Root reinforcement to soils provided by common Ethiopian highland plants for gully erosion control

Abstract

Grasses and trees are often used to stabilize gully banks. However, the effectiveness of such biological conservation measures has not been investigated for the Ethiopian highlands. This study investigates the reinforcement that plant roots may provide to strengthen gully banks in Ethiopia. The root systems of 26 indigenous and exotic plant species of 3 plant life forms (grasses, shrubs, and trees) were sampled, and root tensile strength and distribution were determined. The RipRoot model was used to quantify the additional cohesion derived from the plant roots. Among all tested roots, Eleusine floccifolia (grass), Tephrosia vogelii (tree), and Rosa abyssinica (shrub) had the strongest roots for each life form. The root volumetric ratio (root volume divided by soil volume) in the top 0.6 m of soil ranged from 0.03% to 0.46%. Roots of Digitaria abyssinica provided the maximum added cohesion (10.6 kPa) over this depth. For a given plant species, root volumetric ratio had a greater effect on additional cohesion than root tensile strength. Plant species with a fibrous root system provided greater additional cohesion values in the top 0.6 m (on average 3.4 vs. 1.7 kPa for tap root systems) and could potentially enhance gully bank stability for shallow gullies more than plants having a tap root system. To effectively rehabilitate larger gullies, plants should be integrated with other gully rehabilitation measures, such as regrading of gully banks and structural measures such as check dams to trap sediments, thereby reducing the effective gully bank height relative to rooting depth.

An experimental study on the effects of grass root density on gully headcut erosion in the gully region of China's Loess Plateau

“…We found that the grass root system decreased the soil loss by 45.64–68.45% (Table ) and that the soil loss was also greatly reduced when the root density was low (Figure ). These results can be ascribed to the improvement of the soil cohesion and the shear strength and tensile strength of the soil‐root matrix by the root system (De Baets et al, ; Pollen‐Bankhead & Simon, ; Simon et al, ; Zegeye et al, ). Our results also revealed that the root diameter had a significant negative effect on the SLR (Table ).…”

“…On the other hand, the effect of vegetation on reducing gully erosion is mainly due to the increase in soil resistance, which potentially depends on root characteristics (Allen, Arnold, Auguste, & Dunbar, ; Knapen, Poesen, Govers, Gyssels, & Nachtergaele, ; Torri et al, ; Vannoppen, Vanmaercke, De Baets, & Poesen, ). Different plant species have different root tensile strengths (De Baets et al, ), and plant species with fibrous roots provide greater additional cohesion in soil (Zegeye et al, ). Pollen‐Bankhead and Simon () and Simon, Pollen‐Bankhead, and Thomas () indicated that soil tensile strengths in banks and headcuts increase with increasing root density, root size, and species.…”

Fluvial Geomorphology, Root Distribution, and Tensile Strength of the Invasive Giant Reed, Arundo Donax and Its Role on Stream Bank Stability in the Santa Clara River, Southern California

“…The sample size of A. donax roots tested was 16. Of interest to this study is that the root volumetric ratio (or number of roots per square meter) has a greater effect on additional soil cohesion than root tensile strength [44]. Values in common to nearly all studies on root architecture is the finding that most roots exist in the top 1 m of soil, with the bulk of the roots in the top 30 cm [24,25].…”

The mechanism of the plant roots’ soil-reinforcement based on generalized equivalent confining pressure

“…Plant roots play an important role in improving the overall stability of the superficial slope soil and increasing the safety coefficient of the slope (Zegeye et al, 2018;Zhou & Wang, 2019). The plant root system is a complex and dynamic system, for which non-destructive monitoring is difficult, so it is always a challenging aspect to consider in research regarding the mechanism of plant root reinforcing soil.…”