Since the mid-1800's, the native shrub communities on Santa Rosa Island, California, have been subjected to grazing and browsing by non-native ungulates in support of cattle and big-game ranching. This has resulted in extensive type-conversion of the once dominante chaparral and coastal sage scrub (CSS) shrublands to non-native annual grasslands. In 1998, the cattle were removed from the island and the Roosevelt elk and mule deer herds reduced, relieving the vegetation from intensive grazing, allowing for potential recovery. To characterize recovery trends, we resampled 3 chaparral and 3 CSS sites established in 1997 as part of a multi-island grazing study. Along 3, 30-m transects distributed parallel to the gradient from shrubland to adjacent grassland at each site, we recorded species and substrate cover. We randomly placed quadrats along each transect and recorded shrub cover and density, litter depth, and soil compaction. Within each quadrat, we also recorded height and number of stems of a randomly selected shrub. We collected ungulate use data, counting scat piles, noting evidence of browse, and characterizing trail usage in a 30m x 30m area centered on each transect. Data were analyzed using linear models and analysis of variance tests.
Results/Conclusions
Overall, native shrub cover has increased in both the chaparral and CSS, while non-native annual grass cover has declined. While cover has increased, the density of native shrubs has remained the same in chaparral and decreased in CSS. The number of stems per individual has remained the same in the CSS. Heights of the shrub dominants in both communities significantly increased except in the chaparral shrub transects where height remained the same. These trends indicate that the increase in shrub cover is likely due to increased size of existing individuals and not increased recruitment. All transects, again except the chaparral shrub transects, significantly decreased in ungulate usage as measured by piles of scat. While there are signs of initial recovery overall in both communities, the correlation between unchanged height and undiminished ungulate use in the chaparral shrub transects suggest that ungulate use is continuing to have effects on the chaparral.
