Shrub–steppe

Shrub-steppe is a type of low-rainfall natural grassland. While arid, shrub-steppes have sufficient moisture to support a cover of perennial grasses or shrubs, a feature which distinguishes them from deserts.

The primary ecological processes historically at work in shrub-steppe ecosystems are drought and fire. Shrub-steppe plant species have developed particular adaptations to low annual precipitation and summer drought conditions. Plant adaptations to different soil moisture regimes influence their distribution. A frequent fire regime in the shrub-steppe similarly adds to the patchwork pattern of shrub and grass that characterizes shrub-steppe ecosystems.

North America

The shrub-steppes of North America occur in the western United States and western Canada, in the rain shadow between the Cascades and Sierra Nevada on the west and the Rocky Mountains on the east. They extend from south-central British Columbia down into south central and south-eastern Washington, eastern Oregon, and eastern California, and across through Idaho, Nevada, and Utah into western Wyoming and Colorado, and down into northern and central New Mexico and northern Arizona. Growth is dominated primarily by low-lying shrubs, such as big sagebrush (Artemisia tridentata) and bitterbrush (Purshia tridentata), with too little rainfall to support the growth of forests, though some trees do occur. Other important plants are bunchgrasses such as Pseudoroegneria spicata, which have historically provided forage for livestock as well as wildlife, but are quickly being replaced by nonnative annual species like cheatgrass (Bromus tectorum), tumble mustard (Sisymbrium altissimum), and Russian thistle (Salsola kali).