Index of Species Information

SPECIES:  Chamaecyparis lawsoniana


SPECIES: Chamaecyparis lawsoniana
AUTHORSHIP AND CITATION : Uchytil, Ronald J. 1990. Chamaecyparis lawsoniana. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: [].

ABBREVIATION : CHALAW SYNONYMS : NO-ENTRY SCS PLANT CODE : CHLA COMMON NAMES : Port-Orford-cedar Port Orford-cedar Port-Orford white-cedar Lawson cypress Lawson false-cypress false cypress Oregon-cedar white cedar ginger pine TAXONOMY : The currently accepted scientific name of Port-Orford-cedar is Chamaecyparis lawsoniana (A. Murr.) Parl. [19,21,24]. There are no recognized subspecies, varieties, or forms; however, over 200 cultivars have been developed which vary in size, shape, branching, and coloration [37]. Port-Orford-cedar belongs to the family Cupressaceae. The genus Chamaecyparis includes eight taxa of which Port-Orford-cedar is the largest in size. The range of Alaska-cedar (Chamaecyparis nootkatensis) overlaps that of Port-Orford-cedar, but natural hybrids are extremely rare [37]. LIFE FORM : Tree FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY


SPECIES: Chamaecyparis lawsoniana
GENERAL DISTRIBUTION : Port-Orford-cedar has a very limited distribution, occurring near the Pacific Ocean in southwestern Oregon and northwestern California. The northern limit of its distribution is near Coos Bay, Oregon. The species' range extends southward about 220 miles (350 km) to the central portion of the Mad River drainage in Humbolt County, California [10]. Isolated populations occur near Mount Shasta and the Trinity Mountains in northern California [7,10]. It occurs in greatest abundance within about 40 miles of the coast [7]. Farther inland, its distribution is spotty, and it is mostly limited to sites with abundant soil moisture and/or atmospheric moisture [3,37]. Port-Orford-cedar is cultivated in Hawaii [39]. ECOSYSTEMS : FRES20 Douglas-fir FRES21 Ponderosa pine FRES23 Fir - spruce FRES24 Hemlock - Sitka spruce FRES27 Redwood FRES28 Western hardwoods STATES : CA HI OR BLM PHYSIOGRAPHIC REGIONS : 1 Northern Pacific Border 4 Sierra Mountains KUCHLER PLANT ASSOCIATIONS : K001 Spruce - cedar - hemlock forest K002 Cedar - hemlock - Douglas-fir forest K005 Mixed conifer forest K006 Redwood forest K007 Red fir forest K026 Oregon oakwoods K028 Mosaic of K002 and K026 K029 California mixed evergreen forest SAF COVER TYPES : 207 Red fir 211 White fir 223 Sitka spruce 229 Pacific Douglas-fir 231 Port Orford-cedar 232 Redwood 233 Oregon white oak 234 Douglas-fir - tanoak - Pacific madrone 243 Sierra Nevada mixed conifer 247 Jeffrey pine SRM (RANGELAND) COVER TYPES : NO-ENTRY HABITAT TYPES AND PLANT COMMUNITIES : Port-Orford-cedar is found in many vegetation types where it either forms small, pure stands, codominates with other conifers, or occurs as scattered trees. It is a long-lived, shade-tolerant climax species that dominates or codominates with other coniferous trees to form mature stands within four vegetation zones. The following published classification schemes list Port-Orford-cedar as a climax species or dominant part of the vegetation in community types (cts) or plant associations (pas) within the Sitka spruce (Picea sitchensis), white fir (Abies concolor), western hemlock (Tsuga heterophylla), and mixed-evergreen zones: Area Classification Authority CA, OR: Siskiyou Mtns general veg. pas Atzet & Wheeler 1984 OR: Upper Illinois general veg. cts Atzet 1979 River drainage CA, OR Port-Orford-cedar cts Hawk 1977 OR, WA general veg. cts Franklin & Dyrness 1973


SPECIES: Chamaecyparis lawsoniana
WOOD PRODUCTS VALUE : Since its discovery by European settlers in the 1850's, Port-Orford-cedar wood has been used in manufacturing many diverse products. Early use was primarily as lumber for house and ship building, timbers for mines, and in the manufacture of furniture. Port-Orford-cedar has been used in making a variety of products including airplanes, arrow shafts, boats, cabinets, crates, decking, doors, handles, hangers, lawn furniture, mouldings, plywood, telephone poles, screens, shelves, siding, stools, tables, toys, and yardsticks. During the 1920's and 1930's production increased dramatically because of two specialty industries: the manufacture of battery separators and venetian blinds. Following World War II, substitute materials were found for these products. Subsequently domestic use almost disappeared, and today remains almost nonexistent. Today nearly all harvested Port-Orford-cedar is exported to Japan. Port-Orford-cedar is very similar to hinoki (Chamaecyparis obtusa) wood, which is used in traditional Japanese house and temple construction. On federal timber sales, Japanese trading companies sometimes purchase stumpage on bid after examining individual trees. The wood is regarded so highly as a hinoki substitute that trees are felled with great care; sometimes cables are used to control the fall. Because the supply of hinoki is very limited, Port-Orford-cedar sells for a premium price as a hinoki substitute. Logs exported from the Powers Ranger District, Oregon, in 1981 sold for an average of $2,166 per thousand board feet. (the above information is summarized from Zobel and others 1985 [37] and Zobel 1986 [35]) IMPORTANCE TO LIVESTOCK AND WILDLIFE : As a food source, Port-Orford-cedar is of little importance to wildlife and livestock. Seedlings and saplings within regenerating stands show little browsing damage [37]. Some plantations, however, have shown moderate use. In a wildlife damage study, 19 percent of Port-Orford-cedar in 8- to 26-year-old plantations was moderately or severely damaged from browsing. Sixty percent of the damage was from deer and elk, and 40 percent from domestic livestock and small mammals [13]. Douglas squirrels harvest Port-Orford-cedar cones and eat the seed [32]. Mountain beavers and rabbits occasionally eat the foliage of saplings, and woodrats and porcupines eat the bark [23,37]. Caged white-footed deer mice showed a dislike for Port-Orford-cedar seed [23]. PALATABILITY : Port-Orford-cedar appears to be of low palatability to hooved browsers. NUTRITIONAL VALUE : NO-ENTRY COVER VALUE : NO-ENTRY VALUE FOR REHABILITATION OF DISTURBED SITES : Due to its susceptibility to a fatal root rot, Port-Orford-cedar is probably of very limited use for rehabilitating disturbed sites (see Management Considerations). OTHER USES AND VALUES : Port-Orford-cedar is a commercially important ornamental tree in Europe. Numerous cultivars exist. It was first cultivated in 1854. Within the natural range of Port-Orford-cedar, branches are collected for use in florist's greens [37]. This activity is often regulated by permits. Native Americans used Port-Orford-cedar wood for house planks, canoes, utensils, and arrows, and wove the shredded bark into clothing [37]. OTHER MANAGEMENT CONSIDERATIONS : Port-Orford-cedar is extremely susceptible to a fatal root rot caused by two soil-borne fungi, Phytophthora lateralis and P. cinnamomi. The crown of infected trees changes color from the normal blue-green to gold, bronze, reddish brown, and finally a dull brown. Moisture stress in the spring and summer initiates the rapid death of the entire crown. Within the roots, the fungus moves from the root tips throughout the tissue to the root crown. Roots turn a dark brown and finally black and rot within a few months [35]. Sometime prior to 1923, root rot spread within hundreds of nurseries, ornamentals, and windbreaks in the Pacific Northwest north of the natural range of Port-Orford-cedar and attacked only Port-Orford-cedar [35,37]. In 1952 the disease was introduced into the natural range of Port-Orford-cedar, apparently from infected soil of transplanted ornamentals [35]. The disease has now spread throughout much of the range of Port-Orford-cedar. The fungus is carried through water-borne spores transported primarily by natural water flow or in mud carried by animals or machinery. Thus spread of the disease has been greatly accelerated by road construction and maintenance, logging, and house building [35,37]. In the 1970's mortality of old-growth trees was about 10 million board feet annually and has gradually decreased to about 5 million board feet annually, largely due to the depletion of the resource [37]. About 60 percent of coastal second-growth Port-Orford-cedar which developed following cutting from 1880 to 1930 has been lost to this disease [37]. It may be over 100 years before Port-Orford-cedar harvest can contribute significantly to the regional economy, and this will only happen through proper timber and disease management [37]. There is currently no known cure for trees infected with root rot. Work is being conducted to find a genetic source resistant to root rot for developing planting stock [35]. Root rot can be avoided on sites where topography prevents the flow of runoff water [35]. For future harvests, managers may have to concentrate on growing Port-Orford-cedar on sites unlikely to be reached by the fungus [37]. Current root rot management generally consists of minimizing the spread of the disease by restricting or regulating human activities. Zobel and others [37] discuss ways to manage Port-Orford-cedar to minimize the spread of the root rot disease. With a better understanding of root rot, planting has begun on some federal and forest industry lands. Eight to 12 inch (20-30 cm) tall container stock has been planted at 20 to 26 foot (6-8 m) spacing [37]. The wide spacing minimizes root overlap and root to root spread of the root rot fungus. Because of its high commercial value, numerous Port-Orford-cedar plantations were begun north of its natural range prior to 1950. In the fall of 1955, a severe cold spell caused high mortality of trees on these plantations [14]. Some plantations received up to 100 percent mortality. Because of its susceptibility to cold injury and root rot, Port-Orford-cedar should not be used in forestry projects outside its natural range [14].


SPECIES: Chamaecyparis lawsoniana
GENERAL BOTANICAL CHARACTERISTICS : Port-Orford-cedar is a long-lived, shade-tolerant, coniferous, evergreen tree. Mature trees typically grow up to 200 feet (60 m) tall and have 4 to 6 foot (122-183 cm) diameter trunks [7]. The largest tree on record is 239 feet (73 m) tall with a 12 foot (3.6 m) diameter trunk [11]. Trees can live more than 600 years. Old trees have an enlarged base, a 50 to 70 foot (15.2-21.3 m) long branch-free bole, and a spirelike head of small horizontal or pendulous branches with slender flattened branchlets [24,35]. Occasionally the trunk will fork. The leaves are small, scalelike, and arranged close to the branchlets. Port-Orford-cedar has no taproot but produces vertical sinkers from the wide-spreading horizontal root system [37]. This makes trees subject to windthrow. The bark of mature trees is very thick, up to about 10 inches (25 cm) [37]. Growth and height of mature trees varies considerably among different forest communities. Height-to-age relationships of Port-Orford-cedar trees in different forest communities throughout its range is summarized below [12]: Community Height of Port-Orford-cedar at different ages (years) 100 200 300 meters feet meters feet meters feet western hemlock/swordfern (TSUHET-CHALAW/POLMUN-OXAORE) 30 98 47 154 63 207 western hemlock/rhododendron (TSUHET-CHALAW/RHOMAC-GAUSHA) -- -- 45 148 53 174 mixed fir (Abies spp.-CHALAW/herb) 12 39 36 118 50 164 white fir (ABICON-CHALAW/herb) 13 43 25 82 46 151 tanoak (CHALAW/LITDEN) 12 39 29 95 44 144 white fir-hemlock (ABICON-TSUHET-CHALAW) 12 39 26 85 41 134 western hemlock/beargrass (CHALAW-TSUHET/XERTEN) 13 43 25 82 31 102 mixed pine (Pinus spp.-CHALAW/QUEVAC/ 18 59 21 69 29 95 XERTEN) Port-Orford-cedar readily grows under the shade of other conifers but grows faster in the open [13]. Generally it grows slower than Douglas-fir (Pseudotsuga menziesii). Recent research suggests that Port-Orford-cedar is one of the most shade-tolerant conifers throughout its range [12,36]. Seedlings and saplings are often found in the shade of old-growth forests. RAUNKIAER LIFE FORM : Undisturbed State: Phanerophyte (megaphanerophyte) Burned or Clipped State: Therophyte REGENERATION PROCESSES : Sexual regeneration: The primary method of natural reproduction of Port-Orford-cedar is via seed. Trees produce seed in sufficient abundance to ensure seedling establishment under forest stands. Currently, where root rot is not a problem, Port-Orford-cedar is reproducing itself in almost all Port-Orford-cedar communities [12]. Male and female flowers are found on the same branch but on different branchlets. Flower buds begin growth in the spring and become fully developed by the end of the summer. Pollination occurs the following spring, and seeds become fully developed by September or October [13]. The seeds are borne in small cones that are from 0.25 to 0.5 inch (0.6-1.2 cm) in diameter [11]. Port-Orford-cedar seeds have small, thin marginal wings, weigh about 2 mg each, and are about 0.11 to 0.16 inch (3-4 mm) long [37]. Harris [11] reports that seeds are quite variable in weight and size, requiring from 60,000 to 600,000 to equal a pound. Port-Orford-cedar begins to produce seed early, between 5 and 9 years of age. Cone production becomes greatest at about age 100 and continues throughout the life of the tree [13]. Although trees produce seed every year, heavy seed crops are produced every 4 or 5 years [13,32]. Zobel [32] found annual seed production to vary considerably from year to year and from site to site within a given year, from 8,097 to 1,862,348 seeds per acre (20,000-4,600,000/ hectare) and from 56 to 17,193 seeds per square foot of tree basal area (600 to 185,000/sq m). The variability was not clearly related to stand or site factors. Seed fall begins in September and continues throughout winter and spring. Generally about 50 to 60 percent of the seed has fallen by mid-January, with 90 percent or more fallen by the beginning of May [13,32]. Dispersal distance is generally short. One to three tree heights is a common distance of invasion into clearcuts [37]. The small wings aid in floating on water. Dispersal by water may be of some importance in streamside habitats. Most Port-Orford-cedar seed germinates the first spring after dispersal, but a very small amount may lay dormant for up to 5 years [13]. Germination generally occurs from mid to late June [33]. Viability of seed can be low. Germination of seed collected from seed traps from many sites ranged from 13.8 to 44.2 percent [32]. In this study, seeds which fell early or late had lower germination percentages than seeds which fell during peak seed fall, and seed collected from trees had higher germination percentages (37, 52, and 55 percent) than seed collected from seed traps [32]. This is much closer to the 48 to 52 percent range reported by Harris [11]. Seed may be stored in sealed containers at temperatures below freezing with seed moisture content below 10 percent. Viability of seed stored in this manner for 7 years dropped from an initial 56 to 43 percent [11]. Seedling establishment on forest floor litter accounts for the majority of natural Port-Orford-cedar reproduction. The litter layer under Port-Orford-cedar is generally shallow, averaging about 0.4 to 1.6 inches (1-4 cm) [12]. First year survival of seedlings is often about 50 percent [13,33] but drops dramatically thereafter. Disturbance of the mineral soil can greatly enhance establishment. Native Port-Orford-cedar seed was sown on plots that were treated as follows: (1) undisturbed with the litter left intact, (2) the litter removed, (3) burned, or (4) spaded after litter was removed. The most germinants and the most surviving germinants after one growing season were found on spaded plots [33]. By the end of two growing seasons, no seedlings survived on plots that were burned or had the litter removed. After three seasons, 5 percent of the original germinants survived on spaded plots and 6 percent survived on undisturbed plots. Seedlings and saplings are often found growing in the open or under shade but not under extremely dense shade. One study found that live seedlings were found growing in 0.7 to 2.5 percent of full light, but that dead or nearly dead seedlings were on sites receiving only 0.2 to 0.4 percent of full light [36]. Thus seeds may germinate in dense, young stands, but extreme shading can cause total mortality of emerging seedlings. Following clearcutting or shelterwood cutting, Port-Orford-cedar successfully establishes from seed within about about 88 to 132 yards (80-110 m) from a seed tree [18]. Emerging seedlings are delicate and probably sensitive to drought [13]. Within a deer exclosure 1-year-old seedlings averaged 1.4 inches (3.6 cm) in height, and 2-year-old seedlings averaged 3.1 inches (7.9 cm) [11]. Vegetative regeneration: Vegetative regeneration is very limited in Port-Orford-cedar. Plants do not naturally sprout. However, stem cuttings root relatively easily if proper methods are followed [5,37]. Layering occurs infrequently and is restricted mostly to trees buried by sand or thrown by wind [37]. SITE CHARACTERISTICS : Although restricted to a small range that covers only 220 miles (350 km) from north to south, Port-Orford-cedar occupies many vegetation zones, soil types, and elevations. It commonly grows in mixed stands but occasionally forms pure stands. It occurs mainly within Sitka spruce, western hemlock, white fir, redwood (Sequoia sempervirens), red fir (Abies magnifica), mixed-pine, and mixed-evergreen forests [3,8,10,12,27,28,31]. Within each forest, Port-Orford-cedar is primarily restricted to moist locations such as benches, drainageways, or some type of concavity which receives a constant seepage of water [3,12,36,37]. It is mostly absent from ridges and upper slopes due to the lack of water; however, some coastal Oregon and upper elevation Klamath Mountain stands do occupy top-slope positions [12,36,37]. Port-Orford-cedar also occurs on coastal dunes and in bogs with ultramafic soils. Common associates: Besides the above mentioned species, Port-Orford-cedar is commonly associated with Douglas-fir, grand fir (Abies grandis), lodgepole pine (Pinus contorta), western redcedar (Thuja plicata), and Pacific yew (Taxus brevifolia) in coastal areas [12,13]. Inland tree associates include sugar pine (P. lambertiana), western white pine (P. monticola), incense-cedar (Libocedrus decurrens), and Pacific yew [3,12,13]. Hardwood tree associates include tanoak (Lithocarpus densiflorus), Pacific madrone (Arbutus menziesii), golden chinkapin (Castanopsis chrysophylla), red alder (Alnus rubra), and canyon live oak (Quercus chrysolepis) [3,12,13]. Associated shrubs include dwarf Oregongrape (Berberis nervosa), salal (Gaultheria shallon), oceanspray (Holodiscus discolor), the shrub form of tanoak (L. densiflorus var. echinoides), Sadler oak (Q. sadleriana), huckleberry oak (Q. vaccinifolia), Pacific rhododendron (Rhododendron macrophyllum), western azalea (Rhododendron occidentale), baldhip rose (Rosa gymnocarpa), red huckleberry (Vaccinium parvifolium), and evergreen huckleberry (V. ovatum) [3,12,13]. Soils: Port-Orford-cedar occurs on many different soil types including dune sands, organic bog soils, and soils derived from gabbro, diorite, serpentine, peridotite, river alluvium, and other rock types [30,37]. On diorite it is more commonly found above 2,500 feet (760 m) [30]. Most low elevation Port-Orford-cedar forests occur on soils dervived from ultramafic parent materials [37]. Port-Orford-cedar is more successful in communities where the parent material is at least partially derived from ultramafic rock and where competition is somewhat reduced [77]. On all soil types, Port-Orford-cedar is limited to mesic situations [37]. Litter: The litter layer under eight Port-Orford-cedar communities was found to be relatively shallow, averaging only 0.4 to 1.6 inches (1-4 cm) deep [12]. The foliage of Port-Orford-cedar is less acidic than Pinaceae. Thus the litter and soil under Port-Orford-cedar stands are less acidic than under nearby conifer stands [37]. Climate: Port-Orford-cedar is distributed over an area that has warm, dry summers and cool, wet winters. Most stands in California receive at least 59 inches (150 cm) of precipitation annually [37]. Inland disjunct stands receive at least 49 inches (125 cm) of precipitation annually. Elevation: Port-Orford-cedar is found from sea level to 5,100 feet (1,554 m) in elevation [3]. SUCCESSIONAL STATUS : Port-Orford-cedar occurs as both an early seral invader and as a long-lived, shade-tolerant climax species. Seedlings become established after disturbances such as clearcutting or fire but also become established within mature forests. Continual seedling establishment and shade tolerance produce stands with many age classes [12]. Following disturbances such as fire or cutting, Port-Orford-cedar readily establishes where a seed source exists. Fire can eliminate young trees, but old-growth trees are very fire-resistant and often survive fire to reseed the site. In some old forests, two or more size classes of Port-Orford-cedar may exist, resulting from the establishment of trees following periodic fires [12]. SEASONAL DEVELOPMENT : Shoot growth of Port-Orford-cedar differs greatly from that of pines and firs. Pines and fir species have bud tissue which preforms the following year's shoots. Port-Orford-cedar does not have preformed buds; therefore shoot elongation over the summer takes longer than competing Pinaceae. Port-Orford-cedar grows much slower than Douglas-fir, and in the northern part of its range where Port-Orford-cedar grows best, prolonged shoot elongation may be necessary for it to compete. Port-Orford-cedar's twig growth phenology may partially explain its northern distributional limit. North of its range, the prolonged shoot elongation needed to make plants more competitive with other conifers would make them susceptible to frost. Port-Orford-cedar grows on hot open sites and tends to initiate twig growth earlier and often completes growth more quickly than trees on colder sites. (the above information is summarized from Zobel 1983 [34]) Port-Orford-cedar flower buds are typically set in the fall with pollination taking place the following spring [13]. Cones ripen in September or October with seed dispersal occurring immediately thereafter and continuing until spring [11,32].


SPECIES: Chamaecyparis lawsoniana
FIRE ECOLOGY OR ADAPTATIONS : Although young Port-Orford-cedar trees are easily killed by fire, relatively old trees are very fire resistant because their bark may be up to 10 inches (25 cm) thick. It is apparently less fire resistant than Douglas-fir, Ponderosa pine, sugar pine, Jeffrey pine, and incense-cedar, but more fire resistant than true firs and hemlocks [27,37]. Many vigorous old trees show evidence of repeated burning and have large fire scars [8,37]. A stump in Oregon that was 21 inches (54 cm) in diameter and 285 years old had fire scars at 35, 183, and 228 years [37]. Some fires have removed all but a thin, incomplete outer shell of wood and bark at the tree base, yet trees remain healthy [37]. These surviving trees provide a seed source for postfire seedling establishment. Pole-sized trees have moderate fire resistance and can probably withstand ground fires [37]. Port-Orford-cedar drops much less litter on the forest floor than Douglas-fir [1]. Fire frequency is partially dependent upon this fuel accumulation. Atzet [1] rated the likelihood of fire occurring under different conifer stands as follows: Less Likely ----------- red fir Jeffery pine Port-Orford-cedar tanoak Douglas-fir white fir ----------- More Likely On inland sites Port-Orford-cedar mostly occurs along stream channels, boggy drainages, other moist topographic concavities or north aspects [3]. These sites have a low probability of fire carrying after ignition [2]. POSTFIRE REGENERATION STRATEGY : crown-stored residual colonizer; short-viability seed in on-site cones off-site colonizer; seed carried by wind; postfire years 1 and 2


SPECIES: Chamaecyparis lawsoniana
IMMEDIATE FIRE EFFECT ON PLANT : Relatively small Port-Orford-cedar trees are easily killed by fire. Repeated fires can eliminate all the Port-Orford-cedar regeneration size classes from mature forest understories [1]. This is probably why Port-Orford-cedar is rare where fires occur frequently [2]. DISCUSSION AND QUALIFICATION OF FIRE EFFECT : NO-ENTRY PLANT RESPONSE TO FIRE : Mature Port-Orford-cedars are very fire resistant and often survive fire. Seed dispersed from surviving trees allows Port-Orford-cedar to rapidly establish numerous seedlings. Seedlings may maintain dominance for a few years but are usually overgrown by faster growing conifers within about 20 to 25 years [13]. Since Port-Orford-cedar is very shade tolerant, trees established following a fire will persist in the understory and eventually replace other conifers such as Douglas-fir if there is a sufficient fire-free interval to allow trees to grow to a fire-resistant size [1,13]. Some sampled stands have two or more distinct size classes, each thought to have become established following a fire [12,37]. DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : NO-ENTRY FIRE MANAGEMENT CONSIDERATIONS : NO-ENTRY

References for species: Chamaecyparis lawsoniana

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11. Harris, A. S. 1974. Chamaecyparis Spach white-cedar. In: Schopmeyer, C. S., technical coordinator. Seeds of woody plants in the United States. Agric. Handb. 450. Washington, DC: U.S. Department of Agriculture, Forest Service: 316-320. [7586]
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17. James, George A. 1958. Port-Orford-cedar plantations in the Pacific Northwest. Res. Note No. 164. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 2 p. [29663]
18. James, G. A.; Hayes, G. L. 1954. Highlights of a Port-Orford-Cedar regeneration study. Journal of Forestry. 52: 852-855. [9061]
19. Kartesz, John T.; Kartesz, Rosemarie. 1980. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. Volume II: The biota of North America. Chapel Hill, NC: The University of North Carolina Press; in confederation with Anne H. Lindsey and C. Richie Bell, North Carolina Botanical Garden. 500 p. [6954]
20. Kuchler, A. W. 1964. Manual to accompany the map of potential vegetation of the conterminous United States. Special Publication No. 36. New York: American Geographical Society. 77 p. [1384]
21. Little, Elbert L., Jr. 1979. Checklist of United States trees (native and naturalized). Agric. Handb. 541. Washington, DC: U.S. Department of Agriculture, Forest Service. 375 p. [2952]
22. Stickney, Peter F. 1989. Seral origin of species originating in northern Rocky Mountain forests. Unpublished draft on file at: U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Fire Sciences Laboratory, Missoula, MT; RWU 4403 files. 10 p. [20090]
23. Moore, A. W. 1940. Wild animal damage to seed and seedlings on cut-over Douglas-fir lands of Oregon and Washington. Technical Bulletin No. 706. Washington, DC: U. S. Department of Agriculture, Forest Service. 28 p. [9254]
24. Munz, Philip A. 1973. A California flora and supplement. Berkeley, CA: University of California Press. 1905 p. [6155]
25. Raunkiaer, C. 1934. The life forms of plants and statistical plant geography. Oxford: Clarendon Press. 632 p. [2843]
26. Ruth, Robert H. 1957. Ten year history of an Oregon coastal plantation. Research Paper 21. Portland, Oregon: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 15 p. [9934]
27. Sawyer, John O.; Thornburgh, Dale A. 1977. Montane and subalpine vegetation of the Klamath Mountains. In: Barbour, Michael G.; Major, Jack, eds. Terrestrial vegetation of California. New York: John Wiley & Sons: 699-732. [685]
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