Vegetation Zones of Washington

 

•Natural Vegetation of Oregon and Washington

•JF Franklin and CT Dyrness

•1973 (revised 1988)

Factors affecting vegetation

•Topography

•Moisture

•Temperature

 

Topography

Olympic Mountains (Hurricane Ridge)

Cascade Range (Mount Rainier and Mount Baker)

Columbia Basin (southeastern Washington)

Okanogan Highlands (northeastern Washington)

 

Washington’s Ecological Diversity

average annual precipitation

January mean minimum temperature

July mean maximum temperature

Vegetation Zone names

•Vegetation zones are named for the dominant, late-successional species

•This species will not always be the most common

 

Picea sitchensis (sitka spruce) zone

Picea sitchensis (sitka spruce) zone

Picea sitchensis (sitka spruce) zone

•75-140 inches precipitation

•summer fogs increase soil moisture

•mild climate

 

coastal forests

dominant trees include sitka spruce

western hemlock

western redcedar

Douglas-fir

lodgepole pine (known as shore pine on the coast)

understory plants include sword ferns

temperate rainforest subzone

big leaf maple with epiphytic mosses and lichens

nurse logs

Next: Tsuga heterophylla (western hemlock) zone

Tsuga heterophylla (western hemlock) zone

Tsuga heterophylla (western hemlock) zone

•Elevation sea level - 2100 feet

•35-100 inches precipitation

•Mild temperatures

•Few freezing days in winter

•Relatively dry summers

 

 

Best timber production region;
clearcuts and second growth forests common

Dominant trees include western hemlock

Douglas-fir

grand fir

western redcedar

black cottonwood

Oregon ash

Understory plants include salal

vine maple

Puget Sound area is special sub-zone;
less rainfall and gravelly glacial soils

western white pine

Pacific madrone

Poison oak

Mima mounds prairie (between Olympia and Centralia)

Oregon white oak woodlands (near Fort Lewis)

San Juan Islands (northern Puget Sound)

grassland and forest vegetation

Rocky Mountain juniper

Abies amabalis (Pacific silver fir) zone

Abies amabalis (Pacific silver fir) zone

Abies amabalis (Pacific silver fir) zone

•Elevation 2100-4200 feet

•Wetter than Tsuga heterophylla zone

•much of precipitation as snow

•Cooler than Tsuga heterophylla zone

 

Pacific silver fir

noble fir

avalanche zone

Sitka alder

Alaska yellow cedar

Tsuga mertensiana (mountain hemlock) zone

Tsuga mertensiana (mountain hemlock) zone

Tsuga mertensiana (mountain hemlock) zone

•Elevation 4100 feet – treelilne

•One half of precipitation as snow

•Snow covers ground for six months

•Temperatures cool to freezing

closed forest

parkland

mountain hemlock

subalpine fir

Alaska yellow cedar

wildflower meadow at Mount Rainier

Alpine zone is treeline to about 7500 feet

Alpine zone vegetation is unforested

above alpine zone is rock and ice

deep snowpack limits vegetation cover in alpine zone

short stature plants dominate, including heather

lupine

many wildflowers

Trees survive only under snowpack as
Krummholz (“crooked wood”)

Abies lasiocarpa (subalpine fir) zone

Abies lasiocarpa (subalpine fir) zone

Abies lasiocarpa (subalpine fir) zone

•Elevation 4200 feet to treeline

•Coldest and moistest of eastern Washinton

•Deep snow packs up to six months

•Temperatures more extreme and moistures less than T. mertensiana zone

parklands of meadows and tree clumps

subalpine fir

Engelmann spruce

white bark pine

subalpine larch

Pseudotsuga menziesii (Douglas-fir) and
Abies grandis (grand fir) zones

Pseudotsuga menziesii (Douglas-fir) and
Abies grandis (grand fir) zones

•Elevation 2000-4500 feet

•Precipitation average 25-30 inches

•Cooler temperatures than lower Pinus ponderosa zone

 

Douglas-fir is smaller and slower-growing in interior

Douglas-fir seedling can grow in less-shady understory

other trees include ponderosa pine

lodgepole pine

western larch

Understory plants include grasses

Pinus ponderosa (ponderosa pine) zone

Pinus ponderosa (ponderosa pine) zone

Pinus ponderosa (ponderosa pine) zone

•Elevation 1800 to 4000 feet

•Short growing season

•Precipitation 15 – 24 inches

•Wide temperature fluctuations

dry conditions result in open forest stands

lodgepole pine found here on both dry sites…

and wet sites

trembling aspen

Shrub – steppe zone

Shrub – steppe zone

Shrub – steppe zone

•Precipitation average 7-10 inches

•Summers hot

•Winters freezing November to March

bunchgrass and sagebrush dominate

sagebrush

trees found only along streams

juniper found on rocky slopes

heavy irrigation makes farming possible

Bunchgrass – steppe zone

Bunchgrass – steppe zone

•Elevation 1500-2400 feet

•Precipitation average 10-15 inches

•Summers hot

•Winters mostly freezing

sagebrush and other shrubs absent

bunchgrasses dominate

wheat farming productive with irrigation

scablands near Cheney

lodgepole pine, aspen

wet areas resulting from post-glacial flooding

Washington vegetation zones in review

 

Credits

Produced by David C Martin

Revised by Lisa J Carlson

 

Climate maps from PRISM, Oregon State University

Digital Elevation Model, USGS

Ecoregion Map, WA DNR

Vegetation Zones, Washington Gap Analysis Project