Vegetation of Northwestern 

North America, as an Aid 

in Interpretation of 

Geologic Data 

By ROBERT S. SIGAFOOS 

CONTRIBUTIONS TO GENERAL GEOLOGY 

GEOLOGICAL SURVEY BULLETIN 1061-E 

A map and description of 

the boreal forest and some 

treeless vegetation 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1958 
UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. SEATON, Secretary 

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director 

Sigafoos, Robert Sumner, 1920-

Vegetation of northwestern North America, as an aid in. 

interpretation of geologic data. Washington, U. S. Govt. 

Print. Off., 1958. 

iii, 165-185 p. illus., maps ·(1 col. in pocket) 25 em. (U. S. Geological Survey. Bulletin 1061-E. Contributions to general geology) 

"References pertaining to key map": p.169-171. 

"References cited"; p. 182-183. 

1. Phythogeography. 2. Botany-North America. 3. BotanyEcology. I. Title. (Series: U. S. Geological Survey. Bulletin 

1061-E. Series: U. S. Geological Survey. Contributions to general geology) 

581.9711 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington 25, D. C. .. Price 75 cents (paper cover) 
CONTENTS 

Page 

Abstract---------------------------------------------------------- 165 

Introduction------------------------------------------------------ 165 

~apunits---------------------------------------------------- 167 

References pertaining to key maP-------------------------------- 169 

Acknowledgments--------------------------------------------- 171 

Interior spruce and birch forest region-------------------------------- 171 

White spruce__________________________________________________ 172 

White spruce and white birch----------------------------------- 172 

Balsam poplar------------------------------------------------ 173 

Blackspruce-------------------------------------------------- 173 

Aspen and birch----------------------------------------------- 174 

Lodgepolepine------------------------------------------------ 174 

White spruce, alpine fir, lodgepole pine, and black spruce___________ 174 

Treeless communities __________________ --------------- __ ------- 174 

Timberlineforest---------------------------------------------- 175 

Coastal spruce and hemlock forest region----------------------------- 176 

Sitka spruce and western hemlock_______________________________ 176 

Sitkaspruce-------------------------------------------------- 177 

Westernredcedar--------------------------------------------- 177 

Alder and black cottonwood ___ --------------------------------- 177 

Lodgepole and mountain hemlock ____ --------------------------- 178 

Coastal timberline forests ____________ -' ______ ------- ____ ------___ 178 

Engelmann spruce and lodgepole pine forest region____________________ 178 

Treeless region____________________________________________________ 178 

Geographic distribution of prominent tree species---------------------- 180 

List of species _________________________________ -------_____________ 181 

References cited___________________________________________________ 182 

Index------------------------------------------------------------ 185 

ILLUSTRATIONS 

Pace 

PLATE 9. Vegetation map of northwestern North America _________ In pocket 

10. Woods adjoining tundra communities __ --------------- Facing 168 

11. Treeless communities on the Seward Peninsula ___ ----- Follows 168 

12. Views of the interior spruce and birch forest region. A, 

Mature white spruce forest growing on alluvial fan. B, 

Forest, shrub, and grassland communities resulting from 

repeated fires __________________________________ Follows 168 

13. Trees growing on thawed stream banks_________ _ __ _ _ _ Facing 169 

FIGURE 31. Key map of northwestern North America showing sources of 

data------------------------------------------------ 168 

32. Distribution of 12 common species of trees_________________ 180 

m 

CONTRIBUTIONS TO GENERAL GEOLOGY 

VEGETATION OF NORTHWESTERN NORTH AMERICA, 

AS AN AID IN INTERPRETATION OF GEOLOGIC DATA 

BY RoBERT S. SIGAFoos 

ABSTRACT 

A distribution map of the major forest groups of northwestern North America 

and some treeless vegetation types of parts of Alaska has been prepared from 

published large-scale maps and data collected during recent field studies by the 

U. S. Geological Survey. The most common plant communities in the interior 

spruce and birch forest, coastal spruce and hemlock forest, and treeless regions 

are briefly described. Engelmann spruce and lodgepole pine grow in the extreme southeastern part of the region mapped. Examples are cited to demonstrate the importance of a knowledge of vegetation in aiding in interpretation of 

local distribution of permafrost, and the significance of upper Pleistocene and 

recent fossil plants, and as a part of background material for future ecologic, 

geomorphologic, and hydrologic studies. The usefulness of accurate knowledge of the geographic distribution of various species is discussed and maps 

of the principal tree species are included. 

INTRODUCTION 

A distribution map of major forest groups in North America north 

and west of Hecate Strait, British Columbia, and some treeless vegetation types in parts of Alaska has been compiled from published largescale vegetation maps and data collected during recent field studies 

incidental to the geological and ecological research program of the 

U. S. Geological Survey. Although a preliminary map initially 

compiled for the writer's use, it may be useful to others as an aid 

in the interpretation of much geologic data. 

Comments on the relationship between the distribution of vegetation 

and what is loosely called permafrost are read in the literature. 

Forest and treeless vegetation, with the exception of some mosses and 

lichens, grow only on unconsolidated surficial deposits in Alaska, and 

a comparison of the vegetation map with the map of permafrost zones 

(Hopkins and l{arlstrom, 1955, p. 116) shows no correlation between 

the distribution of vegetation and permafrost. The distribution of 

forest vegetation and factors responsible for keeping surficial materials frozen (Hopkins and Karlstrom, 1955, p. 115-116) are determined by past and present climatic, biotic, and physical variables. 

The distribution of vegetation is determined, in part, by the present 

and past effects of many environmental variables upon the phjrsiology 

165 
166 CONTRIBUTIONS TO GENERAL GEOLOGY 

of the component species; the temperature and physical characteristics 

of the subsoil are but two of these factors. 

Locally, plant communities in both the treeless vegetation and white 

spruce and white birch forest regions and the local boundaries between them can be correlated with factors related to the depth of 

perennially frozen materials. More deeply thawed soil is more stable 

(Hopkins and Sigafoos, 1951, p. 63-65; Raup, 1951, p. 111) because 

it is better drained and is, therefore, subject to less intense frost 

action. Willow shrubs and scattered trees in areas of predominantly 

treeless vegetation grow along streams where fine soil thaws to greater 

depths than in surrounding areas (pl. 13). Forest grows on slopes 

mantled-with silty soils that thaw completely or thaw to considerable 

depths each summer in western Alaska; in nearby areas, tundra communities grow on silty soil that thaws to depths from 1 to 2 feet. In 

parts of the Kobuk River valley, Alaska, white spruce woods grow on 

parts of small sand dunes that completely thaw during each summer. 

Adjoining surfaces, upon which the dunes are being deposited, are 

characterized by tundra communities and are underlain by perennially 

frozen sand that lies at depths ranging from 1 to 2 feet (pl. 10). On 

the north side of the Alaska Range in the vicinity of the railroad near 

Healy, black spruce grows more rapidly and to greater heights on 

well-drained, unfrozen, gravelly soil than on sites that are underlain 

by perennially frozen silt and clay. Black spruce, on sites underlain 

by perennially frozen materials, grow faster where depth to the 

frozen layer is deeper. 

The geologic and climatic significance of fossil plants is inferred 

from the present distributional relationships of the species or of closely 

related ones. Because of increased interest and activity in the study 

of glacial problems in Alaska and other parts of the north country, an 

increasingly large number of fossils are being collected and identified 

(Hansen, 1953; Hopkins and Benninghoff, 1953; Heusser, 1955; 

Livingstone, 1955; and Benninghoff, 19G7). The vegetation map depicts the present distribution of the major vegetation types, which 

include most of the living representatives of plant species found in 

upper Pleistocene and Recent deposits in Alaska. A knowledge of 

the distribution of these species and an understanding of their significance will aid in the interpretation of the fossils. The existing maps 

(Hulten, 1941, p. 120-121, figs. 55-66; Taylor and Little, 1950, p. 

30-31; and Hustich, 1953, p. 152-154, figs. 2-5) are published on a 

small scale and thus are difficult to use. Heusser's maps (1955, p. 

190, fig. 3) are on a larger scale but show only a small part of the area. 

The vegetation map is an index map upon which ecological, combined e~logical and geological, and hydrologic studies may be placed 
VEGETATION OF NORTHWESTERN NORTH AMERICA 167 

with reference to the vegetation. Because most Alaskan vegetation 

grows only in unconsolidated deposits, which are widespread, studies 

of surficial geology must be concerned with the vegetation. Many 

early reports of the U. S. Geological Survey on the geography and 

geology of selected areas in Alaska invariably discussed mass movement of surficial materials-noting the significance of vegetation in 

the development of small landforms. 

The importance of vegetation in the water cycle in temperate latitudes is becoming better understood. The relationship of vegetation 

to the water cycle in Alaska is almost unknown, but investigations 

in this field will undoubtedly occupy part of future hyrdologic studies. 

As pointed out by Hopkins and Karlstrom (1955, p. 114), inadequate 

water supply contributes to limiting the economic development of 

Alaska. Increasing demand for water for domestic and industrial 

uses will require comprehensive studies of the water cycle, including 

the role of vegetation. 

The map (pl. 9) will probably be of value to persons interested in 

problems of wildlife research, soil genesis and classllication, land 

management and land-use planning, as well as other studies in natural 

history. 

MAP UNITS 

The map indicates the regions in which forests may be expected and 

wl?:ere some different types of treeless vegetation predominate. The 

great rom.plexity of different habitats-especially within the mountainous regions-and large areas that are only partly known botanically~ make mapping of many types almost impossible on the present 

scale. The boundaries between different vegetation units are largely 

inferred from the known relationship between the distribution of the 

vegetation types and topography. Most lines are arbitrary because 

different vegetation types grade into each other. Most forest communities, especially those within the white spruce and birch region, 

are successional types that have developed after fire. Some of the 

species are shorter lived than others and thus have only, a m()re or 

less temporary existence in the community. The old woods and successional types are discussed for each region. 

The clear areas shown on the map are representations of regions 

above and beyond timberline. Bare rock is common; the predominant 

vegetation consists of low treeless types. 

The interior spruce and birch forest corresponds to the Northern 

Interior group of forest-cover types, of the Society of American 
168 CONTRIBUTION8 TO GENERAL GEOLOGY 

Foresters (1954, p. 39), with the addition of lodgepole pine. The 

coastal spruce and hemlock forest consists of the northern representatives of the Society's North Pacific group. Englemann spruce and 

lodgepole pine forest corresponds to the Society's Englemann sprucealpine fir type. The groups used in the compilation of Alaskan vegetation are the same as those used by Taylor and Little {1950), except 

that they separated lowland spruce and birch forest from that growing 

on the uplands. 

The forest distribution in Alaska was compiled from field sketch 

maps published in U. S. Geological Survey bulletins and from field 

notes (fig. 31}. The map by Taylor and Little {1950) was used for 

z 

c 

PAOIFIC 

200 0 

EXPLANATION 

OJ 

Mapped area; number 

referred to in text 

Unmapped area 

OCEAN 

400 Miles 

FIGURE 31.-Key map of northwestern North America showing sources of data. 

areas not included in these field studies. Vegetation of northwestern 

British Columbia and southern Yukon Territories (area 48) 1 was 

compiled from an earlier investigation by Raup and Denny (1950). 

They rna pped the vegetation on a larger scale and showed forest types 

not included on this map. The list of vegetation of the rest of Yukon 

Territory and Mackenzie district, except for that along the Canol 

1 References noted by area number refer to key map (fig. 31). 
GEOLOGICAL SURVEY Jn;LLETJN J OGl PLATE 10 

WOODS ADJOINING TUNDRA COMMUNITIES 

White spruce and white birch growing on wdl-drained, deeply thawed sand dune. Herbaceous, lichen, and shrub tundra communities are in middle ground 

rlrained sand which is frozen within 18 inches of the surface. Kobuk River Valley, Alaska, August 1952, 

poorly 
GEOLOGICAL SURVEY BULLE1'1N 1061 PLATE 11 

TREELESS COMMUNITIES ON THE SEWARD PENINSULA 

Treeless vegetation consists of shrub and herbaceous communities. Dark shrubs in foreground are dwarf birch and heath; cottongrass tussocks are at right foreground. 

Light grasslike plants arc sctlges. Near Dahl, Alaska. August 15, 1950. 
GEOLOGICAL SURVEY BULLETIN l 0 61 PLATE 12 

VIEWS OF THE INTERIOR SPRUCE AND BIRCH FOREST REGION 

A, Mature well-formed white spruce trees on a lluvial fan in valley of the Nenana River between .McKinley 

Park and Windy, Alaska. July 20, 1953. B, Forest, shrub, and grassland communities resulting from 

repeated fires in area north of Suntrana at Healy Creek, Alaska. July 25, 1953. 
GEOLOGICAL SUR\.EY DL'LLETii\' 1 OGI PLATE 1B 

TREES GROWING ON THAWED STREAM BANKS 

Scattered white spruce, white birch, and willow shrubs growing on well·draineu, deeply thaweu stream 

banks. Herbaceous tundra communities are characteristic of the surface underlain by perennially frozen 

ice·wedge polygons in right foreground. Kobuk River Valley, Alaska. June 1952. 
VEGETATION OF NORTHWESTERN NORTH AMERICA 169 

Road, was compiled from the small-scale Canadian Resources Map 

(areas 7, 8). The small patch of forest depicted on the map along 

the mouth of the Andraefsky River, on the lower part of the Yukon 

River, was reported by Harrington (1918) as the extreme western 

limit of forest along the river. He further reported that spruce grows 

on the hills near the Yukon River, upstream from the Andraefsky 

River but did not include a map in his report or specifically locate 

other patches of woods. The vegetation of Seward Peninsula, Kobuk 

River valley and about Healy, Alaska, was mapped from field studies 

made by the writer and from the interpretation of aerial photographs. 

REFERENCES PERTAINING TO KEY MAP 

[Numbers refer to area shown on figure :31] 

Field notes: 

1. W. S. Benninghoff 

2. W. H. Drury 

3. D. M. Hopkins 

D. R. Nichols 

4. E. H. Muller 

5. R. S. Sigafoos 

6. J. R. Williams 

Published maps: 

7. Canada, Department of Mines and Resources, 1944, Map of Canada 

Natural Resources; Scale, 1:636,000, Ottawa. 

8. Canada, Department of Resources and Development, 1950, Native trees 

of Canada ; Canada Dept. Resources and DevE~l. Bull. 61, 293 p. 

9. Capps, S. R., 1913', The Yentna district, Alaska: U.S. Geol. Survey Bull. 

534, 75 p. 

10. -- 1915, The Willow Creek district, Alaska: U. S. Geol. Survey 

Bull. 607,86 p. 

11. -- 1916, The Chisana-White River distriet, Alaska: U. S. Geol. 

Survey Bull. 630, 130 p. 

12. -- 1916, The Turnagain-Knik region: U. S. Geol. Survey Bull. 

642-E., p. 147-195. 

13. -- 1919, The Kantishna region, Alaska: U. S. Geol. Survey Bull. 

687,118 p. 

14. --- 1927, The Toklat-Tonzona region: U. S. Geol. Survey Bull. 

792-C, p. 73-111. 

15. -- 1929, The Skwentna region, Alaska: U. S. Geol. Survey Bull. 

797-B, p. 67-99. 

16. -- 1930, The Chakachamna-Stony region: U. S. Geol. Survey 

Bull. 813-C, p. 97-125. 

17. -- 1930, The Mount Spurr region: U. S. Geol. Survey Bull. 810-

C, p. 141-172. 

18. -- 1931, The Lake Clark-Mulchatna region, Alaska: U. S. Geol. 

Survey Bull. 824-C, p.125-154. 

19. -- 1932, The eastern portion of Mount 1\1:cKinley National Park: 

U.S. Geol. Survey Bull. 836-D, p.129-300. 

20. -- 1935, The southern Alaska Range: U. S. Geol. Survey Bull. 

862, 101 p. 

467777-58-2 
170 CONTRIBUTIONS TO GENERAL GEOLOGY 

Published maps-Continued 

21. --- 1937, Kodiak and adjacent islands: U. S. Geol. Survey Bull. 

880-C, p. 111-184. 

22. --- 1937, Kodiak and vicinity: U. S. Geol. Survey Bull. 868-B, 

p. 93-133. 

23. Capps, S. R. and B. L. Johnson, 1915, The Ellamar district, Alaska: 

U.S. Geol. Survey Bull. 605,125 p. 

24. Capps, S. R. and Mertie, J. B., Jr., 1927, Geology of the upper Matanuska 

Valley, Alaska: U.S. Geol. Survey Bull. 791,92 p. 

25. Capps, S. R. and Tuck, Ralph, 1935, The Willow Creek-Kashwitna 

district, Alaska: U. S. Geol. Survey Bull. 864-B, p. 95-113. 

26. Chapin, Theodore, 1918, The Nelchina-Susitna region, Alaska: U. S. 

Geol. Survey Bull. 668,67 p. 

27. Eakin, H. M., 1914, The Iditarod-Ruby region, Alaska: U. S. Geol. 

Survey Bull. 578, 45 p. 

28. --1916, The Yukon-Koyukuk region, Alaska: U. S. Geol. Survey 

Bull. 631, 88 p. 

29. Johnson, B. L., 1914, The Port Wells gold-lode district: U. s~ Geol 

Survey Bull. 592-G, p. 195-237. 

30. Maddren, A. G., 1913, The Koyukuk-Chandalar region, Alaska: U. S. 

Geol. Survey Bull. 532, 119 p. 

31. Martin, G. C., and Katz, F. J., 1912, A geologic reconnaissance of the 

Iliamna region, Alaska: U. S. Geol. Survey Bull 485, 138 p. 

32. Mertie, J. B., Jr., 1925, Geology and gold placers of the Chandalar 

district: U.S. Geol. Survey Bull. 773-1, p. 215-267. 

33. --- 1929, The Chandalar-Sheenjek district, Alaska : U. S. Geol. Survey Bull. 810-B, p. 87-139. 

34. --- 1931, A geologic reconnaissance of the Dennison Fork district, 

Alaska: U.S. Geol. Survey Bull. 827,44 p. 

35. -- 1938, The Nushagak district, Alaska : U. S. Geol. Survey Bull. 

903, 96 p. 

36. Mertie, J. B. and Harrington, G. L., 1924, The Ruby-Kuskokwim region, 

Alaska: U. S. Geol. Survey Bull. 754, 129 p. 

37. Moffit, F. H., 1914, Geology of the Hanagita-Bremner region, Alaska: 

U.S. Geol. Survey Bull. 576,56 p. 

38. --- 1915, The Broad Pass region, Alaska: U. S. Geol. Survey Bull. 

608, 80 p. 

39. --- 1918, The upper Chitina Valley, Alaska: U. S. Geol. Survey 

Bull. 675, 82 p. 

40. --- 1927, The Iniskin-Chinitna Peninsula and the Snug Harbor 

district, Alaska: U. S. Geol. Survey Bull. 789, 71 p. 

41. Moffit, F. H. and Mertie, J. B., Jr., 1923, The Kotsina-Kuskulana district, Alaska: U. S. Geol. Survey Bull. 745, 149 p. 

42. Porsild, A. E., 1951, Botany of southeastern Yukon adjacent to Canol 

Road: Canada Nat. Mus. Bull. 121, p. 1-400. 

43. Prindle, L. M., 1906, The Yukon-Tanana region, Alaska: U. S. Geol. 

Survey Bull. 295, 27 p. 

44. --- 1908, The Fairbanks and Rampart quadrangle, Yukon-Tanana 

region, Alaska: U.S. Geol. Survey Bull. 337,102 p. 

45. --- 1909, The fortymile quadrangle, Yukon-Tanana region, Alaska: 

U.S. Geol. Survey Bull. 375,52 p. 
VEGETATION OF NORTHWESTERN NORTH AMERICA 171 

PubZi8hed, maps-Continued 

46. -- 1913, A geologic reconnaissance of the Circle quadrangle, 

Alaska : U. S. Geol. Survey Bull. 538, 82 p. 

47. -- 1913, A geologic reconnaissance of the Fairbanks quadrangle, 

Alaska: U.S. Geol. Survey Bull. 525,220 p. 

·48. Raup, H. M. and Denny, C. S., 1950, Photo interprE,tation of the terrain 

along the southern part of the Alaska Highwa;r: U.S. Geol. Survey 

Bull. 963-D, p. 95-135. 

49. Smith, P. S. 1917, The Lake Clark-central Kuskokwim region, Alaska: 

U.S. Geol. Survey Bull. 655,162 p. 

50. Smith, P. S., and Eakin, H. M., 1911, A geologlc reconnaissance in 

southeastern Seward Peninsula and Norton Bay-Nulato region, 

Alaska: U. S. Geological Survey Bull. 449, 146 p. 

51. Smith, P. S., and Mertie, J. B., Jr., 1930, Geol•Jgy and mineral resources of northwestern Alaska : U. S. Geol. Survey Bull. 815, 351 p, 

52. Tuck, Ralph, 1934, The Curry district, Alaska: U. S. Geol. Survey Bull. 

857 -C, p. 99-140. 

ACKNOWLEDGMENTS 

Sincere appreciation is expressed to the individuals who contributed 

information on the following areas : parts of the Brooks and Alaska 

ranges, northern Yukon Territory, and Mackenzie district by W. P. 

Brosge, M.D. Mangus, and T. L. Pewe of the U.S. Geological Survey 

and Galen Smith of the U.S. Air Force; the upper Kushokwim River 

region by W. H. Drury of Lincoln, Mass. ; and the Kenai PeninsulaCook Inlet area by J. W. Scott of the Bureau of Land Management. 

R. R. Robinson of the Bureau of Land Management, R. F. Taylor 

of the U. S. Forest Service, Drury, and Scott k.ndly reviewed an 

early draft of the manuscript. 

INTERIOR SPRUCE AND BIRCH FORBST REGION 

The region mapped as interior spruce and bireh :forest is the northwestern extension of the Canadian boreal forest ~Lnd contains many 

forest types, including some treeless plant communities. Many forest 

types have developed as the result of fires on sites that prior to burning 

varied greatly in forest and physical characteris~~ics. The existing 

stands show differences in species composition, plant form, and age 

(pl. 12B). Lutz (1956) has described the most cummon forest communities located mostly along the highways in east central Alaska. 

He points out, as did Raup (1945) and Raup and Denny (1950), that 

the significance of the communities in terms of vegetation development 

and history of the land surface can be perceived only if the importance 

of fire is appreciated. The development of vegetation after fire is 

extremely complex and will not be discussed here; Lutz (1956) has 

thoroughly discussed the ecological effects of fire on forests in the 

interior of Alaska. He relates differences in morphology and seeding 
172 CONTRIBUTIONS TO GENERAL GEOLOGY 

habits of species to establishment and maturation of forests. Raup 

and Denny ( 1950) describe succession of vegetation types following 

fire in the forests in parts of British Columbia. 

The forest throughout the region has hardly been exploited, but 

some white spruce and white birch are cut for local consumption. 

Only the larger areas of treeless communities within the forested 

region have been mapped. Treeless communities result from poor 

drainage or soil instability, which prevents tree growth, or from repeated burning of forests. 

WmTE SPRUCE 

Pure white spruce forest and a mixture of white spruce and white 

birch forest are characteristic of most of the forested lowlands and 

well-drained uplands in a larger part of the interior spruce and 

birch forest region. 

Mature stands of white spruce, either pure or with some admixtures 

of white birch, form dense forests. The trees on most lowland sites 

reach heights ranging from 50 to 70 feet, and some of their trunks 

range from about 10 to 20 inches in diameter, although they are 

smaller in most stands. Trees grow most rapidly, attain their greatest 

height and diameter, and trunks show less tapering on well-drained 

~alluvial fans underlain by coarse material (pl. 12A). On flood plains 

in the interior of British Columbia, the height of some trees is more 

than 100 feet, and diameters range from 18 to 24 inches (Raup and 

Denny, 1950, p. 07). The understory, composed of willow, alder, 

and heath shrubs, may be either dense or sparse, depending on spacing 

of the trees and density of the canopy. 

Pure stands of white spruce are characteristic of the western and 

northern limit of forest on Seward Peninsula and southward-trending 

river valleys through the Brooks Range. They are also common in 

lowlands throughout the interior spruce and birch forest region. 

White spruce stands are prevalent on uplands, but commonly contain 

small numbers of white birch, aspen, and balsam poplar. Poplar and 

aspen, which are short lived, grow in openings in forests of older 

spruce. White spruce with local admixtures of scattered lodgepole 

pine and aspen are characteristic of rolling uplands in British Columbia, except in the coastal mountains region (Raup and Denny, 1950, 

p.109) 0 

WHITE SPRUCE AND WHITE BIRCH 

White spruce and white birch forests are characteristic of some 

lowlands and well-drained uplands and river terraces throughout 

the forest region. These forests are similar to white spruce forests 

except that they are somewhat more open owing to the thin, feathery, 
VEGETATION OF NORTHWESTERN NORTH AMERICA 173 

white birch canopy. Some additional willow species and rosaceous 

species occur in the shrub layer, which is typically more dense than 

that under white spruce--possibly because of the rrLore open nature 

of the forest. 

White birch deteriorates before white spruce in some older stands, 

suggesting that white birch is only a temporary member of the forest. 

However, some old white birch produce vigorous sprouts when the 

main stem dies; and thus, the ratio of white birch trees to white spruce 

trees is maintained for long periods of time. Lutz (1956, p. 41) 

believes that the white spruce and white birch fo1est is a stage in 

succession following fire. 

Scattered black spruce are locally associated with white spruce and 

white birch on uplands in the Mackenzie Mountains (Porsild, 1951a, 

p.28). 

BALSAM POPLAR 

Dense stands of large balsam poplar with some white birch grade 

into pure white spruce and into white spruce and white birch forests 

on river flood plains throughout the region. Lutz (1953, p. 23} 

reports that young balsam poplar stands are dense, remaining so 

even in old stands. Mature trees range from 70 to 100 feet in height 

and are as much as 36 inches in diameter. White spruce is commonly 

associated with balsam poplar in older stands, and together they 

form a tall, dense forest characteristic of older surfaces along large 

rivers. Pure stands of poplar that range from 30 to 40 feet in height 

and 4 to 6 inches in diameter grow along flood plains beyond the 

northern limit of white spruce in the Brooks Range (Spetzman, 

Minnesota Univ. unpublished thesis, 1951); standB of smaller trees 

grow as far west as N orne, Alaska, on the Seward Peninsula. 

Balsam poplar is the first tree species, excluding willows, to invade 

recently deposited alluvium along river flood phtins. Stands are 

invaded by white spruce, but because the poplar is relatively long 

lived, it persists for long periods. 

BLACK SPRUCE 

Black spruce stands vary widely in form, density, and structure. 

The trees range from a few feet to 50 feet in height and from scrubby 

to nearly symmetrical form. The density of the stands ranges from 

those that contain scattered, poorly formed individuals to stands with 

large, straight-trunked trees from 2 to 5 feet apart. 

Black spruce in pure stands is characteristic of poorly drained sites, 

underlain by thick peat layers and fine-grained soils, throughout the 

interior spruce and birch forest region. It a]so grows on steep, rocky 

slopes in British Columbia (Raup and Denny, 1950, p. 107-108) and 
174 CONTRIBUTIONS TO GENERAL GEOLOGY 

in northern and central Alaska. Pure stands of black spruce and 

some with admixtures of aspen and white birch grow on well-drained 

uplands throughout the region. Lutz (1956, p. 67-68) believes that 

in some places the black spruce has invaded previously burned over 

areas. Stands are common on sand dunes in parts of western Alaska. 

In parts of the Mackenzie Mountains, black spruce and scattered 

white birch grow on heavy, glaciated soils (Porsild, 1951a, p. 28). 

Black spruce, lodgepole pine, and white spruce grow on heavy clay 

soils in interior British Columbia (Raup, 1945, p. 32). Larch is associated with black spruce in some low land depressions in parts of 

central Alaska, Yukon, and British Columbia. 

ASPEN AND BIRCH 

Pure stands of aspen, pure stands of birch, and mixtures of the 

two species are common throughout Alaska in areas of recent fires. 

Pure aspen stands grow on the better-drained ridges throughout 

the region and follow burning on drier sites. Trees reach heights 

ranging from 30 to 50 feet in mature woods and trunk diameters range 

from less than 1 to 8 inches. White spruce commonly invades aspen 

and birch stands and replaces them if the site is not burned over (Lutz, 

1956, p. 37-39, 45-47). Aspen and birch appear to persist for long 

periods on many of the driest sites, because they are the only tree 

species that produce seedlings here. Raup and Denny (1950, p. 109) 

found pure aspen stands on dry, southward-facing slopes in British 

Columbia; and they, too, believe that the type persists for long periods of time. 

LODGEPOLE PINE 

Open stands of lodgepole pine are characteristic of sandy, welldrained soils throughout central and northern British Columbia, and 

on heavier soils where spruce forest has been burned off (Raup and 

Denny, 1950, p. 108-109). Lodgepole pine replaces itself only on 

well-drained soils and elsewhere it is replaced by white spruce. 

WHITE SPRUCE, ALPINE FIR, LODGEPOLE PINE, AND BLACK SPRUCE 

Alpine fir grows in tall forests with white spruce, lodgepole pine, 

and black spruce on some steep mountain slopes in interior British 

Columbia in areas that have not been burned recently (Raup and 

Denny, 1950, p. 112-113). The forests are generally old. 

TREELESS COMMUNITIES 

Communities of characteristic shrubs, grasses, or grasslike plants 

are distributed throughout the interior spruce and birch forest. The 

shrub communities consist of various mixtures of dwarf birch, wil-
VEGETATION" OF NORTHWESTERN NORTH AM·ERICA 175 

lows, and heaths. They grow throughout interior Alaska (Lutz, 

1953, p. 28) and British Columbia (Raup and Denny, 1950, p. 113) 

where forests have been repeatedly burned. Shrub communities in 

western and central Alaska grow with small white spruce stands near 

altitudinal and regional ti1nberlines; stands that have not been burned 

appear to be old. Alder is an important component of the shrub 

community in timberline areas. 

Extensive grasslands, which Raup and Denny (1950, p. 115-117) 

have termed prairies, occur throughout Alaska and British Columbia. In parts of western Alaska they appear to persist for long 

periods of time. In central Alaska the grasses grow on sites that 

are underlain by silty soil and have been repeatedly burned over. 

Throughout the interior spruce and birch forest, cottongrass tussocks 

and low woody plants are characteristic of poorly drained sites underlain by peat or silty soil. 

TIMBERLINE FOREST 

White spruce trees form upper timberline throughout most of the 

interior white spruce and white birch :forest region. Local timberline is abrupt, especially in western Alaska; and in many places trees, 

comparable in size, form, and growth rate to those of the area as a 

whole, grow within a :few tens of feet of treeless vegetation. The 

abrupt change from vegetation composed of large trees to tundra 

communities has been reported by many persons who have written 

vegetation descriptions in U. S. Geological Survey bulletins that describe the geology and geography of western and central Alaska. 

Typical of such reports is that of Smith and Mertie ( 1930, p. 72). 

At both of these places (Alatna and Noatak River valleys in the Brooks 

Range) the northern limit of trees comes 'abruptly. A few hundred yards south 

of the actual limit the trees are of about the same size as they are scores 

of miles to the south. . . . On the Unakserak spruce trees 8 to 10 inches 

in diameter, 30 feet tall, and nearly straight ... were found ... , but 100 

yards beyond there were not even dwarf trees or any signs that there had 

been trees within many miles. 

Alpine fir is the timberline tree at places in the Mackenzie Mountains (Porsild, 1951a, p. 28) and southward (Raup, 1945,. p. 128). 

Lodgepole pine and white spruce grow on mountain slopes below altitudinal timberline in. British Columbia (Raup and Denny, 1950, p. 

128). 

Timberline ranges in altitude from 200 to 800 feet above sea level in 

western Alaska, 1,000 to 1,500 feet on the south slopes of the Brooks 

Range, 2,000 to 3,000 :feet in interior Alaska, and 4,000 to 5,000 :feet 

in Yukon and interior British Columbia. 
176 CONTRIBUTIONS; TO GENERAL GEOLOGY 

COASTAL SPRUCE AND HEMLOCK FOREST REGION 

The upland forests of coastal southern Alaska and extreme northern British Columbia consist primarily of pure stands of Sitka 

spruce or mixtures of spruce and western hemlock. In southeastern 

Alaska, Alaska cedar and western red cedar grow locally in pure 

stands or with spruce and hemlock. Pacific silver fir forms pure 

stands and is associated with spruce and hemlock in extreme southeastern Alaska and British Columbia. Successional stages of alder 

and cottonwood characterize lowlands along streams. 

The coastal spruce and hemlock forest has only recently been 

utilized for lumber products and pulp. The average volume of 

timber in the coastal forest was estimated by Heintzlemann (1928) to 

be about 25,000 board feet per acre. 

SITKA SPRUCE AND WESTERN HEMLOCK 

Sitka spruce and western hemlock form dense stands in mixed 

forests on well-drained uplands from the eastern side of Kenai Peninsula to British Columbia. Western hemlock comprises from 70 to 

80 percent of mature stands; Sitka spruce, 20 to 30 percent. Hemlocks range from 100 to 120 feet in height and 18 to 25 inches in 

diameter at 4% feet above the ground. Some trees reach heights 

of 140 feet and diameters ranging from 3 to 4 feet. Mature spruce 

trees range from 160 to 200 feet in height and from 3 to 4 feet in 

diameter, although the maximum diameter may be as much as 6 feet. 

Hemlock forms the main canopy throughout the area and is overtopped by individuals or small groups of Sitka spruce. Small hemlocks, heath species, and other shrubs form a dense understory that, 

together with the other forest trees, forms a forest community of 

almost tropical luxuriance. Fruticose and foliose lichens covering 

all tree trunks and shrub stems, an abundance of fallen trees, and a 

moss carpet ranging from 6 to 15 inches in depth are characteristic of 

the forest. 

Other forest types, similar in form and somewhat similar in species 

composition have been defined (Soc. Am. Foresters, 1954). Within 

the coastal forest region, local stands of nearly pure western hemlock 

occupy sites comparable to those that elsewhere are characterized by 

Sitka spruce and western hemlock forest. From Valdez, Alaska, 

southeastward, Alaska cedar is associated with the western hemlock. 

In places south of Petersburg, Alaska, western red cedar is mixed with 

hemlock in sufficient numbers to noticeably change the nature of the 

forest. Such a forest type is called western red cedar and hemlock 

(Soc. Am. Foresters, 1954, p. 52). In extreme southeastern Alaska 

and coastal British Columbia, Pacific silver fir and western hemlock 
VEGETATION OF NORTHWESTERN NORTH AMERICA 177 

are characteristic of the upland sites. Sitka spruce is in all these 

forests but in smaller numbers than in the typical Sitka spruce and 

hemlock forest. · 

SITKA SPRUCE 

The pure stand of Sitka spruce, of the same size and structure as 

the spruce and hemlock forest, is a successional type which grows on 

recently deposited alluvium and glaciated materials. In the older 

stands western hemlock seedlings are abundant-as the spruce dies, it 

is replaced totally or partly by the hemlock (Taylor, 1932). 

The coastal forest in southwestern Kenai Peninsula and on the west 

side of Cook Inlet is largely composed of Sitka spruce. Mountain 

hemlock grows only locally in northern Kenai Peninsula, where it 

comprises from 15 to 20 percent of mixed stands (J. W. Scott, personal communication, 1955). Western hemlock, an important component of the coastal forest elsewhere in Alaska, is not present in 

the Cook Inlet region. Sitka spruce is smaller in the Cook InletKenai Peninsula region than in the coastal areas to the southeast and 

is comparable in size to white spruce. 

In southwestern Kenai Peninsula, Sitka spruce forest grades northward into the interior spruce and birch forest. Along the line shown 

on the map separating the two types, the forest is a mixture of Sitka 

and white spruce, which also have hybridized; the hybrid has characteristics between the two parent species (Little, 1953). 

WESTERN RED CEDAR 

Pure western red cedar stands of limited distribution grow on 

moist slopes and in low lands along the coasts of southeastern Alaska 

and British Columbia (Soc. Am. Foresters, 1954, p. 53). Western 

red cedar is more extensive southward toward Washington, and its 

presence in Alaska is noted because of its commercial importance. 

Trees are large, reaching heights of more than 150 feet and trunk 

diameters of as much as 6 feet. They are spaced from 50 to 75 feet 

apart, making an extremely dense forest (Canada, 1950, p. 73, 76). 

ALDER AND BLACK COTTONWOOD 

Red alder and black cottonwood form extensive stands on welldrained low lands throughout the coastal forests and are most prominent on recently deposited alluvium and glacial materials (Cooper, 

1933). Alder and cottonwood each form pure stands; and even 

though each type may occupy a small area and both are replaced by 

Sitka spruce, the two species generally do not intermingle. Alder 

commonly invades surfaces exposed by avalanches on steep slopes' 

where it persists for long periods of time and forms dense stands. 
178 CONTRIBUTIONS TO GENERAL GEOLOGY 

The Society of American Foresters (1954, p. 50-51) has separated 

stands of the two species, describing them as red alder and a type 

composed of black cottonwood and willow. Because both grow in 

similar environments and are successional types, they are discussed 

here together. 

LODGEPOLE PINE AND MOUNTAIN HEMLOCK 

On poorly drained upland sites underlain by peat deposits, bent and 

malformed mountain hemlock grows both as isolated individuals and 

in scattered dense thickets. As far north as Skagway, lodgepole pine 

and a small number of Alaska cedar are associated with the hemlock 

in the bogs ( Heintzlemann, 1928) . 

COASTAL TIMBERLINE FORESTS 

From Skagway southeastward, trees of commercial value extend 

from sea level to an altitude of about 1,500 feet (Heintzlemann, 1928). 

Because of local relief from Yakutat Bay to Kenai Peninsula, most 

commercial forests are limited to coastal lowlands and are less extensive than in the area from Skagway southeastward. Trees of lesser 

or no com.mercial value grow at altitudes from 1,500 to 3,500 feet in 

coastal southeastern Alaska and British Columbia. Western hemlock and white spruce are the timberline species from Kenai Peninsula to the mouth of Copper River. Southeast of Skagway, mountain hemlock, apline fir, and scattered Alaska cedar grow at timberline. 

ENGELMANN SPRUCE AND LODGEPOLE PINE 

FOREST REGION 

The small area of Engelmann spruce and lodgepole pine in British 

Columbia is the northwestern limit of two somewhat extensive Rocky 

Mountain forest types. In the area shown on the map, the forest consists of relatively open Engelmann spruce on the mountain slopes and 

local admixtures of lodgepole pine. In places lodgepole pine forms 

pure stands. Locally, aspen and white birch have invaded burnedover spruce. Alpine fir is generally the only tree species at timberline, which is at an altitude of about 5,000 feet (Halliday, 1937). 

TREELESS REGION 

The region mapped as treeless includes several types of vegetation 

and several kinds of ground. Barren bedrock and rubble, and treeless 

vegetation characterize the land surface. The vegetation in this region consists of four major types: (a) Rock desert plant communities 

cover only a small fraction of the surface, which is dominated by 

rubble or gravel. They predominate in areas of high altitude and 
VEGETATION OF NORTHWESTERN NORTH AMERICA 179 

also are common near sea level where the bedrock is exposed or rubble 

is at the surface; (b) tuadra plant communities consist of types in 

which the plants dominate the surface; these communities are mixtures of. herbaceous and sihrubby plants tha:t form the most common 

types of vegetation in the treeless region (pl. 11}. They are chara.cteristic of surfaces underlain by fine-grained soil materials. (a) 

Strand communities grow along the coasts; and (d) meadow plant 

communities are peculiar to parts of the Aleutian Islands and Bering 

Sea coast areas; this classification has been modified after Porsild 

(1951b,p. 12). . . 

The patterns of Seward Peninsula outlined on the map, along the 

Kobuk River Valley and! around Healy, Alaska, are a.reas in which 

the listed vegetation is predominant. Within any pattern other types 

are present, but generally occupy too small an area to map at this 

scale. Herbaceous tundra in the area consists mostly of cottongrass 

tussock, birch, and heath vegetation on poorly drained uplands and 

sedge sod in sluggish drainage channels and bogs. Shrub tundra consists of thickets of willow species, alder, and large dwarf birch and 

heaths. Shrub tundra grows on better drained soils, such as those 

on stream banks and hillsides mantled with silt and coarser materials. 

It grows within the are~ mapped as herbaceous tundra primarily 

along stream and lake bap.ks. Herbaceous tundra grows in the areas 

mapped as shrub tundra land rock desert on all poorly drained soils. 

More detailed descriptions of these types and their relation to the 

environment have been d¢Scribed (Hopkins and Sigafoos, 1951; Hopkins and Sigafoos, 19£•4; Sigafoos, 1951; Sigafoos, 1952; and Sigafoos 

and Hopkins, 1952). 

The vegetation of St. Lawrence Island was compiled from the interpretation of aerial photographs. W. S. Benninghoff (personal communication, 1956) states that most of the herbaceous tundra is composed of a discontinuous~ sedge sod, scattered low woody plants, and 

herbaceous dicotyledonous plants. Complete sedge sods grow on the 

wettest soils. 

Bedrock is characteristic of extensive areas in the region and are 

completely void of p1ants. Barren bedrock is also characteristic of 

much of the surface at. high altitudes of the Brooks and Alaska 

Ranges; outcrops of bedrock at lower altitudes are also barren. 
180 CONTRIBUTIONS TO GENERAL GEOLOGY 

GEOGRAPHIC DISTRIBUTION OF PROMINENT TREE 

SPECIES 

The presence of a species at any particular site is determined by 

local environmental factors only if the site is within the present distributional range of the species. Thus, to understand the significance 

of the forest types, it is necessary to consider the distributional ranges 

of the dominant tree species (fig. 32). Of the approximately 15 tree 

WHITE SPRUCE WHITE BIRCH BALSAM POPLAR 

BLACK SPRUCE LARCH ALPINE FIR 

LODGEPOLE PINE SITKA SPRUCE· MOUNTAIN HEMLOCK 

WESTERN HEMLOCK ALASKA CEDAR WESTERN REO CEDAR 

FIGURE 32.-Distribution of 12 common species of trees. 
I 

VEGETATION OF NOR~HWESTERN NORTH AMERICA 181 

species that grow in the m~pped area, the ranges of the 12 most 

common ones were compiled 1 

from the following sources: Canada 

(1950); Hulten (1941); Porsild (195la); Raup and Denny (1950); 

Spetzman (Minnesota Univ. pnpublished thesis, 1951) ; and Taylor 

and Little ( 1950). ! 

Several species have been eliminated from consideration owing to 

their apparently temporary e*istence in forest development. Aspen, 

alders, and willows fill this ro~e on most uplands in the interior spruce 

and birch forest, and in th,~ coastal spruce and hemlock forest. 

Lodgepole pine in Yukon aljld British Columbia, possibly a component of a temporary fores~ type, is included. Black cottonwood, 

characteristic of well-draine<l lowlands in the coastal spruce and 

hemlock forest, is not includ~d because cottonwood forests are succeeded by Sitka spruce. Th~ range of Pacific silver fir nearly coincides with that of western ¢d cedar in Alaska; therefore, silver fir 

hasnot been included. ' 

The interior spruce and bi(rch forest at its western limit consists 

generally of white spruce a:dd local stands of balsam poplar. Although balsam poplar grows peyond the western and northern limits 

of white spruce, the limit of the forest is considered to coincide with 

the distribution of spruce. ! Eastward, the number of species increases; black spruce and white birch being the first additional species 

found. Larch grows only ~ the central part of the forest zone. 

Alpine fir and lodgepole pine! grow farther eastward in the Canadian 

mountains. 

Sitka spruce is the only representative of coastal forest tree species 

at the western limit of the constal forest. Eastward and southward, 

mountain hemlock is followed in order by Alaska cedar and western 

red cedar. The southern li~it of white spruce in Alaska overlaps 

part of the ranges of coastal' forest types. The distributional range 

of white birch, which is considered a characteristic tree of the interior 

forest, overlaps nearly all ranges of the coastal forest tree species 

in the region covered by th¢ map. 

Although some tree specie$ are common to both forest zones mentioned, other species and tred forms are so strikingly dissimilar that 

separation of them as distinct~ve units is justified. 

LIS'Jl OF SPECIES 

Common name I Latin name Alaska cedar ___________________ ! Ohamaecypari8 nootkatensis (Donn) Spach 

Alder-------------------------- Alnus sp. Alpinefir _______________________ A.bieslasiocarpa (Hooker) Nuttal 

Aspen-------------------------· Populus tremuloides Michaux 

Balsam poplar ------------------1 

Black cottonwood---------------• 

balsamifera Linnams 

trichocarpa 'Torrey and Gray 
182 CONTRIBUTIONS TO GENERAL GEOLOGY 

Oommon name Latin name 

Black spruce-------------------· Picea mariana (Miller) Britton, Sterns, and 

Poggenburg 

Cottongrass-------------------- Eriophorum vagina tum Linnreus 

anoustifolium Honckeny 

Devilsclub _____________________ , OplopanafiJ horridus (Smith) Miquel 

Dwarf birch-------------------- Betula nana. Linnreus 

Engelmann spruce--------------· Picea engelmannii Parry 

Heath-------------------------· V accinium sp. 

Larch-------------------------- Lari(JJ laricina (DuRoi) K. Koch 

Lodgepole pine-----------------· Pinus contorta Douglas 

Mountain hemlock-------------- Tsuoa mertenaiana (Bongard) Carriere 

Pacific silver fir _________________ Abies amabiliB (Douglas) Forbes 

Red alder ______________________ Alnus rubra Bongard 

Sedge __________________________ Oare(JJ aquatilis Wahlenberg 

Sitka spruce____________________ Picea sitchenaiB (Bongard) Carriere 

Western hemlock ________________ Tsuga heterophylla (Rafinesque) Sargent 

Western red cedar _______________ Thuja plicata Donn 

White birch--------------------· Betula papyrifera Marshall and varieties 

White spruce------------------- Picea glauca (Moench) Voss 

Willow------------------------- Sali(JJ sp. 

Yew--------------------------- Ta(JJUS Brevi folia Nuttal 

REFERENCES CITED 

Benninghoff, W. S., 1957, Quarternary vegetation of central Alaska: Internat. 

Botany Cong., 8th, Paris, 1954, Proc. (abstract). 

Canada, Department of Resources and Development, 1950, Native trees of Canada: 

Canada Dept. Resources and Devel. Bull. 61, p. 1-293. 

Cooper, W. S., 1933, The recent ecological history of Glacier Bay, Alaska : 

Ecology, v. 4, p. 93-128; 223-246; 355-365. 

Halliday, W. E. D., 1937, A forest classification for Canada : Canada Forest 

Service Bull. 89, p. 1-50. 

Hansen, H. P., 1953, Postglacial forests in the Yukon Territory and Alaska : 

Am. Jour. Sci., v. 251, p. 505-542. 

Harrington, G. L., 1918, The Anvik-Andraefski region, Alaska: U. S. Geol. 

Survey Bull. 683, 70 p. 

Heintzleman, B. F., 1928, Pulp-timber resources of southeastern Alaska: U. S. 

Dept. Agriculture Misc. Pub. 41,72 p. 

Heusser, C. J., 1955, Pollen profiles from Prince William Sound and southeastern 

Kenai Peninsula, Alaska : Ecology, v. 36, p. 185-201. 

Hopkins, D. C. and Benninghoff, W. S., 1953, Evidence of a very warm Pleistocene interglacial interval on Seward Peninsula, Alaska : Geol. Soc. America 

Bull., v. 64, p.1435-1436. 

Hopkins, D. M. and Karlstrom, T. N. V., 1955, Permafrost and ground water in 

Alaska: U.S. Geol. Survey Prof. Paper 264-F, p.113-146. 

Hopkins, D. M. and Sigafoos, R. S., 1951, Frost action and vegetation patterns 

on Seward Peninsula, Alaska: U. S. Geol. Survey Bull. 974-C, p. 51-100. 

---1954, Role of frost thrusting in the formation of tussocks: Am. Jour. 

Sci., v. 252, p. 55-59. 
VEGETATION OF NOR'.ljHWE'STERN NORTH AMERICA 183 

Hulten, Eric, 1941, Flora of Alask~ and Yukon: Lunds Univ. Arssk. band 37, 

no.1, pt. 1, p.1-127. 

Hustich, Ilmari, 1953, The boreallimlts of conifers, v. 6, p. 139-62. 

Little, E. L., Jr., 1953, A natural hybrid spruce in Alaska: Jour. Forestry, v. 51, 

p. 745-747. 

Livingstone, D. A., 1955, Some pollen profiles from Arctic Alaska: Ecology, 

v. 36, p. 587-600. 

Lutz, H. J., 1953, The effects of fore$t fires on the vegetation of interior Alaska: 

Alaska Forest Research Center *ation Paper 1. 

--- 1956, Ecological effects of f~rest fires in the interior of Alaska : U. S. 

Dept. of Agriculture Tech. Paper11133, p.1-121. 

Porsild, A. E., 1951a, Botany of soiJtheastern Yukon adjacent to Canol Road: 

Canada Nat. Mus. Bull. 121, p. 1-400. 

--- 1951b, Plant life in the Arctic: Canada Geog. Jour., v. 43, no. 3, p. 1-27. 

Raup, H. M., 1945, Forests and gardens along the Alaska Highway: Geog. Rev., 

v. 35, p. 22-48. 

--- 1947, The botany of southwestern Mackenzie: Sargentia VI, p. 1-275. 

--- 1951, Vegetation and cryoplanation: Ohio Jour. Sci., v. 51, p. 105-116. 

Raup, H. M., and Denny, C. S., 1950, Photo interpretation of the terrain along 

the southern part of the Alaska Highway: U. S. Geol. Survey Bull. 963-D, 

p. 93-135. 

Sigafoos, R. S., 1951, Soil instability in tundra vegetation: Ohio Jour. Sci., v. 

51, p. 281-298. 

-- 1952, Frost action as a primary physical factor in tundra plant communities: Ecology, v. 33, p. 480--487. 

Sigafoos, R. S., and Hopkins, D. :M., 1952, Soil instability on slopes in regions 

of perennially frozen ground, i~ Frost action in soils-A symposium: Natl. 

Research Council Pub. 213, Highway Research Board Special Rept. 2, 

p.176-192. 

Smith, P. S., and Mertle, J. B., Jr., 1930, Geology and mineral resources of northwestern Alaska: U. S. Geol. Survrey Bull. 815, 351 p. 

Society of American Foresters, 19$4, Forest cover types of North AmericaReport of the Committee on Forest Types: Soc. Am. Foresters, p. 1-67. 

Taylor, R. F., 1932, The successional trend and its relation to second-growth 

forests in southeastern Alaska: Ecology, v. 13, p. 381-391. 

Taylor, R. F. and Little, E. L., Jr., 1950, Pocket guide to Alaska trees: U. S. 

Dept. Agriculture Handb. 5, p. 1-63. 

INDEX 

Page 

Alaska, glacial problems______________________ 166 

Alaska cedar ___ -------------------- 176, 178, 180, 181 

Alaska Range-----------·--------------------- 166 

Alder _______________________________ 176,177,179,181 

Alluvium ____________ ----·-------------------- 177 

Alpine fir--------------------------- 174,178,180,181 

Andraefsky River·--------------------------- 169 

Aspen.------------------------------------- 174,181 

'Balsam poplar __________________________ 173,180,181 

density of stands_________________________ 173 

Birch •• ------------------------------------- 174,179 

Black cottonwood---------------------- 177, 178, 181 

Black spruce._--------------------- 173-174,180,181 

Boreal forest, Canadian_______________________ 171 

British Columbia, clay soils, heavy___________ 174 

Canadian boreal forest------------------------ 171 

Coastal spruce and hemlock forest region_____ 168, 

17'6, 181 

timber, average volume___________________ 176 

Cottongrass tussock.------------------------- 179 

Cottonwood---------------------------- 176, l'il7, 181 

Dicotyledonous plants, herbaceous___________ 179 

Ecological effects of fire on vegetation_________ 171 

Engelmann spruce and lodgepole pine forest.. 168, 

178 

Englemann spruce-alpine fir type_____________ 168 

Page 

Rock desert plant communities •• _____________ 178 

Sand, frozen perenniallY---------------------- 166 Sand dunes, Alaska ________________________ 166,174 

Sedge sod •• ----------------------------------- 179 

Shrubs.-------------------------------- 174-175, 179 

Silver fir-------------------------------------- 181 

Sitka spruce·--------------------------- 176,177,180 

hybrid.---------------------------------- 177 

Soils, barren bedrock----------------------- 178,179 

clay, heavY------------------------------- 174 

fine •..• ------------------------------------ 166 

glaciated.------------------------------ 174,177 

gravelly_--------------------------------- 166 

perennially frozen._---------------------- 166 poorly drained____________________________ 173 

rubble _______ ----------------------------- 178 

sandy __ ---------------------------------- 174 

silty-------------------------------------- 166 

unfrozen _____________ -----------------____ 166 

well-drained---------------------------- 166,174 

Spruce, consumption------------------------- 172 

Spruce and birch forest, interior______________ 171 

lowland. __ ------------------------------- 168 

Strand communities__________________________ 179 

Subsoil, physical characteristics______________ 166 

Subsoil, temperature·------------------------ 166 

Surficial deposits, frozen, factors______________ 165 

unconsolidated------------------------- 165,167 

Fossil plants---------------------------------- 166 Timberline _________________________________ 175,178 

interpretation. __ ------------------_______ 166 altitudinal ________ ------------------------ 175 

Trees, commerciaL--------------------------- 178 

Geographic distribution, prominent tree Treeless communities ___________ 172,174-175,178,179 

species--·------------------------- 180 Tundra plant communities _________________ 175,179 

Geology, surficiaL___________________________ 167 

Glacial problems, Alaska.____________________ 166 

Grasses ••. ------------ __ -------------------- 174-175 

Grasslike plants---------------------------- 174-175 

Heath vegetation _______ -------------------- __ Herbaceous tundra. _________________________ _ 179 

179 

Interior spruce and birch forest _____________ 167,171 

Larch __ ------------------------------------ 174, 180 

Lodgepole pine _________ ---- 168,174,175,178,180,181 

Lumber products ___________________________ 176,178 

Meadow plant communities------------------ 179 

Mountain hemlock _________________________ ~77, 180 

North Pacific group. ___ ---------------------- Northern Interior group, forest-cover types __ _ 

168 

167 

Pacific silver fir----------------------------- 176,181 

Perennially frozen material depths, __________ .. 166 

Vegetation, distribution ________________ 165,166,167 

ecological effects of fire____________________ 171 

forest, distribution________________________ 166 

relation to topography____________________ 167 

successional types after fire _____ 167,171,172,174 

treeless.-------------------- 172, 174-175, 178, 179 

water cycle------------------------------- 167 

Vegetation map, index________________________ 166 

Water cycle, vegetation_______________________ 167 

Water supply __ ------------------------------ 167 

Western hemlock.. __________________________ 176,180 

seedlings_------------------------------ 177,178 Western red cedar __________________ 176,177,180,181 

White birch ________________________ 172,173,180,181 

White spruce ___________ 172,174,175,177,178,180,181 

hybrid.---------------------------------- 177 Willow _________________________________ 178,179,181 

Wood pulP----------------------------------- 176 

Permafrost._--------------------------------" 165 Yukon, lodgepole pine.------------------------- 181 

185 

0