| As an important aspect of global change,climate warming has a great impact on human living environment,which has aroused widespread concern and become a hot issue.Southeast Inner Mongolia is a key area of forest to grassland transition,which is affected by Asian monsoon,westerly and Mongolian high,and becomes a sensitive area in response to climate change.In particular,extreme drought events occurred frequently in this area,which seriously affected the forest ecosystem of the study area.As a representative of high-resolution indicators of the past climate change,tree rings can provide us with a clear outline of climate change and help us to predict the trend of climate change in the future.(1)In this study,the basic methods and principles of dendrochronology were used,and Larix gmelinii tree ring chronology of Baiyinhan mountain in Southeast Inner Mongolia was selected as the research object.Finally,various types of Larix gmelinii tree ring chronology were obtained: total ring width chronology(RW)(1868-2018),earlywood width chronology(EW)(1868-2018),latewood width chronology(LW)(1873-2018)and latewood blue intensity chronology(LWBI)(1894-2018).The basic statistics of each chronology contains more environmental information,which is suitable for further research.(2)Based on the correlation analysis of chronology and climatic factors,the climatic factors limiting the radial growth and density change of Larix gmelinii and their response characteristics to climatic factors were explored.The correlation analysis between the established chronology and the meteorological data of Balinzuoqi meteorological station(1953-2018)and the Standardized Precipitation and Evapotranspiration Index(SPEI)data.The results show that the moisture in the study area plays a promoting role in the growth of Larix gmelinii,which is mainly reflected in the growth of tree ring earlywood and spring and early summer(period from April to July,in the middle and early growing season)There was a significant positive correlation between SPEI in summer and early autumn(period from July to September).The results showed that both temperature and moisture were important factors affecting the density of Larix gmelinii in the study area.The latewood blue intensity of Larix gmelinii had a significant positive response to the monthly mean temperature from June to August,and a significant negative response to the precipitation from June to August and the SPEI from July to October.The results showed that tree ring width and latewood blue intensity had significant differences in response to climate change,and the effects of climate change on the two stages of lignification of Larix gmelinii cells were different.(3)Based on the study of the response characteristics and relationship of each chronology to climate factors,the EW chronology which is most sensitive to climate change is selected.By defining the criteria of extreme drought and humid years,we found 11 extreme drought years and 11 extreme humid years in EW series.Compared with the historical records,there are 7 extremely dry periods and 4 extremely wet periods were confirmed.Six dry periods were found in the series: 1881-1888,1900-2012,1917-1927,1937-1959,1963-1970 and 1997-2008,and four wet periods: 1872-1880,1889-1899,1928-1936 and 1971-1996.By comparing with the regional dry and wet changes based on tree ring in the surrounding area,it is found that the longest drought period from 1937 to 1959 is not synchronous with the surrounding area.Compared with the reconstruction of regional Dry and wet changes based on tree rings in central and Northern China,it is found that the dry and wet changes recorded in EW chronology and the dry and wet periods revealed by these reconstructions are mostly in reverse.(4)The results of cycle analysis show that the EW series contains 3-7 and 12 years periodicity,which indicates that the tree growth in the study area may be related to El Nino Southern Oscillation(ENSO)and solar activity.The correlation analysis with SST shows that the tree growth in the study area is related to SST in the Pacific Ocean.The results of composite analysis show that the SST characteristics in dry year correspond to the cold period of ENSO,and that in wet year correspond to the warm period of ENSO.At the same time,the EW series is significantly positively correlated with the PDO series.To sum up,the high Pacific SST may increase the precipitation in the study area and promote Larix gmelinii to form wider rings,while the low Pacific SST may reduce the precipitation in the study area and promote Larix gmelinii to form narrower rings.The response of Larix gmelinii tree ring width and latewood blue intensity to climate factors revealed the different effects of temperature and water on tree growth and density change,which could provide theoretical support for tree protection in the study area.The research on the dry and wet change of tree records and its possible driving mechanism can provide scientific support for the relevant departments to carry out climate prediction. |
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