Effects of post-fire grass seeding on native vegetation in southern California chaparral

Abstract

For decades, managers have seeded burned slopes with annual grass in an attempt to increase postfire plant cover and reduce the accelerated hillslope erosion, runoff, and debris flows that typically occur during the first winter after fire. In California, annual ryegrass (Lolium multiflorum) was commonly used for this purpose. Critics argue that ryegrass and other seeded grasses suppress native plant regeneration and increase the risk of early reburn. Similar to other researchers, we found that cover of native herbaceous plants was reduced on seeded sites compared to unseeded areas in the first or second year after fire. Density of shrub seedlings was not significantly different between seeded and unseeded plots in our study, but others have found shrub and tree see lings less abundant on seeded sites. In our southern California sites, seeded ryegrass seldom significantly increased plant cover the first growing season after fire, when hillslope erosion was highest. Ryegrass tended to produc greater cover in subsequent postfire years, when native vegetation cover was higher as well. The long-to impact on herbaceous species of suppression by seeded grasses requires further investigation.

Citation

Beyers, Jan L.; Wakeman, Carla D.; Wohlgemuth, Peter M.; Conard, Susan G. 1998. Effects of post-fire grass seeding on native vegetation in southern California chaparral. In: Proceedings, Nineteenth Annual Forest Vegetation Management Conference: Wildfire Rehabilitation. Forest Vegetation Management Conference, Redding, CA. pp. 52-64.