pine

pine, (genus Pinus), genus of about 115 species of economically and ecologically important evergreen conifers (family Pinaceae), 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. 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.

Uses

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.

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.

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Physical description and natural history

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Many botanists consider the genus Pinus to contain two subgenera: Haploxylon, or soft pines, which have one fibrovascular bundle in the leaves, and Diploxylon, or hard pines, which have two. 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; and the sheaths of the leaf clusters are deciduous. 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-colored, with pale, often thick sapwood; and the sheaths of the leaf clusters are persistent.

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.

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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.

(Read Britannica’s “The 7 Best Pinecones [Really!]”)

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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. Despite their susceptibility to fires, many pines actually depend on such ecological disturbance for regeneration. In such fire-dependent forests, the dominant pine species are unable to regenerate among the more shade-tolerant species that grow up around them with time. Fires clear the understory to bare soil, stimulating the germination and establishment of seeds. Most of those species have cones that protect the seeds from the worst of the fire and then open to scatter them on the ash-fertilized seed bed. Many pines can tolerate drought but require full sunlight and clean air for good growth and reproduction.

(Read Britannica’s “Playing with Wildfire: 5 Amazing Adaptations of Pyrophytic Plants”)

Major Eurasian pines

The Scotch pine (P. sylvestris) of northern Europe, when grown under optimum conditions, attains a height of 20 to 40 meters (70 to 130 feet). It is conical in youth, acquires a mushroom-shaped crown in maturity, and has a straight trunk as much as one meter (about three feet) in diameter, fiery red-brown bark, and gnarled, twisted boughs densely clothed with blue-green foliage at the extremities. Scotch pine occurs in varying abundance from Finland and Sweden to the mountains of Spain and the higher slopes of Mount Etna and, longitudinally, from the shores of the North Sea to Siberia. Abundant in the Scandinavian Peninsula, it is the “fir” (fur, fura) of the old Norsemen and still retains that name in Great Britain, although it is a true pine. Economically, it is valued for timber and also for turpentine and tar.

Closely allied to the Scotch pine is the mugo pine (P. mugo), a recumbent bush or small tree, generally only a meter or two (3 to 6.5 feet) high, which often has long zigzag stems that root occasionally at the kneelike bends where they rest upon the ground. It abounds in the Bavarian and Tirolese Alps.

The Austrian, or black, pine (P. nigra) grows to a height of 30 or even 45 meters (98 to 148 feet), with a straight trunk and branches in regular whorls, forming in a large tree a pyramidal head. It derives its name from the sombre aspect of its dark green, sharp, rigid, rather long leaves. The tree displays a deeply fissured bark and light brown branches. This species, widely cultivated as an ornamental, is native to Europe and western Asia.

The cluster pine, or pinaster (P. pinaster), a vigorous grower in coastal sand, has been cultivated extensively for the purpose of stabilizing sand drifts, especially on the dunes of the Bay of Biscay and the Mediterranean. It grows to a height of 12 to 24 meters (39 to 79 feet), and the deeply furrowed trunk occasionally reaches a diameter of a meter or more at the base. Forests of pinaster, apart from the production of timber, have great economic value as a source of turpentine.

Italian stone pines (or umbrella pines, P. pinea) are native to the Mediterranean region and have naturalized in many places. Their spreading rounded canopies of light green foliage, supported on a tall and often branchless trunk, form a particularly striking feature of the landscape of Italy. The cones have been prized from the days of ancient Rome for their edible seeds (pignoli), which are still used for food.

The Himalayan white pine (or blue pine, P. wallichiana) differs chiefly from the Italian stone pine in its longer cones and drooping glaucous foliage. It grows in parts of India, in Bhutan, and on some of Nepal’s ranges, where it attains large dimensions. The chir pine (P. roxburghii) is the dominant tree species in the Himalayans at elevations from 800 to 1,600 meters (2,700 to 5,400 feet).

The Eurasian stone pine (P. cembra) abounds on the Alps, the Carpathians, and the Siberian mountain ranges. The oily seeds are eaten by the inhabitants of the Alps and Siberia and yield a fine oil used for food. The wood is remarkably even-grained and is used by Swiss wood-carvers.