Home is Where the Habitat is - nsf.govTundra and low shrub communities predomi-nate throughout the Arctic Tundra zone. Saturated soils and numerous thaw lakes on the Beaufort Coastal

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The lands and near-shore waters of Alaskastretch from 48° to 68° north latitude and from 130°

west to 175° east longitude. The immense size ofAlaska is frequently portrayed through its super-imposition on the continental U.S., stretching fromGeorgia to California and from Minnesota toTexas. Within Alaska’s broad geographic extentthere are widely diverse ecosystems, includingArctic deserts, rainforests, boreal forests, alpinetundra, and impenetrable shrub thickets. This landis shaped by storms and waves driven across 8000miles of the Pacific Ocean, by huge river systems,by wildfire and permafrost, by volcanoes in theRing of Fire where the Pacific plate dives beneaththe North American plate, by frequent earth-quakes lifting mountains and shifting faults, andby glaciers retreating up to a thousand feet peryear or surging hundreds of feet in a day.

This incredibly beautiful, but constantly shift-ing, land is home for many species of plants andanimals. Some animals come only for the summermonths, to breed, raise young, and retreat towarmer climes before freeze-up, when the cold,dark winter sets in. Other species are year-roundresidents, hibernating through the hungry winteror hunkering down with insulating fat, fur, orfeathers or with high metabolism to survive untilspring.

During 1999–2001 a group of scientists usedold resource and environmental maps of Alaskaand new digital datasets to derive a map illustrat-ing the major ecosystems of Alaska. Extensive dis-cussions among 40–50 scientists from many disci-plines, representing hundreds of years of fieldexperience in the north, helped refine the final dataset. Thirty-two ecoregions were delineated anddescribed, encompassing the landscapes and eco-logical processes of Alaska and nearby Canadaand Russia. These are large ecosystems primarilydefined by climate and topography, with refine-ments from vegetation patterns, disturbanceregimes, bedrock geology, and surficial deposits

remaining from recent geomorphic activities suchas glaciers, floods, and volcanic eruptions.*

Ecosystems in Alaska are spread out alongthree major bioclimatic gradients, represented bythe factors of climate (temperature and precipita-tion), vegetation (forested to non-forested), anddisturbance regime. When the 32 ecoregions arearrayed along these gradients, eight large group-ings, or ecological divisions, emerge. In this paperwe describe the eight ecological divisions, withdetails from their component ecoregions and rep-resentative photos.

Ecosystem structures and environmentalprocesses largely dictate the distribution andbehavior of wildlife species. For example, thenumerous shallow ponds and wetlands of theArctic coastal plain and the Yukon–KuskokwimDelta provide nesting and rearing habitat formillions of waterfowl that migrate north everysummer. However, cold, windy winters freeze theponds, and snow blankets the tundra, turning alush landscape into a frozen barren land. As icefingers reach across the water, the birds fatten up,then swing into the sky and migrate back to theirwintering grounds.

Farther south, coastal brown bears spend thesummer and fall months gorging on nutrient-richsedges, salmon, and berries. As the early snowlinemoves down the mountains, the bears scavengethe final carcasses and head into snug dens tohibernate for the winter. Metabolism rates drop,allowing a bear to survive four to six months onfat reserves. For pregnant sows, this survivalextends to nursing cubs that are born during thewinter.

Home is Where the Habitat isAn Ecosystem Foundation for Wildlife Distribution and Behavior

This article was preparedby Page Spencer,

National Park Service,Anchorage, Alaska;

Gregory Nowacki, USDAForest Service; Michael

Fleming, U.S. GeologicalSurvey; Terry Brock,USDA Forest Service

(retired); and TorreJorgenson, ABR, Inc.

* Full ecoregion descriptions with photos and compila-tion tables of environmental variables are available in theoriginal publication [Nowacki, G., P. Spencer, M. Flem-ing, T. Brock, and T. Jorgenson (2002) Unified Ecore-gions of Alaska: 2001. USGS Open File Report 02-297. 1map.] Digital files of the Unified Ecoregions of Alaskaare available at http://agdc.usgs.gov/data/projects/fhm.

This document has been archived.

Several map versions were generated over a period of one year incorporating suggestions receivedfrom various ecologists, biologists, soil scientists, pilots, and geologists from across the state andadjacent Canadian lands. In areas where data were lacking or pattern changes on the land were indis-tinct, the advice of local experts was used extensively for line placement. The final data set representsthe combined wisdom of 40–50 scientists from many disciplines with hundreds of years of experiencein Alaska and nearby country.

The primary map contributors included Lee Anne Ayers, Chris Dau, Jonathon Hall, Janet Jorgenson,Fran Mauer, Ken Rice, Susan Savage, Lisa Sapperstein, and Mike Vivion of the U.S. Fish and WildlifeService; Blain Anderson, Mary Beth Cook, Bill Eichenlaub, Rich Harris, Penny Knuckles, Lois Dalle-Molle, Bud Rice, Danny Rosenkrans, Patty Rost, Shelli Swanson, and Sara Wesser of the U.S. Na-tional Park Service; Dean Davidson, Rob DeVelice, Gary Fisher (GIS work), Rex Friend, ConnieHubbard, Beth Schulz, Michael Shephard, Ken Winterberger, and Kari Youkey (GIS work) of the U.S.

Forest Service; Mark Clark and Darrell Kautz of the U.S. Natural Resources Conservation Service;David Brew, Alisa Gallant, and Mark Shasby of the U.S. Geological Survey; Keith Boggs and CarolynParker of the University of Alaska; David Banks of The Nature Conservancy; Bob Ritchie of AlaskaBiological Resources, Inc.; Tony Button and Dennis Demarchi of the British Columbia Ministry of theEnvironment, Land and Parks; John Meikle and Jack Schick of the Government of the Yukon; CharlesRoots of the Geological Survey of Canada; and Scott Smith of Agriculture and Agri-Food Canada.

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Moose spend their summers feeding on lushwetland vegetation and new shrub growth, espe-cially in early successional vegetation communi-ties. During winter, however, snow severely limitsfood availability, forcing moose to wade throughdeep snow to browse on shrubs. If the energygained from browsing willow twigs is greater thanthe energy expended reaching them, the moosehave a good chance of surviving until spring.

The animal species discussed in this issuehave each developed adaptations that haveenabled them to survive and persist in the variousecosystems in Alaska.

The Arctic Tundra Division stretches alongthe Arctic Ocean and sweeps inland to includethe Beaufort Coastal Plain, the Brooks Foothills,and the Brooks Range ecoregions. These open,wind-swept lands are gripped by polar conditionsthroughout the year. Cold air off the permanentice pack of the Beaufort Sea has low moisture-holding capacity, and precipitation in this regionis less than 20 inches per year. Summer tempera-tures average less than 50°F within this division,effectively limiting tree growth to the southernfringe of the Brooks Range. Permafrost is nearlycontinuous throughout the region, contributingto saturated organic soils in the summer and avariety of freeze–thaw ground features. Repeatedfreezing and thawing of soils create uniquefeatures such as pingos (ice-cored peat mounds),ice-wedge polygons (a repeating pattern ofhexagons in the tundra vegetation), orientedthaw lakes (linear lakes shaped by prevailingwinds), and solifluction lobes and stone stripes(ground loops and vertical stripes on gentle hillscaused by slumping of the thawed active layer

or by frost pushing larger rocks to the soilsurface).

The Brooks Range represents the northernextension of the Rocky Mountains and is built upby accreted terranes (fault-bounded rock unitswith a unique geologic history) originating fromthe Arctic Ocean. The high central portion of therange possesses steep angular summits of sedi-mentary and metamorphic rock draped with rubbleand scree. Mountain glaciers covered the higherpeaks during the Pleistocene, leaving remnantglaciers in the high cirques (steep-walled semicir-cular hollows created by glacial scouring). Theseglaciers flowed out of the Brooks Range, carvingwide valleys, which serve as corridors for humanand wildlife migrations, and leaving terminalmoraines looped across the Brooks Foothills.The Brooks Foothills are gently rolling hills andbroad exposed ridges flowing out from the north-ern flank of the Brooks Range. Narrow valleys,glacial moraines, and outwash are interspersedamong long linear ridges, buttes, and mesas com-posed of tightly folded sedimentary rocks. Thefoothills flatten out into the Beaufort CoastalPlain, a vast undulating surface underlain byunconsolidated deposits of marine, fluvial (carriedby streams), glaciofluvial (carried by glacial iceand meltwater), and eolian (carried by wind) originand covered with a mosaic of lakes, braided rivers,and wetlands.

River systems arising in the Brooks Range flowsouth into the boreal zone or north to the ArcticOcean. High-energy stream systems cut narrowravines in the mountainous Brooks Range, etchinga deeply incised dendritic pattern. Streams coa-lesce into large braided rivers in the foothills.Some of these streams freeze solid to their bot-toms, causing large deposits of frozen overflow, oraufeis, that last well into summer and provide ref-uge for caribou from voracious flies. Break-up andsnowmelt in the southern Brooks Range oftencause spring flood waters to flow out over still-frozen river channels on the Coastal Plain andflood onto the near-shore ice of the Arctic Ocean.

Tundra and low shrub communities predomi-nate throughout the Arctic Tundra zone. Saturatedsoils and numerous thaw lakes on the BeaufortCoastal Plain support wet sedge tundra in drainedlake basins, swales, and floodplains and tussocktundra and alpine tundra dominated by sedgesand Dryas (mountain avens) on gentle ridges.Vegetation of the foothills and lower mountainslopes of the Brooks Range is dominated by vastexpanses of mixed shrub–sedge tussock tundra,

Migrating caribou swarmacross a braided flood-

plain in the Brooks Foot-hills, with the peaks of the

Brooks Range in thebackground. Late snow-

banks and aufeis depositsprovide a refuge from

biting insects. On eitherside of the river, tussock

tundra and willowsstretch for hundreds of

miles across thefoothills and into the

lower Brooks Range.

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interspersed with willow thickets along rivers andsmall drainages and Dryas tundra on ridges.Alpine tundra and barrens dominate at higherelevations along the entire crest of the range. Onthe south side, lower mountain slopes and valleysare covered with sedge tussocks and shrubs. TheArctic treeline skirts across the Brooks Range inCanada and is restricted to the south side of therange in Alaska. Here, sparse spruce and birchforests and tall shrublands occur in larger valleys.

Fish species and populations are sparse in theswift shallow streams of the Brooks Range. Asstreams become larger and slower, their clearwaters teem with arctic char and arctic grayling.Arctic cisco, broad whitefish, least cisco, andDolly Varden char overwinter in deep holes of thelarger rivers of the coastal plain and migrate tonear-shore marine waters for the summer. Thisregion has been called the “Arctic Serengeti”because of the huge herds of caribou that migrateacross the Brooks Range annually—north to thecoastal plain for calving and summer grazing,south for the winter months. Wolves, arctic foxes,and grizzly bears follow and prey on caribouherds, subsisting on voles, lemmings, arcticground squirrels, or vegetation when caribou arenot available. Muskoxen were heavily hunted onthe coastal plain during the whaling era and are re-establishing themselves from introduced ani-mals (see p. 74). Dall’s sheep occupy the highcountry of the Brooks Range (see p. 68). Severalspecies of whales migrate into the Arctic Ocean insummer, and seals and polar bears are year-roundresidents. The coastal plain is important for breed-ing birds, including a wide variety of shorebirds,ducks, geese, swans, and songbirds.

The Bering Tundra Division includes landsand nearby waters in and near the Bering Sea. TheBering Sea is mostly ice-covered for many monthseach year and cold and stormy the remainingmonths. The Bering Sea has limited warmingeffects on the climate, so the adjacent lands arepredominately cold, wind-swept, and treeless. TheBering Tundra Division includes the KotzebueSound Lowlands, the Seward Peninsula, and theBearing Sea Islands ecoregions. The northernBering Sea covers a large shallow shelf less than250 feet deep, reaching well north in the ChukchiSea, through the Bering Strait, and south to thePribilof Islands. During several glacial maxima, thisshelf has been above sea level and vegetated withtundra and steppe communities. This plain servedas a migration route between North America andEurasia for plants, animals, and humans (see p.55).

Scattered volcanic hills rise above largeexpanses of marine sediments, outwash plains,and sedimentary bedrock. These hills form theexposed Bering Sea Islands and hills of theSeward Peninsula. Several recent lava flows,cinder cones, and hot springs on the Seward Pen-insula indicate ongoing volcanism. The KotzebueSound Lowlands are primarily depositional fea-tures from materials washed and blown off nearbyhills and outwash plains. The Seward Peninsula isgently rolling hills and rounded valleys with a fewmore rugged mountains in the south. Continuouspermafrost of varying thickness underlies thethick wet soils of the Kotzebue Sound rim and thethin rocky soils of the Seward Peninsula andBering Sea Islands.

The cold soils and bitter climate support moistor wet tundra communities of sedges, grasses, lowshrubs, and lichens interspersed with rocky cliffs

The winter sun rises briefly over low mountains andfrozen tundra on the Seward Peninsula. Subdued ter-rain and harsh weather off the Bering Sea are typical ofthe Bering Tundra Division.

Wetlands, oriented lakes,and saturated organic

soils are characteristic ofthe Beaufort Coastal Plain

near Milne Point. Lakesare still ice-covered in

early spring but will soonbreak up and resound to

countless calls of courtingand nesting waterfowl.

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and shorelines. Drier ridgetops on the SewardPeninsula and the islands have alpine Dryas–lichen tundra and barrens with low shrub tundraon hillsides and willows along streams. Scatteredforest patches of balsam poplar and white sprucegrow along the rivers in protected valleys of theeasternmost Seward Peninsula and the Kotzebuelowlands. Strong ecological affinities to Asiaremain to this day, with the presence of Eurasianbirds (gray-headed chickadees, yellow and whitewagtails, and bluethroats), fishes (Alaska black-fish), and flora. Whales, walruses, and polar bearsfunnel through the Bering Strait as they migratebetween the Bering Sea and the Arctic Ocean.Dense concentrations of lakes and ponds supportmany species of nesting birds, including the rarearctic loon. Bears, caribou, snowy owls, arcticfoxes, and hares are common on the mainland.Millions of seabirds (cormorants, kittiwakes,murres, puffins, and auklets) and marine mammals(northern fur seals, ribbon seals, and sea lions)inhabit the rocky outposts of St. Lawrence, St.Matthew, and the Pribilof Islands during thesummer. Wintering flocks of rare spectacled eiderscongregate in small polynyas (openings) in thesea ice south of St. Lawrence Island. Muskoxenand domestic reindeer have been introduced toNunivak Island and the Seward Peninsula.

The ecoregions of the Bering Taiga Divisionspread along the eastern coast of the Bering Seafrom Norton Sound south to Bristol Bay. Although

the area is dominated by a moist sub-polar climate,the southern Bering Sea is not as covered by iceduring the winter as north of St. Lawrence Island.Summers are sufficiently long and warm to allowpatches of stunted trees (taiga) to grow, primarilyalong rivers and streams. However, summer warm-ing is tempered by the cold prevailing winds offthe Bering Sea, which in some years result inpatchy ice as far south as Bristol Bay. The eco-regions of the Bering Taiga are the Nulato Hills,the Yukon–Kuskokwim Delta (often called the Y–K Delta), the Ahklun Mountains, and theBristol Bay Lowlands.

The Bering Taiga Division is made up of twounits of old weathered mountains: the Nulato Hillsand the Ahklun Mountains, with intervening dep-ositional lowlands: the Y–K Delta and the BristolBay lowlands. The Nulato Hills are rolling wavesof regular northeast–southwest-trending moun-tains, with beautiful clear rivers in the valleys. TheNulato Hills and Y–K Delta were largely ice-freeduring the Pleistocene, while the Ahklun Moun-tains spawned mountain glaciers that left U-shaped valleys throughout the unit and spreadterminal moraines across the northwest corner ofthe Bristol Bay lowlands. These lowlands havebeen shaped by multiple huge glaciations out ofthe eastern side the Alaska Range, which left con-centric terminal moraines and large outwash plainsacross the unit and into Bristol Bay. The valleys ofthe Ahklun Mountains are filled with large “finger

The clear waters of theSouth River in the Nulato

Hills are spawninghabitat for hordes of pink

(or humpy) salmon thatprovide fall food for

hungry bears. Sparsetaiga forests grow on

river terraces, gradingupward into low shrubs,shrub tundra, and rocky

alpine tundra.

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lakes” that have filled the glacial basins as the iceretreated. The Y–K Delta and the Bristol Bay low-lands have been formed by the dance of fluctuat-ing sea levels during glacial periods and alluvialdeposition from huge river systems draining cen-tral Alaska. The resulting layers of glacial, alluvial,and marine sediments form low-lying saturatedsoils and an incredible mosaic of ponds, sloughs,and wandering streams. Permafrost is nearly con-tinuous on the Y–K Delta, opening to patchy far-ther south in Bristol Bay. The mountain units havethin rocky soils with sporadic permafrost in thevalleys.

The vegetation patterns of the Bering Taigagenerally follow the terrain. White spruce andbalsam poplar grow in sinuous stands along mostriver systems in the region. Gently rolling sideslopes support black spruce and paper birchforests and tall shrub communities of dwarf birchand alder. The higher elevations are covered withshrub tundra and lichens or barrens on the wind-scoured summits. Lowlands are covered with arich and productive mix of emergent wetlands andsedge–tussock and sedge–moss bogs, withwillows along small streams. Slight rises supportlow shrublands and scattered spruce.

The river systems of this division are incrediblyproductive for various fisheries. The Bristol Baysockeye (red salmon) run is the largest in theworld, and huge pink salmon runs ascend theUnalakleet River every summer. Rural residentsthroughout the region and upstream into Canadadepend on king (chinook), red, and chum salmonfor winter supplies and dog food. These salmonruns feed coastal brown bears, especially in theBristol Bay region. The rapidly rotting spawned-

out carcasses bring vast quantities of marinenutrients to the terrestrial and aquatic ecosystems,where they nourish the next generation of salmonfingerlings. Likewise, the lake and wetlandsystems, particularly of the Y–K Delta, supportmillions of staging and nesting waterfowl andshorebirds. Great numbers of gregarious walrusesand sea lions haul out on rocky beaches, whileseabirds patrol the skies. Moose and beaver thrivealong the rivers, while caribou, wolves, and blackand grizzly bears roam the uplands.

The Intermontane Boreal Division in Alaska isa portion of the largest coniferous forest in theworld. The boreal forest stretches across thenorthern circumpolar regions, including Canada,Alaska, Siberia, and Scandinavia. This intermont-ane terrain, sandwiched between the Brooks andAlaska Ranges, remained largely ice-free duringthe last ice age, forming part of the “Beringia Cor-ridor” that provided a route for animals andhumans moving between Asia and southern partsof North America (see p. 55).

The boreal region is characterized by a conti-nental climate, with extreme weather conditionsranging from long, cold winters to short, warmsummers. The continental climate is fairly drythroughout the year, and forest fires rage duringsummer droughts. The resulting vegetation pat-tern is a constantly shifting mosaic of succes-sional communities in response to wildfire andriver changes. Most of the soils are underlain byice-rich permafrost and are subject to thermokarst-ing where ice lenses melt out or form under insu-lating moss mats. The boreal forests of Alaska,also called taiga from the Russian term meaning“land of little sticks,” is vegetated with blackspruce, tamarack, and paper birch woodlands;shrubby muskeg on permafrost-rich areas; whitespruce and balsam poplar on floodplains wherepermafrost is missing or very deep; and aspen andshrub on upland areas of recent fires and discon-tinuous permafrost.

Alaska ecoregions in the Boreal Division are acombination of large river valleys and old moun-tains. The river valleys include the Yukon–OldCrow Basin, the Tanana–Kuskokwim Lowlandsand the Yukon River Lowlands. Units of old,largely unglaciated mountains are the KobukRidges and Valleys, the Ray Mountains, theDavidson Mountains, the North Ogilvie Moun-tains, the Yukon–Tanana Uplands, and theKuskokwim Mountains.

The boreal lowlands are drained by severallarge river systems, including the Yukon (the

The lower Yukon RiverDelta is typical of

depositional wetlands ofthe Bering Taiga Division.

This maze of lakes,creeks, and wetlands will

soon host millions ofnesting waterfowl andshorebirds during the

summer months.

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fourth longest in North America), Porcupine,Tanana, Koyukuk, and Kuskokwim. The climatebecomes progressively more continental the far-ther east one travels, as the temperature rangesbecome greater and precipitation decreases. Theseriver valleys were largely unglaciated during thePleistocene. However, most of these areas areblanketed in thick loess (fine-grained silt), blownoff the glaciated areas of the Alaska Range, andalluvial deposits from side streams in the hills andmountains. The Yukon Flats and Old Crow Basinsare gently sloping basins composed of deposi-tional fans, terraces, and mountain toeslopes withdeep colluvial (deposited by gravity), alluvial, andeolian deposits underlain by continuous massesof permafrost. The lowlands of the Yukon, Tanana,and Kuskokwim Rivers have deep alluvial sedi-ments overlain by eolian loess. Ice-rich permafrostpermeates organic soils with varying patterns ofthickness and continuity. The resultant flood-plains and wetlands support intricate wetlands,old river sloughs, and subtle hills.

The highly productive vegetation along themajor rivers supports vigorous stands of whitespruce and balsam poplar. Robust wet sedge mead-ows and aquatic vegetation are invading sloughsand oxbow ponds. The adjacent permafrost-dominated lowlands support black spruce wood-lands, dwarf birch and low-growing ericaceousshrubs of the heath family, and sedge–tussockbogs. The rich aquatic habitats support tremen-dous concentrations of nesting waterfowl (in themillions!) and other migratory birds and an abun-dance of moose, bears, furbearers, northern pike,and salmon. Large rivers support important runsof chinook, chum, and coho salmon, while clear

tributary streams support dolly varden and gray-ling. Flat areas are pockmarked with lakes andponds. These areas support large populations ofmoose and black bear; the oxbow sloughs andthaw ponds support abundant waterfowl duringbreeding season; and the lowland forests areimportant to furbearers, including beavers, musk-rats, and martins. Cliffs along the rivers are excel-lent nesting habitat for ravens and raptors such asperegrine falcons. Yellow-cheeked voles are foundin early successional riparian and recently burnedareas throughout the Alaskan and Canadianboreal forests (see p. 48).

Boreal uplands are characterized by low- tomid-height hills and mountains, with subtle topo-graphy from long-term weathering without theimpacts of glaciers. Again, many of the uplandunits, especially the Kuskokwim Mountains andthe Yukon–Tanana Uplands on the southern sideof the intermontane valley, are cloaked with loessblown north from the Alaska Range glaciersduring the Pleistocene. The Kobuk Ridges andValley and the Davidson Mountains on the north-ern side of the boreal division were subject topartial glaciations during the Pleistocene, withmorainal remnants strewn along classic U-shapedvalley walls. The North Ogilvie Mountains are

The broad valley of theKobuk River shows the

mosaic of conifer anddeciduous forests shifting

in response to multiplechanges in the river channel.

Lightening-caused wildfires are constantly burningpatches of the boreal forest, creating a mosaic of suc-cessional vegetation communities that provide habitatfor many wildlife and bird species.

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the oldest portion of Alaska, representing thewestern extent of the North America stable plat-form, where terranes rafting from the Pacific andArctic Oceans finally came to rest and docked.Several of these boreal mountain units are host tohot springs. Vegetation is dominated by whitespruce, birch, and aspen on south-facing slopes,black spruce on north-facing slopes, and blackspruce woodlands and tussock and scrub bogs invalley bottoms. Floodplains of headwater streamssupport white spruce, balsam poplar, alder, andwillows. Above treeline, dwarf birch and erica-ceous shrubs and Dryas–lichen tundra dominate.Lightning from frequent summer thunderstormsstarts many wildfires each year. These fires con-

tribute to the spectacular mosaic of forest succes-sional stages that provide a wide range of habi-tats. Caribou, moose, snowshoe hares, martens,lynx, and black and grizzly bears are plentiful(see p. 63). The clear headwater streams are impor-tant spawning areas for chinook, chum, and cohosalmon.

The Alaska Range Transition Division literallyrises between the continental boreal interior ofAlaska and the marine rainforest coastlands alongthe Gulf of Alaska. The climate of this division hasshorter winters than the continental interior andwarmer, drier summers than the marine-influencedcoastal rainforests. However, the Alaska Range,including Mt. McKinley (Denali) at over 20,000feet, generates its own weather, as moisture-ladenair rises over the massif and releases heavy snow-falls on the upper elevations. Pleistocene glaciersheavily influenced the entire area, and remnants ofglaciers and many glacial features still define thelandscape. Boreal forests are distributed in thevalleys and lowlands of the division, but wildfireand permafrost have much less influence on vege-tation succession and distribution. The eco-regions of the Alaska Range Transition are theLime Hills, the Alaska Range, the Cook Inlet Basin,and the Copper River Basin.

The Alaska Range is a long arcing wall ofaccreted terranes that have fused into a complexmix of folded, fractured, and deformed sedimentaryand metamorphic rocks with intrusions of granite.The Denali Fault runs parallel to and within theAlaska Range for the easternmost 350 miles,

The Alaska Range risesabruptly from nearby

river basins, creating itsown climate, which is a

transition between thecontinental conditions ofinterior Alaska and the

marine systems along thenorth Gulf of Alaska

coast. Sparse taigaforests and wetlands are

common in the Susitnaand Copper River Basins

of the Alaska RangeTransition Division.

Fall colors drape thelowlands of the KenaiPeninsula in the Cook

Inlet Basin. Lakes werecreated from remnant

blocks of ice abandonedby retreating glaciers, and

the mixed forests andwetlands are habitat for

moose, bears, waterfowl,and beavers.

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before the range takes a turn to the south and theDenali Fault continues southwesterly into theKuskokwim Basin. The Alaska Range was the ori-gin for much of the Pleistocene ice that flowed outof the mountains in all directions and substantiallyformed the landscape. Large valley glaciers andice caps still flow off the peaks of the AlaskaRange. The Lime Hills area immediately west of theAlaska Range is a series of east–west-trendingridges and intervening valleys. This area wasrepeatedly scoured by huge valley glaciers flow-ing out of the Alaska Range and, like the CookInlet and Copper River Basins, is covered withglacial moraines, lacustrine sediments depositedin lakes, and outwash plains. The Copper RiverBasin was the location of Great Lake Ahtna, alarge proglacial lake dammed by glaciers blockingthe Chugach Range to the south. The Cook Inletand Susitna valleys are a large trough betweenthe Alaska and Kenai Mountains that has beensubject to repeated glacial advances. Some ofthese glaciations also formed large lakes over thecurrent Kenai Peninsula. The region is coveredwith a subdued pattern of low ridges and lakes orwetlands.

This division forms the headwaters for riversflowing into all the oceans surrounding Alaskaexcept the Arctic Ocean. Glacial rivers are silty andbraided, with broad, gravelly floodplains. Clearstreams are generally smaller with narrower flood-

plains and lose their clear identity assoon as they flow into a glacial stream.Arctic grayling are common in clearmountain streams, and all five species ofPacific salmon migrate into rivers of theAlaska Range Transition.

Soils in the mountainous units of theAlaska Range and Lime Hills are generallythin, rocky, and cold, with scattered pock-ets of permafrost. The Copper River Basinfloor is formed of interleaved lacustrinedeposits, glacial material, and volcanicdebris that forms fine-grained saturatedsoils with ice-rich permafrost. Soils of theCook Inlet Basin are a complex mixture ofalluvial, glacial, volcanic, and lacustrinematerials with occasional patches ofpermafrost. Both basins support borealvegetation patterns, with white spruceand birch on higher ground and blackspruce, low shrubs, sedges, and mossesgrowing in the wetlands. White spruceand balsam poplar form successionalstands along the rivers. The lower slopes

of the Alaska Range and Talkeetna Mountains arecovered with dense thickets of alder that transi-tion to low shrubs in the subalpine and blueberry-rich alpine tundra. Vegetation of all types suc-cumbs to the harsh conditions at about 4000 feet,leaving the higher arena to bare rock, talus (bro-ken loose bedrock), and ice.

The wide variety of habitats, ranging from sealevel to several thousand feet, in a transitionalclimate support many species of mammals andresident and migratory birds. Moose, grizzly andblack bears, wolves, foxes, beavers, and varioussmall mammals are fairly common in the Cook InletBasin and lower reaches of the Alaska Range (seep. 18). Caribou herds roam the Alaska Range, LimeHills, and Copper River Basin (see p. 63). Water-fowl nest in the wetlands of the basins, althoughnot in the concentrations found in the Y–K Deltaor Yukon Flats. Golden eagles nest in the moun-tains and disperse farther south for the wintermonths (see p. 22). Ptarmigan spend the winters inwillow thickets with a white coat of double feath-ers all the way down their feet, and ravens haunturban dumpsters looking for high-calorie treatsand roadkill.

The Coast Mountains Transition Division issimilar to the Alaska Range Transition in that arange of very high mountains is thrust up betweena dry continental climate of the upper Yukon Riverdrainage and the maritime-driven climate of the

A grizzly sow and hercub forage for blueberries

and mossberries in thebrilliant fall colors ofsubalpine ericaceous

shrub tundra. This pairwas photographed in

early September on thenorth slopes of the

Alaska Range.

14

Chugach and St. Elias Ranges. Because of theirsheer height, these mountains capture ocean-derived moisture as it passes inland. Yet, theirproximity to Interior Alaska gives these mountainsa fair degree of seasonal temperature change simi-lar to a continental climate. Climatic influenceschange with elevation, with maritime conditionson mountaintops (feeding ice caps and glaciers)grading to continental conditions at their base(boreal forests). The Wrangell Mountains and theKluane Ranges ecoregions comprise the CoastMountains Transition.

The Wrangell Mountains are a compact layercake of volcanic and deformed sedimentary materi-als, stacked up for thousands of feet, topped byrecent volcanic lava and ash, and etched bymassive glaciers. The abundant maritime snowsfeed extensive icefields and glaciers interspersedby dull gray ridges draped with rock shard slopesand patches of alpine meadows. The KluaneRanges reach east into Canada in the rain shadowof the St. Elias Mountains along the steep slopesof the fault line scarp in the Shakwak Valley.Occasional glaciers flow onto the Kluane Rangesfrom the St. Elias icefields, but the unit is generallyice-free.

Continental climates around the toeslopes ofthe Wrangell Mountains support permafrost soilsand boreal forests of black spruce and birch, grad-ing up into drier shrublands, and typical alpinecommunities of low ericaceous shrubs, lichens,and barrens. The Kluane Ranges have thin rockysoils with discontinuous permafrost. The unstablematerials are constantly moving downslope astalus, stream erosion, or solifluction. The dryclimate supports white spruce woodlands with

balsam poplar and aspen stands, grading upwardinto willow shrubland and typical low and dwarfshrub communities in the alpine areas. Snowshoehares and lynx exhibit cyclic fluctuations in abun-dance, with lynx numbers dropping shortly afterthe peak in hare population. Dall’s sheep roamthroughout the area, along with mountain goats,brown bears, caribou, wolverines, and graywolves.

The Coastal Rainforest Division includes thegreat arc of mountains and the forested fringe thatswing around the north and east shores of theGulf of Alaska. Terranes that originated beneaththe Pacific Ocean have been rafted into place andaccreted in ridges. Frequent earthquakes alongthe dip of the Pacific Plate under the North Ameri-can Plate result from continuing uplifting andfaulting of the sedimentary and volcanic materials.

Dominant storm tracks from late summerthrough early spring curl east from the Aleutiansinto the Gulf. Upon hitting shore, the moisture-laden air rises over the mountains, dropping copi-ous rain at lower elevations and snow at thehigher altitudes. The Gulf of Alaska current flowseast to west along the coast, bringing relativelywarm temperatures throughout the year. Thewarm, wet climate supports lush conifer rain-forests along the coast and large icefields andglaciers at higher elevations. All of the divisionhas been heavily glaciated several times duringthe Pleistocene.

The coastlands reflect their glacial heritage,with steep bedrock fjords, tidewater glaciers, andnumerous rocky islands. The Coastal RainforestDivision includes the mountainous units of theChugach–St. Elias Mountains and the BoundaryRanges and the island and fjord lands of the Alex-ander Archipelago, the Gulf of Alaska Coast, andKodiak Island.

Mountains tower behind the Gulf Coast to alti-tudes over 19,000 feet. The largest icecap outsideof the polar regions drapes the folded sedimentaryrocks of the Chugach and St. Elias Mountains.Huge valley glaciers flow out of this icecap, manyto tidewater. The Bering Glacier, at more than 2000square miles, spreads out over the lowlands of theGulf Coast. The Hubbard Glacier surged duringthe summers of 1986 and 2002, blocking off Rus-sell Fjord for several weeks each time. The Bound-ary Ranges, located farther south and lower inelevation, hold only mountain glaciers. The Alex-ander Archipelago, the Gulf of Alaska Coast, andthe Kodiak Archipelago all face the Gulf of Alaska,with intricate glacier-carved coastlines. Long,

Valley glaciers flowbetween nameless peaksin the towering Wrangell

Mountains. Moisture-laden clouds sweepinginland from the Gulf of

Alaska are cooled as theyrise over the mountains,

and the resultingprodigious snowfalls

create the largest icefieldoutside the Arctic and

Antarctic latitudes.

15

deep fjords formed where glacier-carved terrainfilled with seawater after deglaciation. Thousandsof islands, islets, and rocks indicate the summitsof submerged mountain ranges and present both achallenge and a delight to mariners.

A few areas along this coast remained ice-freeduring one or more glacial advances, providingrefugia for plant and animal species to survive thePleistocene advances. Humans may have alsomigrated along the coast from one ice-free toeholdto another. Movements of the earth’s crustcontinue to raise and lower portions of the coast,creating and deleting coastal lagoons, beaches,and tideflats. Soils are exceptionally thin exceptin riparian zones. Relatively warm winters precludepermafrost.

Short rivers flow out of glaciers in braidedfloodplains or tumble off rocky mountainsides inbarely contained waterfalls. Five species of Pacificsalmon migrate into these fast-flowing streams tospawn. Dolly Varden char and steelhead (ocean-going rainbow) trout live in larger clear-waterstreams along the coast and on Kodiak Island.The land and sea are intimately connected, asspawning salmon return to their native streamsand, in the process, cycle tremendous amountsof nutrients back to the freshwater and terrestrialsystems that bore them life. Streams becomeincreasingly littered with spawned-out carcassesas brown and black bears, bald eagles, and gulls

feast on returning salmon from late spring toearly fall.

The warm maritime environment encourageslush moss-draped conifer forests along the coast.Old-growth forests of Sitka spruce, hemlock, andcedar blanket the lower slopes of the AlexanderArchipelago. Toward the west, cedar drops outin Prince William Sound, and hemlock reaches tothe end of the Kenai Peninsula. On Kodiak, Sitkaspruce is expanding south across the island intonew habitats. Pockets of wetlands have formedon shallow, poorly drained soils on bedrockthroughout the division. The stunted trees, tinyponds, and bedrock outcrops give the appearanceof a giant bonsai garden. Hidden coves and rockyislands are fringed with intertidal communities ofkelps, eelgrass, and barnacles. Upper forests giveway to a narrow subalpine zone of alder andherbaceous meadows and then alpine tundra andbedrock or ice.

Common forest animals include black andbrown bears and Sitka black-tailed deer. Offshorewaters are rich with deepwater fish, such as hali-but and cod. Grey whales migrate along the coast,following the warm Gulf current as far as the ArcticOcean for summer, returning to the Gulf of Mexicofor the winter months. Humpback whales migrateannually between winter calving grounds near theHawaiian Islands and summer feeding groundsnear Glacier Bay (see p. 42). Bald eagles, common

The fjord-studdedAlexander Archipelagowas carved by massive

glaciers rising in thebackground Boundary

Ranges of southeastAlaska. The retreating

glaciers left an intricatecoastline with dense

conifer forests on thelower mountain slopes,rising to alpine tundra

and barrens.

16

murres, Bonaparte’s gulls, Steller sea lions, harborseals, and sea otters teem along its endless shore-lines (see p. 31 and 36).

The Aleutian Meadow Division stretches nearly2000 miles, reaching from Iliamna Lake west to theKomandorskiye Islands near the Kamchatka Pen-insula in Russia. The fog-shrouded AleutianIslands and storm-pounded coasts of the AlaskaPeninsula make up this exposed division, setbetween the cold Bering Sea and the stormy NorthPacific Ocean. This division is defined by cool,moist, and harsh weather, which limits tree growthto a few Sitka spruce perched on rocky promonto-ries on the Shelikof Strait coast. The division isformed by the Pacific Plate Subduction Zone,where the Pacific Plate dives beneath the NorthAmerican Plate, forming one of the most seismi-cally and volcanically active areas in the world.The area hosts 80% of the active volcanoes in theUnited States, and many of the gently steamingcones may erupt at any time.

Glaciers have also played a role in shaping thisland of fire and ice. Thick ice sheets from theAlaska Range and lower Cook Inlet overrode themountains near Iliamna and Katmai, rounding offlower mountains and leaving large basins filledwith freshwater lakes along the western slopes ofthe Alaska Peninsula ecoregion. Glaciers alsoformed on the wetter, southern side of Aniakchak,Veniaminof, and Pavlof volcanoes, expanding

south onto the narrow shelf at the edge of theNorth Pacific. The Aleutian Islands are predomi-nately volcanic features rising above the turbulentseas.

Permafrost is absent from this division, reflect-ing the relatively warm climate dominated byoceanic influences. Soils are a mixture of volcanicmaterials, often reworked by glacial and alluvialagents. Areas of recent glaciations and volcanicactivity such as Katmai and Aniakchak are largelybarren cinder plains. Other parts of the region,well watered by Pacific storms and fertilized bynesting seabirds, support lush meadow and heathvegetation communities, with willows alongstreams. The flora is a blend of species from twocontinents, grading from Asian to North Americanaffinities from west to east.

This division is the domain of seabirds, water-fowl, and marine mammals. Sea otter populationshave rebounded since near extirpation by Russianand American fur traders and are now distributedthrough most of their former range along the Aleu-tian and Gulf of Alaska coasts (see p. 31). Stellarsea lions use low rocky shelves as haulouts andpupping areas, although their numbers havedropped dramatically within the past severaldecades (see p. 36). Several species of whalesreside here or migrate through en route to theArctic Ocean. Onshore, coastal brown bears feedon lush sedge meadows and salmon runs, moose

Bear Glacier, one of thelargest concentrations oftidewater glaciers in the

northern hemisphere,meets the sea along the

Gulf of Alaska coastline.The glacially formed

lagoons and fjords arehabitat for seals, whales,

sea otters, andterrestrial mammals.

17

are expanding gradually down the peninsula, andcaribou are native on the peninsula and UnimakIsland and have been introduced to several Aleu-tian Islands. Foxes, introduced to many islands forfox farming, and rats, introduced accidentally fromships, have nearly decimated ground-nestingwaterfowl, including the Aleutian Canada goose.Fox eradication and careful reintroduction of theAleutian goose on several islands have recentlyresulted in its removal from the endangered spe-cies listing.

Suggestions forFurther ReadingBailey, R.G. (1995) Description of the Ecoregions of

the United States. Second Edition. U.S. Depart-ment of Agriculture Forest Service, Miscella-neous Publication No. 1391 (rev.), Washington,D.C.

Hopkins, D.M. (ed.) (1967) The Bering LandBridge. Stanford University Press, Stanford,California.

Mt. Peulik, a dormantvolcano, rises on the

shores of Becharof Lake.The low shrubs and

sedge tundra are charac-teristic of the Aleutian

Meadow Division.

Krebs, J.C., S. Boutin, R. Boonstra (ed.) (2001)Ecosystem Dynamics of the Boreal Forest. TheKluane Project, Oxford University Press, NewYork.

Nowacki, G., P. Spencer, M. Fleming, T. Brock, andT. Jorgenson (2002) Unified Ecoregions ofAlaska: 2001. U.S. Geological Survey, Open FileReport 02-297. 1 map. Digital files of the UnifiedEcoregions of Alaska are available at http://agdc.usgs.gov/data/projects/fhm

Péwé, T.L. (1975) Quaternary Geology of Alaska.U.S. Geological Survey, Professional Paper 835.U.S. Government Printing Office, WashingtonD.C.

Pielou, E.C. (1991) After the Ice Age: The Return ofLife to Glaciated North America. The Univer-sity of Chicago Press, Chicago, Illinois.

L.A. Viereck, C.T. Dyrness, A.R. Batten, and K.J.Wenzlick (1992) The Alaska Vegetation Classifi-cation. U.S. Department of Agriculture ForestService, Pacific Northwest Research Station.

Williams, H. (ed.) (1958) Landscapes of Alaska,Their Geologic Evolution. University of Cali-fornia Press, Berkeley, California.