黄土高原长武县域植被变化季相趋势及影响因素

黄土高原地区植被生长改善情况已被广泛证实,评价县域季节尺度的植被覆盖变化及影响因素有助于针对性识别植被改善时空效果。本文基于2000-2012年MODIS NDVI数据和Sen+Mann-Kendall模型,对陕西省长武县季相植被覆盖变化趋势的影响因素进行分析,研究结果显示:①2000-2012年长武县的NDVI值呈波动上升趋势,增速为0.064/10a,其中2000-2004年增加最为明显;②长武县植被覆盖总体增加,呈减少趋势区域主要分布在城镇化和工业化快速发展的县城周边;平缓波动趋势区域在空间分布上较集中于北部耕地;③2000-2012年间长武县夏季植被改善情况最为显著;秋季植被改善状况次之;春季改善状况较夏秋弱,北部区域植被覆盖减少像元数增多;④气温和降水的变化促进了植被改善,其中在年际尺度降水为主要影响因素;在季相尺度春季降雨对植被生长具有最显著作用;月际尺度降水的改变对植被生长的影响较小,而气温因素对植被生长的影响较大。不仅退耕还林工程对长武县植被改善有积极影响,农用地撂荒对植被恢复的作用也值得考量。

Trends and factors influencing vegetation seasonal dynamics in Changwu County on the Loess Plateau

Vegetation dynamics across the Loess Plateau,China have been widely observed. The evaluation of vegetation cover change and driving factors at the county level and seasonal scale is useful to evaluate the specific effects of vegetation restoration. Based on MODIS-NDVI data from 2000 to 2012,supplemented by Sen+Mann-Kendall modeling,this study analyzed trends in vegetation cover change in Changwu County,and determined climatic driving factors. We found that the interannual average value of NDVI of the study area was increased with a linear tendency of 0.064/10a;the ecological restoration project achieved remarkable results in Changwu County from 2000 to 2012. Vegetation cover showed an increasing trend in most areas of Changwu County. The number of pixels decreasing was small and mainly distributed in Dizhang town and Zhaoren town resulting from urbanization and industrialization. Trends in vegetation cover changes were different between seasons over the 13 years of data and vegetation improvement was most significant in summer. Although vegetation improvement was apparent in autumn,the area was smaller than in summer. Vegetation improvement in spring was weaker than in summer and autumn. The number of decreasing pixels was large in this season,and mainly distributed in the north of the study area. There was a correlation between vegetation growth and temperature/precipitation. Precipitation was the dominant natural factor driving annual vegetation improvement in Changwu County. Spring rain had a significant influence on vegetation growth. The response of vegetation growth to temperature had a time lag of one month. The effect of precipitation on vegetation growth was relatively small at the month scale,and there was no time lag effect because of irrigation as a human adaption can alleviate the threat of low precipitation. Besides land exploitation which had a negative effect on vegetation growth,planting and mitigation can benefit vegetation improvement. The Grain for Green project should have a positive effect on vegetation improvement in Changwu County.