The terrestrial ecosystems of California's islands have long been described as depauperate, with island peoples relying more heavily on marine resources and trading for plant resources with mainland neighbors. Island plant communities were decimated by more than a century of overgrazing, however, with heavy soil erosion and the introduction of non-native weeds. Since the removal of livestock, island plant communities are recovering dramatically, showing an unparalleled richness in plant taxa. Macrobotanical remains from island archaeological sites provide valuable data about plant use for the past 10,000 years, showing that island geophytes and grassland/forb fields were much more abundant and productive than previously thought. Island plants provided ample food, medicine, fuel, and raw materials for island peoples. This research has implications for understanding the archaeology and historical ecology of other islands or archipelagos where humans have heavily altered island ecosystems.