Linking fine root and understory vegetation to channel erosion in forested hillslopes of southwestern China

Y Li,Z D Zhang,H Q Yu,J Poesen,N Zhou,G Tian

doi:10.1007/s11104-014-2362-8

Abstract

The forestland understory vegetation reduces concentrated overland flow through infiltration improvement by roots and raindrop interception by surface cover. However, little has been done to quantify the linkages between understory vegetation cover, roots, and channel erosion, and such information can help assessing the role of the reforestation in soil erosion control. In this study, we evaluated the relationships between channel density, root density, and vegetation cover in forested hillslopes of southwestern China. Twelve locations (four slopes and three positions) of forested hillslopes with a wide range of understory degradation due to litterfall extraction and livestock grazing were selected for the study. Channel density as a measure of rill and (small) gully erosion, root density of different diameter classes, and vegetation cover of all types were determined using field measuring, soil coring and the line transect method, respectively. Soil loss rates were estimated using the caesium-137 (137Cs) technique. Rills (depth 0.3 m) with a width 0.5–1.0 m were found at the locations of hillslopes with high understory-degradation. Channel density and soil loss rate increased with the increase in understory-degradation in the forested hillslopes. Simple correlation analysis indicated that channel density was negatively correlated with fine root density (diameter < 1 mm and 1–2 mm) and grass and shrub covers, but not with coarse roots (diam. 2–5 mm and 5–10 mm) and mulch and tree covers. The principal component regression revealed fine root density (diam. <1 mm), shrub and grass covers were the most important predictors for channel density in the forested hillslopes. Tree cover, mulch cover and coarse root density were found to have much less influence on channel density. For the model established from this study using principle component regression, vegetation variables could explain 82 % variance of channel density. We conclude that fine root density and grass and shrub covers are the most important factors in controlling soil erosions in forested hillslopes. These parameters should be taken into consideration in assessing reforestation for soil erosion control in hilly areas such as that in southwestern China or other similar regions.

Highlights

Channel erosion by concentrated overland flow is a global concern as it leads to increased sediment production and land degradation (Poesen et al 1998; Li et al 2004; Valentin et al 2005)
We conclude that fine root density and grass and shrub covers are the most important factors in controlling soil erosions in forested hillslopes. These parameters should be taken into consideration in assessing reforestation for soil erosion control in hilly areas such as that in southwestern China or other similar regions
Principal component analysis (PCA) was used to transform the original vegetation variables into a new set of variables called principal components, which could explain some variations of the data set

Summary

Introduction

Channel (rill and gully) erosion by concentrated overland flow is a global concern as it leads to increased sediment production and land degradation (Poesen et al 1998; Li et al 2004; Valentin et al 2005). Understanding the factors that cause channel initiation in a landscape can lead to development of improved management practices that can increase productivity and ecosystem services of the land (Poesen et al 1998). Channel initiation could be related to a wide range of factors, including rainfall intensity, flow hydraulics, topography, soil texture, surface features, vegetation and land use (Valentin et al 2005; Kirkby and Bracken 2009). Surface vegetation reduces waterinduced soil erosion by intercepting runoff, increasing water infiltration, and retarding flow velocities (Styczen and Morgan 1995). The myriad roles that vegetation cover plays in protecting soils from erosion indicate that vegetation functions in a highly

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