Identification of degradation factors in mountain semiarid rangelands using spatial distribution modelling and ecological niche theory

This paper presents an approach to studying rangeland degradation by using remote sensing data, geographic information systems, and ecological niche theory. The role of environmental factors and land use in the spatial distribution of degraded rangelands in the Central Caucasus was assessed. Degradation stages were modelled in R using ENVIREM predictors, VIF test to select noncorrelated variables, ENMeval package to select the optimal model parameters, and the Maxent method to develop distribution models in the dismo package. Selected models had AUCtest, AUCtrain and CBI values close to 1, deltaAICc and AUCdiff values close to 0, and quite low AICc values. Environmental predictors of climate type (Thornthwaite aridity index and Emberger’s pluviothermic quotient) were explanatory variables for least disturbed rangelands, while topography (Terrain roughness index) largely explained the distribution of most disturbed grasslands. Quantitative (Schoener’s D) and graphical (Kernel density estimation, analysis of predictive maps) assessment revealed a significant overlap of ‘ecological niches’ and potential ranges of grasslands at different degradation stages, which indirectly supports the hypothesis of the important role of overgrazing in their degradation. Livestock management is likely to help restore disturbed mountain meadow steppes to steppe grasslands. Restoration of the arid shrub ecosystems to steppe grasslands or meadow steppes probably requires additional agricultural practices.

本文提出了一种结合遥感数据、地理信息系统（Geographic Information Systems, GIS）与生态位理论的牧草地退化研究方法，旨在评估中高加索地区退化牧草地空间分布格局中环境因子与土地利用的作用。本研究基于R语言开展退化阶段建模：采用ENVIREM变量集作为预测因子，通过方差膨胀因子检验（Variance Inflation Factor, VIF）筛选无相关性变量，借助ENMeval软件包选取最优模型参数，并利用dismo软件包中的Maxent方法构建分布模型。所筛选得到的模型，其测试集AUC值、训练集AUC值与连续Boyce指数（CBI）均接近1，ΔAICc与AUC差值（AUCdiff）均接近0，且修正赤池信息准则（AICc）值整体较低。对于受干扰程度最低的牧草地，气候型环境预测因子（汤斯威特干旱指数与恩伯格雨热系数）为其主要解释变量；而地形因子（地形粗糙度指数）则在很大程度上解释了受干扰程度最高的草地的空间分布。通过定量（舍恩氏D指数，Schoener’s D）与可视化（核密度估计、预测地图分析）评估发现，不同退化阶段草地的"生态位"与潜在分布范围存在显著重叠，这间接支持了过度放牧在草地退化中发挥重要作用的假说。家畜管理措施或可帮助将受干扰的山地草甸草原恢复为典型草原草地；而将干旱灌丛生态系统恢复为典型草原草地或草甸草原，则可能需要辅以额外的农业调控手段。