| In the context of global climate change,studying the impact of climate change on tree growth and their response to climate change has become a scientific issue.Zhongtiao Mountains plays an important role in maintaining water conservation,species diversity and regional ecological balance.This area belongs to the warm-temperate to subtropical climate transition zone,where tree growth is more sensitive to climate change.This paper takes four dominant tree species: Pinus tabuliformis,Pinus armandii,Quercus mongolica,Quercus variabilis in the Zhongtiao mountain as the research object.We selected five typical growth equations,and fitted the growth models of the diameter at breast height,height,and volume of each dominant tree species,then analyzed the growth laws.At the same time,based on the data of nearest meteorological stations,a growth model of single tree diameter at breast height,height and volume included climate factors was constructed by using multiple stepwise regression and random forest.The impact of different climate factors on the growth of each dominant tree species was analyzed,and the relative importance of different climate factors on the growth of dominant tree species was calculated.Meanwhile,climate factors for four different climate scenarios(SSP1-2.6,SSP2-4.5,SSP3-7.0,SSP5-8.5)under the BCC-CSM2-MR climate system model of the National Meteorological Center were selected to predict the growth trends of various dominant tree species under future climate scenarios by using the above conclusions.(1)Using five typical growth equations to fit the growth of dominant tree species,including diameter at breast height,height,and volume.The optimal growth model for volume of P.tabuliformis is the Gompertz equation,while the optimal growth models for the others are Richards equations.By using the Richards equation to fit the growth curves of various dominant tree species,it was found that the peak growth period of the DBH、height and volume of P.tabulaeformis was 10-50 years、10-30 years、20-70 years,and the mature age of quantity is 70 years.The peak growth period of the DBH and height of P.armandii is 5-30 years,the peak growth period for volume is 20-90 years,and the mature age for quantity is 90 years.The peak growth period of the DBH、height and volume of Q.mongolica is 10-30 years、5-35 years、10-70 years,and the mature age of quantity is 70 years.The peak growth period of the DBH and height of Q.variabilis is 10-30 years,and the volume is 20-95 years,and the mature age of quantity is 95 years.(2)For the DBH,the accuracy of fitting by the multivariate stepwise regression and the random forest is different.To the P.tabuliformis,the multivariate stepwise regression is superior to the random forest,but the others is the random forest better than the multiple stepwise regression,however the accuracy is not high.The relative importance of climate factors affecting the growth of DBH is consisted,for example mean maximum annual temperature,relative humidity,wind speed,annual precipitation,and standardized precipitation evapotranspiration index have a significant impact on the growth of DBH.The mean maximum annual temperature,relative humidity,and wind speed have a positive effect on the DBH of dominant tree species.The annual precipitation and standardized precipitation evapotranspiration index exhibit a negative correlation.(3)The tree height growth models constructed by the random forest are superior to the models constructed by the multiple stepwise regression for the four dominant tree species.The contribution of climatic factors to tree height growth was basically the same in both algorithms,in the order of mean annual temperature,mean minimum annual temperature,annual minimum temperature,mean annual sunshine hours,relative humidity and wind speed.Tree height growth was negatively correlated with mean annual temperature,and positively correlated with mean minimum annual temperature,annual minimum temperature,mean annual sunshine hours,relative humidity and wind speed.(4)Similar to the fits for DBH and height,the random forest generally is superior to the multiple stepwise regression for volume growth models.The R2 of volume growth models was generally higher than that of the DBH and height.The contribution of climatic factors to volume growth was generally consistent between the random forest and the multiple stepwise regression.Temperature-related climatic factors had a greater effect than moisture-related climatic factors.The mean maximum annual temperature and standardized precipitation-evapotranspiration index were positively correlated with volume growth,while mean annual sunshine hours was negatively correlated.(5)Under the future climate scenarios,the DBH,height,and volume growth of the four dominant species were restrained in varying degrees.By species,the inhibition of total growth at DBH,height and volume was stronger for P.tabuliformis and P.armandii,than Q.mongolica and Q.variabilis.In terms of total growth at DBH and height,the SSP1-2.6 scenario had the strongest inhibiting effect and the SSP2-4.5 scenario had the weakest,but the effect on height growth of the dominant tree species was less than that on DBH.For total volume growth,the SSP1-2.6 scenario had the strongest inhibiting effect and the SSP5-8.5 scenario had the weakest.This paper uses growth models to study the law of the tree growth,attempting to analysis the effects of climate factors on the growth of dominant tree species in the Zhongtiao Mountains and to predict tree growth trends under future climate scenarios.This paper aims to provide a scientific basis for formulating scientific forest management program under the background of climate change and promote sustainable development of the regional foresst. |
