Effects Of Environmental Changes On The Degradation Of Secondary Betula Platyphylla Forests In The North Of The Greater Khingan Mountains

Betula platyphylla Suk.is the main pioneer tree species in temperate secondary forests in China.In recent years,the degradation of secondary B.platyphylla forests in the northern part of the Greater Khingan Mountains has been particularly prominent.In the context of future global climate change,it is important to investigate the relationship between secondary B.platyphylla forest degradation and environmental factors for sustainable forest management in the northern area of the Greater Khingan Mountains.To determine the relationship between changes in climate,disturbance,soil and topography and the degradation of secondary B.platyphylla forests,we used the Biomod2 software package,AMOS software and Ecospat software package to construct models of secondary B.platyphylla forest distribution,stand productivity,stand structure and climatic ecological niche in the northern Greater Khingan Mountains based on field survey data and the second-generation National(Beijing)Climate Center climate system model data(BCC-CSM2-MR),respectively.The models were used to predict the future changes in the distribution and ecological niches of secondary B.platyphylla forest in the northern Greater Khingan Mountains and to analyze the effects of environmental variables on the degradation of secondary B.platyphylla forest.The results of the study show that(1)The distribution of B.platyphylla in the northern part of the Greater Khingan Mountains is most sensitive to changes in climatic variables,the importance of the hottest month with the highest temperature accounting for 35%,and the influence of soil,disturbance and topography factors on the distribution of B.platyphylla is relatively small,most areas in northern Greater Khingan Mountains are currently suitable for the distribution of B.platyphylla,and the overall area of the total suitable area for B.platyphylla in the future period is on a decreasing trend.(2)Climate variables and disturbance variables were the most important factors influencing the stand characteristics of B.platyphylla secondary forests in the northern part of the Greater Khingan Mountains,where the coefficients of climate variables and disturbance variables on the stand productivity of B.platyphylla secondary forests were 0.44 and-0.420,and on the stand structure of B.platyphylla secondary forests were 0.973 and-0.475.(3)The average annual temperature,the hottest monthly maximum temperature and the warmest quarterly precipitation are the main driving factors affecting the change in the climatic ecological niche of B.platyphylla.The overlap between the climatic ecological niche of B.platyphylla and the climatic ecological niche of B.platyphylla under current climate conditions will gradually decrease with climate change in the future,and its original ecological niche may be occupied by other tree species.(4)According to the relationship between climate change and B.platyphylla secondary forest distribution,climatic ecological niche,stand productivity and stand structure,secondary B.platyphylla forest will still be further degraded in the future with climate warming.