Wildfire , Ryegrass Seeding , and Watershed Rehabilitation

Aerial seeding of Italian annual ryegrass (Lolium multiflorum) is a common, but controversial, emergency rehabilitation practice following wildfire in California. Replicated study plots, with and without ryegrass, established after a summertime chaparral wildfire on California's central coast revealed the following: 1. Ryegrass-seeded plots developed significantly greater total plant cover than unseeded plots in the first year. 2. Regeneration and growth of native species were significantly depressed in the presence of ryegrass. 3. Soil erosion was significantly greater on ryegrass-seeded plots than on unseeded plots. 4. Pocket gopher activity was greater on ryegrass-seeded plots than on unseeded plots. These results suggest that ryegrass seeding for emergency rehabilitation of burned areas can be ineffective, and even counterproductive, in certain cases. THE WILDFIRE-GRASS SEEDING CONTROVERSY The 1985 Las Pilitas fire burned 30,000 ha of predominantly chaparral watershed in California's central coastal region (fig. 1). Although fires such as the Las Pilitas are part of the natural order in chaparral, they can cause considerable watershed degradation, and predispose the land to greatly increased water runoff and soil erosion. The ensuing runoff water and erosional sediments may inflict further damage to property lower in the watershed. In an effort to minimize post-fire damage and speed watershed recovery, land management and resource service agencies in California commonly seed severely burned brushlands with one or more plant species that exhibit early germination and rapid growth. Following commonly accepted practice, nearly two-thirds of the Las Pilitas burn was aerially seeded with either Italian annual ryegrass (Lolium multiflorum) or soft chess (Bromus mollis, also known commonly as Blando brome) (Calif. Dept. of For. 1985). Presented at the Symposium on Fire and Watershed Management, October 26-28, 1988, Sacramento, Calif. Professor of Soil Science, and graduate students, respectively, California Polytechnic State University, San Luis Obispo, Calif. USDA Forest Service Gen. Tech. Rep. PSW-109. 1989 Figure 1--Study area location. Since the 1940's, annual rye has been the most common grass seeded on burned chaparral lands of southern California. Its popularity in post-fire emergency rehabilitation work is due to its reliable germination, rapid early growth, short life span, effective ground cover and rooting characteristics, and broad site adaptability in mediterranean climates; moreover, the seed is inexpensive and readily available (Young and others 1975). Although seeding, especially with annual ryegrass, is a common post-fire rehabilitation practice, it is nonetheless highly controversial (Barro and Conard 1987, Gautier 1983). Proponents of ryegrass seeding contend the following: The extreme surface runoff of rainwater from a denuded watershed erodes soil and threatens life and property by flooding and landsliding; therefore, plant cover must be quickly reestablished to mollify destructive forces. Although native species usually begin recolonization soon after a fire, their rate of recovery may be too slow to adequately protect the watershed during the first several years; therefore, artificial seeding is necessary. Some proponents contend that seeded ryegrass is most effective during the first year after the fire, when erosion is greatest. Others argue that ryegrass is nearly ineffective in the first winter, but it becomes increasingly effective in the succeeding two years. Nonetheless, most proponents agree that although ryegrass may interfere with native