20世纪90年代以来中国西南地区土地覆被变化

Analysis of land cover changes in southwestern China since the 1990s

西南地区是我国重要的生态安全屏障区,也是气候敏感区和生态脆弱区。20世纪90年代以来,西南地区土地覆被发生了巨大变化,对生态环境和生态系统服务功能产生重大影响。基于全国30 m土地覆被数据集,分析了近20 a来西南地区土地覆被格局、变化及驱动因素。同时,基于MODIS-NDVI数据,利用像元二分模型估算了2000—2010年250 m分辨率年最大植被覆盖度,对森林、灌丛和草地的植被覆盖度变化进行分析。结果表明:1)2010年西南地区土地覆被以森林和草地为主,分别占总面积的29.08%和24.11%。2)1990—2010年西南地区森林、湿地和人工表面分别增加1.39%、5.86%和48.57%,灌丛、耕地和裸露地分别减少2.12%、2.88%和0.64%,变化的区域主要集中在生态建设重点区、城市圈、地震灾区、三峡库区、三江源区、青藏高原东南部和云南南部。3)2000—2010年西南地区森林、灌丛和草地植被覆盖度呈增加趋势的面积分别占26.54%、32.53%和28.87%,但汶川地震重灾区、横断山区、云南南部等地的森林及灌丛植被覆盖度下降,青藏高原东南部、川西高原草地退化。近20 a来,尽管气候变化对西南地区的土地覆被有一定影响,但人类活动仍然是导致其变化及时空差异的主要原因。

Southwestern China is an important ecological barrier and the major area supplying water to our country and most of East Asia. In light of the impacts of global change, rapid economic development, excessive resource utilization, and a series of ecological construction projects, land cover of southwestern China has changed significantly over the last 20 years. This has had great consequences for the coo-environment. After assessing land cover datasets of China in 1990, 2000, and 2010, we propose a land cover classification system that is appropriate for southwestern China. We analyze the spatial- temporal patterns, changing characteristics, and potential causes. In addition, we estimate fractional vegetation cover from 2000 to 2010 using the dimidiate pixel model, based on MODIS-NDVI data. Results show that： 1 ） in 2010, forest was the dominant land cover type, occupying 29.08%, followed by grassland, which covered 24.11%. 2） From 1990 to 2010, areas of forest, wetland, and artificial surface increased by 1.39%, 5.86% and 48.57%, respectively, but areas of shrubland, arable land, and barren land decreased by 2.21%, 2.88% and 0.64%, respectively. The conversion areas are mainly distributed in the regions where the ecological restoration programs are carried out, the urban circle, the earthquake stricken area, the Three Gorges Reservoir Region, the Three-River Headwater on Qinghai-Tibet Plateau, and the southern Yunan province. 3） The changes in fractional vegetation cover of forest, shrub and grassland showed an overall upward trend in 2000s, but forest and shrub showed a trend of degradation in the Wenchuan earthquake-stricken area, Hengduan Mountains, and southern Yunnan province; grassland also deteriorated in the southeastern Tibet Plateau and western Sichuan Plateau. In summary, in the last two decades, although climate change has affected land cover, policy regulation and economic driving forces are still the primary causes of land cover changes across southwestern China.