近20年防风固沙重点生态功能区植被动态分析

植被是影响防风固沙生态功能的关键指标，也是检验防风固沙区生态保护成效的重要依据。由2010年国务院《全国主体功能区规划》划定的防风固沙类国家重点生态功能区、国家重点生态功能区转移支付县域综合确定研究范围。基于2000-2019年中分辨率成像光谱仪（MODIS）的叶面积指数（LAI）产品，从生态区和像元两个尺度分析近20年防风固沙重点生态功能区植被的时空变化趋势，并进一步探索气候因子对LAI的影响，以期揭示我国北方风沙区生态系统防风固沙功能的现状，为今后生态保护提供支撑。研究结果表明，2000-2019年间，研究区LAI年平均值呈现东高西低的空间格局，随着时间推移有显著增加趋势，平均增幅为0.03 m² m^-2（10a）^-1（P<0.01）。在生态区尺度，LAI在8个生态功能区均表现出不同程度的增长，且2010-2019年间LAI的增长速率高于2000-2009年的，其中，科尔沁草原生态功能区在20年间呈现最为显著的增加趋势，区域平均增幅为0.1154 m² m^-2（10a）^-1（P<0.01）。在像元尺度，近20年LAI显著增长（P<0.05）的区域面积占整个研究区植被面积的41.6%，其中，83.7%的LAI增长区域为草地，11.2%为耕地。增长区域主要集中在研究区东部，呈片状分布，研究区西部的LAI也有一定程度的增长，增长区域呈带状分布。2010-2019年LAI增长的区域面积为7.7%，明显大于2000-2009年LAI增长的区域面积。气候因子对研究区植被的影响为：研究区东部降水的增加对当地植被生长有正向的促进作用，而温度的影响则在整个研究区都较弱。除自然因素外，人为因素（防风固沙政策实施、农业技术进步等）对防风固沙功能区植被状况的改善也至关重要。研究区LAI的显著增加表明我国北方防风固沙屏障的生态功能在近20年有一定程度的提高。

Spatio-temporal dynamics of vegetation in key ecological function zone of wind-break and sand-fixation over the last 20 years

Vegetation is crucial for wind-breaking and sand-fixing, and is an important basis for testing the ecological protection effect of wind-break and sand-fixation regions. The study area is the national key ecological function zones of wind-break and sand-fixation designated by the National Plan for Major Functional Zones of the State Council in 2010, as well as the county areas of transfer payment for national key ecological function zones. Based on the Moderate Resolution Imaging Spectroradiometer (MODIS) Leaf Area Index (LAI) datasets from 2000 to 2019, this paper analyzed the LAI trend of the study area in both ecological zone scale and pixel scale, and the impacts of climate factors on LAI were also analyzed. The above-mentioned works can reveal the state of ecosystem in ecological function zone for wind-break and sand-fixation, providing advices for ecological protection. The results show that, during 2000-2019, annual year average LAI decreases from east to west across the study areas, and an overall increasing exists as time went by, with a rate at 0.03 m² m^-2(10a)^-1 (P<0.01). At the ecological zone scale, the LAI of the eight ecological function zones increases with various amplitudes, and the increasing trend of LAI from 2010 to 2019 is obviously larger than that in 2000-2009. Among the eight ecological function zones, the Horqin Grassland Ecological Function Zone has the largest increasing amplitude (0.1154 m² m^-2(10a)^-1, P<0.01) over the last 20 years. At the pixel scale, the area with significant increase (P<0.05) in LAI accounts for 41.6% of the vegetated regions in the study area, among which 83.7% is covered by grassland and 11.2% is cropland. Pixels with increasing LAI mainly concentrate in the eastern part of the study area, showing a patchy distribution. LAI in the western part has a slight increase, distributing like a strip. Areas with increase in LAI account for 7.7% during 2010-2019, obviously larger than that in 2000-2009. The impacts of climate factors on vegetation in the study area are as follows:the increase of precipitation facilitates vegetation growth in the eastern parts, while in the western parts, these facilitating effects vanish, and the effect of temperature is weak across the whole study area. Apart from the impacts of climate factors, human interventions (implementation of wind-break and sand-fixation policy as well as the progress of agriculture technology) are also crucial on the improvement of vegetation growth. The LAI dynamics indicate that the ecological function for wind-break and sand-fixation in northern China has been improved.