Pine

pine, (genus Pinus), genus of about 115 species of evergreen conifers of the pine family (Pinaceae), distributed throughout the world but native primarily to northern temperate regions. Pines and other conifers are key members of the taiga (boreal forests), coniferous forests, and mixed forests throughout the world, and many pine species are iconic or characteristic constituents of a number of specific ecosystems, such as the longleaf pine (Pinus palustris) ecosystem of the southern United States. Like all trees, the plants provide habitat and a variety of other ecosystem services, and pine seeds are an important food source for birds, squirrels, and other animals. The chief economic value of pines is in the construction and paper-products industries, but they are also sources of turpentine, rosin, oils, and wood tars. Edible pine seeds, which are sold commercially as pine nuts, pignoli, piñons, or pinyons, are produced by several species. Many pines are cultivated as ornamentals, including black, white, Himalayan, and stone pines, and some are planted in reforestation projects or for windbreaks. Pine-leaf oil, used medicinally, is a distillation product of the leaves; charcoal, lampblack, and fuel gases are distillation by-products.

Pines are softwoods, but commercially they may be designated as soft pines or hard pines. Soft pines, such as white, sugar, and piñon pines, have relatively soft timber, needles in bundles of five (less commonly, one to four), stalked cones with scales lacking prickles, and little resin. Their wood is close-grained, with thin, nearly white sapwood; the sheaths of the leaf clusters are deciduous, and the leaves contain a single fibrovascular bundle. Hard pines, such as Scotch, Corsican, and loblolly pines, have relatively hard timber, needles in bundles of two or three (rarely, five to eight), cone scales with prickles, and large amounts of resin. Their wood is coarse-grained and usually dark-coloured, with pale, often thick sapwood; the sheaths of the leaf clusters are persistent, and the leaves have two fibrovascular bundles.

Young pine trees are usually conical, with whorls of horizontal branches. Older trees may have round, flat, or spreading crowns. Most species have thick rough furrowed bark. Pines have two types of branches, long shoots and short shoots, and three types of leaves, primordial, scale, and adult. Seedling plants bear the lance-shaped spirally arranged primordial leaves. The triangular scale leaves, also lance-shaped, are borne on the long shoots of older trees. Both long and short shoots develop in the axils of the deciduous scale leaves. The needlelike photosynthetic adult leaves, with two or more resin canals, are borne in fascicles (bundles) of two to five (rarely, up to eight or solitary) at the tip of each short shoot; they remain on the tree 2 to 17 years.

sugar pine

Learn about female and male pine cones and their roles in pine tree reproductionSee all videos for this article

Pollen-bearing male cones are covered with many fertile scales, each of which bears two pollen sacs. Ovule-bearing female cones, borne on the same tree, have several spirally arranged bracts (modified leaves), each of which is located below a scale with two ovules (potential seeds). In spring or early summer the pollen sacs release pollen through longitudinal slits; each grain has two air bladders for wind dispersal. The scales on the female cones open to receive the pollen and then close; actual fertilization takes place late the following spring. After fertilization, the woody female cone develops over a two- to three-year period. In some species the cones open at maturity and the seeds are released, while in others the cones remain closed for several years until opened by rotting, by food-seeking animals, or by fire. In some pines the scale bearing the nutlike seed may be expanded to form a wing for airborne dispersal.

dwarf mistletoe

Pines are susceptible to several fungal diseases, among them white-pine blister rust, and are attacked by many insects, such as sawflies, weevils, bark beetles, and pine tip moths. Some pines are also susceptible to nematode infections and infestations by parasitic dwarf mistletoes (genus Arceuthobium). Pine forests often suffer severe fire damage, being very combustible because of their high resin content. Pines can tolerate drought but require full sunlight and clean air for good growth and reproduction.

Many botanists consider the genus Pinus to contain two subgenera: Haploxylon, or soft pines, which have one fibrovascular bundle, and Diploxylon, or hard pines, which have two.

Many pines have both lumber trade names and several common names. Numerous trees commonly called pines are not true pines but belong to other genera in the family Pinaceae or to other families of conifers.