Shrub-steppe Plant Adaptations

 

Compared to mobile animals, plants can’t walk away when the weather gets severe and water is scarce.  Plants employ several strategies that allow them to cope with water shortage and to thrive in an arid environment.  Most shrub-steppe wildflowers are long-lived perennials with whose above ground stems and leaves die back, but underground roots remain alive.  Our earliest blooming perennial wildflowers, like yellow bells, bluebells, and shooting star all concentrate their rapid above-ground growth of leaves, stems, flowers, and seeds into a few balmy mild weeks and then quickly wither and die.  Above ground life exists for less than two-months and then roots rest buried in soil until the next spring.

yellow bells

The ability to conserve water and to minimize water loss through evaporation is a key adaptation of most shrub-steppe plants.   Thick gray-green sagebrush leaves are covered in dense short hairs that both deflect sunlight and create a still air layer that slows evaporation, minimizing water loss from the leaf into the air.  During the spring, sagebrush grow a second set of larger, strap-like thin leaves that boost photosynthesis for the shrub during spring, only to be shed once the summer’s searing heat returns.  Arrow-leaf balsamroot leaves have a waxy coating that feels leathery, forming a true physical barrier that seals water inside the plant tissues.

sagebrush

Some of our native plants require a viewer to get down on hands-and-knees for close-up inspections.  Healthy shrub-steppe soils are carpeted with a layer of living cryptobiotic crust:  an interwoven population of mosses, lichens, simple plants, fungi and bacteria that form a multi-layered coating on the land.

cryptobiotic crust

These simple organisms can quickly revert to dormancy when water is scarce.  Try pouring a bit of water onto a patch of shrub-steppe soil and watch for a few moments to see crust suddenly green up as its living members start using sunlight to make food once water is available!  This crust provides essential ecosystem services to other plants by trapping moisture in the soil, transferring nutrients, and holding soil in place.  The crust is easily damaged due to intensive animal and people traffic.  It is very slow-growing, so you can spot lands that have been disturbed by the lack of a crust covered the mineral soils.  By staying on established trails, hikers can help preserve the fragile living crust.

The diversity of wildflowers in central Washington means travelers can find blooming plants from earliest spring into late fall.  Start now by getting out the see the amazing display of color in four types of shrub-steppe eco-regions:

Deep soil Shrub-steppe

This is the most common habitat central Washington.  It includes area where scattered shrubs form a canopy above a ground cover of bunch grasses and wildflowers.  The soil is relatively deep as the main shrub, big sagebrush (Artemesia tridentata), requires a soil depth of at least 1 foot.

bunch grasses and wildflowers

Lithosol Shrub-steppe

Lithosol literally means “rock soil” and is characterized by a very thin layer of soil on top of bedrock, usually basalt in our region. Often, this habitat is found in the scablands, where episodes of the Missoula Floods swept away all topsoil.  Shrubs grow low to ground and often form a low mat.  Scattered bunch grasses and wildflowers provide sparse groundcover.  A common shrub is rigid sagebrush (Artemisia rigida).

rigid sagebrush

Talus- unstable slopes of rock outcrop

The slopes of many hills, coulees, and canyons of central Washington are edged by rocky outcrops and covered with an apron of rock fall, containing all sizes of boulders, typically basalt.  These slopes are unstable.  A combination of shrubs like current (Ribes sp.), serviceberry (Amelanchier alnifolia), and mock orange (Philadelphus lewisii) skirt the slopes.

basalt boulders

Riparian Shrub-steppe

The term riparian describes the tree-and-shrub-dominated plant community that grows adjacent to flowing rivers, creeks, lakes, or ponds. The adjoining ground water table is supplied with water, increasing the water available to plants from precipitation, especially during summer drought.  In the arid West, riparian systems occupy a small percentage of the landscape, yet their presence is vital to most animals living in the adjacent arid lands.  A large number and variety of different plants thrive in riparian areas.  These plants do not have to cope with water shortage and don’t need to put energy into water-saving mechanisms. Trees like cottonwood (Populus trichocarpa), water birch (Betula occidentalis), and aspen (Populus tremuloides), and shrubs like willows (Salix. sp.) form a multi-storied canopy, shading both the water and the banks.

cottonwood, native birch

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