NATIVE BUNCHGRASS RESPONSE TO PRESCRIBED FIRE IN UNGRAZED MOUNTAIN BIG SAGEBRUSH ECOSYSTEMS

Fire was historically a dominant ecological process throughout mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana [Rydb.] Beetle) ecosystems of western North America, and the native biota have developed many adaptations to persist in a regime typified by frequent fires. Following spring and fall prescribed fires conducted in sites of different ecological conditions at the Lava Beds National Monument, California, USA, we examined the reproductive, density, and cover responses of four native bunchgrasses: bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love), Thurber's needlegrass (Achnatherum thurberianum [Piper] Barkworth), squirreltail (Elymus elymoides [Raf.] Swezey), and Sandberg bluegrass (Poa secunda J. Presl). High rates of survival and fire-enhanced flowering were measured following fires. Thurber's needlegrass density decreased following spring burns in sites dominated by cheatgrass (Bromus tectorum L.) (from 3.3 plants m(-2) to 0.8 plants m(-2); P < 0.05). Density of bluebunch wheatgrass decreased following spring fires (from 3.7 plants m(-2) to 1.9 plants m(-2); P = 0.02) and cover was reduced in both spring and fall burn treatments (P = 0.04) in native dominated sites. Fire-enhanced flowering (increases in reproductive efforts) occurred in bluebunch wheatgrass in cheatgrass dominated sites (244% increase in reproductive culms following fire), native dominated sites (350% increase), and woody encroachment sites (500% increase) sites following fall fires. These results show that these native bunchgrasses positively respond to prescribed fire through increases in reproductive efforts and high rates of survival following fires. This suggests that fire can be an important tool for the restoration and conservation of these fire adapted bunchgrasses.