Extreme climate and variation in tree growth: individualistic response in subalpine fir (Abies lasiocarpa)

Dendroecological techniques were used to describe the variation in growth response of subalpine fir (Abies lasiocarpa)to climate across a range of elevations (1350–1850 m) and annual precipitation (125–350 cm y^?1) in the Olympic Mountains, Washington. Correlation analysis is used to describe individual growth-climate relationships. Growth response is quantified in years with unusually warmer, colder, wetter, and drier climates during the period 1895–1990. Combinations of climatic variables that result in unusually fast or slow growth years are also described. Differences in growth-climate relationships among sites, and among individuals from the same site, emphasize within-species variability in response to climate. Growth was not significantly faster or slower on the majority of sites for extreme climate years examined. Few climate variables are correlated with growth of the majority of individuals on most sites, suggesting that some individuals are relatively unresponsive to climate. Individual growth-climate correlations also indicate an increase in the percentage of individuals whose growth is significantly correlated with a climate variable, as the value of the mean site growth correlation increases for that climate variable. Individual differences in growth-climate relationships probably result from microsite variation (soil depth, soil moisture, wind, insolation) and from individual genetic differences. Descriptions of tree species response to climate change need to incorporate both individual and site variation in growth response to climate in order to accurately represent existing environmental heterogeneity.