleberry among 19 to 20 other fleshy-fruited plant species was much lower for yellow-pine chipmunks than for cedar waxwings [23].

Nutritional information related to thimbleberry was limited to the western United States. In western Oregon, thimbleberry was most nutritious in midsummer and was generally a poor winter food; however, winter protein content was much greater on very recently burned sites. On a 6-year-old burned site, the protein content of thimbleberry averaged 4.7%, and on a 3-month-old burned site, protein content averaged 11.6% [61]. When seasonal protein contents were compared on a site burned less than 6 years earlier, summer protein content was twice that of winter. Of the 6 browse species evaluated, thimbleberry had the lowest protein content [62]. In north-central Idaho, researchers found that prior livestock grazing can affect protein content of thimbleberry browse. Within a recent clearcut, fall crude protein and available protein values were higher on plots grazed in early and late summer by domestic sheep than on ungrazed plots [7]. The nutritional content of thimbleberry fruits collected in late summer from grand-fir forests in Washington's Rainbow Creek Research Natural Area, based on dry pulp measurements was: protein 4%, lipid 2.3%, neutral detergent fiber 18.6%, calcium 0.5%, and potassium 1.1%. Compared to other shrub and forb species in the study area protein, lipid, and potassium content for thimbleberry was low, but fiber and calcium content was high [180].

Cover value: Although cover value of thimbleberry was not described in detail in the reviewed literature (as of 2012), its multibranched structure and large, broad leaves (see Botanical description) suggest it probably provides important cover for small mammals and birds.

VALUE FOR REHABILITATION OF DISTURBED SITES:
Use and success of thimbleberry in revegetation projects were not commonly reported in the available literature (2012), but thimbleberry's aggressive natural regeneration on disturbed sites (see earlier discussions of Forest succession, Disturbance tolerance, and Logging and burning) suggests it may have potential in artificial revegetation and rehabilitation. In northwestern Montana, thimbleberry survival was 73% four years after bare root stock was planted on a roadside cut in the Coram Experimental Forest [108].

OTHER USES:
Humans consume thimbleberry fruits; the fruits are considered more flavorful in the eastern than western range or in areas receiving high amounts of rainfall [231]. Fruits are described as tasty in Michigan [232]. The Nez Perce Indians preferred fruits from shrubs growing in mountainous areas [144]. Many indigenous people inhabiting regions along the Pacific Coast, including the Haidi [173], Kwakiutl [224], Hoh, and Quileute Indians [183], ate thimbleberry fruits fresh and preserved them for later use. Thimbleberry sprouts and fruits are high in vitamin C [173]. Other uses included: boiling thimbleberry leaves with trailing blackberry (Rubus ursinus) roots and vines into a tea to treat vomiting and spitting up blood, sprinkling dried thimbleberry leaf powder into wounds to aid healing [224] and into burns to lessen scarring [88], using thimbleberry leaves to catch menstrual blood and shorten the duration of a period [224], boiling thimbleberry leaves into a tea to treat anemia, boiling thimbleberry bark to be used in soap [88], and chewing on dried brown thimbleberry leaves to ease stomach aches or diarrhea [223]. Thimbleberry stems were used by the indigenous people of the Salmon River-Cascade Head area of the Oregon Coast in basket making [249].

OTHER MANAGEMENT CONSIDERATIONS:
See Browsing and Logging and burning for information on thimbleberry's potential response to browsing and impacts on timber species.

APPENDIX: FIRE REGIME TABLE

SPECIES: Rubus parviflorus
The following table provides fire regime information that may be relevant to thimbleberry habitats. Follow the links in the table to documents that provide more detailed information on these fire regimes.

Fire regime information on vegetation communities in which thimble may occur. This information is taken from the LANDFIRE Rapid Assessment Vegetation Models [136], which were developed by local experts using available literature, local data, and/or expert opinion. This table summarizes fire regime characteristics for each plant community listed. The PDF file linked from each plant community name describes the model and synthesizes the knowledge available on vegetation composition, structure, and dynamics in that community. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.
Pacific Northwest California Southwest Great Basin
Northern and Central Rockies Northern Great Plains Great Lakes  
Pacific Northwest
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Pacific Northwest Woodland
Oregon white oak Replacement 3% 275    
Mixed 19% 50    
Surface or low 78% 12.5    
Oregon white oak-ponderosa pine Replacement 16% 125 100 300
Mixed 2% 900 50  
Surface or low 81% 25 5 30
Ponderosa pine Replacement 5% 200    
Mixed 17% 60    
Surface or low 78% 13    
Pacific Northwest Forested
California mixed evergreen (northern California and southern Oregon) Replacement 6% 150 100 200
Mixed 29% 33 15 50
Surface or low 64% 15 5 30
Douglas-fir (Willamette Valley foothills) Replacement 18% 150 100 400
Mixed 29% 90 40 150
Surface or low 53% 50 20 80
Douglas-fir-western hemlock (dry mesic) Replacement 25% 300 250 500
Mixed 75% 100 50 150
Douglas-fir-western hemlock (wet mesic) Replacement 71% 400    
Mixed 29% >1,000    
Mixed conifer (eastside dry) Replacement 14% 115 70 200
Mixed 21% 75 70 175
Surface or low 64% 25 20 25
Mixed conifer (eastside mesic) Replacement 35% 200    
Mixed 47% 150    
Surface or low 18% 400    
Mixed conifer (southwestern Oregon) Replacement 4% 400    
Mixed 29% 50    
Surface or low 67% 22    
Ponderosa pine, dry (mesic) Replacement 5% 125    
Mixed 13% 50    
Surface or low 82% 8    
Pacific silver fir (low elevation) Replacement 46% 350 100 800
Mixed 54% 300 100 400
Pacific silver fir (high elevation) Replacement 69% 500    
Mixed 31% >1,000    
Red fir Replacement 20% 400 150 400
Mixed 80% 100 80 130
Sitka spruce-western hemlock Replacement 100% 700 300 >1,000
Spruce-fir Replacement 84% 135 80 270
Mixed 16% 700 285 >1,000
Subalpine fir Replacement 81% 185 150 300
Mixed 19% 800 500 >1,000
California
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
California Woodland
Ponderosa pine Replacement 5% 200    
Mixed 17% 60    
Surface or low 78% 13    
California Forested
Aspen with conifer Replacement 24% 155 50 300
Mixed 15% 240    
Surface or low 61% 60    
California mixed evergreen Replacement 10% 140 65 700
Mixed 58% 25 10 33
Surface or low 32% 45 7  
Coast redwood Replacement 2% ≥1,000    
Surface or low 98% 20    
Jeffrey pine Replacement 9% 250    
Mixed 17% 130    
Surface or low 74% 30    
Interior white fir (northeastern California) Replacement 47% 145    
Mixed 32% 210    
Surface or low 21% 325    
Mixed conifer (north slopes) Replacement 5% 250    
Mixed 7% 200    
Surface or low 88% 15 10 40
Mixed conifer (south slopes) Replacement 4% 200    
Mixed 16% 50    
Surface or low 80% 10    
Mixed evergreen-bigcone Douglas-fir (southern coastal) Replacement 29% 250    
Mixed 71% 100    
Red fir-western white pine Replacement 16% 250    
Mixed 65% 60 25 80
Surface or low 19% 200    
Red fir-white fir Replacement 13% 200 125 500
Mixed 36% 70    
Surface or low 51% 50 15 50
Sierra Nevada lodgepole pine (cold wet upper montane) Replacement 23% 150 37 764
Mixed 70% 50    
Surface or low 7% 500    
Sierra Nevada lodgepole pine (dry subalpine) Replacement 11% 250 31 500
Mixed 45% 60 31 350
Surface or low 45% 60 9 350
Southwest
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Southwest Grassland
Montane and subalpine grasslands with shrubs or trees Replacement 30% 70 10 100
Surface or low 70% 30    
Southwest Woodland
Riparian deciduous woodland Replacement 50% 110 15 200
Mixed 20% 275 25  
Surface or low 30% 180 10  
Southwest Forested
Aspen with spruce-fir Replacement 38% 75 40 90
Mixed 38% 75 40  
Surface or low 23% 125 30 250
Lodgepole pine (Central Rocky Mountains, infrequent fire) Replacement 82% 300 250 500
Surface or low 18% >1,000 >1,000 >1,000
Ponderosa pine-Douglas-fir (southern Rockies) Replacement 15% 460    
Mixed 43% 160    
Surface or low 43% 160    
Riparian forest with conifers Replacement 100% 435 300 550
Southwest mixed conifer (cool, moist with aspen) Replacement 29% 200 80 200
Mixed 35% 165 35  
Surface or low 36% 160 10  
Southwest mixed conifer (warm, dry with aspen) Replacement 7% 300    
Mixed 13% 150 80 200
Surface or low 80% 25 2 70
Spruce-fir Replacement 96% 210 150  
Mixed 4% >1,000 35 >1,000
Great Basin
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Great Basin Shrubland
Mountain shrubland with trees Replacement 22% 105 100 200
Mixed 78% 29 25 100
Great Basin Woodland
Ponderosa pine Replacement 5% 200    
Mixed 17% 60    
Surface or low 78% 13    
Great Basin Forested
Aspen with conifer (low to midelevations) Replacement 53% 61 20  
Mixed 24% 137 10  
Surface or low 23% 143 10  
Aspen with conifer (high elevations) Replacement 47% 76 40  
Mixed 18% 196 10  
Surface or low 35% 100 10  
Aspen-cottonwood, stable aspen without conifers Replacement 31% 96 50 300
Surface or low 69% 44 20 60
Aspen with spruce-fir Replacement 38% 75 40 90
Mixed 38% 75 40  
Surface or low 23% 125 30 250
Douglas-fir (interior, warm mesic) Replacement 28% 170 80 400
Mixed 72% 65 50 250
Ponderosa pine-Douglas-fir Replacement 10% 250   >1,000
Mixed 51% 50 50 130
Surface or low 39% 65 15  
Ponderosa pine, interior Replacement 5% 161   800
Mixed 10% 80 50 80
Surface or low 86% 9 8 10
Spruce-fir-pine (subalpine) Replacement 98% 217 75 300
Mixed 2% >1,000    
Northern and Central Rockies
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Northern and Central Rockies Shrubland
Riparian (Wyoming) Mixed 100% 100 25 500
Mountain shrub, nonsagebrush Replacement 80% 100 20 150
Mixed 20% 400    
Northern and Central Rockies Forested
Douglas-fir (cold) Replacement 31% 145 75 250
Mixed 69% 65 35 150
Douglas-fir (warm mesic interior) Replacement 28% 170 80 400
Mixed 72% 65 50 250
Grand fir-Douglas-fir-western larch mix Replacement 29% 150 100 200
Mixed 71% 60 3 75
Grand fir-lodgepole pine-western larch-Douglas-fir Replacement 31% 220 50 250
Mixed 69% 100 35 150
Lodgepole pine, lower subalpine Replacement 73% 170 50 200
Mixed 27% 450 40 500
Lodgepole pine, persistent Replacement 89% 450 300 600
Mixed 11% >1,000    
Lower subalpine (Wyoming and Central Rockies) Replacement 100% 175 30 300
Mixed-conifer upland western redcedar-western hemlock Replacement 67% 225 150 300
Mixed 33% 450 35 500
Ponderosa pine (Black Hills, low elevation) Replacement 7% 300 200 400
Mixed 21% 100 50 400
Surface or low 71% 30 5 50
Ponderosa pine (Black Hills, high elevation) Replacement 12% 300    
Mixed 18% 200    
Surface or low 71% 50    
Ponderosa pine (Northern and Central Rockies) Replacement 4% 300 100 >1,000
Mixed 19% 60 50 200
Surface or low 77% 15 3 30
Ponderosa pine (Northern Great Plains) Replacement 5% 300    
Mixed 20% 75    
Surface or low 75% 20 10 40
Ponderosa pine-Douglas-fir Replacement 10% 250   >1,000
Mixed 51% 50 50 130
Surface or low 39% 65 15  
Western larch-lodgepole pine-Douglas-fir Replacement 33% 200 50 250
Mixed 67% 100 20 140
Upper subalpine spruce-fir (Central Rockies) Replacement 100% 300 100 600
Western redcedar Replacement 87% 385 75 >1,000
Mixed 13% >1,000 25  
Northern Great Plains
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Northern Plains Woodland
Great Plains floodplain Replacement 100% 500    
Northern Great Plains wooded draws and ravines Replacement 38% 45 30 100
Mixed 18% 94    
Surface or low 43% 40 10  
Great Lakes
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Great Lakes Woodland
Jack pine-open lands (frequent fire-return interval) Replacement 83% 26 10 100
Mixed 17% 125 10  
Great Lakes Forested
Conifer lowland (embedded in fire-prone ecosystem) Replacement 45% 120 90 220
Mixed 55% 100    
Conifer lowland (embedded in fire-resistant ecosystem) Replacement 36% 540 220 >1,000
Mixed 64% 300    
Eastern white pine-eastern hemlock Replacement 54% 370    
Mixed 12% >1,000    
Surface or low 34% 588    
Great Lakes floodplain forest Mixed 7% 833    
Surface or low 93% 61    
Great Lakes pine forest, eastern white pine-eastern hemlock (frequent fire) Replacement 52% 260    
Mixed 12% >1,000    
Surface or low 35% 385    
Great Lakes pine forest, jack pine Replacement 67% 50    
Mixed 23% 143    
Surface or low 10% 333    
Great Lakes spruce-fir Replacement 100% 85 50 200
Minnesota spruce-fir (adjacent to Lake Superior and Drift and Lake Plain) Replacement 21% 300    
Surface or low 79% 80    
Northern hardwood-eastern hemlock forest (Great Lakes) Replacement 99% >1,000    
Northern hardwood maple-beech-eastern hemlock Replacement 60% >1,000    
Mixed 40% >1,000    
*Fire Severities—
Replacement: Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed: Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects.
Surface or low: Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area [94,135].

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