The influence of geomorphic processes on plant distribution and abundance as reflected in plant tolerance curves

Ecologists describe plant distribution using direct gradient analysis, by which a tolerance curve of species abundance is described along an environmental gradient (any environmental variable that affects plant distribution). Soil moisture is generally the gradient in low relief areas that explains the most variation. Traditional direct gradient analyses have used terrain structure (i.e. transects up or down hillslopes) as a correlate to soil moisture. Here we use a numerical tectonic and geomorphic process-based landscape development model to create two landscapes with different geomorphic characteristics (i) to demonstrate the influence of geomorphic processes on soil moisture patterns and plant distribution and (ii) to evaluate the effectiveness of transects in describing moisture gradients and tolerance curves on landscapes dominated by creep or overland flow. We use a topographic index to approximate the distribution of soil moisture as it is determined by the shape of these differ...生态学家采用直接梯度分析（direct gradient analysis）来描述植物分布格局，该方法可沿环境梯度（environmental gradient，即任何影响植物分布的环境变量）刻画物种丰度（species abundance）的耐受曲线（tolerance curve）。在低起伏地形区域，土壤水分（soil moisture）通常是解释物种分布变异程度最高的环境梯度因子。传统直接梯度分析方法常以地形结构（即沿山坡上下布设的样带（transects））作为土壤水分的关联替代指标。本研究采用基于构造与地貌过程的数值景观发育模型，构建了两类具有不同地貌特征的景观：其一用于阐明地貌过程对土壤水分格局与植物分布的影响；其二用于评估样带在以蠕变（creep）或坡面流（overland flow）为主导的景观中，刻画水分梯度与物种耐受曲线的有效性。本研究利用地形指数（topographic index）来近似模拟由这些差异（原文未完整表述）所决定的土壤水分分布格局。