Deforestation is the clearing of forests to obtain lumber and provide space for either agricultural zones or urban development. As a result of massive global urbanization and agricultural development, deforestation is a major factor contributing to climate change. Deforestation alters not only nearby ecosystems -- communities of interacting organisms and their environments -- but also the atmosphere on a global level, with devastating results.
Biodiversity is the number of species in a given ecosystem. Since different species eat different foods and live in different types of habitats, a diverse set of vegetation can enable a greater variety of animals to live in an area. When forests are cleared to make space for large plantations growing one type of crop such as sugarcane or soy, wildlife diversity tends to plummet as species are displaced. However, if crops are introduced on a smaller scale and don't displace native species, they can actually increase diversity since they can act as a habitat for birds and herbivores.
Deforestation also affects nearby rivers, streams, and other water sources as nutrients from the soil are removed through leaching, which happens when water (e.g., from rain) removes soluble nutrients from the soil and carries them elsewhere. Water sources in deforested areas were shown to have higher nitrate levels, lower dissolved oxygen levels, and somewhat higher temperatures (from 20 to 23 degrees Celsius on average) than in forested areas. Water temperatures increase because the trees that provide cover from sunlight are cut down. All of these factors disrupt a river ecosystem because the species that live in the stream have adapted to conditions before the deforestation and may be negatively impacted by the sudden changes.
Deforestation affects not only a forest and its immediate surroundings but also the atmosphere, which in turn spreads across the biosphere -- all the planet's ecosystems and everything in them. According to a 2010 congressional study, 17 percent of all greenhouse gas emissions come from deforestation, from both burning trees and the resulting loss of photosynthesis, which removes carbon dioxide (a greenhouse gas) from the atmosphere. As trees are cut down and burnt, the carbon they contain is released into the atmosphere. Although the increased levels of carbon dioxide may stimulate forest growth, more data is needed to measure the long-term impact.
The soil that provides nutrients for vegetation in ecosystems is also affected by deforestation. Soil in deforested areas is exposed to more sunlight, which increases the soil temperature and oxidizes the carbon in the soil to carbon dioxide. Some of the carbon dioxide released into the atmosphere comes from dead vegetation that decomposes in the ground. In heavily deforested areas, soil erosion and nutrient runoff are common after a rainfall. Soil erosion tends to be greater in drier, more mountainous areas, where there is less vegetation to prevent the movement of soil and to absorb the nutrients.
One possible indirect consequence of deforestation is the spread of diseases, including those originating from birds, such as avian flu. Climate change has already affected migration patterns, and infected birds may move to deforested areas that are more suitable habitats for them, spreading their diseases to the local bird populations. Diseases that are transmitted through insects, such as malaria and Lyme disease, are more common in open spaces with more sunlight exposure. These diseases infect not only birds and vertebrates found in these ecosystems, but also any humans that are exposed to these insects, either in the wild or in nearby urban areas.