Alpine Timberline Dynamics In Relation To Climatic Variability In The Middle Oilian Mountains

Up to now, most studies of responsing to climate in Qilian Mountain have been focused on alpine timberline. However, few studys on alpine timberline ecotone. In this paper, we sampled tree-ring cores and investigated the plots at seven different altitudes, then constructed seven residual ring-width chronologies chronologies in order to reveal the relationship between the growth of Picea crassifolia and climatic variability. We also introduced the NDVI (Normalized Difference Vegetation Index) data for correlation analysis, finally described trees update dynamic. The main conclusions are as follows:1. During the last47years, the increasing rate of the yearly average temperature on study area in Qilian Mountain was significant(P<0.01); the mean yearly precipitation showed great fluctuation, increasing not significantly. However, NDVI data did not show clear upward trending in the context of global warming, which reflects the complexity of the responsing of vegetation activities to the climate changing.2. In the study of the relationship between tree-ring growth and climatic variability, we found that the climate performs obvious "lag effect" on tree growth, but tree growth showed little relationship with the growing season climatic factors.3. Probably because Picea crassifolia is an evergreen coniferous forest, the NDVI data is a reflection in a regional scale and NDVI slowdown the rate of increasing, when the canopy density is very large, they both did not show obvious relationship.4. Climate change has a significant effect on Picea crassifolia updates, but trees radial growth and update are limited by different climatic factors, they also have no simple relationship. All of these further reflect the complexity of climate change’s effect on vegetation on alpine timberline ecotone.