Research On The Impact Of Climate Change And Human Activities On The Evolution Of Qilian Mountain Grassland

The research of driving force in the process of grassland evolution is the basis of grassland evolution.Climate change and human activities as grassland in the evolution of the two major driving force,the relative role in long time series under different scales both in the quantitative evaluation of grassland in the evolution of grassland and grassland management mode for the evolution of theoretical research is of great significance.The two major driving factors of climate change and human activity change from qualitative to quantified in the process of grassland evolution,it has laid a solid foundation for accurately studying the dynamic process of grassland evolution in long time series,studying and analyzing the response of grassland change to regional climate change,and based on the status,making grassland development strategy and grassland degradation control mechanism.This study takes the Qilian Mountains as the research area,Based on remote sensing image data,meteorological data and so on,On a monthly basis,through linear regression,CASA model,NDVI data interpolation and trend change of method and model,then analyzed the spatial and temporal variation characteristics and trends of the grassland NPPA(atual NPP)in nearly 30 years of Qilian Mountains;at the same time,combined with the meteorological factors of the same period,the influence of climate change as a driving factor on the regional grassland NPPA was analyzed.Based on residual analysis,With pixels as the unit and build a regression model of climate change and NPPA,then separate the two major driving factors that affect the change in the grassland NPPA,finally,from different time scales,the two major driving factors have been quantitatively analyzed in the process of NPP change in grassland.The conclusions of the study are as follows:(1)Through the establishment of cross period of the unary linear regression model,y=0.8748x+0.0147(R=0.9259 P<0.01),interpolated the data of GIMMS NDVI after 2006.By CASA model simulation of the qilian mountain grassland net primary productivity(NPPA),used for nearly three years the field measured data to validate the simulation results,made a result that the correlation of R2 is very high(R2 ? 0.7539),It shows that the CASA model is applicable to the estimation of the grassland NPPA in Qilian Mountains.In this paper,NPPA is corrected for the estimated cross period.The correction formula is y=1.042x+1.219,and the correlation coefficient is up to 0.982(P<0.01).(2)In the past 1985-2015 years,the NPPA of Qilian Mountains showed a trend of fluctuating growth on the whole,and the growth rate was 2.62gC·m-2a-1.The average NPP has changed between 204.92-336.8 in the past 31 years.The growth trend of NPPA before 2000 was obvious.From 2001 to 2015,the rate of growth slowed obviously after the high speed growth before 2000;the NPPA of the grassland showed obvious unimodal patterns,showing overall spatial distribution pattern decreasing from southeast to northwest on the whole.In the seasonal variation trend,the NPP of the four seasons of Qilian Mountains showed a growing trend,and the growth trend in summer was the most obvious,and the growth rate was slow in spring and autumn.In space,the relative increase in summer is significant and the high value area is located in the middle of tianjun county to east of the north and south axis of qilian county.(3)Between 1985 and 2015,the overall precipitation showed an increasing trend,with a growth rate of 8.5mm/10a.annual precipitation gradually decreases from southeast to northwest in space.The average temperature shows a warming trend,and the growth rate is 0.46/10a,which shows the distribution characteristics of the divergence from the center to the periphery in spatial distribution.According to the years that from 1985 to 2015,the NPPA of qilianshan grassland was consistent with the change of precipitation,with the increase of precipitation,NPPA in the study area also showed an increasing trend except for 2011 and 2015;this corresponds to the annual temperature,on the whole,with the increase of temperature,the NPPA of grassland increased,but in some years the curve of NPPA of grassland was lower than that of the curve of temperature.On the seasonal scale,grassland NPP has the highest response to summer precipitation,Summer precipitation is one of the dominant climatic change of grassland NPPA change.The effect of precipitation on NPPA in qilian mountain area is more significant,but the influence of temperature on it cannot be ignored,especially the temperature change in autumn.(4)Statistics on the NPPH(residual NPP)value from 1988 to 2015,we find that on the whole,the NPPH value table of the Qilian Mountains grassland is on the whole rising trend.In terms of space,the residual NPP values of Qilian County,Gangcha County in the central Qilian Mountains,Datongshan Datong River and Laji Mountain in the east have shown an increasing trend.On an inter-annual scale,human activities made 59.84%of the grassland NPPH in different degrees;In seasonal scale,the trend of NPPH change is more significant in summer,NPPH high value area and tendency rate changes significantly and stability of distribution pattern has the relationship between the performance,the high value area,obvious trend,variation,spatial distribution trend of weak stability.Xining City?Haibei Prefecture was selected as the study area of human activities.The main influencing factors for the NPPA were selected from the six factors of human activities,which were the husbandry population and grain sown area,the correlation coefficient reached-0.652 and-0.824.(5)By setting up four scenarios of climate change and human activity in grassland change area,we calculate two kinds of driving factors and make quantitative statistics and partition at different time scales.The area of improvement in the grassland change area between 1988-2000 and 2000-2012 was far greater than that of the degraded area.From 1988 to 2000,climate change was the dominant factor in improving the grasslands during this period.During the period from 2000 to 2012,human activity was the main driving factor in the change of grassland NPPA during this period.During the period 1988-2015,climate change played a leading role in the change of the grass in qilian mountain.In this long time scale,the coexistence of ecological restoration and unreasonable human behavior on grassland destruction in the Qilian Mountains greatly weakened the promotion effect of climate change on grassland vegetation improvement.The change of NPPA in grassland in the plot area from strong to weak was followed by grain sown area,animal husbandry population,precipitation,and temperature.