Effect Of Stand Factor And Climate Change On The Radial Growth Of Populus Tomentosa In Road Shelter Forest In Suburban,Beijing

The suburban landscape road shelter forests play an important role in the construction of the urban ecological environment and the regulation of the regional environment.The health problems of trees,such as dryness and growth decline,have become more serious as the urbanization process accelerates;Radial growth is affected by forest age,stand structure,climate change and site conditions.Dendrochronology can study the response of the radial growth of forest trees to different factors.It is essential for the accurate estimation of urban forest dynamics and the assessment of the growth vulnerability of suburban forest trees under climate change.The research object of this paper is the Populus tomentosa in the green corridors on both sides of the main expressways in Beijing.The tree ring was collected and combined with competition,climate factors,and soil moisture data,finally the changes in the growth of the diameter at breast height of Populus tomentosa and its influencing factors were studied.Use model evaluation factors to screen suitable non-linear models of DBH growth,and then introduce competition factor and climate data on the basis of this model.Finally,a nonlinear model of DBH growth including age,competition and climate effects is established.The main conclusions are as follows:（1）Six non-linear models are used to fit the process of DBH growth of Populus tomentosa.The evaluation results show that the Richards model is the best fit.The model obtained is the best,if the relative tree diameter R_d is introduced into the parameter A that affects the maximum DBH,and the climatic factor introduces the parameter c that related to the assimilation of trees.（2）The radial growth of Populus tomentosa in Beijing road corridors is affected by many climatic factors,including the lowest temperature in March and April of the year,the SPEI value in June of the previous year,the highest temperature in December of the previous year,and the rainfall in the autumn of the previous year.The lowest temperature at the beginning of the growing season has the greatest impact on the radial growth of Populus tomentosa.（3）In this study,the relationship between the effects of stand factor and climate factors on DBH growth is:t>Tmin₃/Tmin₄>R_d>SEp₆.The age of 15 years is the mature period of Populus tomentosa in the study area of Beijing.Therefore,the leading factor for the dead shoots and individual death of Populus tomentosa is that the trees have entered an over-mature period,and their resistance to climate change and increased competition is reduced.（4）In the future,arid and semi-arid areas should adopt a mixed mode to establish road corridor protection forest belts.By increasing management measures such as artificial irrigation,in order to reduce the vulnerability of suburban road forests and increase the resilience of trees.