Study On Potential Distribution Of Pinus Sylvestris Var.mongolica In Inner Mongolica Based On MaxEnt Model

Climate changes will cause unsuitable environmental conditions,leading to the gradual reduction or even disappearance of tree species in this region.P.sylvestris var.mongolica is an important shelter forest in soil and water conservation and wind-break and sand-fixing engineering.In view of its degradation phenomenon,this thesis analyzed the potential distribution changes of P.sylvestris var.mongolica forest spatial pattern under different climate environment changes in Inner Mongolia and the response of climate factors,to provide scientific basis for improving the survival rate of P.sylvestris var.mongolica and promoting scientific planting.In this thesis,Arc GIS software was combined with MaxEnt model to make use of the location distribution data of 45 P.sylvestris var.mongolica in the study area,19 climate factors,17 soil factors and 3terrain factors,a total of 39 environmental factors were obtained for model construction.ROC curve method was used to evaluate the accuracy of MaxEnt simulation results,after comprehensive screening of the contribution rate and importance of MaxEnt model to environmental variables and the regularization training gain of knife cutting method,four main environmental limiting factors affecting the distribution of P.sylvestris var.mongolica were finally obtained,and their response curves were analyzed.The potential spatial distribution of P.sylvestris var.mongolica was simulated under three climate models,green development,moderate development and conventional development,in the historical and future,according to the classification standard of"possibility"of suitable survival of species,divided the potential distribution areas into three categories,the range and area changes of potential distribution area of P.sylvestris var.mongolica under different environments were analyzed.The main research results are as follows:(1)According to the ROC curve drawn by MaxEnt model construction,AUC values of evaluation results under historical and future scenarios were both>0.8.Indicating that the prediction results of the model were good with high accuracy and could be used to predict the distribution of potential habitat in P.sylvestris var.mongolica forest.(2)The four main environmental factors affecting the potential distribution of P.sylvestris var.mongolica are:precipitation in the wettest month(BIO13),isothermal property(BIO3),mean temperature of wettest quarter(BIO8)and mean temperature of driest quarter(BIO9),and the cumulative contribution rate was>80%.Among them,climate is the key factor,followed by terrain and soil factor.(3)Combined with the operation result of MaxEnt model’s fitness index P value,the potential habitat suitability degree of P.sylvestris var.mongolica in the study area was divided into:P<0.05 as unsuitability area,0.05≤P<0.33 as medium suitability area,and P≥0.33 as high suitability area.The prediction results showed that the high suitability area was mainly concentrated in Hulunbuil,northern Hinggan League,Chifeng and Tongliao in the northeast of Inner Mongolia,covering an area of319,429km~2,accounting for 26.99%of the total area of the study area;The middle suitable area is distributed in northeastern and central Inner Mongolia,Ordos and southern Bayannur,covering an area of 555,056km~2,accounting for 46.89%of the total area of the study area;The unsuitable area was mainly concentrated in Alxa League,covering an area of 309,096km~2,accounting for 26.12%of the total area of the study area.(4)By comparing the suitable areas of P.sylvevaris var.mongolica in the historical period and in the future under three climatic backgrounds,it is found that the suitable areas of P.sylvestris var.mongolica in the future shrink to the periphery on the basis of the original range,and the suitable areas decrease greatly,and the distribution areas also migrate to the southwest.In the future climate scenario,with the intensification of global warming,the distribution pattern of P.sylvestris var.mongolica will change.The loss range of suitable areas of P.sylvestris var.mongolica is at the edge of suitable areas,which is a sensitive area susceptible to impacts.These regions need to be given sufficient attention.