Initial changes in forest structure and understory plant communities following fuel reduction activities in a Sierra Nevada mixed conifer forest

The widespread attention that has been devoted to wildfires by the public, as well as by state and federal governments, over the last several years in the United States has created a demand for fuel reduction activities aimed at alleviating wildfire hazard. While the appropriateness of these fuel reduction activities has been discussed in detail in previous studies, only a few studies have experimentally examined the effects of fuel reduction on forests. This paper investigates the initial effects of three different fuel reduction strategies on forest structure and understory plant communities using replicated treatments, which are compared to untreated controls. Understory plants are grouped by plant growth form (shrub, forb, graminoid) and by plant origin (native, exotic). The effects of each treatment alternative: mechanical, prescribed fire, mechanical followed by prescribed fire, and untreated control, are reported for each plant group. Each fuel treatment modified forest structure such that growing space increased and allowed for rapid reestablishment of forbs and graminoids, which did not differ in abundance from pre-treatment levels. The mechanical only treatments (thinning from below and rotary mastication) significantly reduced shrub cover relative to the control, however mechanical plus fire and fire only treatments did not. Mechanical plus fire treatments altered forest structure most substantially, which may explain the observed increases in richness and cover of exotic species. However, the magnitude of these differences was small. Both treatments involving fire decreased native species richness significantly, but differences in native species cover were insignificant for any of the active treatments. These results demonstrate a relatively high degree of resilience in these Sierra Nevada mixed conifer understory communities, at least initially, to fuel reduction activities. (c) 2006 Elsevier B.V. All rights reserved.