Influence Of Stand Density And Soil Conditions On Carbon Allocation Of Poplar Plantation Based On Improved Process Model In Northern Jiangsu

Forests are important carbon sinks that help mitigate global climate change.Reasonable density regulation is beneficial to select suitable plantation tending methods.It improves the quality of plantation resources and enhances plantation productivity and the overall function of forest ecosystem.Appropriate forest management is conducive to the carbon sequestration capacity of industrial timber forests and plays an important role in the sustainable development of plantation in China.In this paper,the carbon allocation mechanism and the parameters of the existing process model,TRIPLEX-Management model,were improved and corrected by considering the light,water availability,and nutrient limitation factor（W-L-N method）.The model was validated by diameter at breast height（DBH）,tree height,and biomass.The research objects of this paper were poplar plantations,which represents the deciduous broad-leaved forest.The improved model was initialized by using the meteorological data from 1980 to 2019 and the sample plot data from the recent literature.The carbon allocation,DBH,tree height,and biomass of poplar plantation were simulated.Under different soil conditions and planting densities(200,400,600,800,1000,and 1200 stems ha^-1),the changes of stand growth and biomass of poplar plantation were explored.The aim is to reveal the effects of density regulation on stand growth and biomass.The main results were as follows:（1）The improved model can better simulate the dynamic changes of carbon in poplar plantation ecosystem in northern Jiangsu,and the model had good performance.The average absolute error（MAE）and normalized root mean square error（NRMSE）of DBH,tree height,aboveground biomass,and underground biomass of the improved model were lower than those of the original model,and the Willmott indexes of agreement（d）of each variable were higher than those of the original model.The simulation results of the model generally reflected the carbon dynamic changes of forest ecosystem under different densities,indicating that the model can be applied to the region.（2）The increase of density was beneficial to stem allocation,and the response of mature forest to density change was more obvious than that of young forest.The increase of density led to the decrease of average DBH,tree height.The responses of aboveground biomass to density were not significantly correlated,showing an increasing and then decreasing trend.Under different soil conditions,the response of each parameter to density was similar with the change trend of forest age.Except tree height,DBH and biomass had little difference with the increase of density under two soil conditions.This study proved that the improved model can accurately simulate the impact of density change on stand dynamics.Under the condition of low density(approximately 400 stems ha^-1),the growth was the best in poplar plantation in northern Jiangsu,and the variation of each variable was small at 800 stems ha^-1.In actual production,appropriate afforestation density or thinning measures can be selected according to forest cultivation objectives.Furthermore,the process model can be used to explain the productivity of plantation and the related problems in timber production in the future,which would provide the expected theoretical basis and data support for forest management,and reduce the cost of long-term test of forest management.