Climate change is likely to alter the growth rate, range, and abundance of dominant boreal forest tree species. Changes in tree growth may alter ecosystem carbon cycling, and thus feedback on the climate system; understanding the likely direction and magnitude of future changes in tree growth is thus an important goal. There is now good evidence, largely from tree-ring studies of tree growth, that the growth of boreal forest trees to climate exhibits complex patterns of variation among individuals, among species, among regions, and over time. We cored trees at sites along the Lena River in Siberia in order to better document patterns of climate response among species and across latitudinal gradients in the Siberian taiga. At the southern end of our transect, near the city of Yakutsk, we cored Pinus sylvestris and Larix cajanderi. In the middle and northern sites of our transect, we cored Larix cajanderi and Picea obovata. Tree cores were measured, and we used standard dendrochronological procedures to quantify the response of individual trees to climate variation.
Results/Conclusions
There were significant differences in long-term growth among species, and these likely reflect the combined influence of climate and disturbance, perhaps by defoliating insects. Correlations between the growth of larch and spruce varied on decadal time scales: periods of high correlation were interspersed, at approximately 60 year intervals, by periods of low correlation. In recent decades, the growth rate of spruce has exceeded that of larch at some sites. If this trend continues, it may result in shifts in the composition of the Siberian taiga. Climate response varied as much among individuals within a species as it did among species. For all species, the majority of trees within each population responded positively to warming. However, a minority of trees (25-40%) within each population responded negatively to warming. The growth of positive responders was highly correlated with early summer temperatures, while the growth of negative responders was highly correlated with late summer temperatures. We were not able to consistently differentiate between positive and negative responders based on size, age or growth rate, and hypothesize that within-population variation in climate response may be a result of fine-scale variation in site conditions. Our results indicate that patterns of climate response are complex, and vary on both fine and broad spatial scales.
