Effects Of Climate And Competition On Radial Growth Of Pinus Kwangtungensis In Mangshan Mountain

As the most important part of the terrestrial ecosystem,the forest ecosystem plays an important role in carbon sequestration.In the context of global climate change,the dynamic change process of the forest ecosystem is one of hot topics at present.Studying the effects of climate and competition,the main factors affecting the dynamic change of forest,on the radial growth of trees is the key to predicting future forest dynamics.Therefore,the study takes Pinus kwangtungensis in the Mangshan Nature Reserve in subtropical zone,a climate change sensitive area,as the study object.The Pinus kwangtungensis Tree Ring Chronology was established by using the dendrochronology method.Correlation analysis of tree-ring width chronology and climate factor was carried out to study the relationship between tree radial growth and climate factors.At the same time,linear mixed effects model was used to quantify the relationship between the Cumulative sectional area growth of the target Pinus kwangtungensis trees and the competition index to clarify the impact of competition on the growth of trees.The main findings are as follows:(1)The radial growth of Pinus kwangtungensis is affected by the combined effects of temperature and rainfall,and the relationship between the radial growth of Pinus kwangtungensis and climatic factor at different altitudes is different.The radial growth of Pinus kwangtungensis at an altitude of 1400m is significantly negatively correlated with the average and maximum temperature in June of the current year,but is significantly positively correlated with the rainfall in April of the current year.The radial growth of Pinus kwangtungensis at an altitude of 1200m is significantly positively correlated with the temperature in March,and the average temperature and minimum temperature in October of the previous year and October of the previous year,but is significantly negatively correlated with the minimum temperature in July of the current year,and is significantly positively correlated with the rainfall in November of the previous year.The radial growth of Pinus kwangtungensis at an altitude of 1000m is significantly negatively correlated with the average temperature and maximum temperature in June of current year,the average temperature and minimum temperature in January of current year,and the minimum temperature in October of the previous year,but is a significantly positively correlated with the rainfall in March and October of the current year,and the rainfall in October of the previous year.(2)The results of analysis of shared interval of the Pinus kwangtungensis chronology in a single year show that the correlation between the radial growth of trees and climatic factor has been basically verified.The tree ring width at an altitude of 1400m is the largest(1.336)in 2017 and is the smallest(0.66)in 2012.The tree ring width at an altitude of 1200m was the largest(1.391)in 2016,and is the smallest(0.741)in 2013.The tree ring width at an altitude of 1000m was the largest(1.225)in 2013,and was the smallest(0.387)in 2008.The distribution of extreme value in the chronology is inconsistent.The ice and snow disaster in 2008 severely affected the radial growth of Pinus kwangtungensis at an altitude of 1000m,so it is the smallest in that year.(3)The linear mixed-effects model shows that the diameter at breast height and SDBH of the competing tree and the cumulative sectional area growth of Pinus kwangtungensis in the past 25 years had the best fit,indicating that the radial growth of Pinus kwangtungensis was significantly affected by the diameter at breast height of the competing tree.In the past 10-25 years,SDBHhas always been the main factor affecting the growth of Pinus kwangtungensis.The reason may be that the competitive tree and the target tree had the same growth,and the competitive pressure between the two is relatively constant.The surface model shows that the annual growth volume gradually decreases with the increase of the competition,and the relationship with climate factor is not obvious.When the competition index is low,the annual growth rate increases with the increase of rainfall.Compared with climate factor,competition has a greater impact on the radial growth of Pinus kwangtungensis.Therefore,the results show that temperature and precipitation affect the radial growth of Pinus kwangtungensis at 1400m,1200m,1000m.The temperature and precipitation at the beginning of growing season and the temperature in summer are the key climatic factors affecting the radial growth.The radial growth of Pinus kwangtungensis at 900m was influenced by the temperature in June,the precipitation in July and the competition.The competition had more influence on the radial growth of Pinus kwangtungensis than the climatic factors.