Fire and vegetation history on Santa Rosa Island, Channel Islands, and long-term environmental change in southern California

The long-term history of vegetation and fire was investigated at two locations - Soledad Pond (275-m; from ca. 12 000-cal. a BP) and Abalone Rocks Marsh (0-m; from ca. 7000-cal. a BP) - on Santa Rosa Island, situated off the coast of southern California. A coastal conifer forest covered highlands of Santa Rosa during the last glacial, but by ca. 11 800-cal. a BP Pinus stands, coastal sage scrub and grassland replaced the forest as the climate warmed. The early Holocene became increasingly drier, particularly after ca. 9150-cal. a BP, as the pond dried frequently, and coastal sage scrub covered the nearby hillslopes. By ca. 6900-cal. a BP grasslands recovered at both sites. Pollen of wetland plants became prominent at Soledad Pond after ca. 4500-cal. a BP, and at Abalone Rocks Marsh after ca. 3465-cal. a BP. Diatoms suggest freshening of the Abalone Rocks Marsh somewhat later, probably by additional runoff from the highlands. Introduction of non-native species by ranchers occurred subsequent to AD 1850. Charcoal influx is high early in the record, but declines during the early Holocene when minimal biomass suggests extended drought. A general increase occurs after ca. 7000-cal. a BP, and especially after ca. 4500-cal. a BP. The Holocene pattern closely resembles population levels constructed from the archaeological record, and suggests a potential influence by humans on the fire regime of the islands, particularly during the late Holocene.