The Past: California's Ancient Oak Woodlands as Revealed Through Blue Oak Tree Ring Analyses

David Stahle, Department of Geosciences, University of Arkansas

In a state famous for exceptional trees, the blue oaks of California may be among the most remarkable.  Old blue oak trees are still widespread across the foothills of the Coast Ranges, Cascades, and Sierra Nevada. The most extensive areas of intact old-growth blue oak woodland appear to survive on rugged and remote terrain in the southern Coast Ranges and on the foothills west Mt. Lassen. Our sampling suggests that most mature blue oak recruited to the canopy in the middle to late nineteenth century. The oldest living blue oak tree sampled was over 459 years old, and several dead blue oak logs had over 500 annual rings. Precipitation sensitive ring-width chronologies up to 700 years long have been developed from ancient blue oak trees and remnant wood. These blue oak chronologies are strongly correlated with cool season precipitation totals, streamflow in the major rivers of California, and the estuarine water quality of San Francisco Bay. Over 40 blue oak chronologies are now available and can be used in conjunction with conifer chronologies to develop seasonally specific tree-ring reconstructions of precipitation that will help to better understand and manage water resources in California. The accurate environmental history of precipitation, fire, and forest dynamics embedded in blue oak tree rings help justify the conservation of these authentic old-growth native woodlands.