A Review of the Mechanical Effects of Plant Roots on Concentrated Flow Erosion Rates. Vannoppen, W., Vanmaercke, M., De Baets, S., & Poesen, J. 150:666–678.
A Review of the Mechanical Effects of Plant Roots on Concentrated Flow Erosion Rates [link]Paper  doi  abstract   bibtex   
Living plant roots modify both mechanical and hydrological characteristics of the soil matrix (e.g. soil aggregate stability by root exudates, soil cohesion, infiltration rate, soil moisture content, soil organic matter) and negatively influence the soil erodibility. During the last two decades several studies reported on the effects of plant roots in controlling concentrated flow erosion rates. However a global analysis of the now available data on root effects is still lacking. Yet, a meta-data analysis will contribute to a better understanding of the soil-root interactions as our capability to assess the effectiveness of roots in reducing soil erosion rates due to concentrated flow in different environments remains difficult. The objectives of this study are therefore: i) to provide a state of the art on studies quantifying the effectiveness of roots in reducing soil erosion rates due to concentrated flow; and ii) to explore the overall trends in erosion reduction as a function of the root (length) density, root architecture and soil texture, based on an integrated analysis of published data. We therefore compiled a dataset of measured soil detachment ratios (SDR) for the root density (RD; 822 observations) as well as for the root length density (RLD; 274 observations). A Hill curve model best describes the decrease in SDR as a function of R(L)D. An important finding of our meta-analysis is that RLD is a much more suitable variable to estimate SDR compared to RD as it is linked to root architecture. However, a large proportion of the variability in SDR could not be attributed to RD or RLD, resulting in a low predictive accuracy of these Hill curve models with a model efficiency of 0.11 and 0.17 for RD and RLD respectively. Considering root architecture and soil texture did yield a better predictive model for RLD with a model efficiency of 0.37 for fibrous roots in non-sandy soils while no improvement was found for RD. The unexplained variance is attributed to differences in experimental set-ups and measuring errors which could not be explicitly accounted for due to a lack of additional data. Based on those results, it remains difficult to predict the effects of roots on soil erosion rates. However, by using a Monte Carlo simulation approach, we were able to establish relationships that allow assessing the likely erosion-reducing effects of plant roots, while taking these uncertainties into account. Overall, this study demonstrates that plant roots can be very effective in reducing soil erosion rates due to concentrated flow. [Excerpt: Conclusions] Vegetation can be used to reduce soil degradation by soil erosion processes. This study showed that plant roots can be very effective in controlling soil erosion rates due to concentrated flow. A combination of a well-established vegetation cover together with a dense root system in the topsoil is therefore most effective and recommended to protect the soil against soil erosion processes by water. The erosion-reducing potential of plant roots can be explained by their indirect negative effect on soil erodibility through affecting various soil properties (e.g. aggregate stability, cohesion, organic matter content, infiltration rate and moisture content). However both the environment and management practices have to be taken into account as they influence the effectiveness of plant roots in reducing soil erosion rates. Analysis of a global dataset based on published data showed that the decrease in SDR as a function of RD or RLD could be best described by a Hill curve model. Root architecture and soil texture were further considered as an attempt to improve the models. This resulted in better predictive models for RLD (for fibrous roots in non-sandy soils) while no improvement could be observed for RD. Consequently, it remains difficult to predict the erosion-reducing effects of plant roots on concentrated flow erosion rates as still a large part of the variance remains unexplained. Results of the Monte Carlo analyses ( Fig. 5) present confidence intervals on estimated SDR values for the proposed models that should be used as an estimation of the uncertainty range. As such, the established relationships between root (length) density and the soil detachment ratio allow for meaningful estimations of the mechanical effects of plant roots on concentrated flow erosion rates. The advantage of this approach is that the results of this study can be extrapolated to different environments to examine the likely root effects on erosion rates, as we implicitly take into account the variability in root and soil characteristics. [\n] As tap root systems are less effective in controlling soil erosion compared to fibrous roots, we furthermore prefer the use of RLD as root variable as it indirectly takes into account the root architecture. The influence of soil texture on erosion-reducing potential could not be demonstrated due to a lack of sufficient data on the erosion-reducing potential of plant roots in different soil textures. More empirical studies are needed to examine the role of soil texture on the erosion-reducing potential. Moreover, a more accurate global database is needed to unravel the influence of additional soil, root and environmental variables on the erosion-reducing potential of plant roots and to improve the predictive quality of the models.
@article{vannoppenReviewMechanicalEffects2015,
  title = {A Review of the Mechanical Effects of Plant Roots on Concentrated Flow Erosion Rates},
  author = {Vannoppen, W. and Vanmaercke, M. and De Baets, S. and Poesen, J.},
  date = {2015-11},
  journaltitle = {Earth-Science Reviews},
  volume = {150},
  pages = {666--678},
  issn = {0012-8252},
  doi = {10.1016/j.earscirev.2015.08.011},
  url = {https://doi.org/10.1016/j.earscirev.2015.08.011},
  abstract = {Living plant roots modify both mechanical and hydrological characteristics of the soil matrix (e.g. soil aggregate stability by root exudates, soil cohesion, infiltration rate, soil moisture content, soil organic matter) and negatively influence the soil erodibility. During the last two decades several studies reported on the effects of plant roots in controlling concentrated flow erosion rates. However a global analysis of the now available data on root effects is still lacking. Yet, a meta-data analysis will contribute to a better understanding of the soil-root interactions as our capability to assess the effectiveness of roots in reducing soil erosion rates due to concentrated flow in different environments remains difficult. The objectives of this study are therefore: i) to provide a state of the art on studies quantifying the effectiveness of roots in reducing soil erosion rates due to concentrated flow; and ii) to explore the overall trends in erosion reduction as a function of the root (length) density, root architecture and soil texture, based on an integrated analysis of published data. We therefore compiled a dataset of measured soil detachment ratios (SDR) for the root density (RD; 822 observations) as well as for the root length density (RLD; 274 observations). A Hill curve model best describes the decrease in SDR as a function of R(L)D. An important finding of our meta-analysis is that RLD is a much more suitable variable to estimate SDR compared to RD as it is linked to root architecture. However, a large proportion of the variability in SDR could not be attributed to RD or RLD, resulting in a low predictive accuracy of these Hill curve models with a model efficiency of 0.11 and 0.17 for RD and RLD respectively. Considering root architecture and soil texture did yield a better predictive model for RLD with a model efficiency of 0.37 for fibrous roots in non-sandy soils while no improvement was found for RD. The unexplained variance is attributed to differences in experimental set-ups and measuring errors which could not be explicitly accounted for due to a lack of additional data. Based on those results, it remains difficult to predict the effects of roots on soil erosion rates. However, by using a Monte Carlo simulation approach, we were able to establish relationships that allow assessing the likely erosion-reducing effects of plant roots, while taking these uncertainties into account. Overall, this study demonstrates that plant roots can be very effective in reducing soil erosion rates due to concentrated flow.

[Excerpt: Conclusions]

Vegetation can be used to reduce soil degradation by soil erosion processes. This study showed that plant roots can be very effective in controlling soil erosion rates due to concentrated flow. A combination of a well-established vegetation cover together with a dense root system in the topsoil is therefore most effective and recommended to protect the soil against soil erosion processes by water. The erosion-reducing potential of plant roots can be explained by their indirect negative effect on soil erodibility through affecting various soil properties (e.g. aggregate stability, cohesion, organic matter content, infiltration rate and moisture content). However both the environment and management practices have to be taken into account as they influence the effectiveness of plant roots in reducing soil erosion rates. Analysis of a global dataset based on published data showed that the decrease in SDR as a function of RD or RLD could be best described by a Hill curve model. Root architecture and soil texture were further considered as an attempt to improve the models. This resulted in better predictive models for RLD (for fibrous roots in non-sandy soils) while no improvement could be observed for RD. Consequently, it remains difficult to predict the erosion-reducing effects of plant roots on concentrated flow erosion rates as still a large part of the variance remains unexplained. Results of the Monte Carlo analyses ( Fig. 5) present confidence intervals on estimated SDR values for the proposed models that should be used as an estimation of the uncertainty range. As such, the established relationships between root (length) density and the soil detachment ratio allow for meaningful estimations of the mechanical effects of plant roots on concentrated flow erosion rates. The advantage of this approach is that the results of this study can be extrapolated to different environments to examine the likely root effects on erosion rates, as we implicitly take into account the variability in root and soil characteristics.

[\textbackslash n] As tap root systems are less effective in controlling soil erosion compared to fibrous roots, we furthermore prefer the use of RLD as root variable as it indirectly takes into account the root architecture. The influence of soil texture on erosion-reducing potential could not be demonstrated due to a lack of sufficient data on the erosion-reducing potential of plant roots in different soil textures. More empirical studies are needed to examine the role of soil texture on the erosion-reducing potential. Moreover, a more accurate global database is needed to unravel the influence of additional soil, root and environmental variables on the erosion-reducing potential of plant roots and to improve the predictive quality of the models.},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-13794980,~to-add-doi-URL,boreal-forests,comparison,eucalyptus-citriodora,forest-resources,macchia,modelling,pinus-tabulaeformis,review,robinia-pseudoacacia,sclerophyllous,soil-erosion,soil-resources,stabilization,uncertainty,vegetation}
}
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