| Since the 20 th century,the global climate has become warmer,and the range,frequency and intensity of extreme climate events have increased significantly,and the extremes of climate change have become more obvious.Compared with conventional climate change,extreme climate will have a greater impact on the forest ecosystem,increasing the survival pressure of forest communities and the potential risk of local extinction.Tianshan is the largest mountain system in the arid and semi-arid region of Central Asia.Due to its special geographical location and ecological environment,the climate in this area fluctuates greatly and is very sensitive to global climate change.Plant growth is more affected by climate change.The climate in the eastern Tianshan Mountains is more arid,the living conditions of trees are harsher,and they are more sensitive to climate change.Conventional climatic factors such as mean temperature and total precipitation often ignore the characteristics of climate change under extreme conditions.However,the impact of extreme climate on forest ecosystems is constantly strengthening.Research on forest ecology and the response of tree radial growth to extreme climate change is not yet complete.Therefore,it is necessary to carefully analyze the characteristics of extreme climate changes in the region under future climate change,and conduct a comprehensive analysis based on the response characteristics of forest ecosystems to extreme climates and the dynamic changes of the growth of dominant trees,and grasp the main climatic factors that affect the forest change in the region and the future development model of the forest.Dendrochronology has the advantages of accurate dating,convenient material acquisition,and high time resolution.It is an important method for the study of climate change and forest dynamic response,and it has been widely used in studying the impact of climate change on forest ecology.This paper selects two dominant conifer species,P.schrenkiana Fischet Mey.and Larix sibirica Ledeb.,near the forest line on the Barkol Mountain in the eastern Tianshan Mountains,and establishes the tree-ring width chronologies of the two species respectively.The characteristics of extreme climate change and the statistical differences of the two tree species chronologies were analyzed in the study area.The relationship between the radial growth of the two tree species and the response to regular climate and extreme climate changes and their resistance differences were comprehensively compared.The main climatic factors affecting the growth of trees are clarified,and the radial growth of the two tree species from 2020 to 2100 is predicted and analyzed based on the CMIP5 data.The main conclusions are as follows:(1)The climate of the eastern Tianshan Mountains showed an obvious warming trend,and the precipitation also showed a slight increasing trend(temperature 0.61?/10 a,precipitation 6.90 mm/10a).The extreme temperature warmth index has an obvious upward trend,and the extreme temperature cold index has shown a significant downward trend;The precipitation intensity(SDII)and short-term heavy precipitation in all extreme precipitation indexes have increased significantly.After 28 climate indicators was tested by the Pettitt test,it was found that 19 climate indicators had obvious abrupt changes around 1985 from 1958 to 2012.(2)Through the analysis of the chronologies of Schrenk spruce and Siberian larch and their statistical parameters,it is found that the standard chronologies of the two tree species have high mean sensitivity(MS)and expressed population signal(EPS).It shows that the established tree-ring standard chronologies contains rich climate signals and the quality of the chronologies is great.At the same time,the signal-to-noise ratio(SNR)and correlation coefficients(R,R1,R2)of Schrenk spruce are higher than those of Siberian larch,indicating that the Schrenk spruce has a higher consistency in the chronology and was more sensitive to climate change.After analyzing the trend of the chronologies,it was found that the radial growth of the Schrenk spruce showed a fluctuating downward trend,which showed a significant downward trend after 1950;while the inter-annual change of the radial growth of Siberian larch was not obvious.(3)After the abrupt climate change,the influence of Schrenk spruce and Siberian larch is significantly increased by extreme weather.After the abrupt climate change,the number of Schrenk spruce chronology has a significant correlation with 28 climate indexes from September of the previous year to October of the current year and each season from 14 to 38;The main manifestation is that the correlation with various extreme temperature factors has been significantly enhanced.The temperature changes in the autumn of the previous year,spring and summer of the current year have more obvious restrictions on the Schrenk spruce.However,the number of Siberian larch chronology has a significant correlation with 28 climate indexes in each time period from 12 to 25.At the same time,the response relationship between Siberian larch and most of the extreme temperature indexes has changed from positive correlation to negative correlation,and the negative correlation with extreme precipitation in winter and autumn has increased;the climate factors of the previous winter and the fall of the current year have increased the restriction of Siberian larch.(4)Analyzing the resistance difference between Schrenk spruce and Siberian larch,it is found that the overall adaptability of Siberian larch to climate disturbance is better than Schrenk spruce.In 1981,the resistance(RT),recovery(RC)and resilience(RS)of the Schrenk spruce were significantly lower than the Siberian larch(P<0.05).In2003,the resistance?recovery and resilience of the Schrenk spruce are still lower than Siberian larch(P<0.05).Compared with before the abrupt climate change,the three resistance indexes of Schrenk spruce and Siberian larch were all reduced,and the resistance difference between the two tree species was reduced in 2003.(5)After the extreme climate index were added,the fitting results of the tree-ring width chronology show that the model's fitting accuracy for the tree-ring width chronology of the two tree species has been significantly improved,and the correlation between the fitting results and the original measured chronology has increased significantly.Based on the CMIP5 data and the fitting results from 1985-2012,the growth of the two tree species from 2020 to 2100 were predicted.It is found that the tree ring width of Schrenk spruce and Siberian larch shows a consistent downward trend under the RCP4.5 and RCP8.5 greenhouse gas emission model.Under the RCP8.5model,the downward trend of the two tree species was significantly higher than the RCP4.5;In the same situation,the decline trend of Schrenk spruce(RCP4.5,-0.015/10 a,RCP8.5,-0.031/10a)was significantly higher than that of Siberian larch(RCP4.5,-0.011/10 a,RCP8.5,-0.02/10a). |
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