About Pinus jeffreyi Balf.
Pinus jeffreyi Balf., commonly known as Jeffrey pine, is a large coniferous evergreen tree. It typically grows 25 to 40 meters (82 to 131 feet) tall, and rarely reaches up to 53 meters (174 feet) tall; trees growing at or near tree line stay smaller in size. Its leaves are needle-like, produced in bundles of three, are stout and glaucous gray-green, and measure 12 to 28 centimeters (4+3⁄4 to 11 inches) long. Its cones are 12 to 30 centimeters (4+3⁄4 to 11+3⁄4 inches) long; they are dark purple when immature and ripen to pale brown, with thinly woody scales that bear a short, sharp inward-pointing barb. The brownish seeds are 10 to 12 millimeters (3⁄8 to 1⁄2 inch) long, with a large wing that measures 15 to 25 millimeters (5⁄8 to 1 inch) long. Jeffrey pine is closely related to, and similar in appearance to, Pinus ponderosa (ponderosa pine). A key way to distinguish the two species is by the barbs on their cone scales. The sharp barbs on P. jeffreyi cone scales point inward, so the cone feels smooth when rubbed across the palm of the hand; P. ponderosa cone scale barbs point outward, so they feel sharp and prickly to the palm. The mnemonic 'gentle Jeffrey' and 'prickly ponderosa' is commonly used to remember this difference. Other distinguishing characteristics include P. jeffreyi's glaucous, less bright green needles compared to P. ponderosa, plus its stouter, heavier cones with larger seeds and inward-pointing barbs. P. jeffreyi can also be told apart by its relatively smaller scales of reddish-brown bark, compared to the larger orangish bark plates of ponderosa pine. The scent of P. jeffreyi is variously described as similar to vanilla, lemon, pineapple, violets, apple, and most commonly butterscotch. This scent can be detected by breaking off a shoot or needles, or by smelling the resin between the bark's plates. The scent is linked to the very unusual composition of the tree's resin, where the volatile component is almost entirely pure n-heptane. Because of this trait, the species is sometimes called the gasoline tree. The easy availability of pure n-heptane from this tree became the basis for the modern octane rating system in the late 1920s. The largest known specimen by trunk volume is the Eureka Valley Giant, located in Stanislaus National Forest. Its trunk holds 129 cubic meters (4,600 cubic feet) of wood, it stands 59 meters (194 feet) tall, and has a trunk diameter of 2.5 meters (8 feet 2 inches). Pinus jeffreyi occurs from southwestern Oregon south through much of California, mainly on the eastern side of the Sierra Nevada, to northern Baja California in Mexico. It is a high-altitude species: in the northern part of its range, it grows widely at 1,500 to 2,100 meters (4,900 to 6,900 feet) altitude, and grows at 1,800 to 2,900 meters (5,900 to 9,500 feet) in the southern part of its range. Jeffrey pine is more stress tolerant than ponderosa pine. At higher elevations, on poorer soils, and in colder, drier climates, P. jeffreyi replaces P. ponderosa as the dominant tree. It is also tolerant of serpentine soils, and is often dominant in these conditions, even on dry sites at fairly low altitudes. Pinus jeffreyi can hybridize with P. ponderosa and Coulter pine, but this happens very rarely because the three pine species release pollen at different times of the year. Mammals and birds collect the seeds of P. jeffreyi. The wood of Pinus jeffreyi is similar to ponderosa pine wood, and is used for the same purposes. Crystallized sap from P. jeffreyi has been eaten as candy. The exceptional purity of n-heptane distilled from P. jeffreyi resin led to n-heptane being selected as the zero point on the octane rating scale for petrol. Because its resin consists mainly of n-heptane, it is a poor source of turpentine. Before P. jeffreyi was recognized as a separate species from ponderosa pine in 1853, resin distillers working in its range experienced a number of 'inexplicable' distillation explosions, now known to be caused by the unintended use of Jeffrey pine resin.
