Abstract

California's central coast contains high species richness and plant endemism that is threatened by ongoing land use and climate change. Better understanding of regional vegetation dynamics is needed, where its vegetation mosaic and stand succession interact with a strong Mediterranean climate, wildfire, and grazing. We examined what historical data could reveal about these interactions by using two lines of evidence—historical aerial photographs from 1938 and vegetation maps surveyed in the 1930s—and comparing them to other photographs and maps up to 2015. We used the recently established Jack and Laura Dangermond Preserve as the study area. The Preserve, stretching from the coast near Point Conception to the Santa Ynez Mountains, encompasses chaparral, grassland, oak woodlands, coastal scrub and closed-cone pine vegetation types. We asked what long-term vegetation change has occurred, and if we could detect the influences of wildfire frequency and grazing pressure. Across the 80-year time period, we found that grassland cover decreased by 26%, while shrubland and oak woodland cover increased by 31% and 16%, respectively. Our results were consistent across both historic datasets, lending confidence to the trends observed over time. These trends are consistent with other similar analyses along coastal California, supporting the long-held hypothesis that coastal grassland communities, and their unique biodiversity values, are lost as grazing and fire decrease. Our results motivate future work on the restoration of native grassland species and point to the possibility of using designed spatial patterns of coastal California vegetation mosaics to preserve long term habitat dynamics for the region's native plant communities in this biodiversity hotspot.