半干旱典型风沙区植被覆盖度演变与气候变化的关系及其对生态建设的意义

中国北方四大沙地（毛乌素沙地、浑善达克沙地、科尔沁沙地、呼伦贝尔沙地）是半干旱地区荒漠化发展的典型地区和荒漠化防治的重点区域。分析四大沙地植被覆盖度的时空演变规律及其对气候要素的响应机制，对保护北方生态脆弱区的生物多样性与生态安全具有重要意义。基于1998—2018年SPOT-VEGETATION的植被覆盖度指数（NDVI）数据，结合相应气候资料数据分析发现：四大沙地NDVI年际波动较大，毛乌素沙地和科尔沁沙地植被覆盖度总体趋于好转态势，分别有75.22%和42.06%的面积植被得到改善，而浑善达克沙地和呼伦贝尔沙地植被覆盖度呈非显著下降趋势，其发生植被退化的面积比例分别为60.04%和51.4%。结合极端气候指数分析表明，呼伦贝尔沙地NDVI与持续湿润指数（CWD）的正相关系数最高（r=0.429），而浑善达克沙地NDVI与持续干旱指数（CDD）的负相关系数最大（r=-0.264），表明呼伦贝尔沙地和浑善达克沙地植被分别对持续湿润和持续干旱事件响应最为敏感。基于不同沙地的植被变化驱动分区，建议在毛乌素沙地非气候驱动区域继续实施禁牧封育和飞播造林技术，而在气候驱动区域主要采取封育措施；在浑善达克沙地实施生态移民和“以地养地”模式；对科尔沁沙地的疏林草原应采取严格的封育措施；在呼伦贝尔沙地要坚持生物措施与工程措施相结合，形成“外围封禁、边缘治理、内部发展”的生态发展格局。

Relationship between vegetation coverage and climate change in semiarid sandy land and the significance to ecological construction

The four major sandy lands in the north of China include the Mu Us Sandy Land,Hunshandake Sandy Land,Horqin Sandy Land and Hulunbuir Sandy Land,where are typical areas for desertification development and key areas for desertification control in semi-arid area.Analysis on the temporal and spatial evolution of vegetation coverage in these four sandy lands and their response mechanisms to climatic change is of great strategic and scientific importance to the protection of biodiversity and ecological security in ecologically fragile areas of north China.Based on the analysis of Normalized Difference Vegetation Index(NDVI)and the corresponding climate data during 1998-2018,it is found that the four major sandy land areas have large inter-annual fluctuations in NDVI.The vegetation coverage of the Mu Us Sandy Land and Horqin Sandy Land generally tend to improve,with 75.22%and 42.06%of the area vegetation being improved,respectively.The vegetation coverage of the Hunshandake Sandy Land and Hulunbeier Sandy Land showed a non-significant decline,the corresponding degraded proportions were 60.04%and 51.4%,respectively.As the four major sandy lands are mainly distributed in typical arid and semi-arid climate zones,the vegetation growth is mainly affected by precipitation,and the synergistic effect of temperature and precipitation cannot be ignored.In addition,the NDVI showed highest positive correlation with continuous humidity index(CWD)in Hulunbuir Sandy Land(r=0.429),while the highest negative correlation coefficient between NDVI and continuous drought index(CDD)was found in Hunshandake Sandy Land(r=-0.264),indicating that the vegetation growth in Hulunbuir Sandy Land and Hunshandake Sandy Land are most sensitive to the continuous humid and continuous drought events,respectively.In the end,based on the vegetation-driven zones of different sandy lands,we suggest that the enclosure and grazing prohibition and aerial seeding afforestation should continue to be implemented in the non-climate-driven areas of the Mu Us Sand Land,and the main measures of enclosure should be adopted in the climate-driven areas.Ecological migration and the“retaining land with land”model should be implemented in Hunshandake Sandy Land;Strict enclosure measures should be taken for the grassland with sparse forest in Horqin Sandy Land while taking into account the development of economic benefits;In the Hulunbuir Sandy Land,we must adhere to the combination of biological and engineering measures to establish an ecological development pattern of“peripheral closure,marginal governance,and internal development”.