Differences in growth response of Larix chinensis to climate change at the upper timberline of southern and northern slopes of Mt. Taibai in central Qinling Mountains, China
The impact of climate change on the plant growth has gained attentions,especially for those boreal trees growing at the timberline area. Topographical character such as slope aspect may affect the response of plants growth to climate even if with the same stand condition. This is especially significant between southern and northern slopes of Mt. Taibai,the main geographical watershed of Qinling Mountains. In this study, the chronologies were established by exploiting Larix chinensis tree-ring samples that collected from both northern and southern slopes of Mt. Taibai with a similar elevation of 31003200 meters. The characteristics of the chronologies were compared and the correlations between tree ring width indices and climatic factors were analyzed for both slopes of Mt. Taibai, respectively. The mean sensitivity, sample inter-correlation coefficients,overall sample representative and other values of the chronology characteristics are all very high,indicating that the tree-ring samples collected from both slopes of Mt. Taibai contained enough environmental information, and the plants at the timberlines were more sensitive to climate change on the northern than on the southern slope. According to the correlation analysis,radial growth of the Larix chinensis in different slopes were mainly affected by different aspects of the climatic factors from different months. Residual chronology was correlated positively with mean air temperature during January to June on the northern slope, while only with that during May to June on the southern slope. The Larix chinensis' growth on both northern and southern slopes were correlated positively with the precipitation occurred in June of the previous year. However, the tree-ring width indices had a significant positive correlation with precipitation occurred in August of current year on the northern slope,while had a significant negative correlation with the mean precipitation from January to April of current year on the southern slope. The multi-variant liner step-wise regression modeling showed that the maximum contribution values of the air temperature factor in both regression functions are greater than that of the maximum value of attribution from precipitation,indicating that the change in tree-ring width of Larix chinensis was due to the variations in temperature than in precipitation in Mt.Taibai. Moreover,the tree-ring width residual chronology was more sensitive to temperature on the northern slope than on the southern slope since the temperature contribution to the function on the northern slope was higher than that on the southern slope which is also confirmed by the correlation analysis between the residual chronologies and the climate factors.