The effect of fire upon soil needs to be considered in the context of the surrounding ecosystem. In some cases, fires are beneficial, and may even be necessary to maintain the equilibrium of an ecosystem. For example, climax tallgrass prairie requires regular fires to prevent the growth of trees and bushes and to clear away the dead grass, so that the new grass doesn't have to compete with dead plants for sunlight. In such a case, fire actually helps the soil, for in encouraging the growth of grass and preventing the growth of trees, it helps maintain the ecosystem, and thus maintain the thick layer of sod which prevents erosion.