Response Of Juniperus Przewalskii Tree-ring Widths To Climate Change In The Difference Regions Of Qilian Mountains

Qilian mountain is located in the sensitive area of climate change response,but also is the water resources conservation land of Hexi Corridor of the " Silk Road Economic Zone ",which is very important in the fields of politics,ecology,economy,culture and so on.Juniperus przewalskii is one of constructive species in this area,its tree ring records have been widely used in dendroclimatology and dendroecology etc..Therefore,studies on Juniperus przewalskii tree-ring growth response to climate change in Qilian Mountain,which is great significance for us to understand the proxy index and the future forest management.The studies base on the tree-ring records of Juniperus przewalskii collected from Qilian mountains.Firstly,the tree radial growth characteristics and climate-growth relationships along altitudinal gradients were examined by using tree-ring records from the middle Qilian mountain.Secondly,using the increments and disk of Juniperus przewalskii at up forest limite of eastern Qilian mountain to analyze tree rings response to climate change and describe the variation of seedling population and explore the causes of seedling death.Finally,comparing the tree rings response to climate change of different age classes chronologies at middle and eastern Qilian mountain and the influence degree of climatic and age factors at middle Qilian mountains.The main conclusions of this dissertation are summarized as follows:1)Tree ring widths response to climate change had the gently differences at three different elevations sites in the middle of Qilian Mountains.The low altitude sample is more vulnerable to drought stress,while the high altitude sample is more likely to be restricted by the low temperature and the time limit is longer.However,the climate–growth relationships were unstable.With an increase in temperature,the sensitivity of tree growth to temperature variation had increased over the past few decades.2)There is a positive correlation between the four residual chronologoies at up forest limit of eastern Qilian mountains and the temperature of the fall and winter(P9C2).With an increase in temperature,the sensitivity of tree radial growth to temperature variation had decreased.The seedling population had been increased during 1930-1949 AD and the position of the seedlings had a tendency to climb upward in the meanwhile.However,at the beginning of this century,a large number of seedlings died,which may be related to the water deficit caused by continuous drought events.And the year of trees death has lagged behind drought years.3)The response of tree-ring widths to climate change in the eastern Qilian mountain is age independent.At the middle Qilian mountain,different age classes had the same climate-growth relationship,but differences in the degree of response.it can be concluded that the young trees are more sensitive to the temperature,while the old trees have a significant response to precipitation.The age factor played a more important role in the response of tree radial growth to temperature variation than altitude factor.