Some is caused by a combination of human and natural factors like wildfires and subsequent overgrazing, which may prevent the growth of young trees. Deforestation and forest degradation can cause biodiversity to decline. When forest cover is removed, wildlife is deprived of habitat and becomes more vulnerable to hunting. Considering that about 80% of the worlds documented species can be found in tropical rainforests, deforestation puts at risk a majority of the Earths biodiversity. Healthy forests help absorb greenhouse gasses and carbon emissions that are caused by human civilization and contribute to global climate change.
Without trees, more carbon and greenhouse gasses enter the atmosphere. As a result of deforestation, trees no longer evaporate groundwater, which can cause the local climate to be much drier. Deforestation accelerates rates of soil erosion, by increasing runoff and reducing the protection of the soil from tree litter. Millions of people rely directly on forests, through small-scale agriculture, hunting and gathering, and by harvesting forest products such as rubber. Deforestation continues to pose severe social problems, sometimes leading to violent conflict. An estimated 18 million acres (7.3 million hectares) of forest are lost each year, according to the United Nations Food and Agriculture Organization (FAO).