Tree Mortality Dynamic And The Ecosystem Response In Broad-leaved Forest In Southern Daxinganling

The southern Daxinganling is located at a forest-steppe ecotone in Inner Mongolia,where shows strong effect of edge and with complex ecosystem structure,functions and ecological process.With high biodiversity and productivity,ecosystems of this region have poor anti-interference ability.Trees death of large area with many patched phenomenon has appeared in broad-leaved forests in southern Daxinganling,which seriously affects stability of structure and functions of the regional forest ecosystems.Our research objective is broad-leaved forest in southern Daxinganling,where located at the arid and semi-arid area.The phenomenon of tree death as the background,there was the first time that forest ecosystem responses under the interference of trees death were deeply studied.Point pattern analysis,the redundance analysis and many others statistical analysis methods were used,at the same time the generalized linear model was also conducted to reveal communities structure,seedlings recruitment,biodiversity,etc.of the main characteristics of the response to trees death in broad-leaved forests.The results showed that:1.The individual number of trees with DBH(diameter at breast height)>lcm is total of 23035 in 2015,which was about 1.66 times of the investigation in 2012,besides the individual number of aspens was increased by 104%compared with 2012.The high peak values of the frequency distribution of trees high were more concentrated in small area of trees high and most of community individuals were low.In 2012-2015,the recruitment rate is higher than the death rate.2.A significant turning point was occurred at the moment that individuals gathered intensity is equal to 8.7 in the distribution of broad-leave forest,then the gathered intensity growth slow than before.But the gathered intensity of individuals' distribution in 2015 had no obvious turning point.The gathered intensity of Mongolia oaks was the highest in 2012.The values range of gathered intensity in 2015 had no obvious difference compared with 2012.In a small space scale,gathered intensity of individual death was growing faster,but in a bigger space scale,the growth was weakened.3.Soil pH,soil total nitrogen content and average DBH were extremely significant related with tree mortality(p<0.001),while the negative coorelation was showed on soil pH and soil total nitrogen(?<0).The results of model fitting showed that all of explained variables were soil factors except DBH,also explained rate of many soil variables was higher in the model.4.A total of 66 species was occurred in the understory herb layer of broad-leave forest,which was belonged to 25 families,the plants of Compositae accounted for the largest number of individual number.The species number of herb layer was higher in tree mortality level ?.Shannon-Wiener index and Simpson index were generally higher than the same months in 2015,Whittaker index was generally increased with rising tree mortality.The higher species richness of herb layer was appeared in forest stand with lower tree mortality in broad-leaved forests.5.Seedling recruitments of Mongolia oaks and aspens were higher in broad-leave forests.Besides seedlings in the plot were mainly growed from seeds.There was significantly positived correlation between slope position and total recruited seedlings(?>0,p<0.001).Tree mortality and seedlings number of aspens had extremely significant positived correlation(?>0,p<0.001),soil available potassium content was extremely significant negative related with the number of aspen seedlings(?<0,p=0.009).Tree mortality and seedlings number of white birch had extremely significant negative coorelation(?<0,p=0.009),and soil total nitrogen content was extremely significant positively related with the seedlings number of Mongolian oaks(?>0,p=0.005).