Early Days: Documenting Historical Plant Cover on Santa Rosa Island, California

Santa Rosa Island is one of the Channel Islands off the coast of Southern California. Prior to joining Channel Islands National Park in 1986, Santa Rosa Island was a private ranch. The ranchers brought cattle, sheep, and other domesticated animals to the island in the mid-1800s. Intense agricultural operations had significant effects on the native plant cover. These nineteenth-century land cover changes occurred before documentation with aerial photographs or satellite images. This study relies on nineteenth-century documents, including a published letter, botanical floras, maps and notes from the U.S. Coast Survey, and magazine articles, to characterize the island's native plant cover and widespread disruptions during the five decades immediately after the establishment of the ranch. Based on the mid-nineteenth-century documents, (1) native shrubs were present on hillslopes, (2) non-native annual grasses were widespread, and (3) large patches of cacti existed. Thus, introduced grazing notably altered the plant cover by the late 1800s. Researchers and land managers can use these baseline results to inform more-extensive, twentieth-century land cover studies and the current restoration efforts of Channel Islands National Park.