Rice straw mulch for post-fire erosion control: assessing non-target effects on vegetation communities

Straw mulch is commonly used for post-fire erosion control in severely burned areas but this practice can introduce non-native species, even when certified weed-free straw is used. Rice straw has recently been promoted as an alternative to wheat under the hypothesis that non-native species that are able to grow in a rice field are unlikely to establish in dry forested habitats. We investigated this hypothesis in the severely burned areas of the 2013 Rim Fire in the Sierra Nevada that were treated with rice straw post-fire. In 2014, we installed 134 plots in mulched and control areas with >95% tree mortality and re-measured a subsample in 2015. Mulched areas had significantly higher non-native forb cover, non-native graminoid cover and non-native species richness. In addition, 25 non-native species occurred exclusively in mulched areas; collectively, these responses contributed to more homogenous plant communities in mulched areas than in unmulched areas in 2015. In contrast, mulch had no effect on total plant cover, and conifer regeneration densities were generally unaffected with the exception of a slight positive effect on Douglas-fir. We recommend more stringent testing for weed-free certification and that funding for non-native species eradication be included with post-fire rehabilitation plans.