Analysis Of Grassland Degradation And Driving Forces In Qilian Mountain From 1986 To 2017

Qilian mountain are located in the northeast edge of Qinghai-Tibet plateau,which is an important ecological safety barrier in northwest China.Grassland ecosystem is one of the main ecosystems in Qilian mountain,which plays an important role in maintaining the ecological balance and stability of Qilian mountain.The study of grassland degradation and its driving force in Qilian mountain area is of great significance to the protection and rational utilization of grassland resources in Qilian mountain area.In this paper,Landsat NDVI time series data from 1986 to 2017 were used as the data source,and spatial analysis and mathematical statistical analysis methods were used to analyze the temporal and spatial change characteristics of grassland coverage,grassland degradation status and dynamic changes of grassland degradation in different periods in Qilian mountain area.Based on the analysis of climatic factors and human activities,the main driving forces of grassland degradation in Qilian mountain are summarized as follows:(1)The grassland coverage increased significantly from 1986 to 2017,with the maximum and minimum values appearing in 1987 and 2005.In terms of spatial distribution,the high value of grassland coverage was distributed in the eastern and middle sections with good vegetation growth conditions,while the low value was mainly distributed in the western section of Qilian mountains,which showed a decreasing spatial distribution pattern from east to west on the whole.In terms of spatial variation,the increasing area of grassland coverage in Qilian mountain area was mainly distributed in the middle and west part of Qilian mountain area,and the significantly decreasing area was mainly distributed in the east part of Qilian mountain area,and the increasing area was larger than the decreasing area.Compared with the eastern part,the grassland coverage in the western part of Qilian mountain fluctuates greatly from year to year and is more vulnerable to climate change and human activities.(2)The average grassland degradation index in Qilian mountain from 1986 to 2017 was 1.97,which was in a state of mild degradation.From the perspective of different periods,the period from 1986 to 1995 was the most significant period of grassland degradation,which was dominated by severe degradation.The period from 1996 to 2005 was a stable period of grassland degradation.The grassland degradation was still mainly severe degradation,but the proportion decreased.The period from 2006 to 2017 was a period of significant improvement in grassland degradation.Grassland degradation was mainly mild degradation,while the proportion of grassland with moderate degradation and severe degradation was reduced.From 1996 to 2005,compared with 1986 to 1995,the transfer of grassland degradation grade was mainly from mildly degraded grassland to non-degraded grassland,and from moderately degraded grassland to mildly degraded grassland.From 2006 to 2017,compared with 1986 to 1995,there were mainly transfers from mildly degraded grassland,moderately degraded grassland to non-degraded grassland,and from severely degraded grassland to mildly degraded grassland.(3)There was a significant partial correlation between grassland coverage and average air temperature in Qilian mountain from 1986 to 2017,and a weak correlation between the partial correlation and precipitation,indicating that air temperature was the main limiting factor for grassland growth in Qilian mountain.The residual analysis was used to separate the influence of climate factors and human activities on the grassland coverage,and it was found that the grassland in Qilian mountain area was mainly affected by human activities,and the positive interference of human activities on the grassland was greater than the negative interference of human activities on the grassland.