Effects Of Climate Change And Thinning On Growth And Yield Of Larch Plantations Based On 3-PG_mix Model

Global climate change poses a new challenge to sustainable forest management.It is necessary to predict the impact of future climate change on forest growth and yield for adaptive forest management decision-making.Larch is the main tree species for afforestation in China,but the effects of future climate change on the growth and yield of larch plantations at regional scales are still unclear.Based on the data of 552 permanent sample plots of larch plantations(Larix olgensis,Larix gmelinii,Larix principis and Larix kaempferi)from the fifth to the eighth National Forest Inventory and meteorological data in seven provinces of northeast and north China(Beijing,Hebei,Shanxi,Liaoning,Jilin,Heilongjiang and Inner Mongolia),the effects of climate change and thinning on the growth and yield of larch plantations were explored by using the process-based model(3-PGmix).The main conclusions are as follows:(1)The 3-PGmix model is suitable for simulation of growth and yield of larch plantations in north and northeast China,and the model parameters of larch plantations were obtained by calibration and verification.The simulated and measured values of stand variables were consistent with each other(R2 was between 0.71 and 0.96).The model results are biologically rational and could be used to simulate the growth and yield of larch plantations under future climate change.(2)Future climate change(increased temperature,precipitation and CO2 concentration)could promote the growth of four larch species.Compared with the current climate,the stand variables showed an increasing trend in the 90 year simulation period with the same trend of RCP 8.5 > RCP 4.5 > current climate.Specifically,the average DBH will increase by 3.01%~105.21%,average height 2.75%~56.73%,stand volume 5.10%~127.46%,total biomass 4.17%~79.19%,mean annual increment 1.47%~71.65%,and net primary productivity 5.67%~35.14%.However,future climate change will accelerate the mortality of four larch species,but the increased range is small(-0.64%~7.13%).The growth and yield tables of four larch species were generated from 3-PGmix model.(3)The response of different larch species to future climate change is different by stand variables,but the overall trend is that under the RCP 4.5 climate scenario,the sensitivity is in the order of larix principis > larix gmelinii > larix olgensis > larix kaempferi;under the RCP 8.5 climate scenario,the sensitivity is in the order of larix kaempferi > larix gmelinii > larix principis > larix olgensis.(4)The response of larch plantations to climate change varied with site levels.With the exception of larix kaempferi,the increased size of stand growth at low site levels was larger than that of high site level;but the increased mortality at high site level was larger than that of low site level.(5)Future climate change would shorten the biological rotations of wood and carbon of four larch species.Compared with the current climate,the biological rotations of wood and carbon of larix kaempferi was shortened by 0.2~0.9 years and 0.3~0.7 years,respectively;larix principis was shortened by 0.3~0.8 years and 0.1~0.7 years,respectively;larix gmelinii was shortened by 0.5~2.2 years and 0.6~2.7 years,respectively;larix olgensis was shortened by 0.2~2.0 years and 0.1~1.5 years,respectively.It can be seen that the impact of climate change on the maturity of larch plantations varied with site levels and tree species.(6)Under the same climate scenario,the effect of thinning on the growth and yield of larch plantations showed the same trend.The stand volume,total biomass,mean annual increment and productivity were the largest and the smallest for stands with long thinning interval and light thinning,and short thinning interval and heavy thinning,respectively.Stand mortality decreased with the increase of thinning intensity and the extension of thinning interval.(7)There were some uncertainties about the effect of thinning and climate interaction on the growth of larch plantations.Compared with the current climate,all larch species under heavy thinning showed positive effects of climate change impact,while moderate and light thinning was not consistent.The interaction between climate change and thinning had no significant effects on stand volume,total biomass,mean annual increment and net primary productivity.Except for Larix kaempferi,the interaction between climate change and thinning has a significant positive effect on stand mortality.To our knowledge,this is the 1st time to apply the process-based 3-PGmix model to explore the growth and yield of four larch species at regional scales under the future climate change.The 3-PGmix model can be effectively used to predict the growth and yield of the four larch species under the climate change.Using the3-PGmix model,the stand growth tables were produced.The model simulated the impact of climate change on the average DBH,average height,stand volume,total biomass,mortality,mean annual increment,net primary productivity and biological rotation of larch plantations in the next 90 years,and the interaction of climate change and thinning on the stand growth.These results are useful for adaptive management of larch plantations in the regions.