黄土高原丘陵沟壑区植被覆盖度变化监测

  目的  研究黄土高原水土流失严重区域实施“三北”(西北、华北和东北)防护林、退耕还林等林业生态工程以来的植被变化，为制定合理的生态修复和管理对策提供依据。  方法  以陕西省延安安塞区为例，基于Landsat TM/OLI影像，运用像元二分法估算2000和2017年的植被覆盖度，结合海拔、坡度和坡向分析其地形分异特征。  结果  ①安塞区平均植被覆盖度从2000年的24.98%增长到2017年的53.34%，显著提高；②植被覆盖度变化中极显著增加面积占比最大，为44.70%，集中在河流沿岸；③2000年植被覆盖度随海拔升高逐渐减小，2017年随海拔升高先增加后减小。2000和2017年植被覆盖度随坡度先增加后减少，在坡度25°~35°出现最大值。植被覆盖度随坡向的变化从大到小依次为阴坡、半阴坡、半阳坡、阳坡；④海拔＜1 300 m，坡度15°~35°，平地、阴坡和半阴坡水热条件好，植被恢复容易，高植被覆盖度面积比例最大。  结论  2000?2017年安塞区植被呈改善趋势，海拔、坡度和坡向等地形条件下植被覆盖度存在差异，生态恢复要因地制宜制定对策。图2表6参27

Monitoring of vegetation coverage change in hilly and gully regions on the Loess Plateau

  Objective  The present study is to analyze the vegetation changes in areas with severe soil erosion on the Loess Plateau since the implementation of forestry ecological projects such as the Three-north (northwest, north and northeast) Shelterbelts and Conversion of Farmland to Forests, so as to provide basis for formulating reasonable ecological restoration and management countermeasures.  Method  Taking Ansai District of Yan’an City in Shaanxi Province as an example, the vegetation coverage in 2000 and 2017 was estimated by pixel dichotomy based on Landsat TM/OLI image, and topographic differentiation characteristics were analyzed in combination with altitude, slope and slope direction.  Result  (1)Vegetation coverage significantly increased from 24.98% in 2000 to 53.34% in 2017. (2)The proportion of vegetation coverage with extremely significant increase in the study area accounted for 44.70%, which was concentrated along rivers. (3)In 2000, the vegetation coverage gradually decreased with the increase of altitude. In 2017, the vegetation coverage increased first and then decreased with the increase of altitude. In 2000 and 2017, the vegetation coverage increased first and then decreased as the slope increased, and reached its maximum value at the slope of 25°?35°. The order of vegetation coverage from large to small with the change of slope direction was shady slope, semi shady slope, semi sunny slope, and sunny slope. (4)When the altitude was less than 1 300 m and the slope was 15°?35°, flat land, shady and semi shady slopes had good water and heat conditions, with easy vegetation recovery and the largest proportion of high vegetation coverage area.  Conclusion  The vegetation in Ansai District showed a trend of improvement from 2000 to 2017, with differences under terrain conditions such as altitude, slope, and slope aspects. Ecological restoration countermeasures should be formulated based on local conditions. [Ch, 2 fig. 6 tab. 27 ref.]