Growth Trends of Whitebark Pine and Lodgepole Pine in a Subalpine Sierra Nevada Forest, California, U.S.A.

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Abstract
Growth trends of whitebark pine and lodegpole pine in a subalpine forest of the sierra Nevada were studied with dendroecological methods. Principal components analyses show a dominant trend of increasing basal area increment over time in all age classes of both species. Although this pattern is normal for young trees, it is unusual for old conifers. Climatic variables account for a relatively small portion of the variance in short-term tree growth, and there is no clear relationship with long-term growth. Growth trends in this study resemble those of bristlecone pine at other high elevation sites in California but differ from those of conifers at lower elevations in the Sierra Nevada. Possible causes for the striking growth increase are stand dynamics effects, climatic factors not evaluated in this study, or increased atmospheric CO2 concentrations. Minor trends in the basal area time series were probably caused by insect attack, avalanches, or other transient disturbances.