1980—2015年青藏高原植被变化研究

Study on Vegetation Change in the Qinghai-Tibet Plateau from 1980 to 2015

青藏高原地形复杂,气候类型独特,是北半球气候变化的调节器。全球气候变化直接影响植被变化,探讨植被变化对了解青藏高原的环境状况及环境保护与恢复具有重要意义。选取青藏高原作为研究区域,基于1980年和2015年的1 km土地利用数据利用转移矩阵研究植被的转换变化,利用1981—2015年的GIMMS-NDVI数据借助趋势分析法分析土地利用未变化区域的植被覆被变化,并通过相关分析法研究植被变化与气候因子的关系。研究表明:1980—2015年,青藏高原植被的转换变化表现为转入面积大于转出面积,植被面积整体增加。植被类型变化的主要表现形式为农作物和草地面积增加,乔木林地和灌木林面积减少;草地的面积变化最大,农作物、乔木林地和灌木林面积变化很小。从不同植被类型和生态分区来看,植被覆被变化表现为农作物面积较小,分布于半干旱地区,NDVI呈上升趋势;乔木林地位于东南部湿润半湿润地区,生长状况呈现退化趋势;灌木林位于东部边缘和东南部的湿润半湿润和半干旱地区,呈退化趋势;草地分布范围最大,生长情况趋于改善。近35年来,青藏高原的植被覆盖整体趋于好转,低覆盖度、干旱半干旱地区趋于改善,高覆盖度、湿润半湿润地区出现退化。研究时段内,青藏高原趋于暖湿化,NDVI变化与年平均气温、年降水量变化呈正相关,对降水变化更为敏感。不同植被类型对气候变化响应不同,农作物相关系数最高。乔木林地与气温和降水变化呈负相关,农作物和草地则呈正相关,灌木林与降水变化呈正相关,与气温变化呈负相关。

The Qinghai-Tibet Plateau,with its complex terrain and unique climate type,is the regulator of climate change in the Northern Hemisphere.Global climate change directly affects vegetation change.It is of great significance to study vegetation change for understanding the environmental status and protecting and restoring the environment of the Qinghai-Tibet Plateau.The Qinghai-Tibet Plateau was selected as the research area.Based on the 1km land use data of 1980 and 2015,the change of vegetation conversion was studied by using the transfer matrix.The GIMMS-NDVI data from 1981 to 2015 were used to analyze the change of vegetation cover in the unchanged land use area by using trend analysis.The relationship between vegetation change and climate factors was studied through correlation analysis.The results show that from 1980 to 2015,the change of vegetation conversion on the Qinghai-Tibet Plateau is manifested as the transfer-in area is greater than the transfer-out area.The vegetation area increased as a whole.The main manifestations of changes in vegetation types are the increase in the area of crop and grassland,and the decrease in the area of arbor forest and shrub forest.The area of grassland has the largest change,while the area of crop,arbor forest and shrub forest has little change.From the perspective of different vegetation types and ecological zones,the vegetation cover change shows that the crop area is small and distributes in semi-arid regions,and NDVI shows an upward trend.The arbor forest is located in the southeast humid and sub-humid area,and its growth condition shows a trend of degradation.Shrub forest is located in the eastern margin and the southeast of the humid and semi-humid and semi-arid areas,showing a trend of degradation.Grassland distribution area is the largest,and the growth situation tends to improve.In the past 35 years,vegetation coverage on the Qinghai-Tibet Plateau has tended to improve on the whole.Low vegetation coverage and arid and semi-arid areas tend to improve,while high vegetation coverage and humid and sub-humid areas showing degradation.During the study period,the Qinghai-Tibet Plateau tends to be warmer and wetter.The NDVI change is positively correlated with annual mean temperature and annual precipitation,and is more sensitive to precipitation change.Different vegetation types have different responses to climate change.The correlation coefficient of crop is the highest.Arbor forest is negatively correlated with temperature and precipitation change,while crop and grassland are positively correlated.Shrub forest is positively correlated with precipitation change and negatively correlated with temperature change.