Deforestation is generally defined as the sustained removal of trees. This often is a result of human activities.

Deforestation has been practiced by humans for thousands of years chiefly as a result of clearing land for commercial and industrial development, cutting wood for house building and furniture-making, making paper, intensive collection of firewood, road construction, clearing of land for growing crops and to develop pasture for grazing animals.

The rate of clearance increased during the second half of the 19th century due to agricultural expansion in Europe. There have been massive increases since then. Currently major worries concern the loss of tropical rainforest, one fifth of which was destroyed between 1960 and 1990. Estimates of deforestation of tropical forest for the 1990s range from ca. 55,630 kmē to ca. 120,000 kmē each year. At this rate, all tropical forests may be gone in less than 80 years.

Deforestation is often cited as one of the major causes of the enhanced greenhouse effect. Trees and other plants remove carbon (in the form of carbon dioxide) from the atmosphere during the process of photosynthesis. Both the rotting and burning of wood releases this stored carbon dioxide back in to the atmosphere.

Pressure has been exerted on forests by the worldwide demand for wood and by local people who clear forests in their quests to establish an agrarian land base. Clearing of forests for the development of pasture for cattle has also resulted in deforestation, as has the encroachment upon forests due to increasing human populations.

Deforestation promotes erosion of soil. Under normal circumstances trees and bushes and the forest floor act as a "sponge" for rainfall, slowing its overland and underground flow and releasing it back into the atmosphere through transpiration. Without the buffering effect of forest cover, rain impacting bare soil runs off, carrying away topsoil and often causing flooding. In this environment, nutrients in the soil are leached off and the microorganisms that can replenish these nutrients are disturbed.

Some forests are rich in biological diversity. Deforestation can cause the destruction of the habitats that support this biological diversity.

While the earliest example of deforestation is unclear (there is some controversy over the origin of the Sahara Desert for example), examples such as that of Easter Island show clear evidence of the ecological impact of human activity.

Answers

One answer to the problem of deforestation is to build houses out of non-wood materials, such as brick, stone, concrete, and fiberglass. These materials have the additional benefits of being fireproof, waterproof, and pest-proof. Paper can be made of hemp fiber instead of wood. Although there are strong arguments stating that farming trees may create more forests than farming hemp. Recycled paper reduces the number of trees cut down. E-mails and web pages reduce the amount of wood paper used as well. Some lumber companies are planting trees to replace the trees taken. Hay, dry weeds, trash, garbage, husks, and stalks can be burned for energy instead of wood, although this still causes air pollution. Non-polluting energy generation includes solar cells, windmills, and geothermal energy. New methods are being developed to farm more food crops on less farm land, such as high-yield hybrid crops, greenhouses, autonomous building gardens, and hydroponics. The reduced farm land means less land is cleared for growing crops. In cyclical agriculture, cattle are grazed on farm land that is resting and rejuvenating. Cyclical agriculture prevents the soil from being overfarmed and stripped of its nutrients. Grass is allowed to grow on the resting farm land. The cows eat the grass and leave behind their dung, which is also a source of fertilizer. This also reduces deforestation by using farmland to graze instead of using forest land.

Some societies are making efforts to stop or slow deforestation. In China, where large scale destruction of forests has occurred, each citizen must plant at least 11 trees every year. In western countries, increasing consumer demand for wood products that have been produced and harvested in a sustainable manner are causing forest landowners and forest industries to become increasingly accountable for their forest management and timber harvesting practices.

The Arbor Day Foundation's Rain Forest Rescue program is a charity that helps to prevent deforestation. The charity uses donated money to buy up and preserve rainforest land before the lumber companies can buy it. The Arbor Day Foundation then protects the land from deforestation. This also preserves the way of life of the primitive tribes living on the forest land.