Paper No. 7
Presentation Time: 2:30 PM
VEGETATION AND BIOLOGICAL SOIL CRUST SUCCESSION ON THE SAND DUNES OF SAN MIGUEL ISLAND, CHANNEL ISLANDS NATIONAL PARK, CALIFORNIA
San Miguel is the westernmost of the California Channel Islands, and one of the windiest areas on the west coast of North America. The majority of the island is covered by coastal sand dunes, which were stripped of vegetation, and subsequently mobilized, due to droughts and sheep ranching during the late 19th century through the early 20th century. Since the removal of grazing animals, vegetation and biological soil crusts have once again stabilized many of the island’s dunes. This project utilizes both old and new remote sensing technology, a geographic information system (GIS), and a modified point-intercept transect vegetation survey design to decipher the pattern of vegetation and biological soil crust succession on the sand dunes of San Miguel Island. Historic aerial photographs dating back to 1929 were georeferenced in a GIS, and active dune extents were digitized for each year that imagery was available. During field work, current vegetation and biological soil crust communities were identified and mapped along thirty 200-meter transect vegetation surveys that were distributed throughout San Miguel’s central dune field. These data were then overlaid in a GIS and analyzed for spatial and temporal patterns. The end product is a series of maps and graphs that illustrate the pattern of vegetation and biological soil crust succession that occurs on the San Miguel Island dunes. The results of this study show that highly-specialized native vascular vegetation are the pioneer stabilizers of the dunes. This pioneer community is replaced in later stages of vegetation succession by communities that are dominated by native shrubs. Many of the dunes that have been stabilized the longest are dominated by exotic species. This trend may indicate that exotic plants out-complete the native vegetation during the latest stages of succession. Stands of biological soil crusts are found only on dunes where vascular vegetation is already present. Biological soil crusts are not found on dunes exhibiting later stages of vegetation succession, which may indicate that their role in dune stabilization on the island is transitory.