A wind barrier is usually a row of trees planted on the edge of a farm. This reduces erosion in two ways. First of all, it slows down the prevailing winds when they encounter the barrier. This prevents topsoil from being carried away as dust and debris. The trees serve an additional purpose to prevent erosion due to the fact that their roots help to anchor the soil, thus preventing it from blowing away . Also, groundwater is retained in the soil and absorbed by the trees, which additionally prevents further erosion of soil due to running water. Native vegetation, ground cover and trees are all essential at preventing erosion due to wind.