生态恢复工程对陕北地区生态系统格局的影响

Impacts of ecological restoration projects on the ecosystem in the Loess Plateau

以生态环境脆弱的陕北地区为研究对象,利用TM遥感影像解译陆表生态系统的分布特征,从生态系统转移矩阵、单一生态系统动态度和综合生态系统动态度等方面探索了生态恢复工程实施20年来研究区生态系统的时空演变规律。同时,利用最小二乘趋势分析法和人类扰动指数分析气候条件和生态恢复工程的驱动机制。研究结果表明:(1)1997—2018年陕北地区生态系统格局发生显著变化,主要表现为林木、草地的面积占比分别增加19.34%和6.91%;耕地面积占比减少22.15%;未利用地面积占比减少5.01%;陕北地区生态系统格局已由生态恢复工程实施前的耕地占主导转化为林木占主导。(2)受退耕还林工程的影响,黄土高原丘陵沟壑区生态系统流转方向主要表现为耕地转化为林木和草地;防风固沙工程促使毛乌素沙漠区域未利用地转化为草地。(3)研究时间段内陕北地区年均气温基本无变化,年降水量显著呈增加趋势,整体向湿润化发展,适合地表植被生长和恢复。在这样的气候背景下,榆林和延安两市生态系统变化速度明显高于铜川市,说明生态恢复工程是研究区生态系统格局演变的主要驱动力,气候背景变化是辅助驱动力。

Remote sensing shows considerable potential for ecological monitoring, ecological restoration and sustainable development. The Loess Plateau has been experiencing reforestation, reducing arable land area since the ecological restoration projects kept on increasing in the past two decades. Those projects were being developed for improvement of the degraded forest and sustainable development, which have resulted in significant changes in the ecological environment and ecological layout of the Loess Plateau. The spatio-temporal evolution of the ecosystem in the Loess Plateau was analyzed based on the TM satellite retrieved land use information. The results showed that:(1) from 1997 to 2018, significant changes have taken place in the ecosystem pattern of the Loess Plateau, mainly represented by an increase of 19.34% and 6.91% in the area of forest and grassland, a decrease of 22.15% in the arable land area, and a decrease of 5.01% in the area of unused land. Ecosystem pattern in the Loess Plateau has shifted from the cultivated land domination to forests domination. The arable land area in the Loess Plateau decreased the most, by a magnitude of 18554.54 km2, which decreases of 61%, mainly converted to forest and grasslands, 11617 km2 and 11442 km2 respectively.(2) During the past two decades, temperature has shown a weak decreasing trend about 0.06 ℃ while precipitation has shown an increasing trend about 57%, with a magnitude of 197 mm, which is suitable for reforestation and vegetation restoration. There were obvious regional differences in ecosystem changes in the Loess Plateau. The overall climate changes were in a direction in favor of vegetation restoration. However, the changes in the regional ecosystem pattern of the Loess Plateau were significantly different. Under such a climatic background, the changes of ecosystems in Yulin and Yan′an were considerably higher than those in Tongchuan, indicating that ecological restoration projects were the main driving for studying changes in ecosystem patterns, and climate background changes were auxiliary driving factor.(3) Affected by the ecological restoration projects, the transfer direction of the ecosystem in the hilly and gully region of the Loess Plateau mainly showed the conversion of arable land into forests and grasslands;the wind and sand fixation projects promoted the conversion of unused land in the Maowusu Desert area into grasslands.(4) The impacts of human activities on the ecosystem were reduced, from 、0.08% to-16.06%, which mainly because of the conversion of farmland to forests, and windbreak and sand fixation projects have transformed sandy land into grassland. The results show that the ecological restoration projects have made a significant reduction in arable and unused land in the Loess Plateau, and that forests and grasslands have been greatly reduced. Implementation of restoration projects was the primary driving force, and climate background changes were auxiliary factors. However, this study has not addressed the quantitative assessment of the contribution of the driving factors, which were also one of the key directions for the future research. Meanwhile, it was found that in the past 10 years, two types of changes have occurred in the Maowusu desert in northern Yulin City. The development of agriculture activities will play a major role in promoting the local grain output and economic growth, but the impact of this change on the effectiveness of desert management needs to be addressed in a future study.