ABSTRACT
By using an empirical 'signal-free' standardization approach, we constructed four Picea purpurea and Abies faxoniana tree-ring chronologies at southeast and northwest slope aspects of Erdaohai and east slope aspect of Zharisi, Songpan, west Sichuan, China. The response analysis and multivariate analysis of variance between tree rings and climatic variables were conducted to explore the divergent responses of tree growth at different slope aspects to the recent warming climate. Results showed that tree growth of P. purpurea at east slope aspect was obviously accelerated (0.011 a-1) since rapid warming in 1980, whereas those at northwest slope aspect was significantly reduced (-0.006 a-1). Tree growth of P. purpurea at southeast slope aspect and A. faxoniana at northwest slope aspect decreased in significantly. With the rapid warming, growth-climate relationships of P. purpurea and A. faxoniana at different slope aspects changed significantly. After rapid warming in 1980, the promoting effects of growing season temperature (GST) on P. purpurea growth at east slope increased significantly, while the inhibitory effects of GST on its growth at southeast and northwest slopes also increased significantly. However, the effects of GST on A. faxoniana growth at northwest slope did not change significantly before and after rapid warming. The effects of precipitation in May (PM) on P. purpurea growth at east slope was changed from inhibition before rapid warming to significant promotion after rapid warming, while the inhibitory effects of PM on P. purpurea growth at southeast and northwest slopes increased significantly. For A. faioniana at northwest slope, however, it did not change obviously before and after rapid warming. The response analysis between tree growth and the Palmer drought severity index (PDSI) showed that soil moisture variations at different slope aspects were an important reason of tree-ring growth response difference since rapid warming. In addition, the results of multivariate analysis of variance indicated that the combined effects of slope aspect, temperature and precipitation factors were the most important limited factors for tree growth variability in western Sichuan. Therefore, we should consider the combined effects of temperature, precipitation and different slope aspects when simulating and predicting tree-growth response to the recent climate warming trend.
