Effects Of Unprecedented Drought On Forest Tree Mortality Rate And Biomass Loss Of Eastern Texas

In 2011,Texas experienced the most serious drought in the history of a century,resulting in the death of more than 300 million trees,which has a great impact on the forest ecosystem.The purpose of this study is to understand the long-term and comprehensive impact of drought on forest tree death.The trend and main reasons of tree mortality and biomass change at sample plot level in East Texas forest region in recent 20 years were studied.In this study,209663 trees from 1797 sample plots were collected from the forest inventory and analysis database of eastern Texas.the forest trees in eastern Texas were divided according to different types and regions,including tree species,DBH,height,stand origin,latitude,elevation,ecological region,and northeast,northwest,southeast,southwest of eastern Texas.The number of live and dead trees and corresponding biomass in different weeks were counted,and the number of deaths caused by different reasons in different years was further counted on this basis,the mortality rate and biomass loss rate of forest trees can be obtained,so as to further understand the response of forest trees to drought.Drought severity and drought length are used as drought indicators;tree density,tree base area,forest age and sample plot investigation time interval are used as tree competition indicators,and principal component analysis is conducted on these six factors in addition,the regression analysis between drought intensity and drought length and the biomass loss rate of forest trees was carried out.In terms of biomass,pine trees have the lowest biomass loss rate compared with other tree species,which is consistent with the lowest mortality rate of pine trees;similarly,according to DBH and height,the biomass loss rate of trees with low height and small DBH is higher;the biomass loss rate of natural forest is higher than that of artificial forest;the biomass loss rate of latitude ≤ 31.5 ° is slightly higher than that of latitude > 3 The biomass loss rate of trees at 1.5 ° and those with altitude≤ 100 m were higher than those with altitude > 100 m,but the difference was not significant;in addition,the biomass loss rate of trees was consistent with the mortality trend according to the ecological and geographical regions;In the regression of drought intensity,drought length and biomass loss rate,the effect of drought intensity on biomass loss is greater.The results showed that: among the effects of drought on the mortality of different types of trees,the mortality of Pinus was the lowest,according to the tree species group;the mortality of trees with the lowest height and diameter at breast height was the highest,according to the height and diameter at breast height;the mortality of trees in plantation forest was lower than that in natural forest according to the site origin,the mortality of trees in Western Gulf Coastal Plains ecological region was higher than that in natural forest according to the ecological region The results showed that the mortality rate was the highest after drought;the mortality rate was the highest after drought in the southwest of eastern Texas according to geographical region;there was no significant difference in tree mortality rate according to altitude and latitude.On the whole,the effect of drought on tree death is greater than that of competition,and the effect of drought intensity and drought length on tree death is similar.From the perspective of mortality,we can see that:(1)in the six tree species groups,the mortality of pine trees in different periods is the lowest,so pine trees are more drought tolerant than other tree species;(2)under drought,the mortality of trees with small DBH and height is higher than that of trees with large DBH and altitude,so the impact of drought on small trees is more significant than that of big trees;(3)drought on natural trees The impact of forest is more significant than that of plantation;(4)principal component analysis shows that drought is the main cause of tree death compared with competition;and the intensity and duration of drought have the same effect on tree death;From the perspective of biomass,before and after drought,the biomass loss rate of trees is consistent with the mortality rate,and the biomass loss is significantly correlated with climate drought,The drought intensity and drought length are positively correlated with biomass loss,that is the greater the drought intensity is,the greater the biomass loss rate is,the longer the drought length is,the greater the biomass loss rate is,and the drought intensity has a negative impact on the biomass loss The impact is slightly higher than the drought length.