Wind and water are the main agents of soil erosion. The amount of soil they can carry away is influenced by two related factors:
• Speed - the faster either moves, the more soil it can erode;
• Plant cover - plants protect the soil and in their absence wind and water can do much more damage.
Plants provide protective cover on the land and prevent soil erosion for the following reasons:
• Plants slow down water as it flows over the land (runoff) and this allows much of the rain to soak into the ground;
• Plant roots hold the soil in position and prevent it from being washed away;
• Plants break the impact of a raindrop before it hits the soil, thus reducing its ability to erode;
• Plants in wetlands and on the banks of rivers are of particular importance as they slow down the flow of the water and their roots bind the soil, thus preventing erosion.
The loss of protective vegetation makes soil vulnerable to being swept away by wind and water. In addition, over-cultivation and compaction cause the soil to lose its structure and cohesion and it becomes more easily eroded. Erosion will remove the top-soil first. Once this nutrient-rich layer of soil is gone, few plants will grow in the soil again. Without soil and plants the land becomes desert-like and unable to support life.
This is a short description of the cycle between the loss of living plant root and soil erosion, and erosion to prevention of ability to generate new roots:
The plant grows as it feeds from the nutrients available in the soil; after the plant dies it actually replenishes the soil. The new seed grows into a new root and the same cycle starts again, and the soil continues to get better.
As for the other side of the story, the plant dies and nourishes the soil, but the erosion washes away the nutrient rich soil. The exposed rock mud or sand fails to support the next generation of the plant. In other words, the next plant does not grow which leads for the sun to superheat the soil so it breaks and cracks. Next, the cracked soil accelerates erosion which means that no further plant life can grow in this erosion. The erosion continues to expand, eating the edges of surrounding plant life.
Further information at: http://www.bcb.uwc.ac.za/Envfacts/facts/erosion.htm
Photo link: http://www.arthursclipart.org/nature/nature/soil%20erosion.gif