| Grassland plays an important role in global carbon cycle and climate regulation.In recent decades,with the aggravation of human activities and climate change,grassland ecosystem is threatened by a large area of degradation.Climate change and human activities are the most important factors for grassland change,and the relative role how to quantitatively assess the two factors on grassland productivity from the grid scale has important theoretical significance to understanding the driving mechanism of grassland degradation in different areas of grassland degradation and recovery.In this study,on the use of NDVI data,meteorological data,and adopting the methods of data interpolation,CASA model,Thornthwaite model,linear regression model and so on,three kinds of NPP were analyzed in different ecological regions of Qinghai Province.we discriminated and quantified the effects of climate change and anthropogenic activities on alpine grassland ecosystem in the Qinghai and determined the dominant grassland restoration area and the dominant degradation area by the percentage of the 4 ecological factors.According to the distribution of the dominant grassland restoration area and the dominant degradation area,Xining,Maduo and Wulan county were represented the human led recovery type,climate recovery and grassland degradation area,respectively.Based on the data of social factors and meteorological data,the main driving factors and contribution ratio of grassland degradation and restoration in 3 administrative units were determined.The following conclusions are concluded:(1)The linear model was established by using the GIMMS-NDVI and MODIS-NDVI in the cross period from 2001-2006.The significance test(R=0.984,P<0.01)was best,which showed that the regression model was feasible for the interpolation of the data.We can see that Qinghai province has warm climate phenomenon,the increase rate of precipitation,temperature and solar radiation was 15.25mm/10a,0.56 ?/10a,12.15MJ/M2,respectively.The annual NDVI showed an overall increasing trend,the increase rate of NDVI in spring and summer was higher than that in autumn and winter in nearly 30 years.(2)The simulated of the CASA model and measured values passed the significance test(R=0.841,P<0.001),which showed the feasibility of the model in Qinghai province.The model was established by using the two kinds of NPPA in the cross period,which passed the significance test(R=0.980,P<0.01).In the last 30 years,the average NPPA of grassland was 112.94gC/m~2/a,the NPPA were 105.02gC/m~2/a and 121.99gC/m~2/a in the first 16year and the last 15-year respectively.(3)By analyzing the trend of NPPA,NPPP and NPPH in the past 30 years,it can be found that the three NPP were different in different ecological regions of 1985-2000 and 2001-2014.For NPPA,I(The Qaidam Basin Desert Ecological region),II(Alpine region),?I(The Three-river headwaters region),IV(Qilian Mountains ecological region)were increased from 1.22gC/m~2/a to 1.49gC/m~2/a,from 0.58gC/m~2/a to 0.69gC/m~2/a,1.36gC/m~2/a to 1.59gC/m~2/a,1.53gC/to 2.09gC/m~2/a m~2/a,respectively.For NPPP,I(The Qaidam Basin Desert Ecological region),II(Alpine region)were increased from-1.61gC/m~2/a to 2.41gC/m~2/a,0.75gC/m~2/a to 6.31gC/m~2/a,respectively.III(The Three-river headwaters region)and IV(Qilian Mountains ecological region)Showed a slight decrease trend to moderate increase trend.For NPPH,I(The Qaidam Basin Desert Ecological region),II(Alpine region),III(The Three-river headwaters region),IV(Qilian Mountains ecological region)were increased from was decreased from-1.63gC/m~2/a to-3.76gC/m~2/a,increased from 0.67gC/m~2/a to 2.01gC/m~2/a,increased from-1.03gC/m~2/a to 4.58gC/m~2/a,decreased from-1.69gC/m~2/a to-5.01gC/m~2/a,respectively.(4)According to the trend of NPPA,the degradation of grassland in Qinghai province declined from 2000 to 18.71%before 2000 after 12.9%,the proportion of grassland restoration increased from 81.29%to 87.1%.Only the degraded area of II(Alpine region)was increased,and the other 3 ecological regions were reduced.According to the contribution of climate change and human activities in grassland degradation and restoration,the dominant and degraded dominance of Qinghai Province was determined.In the dominant grassland restoration,Human dominant restoration area includes I(The Qaidam Basin Desert Ecological region),III(The Three-river headwaters region)and IV(Qilian Mountains ecological region),climate dominant restoration area includes II(Alpine region)from 1985 to 2000;After 2001 year,Human dominant restoration area includes I(The Qaidam Basin Desert Ecological region),climate dominant restoration area includes II(Alpine region)and lII(The Three-river headwaters region).In the dominant degradation area,human and climate dominant restoration area includes II(Alpine region)and IV(Qilian Mountains ecological region),climate dominant restoration area includes I(The Qaidam Basin Desert Ecological region)and IV(Qilian Mountains ecological region);After 2001 year,climate dominant restoration area includes I(The Qaidam Basin Desert Ecological region),and the other 3 ecological regions are the dominant degradation type.(5)According to the dominant type distribution area,it is determined that the three administrative units represent the respective types of degradation and recovery.Xining and Maduo counties represent the dominant grassland restoration area and the climate-dominated recovery region,and the Wulan County represents the grassland degraded region.The main driving force of Xining grassland restoration was the graincrop,its contribution rate was 43.55%,the second driving factors was livestock population,its contribution rate was 26.49%,the third driving factors was precipitation,its contribution rate was 22.70%,Humans have effectively improved the local pastures by returning farmland to grass and reducing the pressure on grassland populations;The maximum driving force of grassland restoration in Maduo County is precipitation,and its contribution rate is 54.61%,the second driving force factor is temperature,its contribution rate is 25.70%.Natural contribution rate was 80.31%,which is much higher than that of human factors;The contribution rate of grassland degradation in Wulan County was 39.83%,the second driving force was the first GDP,its contribution rate was 35.14%,the third driving force was temperature,its contribution rate was 16.93%.It can be seen that both human activities and climate change have a significant negative impact on the growth of grassland in Wulan. |
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