Background: California is a global biodiversity hotspot, yet increased urbanization of wildlands, warming temperatures, and invasion of nonnative species pose serious risks to these areas due to an increase in wildfire frequency. Fuel management is a tool for reducing fire risk to neighboring communities and natural resources that involves a two-step process requiring an initial reduction of woody vegetation followed by a repeated control of woody plants and reduction of herbaceous cover. To understand the compositional and structural changes resulting from fuel treatment methods in southern California chaparral, we evaluated the compositional and structural impacts of a recently created fuel break established around the Lake Morena community on the Cleveland National Forest. The area was initially treated with cut and pile burning, then treated with herbicide, and lastly grazed by 1,200 goats. The purpose of this study is to (1) evaluate the compositional and structural differences associated with the initial fuel break, and (2) quantify compositional shifts in herbaceous and woody vegetation caused by goat grazing over time.
Results: Plots on fuel breaks and in adjacent wildlands exhibited significantly different species assemblages. Total herbaceous cover (both native and nonnative) was 92 times greater on fuel breaks than in adjacent chaparral-dominated wildlands and native shrub cover was 55.3 times greater in adjacent wildlands than on fuel breaks. Goats had a significant impact on reducing native and nonnative herb cover (87% reduction in cover, 92% reduction in height), but were ineffective at reducing the cover and height of most woody species such as Adenostoma fasciculatum, Eriogonum fasciculatum, Quercus berberidifolia, and Artemisia tridentata. However, goats were found to be effective in controlling nonnative grasses including Bromus diandrus and Bromus madritensis.
Conclusion: Initial fuel break creation was effective at reducing wood biomass and height, simultaneously giving rise to an abundance and diversity of native and nonnative herbaceous species. Although targeted goat grazing was successful at reducing herbaceous biomass, it was ineffective at reducing woody biomass which is often one of the most important goals for fuel management in chaparral ecosystems.