The world's great forests influence the biosphere in many ways. Like giant sponges, forested watersheds absorb hold, and gradually release water. Forests also help control soil erosion, flooding, and sediment buildup in rivers, lakes, and reservoirs Deforestation is the name for removal of all trees from large tracts of land for logging, agricultural, or grazing operations. The loss of vegetation exposes the soil, and this promotes leaching of nutrients and erosion, especially on steep slopes. Cleared plots soon become infertile and are abandoned. The photograph a shows forest destruction in the Amazon basin of South America. Deforestation is linked with several ecological problems. One of the most troubling effects relates to the global carbon cycle. Tropical forests absorb much of the sunlight reaching equatorial regions of Earth's surface. When the forests are cleared, the land becomes "shinier," and reflects more incoming energy back into space. The many millions of photosynthesizing trees in these vast forests help sustain the global cycling of carbon and oxygen. When trees are harvested or burned, carbon stored in their biomass is released to the atmosphere in the form of carbon dioxide- and this may be boosting the greenhouse effect. About half the world's tropical forests have been cut down for cropland, fuel wood, grazing land, and timber