Monitoring Understory Composition of Blue Oak Woodlands on Conservation Easements

Conservation easements are an increasingly popular strategy for conserving biological diversity on private land. Long-term vegetation monitoring on conservation easements can provide critical information on persistence of biological diversity and abundance of invasive species. We sampled understory plant composition on five of The Nature Conservancy’s conservation easements in the Mt. Lassen foothills of Northern California. We established 73 plots of 10-meter radius, measured species composition with the point-intercept method, and compiled a full species list for each plot in 2005 and 2006. We found significant differences in the relative cover of native and non-native annual grasses and annual forbs among easement properties. Relative cover of native plants was significantly higher in herbaceous plots (50 percent) than in plots with blue oak (Quercus douglasii) canopy (21 percent). We found medusahead (Taeniatherum caput-medusae) in 64 percent of plots and yellow star thistle (Centaurea solstitialis) in 9 percent of plots. Overlap of species composition between years was correlated with difference in date sampled each year but not correlated with confidence in plot relocation. Our analysis of community diversity and relative abundance provides a baseline for future change. Finally, we make recommendations for the design of future monitoring efforts on conservation easements.