Control of soil erosion and motion with the water cycle is often an integral part of activity. Lately more and more people are hoping for vegetation to overcome the problem of water cycling and landslide control. The role of vegetation in slope protection is, among other things, evapotranspiration, infiltration, percolation, humidity moisture below and above the surface, the nature of vegetation that can play a role such as forest in water cycling control are:
Its dynamic depends on the time
The value of its role is determined by the extent, type, growth character, growth state and forest structure (vegetation)
It should be recognized that the role of forests in controlling water cycles, in landslide control and slope protection for a given forest ecosystem situation is limited by climatic, geological, soil and geomorphological conditions (landscape).
The role of vegetation is its presence in a region influenced by environmental factors, namely climate factors and physiographic factors.
- Climate Factor
Climatic factors covering the general characteristics of the climate of the region / region that includes the duration of solar radiation, temperature, rainfall, the evaporation of air and wind.
- Physiographic Factors
Physiographic factors are factors caused by the arrangement and behavior of the earth’s surface, such as slope, altitude, geodynamic processes (sedimentation and erosion) and geological conditions. Extreme physiographic factors tend to create an extreme climate, for example at the top of the mountain range will be different from the slopes and valleys. This will affect the existing vegetation type. Physiographic factors will affect the microclimate of the region, which will affect the existing vegetation type as well. Besides that the different types of soil often affect vegetation type although in the same climate (Nicholas Polunin, 1960).
According to Stocking (1988), soil and vegetation undergo an interactive process that affects surface runoff and erosion, the process includes:
the physical bonding of the soil by the roots and electrochemis and nutrients between the roots and the soil
rainwater drops and runoff water by organic litter
increased infiltration along root areas
increase of organic matter into the soil, so that the soil structure and quality of water holding (water holding) better
increased biological activity in the soil so that the soil structure is better
Effect of vegetation on slope stability
Vegetation is very influential to the stability of the slope, which is caused by the wind that hit the vegetation on the slope will affect the slope to reduce the safety factor, ie the wind conditions can uproot the trees.
Another effect of vegetation is on adding slope loads, adding to shear stress, force or holding force. The plant / vegetation load will increase the steepness of the slope at a slope angle of about 34 degrees or less, while for a larger angle the burden of the plant will disrupt the stability of the slope. Rooting systems from plants will be able to increase cohesion that will inhibit the occurrence of landslides (Shelby, 1990), see Figure below. Vegetation will modify the water content in the soil by lowering the groundwater surface due to evapotranspiration, so it can delay the saturation level of ground water. This will increase the steepness of the slope.
Besides, the vegetation will produce litter that will keep the soil moisture, so that the formation of cracks in the soil can be controlled. With the reduction of cracks in the clay soil in the water becomes reduced so that the slope becomes more stable.
Effect of vegetation on the slopes hydrology
Land cover by vegetation of all shapes can affect the flow of water on a slope. The vegetation cover can be natural forest, cultivated vegetation, vegetation as a hedge, or monoculture vegetation (eg, industrial plantation forest).
The effect of vegetation on hydrology of the slopes is as follows:
Blocks rainwater from falling directly on the soil surface, so the power to destroy the soil can be reduced.
Inhibits surface flow and multiplies infiltration water.
The absorption of water into the soil is enhanced by transpiration (evaporation) through vegetation