Study On The Relationship Between Radial Growth And NDVI Of Larix Gmelinii In Greater Khingan Mountains

As the main body of terrestrial ecosystems,forests play an important role in the global carbon cycle.The forest canopy fixes carbon dioxide in the atmosphere through photosynthesis,and the tree trunk cambium uses the organic matter generated by the canopy for cell division and thicken.Whether the assimilation of the tree canopy and the radial growth of the trunk change synchronously in the process of climate change is still controversial.Whether the synchronous or differential changes are related to the response of the two processes to climate is also a hot topic at present,especially for same tree species at different climate backgrounds.Larix gmelinii,as the dominate coniferous forest tree species in cold temperate zone of China,is sensitive to climate change.Therefore,this paper selects three sites of differ latitude at Greater Khingan Mountains,include Aershan(AES),Kuduer(KDE)and Dabaishan(DBS).The normalized difference vegetation index and ring width index are used to represent the growth status of tree canopy and trunk respectively.Using segmentation functions and correlation analysis to explore the relationship between tree canopy and trunk growth and the difference on climate driving factors under different climatic backgrounds.The main results are as follows:(1)The interannual variation of the highest temperature in the Greater Khingan Mountains from 1982 to 2015 has stage characteristics,including rapid warming and warming slowdown period.During the rapid warming period,the change of maximum temperature has obvious seasonal characteristics,which is mainly due to the significant increase of maximum temperature in winter,while the seasonal change of precipitation is not obvious.During the warming slowdown period,the minimum temperature change has obvious seasonal characteristics,mainly because the summer minimum temperature increases significantly,and the summer precipitation also increases significantly.The temporal changing points of the highest temperature are different in space.The highest temperature in the southern and central regions are 1998,and the highest temperature in the northern region around 2002.(2)There were differences in the consistency of temporal change of NDVI and tree ring width in the growing season of during the rapid warming period and the warming slowdown period.During the rapid warming period,NDVI increased significantly in the growing season,with an average increase of 0.027/10 a,mainly due to the accelerated growth of the canopy in the early and late growing seasons,while the tree ring width decreased significantly.During the warming slowdown period,the NDVI in the growing season was still significantly increased,with an average increase of 0.05/10 a,which was mainly manifested by the accelerated growth of the canopy in the vigorous growth period and the later growing season,while the tree ring width showed an upward trend except for the Kuduer area.(3)Whether there is a difference in the response of canopy and trunk growth to common driving climate factors and the characteristics of changes the climate factor determine the consistency of temporal change for canopy and trunk growth.During the rapid warming period,the significant increase of the highest temperature in February inhibited the radial growth of trees and promoted the increase of NDVI in the growing season,making the negative relationship between tree ring width index and NDVI.During the warming slowdown period,the significant increase in the minimum and average temperature in May in the southern and northern regions of the Greater Khingan Mountains at the main factor drove the growth of trunks and canopy,making the tree ring width index positively correlated with NDVI.The negative correlation between trunk and canopy growth in the central site during this period is due to the difference in their response to common climate driving factors as precipitation in October of the previous year.The overall results showed that the consistency of canopy and trunk growth relationship of Larix gmelinii trees in the Greater Khingan Mountains in the past few decades was different during the rapid warming and warming slow down stages.If the response of canopy and trunk growth to a common climate driving factor is different,and the driving factor belongs to the main climate change factor,which will weaken the consistency in tree canopy and trunk growth.If the response of tree canopy and stem growth to a common climate driving factor is consistent,and the driving factor belongs to the main climate change factor,which will enhance the consistency in tree canopy and stem growth.