Biological measures for soil and water conservation work by their protective impact on the vegetation cover. A dense vegetation cover

• prevents splash erosion;
• reduces the velocity of surface runoff;
• facilitates accumulation of soil particles;
• increases surface roughness which reduces runoff and increases infiltration;
• the roots and organic matter stabilise the soil aggregates and increase infiltration (Morgan 1999; Richter 1998; Hurni et al. 2003).

These effects entail a low soil erosionrate compared with an uncovered soil which shows in general a high soil erosion rate. Even cultivated crops in agricultural areas are a better protection against soil loss than uncovered soil (relatively high soil erosion rate) (Morgan 1999). Other positive impacts have been observed, such as improved soil moisture condition (or protection against erosion by wind).

Thus, biological measures are an effective method of soil and water conservation, especially since they are low in cost (Heathcote 1998). Additionally, these can be used with structural and agronomic measures.

Several types of biological soil and water conservation measures exist (see figure).

Afforestation is presented on the following page.