Native plant regeneration and introduction of non-natives following post-fire rehabilitation with straw mulch and barley seeding

Abstract

To reduce soil erosion after fires, forest managers commonly employ rehabilitation treatments, including application of grass seed or mulching with straw. In 1999 the Megram fire burned 24,000 ha of mixed conifer/tanoak forest in northern California, USA. In the subsequent year, some areas were aerially seeded with barley and others were mulched with rice straw; some areas received both treatments. We investigated how these treatments affected these aspects of ecological recovery: (a) the introduction of non-native plants, (b) percent vegetative cover, (c) the diversity and density of regenerating native plants, and (d) the density and frequency of conifer seedlings. We found that mulched quadrats had a significantly higher occurrence of non-native species than untreated quadrats did. In addition, we found little evidence that mulching or mulching+seeding facilitated recovery of the native plant community. Percent vegetative cover was no higher in treated quadrats than in untreated quadrats. While annuals were present in significantly higher densities in the mulched+seeded quadrats compared to the other treatments, perennial density and overall plant density were not affected by treatment. Mulching and mulching+seeding significantly reduced the density and frequency of conifer seedlings. While we found similar native species richness on a per-quadrat basis for all three treatments, the cumulative number of native species in untreated quadrats taken as a whole exceeded the numbers found in mulched-only and mulched+seeded quadrats. We recommend that managers take steps to assure that mulch is free of non-native seed, and that further efforts be made to investigate systematically aspects of ecological recovery after the application of rehabilitation treatments.