Climatic Significance Of The Earlywood And Latewood Width Of Pinus Taiwanesis And Pinus Massoniana At Different Microtopography In Southeast China

The subtropical monsoon region in Southeast China has superior precipitation and heat conditions.The growth of trees is affected by the complex climate environment.It is difficult to extract climate signals from tree rings.Climatic studies based on tree-ring width have made great progress during the past decade.However,most studies are mainly based on the total ring width.Some tree ring widths contain climatic signals of different seasons,which restrict the climate reconstruction.Reliable climatic signals have been successfully extracted by splitting tree-ring width into earlywood-and latewood-width.Then whether the corresponding earlywood-and latewood-width chronologies contained similar climatic signals with total ring width chronologies in different habitats,and whether they can provide more climate information? This study explores the law of the earlywood and latewood width in different habitats in response to climate in southeast China.And it can provide a reference for further study based on tree-ring width,earlywood-and latewood-width in this area.3 groups of tree-ring samples were collected in different altitudes.The sampling sites are Xiaodai Village(XDC,390～480 m),Qingliang Mountain(QLF,1000～1050 m)and Sanqing Mountain(SQS,1550～1600 m).The species are Pinus massoniana and Pinus taiwanensis.The widths of the earlywood and latewood of the three groups of samples were measured separately,and the widths of the entire round were combined by them.According to these,earlywood,latewood and tree-ring chronologies were established.The correlation analysis of the chronology with the local CRU grid points and the climate element data of the nearby weather stations were conducted.The results show that the sensitivity of the growth of tree rings at different altitudes to climate elements is different and presents a certain pattern,while the response of tree ring width to precipitation changed from a positive correlation to a negative correlation with elevation.Therefore,we conclude that temperature was the major climate factor that indirectly or directly controlled the radial growth of trees at different altitudes.Temperature increase is detrimental to trees at the lower altitudes by possibly controlling the water availability through evaporation and transpiration of trees and soil.The radial growth of trees is more sensitive to water in the relatively dry months of the year.However,temperature increase is favorable to plant growth at the high altitudes by breaking dormancy and extending the growing season,as well as directly promoting the photo synthesis of trees.In addition,the precipitation in mountainous areas lead to the increase of clouds,which inhibits the growth of trees.As the altitude increased,the correlation between the earlywood-and latewoodwidth chronologies gradually increased.The radial growth of trees was gradually strengthened by the impact of the year before the growing season.In terms of response to climate factors,both the sub-annual chronologies were found to have the same dominating climatic factor as the original chronology.Due to the short growing season at high altitudes,the growth of earlywood and latewood mainly uses photosynthetic products accumulated in the previous year.So different or stronger climate signals cannot be extracted from the earlywood or latewood width than the tree ring width.The tree-ring width chronologies at middle altitudes reflected that tree growth was also affected by a certain degree of “lag effect”.But the early nutrient accumulation mainly affected the growth rate in the early growing season.Therefore,the response of earlywood to the temperature in winter and spring before the growing season is more prominent.The growth of low-altitude trees was very sensitive to the drought stress caused by the high temperature and less precipitation in July in the current year.June and July were also the time for Pinus to transition from earlywood to latewood.And they were very sensitive to climate signals.This climate signal was more prominent in the adjusted latewood chronologies.The site environment with steep slope and thin soil layer also highlighted the limiting effect of water.