Human Impacts On Vegetation Net Primary Productivity In China Since 2000

Human activities have an important impact on the Net Primary Productivity?NPP?of vegetation.In this paper,a potential NPP?PNPP?calculation method based on undisturbed grids was proposed,which provides a new algorithm for the calculation of NPP influenced by human?HNPP?.In this study,China was taken as the study area and the improved CASA model was used to estimate the actual NPP?ANPP?.Based on the coincidence ratio of climate change and NPP change,this paper identified the undisturbed grids to estimate the potential NPP based on Random Forest which named as PNPP_H.Meanwhile,based on the Thornthwaite Memorial model and improved CASA model which based on the FPAR,this paper estimated other potential NPPs which named as PNPP_T and PNPP_F respectively,and then comparing and analyzing above three potential NPP.The results showed that the potential NPP calculation method based on undisturbed grids is more reasonable,and based on this potential NPP,the actual NPP and potential NPP difference method is used to calculate the NPP influenced bu human,and then the temporal and spatial characteristics of the ANPP,PNPP and HNPP were analyzed.Finally,the effect of human activities and climate change on the ANPP change is discussed.Main conclusions are as follows:?1?The overall trend of annual spatial distribution of ANPP in China from 2001 to2017 is decreasing from southeast to northwest.During the study period,the annual mean ANPP was 538.86 gCm^-2a^-1,and the total amount was 5.11 PgCa^-1.In terms of three natural areas,the annual mean ANPP was:Eastern monsoon area>The Tibetan plateau cold area>Arid and semi-arid region of northwest China.The annual mean ANPP in China increased at the rate of 4.22 gCm^-2a^-1.?2?In terms of land use types,the annual mean ANPP of forest in China was the highest,which was 947.32 gCm^-2a^-1,followed by cultivated land,the annual mean ANPP of which was 755.78 gCm^-2a^-1,grassland,water,construction land and desert decreased in turn.?3?From 2001 to 2017,the three potential NPP showed a decreasing trend from southeast to northwest.By spatial comparison of the three potential NPP,the results showed that the potential NPP estimation based on undisturbed grids was the best,the annual mean of which was 529.17 gCm^-2a^-1,showing an increasing trend at the average speed of 1.48 gCm^-2a^-1.?4?The annual mean HNPP was 7.53 gCm^-2a^-1,and the total was 71.42 TgCa^-1,showing a positive influence.During the study period,them mean value of positive HNPP was 69.72 gCm^-2a^-1,and the total was 5.18 TgCa^-1.The mean value of negative HNPP was-64.91 gCm^-2a^-1,and the total was-4.3 TgCa^-1.The annual mean HNPP was:The Tibetan plateau cold area(35.15 gCm^-2a^-1)>Arid and semi-arid region of northwest China(25.12 gCm^-2a^-1)>Eastern monsoon area(-17.41 gCm^-2a^-1).?5?During the study period,annual mean HNPP showed a positive increase trend at a rate of 2.7 gCm^-2a^-1,indicating that the influence of human activities on the vegetation in China is increasing in a positive direction,and the ecological environment is improving better.?6?The area with positive increasing influence of human activities accounted for40.01%of the Chinese land area,accounting for the largest proportion.?7?Among the six scenarios in which the relative contribution of human activities and climate factors to ANPP change is analyzed,scenario 1?The increase of ANPP is co-dominated by climate and human activities?accounted for 41.36%of the Chinese land area,accounting for the largest proportion.In addition,the area dominated by human activities is larger than that dominated by climate factors.?8?Among the relative contribution index of human activities,the region with RCI?0.3 accounts for 70.22%of the national land area,which indicates that the disturbance index of human activities to vegetation growth is small and does not occupy a dominant position in most areas of the nation.From 2001 to 2017,the RCI showed a slow increase trend at the rate of 0.002a^-1,indicating that the disturbance degree of human activities increased slightly,and reached the highest level in 2017.Generally speaking,the potential NPP estimation method based on undisturbed grids proposed in this study is effective and can be used as a supplementary method to estimate the NPP influenced bu human.The study on the influence of human activities on the vegetation NPP in China,and the increase of ANPP caused by human activities and climate factors is the main trend of vegetation change.