The Radial Growth Process And Response To Climate Change Of Two Dominant Coniferous Tree Species In The Eastern Of Qilian Mountain

The responses of different dominant tree species to climate change in forest ecosystems,which lead to the complexity of radial growth process characteristics under the global climate change.Therefore,it is necessary to explore the radial growth processes of different tree species,as well as the growth response to the climate in the forest.Forest ecosystems,as sensitive regions,are affected strongly by climate change.Meanwhile,the Qilian Mountains,as an important mountain,responding to climate change is sensitive in the forest ecosystem in northwest China.At the present,numerous studies on dendrochronology have been done based on the method of tree-ring in Qilian Mountains,but mainly focused on historical climate reconstruction and analysis of dominant climate factors,and not enough on the responsive dynamic and mechanism of tree radial growth process of trees under climate change.Meanwhile,the research on tree growth process simulation and growth process mechanism was relatively poorly based on the advantage of the long series of tree ring under climate change.Two dominant conifer species,Qinghai spruce(Picea crassifolia)and Chinese pine(Pinus tabulaeformis),were selected in the eastern Qilian Mountains in this paper,and the VS-oscilloscope model was used to simulate the tree-ring series of Qinghai spruce and Chinese pine.The radial growth process was described,the response dynamics of the growth-climate factors were evaluated,and the driving mechanisms of the radial growth process of Qinghai spruce and Chinese pine to climate change response dynamics,including the mechanisms of phenological dynamics and the water-heat contribution to the radial growth rate,were analyzed.The results of the study help to understand the climate change effects on tree growth in the eastern Qilian Mountains,and to provide scientific support for the conservation and management of subalpine forest ecosystems in semi-arid regions.Major research results as follows:(1)The chronologies of Qinghai spruce and Chinese pine tree have high quality,with high expressed population signal(EPS)and mean sensitivity(MS)of the parameters,and the chronologies contain richer climate signals.Comparing the radial growth process trends of the two species,the Qinghai spruce radial growth process maintained an increasing trend(2.99 cm~2/10a),and the increasing trend was more stronger in the late 20th century(7.69 cm~2/10a);however,the Chinese pine radial growth process trend no significant increasing trend(0.90 cm~2/10a),and showed a strong decreasing trend in the late 20th century(-0.56 cm~2/10a).(2)The dominant climate factors of Qinghai spruce and Chinese pine to climate change showed significant differences.The dominant control factors for radial growth of Qinghai spruce were mean temperature and mean minimum temperature,while the dominant control factors for radial growth of Chinese pine were mean temperature and mean maximum temperature,while the relationship between radial growth of Chinese pine and standardized precipitation evapotranspiration index(SPEI)was more correlated.Meanwhile,comparing the effects of precipitation on the radial growth process of two conifer species,the sensitivity of the response of Qinghai spruce to precipitation was stronger than that of Chinese pine.However,the response of Qinghai spruce to temperature diverged,while the response of Chinese pine to temperature and SPEI remained stable.(3)Phenological dynamics of radial growth processes of two tree species are differences,based on VS-oscilloscope tree growth physiology model simulations.The Qinghai spruce radial growth showed earlier start of growing season(BOG)and later end of growing season(EOG)(BOG:0.13 d/a,EOG:0.15 d/a)(P<0.05),the Chinese pine radial growth showed earlier start and end of growing season(BOG:0.20 d/a,EOG:0.14 d/a)(P<0.05).Qinghai spruce has longer growing days to ensure growth,resulting in radial growth increased,while Chinese pine suffers from earlier growing season end days,as the main driving mechanism,for the decline in radial growth under the climate warming.(4)Water-heat contribution to radial growth rate of two tree species are differences within years,based on VS-oscilloscope tree growth physiology model simulations.In the heat dynamics,the temperature contribution to the Qinghai spruce growth showed a gradual increasing trend in 2000s and 2010s,while Chinese pine was more vulnerable to the growth constraint by temperature.Meanwhile,in the moisture conditions,soil moisture conditions were mainly in the middle of the growing season for both tree species,and in the 2010s,the soil moisture-induced growth rate of Qinghai spruce showed an increasing trend,while soil moisture gradually enhanced the growth constraint of Chinese pine,especially soil moisture conditions showed a more obvious performance at the end of the growing season.And,the drought stress had become a key factor limiting the radial growth process of Chinese pine.