CLIMATE RESPONSE FUNCTIONS FOR BIGCONE SPRUCE: A MEDITERRANEAN CLIMATE CONIFER

Bigcone spruce is a conifer endemic to southern California. Two new tree-ring chronologies were developed utilizing individuals of this species growing at two sites in the San Rafael mountains of Santa Barbara County. Climate growth response functions were determined for these chronologies and for an existing bigcone spruce chronology from the San Bernardino mountains farther east. Bigcone spruce is particularly well suited for dendrochronological analysis given its longevity (800 years) and the strong relationship between growth and precipitation. Growth in the current year depends strongly on growth in the previous two years (22-46% of total chronology variance). After removing the effects of prior growth, response functions based on precipitation alone account for 43-51% of chronology variance, while those based on precipitation and temperature explain 52-76% of total variance. Response functions indicate a strong positive relationship between growth and winter and spring precipitation, and a negative relationship with early spring and early summer temperatures. The response functions for big-cone spruce are distinctive from those published for other western conifers, and are consistent with the unique characteristics of the mediterranean climatic regime.