Study On The Response Of Abies Fargesii Radial Growth To Climate Change In The Niubeiliang Nature Reserve Of The Qinling Mountains

The Qinling Mountains is an important dividing line in China's climate division.The timberline in the region has a very sensitive reflection on global and regional climate change,which is of great significance to the study of global change and ecosystem.Therefore,the Qinling Mountains became one of the earlier areas of the study of tree-ring climatology in China.However,previous studies focused on the use of linear regression of a single point of tree-ring reconstruction of climate aspects,but very few focus on physiological response analysis,divergence problem or nonlinear model,though it is very important.In this paper,the relationship between the radial growth and climatic factors of Abies fargesii in the Niubeiliang Nature Reserve of the Qinling Mountains is discussed using the simple near linear relationship.Whether the divergence problem exists and further analysis of its specific performance characteristics are presented.At the same time,the response relationship between the radial growth of A.fargesii and its main limiting climatic factors in the study area was revealed and analyzed by the tree-ring physiological model Vaganov-Shashkin-Lite(V-S Lite).To investigate the chronological characteristics and the relationship between A.fargesii growth and climatic variability along the elevations gradient in the Niubeiliang Nature Reserve of the Qinling Mountains,we used dendroclimatology methods,which based on the assumptions of stationary proxy-climate behavior.The results showed,the sample cores contain a wealth of climate change information,which can well reflect the consistency of climate change in the study area and can meet the requirements of further analysis.With the increase of elevation,the sensitivity of tree growth to climate factors becomes higher.However,the consistency of the series and the amount of the climate information decreases first and then increases.The correlation analysis showed that at the timberline of the study area,A.fargesii growth at different altitudes may had different response mechanisms to the climatic variables,such as temperature and precipitation.The heterogeneity characteristics between free-ring width of A.fargesii and climate change in the Niubeiliang Nature Reserve of the Qinling Mountains were also analyzed by dendroclimatological methods,during 1969-1992 and 1993-2013.The results showed that a divergence problem exists in the radial growth responses of A.fargesii relative to temperature indicators in the study area.This study indicated that in the context of global warming,the response of A.fargesii radial growth for the response characteristics of to climatic variables were different in the two time periods in the Niubeiliang Nature Reserve of the Qinling Mountains.Thus,it is necessary to apply process-based models,such as the VS-Lite model,to link tree-ring indices and climatic factors directly and to give tree-ring growth response to climate an explicit physiological meaning.In this paper,we use the VS-Lite model to simulate climatic response of A.fargesii in the Niubeiliang Nature Reserve of the Qinling Mountains.The results could explain the relationship between tree-ring widths and climatic factors more reasonably.It has been found that the variation of tree-ring width is mainly controlled by the mean temperature from April to May and the soil moisture from June to August.In September,the temperature was the main limiting factor of the radial growth of A.fargesii.The high temperature indirectly results in slow growth by increasing the loss of soil moisture.At the same time,with the global warming,its growing season has been extended.In this study,the relationship between the radial growth of A.fargesii and its main limiting climatic factors was analyzed by simple linearity and non-linear process-based model(VS-Lite).The results showed that the divergence problem exists in the study area,and the higher temperature in April can stimulate the activity of the A.fargesii,extend the growing season.In June,the main limitation factor of the radial growth of A.fargesii is soil moisture,too high temperature will inhibit the growth of trees.Abundant precipitation will make the soil moisture in the study area conducive to the growth of A.fargesii.Using the process-based model VS-Lite to stimulate the growth of A.fargesii in the study area,the main limiting factors of radial growth of A.fargesii can be identified better,and the response relationship between radial growth and climatic factors can be revealed.