The forest
Complex ecosystem in which trees are the dominant life-form.
Tree-dominated forests can occur wherever the temperatures rise above 50 °F (10 °C) in the warmest months and the annual precipitation is more than 8 in. (200 mm). They can develop under various conditions within these limits, and the kind of soil, plant, and animal life differs according to the extremes of environmental influences. In cool, high-latitude subpolar regions, taiga (boreal) forests are dominated by hardy conifers. In more temperate high-latitude climates, mixed forests of both conifers and broad-leaved deciduous trees predominate. Broad-leaved deciduous forests develop in midlatitude climates. In humid equatorial climates, tropical rainforests develop. There heavy rainfall supports evergreens that have broad leaves instead of the needle leaves of cooler evergreen forests. Having extensive vertical layering, forests are among the most complex ecosystems. Conifer forests have the simplest structure: a tree layer, a shrub layer that is spotty or even absent, and a ground layer covered with lichens, mosses, and liverworts. Deciduous forests are more complex (the tree canopy is divided into an upper and lower story), and rainforest canopies are divided into at least three layers. Forest animals have highly developed hearing, and many are adapted for vertical movement through the environment. Because food other than ground plants is scarce, many ground-dwelling animals use forests only for shelter. The forest is nature's most efficient ecosystem, with a high rate of photosynthesis affecting both plant and animal systems in complex organic relationships.

The forestry
Management of forested land, together with associated waters and wasteland, primarily for harvesting timber but also for conservation and recreation purposes.
The science of forestry is built around the principle of multiple-use land management, though the harvesting and replanting of timber are the primary activities. The main objective is to maintain a continuous supply of timber through carefully planned harvest and replacement. The forest manager is also responsible for the application of other land controls, including the protection of wildlife and the implementation of programs to protect the forest from weeds, insects, fungal diseases, erosion, and fire. The planned management of forests originated in early medieval Europe, where laws regulated the felling of timber and the use of forests for hunting. In the 19th century private forestry schools were established in Europe; and in 1891 the U.S. government authorized its first reserves of forested land. During the 20th century many nations have undertaken reforestation or afforestation programs

The deforestation
Process of clearing forests.
Rates of deforestation are particularly high in the tropics, where the poor quality of the soil has led to the practice of routine clear-cutting to make new soil available for agricultural use. Deforestation can lead to erosion, drought, loss of biodiversity through extinction of plant and animal species, and increased atmospheric carbon dioxide. Many nations have undertaken afforestation or reforestation projects to reverse the effects of deforestation, or to increase available timber.