The Response Of The Growth Of Larix Gmelinii To Extreme Climate In Da Hinggan Ling Prefecture

Since the 20th century,global warming has intensified under the influence of human activities,and the frequency and intensity of extreme events increase significantly.Climate will even have a great impact on human life.Once an extreme climate event occurs,it may have a huge impact on the ecosystem in the region,causing sudden and drastic changes in the ecological environment.Da Hinggan Ling Prefecture is located in the Eurasian permafrost zone,and is the natural forest region with the highest latitude in China.Larix gmelinii is a local zonal vegetation,which is very sensitive to climate change.In order to understand the impact of extreme climate events on the radial growth of trees in Da Hinggan Ling Prefecture,this paper uses the method of tree ring climatology to establish the standard chronology of larch at four sampling points in Da Hinggan Ling Prefecture,analyze the extreme climate index and its trend at each sampling point,study the response of radial growth of larch at each sampling point to the extreme climate index,and use the LASSO regression model to screen the main control factors and simulate the tree ring chronology,Then,the spatial correlation analysis is used to study the spatial correlation between the calculation of the tree-ring chronology and the spatial correlation characteristics of the climate factors,and its spatiotemporal change rules are studied.Finally,the future radial growth of tree rings is simulated and predicted based on the SSP245 model data under the CMIP6 scenario.The main conclusions are as follows:(1)By analyzing the climate indexes in the study area,it is found that there is an obvious warming trend in the Da Hinggan Ling Prefecture region,and the precipitation is not significantly increasing.The temperature in the Da Hinggan Ling Prefecture is cold and warm alternating on the scale of 20 years;Through wavelet analysis,it is found that the rainfall frequency alternates from high to low at the scale of 7a,and the rainfall alternates from less to more to less to more at the scale of 15a.The change cycle of extreme climate is 2-7a,with an interannual change of 10-16a;(2)The standardized chronology of larch tree ring width at four sampling points was established.After the study,it was found that the quality of the chronology of tree ring width in the study area was good,and there were abundant climate signals in the chronology,which could be used to analyze the response of tree radial growth to climate change;(3)The correlation of tree ring width chronology with extreme climatic factors proved that: the tree ring width index in the sampling site of Amur was significantly negatively correlated with the max Tmax in June and July of the current year.The tree ring width index was significantly negatively correlated with the cool nights and diurnal temperature range in July of the current year,was significantly negatively correlated with the min Tmax in November of the previous year,the number of warm days and warm nights in December of the previous year,the number of cold nights in May of the current year,and the min Tmax in June of the current year.The tree ring index was significantly positively correlated with the number of warm nights and cool days in July of the current year,max Tmin in August of the current year.the tree ring width index and was positively correlated with the max 1-day precipitation amount in December of the previous year,the precipitation in June of the current year,and the average temperature in May of the current year.The tree ring width index in sampling site of Tahe was significantly negatively correlated with the max Tmax in June and July of the current year,the min Tmin in March of the current year,the diurnal temperature range in June of the current year and the max 1-day precipitation amount in October of the current year.The tree ring width index was negatively correlated with max Tmax and average temperature in September of the previous year,the warm days in November of the previous year,the min Tmax in January of the current year,and the max Tmax in February of the current year,the warm days and average temperatures in June and July of the current year and max 5-day precipitation amount in October of the current year.The tree ring width index was significantly positively correlated with cold days in June of the current year.The tree ring width index in the sampling site in Hanjiayuan was significantly negatively correlated with max Tmax and the warm days in October of the current year.The tree ring width index was negatively correlated with the max 1-day precipitation amount in April of the current year,the max Tmax and the warm nights in July of the current year,the min Tmin and diurnal temperature range in October of the current year.The tree ring index was significantly positively correlated with the max1-day precipitation amount and precipitation in May of the current year and cold days in September and October of the current year.The tree ring width index in the sampling site of Xinlin was significant negatively correlated with diurnal temperature range of January,July and October in the currrent year.The tree ring width index was negatively correlated with and diurnal temperature range of September and November in the previous year and March,August and September in the current year,cool nights in August and warm days in October in the current year.The high temperature in winter inhibits the radial growth of trees,negatively correlates with the extreme high temperature in the growing season of the year,negatively correlates with the extreme temperature,and significantly positively correlates with the precipitation in the growing season of the year.The climate warming process is not suitable for the growth of local larch;(4)The equation established by LASSO regression model is used to fit the tree-ring width chronology.The fitting result is better after adding the extreme climate index,and the extreme climate factor can better reflect the abnormal value;(5)Using CRU data,we analyzed the response of the tree ring width chronology of Larix gmelinii in Tahe to the maximum average maximum temperature,the number of warm days,the maximum minimum air temperature and the precipitation value in June and July of that year,and found that the first three items were significantly negative correlation,and the precipitation value was significantly positive correlation.The response center of extreme temperature index and precipitation are both shifted from north to south.The southward shift of the response center may be due to the weakening of the summer monsoon activity in Da Hinggan Ling Prefecture,which is located in the swing zone of the East Asian summer monsoon margin.(6)Based on the univariate linear regression of the extreme climate index under the SSP245 model of CMIP6,it was found that the extreme high temperature increased significantly,the extreme low temperature decreased,and the precipitation and precipitation frequency increased in 2019 to 2100;The established model is used to fit the tree ring width index chronology of Larix gmelinii from 2019 to 2100.After linear regression and growth analysis,it is found that the tree ring width index is gradually decreasing,the radial growth of the tree ring is obviously decreasing,and the growth range is greatly reduced.