| Qinling Mountains,located in the north-south transition zone of China,is very sensitive to climate change and has attracted much attention from the academic community.Previous studies on the global changes in the Qinling area show that the climate change in the Qinling area has shown a trend of drying and warming in recent decades,which is bound to have a profound impact on the ecological environment changes in the Qinling Mountains.Affected by the trend of climate change of drying and warming,the forest ecosystem in Qinling Mountains is being threatened and negatively impacted.Tree rings recording the track of the annual tree growth are indicators of the growth condition of trees,it is often used as an alternative indicator to study climate and environmental change in the past.Therefore,a large number of scholars have carried out studies on dendroclimatology in Qinling Mountains.At present,most of the studies are aimed to reconstruct the historical climate of Qinling Mountains with the tree-ring width.However,response research on the forest coverage change and tree growth to climate change of drying and warming in Qinling Mountains is limited against the background of the trend of climate change of drying and warming.Therefore,Taibai Mountain,the main peak of Qinling Mountains,is selected as the research area in this paper,firstly monthly,seasonal and annual standardized precipitation evaporation index(SPEI)of two weather stations,namely Meixian weather station on the north slope of Taibai Mountain and Foping weather station on the south slope is calculated to analyze the correlation between tree-ring chronology and monthly temperature,precipitation data and SPEI index at different scales in the hope of reflecting the response of tree growth to SPEI drought index;secondly to establish tree-ring-width chronology on the north-south slopes of Taibai Mountain by using samples of tree core of sequoias in the subalpine zone on the north-south slopes of Taibai Mountain;thirdly,downloading NDVI data of Taibai Mountain and trying to reconstruct the historical NDVI of the region through the correlation between tree rings and NDVI.The results show that:(1)The radial growth of trees in the subalpine zone on the north-south slopes of Taibai Mountain has different responses to SPEI drought index at different scales.At the monthly scale,there is a negative response to the drought in the early months of the tree growing season.At the seasonal scale,there is a negative response to spring drought,and the temperature in spring is the main factor affecting the radial growth of trees in the subalpine zone of Taibai Mountain.The annual response to drought is negatively correlated,and drought is not a limiting factor affecting the radial growth of trees in the subalpine zone of Taibai Mountain.(2)The radial growth of tree rings and drought occurrence in the subalpine zone on the northsouth slopes of Taibai Mountain have periodic variations of 3a-7a and quasi 11 a.There is a negative correlation between tree radial growth in Taibai Mountain and drought in a wider range.Tree rings in the northern slope are more suitable for drought response research in a wider range.(3)The annual variation of NDVI in Taibai Mountain is consistent with vegetation growth cycle.Water and heat conditions in growing season are the main factors controlling NDVI value;tree-ring width is positively correlated with NDVI in growing season,and the correlation is the strongest in July.(4)By using tree-ring-width chronologies of long time series to reconstruct the NDVI varying series in July in the historical periods of Taibai Mountain,it is found that there are five low-value periods and five high-value periods in the reconstructed NDVI varying series in July in the historical periods,which correspond to the trend of climate change and drought records in Qinling Mountains;there are quasi-periodic variations of about 60 years reflected by the reconstructed NDVI varying series in July in the north-south slopes of Taibai Mountain. |
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