地形位指数模型改进及其在植被覆盖评价中的应用

地形作为影响植被覆盖的重要因素，对植被恢复评价以及生态修复规划意义重大。地形位作为测度地形因子综合效应的指标，具有单一地形因子难以比拟的优势。然而，现有地形位指数算法以整个研究区为参照，未考虑空间异质性，难以反映植被生长的局部环境特征。基于地理学第三定律对地理环境相似的强调，融合“空间位置邻近”和“环境特征相似”，对传统地形位模型进行改进：(1)引入局部窗口算法，以突出局部地形特征；(2)在不同生境因子组合下测算地形位指数，以排除环境差异对地形位作用的干扰。案例研究表明，新模型有效提升了地形位指数对植被覆盖水平的解释力度；当考虑生境因子组合，且采用最优窗口时，局部窗口地形位指数与植被覆盖度之间的相关性最高。此外，通过观察不同生境组合下的地形位指数发现，在高热少水阴坡和高热少水阳坡条件下，植被覆盖度与局部窗口地形位指数具有更高相关性；可见，越是水资源相对匮乏区域，植被覆盖对局部窗口地形位的响应越敏感。本文有望为植被恢复评价与规划提供新的指标。

Improvement of terrain niche index model and its application in vegetation cover evaluation

As an important factor affecting vegetation coverage, the terrain is of great importance to vegetation restoration evaluation and ecological restoration planning. The terrain niche index (TNI), a comprehensive index proposed to measure the combined topographic effect, has incomparable advantages over any single terrain factor. However, the whole study area was taken as a unit reference for the TNI calculation in the previous algorithms, which did not consider the spatial heterogeneity of terrain factors. As a result, the old TNI cannot well reflect the local environment of vegetation growth. Inspired by the geographical environment similarity emphasized in the Third Law of Geography, this study integrated the "proximity of spatial location" and the "similarity of environmental characteristics", and modified and improved the traditional TNI model in the following two aspects: (1) local window algorithm was introduced to highlight the local terrain features; and (2) the new TNI was calculated in each habitat unit formed by the combination of different environmental factors to eliminate the interference of environmental heterogeneity on the topographic effect. The case study shows that the improved model can increase the explanatory power of TNI on vegetation coverage, and the correlation coefficient between TNI and vegetation coverage can be maximized when considering the habitat unit and adopting the optimized local window. In addition, among different habitat factor combinations, it can be found that locations with higher temperature values and less precipitation values show a much closer correlation between the new TNI and vegetation coverage, which indicates that the more the water-deficient areas are, the more the sensitive vegetation coverage is to the local terrain conditions. As a result, this study is expected to provide new indicators for vegetation restoration evaluation and planning.