U.S. Joint Fire Science Program



Date of this Version


Document Type



Fire Science Brief, Issue 27, December 2008


US government work.


Sagebrush steppe has been rapidly changing into woodlands of western juniper and pinyon pine since Euroamerican settlement of the West in the middle of the nineteenth century. The change from the dry scattered shrub and grasslands to woodlands has changed more than plants—it has also changed the fi re regime. Studies have revealed a threshold at which understory plants may not rebound after a disturbance—when trees have reached 40- to 50-percent cover. Disturbance—by fi re and overgrazing—also makes resources such as nutrients and soil water available for weeds to exploit, allowing invasives such as cheatgrass to establish and expand into sagebrush lands. The presence of native, perennial herbaceous plants help a landscape resist weed invasion, and measures to prevent initial establishment by weeds such as cheatgrass may be as, or more effective than reducing or eliminating established populations.