Population Genetic Structure of California Hazelnut, An Important Food Source for People in Quiroste Valley in the Late Holocene

California hazelnuts (Corylus cornuta var. californica) are abundant in the archaeological record of site CA-SMA-113 in Quiroste Valley Cultural Pre- serve, and hazel management on the Central Coast was recorded in late 18th century Spanish accounts. However, this species is currently absent from Quiroste Valley proper and rare in the watershed, though it is locally common elsewhere in the Santa Cruz Mountains. Because high California hazelnut abundance is associated with frequent fire regimes, we believe that its current low abundance could be due to fire suppression enforced in the region for the past two hundred years. We sequenced nuclear microsatellites from ten popu- lations of California hazelnuts to test the hypothesis that this species has experienced demographic changes in response to changing climate and land management practices. We found that all populations exhibited high levels of genetic variation and negative population growth consistent with large popu- lation sizes in the past with some decline over time. We also found subtle pat- terns of geographic structure suggesting that Quiroste Valley and neighboring Butano may have been important refugia habitats during past climate warming events. These results provide an important foundation demonstrating that