The pine family (Pinaceae), which contains over 50 species in cultivation in the United States, represents a group of magnificent evergreen species that have tremendous value both as ornamentals and as timber trees. Almost all pines have a continuous trunk that displays whorls or tiers of branches, with deviant branches only randomly and rarely appearing outside the whorl.

View a low magnification image of the pine stem.

View a medium magnification image of the pine stem.

View a high magnification image of the pine stem.

The yellow or loblolly pine, Pinus taeda, displays needle-like leaves that are borne in sheathed clusters of three, and grow 6 to 9 inches long. The cones range from 3 to 5 inches in length and have long scales with very sharp points. Although the yellow is not the most beautiful of pine trees, it is tolerant of a wide range of soil conditions, and is seldom seriously affected by insects or diseases. Young yellow pines grow rapidly, reaching a height of 90 feet at maturity.

Chief uses for wood from the southern pine family are pulpwood, hard and particle board, poles, mine timbers, pilings, railroad ties, veneer and construction plywood, structural timbers, building construction (all phases), boxes, baskets, mill products, woodenware, novelties, paving blocks, tanks, and silos. Although usually grown in even-stand plantations with greatly reduced habitat diversity, many species of birds and mammals thrive in woods dominated by yellow pines.

When examined under the microscope in thin section, pine tree specimens reveal an abrupt transition from spring to summer wood. Tracheids average 35 to 45 micrometers in diameter, and bordered pits occur in a single row, or paired on the radial walls. Longitudinal parenchyma is lacking, and the rays are of two types: uniseriate and fusiform. Resin canals have thin-walled epithelium and are frequently occluded with tylosoids in the heartwood of yellow pines. Although not well studied, older pine trees exhibit senescence by reducing or eliminating cone formation, and this aging process is reportedly accelerated by air pollution.

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