Prescribed Fire Effects on Population Dynamics of an Annual Grassland

Medusahead (Elymus caput-medusae [L.] Nevski) is a highly damaging invasive annual grass in California rangelands. While it has been shown that prescribed fire can be a successful tool in controlling medusahead populations, fire treatments are not always successful. Given the sociological and economic constraints of prescribed fire use, it is critically important that we maximize likelihood of treatment success. We conducted experimental investigation of population dynamics of competing species from different functional groups: invasive annual medusahead, naturalized but forageable nonnative wild oat (Avena spp. Pott ex Link), and native perennial purple needlegrass (Stipa pulchra [Hitchc.] Barkworth). We observed population dynamics at the 1-m2 scale before and after treatments of prescribed fire and seed-limitation (weed whipping in a 1-m buffer area). We asked 1) what is the role of seed dispersal from burn edges on subsequent medusahead population size? and 2) how do density and fecundity of the dominant species respond to fire? Results showed that 1) seed dispersal is an important factor in recovery dynamics and 2) wild oat fecundity significantly increases in the year after fire while medusahead and needlegrass fecundity seem minimally affected. Ultimately, managers should consider fire as a preferable first-entry tool and should thoroughly consider shape and size of planned burns, as well as what vegetation is present to play a role in post-treatment seed-dispersal dynamics.