2.11 Vegetation

Plant roots provide a strong interlocking network to hold unconsolidated materials together and prevent flow. Furthermore, plants are very effective in removing water from the soil, thus increasing the shear strength. Although, the extra weight of plants may cause a slight destabilizing effect if the root network is of limited extent, the overall vegetation increases stability of a slope. Different types of vegetation like grasses, herbs, shrubs and trees are used to stabilize the slope stability and reinforcement of the soil (Coppin and Richards, 1990) (figure 10). Grasses are quick to establish, versatile and cheap and have wide range of tolerance, with dense cover but shallow rooting requiring regular maintenance. Herbs have deeper rooting, nitrogen fixers, compatible with grasses but they have expensive seed, difficult establishment and winter dieback. Shrubs have deeper rooting and robust and cheap requiring low maintenance. It offers substantial ground cover and available in many ever green species. Trees have substantial rooting, low maintenance but require long time to establish and are slow growing. The relative effectiveness of these different vegetation patterns in a specific locale is a function of quality of vegetation, topography, slope, hydrology, geology, and soils characteristics. ญญThe loss or removal of slope vegetation can result in either increased rates of erosion or higher frequencies of slope failure.


Figure 10.  Mechanisms of root reinforcement of grass plants and tree