The Response Of The Qinling Tree Line Trees’ Radial Growth To Climate Based On The Vaganov-Shashkin Model

In numerous climate substitute materials,tree ring has been widely applied to historical climate change researches because of its accuracy,continuity and high resolution.As China’s important geographical boundary,Qinling Mountains has always been one of the hot study area of dendroclimatology.At present,researches on this region are mainly through the establishment of linear regression equation between tree ring sequences and instrumental records to reconstruct climatic factors,but few on nonlinear relationship between tree ring and climatic factors,and on forecasting tree radial growth trend in the future climate change scenarios.Tree ring physiological models simulate trees’ growth process under the change of multiple environmental factors based on the response relationship between the radial growth of trees and the climatic factors,such as,light,temperature,and precipitation,thus analyzing the nonlinear relationship between the trees’ growth and the external environment and quantifying the contribution weight of each factor to the growth of trees.Tree ring width chronologies were established by core samples of Larix chinensis collected from the Herb Temple in southern slope and the Shangban Temple in northern slope of Taibai Mountain,and Abies chensiensis from the Crown Peak on Muwnag Mountain respectively.Based on the Vaganov-Shashkin(VS)model,this paper explained the physiological process of Larix chinensis and Abies chensiensis’ radial growth,and analyzed the response relationship between the radial growth of trees and the restrictive climate factors in Qinling Mountains.In addition,we compared the response difference between the trees’ radial growth and the restrictive climate factors of different tree species and the same tree species in different habitats.On this basis,daily weather data generated by the global climate scenarios CNRM-CM5 was used to simulate the growth trend of Larix chinensis and Abies chensiensis in Qinling Mountains area in future climate scenarios,including the phenological trend of tree growth,the trend of tree radial growth and the influence of climate factor changes on the growth of trees.The results showed that:(1)VS model is suitable for the two tree line species of Larix chinensis and Abies chensiensis in Qinling Mountains.It can accurately simulate the physiological process of them,and reflect the response relationship with the current climatic factors.The results showed that the tree line species in Qinling Mountains area were limited by temperature and precipitation in the current growth season,of which temperature was the dominant limiting factor.(2)The temperatures of growing season(from April to August),the precipitation in early-stage of growth and in July to August are the main climatic factors limiting the growth of Larix chinensis.The higher temperature is favorable for the growth of trees,but precipitation in the early stage of growth inhibits it;Larix chinensis from the southern and northern slope of Qinling Mountains show different responses to precipitation in July to August,in which abundant precipitation promotes the growth of Larix chinensis from the northern slope,while inhibiting the growth of Larix chinensis from the southern slope(3)The temperatures of the early growing season(from March to May)and the precipitation in April and May are the main climatic factors limiting the growth of Abies chensiensis.Warming in the spring can promote the formation and division of cambium cells,thus promoting photosynthesis and accumulation of organic matter,thus,temperature conditions are beneficial to the growth of trees.However,due to the drought stress caused by rapid warming in spring,adequate precipitation is needed to supplement the loss of soil moisture.Therefore,precipitation in April and May can promote the growth of Abies chensiensis.(4)It was found that the minimum temperature for tree growth is higher and required minimum soil moisture is lower for Larix chinensis compared with Abies chensiensis by Comparing and analyzing the growth parameters of Larix chinensis and Abies chensiensis.Moreover,Even in the same slope,different sampling sites with different altitudes own discrepant physiological parameters.The Larix chinensis at higher altitude sampling site need lower growth temperature than that at lower altitude sampling site,but the former demand greater soil moisture than the latter,which confirms the growth environment’s significant influence on the trees.(5)The start day of growth have a great influence on the radial growth of Larix chinensis because tree-ring width simulation values of all samples are significantly correlated to it,it will form a wide ring when growth starts early.however,the end day of growth only has significant correlation to sample of the southern slope,it will form a narrow ring when growth starts late.But the start day and end day of the growth has little influence on the tree ring width of Abies chensiensis.(6)With global warming,the growth starting day of Larix chinensis and Abies chensiensis are tend to be ahead,the growth ending day are tend to be delay and the growing season will keep increasing simulated by the VS model under the global climate scenarios CNRM-CM5.Meanwhile,the rising temperature will promote a significant increase in the radial growth of trees in the next century.