U.S. DEPARTMENT OF THE INTERIOR
U.S. GEOLOGICAL SURVEY

ECOREGIONS OF ALASKA

By Alisa L. Gallant!, Emily F. Binnian?, James M. Omernik?, and Mark B. Shasby*
1995

Professional Paper 1567
Plate 1

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This map of ecoregions has been produced for Alaska as a framework for organizing
and interpreting environmental data for State, national, and international level inven-
tory, monitoring, and research efforts. The map and descriptions for 20 ecological
regions were derived by synthesizing information on the geographic distribution of
environmental factors such as climate, physiography, geology, permafrost, soils, and
vegetation. A qualitative assessment was used to interpret the distributional patterns
and relative importance of these factors from place to place.

Numeric identifiers assigned to the ecoregions are coordinated with those used on
the map of “Ecoregions of the Conterminous United States” (Omernik 1987) as a
continuation of efforts to map ecoregions for the United States. Additionally, the
ecoregions for Alaska and the conterminous United States, along with ecological
regions delineated for Canada (Wiken 1986), have been aggregated at a coarser
level into a map of North American ecological regions (Omernik 1995).

~y j ——
Up, Cp Omernik, J.M., 1987, Ecoregions of the Conterminous United States: Annals of the Association of Ameri-
J < can Geographers, v. 77, no. 1, p. 118-125.
D We | = ee Ecoregions: a Framework for Managing Ecosystems: The George Wright Forum, v. 12, no. 1,
? ~é 3 p. 35-51.
Y, Wiken, E.B., 1986, Terrestrial Ecozones of Canada: Lands Directorate, Environment Canada Ecological
Land Classification Series 19, 26 p.

110

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For table of major environmental characteristics occurring in each ecoregion, see reverse side.

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165° 160° 155° 150° 145° 140° INTERIOR-GEOLOGICAL SURVEY, RESTON, VRGNIA-1055 4.350
AUTHOR AFFILIATIONS SCALE 1:5 000 000 ROADS
Forest Sciences Department, Colorado State University, Fort Collins, Colorado.
Work performed under USGS Cooperative Agreement #1434-93-A-00760. 100 0 100 200 300 400 500 KILOMETERS TRANS-ALASKA PIPELINE
2Hughes STX Corporation, U.S. Geological Survey, EROS Alaska Field Office, Anchorage, Alaska. Le! i 1
Work performed under USGS Contract #1434-92-C-4004. 100 0 100 200 300 MILES — --—-— INTERNATIONAL BOUNDARY
3Environmental Protection Agency, Environmental Research Laboratory, Corvallis, Oregon. [ it it —L_ |
4U.S. Geological Survey, EROS Alaska Field Office, Anchorage, Alaska. Albers Equal Projection

Prepared by USGS in cooperation with Colorado State University and Environmental Protection Agency

Standard Parallels: 55°N, 65°N.

Arctic Coastal Plain 50,000 sq km

The northernmost ecoregion is bounded on the north and the west by the Arctic Ocean and stretches
eastward nearly to the international boundary between Alaska and the Yukon Territory, Canada.
The poorly drained, treeless coastal plain rises very gradually from sea level to the adjacent foothills.
The region has an arctic climate, and the entire area is underlain by thick permafrost. Because of
poor soil drainage, wet graminoid herbaceous communities are the predominant vegetation cover,
and numerous thaw lakes dot the region.

{HCN arctic Foothills 124,000 sq km

This ecoregion consists of a wide swath of rolling hills and plateaus that grades from the coastal plain
‘on the north to the Brooks Range on the south. The east-west extent of the ecoregion stretches from
the international boundary between Alaska and the Yukon Territory, Canada, to the Chukchi Sea.
The hills and valleys of the region have better defined drainage patterns than those found in the
coastal plain to the north and have fewer lakes. The area is underlain by thick permafrost and many
ice-related surface features are present. The region is predominantly treeless and is vegetated
primarily by mesic graminoid herbaceous communities.

[HAY Brooks Range 134,000 sq km

This ecoregion consists of several groups of rugged, deeply dissected mountains carved from uplifted
sedimentary rock. The region traverses much of the east-west extent of northern Alaska, from the
Canadian border to within 100 km of the Chukchi Sea. Elevation of mountain peaks ranges from 800 m
in the relatively low Baird Mountains in the west to 2,400 m in the central and eastern Brooks Range.
Pleistocene glaciation was extensive, and small glaciers persist at elevations above 1,800 m. An
arctic climatic regime and unstable hillslopes maintain a sparse cover of dwarf scrub vegetation
throughout the mountains, though some valleys provide more mesic sites for graminoid herbaceous
communities.

{04 interior Forested Lowlands and Uplands 269,000 sq km

This ecoregion represents a patchwork of ecological characteristics. Regionwide unifying features
include a lack of Pleistocene glaciation, a continental climate, a mantling of undifferentiated alluvium
and slope deposits, a predominance of forests dominated by spruce and hardwood species, and a
very high frequency of lightning fires. On this backdrop of characteristics is superimposed a finer
grained complex of vegetation communities resulting from the interplay of permafrost, surface water,
fire, local elevational relief, and hillslope aspect.

Interior Highlands 115,000 sq km

This discontinuous ecoregion is composed of rounded, low mountains, often surmounted by rugged
peaks. The highlands primarily sustain dwarf scrub vegetation and open spruce stands, though
graminoid herbaceous communities occur in poorly drained areas. Mountains in most parts of this
region rise to at least 1,200 m, and many rise higher than 1,500 m. Most of the higher peaks were
glaciated during the Pleistocene epoch.

HG interior Bottomlands 103,000 sq km

This ecoregion is composed of flat to nearly flat bottomlands along larger rivers of interior Alaska.
The bottomlands are dotted with thaw and oxbow lakes. Soils are poorly drained and shallow, often
over permafrost. Predominant vegetation communities include forests dominated by spruce and
hardwood species, tall scrub thickets, and wetlands.

(FGA Yukon Fiats 33,000 sq km

This ecoregion is a relatively flat, marshy basin floor in east central Alaska that is patterned with
braided and meandering streams, numerous thaw and oxbow lakes, and meander scars. Sur-
rounding the basin floor is a variable band of more undulating topography with fewer water bodies. In
many respects, the ecoregion is similar to the Interior Bottomlands Ecoregion, but differs in climatic
characteristics. Temperatures tend to be more extreme; summers are warmer and winters are colder
than in other areas of comparable latitude. The ecoregion also receives less annual precipitation than
the Interior Bottomlands. Forests dominated by spruce and hardwood species, tall scrub com-
munities, and wet graminoid herbaceous communities are the predominant vegetation types.

{408 Ogilvie Mountains 11,000 sq km
This ecoregion, along the eastern edge of Alaska, consists of flat-topped hills eroded from a former
plain and broad pediment slopes built up from mountains that are much subdued from their former
stature. Karst topography is common. Mesic graminoid herbaceous communities and tall scrub
communities are widespread throughout the region. Forest communities occupy lower hillslopes and
valleys.

[H@9]) subarctic Coastal Plains 91,000 sq km

This ecoregion mainly includes coastal plains of the Kotzebue Sound area and the Yukon and
Kuskokwim River delta area. Flat, lake-dotted coastal plains and river deltas are characteristic of the
region. Streams have very wide and serpentine meanders. Soils are wet and the permafrost table is
shallow, providing conditions for wet graminoid herbaceous communities, the predominant vegetation
type. The region is affected by both marine and continental climatic influences.

Seward Peninsula 47,000 sq km

‘Some of the oldest geologic formations in Alaska provide a backdrop for this predominantly treeless
ecoregion. Mesic graminoid herbaceous and low scrub communities occupy extensive areas. The
ecoregion is surrounded on three sides by water, yet this has little ameliorating effect on the climate.
Winters tend to be long and harsh and summers short and cool.

UY Transitional Areas

(A) Anklun and Kilbuck Mountains 51,000 sq km

Located in southwestern Alaska off Bristol and Kuskokwim Bays, this ecoregion is composed of
steep, sharp, often ringlike groupings of rugged mountains separated by broad, flat valleys and
lowlands. The mountains were glaciated during the Pleistocene epoch, but only a few small glaciers
persist. Dwarf scrub communities are the predominant vegetation cover in the mountains. Tall scrub
and graminoid herbaceous communities are common in valleys and on lower mountain slopes.
Valley bottoms may support stands of spruce and hardwood species.

{QJ Bristol Bay-Nushagak Lowlands 61,000 sq km

This lowland ecoregion is located in southwestern Alaska off Bristol Bay. The region has rolling
terrain, formed from morainal deposits. Soils of the lowlands are somewhat better drained than soils
of the Subarctic Coastal Plains Ecoregion. Dwarf scrub communities are widespread, but large areas
of wetland communities occur. Lakes are scattered throughout the lowlands, but are not nearly as
numerous as in the Subarctic Coastal Plains.

{3 Alaska Peninsula Mountains 48,000 sq km

This ecoregion is composed of rounded, folded and faulted sedimentary ridges intermittently
surmounted by volcanoes. The mountains were heavily glaciated during the Pleistocene epoch. A
marine climate prevails, and the region is generally free of permafrost. Many soils formed in deposits
of volcanic ash and cinder over glacial deposits and are highly erodible. Vegetation cover commonly
consists of dwarf scrub communities at higher elevations and on sites exposed to wind, and low scrub
communities at lower elevations and in more protected sites.

Aleutian Islands 12,000 sq km

This ecoregion in southwestern Alaska is composed of a chain of sedimentary islands (eroded from
older volcanic formations) that are crowned by steep volcanoes. Maritime climate prevails. The
region is south of the winter sea ice pack and is generally free from permafrost. Vegetation cover
mainly consists of dwarf scrub communities at higher elevations and on sites exposed to wind, and of
graminoid herbaceous communities in more protected sites.

GBI Cook Inlet 28,000 sq km

Located in the south central part of Alaska adjacent to the Cook Inlet, the ecoregion has one of the
mildest climates in the State. The climate, the level to rolling topography, and the coastal proximity
have attracted most of the settlement and development in Alaska. The region has a variety of
vegetation communities but is dominated by stands of spruce and hardwood species. The area is
generally free from permafrost. Unlike many of the other nonmontane ecoregions, the Cook Inlet
Ecoregion was intensely glaciated during the Pleistocene epoch.

BY alaska Range 117,000 sq km
The mountains of south central Alaska, the Alaska Range, are very high and steep. This ecoregion is

=| covered by rocky slopes, icefields, and glaciers. Much of the area is barren of vegetation. Dwarf

‘scrub communities are common at higher elevations and on windswept sites where vegetation does
exist. The Alaska Range has a continental climatic regime, but because of the extreme height of
many of the ridges and peaks, annual precipitation at higher elevations is similar to that measured for
some ecoregions having maritime climate.

fiz Copper Plateau 17,000 sq km

This ecoregion in south central Alaska occupies the site of a large lake that existed during glacial
times. The nearly level to rolling plain has many lakes and wetlands. Soils are predominantly silty or
clayey, formed from glaciolacustrine sediments. Much of the region has a shallow permafrost table,
and soils are poorly drained. Black spruce forests and tall scrub, interspersed with wetlands, are the
major types of vegetation communities.

(iis) Wrangell Mountains 29,000 sq km

This ecoregion consists of steep, rugged mountains of volcanic origin that are extensively covered by

# ice fields and glaciers. Most slopes are barren of vegetation. Dwarf scrub tundra communities,

consisting of mats of low shrubs, forbs, grasses, and lichens, predominate where vegetation does
‘occur. The climate has harsh winters and short summers.

i119 | Pacific Coastal Mountains 106,000 sq km

The steep and rugged mountains along the southeastern and south central coast of Alaska receive
more precipitation annually than either the Alaska Range or Wrangell Mountains Ecoregions.
Glaciated during the Pleistocene epoch, most of the ecoregion is still covered by glaciers and ice
fields. Most of the area is barren of vegetation, but where plants do occur, dwarf and low scrub
communities dominate.

|) Coastal Western Hemlock-Sitka Spruce Forests 61,000 sq km

Located along the southeastern and south central shores of Alaska, the terrain of this ecoregion is a
result of intense glaciation during late advances of the Pleistocene epoch. The deep, narrow bays,
steep valley walls that expose much bedrock, thin moraine deposits on hills and in valleys, very
irregular coastline, high sea cliffs, and deeply dissected glacial moraine deposits covering the lower
‘slopes of valley walls are all evidence of the effects of glaciation. The region has the mildest winter
temperatures in Alaska, accompanied by large amounts of precipitation. Forests of western hemlock
and Sitka spruce are widespread.

Cross-hatched portions along the ecoregion boundaries represent transitional areas sharing charac-
teristics of two or more adjacent ecoregions. Due to the map scale and resolution, as well as to the

resolution of the information used to derive the map, not all transition zones can be represented.