DOI: 10.5061/dryad.4pf4t
title: Data from: The influence of geomorphic processes on plant distribution and abundance as reflected in plant tolerance curves

description: 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
 different landscapes. Transects are placed on hillslopes in each model
 landscape and used to construct tolerance curves. Results show that
 transect methods that use the distance from the channel to the ridgeline
 as an approximation of soil moisture create variable tolerance curves for
 the same plant both within a single landscape and between different
 landscapes. The reason for these differences is that transects do not take
 into account the 3-dimensional landscape form that explains water
 movement. Landscapes have regions of convexity and flow path divergence
 and regions of concavity and flow path convergence which, along with
 hillslope length, determine contributing area. In addition, hillslope
 curvature results in varying capacities to retain water. However, when the
 topographic index is used instead of hillslope transect position,
 tolerance curves from the same and different landscapes reflect the
 differences the topographic structure has on soil moisture. We thus show
 that traditional methods of direct gradient analysis are not always
 adequate as they do not tend to consider that soil moisture depends on
 hillslope length, curvature, and slope. Furthermore, we show that within
 and between landscapes there are differences in spatial distributions of
 soil moisture that are reflections of the geomorphic processes that
 created them.
description: creep_dinfHillslope transects obtained from the creep-dominated landscape. Obtained using the input file creep.in in the Channel Hillslope Integrated Landscape Development model (CHILD) version RI8.12 (Tucker et al. 2001), and the matlab scripts ridgeline.m, trace_down.m, and trace_up.m. See Ecological Archives for the input and matlab files.overlandflow_dinfHillslope transects obtained from the overland flow-dominated landscape. Obtained using the input file overlandflow.in in the Channel Hillslope Integrated Landscape Development model (CHILD) version RI8.12 (Tucker et al. 2001), and the matlab scripts ridgeline.m, trace_down.m, and trace_up.m. See Ecological Archives for the input and matlab files.