Effects Of Nearly 20 Years Of Drought On Forest Biomass In East Texas,USA

Large-scale drought can greatly change the composition and structure of forests,and changes of forest conditions can affect the economic and ecological characteristics of a region,and the overall influence depends on the intensity and duration of drought.Eastern Texas was chosen for the research because of three great droughts in this state over the past 20 years,respectively in 1999-2000,2005-2006 and 2010-2012.Texas is the largest continent in the United States,and its economic and ecological functions are significant,so it is necessary to study the drought development,characteristics and impact of the eastern Texas forest region.Therefore,this research takes the eastern Texas forest as the research object,analyzes the distribution characteristics and influencing factors of drought and forest biomass in eastern Texas,and provides a theoretical basis for improving forest defense and reducing forest biomass losses caused by drought disasters.This paper mainly obtains the following research results:1.In recent years,the forest biomass in eastern Texas has steadily increased,which results from the decline in biomass because of the extensive extreme drought in 2011 and the timely availability of new tree biomass,thus the standing biomass keeps a stable increasing trend.2.Since 2000,the eastern Texas of the United States showed a climate response such as increased temperature,reduced precipitation,and increased extreme weather events.The extreme drought that occurred in eastern Texas in the United States in 2011,which affected the eastern part of Texas as a whole and resulted in significant losses in forest biomass.The 12 months from October 2010 to September 2011 were the driest period in Texas history,which is the worst drought in Texas according to the statewide weather records since 1895.The reported precipitation in many areas is less than 25 percent of the normal 12 month precipitation.Average temperatures from June to August in 2011 were more than 1.1℃,higher than previously recorded,close to the highest summer temperatures recorded in the United States.According to SPEI,it will not return to a normal level until August 2012,and the large area of drought would not be completely ended until 2014.3.Correlation analysis and multiple regression analysis related to multi-climate factors and forest biomass are presented in thesis,and the structural equation model was established.Strong evidence has been found to support the hypothesis in this thesis that large areas of extreme drought lead to significant reductions in forest biomass.The results showed that the average annual temperature,annual precipitation,annual evaporation and drought index had direct effects on biomass.Among them,the correction between drought index and biomass are most significant(p<0.01),and the biomass increased with the increase of drought index and annual temperature,showing a significant positive correction(p<0.01).The higher the annual precipitation is,the less the biomass loss is.Conversely,when the annual precipitation decreases(drought increases),the biomass loss of trees increases.The research results of drought index,drought length and loss of biomass due to climate disturbance show that the higher the drought index(representing wetting)and the shorter the drought length is,the biomass loss is less,while the lower the drought index(representing drought)and the longer the drought length is,biomass loss increases more,which indicates that the degree of drought is stronger,the longer the drought persistence lasts,and the biomass loss is more.