Climatic fluctuation causes synchronous tree-ring variations along the elevation gradient in Wolong Natural Reserve, western Sichuan of China

Background/Question/Methods

Improved understanding of elevational growth response to climate may provide ground-truth information on modeling and predicting variation in the response of forests to future climate change. Here we explore tree-growth response to climate as a function of elevation in Wolong Natural Reserve (western Sichuan Province, China). This study presented here will therefore be used to assess forest growth related to future climatic change and benefit the successful management strategies for local coniferous forests. Dendroclimatological techniques were used to process about 400 increment cores of fir trees collected from two parallel elevation gradients (from interior forest site at 3000 m to treeline site at 3450 m). A network of ten tree-ring width chronologies was constructed from the elevation gradients. The common variation of the stand chronologies was determined by inter-site correlations and principal component analysis. Two different and independent techniques were applied to evaluate growth-climate relationships: correlation statistic and spatial regression analysis.  

Results/Conclusions

The ten fir chronologies display significant inter-site correlations (mean R=0.647, p<0.001) and the first principal component (PC1) can account for 68.32% of the total variation of the chronologies. This describes the high degree of similarity of growth variation contained in the elevation gradients. Correlation analysis using monthly climate data indicates that the radial growth of fir trees along the elevation gradient is markedly similar in response to common climatic signals, such as sunshine duration and cloud cover from late winter to early spring (January to March) and precipitation in October and November of the prior year. In contrast, site chronologies have no determined elevation-dependent growth responses to temperatures, and predominant temperature (prior and current summers) influences on cambial activity is only evident at intermediate elevation sites (3300 m). Irrespective of elevation differences of the sample sites, an anomalous reduction in radial growth occurring consistently since 1960s, demonstrating an evident divergence with instrumental temperature records since 1990s, might be ascribed to the accelerated winter freezing stress in recent decades.