Desertification is the accumulated result of inappropriate land use and a harsh climate. Over-cultivation exhausts the soil, overgrazing leaves behind little vegetation that protects it from erosion, deforestation destroys the trees that bind the soil to the land and underdeveloped irrigation systems turn croplands salty. The semi-dry lands bordering desert exist in a delicate ecological balance and are limited in their potential to adjust to increased environmental pressures. The causes are multiple and interact in a complex manner. Lacking alternative survival strategies, farmers tend to over-exploit natural resources. Soil nutrients and organic matter begin to diminish once intensive agriculture consumes quantities of nutrients greater than the soils natural regeneration capacities.