黔桂喀斯特山区植被变化及其地形效应

Vegetation change and its topographic effects in the karst mountainous areas of Guizhou and Guangxi

为科学认识喀斯特山区植被变化及其地形效应,基于MODIS NDVI数据,采用统计学方法,系统分析2000-2016年喀斯特山区植被变化的时空特征及其与海拔、地形起伏度、坡度、坡向的关系。研究表明,黔桂喀斯特山区植被绿度中部高,西北及东南较低,年均NDVI随海拔和地形起伏度的增加呈单峰曲线变化,峰值位于400～600 m,NDVI随坡度和坡向的变化不明显;2000-2016年大部分地区NDVI呈增长趋势,其中超过20%的地区呈显著增长(P<0.05),年均增长率约0.0018。西部和东南部绿化趋势最为显著,仅在东北和中东部,NDVI呈下降趋势;NDVI呈增长趋势的比例随海拔的增加而增加,说明该喀斯特山区近年来植被恢复向着良性化方向发展,高海拔植被恢复速率更快,低海拔缓坡处的植被生态建设需要进一步加强。

Rocky desertification is one of the most severe ecological issues that restrict the sustainable development of karst area in southwestern China.Compared with other ecosystems, mountain ecosystem is more sensitive to climate change due to its complex topography. Understanding the variation of vegetation growth associated to topographic factors is critical to promote ecological management in karst mountainous areas.Based on the Moderate Resolution Imaging Spectroradiometer Normalized Difference Vegetation Index (MODIS NDVI)data from 2000to 2016,the spatial-temporal variation of NDVI in the karst mountainous area of Guizhou and Guangxi was analyzed.The topographical factors,including altitude,slope gradient,aspect and relief amplitude were introduced to examine the response of vegetation variation to topographical factors.The results showed that NDVI in the middle of karst mountainous area was higher than that in the northwest and southeast.Averaged NDVI during growing season showed a single-peak curve distribution with altitude,with the largest value (0.67)at an elevation of 400-600m.However,no significant difference was found along the slope and aspect gradient.A greening trend occurred in the karst mountainous area,with an averaged increasing rate of 0.0018yr-1,illustrating that the vegetation restoration in recent years tended to be better.More than 75%of the study area showed an increasing trend of NDVI,and about 20%of the study area,distributed in the western and southeastern parts of the region (southwest Guizhou and central Guangxi),performed a significant increase.Pixels with a decreasing trend of NDVI were only observed in the northeast and middle-eastern parts.The percentage of pixels with a significant increasing trend increased with the elevation gradient. The increased rate is higher at high altitude than that at low altitude,indicating that the ecological construction of vegetation at low altitude with gentle slope should be strengthened. These conclusions provide a scientific basis for the comprehensive treatment of rocky desertification and improvement of fragile ecological environment in the karst mountainous area in a certain sense.