Modelling biome‐scale root reinforcement and slope stability

Abstract

Rapid changes in the composition of hillslope vegetation due to a combination of changing climate and land use make estimating slope stability a significant challenge. The dynamics of root growth on any individual hillslope result in a wide range of root distributions and strengths that are reflected as up to an order of magnitude variability in root cohesion. Hence the challenge of predicting the magnitude of root reinforcement for hillslopes requires both an understanding of the magnitude and variability of root distributions and material properties (e.g. tensile strength, elasticity). Here I develop a model for estimating the reinforcement provided by plant roots based on the distribution of biomass measured at the biome level and a compilation of root tensile strength measurements measured across a range of vegetation types. The model modifies the Wu/Waldron method of calculating root cohesion to calculate the average lateral root cohesion and its variability with depth using the Monte Carlo method. The model was validated in two ways, the first against the predicted depth-reinforcement characteristics of Appalachian soils and the second using a global dataset of landslides. Model results suggest that the order of magnitude difference in root cohesions measured on individual hillslopes can be captured by the Monte Carlo approach and provide a simple tool to estimate root reinforcement for data-poor areas. The model also suggests that future hotspots of slope instability will occur in areas where land use and climate convert forest to grassland, rather than changes between different forest structures or forest and shrubland.

Root traits as drivers of plant and ecosystem functioning: current understanding, pitfalls and future research needs

“…So far, few studies have tested to what extent the knowledge gained on the linkages between single-species or pooled-species functional traits and plant and ecosystem functioning can be used to infer such relationships in complex ecosystems (Garnier et al, 2004;Vile et al, 2006;Hales, 2018;De Long et al, 2019). Taking the example of root trait effects on plant N uptake, empirical studies most often measure the physiological ability of distinct species to New Phytologist (2021) 232: 1123-1158 Ó 2021 The Authors New Phytologist Ó 2021 New Phytologist Foundation www.newphytologist.com…”

Evaluating the Effect of Root Cohesion on Shallow Landslides for Physically Based Modeling

“…(37) Investigation of differences in soil cohesion values according to tree growth and tree species can help to understand potential changes in landslides without a priori knowledge of the rooting strengths and distributions. (55) At this point, the simulation results of this model could be used to identify the effect of changes in vegetation on slope stability. Note that the result of a model reflecting land-use changes, such as the removal (i.e., logging) of individual species in simple forests, is likely to be sensitive to slope stability.…”

Root Reinforcement in Slope Stability Models: A Review

“…The inference of the belowground biomass starting from aboveground properties of plants has been also exploited to develop root reinforcement estimate methods not based on the remote sensing. Hales (2018) [82] developed a model to estimate the root reinforcement of slopes, using distributions of biomass measured at the biome level [83], root tensile strength values of different vegetation species from previous studies, and deriving the root densities from the global wood density database [81,84]. The values of root cohesion resulting from the application of the model were subjected to a sensitivity analysis, demonstrating that tensile strength and root density-the parameters determining root cohesion values on slopes-affect the modelled cohesions more than the parameter associated with model uncertainty-the reduction parameter that accounts for the wellknown overestimation of root reinforcement by the Wu method.…”

“…Measures on Roots Roots Modeling Slope or Smaller Scale SSM Basin or Larger Scale SSM Other Abdi et al 2018 [49] x Arnone et al 2016 [87] x x Bordoni et al 2020 [102] x x x Bordoni et al 2016 [100] x x Chiaradia et al 2016 [104] x x x Chok et al 2015 [36] x x Cislaghi et al 2017 [101] x x Cislaghi et al 2017 [85] x x x Cislaghi et al 2018 [86] x Cislaghi et al 2019 [114] x x x Cuomo et al 2020 [91] x Dazio et al 2018 [57] x x Gehring et al 2019 [121] x x Giadrossich et al 2017 [48] x Gonzalez-Ollauri 2017 [99] x x x Hales et al 2018 [82] x x Hales and Miniat 2017 [43] x x x Hwang et al 2015 [81] x x x Kokutse et al 2016 [35] x x Likitlersuang et al 2017 [106] x Masi et al 2020 [70] x Moos et al 2016 [111] x x x Rickli et al 2019 [112] x Rossi et al 2017 [107] x Saadatkhah et al 2016 [93] x x Salvatici et al 2018 [89] x Schmaltz and Mergili 2018 [113] x x Schmaltz et al 2019 [116] x x Switala and Wu 2018 [95] x Switala and Wu 2019 [97] x Vergani et al 2017 [11] x Vergani et al 2017 [118] x x Vergani et al 2015 [21] x x Wang et al 2017 [105] x x x Wang et al 2018 [117] x x Wang et al 2019 [103] x In the last few years, a challenging research trend emerged in the field of slope stability modelling: the progressive widening of application areas from slope to catchment and regional scale-i.e., over dozens or hundreds of squared kilometer-wide areas. Although advances made in the modelling of the mechanica...…”

“…Although advances made in the modelling of the mechanical behavior of roots in soils [13,51], in the evaluation of root tensile strength [44,47,50], and in the spatial distribution modelling of root reinforcement at the stand level [3,54], we could find that estimating the root reinforcement at the regional scale remains challenging, and it represents one of the main limits of the distributed slope stability analyses in wide areas. Slopes scale methodologies of analysis are quite well established, applications over small catchments have become recurrent, but large-dozens or hundreds of km 2 -areas are investigated only in a few recent works: Cuomo (2020) [91], Hales (2018) [82], Hwang (2015) [81], Salvatici (2018) [89], Rossi (2017) [107], and Saadtkhah (2016) [93]. Studies reporting on slope scale analyses or numerical simulations of synthetic slopes are also essential for the scientists working on wider areas, as they investigate new parameterization strategies, new modeling approaches and sensitivity issues.…”