基于“DEM-NDVI-土地覆盖分类”的天山博格达自然遗产地山地垂直带提取与变化分析

本文基于Landsat影像数据获取天山博格达自然遗产地土地覆盖分类,结合归一化植被指数（NDVI）和数字高程模型（DEM）构建“DEM-NDVI-土地覆盖分类”散点图分析研究区植被受海拔和坡向的水热空间变化影响的分布特征,通过概率统计分析提取博格达遗产地山地垂直带,并结合研究区的气温、降水数据和NDVI变化特征分析垂直带变化的原因。研究结果表明：① 本文利用“DEM-NDVI-土地覆盖分类”散点图,揭示了研究区1989年和2016年的NDVI值和分类类别随着海拔上升的变化特征,其中NDVI值随着海拔上升呈现“倒U形”变化,而不同分类类别在一定的海拔区间内呈现出聚集效应,且不同分类类别有明显的高程界限。② 1989年和2016年博格达遗产地山地垂直带分带上限分别为：1278 m和1185 m（温带荒漠草原带）、1784 m和1759 m（山地草原带）、2706 m和2730 m（山地针叶林带）、3272 m和3293 m（高山草甸带）、3636 m和3690 m（高山垫状植被带）。③ 博格达遗产地1989年和2016年山地垂直带受区域气温升高和降雨增加的影响有较为明显的改变,其中温带荒漠草原带最为敏感,其上限变化最大,向下收缩93 m;山地针叶林带的分布范围则向两侧扩张49 m;山地草甸带带宽基本保持不变,但整体上移了约20 m;冰雪带则受到全球气候变暖的影响向上退缩54 m。

Identification and Change Analysis of Mountain Altitudinal Zone in Tianshan Bogda Natural Heritage Site Based on “DEM-NDVI-Land Cover Classification”

The mountain altitudinal zone in Bogda Natural Heritage Site, one of the most typical representatives in the northern slope of Mount Tianshan, reflects the distribution characteristics and change rules of vegetation in the temperate desert region. To obtain the characteristics of the vegetation distribution, several steps have been designed and implemented. Firstly, the Landsat images were classified by supervised classifier for producing land cover classification results. Secondly, the vegetation coverage characteristics in Bogda Natural Heritage Site were described by a special scatterplot which integrated the land cover classification with the Normalized Difference Vegetation Index (NDVI) and Digital Elevation Model (DEM). Thirdly, the quantity ratios of each land cover type were calculated in different altitude ranges using the window-sliding method, and the boundary altitudes of two adjacent zones were identified based on the thresholding analysis of the quantity ratios. Lastly, the attribution analysis of vertical vegetation zone changes was conducted by combing the climate data (temperature and precipitation) and NDVI. The results indicated that: (1) the DEM-NDVI-Land Cover Classification Scatterplot showed the change characteristics of both NDVI and land cover classification with increasing altitude in Bogda: the NDVI changed in an inverted U-shape and the land cover classification displayed agglomeration effect in a fixed altitude range. (2) in 1989 and 2016, the upper and lower boundary altitudes of the bottom-up six vegetation zones were 1278, 1784, 2706, 3272, 3636 and 1185 m, 1759, 2730, 3293, 3690, respectively. (3) during the period of 1989-2016, the mountain altitudinal zones have an obvious response to the rising of the temperature and rainfall. The Temperate Desert Steppe Zone, shrinking downward about 93 m of its upper boundary, was the most sensitive one to the climate changes. The range of Mountain Coniferous Forest Zone expanded by 49 m to both upper and lower directions. The Mountain Meadow Zone monolithic moved up about 20m with an unchanged span, and the Alpine Snow-Ice Zone, retreating upward about 54m of its lower boundary, was affected by the global warming.