Spatio-temporal Distribution And Driving Forces Of Vegetation Productivity In Northeast China

Northeast China is one of the country's largest forest ecosystems,and it is also located in the region most affected by climate in China.The vegetation structure and growing conditions in this region have a significant impact on climate change and carbon sources/sinks in China and even in the Asia Pacific region.Studying the spatial-temporal distribution pattern and its driving mechanism of net primary productivity(NPP)of terrestrial ecosystems in northeast China is of great significance for understanding and evaluating the distribution and intensity of terrestrial ecosystem carbon budgets in the northeast China.In this paper,the northeast China as the research object,and the simulation of vegetation productivity in site and regional scale were carried out based on the ecological process model(BEPS model).The main research contents and achievements are summarized as follows:(1)To simulate and verificate the vegetation productivity based on BEPS model.High quality model input data were selected to drive the BEPS model to carry on the vegetation productivity estimation in five sites for five vegetation types(CBS-mixed forest,HB-shrub,XLGL-grass,QYZ-evergreen coniferous forest,YC-crop),and the results were compared with observation data at the flux station.The results showed that except the YC station,other four sites have higher precision,but an obvious underestimate phenomenon appear in the YC station,R2is only 0.47.Using vegetation area ratio in mixed pixels to correct the GLASS LAI in crop area and then apply to the model,the R2 was increasing to 0.77,which met the simulation accuracy requirement.(2)Exploring the regional vegetation NPPs verification and the spatio-temporal distribution characteristics of vegetation NPPs in northeast China.To verificate the accuracy of regional NPP through the forest productivity survey data and to analyze the spatial and temporal distribution characteristics of NPPs in the study area based on the NPP results in northeast China from 2003 to 2012 by using the BEPS model.The results showed that the local NPPs decreased from high values in the northeast part to the low values in the southwest part.From 2003 to 2012,the fluctuation of the total annual NPPs are within 0.52?0.58 Pg C/a range,with a mean of 0.55 Pg C/a,the NPPs of forest showed the most notable increase among all vegetation types,followed by the crop with a slight increase.There was no obvious increasing or decreasing trends for the shrub,and the grass had a slight decreasing trend.(3)Exploring the response of vegetation NPPs to climate change in northeast China.To study the impact of climate change on variations of NPPs during growth season based on linear regression slope method,partial correlation analysis and backward analysis methods,and found that the change of temperature is the main factor for the NPPs change of the deciduous needleleaf forest,deciduous broadleaf forest and mixed forest type;Evergreen needleleaf forest are greatly affected by solar radiation.The variation of grass's NPP and precipitation are relatively close.The interannual variations of shrub's and crop's NPPs are more affected by relative humidity.The lag time of NPP response to precipitation prolonged with the growth of vegetation in the growing season,and the lag period of the forest was longer than that of grass and crop,while the accumulated lagging months of the forest were smaller than the accumulated lagging months of grass and crop.