Coupling effects of topography and the spatial distribution of cypress
on surface runoff coefficient on a steep forested slope in southwest
China
Abstract
Interactions between topography and the spatial distribution of cypress
give rise to the spatial heterogeneity of surface runoff on steep
forested slopes in southwest China. To reduce surface runoff and improve
the water conservation capacity of cypress forests, the coupling effects
of topography and the spatial distribution of cypress on surface runoff
coefficient were studied through the Structural Equation Modeling (SEM)
and the Response Surface Method (RSM) based on twelve natural runoff
plots. Results showed that the surface runoff coefficient increased
monotonically with the increase of the composite index of topography
(topographic relief× runoff path density/ surface roughness), and
increased first and decreased later with the increase of the composite
index of the spatial distribution of cypress (stand density of cypress×
contagion index of cypress). To reduce surface runoff coefficient from a
larger value (>0.5) to less than 0.3, two strategies of
stand structure adjustment could be adopted, including only increasing
the stand density of cypress or increasing both the stand density and
the contagion index of cypress, and which strategy should be adopted
depended on the initial stand density of cypress. When the initial stand
density of cypress was relatively low (<20 ind/100m2), the
first step was to increase the stand density of cypress, and until the
stand density of cypress reached to a moderate level (20-50 ind/100m2),
adjusting the spatial structure of cypress from relatively regular to
relatively clumped could reduce surface runoff coefficient to a greater
extent.