Forestry is the science and practice of managing a forest for some goal. Prior to the establishment of forestry as a science-based discipline, the exploitation of forests for various products was carried out without sufficient regard for consequences. For example, trees were cut without ensuring tree regeneration. Logged areas were often burned catastrophically without regard for soil resources and logs dragged or flushed down stream valleys to a mill without concern for the stream habitat or water quality.
Scientific forestry is intended to alleviate these unintended consequences by basing management on research and a goal of sustainable management. The practice of forestry encompasses forest protection, forest engineering, silviculture, forest ecology, economics, biometrics, hydrology, wildlife management, and other disciplines.
Forests face multiple threats, such as fire, disease, insect outbreak, and air pollution. Some of these factors can negatively impact large forest areas over short time periods. Other factors may create chronic stresses which may have long-term consequences on the nature of a forest ecosystem and the species within. Forest management activities are, therefore, undertaken to reduce fire risk, control pests, and to guide forest development processes towards specific, often multiple-use, management goals. Techniques include thinning and controlled burns to reduce fire risk, application of pesticides to control insect outbreaks, removal of diseased trees, and etc.
Modern forestry utilizes large equipment, and thus must utilize engineers. Unique achievements of forest engineers include cable yarding systems, the design of forest roads that produce less sediment, and the development of field harvesting equipment that increases efficiency.
Silviculture is the art and science of growing trees. Various silvicultural systems have been devised to harvest a stand (or selected trees) at lowest cost and with minimal damage, to ensure restocking of the site, to help trees grow rapidly, to favor particular species, and to protect biodiversity.
Forest ecology is the study of the forest as an ecological system. Facets of this science include tree physiology and life history, wildlife biology, nutrient cycling, biogeography, and other topics. The results of studies in forest ecology help inform silviculture as well as efforts to document and conserve biodiversity.
Since forestry is often conducted as a business, the economic aspect of forestry has long received attention. Forest economics encompasses field operations (such as harvesting), long-term stand management strategies, firm-wide (or forest-wide) economic planning, assessments of the impact of forest policy on nearby communities, and even international market assessments of wood supply and effects of tariffs and tax policies.
Biometrics and forest mensuration are concerned with sampling and measuring properties such as stem form and biomass, site index, stand wood yield, etc. These fields are called upon also for the design of forest inventories and analysis of inventory data.
Forest management is typically extensive rather than intensive. The basic spatial unit of management is the forest stand, which is a more-or-less homogenous and identifiable spatial unit. When a prescription like thinning or fertilization is applied, it is applied to one or more stands as whole units. This is because operational efficiencies can only be achieved in this manner and because detailed spatial manipulations (e.g., fertilizing at different levels for each tree) are not feasible with the information and techniques available. While certain scales of complexity of spatial pattern can be achieved, such as by selection or strip cutting or leaving remnant trees or patches, not all possible configurations are feasible. In addition, there may not be any known prescription that would favor a particular species (such as an endangered species) or remove a pest species.
Commercial forestry is necessarily carried out based on an expectation of profit. Non-market benefits (e.g., biodiversity goals, aesthetics) can and need to be accommodated to maintain a social license to manage the forest but they must not be too demanding of corporate resources (e.g., staff time, land area) or competing land-uses will be selected. Forests on public lands, and particular those located in designated wilderness areas, are sometimes managed for non-commercial goals, including wildlife habitat restoration, old-growth preservation, water resource protection, preservation of biodiversity, and rare or endangered species conservation. Management strategies for preservation-related purposes may not generate net income from the harvesting of forest resources although other local and regional economic benefits may be derived from recreation related activities and by other environmental services provided by forests such as water and air protection and purification.