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Macropores in the soil of vegetated slopes greatly affect the rainfall infiltration process. In this paper, a realistic 3D macropore network model of a soil column sample is established by CT scanning. Then, the transmission process of the macropore flow is simulated based on MODFLOW. The results show that (1) the shapes of macropores in the soil contain not only the dominant proportion of the circular tube but also a small proportion of the flake. (2) The velocity of macropore flow has a maximum of up to 0.2~0.3 m/s, which is much higher than that of matrix flow. In every single macropore, the flow velocity is the greatest at the central axis perpendicular to the extension and at the throat along the extension. (3) Due to the development of the macropore network system, rainwater can quickly pass through the soil profile in the form of preferential flow or pipe flow, which shortens the lag time of the peak discharge response to rainfall. This process can free up space for the next recharge, but reduce the overall quality of the soil, laying the foundation for the slope failure. Our work helps to unravel the mechanism of rainfall-induced landslides and promote harmony and sustainable development between humans and nature. [ABSTRACT FROM AUTHOR]

The moisture and thermal characteristics of expansive soil slopes have a significant impact on the strength and overall stability of the soil. In this study, the medium-strength expansive soil vegetated slope in Baise, Guangxi, was taken as the research object. Through the combination of numerical simulation and measured meteorological data, the impact of moisture and heat characteristics on slope stability was then analyzed, and optimal geometric parameters conducive to the stability of vegetated slopes were proposed based on these findings. The research results indicate that under long-term climatic conditions, solar net radiation has the most sensitive effect on the evaporation of slope soil. During the evaporation process, vegetation transpiration dominates in the vegetation-covered layer, while below the depth of the vegetation cover layer, soil evaporation itself plays a dominant role. Under the conditions of evaporation-rainfall-evaporation, slopes with a smaller permeability coefficient in the vegetation cover layer have significantly higher safety factors than slopes with a larger permeability coefficient and bare slopes. A steep vegetated slope with a slope gradient of 50° can maintain slope stability with proper handling of its height. The research findings have reference value for the design and construction of vegetated slopes with expansive soil. [ABSTRACT FROM AUTHOR]

The influencing mechanism of vegetation on slope stability has drawn much attention in recent years. Most studies focus on the soil reinforcement by roots, and the effectiveness on the slope stability, or the dynamic impacting mechanism that is caused by root hydrological coupling effects (i.e. rainfall infiltration or evapotranspiration conditions). It is still lacking root-soil plate deformation and slope stability under wind load conditions. This study aims to clarify the slope stress field and stability influence under wind load. Three typical trees (according to the root structures and crown pattens, C. lanceolata, M. nanmu, and G. acuminata) were selected from the early regional survey as the research objects. And then nine numerical vegetated slope models were established with three slope gradients of 20°, 30°, and 45° under continuously increasing wind velocity from 0-30 m/s using Geo-studio software. Among them, the plant root structure was defined as the virtual 1-dimensional beam units that assigned values, according to the actual root-soil plate geometric features. A comparison was made on the stress, displacement, and the factor of safety in each slope model. Results showed that: 1) The stress concentration occurred at the root-soil plate under the action of wind load. There were the total pressure and tension stress on the upper and lower soil of the root-soil plate at the windward side zone, respectively, whereas, the opposite trend was found at the leeward side. The total stress deviation and the overall rotation trend were intensified with the increase of wind velocity and slope gradient. The ranking order of the average total stress was the Machilus nanmu> Cunninghamia lanceolata> Gordonia acuminata under the same wind velocity and slope. 2) The slope mainly suffered from the local deformation with the continued increase in wind velocity, where the maximum total displacement was concentrated at the root-soil plate zone. The total displacement of the root-soil plate was ranked in the descending order of the middle-slope > upslope > downslope position, which was positively related to the slope gradient with the wind velocity. The order of displacement was consistent with that of average stress under the same wind velocity and slope gradient condition. 3) The factor of safety increased slightly and then decreased rapidly on the steep slope gradient with the increase in wind speed. By contrast, the factor of safety decreased monotonically on the gentle slope gradient. This trend was attributed to the transformation of deep and shallow critical sliding surfaces with wind velocity. The stability of Gordonia acuminata slope was the least affected by the wind and followed by the Cunninghamia lanceolata and Machilus nanmu. It was also found that the factor of safety under the wind load was more sensitive to the crown width and root-soil plate diameter than the root-soil plate depth or crow height, especially at high wind velocity. It implies that the vegetated slopes with the large crown and narrow lateral root-spreading trees were vulnerable to the wind load. To sum up, less influence of wind load was found on the slope that was protected by trees (like G. acuminata) with a large root-soil plate diameter and smaller crown height. But the trees protected slopes (like M. nanmu and C. lanceolata) were characterized by the large crown height, and smaller root-soil plate diameter. The large root depth was dramatically affected by the wind. Thus, M. nanmu and C. lanceolata cannot be recommended as the high-slope protection projects in windy areas. [ABSTRACT FROM AUTHOR]

The soil–water characteristic curve is an important tool to evaluate the water-holding capacity of unsaturated soil. Plant roots can affect the matric suction of soil and the water-holding capacity and permeability of the soil. Therefore, the morphological characteristics of plant roots will lead to the difference in soil–water characteristics between soil slope and plant-covered slope. This study aims to investigate the effect of Vetiver root morphology on soil–water characteristic curves of plant-covered slope soil. The hydrological effect of the root distribution on the root–soil system was also discussed. The results showed that: (1) The root surface area index (RAI) and root volume ratio (Rv) of each soil section of the vetiver root system varied with depth in accordance with the Gaussian function distribution; (2) In the process of natural drying, the matric suction generated within the root system is significantly higher than that generated by evaporation of bare soil in the same soil layer. The ability of vegetation soil to enhance soil matrix suction increases with the increase of soil root surface area index; and (3) The α and n values of the SWCC model decreased with the increase of Rv (root volume ratio of soil), while the air entry value increased. Under the same water content, the matric suction corresponding to vegetation soil is significantly greater than bare soil. In addition, the soil–water characteristic curve can be effectively predicted by combining the Rv of vegetated soils. [ABSTRACT FROM AUTHOR]

The presence of vegetation in urban soil is both visually appealing and environmentally beneficial. Vegetation contributes to changes in soil water content (SWC) and soil suction (SS) through transpiration. These changes ultimately affect slope stability, soil erosion, runoff generation, and water infiltration. This study closely examines the impact of tree canopy covers on SWC and SS dynamics in an urban slope site with a diverse mix of vegetation (trees and grass) in a tropical region. Field monitoring revealed that slope areas with higher tree canopy cover consistently exhibited lower SWC and higher SS at shallower depths, highlighting the stabilizing effects of vegetation. During wet periods, the difference in SWC between high and low canopy cover areas increased by 36% compared to dry periods, emphasizing the role of canopy cover in regulating soil moisture under varying climatic conditions. Furthermore, stations with lower canopy cover demonstrated a stronger correlation between SWC and relative humidity (R values of 0.64 in dry and 0.71 in wet periods) than those with higher canopy cover (R values of 0.57 in dry and 0.63 in wet periods), indicating distinct soil moisture retention patterns based on canopy density. These findings underscore the critical role of tree canopy cover in controlling SWC and SS dynamics, particularly for urban slope stability and sustainable landscape management., Competing Interests: Declarations. Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)

Planting vegetation is an environmentally friendly method for reducing landslides. Current vegetated slope analysis fails to consider the influence of different root architectures, and the accuracy and effectiveness of the numerical simulations need to be improved. In this study, an explicit smoothed particle finite element method (eSPFEM) was used to evaluate slope stability under the influence of vegetation roots. The Mohr–Coulomb constitutive model was extended by incorporating apparent root cohesion into the shear strength of the soil. The slope factors of safety (FOS) of four root architectures (uniform, triangular, parabolic, and exponential) for various planting distances, root depths, slope angles, and planting locations were calculated using the shear strength reduction technique with a kinetic energy-based criterion. The results indicated that the higher the planting density, the stronger the reinforcement effect of the roots on the slope. With increasing root depth, the FOS value first decreased and then increased. The FOS value decreased with an increase in slope angle. Planting on the entire ground surface had the best improvement effect on the slope stability, followed by planting vegetation with a uniform root architecture in the upper slope region or planting vegetation with triangular or exponential root architecture on the slope's toe. Our findings are expected to deepen our understanding of the contributions of different root architectures to vegetated slope protection and guide the selection of vegetation species and planting locations. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Vegetation in slopes can effectively improve slope stability. However, it is difficult to estimate the effects of vegetation on slope stability because of variations in plant species and environmental conditions. Moreover, influences of plant growth on slope stability change with time, resulting in changes in the safety factor. This study was conducted to evaluate the stability of vegetated slopes with time and investigate the effects of different layouts of plant species on slope stability. Here, we used a plant growth model and slope stability analysis to build an evaluation model. To accomplish this, one species of tree, shrub and grass was chosen to set six layout patterns. A slope with no vegetation served as a control. The safety factors of the seven slopes were then calculated using the developed evaluation model and differences in the safety factors of slopes were compared and discussed. The slope vegetated with Platycladus orientalis reached the most stable state at the age of 60 years. Shrub slope (Vitex negundo) had the maximum safety factor after 20 years. Overall, the safety factor of vegetated slopes increased from 12.1% to 49.6% compared to the slope with no vegetation. When wind force was considered, the safety factor value of the slope changed from 3.5% to 43.5%. Vegetation mixtures of trees and grasses resulted in the best slope stability. Planting grasses on slopes can improve slope stability of trees to a greater degree than that of slopes with shrubs in the early stage of growth. [ABSTRACT FROM AUTHOR]

• Reinforcement mechanisms of plant roots in different morphologies were revealed. • Highly-bionic root morphological models were developed for DEM simulation. • Real-time changes in contact forces of root branches and morphologies were analyzed. Currently, the research regarding the effects of plant roots on stabilizing earthen slopes lagged behind engineering practices and the relevant reinforcement mechanism from a microscopic perspective still remains uncertain. In this study, the stability of soil slopes reinforced by the plant roots in three different morphologies (the uniform, the upside-down triangular and the fusiform) was numerically simulated, which was verified by physical rainfall experiments. Then, computational fluid dynamics and discrete element method (CFD-DEM) coupling simulation was adopted to explore the different reinforcement mechanisms of the plant-root systems in different morphologies on the soil slope stability under heavy rainfall. It was disclosed that the roots in a uniform morphology reinforced the slope toe effectively by providing strong shear resistance in the middle and anchoring forces at the end of the root system. The roots in an upside-down triangular morphology strengthened the upper slope by virtue of its wide upper roots extending deeply into the lower soils and hence giving a full play to larger tensile forces. Compared with the previous two root systems, the roots in a fusiform morphology showed the weakest reinforcement effects due to the narrow upper roots and fewer lower roots for anchoring. During the rainfall-induced slope slip failure, the soil particles near the middle-upper part of slope featured faster sliding speed, longer sliding path and larger rolling angle than those closer to the lower slope. The existence of plant roots hindered soil particles from sliding and slowed down the development of slip surface, having the displacement area limited within the rhizosphere zone. The contact forces of roots declined first as the slip surface expanded upward and then increased slowly due to mobilization of the friction between the roots and soil particles. During the rainfall-induced slope failure, the lateral roots toward the slope interior had larger tensile forces; the longest tap-root in the middle of the root system was not always the one having the strongest tensile force, which changed over time. [ABSTRACT FROM AUTHOR]

Soil bioengineering using vegetation is an environmentally friendly solution to maintain the stability of shallow earthen slopes. To explore the microscopic mechanical reinforcement mechanism of plant roots on slope stabilization, the stabilities of three soil slopes covered by live grasses in different root morphologies under intense rainfall were examined extensively by both experimental tests and numerical simulations. Highly-bionic root morphological models were developed and validated to simulate the changes in root morphologies and root axes contact-forces. It was revealed that the roots in a uniform morphology effectively strengthened the slope toe through strong shear resistance in the middle and anchoring force at the end of root system; the roots in an upside-down triangular morphology maintained the stability of upper soil slope through its wide upper roots, which extended deeply into the slope interior and hence gave full play to tensile force. Compared with the previous two, the roots in a fusiform morphology had the weakest soil reinforcement and the slope experienced a series of retrogressive failures until the upper residual slope soil collapsed eventually. The significant increase in shear strength of root-soil composites derived primarily from the increase in cohesion. The root axis with the strongest contact-force during slope failure was not necessarily the longest taproot in the middle of root system but a single-root on one side. • Stability of vegetated earthen slopes under rainfall was investigated. • Highly-bionic morphological models were developed to simulate root effects. • Effects of plant roots in different morphologies on slope stability were compared. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• A nonlinear mathematical model is established to study the flow field characteristics and incipient scouring erosion of the vegetated slope under the coupling between turbulent and seepage. • Parameters sensitivity is discussed for eight categories, i.e., turbulent depth, vegetation height, vegetation permeability, energy slope, turbulence coefficient, jump coefficient of stress, soil permeability, and particle diameter. • Physical and numerical (CFD-DEM coupling) flume scouring tests are designed to observe the particle incipient motion of the slope with rigid vegetation under different conditions. • The nonlinear seepage width and the stable Darcy flow width in the soil region are studied. Under the action of continuous rainfall, the coupling linkage between runoff and seepage can cause erosion of non-cohesive soil particles on vegetated slopes. A nonlinear turbulent-seepage coupling model is established to study the flow field characteristics and incipient scouring erosion of the vegetated slope. The fluid in the turbulent region is governed by the Reynolds averaged Navier-Stokes. Biot's poroelasticity theory describes the flow in the vegetation region. The seepage in the soil region obeyed the Darcy-Brinkman equation. Analytical solutions of the vertical velocity profile and safety factor (sliding and rolling) of the particle incipient motion are derived based on the coupling between turbulence and seepage. The velocity expression is found to be in good agreement with the existing experimental data of both emerged and submerged vegetation conditions, respectively. The velocity distribution above the surface follows a logarithmic pattern, while below the surface, non-linear seepage occurs with a transition layer that deviates from Darcy seepage. In addition, the particle incipient motion is verified by the physical flume souring test under none, sparse, and dense vegetation, respectively. The absolute error between the theoretical calculation and the physical test is within 5%. Furthermore, the critical water depth is nonlinearly negatively correlated with the energy slope. Finally, a CFD-DEM coupling numerical model is employed to further observe the scouring erosion of the sparse and dense vegetated slopes with the same conditions as the physical test. The numerical results show that the scouring erosion exhibits discontinuous behavior and the soil particles between the two vegetation are more vulnerable to scouring than those in other locations. After scouring, the inertial porosity of the vegetated soil slope decreases while the porosity in the surface area increases. [ABSTRACT FROM AUTHOR]

The ecological concept has become more widespread and biotechnical slope protection has been accepted by more people as environmental policies become more stringent. Biotechnical slope protection has become widely used because of its unique features, which include wave resistance, waterproof flow-scour protection, greening and landscaping effects, environmental friendliness, and positive social benefits. Slope surfaces are exposed to and affected by natural conditions, particularly storm-water scouring, which has an obvious impact on slope instability. However, most previous studies have focused on soil reinforcement by plant root systems in non-saturated soil conditions, and soil reinforcement in saturated soil conditions after rainfall has rarely been studied. In this study, we conducted laboratory-based storm-water scouring experiments to assess the erosional effect of storm-water scouring on slopes, reveal the mode and process of failure of natural and vegetated slopes under storm-water scouring, and develop and refine the mechanism and theoretical understanding of soil reinforcement by plants. [ABSTRACT FROM AUTHOR]

A new methodology to incorporate the mechanical root anchorage effects in both short- and long-term slope stability analysis is proposed based on observed and assumed behaviour of rooted soil during shear failure. The main focus of the present work is the stress–strain range comparison for both soil and roots and development of a stability model that would incorporate relevant root and soil characteristics based on the fact that available soil–root composite shear resistance depends on the magnitude of the shear strain. This new approach, combining stress–strain analysis, continuum mechanics, and limit equilibrium stability assessment, allows for a more realistic simulation of the rooted soil composite whereby the stabilising effect of the rooted soil is incorporated in the slope stability calculations by means of the synchronisation of root and soil mechanical behaviour during failure. The stability of vegetated terraces in a study area in Spain is used as a case study to demonstrate the proposed methodology and to compare the results with the traditional use of the perpendicular root reinforcement model. The results of the study show that as the shear displacement (strain) increases, the stress is transferred from the soil that provides most of the resistance at low strains onto the roots that provide the most of the resistance to shear at high strains. Including this behaviour in the overall resistance to failure of the root–soil continuum resulted in a more conservative and realistic assessment of the stability of a vegetated slope immediately after a precipitation event when a progressive failure is most likely to be triggered. [ABSTRACT FROM AUTHOR]

ABSTRACT Wind flow and sand transport intensity were measured on the seaward slope of a vegetated foredune during a 16 h storm using an array of sonic anemometers and Wenglor laser particle counters. The foredune had a compound seaward slope with a wave-cut scarp about 0.5 m high separating the upper vegetated portion from the lower dune ramp, which was bare of vegetation. Wind direction veered from obliquely offshore at the start of the event to obliquely onshore during the storm peak and finally to directly onshore during the final 2 h as wind speed dropped to below threshold. Sand transport was initially inhibited by a brief period of rain at the start of the event but as the surface dried and wind speed increased sand transport was initiated over the entire seaward slope. Transport intensity was quite variable both temporally and spatially on the upper slope as a result of fluctuating wind speed and direction, but overall magnitudes were similar over the whole length. Ten-minute average transport intensity correlates strongly with mean wind speed measured at the dune crest, and there is also strong correlation between instantaneous wind speed and transport intensity measured at the same locations when the data are smoothed with a 10 s running mean. Transport on the beach for onshore winds is decoupled from that on the seaward slope above the small scarp when the wind angle is highly oblique, but for wind angles <45° from shore perpendicular some sand is transported onto the lower slope. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Grasses and shrubs occupy large areas of fragile ecosystems following ecological restoration. Therefore, it is increasingly important to assess and monitor the environmental safety of pastures. However, previous studies on this topic lacked systematicity and directionality. In this study, we reviewed the literature on runoff and erosion to summarise the core issues for future research, resolve the current research bottleneck, and promote the balance of soil, water, and energy in fragile ecological areas. The results of the review indicate that coverage remained the main vegetation feature considered when characterising rangeland slope erosion and runoff. Erosion energy should be comprehensively considered based on the influence of vegetation on rainfall distribution and runoff erosivity. Rangeland slope erosion and runoff changes can only be explained by integrating the above- and below-ground characteristics of vegetation. Additionally, the impact of vegetation on runoff separation and the sediment transport processes at different erosion stages under rainfall conditions vary. Therefore, studying the comprehensive indicators of vegetation at different erosion stages in response to erosion and runoff will be vital in rangeland erosion research. From the perspective of disciplinary development, this study can promote the further development of soil erosion, ecology, soil science, hydrology, hydraulics, and other disciplines. • Research on soil erosion and overland flow on rangeland slopes lacks systematicity. • Effect of plants on runoff separation under rainfall varies between erosion stages. • Vegetation also affects sediment transport differently under rainfall. • Responses of comprehensive vegetation indicators to erosion and runoff are important. • Vegetation indicators will offer a breakthrough in rangeland research. [ABSTRACT FROM AUTHOR]

Although ecosystem degradation is often caused by existing slopes vegetated with commercial species, limited data are available for implementing practical approaches for nature restoration by transplanting native species to those vegetated slopes. Existing vegetated slopes are characterized by spatial heterogeneity in the habitat environment and competition with existing vegetation, which affect the behaviors of transplanted native species. In this study, we examined the factors affecting the survival, growth, verticillation, and flowering of Lilium pensylvanicum , a native coastal-meadow species transplanted to a vegetated road slope in Hokkaido, Japan. In the fourth year after transplantation, the number of surviving plantlets was 364 (57% of 640 transplanted plantlets) and the number of plantlets that shifted to verticillate leaves was 181 (50% of the survivors). The flowering plantlets accounted for 9% (n = 34) of the survivors. The generalized linear model showed that plantlet survival is strongly promoted by a larger bulb scale, that is, nutrient reserves. Furthermore, the survival ratio was greatly improved in the drought-prone, stressful habitats with low vegetation coverage, even for plantlets with relatively smaller bulb scales. However, in the moist habitat with high coverage, the survival ratio was greatly decreased regardless of the bulb scale size. Growth, verticillation, and flowering were facilitated by higher soil nutrient availability, such as a lower C/N ratio and thicker soil layer. Therefore, transplanting of native species to vegetated slopes requires the selection of stress-tolerant species with large nutrient reserves and identification of optimal habitats for transplanting, namely stressful environments with reduced vegetation coverage. • The transplantation of native species on slopes for nature restoration was examined. • Plantlet survival was most strongly affected by nutrient reserves. • Survival negatively correlated with vegetation cover and soil water content. • Plantlet growth and flowering were facilitated by higher nutrient availability. [ABSTRACT FROM AUTHOR]