Slope Vegetation Research Articles

Modeling the mudslide aftermath of the 2007 Southern California Wildfires

An investigation is made of the influence of fire-caused deforestation on precipitation-triggered, shallow landslide susceptibilities in southern California, using a scalable and extensible geo-fluid model (SEGMENT), that accounts for soil mechanics, root distribution, and relevant hydrologic processes. SEGMENT is applicable to variable regional topography, soil thickness profiles, and vegetation coverage. In this study, for southern California following the 2007 wildfires, three experiments were performed with rainfall recurrence periods chosen to be 2, 10, and 25 years. These intervals correspond to 24-h storm rainfall totals of 17, 25.4, and 33 mm. The model generated landslide stability maps that identified three areas of high instability. These unstable regions are located in the San Fernando Valley, the San Gabriel Mountains, and the Santa Monica Mountains. In each case, the vegetation cover had been severely burned during the preceding 2007 wildfires. The model results showed that burning from wildfires is a major destabilizing factor for southern California. Burn sites are more prone to landslides than vegetated slopes because the soil more readily exceeds its critical moisture content. Severe droughts in a future warming climate are expected to increase the likelihood of more frequent and intense wild fires. Higher temperatures combined with decreased total rainfalls facilitate more intense landslides, including devastating mudslides, following heavy precipitation. Finally, the model is designed to assist in developing timely mitigation measures for post-fire, storm-triggered landslides.

Mechanical analysis of interaction between plant roots and rock and soil mass in slope vegetation

With the help of plant roots, slope vegetation makes the slope soil mass become a composite material of soil and roots, and thus enhances shear strength of the slope soil mass and stability of the slope. However, the related studies at present are still qualitative. In this paper, quantitative analysis of the interaction between roots and soil mass are made. By the analysis of the interaction between herbaceous plant roots including lateral roots of woody plants and rock and soil mass, a mechanical model of the interaction between frictional roots and soil is established, and its correctness is shown. A mechanical model of the interaction between anchorage root, namely, woody plant taproot, and soil is also established. The establishment of the models provides a useful means in quantitative analysis of the interaction between plant roots and soil, and has practical values.

Eroding Australia: rates and processes from Bega Valley to Arnhem Land

Abstract We report erosion rates determined from in situ produced cosmogenic 10 Be across a spectrum of Australian climatic zones, from the soil-mantled SE Australian escarpment through semi-arid bedrock ranges of southern and central Australia, to soil-mantled ridges at a monsoonal tropical site near the Arnhem escarpment. Climate has a major effect on the balance between erosion and transport and also on erosion rate: the highest rates, averaging 35 m Ma −1 , were from soil-mantled, transport-limited spurs in the humid temperate region around the base of the SE escarpment; the lowest, averaging about 1.5 m Ma −1 , were from the steep, weathering-limited, rocky slopes of Kings Canyon and Mt Sonder in semi-arid central Australia. Between these extremes, other factors come into play including rock-type, slope, and recruitment of vegetation. We measured intermediate average erosion rates from rocky slopes in the semi-arid Flinders and MacDonnell ranges, and from soil-mantled sites at both semi-arid Tyler Pass in central Australia and the tropical monsoonal site. At soil-mantled sites in both the SE and tropical north, soil production generally declines exponentially with increasing soil thickness, although at the tropical site this relationship does not persist under thin soil thicknesses and the relationship here is ‘humped’. Results from Tyler Pass show uniform soil thicknesses and soil production rates of about 6.5 m Ma −1 , supporting a longstanding hypothesis that equilibrium, soil-mantled hillslopes erode in concert with stream incision and form convex-up spurs of constant curvature. Moreover, weathering-limited slopes and spurs also occur in the same region: the average erosion rate for rocky sandstone spurs at Glen Helen is 7 m Ma −1 , similar to the Tyler Pass soil-mantled slopes, whereas the average rate for high, quartzite spurs at Mount Sonder is 1.8 m Ma −1 . The extremely low rates measured across bedrock-dominated landscapes suggest that the ridge–valley topography observed today is likely to have been shaped as long ago as the Late Miocene. These rates and processes quantified across different, undisturbed landscapes provide critical data for landscape evolution models.

Desirable plant root traits for protecting natural and engineered slopes against landslides

Slope stability models traditionally use simple indicators of root system structure and strength when vegetation is included as a factor. However, additional root system traits should be considered when managing vegetated slopes to avoid shallow substrate mass movement. Traits including root distribution, length, orientation and diameter are recognized as influencing soil fixation, but do not consider the spatial and temporal dimensions of roots within a system. Thick roots act like soil nails on slopes and the spatial position of these thick roots determines the arrangement of the associated thin roots. Thin roots act in tension during failure on slopes and if they traverse the potential shear zone, provide a major contribution in protecting against landslides. We discuss how root traits change depending on ontogeny and climate, how traits are affected by the local soil environment and the types of plastic responses expressed by the plant. How a landslide engineer can use this information when considering slope stability and management strategies is discussed, along with perspectives for future research. This review encompasses many ideas, data and concepts presented at the Second International Conference ‘Ground Bio- and Eco-engineering: The Use of Vegetation to Improve Slope Stability—ICGBE2’ held at Beijing, China, 14–18 July 2008. Several papers from this conference are published in this edition of Plant and Soil.

Instability Analysis of Terrain-Induced Canopy Flows

Abstract Tall vegetation and complex terrain create difficult conditions for measuring and modeling net ecosystem–atmosphere exchanges of carbon, water vapor, and pollutants. The instability of canopy flow regimes over complex terrain is critical for understanding what factors are essential to control exchanges between different canopy flow regimes. In this paper, an analytical criterion of instability of the terrain-induced canopy flows is derived from the simplified thermal-hydromechanical equations by nonlinear instability analysis. The stability of the terrain-induced canopy flows and an oscillation solution are predicted based on the instability criterion. It is found that the critical values of control parameters are determined by the terrain slope, drag coefficient, and leaf area density of vegetation.

Image interpretation and statistical analysis of vegetation damage caused by the Wenchuan earthquake and related secondary disasters

Damage to vegetation caused by secondary disasters of the Wenchuan earthquake in severely damaged counties was estimated through the visual comparison of SPOT images acquired before the earthquake and ADS40 aerial images acquired after the earthquake, and a series of spatial analyses. In this paper, we (1) interpret 2-meter resolution aerial images that cover areas severely affected by the earthquake, and obtain statistical information on vegetation damage for the counties of Beichuan, Wenchuan, Maoxian, Lixian, Pingwu, Qingchuan, Anxian and Jiangyou; (2) spatially analyze the relationships between vegetation damage and slope gradient and distance from active faults using ArcGIS software to obtain information on vegetation damage under different geologic and geomorphologic settings; and (3) estimate the area of vegetation damage for the whole region using the above results for the areas covered by imagery. The results indicate that (1) farmland and grassland were less damaged than forestland was since they are mostly located on less steep slopes; (2) Wenchuan was the worst damaged county; and (3) the proportion of damage to vegetation first decreased and then increased with increasing distance from the three main faults of the Longmenshan fault zone owing to the combined effects of the three faults and the effects of regional geology and landforms.

Dendrogeomorphically derived slope response to decadal and centennial scale climate variability: Black Mesa, Arizona, USA

Abstract. A major impediment to an understanding of the links between climate and landscape change, has been the relatively coarse resolution of landscape response measures (rates of weathering, sediment production, erosion and transport) relative to the higher resolution of the climatic signal (precipitation and temperature on hourly to annual time scales). A combination of high temporal and spatial resolution dendroclimatic and dendrogeomorphic approaches were used to study relationships between climatic variability and hillslope and valley floor dynamics in a small drainage basin in the Colorado Plateau of northeastern Arizona, USA Dendrogeomorphic and vegetation evidence from slopes and valley bottoms, including root exposure, bending of trunks, change in plant cover and burial and exhumation of valley bottom trees and shrubs, suggest that the currently observed process of root colonization and rapid breakdown of the weakly cemented bedrock by subaerial weathering, related to periodic dry/wet cycle induced changes in vegetation cover, has lead to a discontinuous, climate-controlled production of sediment from these slopes. High-amplitude precipitation shifts over the last 2000-years may exert the largest control on landscape processes and may be as, or more, important than other hypothesized causal mechanisms (e.g. ENSO frequency and intensity, flood frequency) in eroding slopes and producing sediments that ultimately impact higher order drainages in the region. Current vegetation response to a prolonged drought over the past decade suggests that another major transition, incorporating vegetation change, slope erosion, sediment production and subsequent valley floor deposition, may be in its initial phase.

Study on Systematizing Design of Ecological Engineering Technology in Right of Highway

AbstractFor analysis of ecological recovery in right of highway, the function, principle and key technologies were described. A concept, main contents and theoretical basis of systematizing design on ecological recovery in right of highway were put forward. Systematizing design of ecological recovery with vegetation selection, soil nutrition improvement and vegetation restoration and reconstruction engineering technology was studied. Theoretical basis and planting technique system support to design of slope ecological recovery and vegetation restoration in different region were put forward.

Study on Thick-lift Base Material and Seed Spraying for Side Slope Engineering Protection

The arid area highway roadbed slope vegetation restoration presents a challenge. The concept, the principle, the material composition, and the construction craft of the thick-lift base material and seed spraying for the side slope protection are analyzed in this paper. Through the project practice, the spraying base material and seeds suitable for the Xining area are proposed, including the plant material of alfalfa, the lemon strip, the old awn wheat, the alkali grass, China Tall fescue, the alkali cogon grass, and so on, for the slope vegetation restoration and the plant choice principle. The suitable mixing ratio is analyzed as well as the spraying, the coverage, and the later period management. It is an effective technology to address lithoid slope ecology and the vegetation restoration, especially for large slopes or difficult areas for construction.

Effect of vegetation on runoff-sediment yield relationship at different spatial scales in hilly areas of the Loess Plateau, North China

Whether vegetation reduces soil loss by reducing runoff volume or rather by changing runoff-sediment yield relationship has received little attention. Base on the observed data from monitoring stations and the published data from other research, this issue is addressed at different scales in hilly areas of the Loess Plateau, North China. At the plot scale, vegetation helps reduce soil loss not only by reducing runoff volume, but also by changing the runoff-sediment yield relationship, resulting that the sediment-reduction rate is higher than the runoff-reduction rate. At the watershed scale, gully erosion and mass wasting process are dominant. Vegetation measures are insufficient to control local mass movement, implying that sediment availability remains high even after vegetation is established. It is also hard for slope vegetation to change the capacity of the sediment transport system at the watershed scale. Therefore, vegetation cannot change the runoff-sediment yield relationship at the watershed scale. This implies that vegetation reduces sediment yield only by reducing runoff volume and the sediment-reduction rate approximates the runoff-reduction rate at the watershed scale. Other slope measures for soil conservation such as terraces are considered to have the same effect on the runoff-sediment yield relationship as the vegetation. Several case studies involving different spatial scales are presented and confirm this conclusion.

Simulation of soil water dynamics in a Caragana intermedia woodland in Huangfuchuan watershed

As vegetation coverage increases, soil water content can decrease due to water uptake and evapotranspiration. At a very high level of plant density, poor growth and even mortality can occur due to the decrease of soil water content. Hence, a better understanding of the relationship between soil water content and the density of plants is important to design effective restoration projects. To study these relationships, we developed a soil water dynamic simulation model of a Caragana intermedia woodland under different slope gradient and slope aspect conditions in the Huangfuchuan watershed on the basis of the previous studies and field experiments. The model took into account the major processes that address the relationships of plants and the environment, including soil characteristics, precipitation, infiltration, vegetation transpiration, and soil evaporation. Daily changes in soil water content, transpiration, and evaporation of the Caragana intermedia woodland with different vegetation coverage, slope gradient, and slope aspect were simulated from 1971 to 2000. Based on the model simulations, we determined the functional relationships among soil water content, plant coverage and slope as well as the optimal plant density on flat slopes. We also determined the effects of slope gradient and slope aspect on soil water content. When slope gradient was less than 10°, the optimal plant density was sensitive to slope gradient. In the slope range from 10° to 30°, plant density was not sensitive to slope gradient. Therefore, it is important to consider planting densities on the hillsides with slope gradients less than 10° for reconstructing vegetation.

Road Slope Revegetation in Semiarid Mediterranean Environments. Part I: Seed Dispersal and Spontaneous Colonization

Abstract The importance of neighboring vegetation as a seed reservoir for spontaneous colonization of adjacent road slopes was analyzed in a semiarid region of east Spain. Two independent methodological approaches were used to examine the relative contribution of seed from neighboring vegetation and the efficiency of different seed dispersal strategies in plant colonization. We first used a randomization test to compare floristic similarity between road slopes, neighboring flora, and local flora (the regional species pool found in the same climate and soil conditions as the road slopes). Second, we compared seed dispersal mechanisms of road slope vegetation with those of the surrounding area using frequency analysis. Species composition of road slopes was more similar to that of the flora of adjacent surrounding areas than expected by chance. Anemochorous (wind‐dispersed) plants were over‐represented in road slopes 8 years after road slopes were built. We concluded that seed dispersal from neighboring vegetation is an important factor in the vegetative colonization of road slopes. However, this initial species pool was also strongly shaped by the harsh environmental conditions of roadcuts and southern aspect. These results have important implications in road slope restoration because they suggest that naturally vegetated areas should be maintained adjacent to road slopes to enhance seed immigration from species adapted to local site conditions, which will accelerate the successional process. The application of this single reclamation strategy and mixed strategies that combine the use of natural colonization and soil amendment for road slope restoration in Mediterranean environmental conditions is discussed.

Parameter determination of a mathematical model for soil moisture.

The field measurement for the soil moisture is not an easy work. We will determine the parameter of mathematical model for distribution of soil moisture on the hill slope based on limited measured data;.after that we can determine and predict the soil moisture. The model involve following factors: slope gradient, land use, vegetation cover and surface water diffusion features together with the field measurements of soil moisture data.

Chipping and Softening Driftwood in Dam Reservoir to Use it as Base Materials for Slope Vegetation Work

Chipping and Softening Driftwood in Dam Reservoir to Use it as Base Materials for Slope Vegetation Work

Land Degradation in the Heihe River Basin in Relation to Plant Growth Conditions

Land degradation is a crucial issue in semi-arid and arid areas. The Heihe River basin is the second largest inland river basin in the arid regions of Northwest China. Land degradation is a serious passive problem for the socioeconomic development in this region. In this paper, we develop a land degradation model. Land Degradation Index (LDI), which integrates the main factors influencing land degradation. The factors are mainly those related to plant growth conditions: precipitation, potential evapo-transpiration (PE), vegetation fraction cover, slope and aspect, soil type, and land cover. We find that our model can be used to effectively monitor land degradation over this region.

Simulation of energy and water balance in Soil-Vegetation-Atmosphere Transfer system in the mountain area of Heihe River Basin at Hexi Corridor of northwest China

In the mountain area of inland Heihe River Basin at Hexi Corridor of northwest China during the vegetation growing season from May to September, the Simultaneous Heat and Water (SHAW) model of Soil-Vegetation-Atmosphere Transfer (SVAT) system is applied to simulating and studying energy and water balance of the soil-residue-plant canopy layers in the Picea crassifolia forest and the grassland by the forest at the shaded slope and the grassland at the sun-facing slope. The simulation of energy balance indicates that net radiation of the grass-land at the sun-facing slope is more than that of the Picea crassifolia forest and the grassland by the forest at the shaded slope. The energy outgoing components are the first latent heat and next sensible heat from the grassland both at the shaded slope and the sun-facing slope, but those at the former are less. The energy outgoing components are the first sensible heat and next latent heat from the Picea crassifolia forest. The composition and distribution of energy in the soil-residue-plant canopy layers in the Picea crassifolia forest and the grassland by the forest at the shaded slope make the soil layer receive less energy, which therefore, especially the forest possesses the energy conditions for soil water conservation. The simulation of water balance indicates that the water loss of the grassland at the sun-facing slope is mainly caused by soil evaporation, while evapotranspiration of the Picea crassifolia forest and the grassland by the forest at the shaded slope is less than that of the grassland at the sun-facing slope. Half of the evapotranspiration of the Picea crassifolia forest and the grassland by the forest at the shaded slope is consumed by transpiration. After precipitation, the soil water storage is increased much more for the Picea crassifolia forest and also more for the grassland by the forest at the shaded slope. Therefore the shaded slope vegetation, especially the forest is favorable for soil water storage.

The Plant Community of Nanjido, a Representative Nonsanitary Landfill in South Korea: Implications for Restoration Alternatives

Vegetation and soil analyses of the slopes of the Nanjido, a nonsanitary landfill in South Korea, were conducted to investigate the colonization status of plant communities, and to suggest restoration alternatives by comparing the vegetation of the landfill and the nearby forests. The vegetation of the Nanjido landfill and the control sites was surveyed by using 10 ×: 10 m quadrats. The soils were analyzed for pH, electrical conductivity, organic matter content, Total-N, P, K, Ca, Mg, sand, silt, and clay. Canonical correspondence analysis (CCA) was performed by using the extent of cover for all the recorded species, and the physical and chemical variables of soil. Salix babylonica, Platanus orientalis, Rosa multiflora, Prunus persica,Albizzia julibrissin, Indigofera pseudo-tinctoria, Robinia pseudoacacia, Amorpha fruticosa, Ailanthus altissima, Forsythia koreana, and Paulownia tomentosa were the commonly found tree species.Quercus mongolica, considered to be the natural late successional species of temperate South Korea, was recorded at the Nanjido landfill. Levels of pH, the electrical conductivity and concentrations of P, Ca, and Mg in landfill soils were significantly higher than the forest control site soils (P < 0.05). In CCA ordination space, landfill quadrats clustered in less acidic soils, rich in Ca and Mg, while forest control site quadrats clustered in acidic, low P soils. This study found several indications that it is possible for a nonsanitary landfill to support succession to typical and natural forests. In addition, the landfill slope vegetation could function as a biological source for the restoration of the other landfill areas that remain barren, if planned efforts are made for conservation and rehabilitation.

Storm Water Pollutant Removal in Roadside Vegetated Buffer Strips

A 2-year water quality monitoring project was conducted to evaluate the removal of storm water contaminants by existing vegetated slopes adjacent to freeways. Objectives of the study were to generate design criteria and to determine whether standard roadway design requirements result in buffer strips with treatment equivalent to those specifically engineered for water quality performance. Variables such as width, slope, vegetation density, and hydraulic loading were evaluated by studying the runoff through existing vegetated slopes at four locations in northern California and four locations in southern California. At each location, concrete channels were constructed to capture freeway runoff after it passed through existing vegetated strips of varying widths. The quantity and quality of the runoff discharged from the buffer strip were compared with freeway runoff collected at the edge of pavement. Buffer strips consistently reduced the concentration of suspended solids and total metals in storm water runoff. The strips were also effective in removing dissolved metals when the edge of pavement concentrations were sufficiently high. Little or no change in concentration was observed for nitrogen and phosphorus. Concentrations of organic carbon, dissolved solids, and hardness increased. For the constituents exhibiting a decrease in concentration, steady-state levels were generally achieved within 5 m (16 ft) of the pavement edge for slopes commonly found on highway shoulders and where the vegetation coverage exceeded 80%. Slope, vegetation type and height, highway width, and hydraulic residence time had little or no impact on the discharge concentrations.

現地測量の成果を用いた航空レーザ測量ＤＴＭの高さ方向の精度検証

Airborne laser scanning has become an established tool for generating digital terrain model (DTM) . To obtain DTM in the vegetative area, laser-reflected points on the canopies should be filtered out from digital surface model (DSM) . The filtering is automatically and manually performed, but it is difficult to obtain the perfect DTM, especially in the vegetative hills or mountain areas. In this study accuracy of the“DTM”, which was obtained in the winter of December 2001 and 2002, is validated with ground control points, surveyed by traversing. As a result, root mean square errors (RMSE) are about 0.15m and 0.4-0.6m in the bare flat areas and vegetative slope areas, respectively. Moreover, penetration ratio which is defined by the number of reflected points in DSM divided by the number in DTM, was examined with the RMSE. It was found that the more the penetration ratio increases, the smaller the RMSE is.

Using multiple image endmember spectral mixture analysis to study chaparral regrowth in southern California

This research tested the ability of a multiple endmember (EM) spectral mixture analysis (SMA) approach, applied to multi-temporal Landsat Thematic Mapper (TM) data, to produce realistic and meaningful EM fractions for the study of post-fire regrowth in a southern California chaparral landscape. Eight different image EMs were used, two types for each EM class of interest (green vegetation (GV), non-photosynthetic vegetation (NPV), soil, and shade); the best EM combination was selected for each pixel. These EM fractions were validated with fractions derived from 1 m Airborne Data Acquisition and Registration multi-spectral image data. The EM fractions from the two datasets were similar (r=0.873, 0.776, 0.790 for GV, NPV, and soil, respectively). Chaparral stands were delineated using vegetation type, fire history and slope aspect GIS layers. Mean EM fractions were calculated for each stand, and analysis of variance was performed to determine if EM fractions were different for stands of different age. Short-term trajectories of individual stands appeared to exhibit trends consistent with trends reported in the literature. However, only the youngest and oldest stands were consistently significantly different.