When this warm, moisture-laden air cools, the water vapour condenses and falls to the land as rain. Where there is plenty of vegetation cover, only a small amount of water will run off. When raindrops fall onto bare earth, they loosen particles of soil which are then washed into creeks and rivers. When this happens on an even slope, the result is sheet erosion. On an uneven slope, the water flows in channels, forming rills which can join up to make gullies.
Trees are an important part of the water cycle.
They take up water through their roots and return it to the environment through transpiration . Soil erosion does not occur where there is a good coverage of trees and other vegetation. Although soil erosion is a big problem for the High Country, there are measures which can be taken to control and repair the damage. Reducing the grazing stock and using the same land for several purposes can help control soil erosion. Graziers often plant trees like Radiata pine which will grow quickly and can be sold.