Pinus ponderosa

Ponderosa pine

Pinaceae

The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Coniferophyta (conifers). Class - Pinopsida. Order - Pinales. Family - Pinaceae (pine). Genus - Pinus L. Species - Pinus ponderosa Douglas ex Lawson & C. Lawson

Ecology: Ponderosa pine is one of the most widely distributed pines in western North America. Ponderosa pine can be either a climax or a seral species. It is a climax species at the lower limits of the coniferous forests, and a seral species in higher elevation mesic forests where more competitive conifers are capable of growing. In climax forests, ponderosa pine stands often contain many small, even-aged groups rather than a true uneven-aged structure. The successional status of ponderosa pine ranges from seral to climax depending on specific site conditions. It plays a climax role on sites toward the extreme limits of its environmental range and becomes increasingly seral with more favorable conditions. On sites with favorable moisture, pines encounter greater competition and must establish opportunistically. On moist sites it is usually seral to Douglas-fir and firs (mainly grand fir and white fir). On severe sites it are climax by default because other species cannot establish. The ability of ponderosa pine seedlings to grow vigorous taproots is one reason for their tenacity on severe sites where associated species often fail.

Near the Yosemite Forest Dynamics Plot (YFDP), Pinus ponderosa is abundant on south facing slopes and lower elevations. Within the YFDP, which is mostly north-facing, Pinus ponderosa is rare. The elevation of the Utah Forest Dynamics Plot (UFDP) is at the upper limit of the range of Pinus ponderosa, but there are a few individuals found on open, south-east facing slopes.

Identification

Trees to 72m; trunk to 2.5m diam., straight; crown broadly conic to rounded. Bark yellow- to red-brown, deeply irregularly furrowed, cross-checked into broadly rectangular, scaly plates. Branches descending to spreading-ascending; twigs stout (to 2cm thick), orange-brown, aging darker orange-brown, rough. Buds ovoid, to 2cm, fully 1cm broad, red-brown, very resinous; scale margins white-fringed. Leaves 2--5 per fascicle, spreading to erect, persisting (2--)4--6(--7) years, 7--25(--30)cm (1--)1.2--2mm, slightly twisted, tufted at twig tips, pliant, deep yellow-green, all surfaces with evident stomatal lines, margins serrulate, apex abruptly to narrowly acute or acuminate; sheath 1.5--3cm, base persistent. Pollen cones ellipsoid-cylindric, 1.5--3.5cm, yellow or red. Seed cones maturing in 2 years, shedding seeds soon thereafter, leaving rosettes of scales on branchlets, solitary or rarely in pairs, spreading to reflexed, symmetric to slightly asymmetric, conic-ovoid before opening, broadly ovoid when open, 5--15cm, mostly reddish brown, sessile to nearly sessile, scales in steep spirals (as compared to Pinus jeffreyi ) of 5--7 per row as viewed from side, those of cones just prior to and after cone fall spreading and reflexed, thus well separate from adjacent scales; apophyses dull to lustrous, thickened and variously raised and transversely keeled; umbo central, usually pyramidal to truncated, rarely depressed, merely acute, or with a very short apiculus, or with a stout-based spur or prickle. Seeds ellipsoid-obovoid; body (3--)4--9mm, brown to yellow-brown, often mottled darker; wing 15--25mm.

Threats

Fire effects: Ponderosa pine has evolved with a thick bark and open crown structure that allows them to survive most fires. Mature trees self-prune, leaving a smooth bole that reduces aerial fire spread. Other fire adaptations include deep roots, high foliar moisture content, insulated bud scales, and medium to light lichen growth. Seedlings prefer the mineral-soil seedbeds created by fire. Fires have had a profound effect on the distribution of ponderosa pine. Although the seedlings are readily killed by fire, larger trees possess thick bark, which offers effective protection from fire damage. Competing tree species, such as grand fir (Abies grandis) and Douglas-fir, are considerably less fire tolerant, especially in the sapling and pole size classes. Ponderosa pine, therefore, was able to maintain its position as a dominant seral species on large areas of middle-elevation forests in the West.

Pests and pathogens: The most damaging of the tree-killing insects are several species of native Dendroctonus, most notably Dendroctonus ponderosae, or mountain pine beetle. Trees also die from the combined effects of a blue stain fungus transmitted by the beetle and extensive larval consumption of the phloem. Among bark beetles, Ips species are second in destructiveness only to Dendroctonus Ips are present naturally in all stands, where they usually breed in slash. Dwarf mistletoe (Arceuthobium vaginatum ssp vaginatum in the Southwest, and A. campylopodium in California and the Northwest) is ponderosa pine's most widespread disease, absent only in the Black Hills. It seems to be particularly devastating in the Southwest, where it infects trees on about one-third of the commercial acreage.

Reproduction

Flowering and Fruiting - Ponderosa pine is a monoecious gymnosperm. At pollination the male strobili, borne in short, dense clusters, are 2 to 3 cm long and female conelets are 2.5 cm long.

Seed Production and Dissemination - Ponderosa pine bears cones as early as 7 years and continues to produce good seeds to at least 350 years. Ponderosa pine seeds are consumed by a great many birds and small mammals such as mice, chipmunks, and tree squirrels. In years of low cone production, the potential seed crop may be severely reduced

Seedling Development - Germination of ponderosa pine is epigeal. Moisture stress reduces seed germination as well as initial seedling survival and growth. Older seedlings, however, are able to cope with limited moisture supplies by reducing transpiration and by vigorously extending their root systems.

Vegetative Reproduction - Ponderosa pine does not reproduce naturally by vegetative methods. It can be propagated by rooting and grafting, but success decreases rapidly when scions are taken from trees older than 5 years.

Species Distribution

Citation

USDA Plants Database
USDA, NRCS. 2016. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.

USFS Plant Database
Habeck, R. J. 1992. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.

Flora of North America
Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 19+ vols. New York and Oxford.

Silvics of North America
Burns, R.M., and B.H. Honkala. 1990. Silvics of North America (Volume 1: Conifers, Volume 2: Hardwoods). USDA Forest Service Agricultural Handbook 654.

The Jepson Herbarium
The Jepson Manual: Vascular Plants of California. B.G. Baldwin, D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken [editors]. 2012. 2nd edition, thoroughly revised and expanded. University of California Press, Berkeley, CA.

USGS Plant Species Range Maps
Critchfield, W.B., and Little, E.L., Jr., 1966, Geographic distribution of the pines of the world: U.S. Department of Agriculture Miscellaneous Publication 991, p. 1-97. Little, E.L., Jr., 1971-1978, Atlas of United States trees, volume 1,3,13,17, conifers and important hardwoods: U.S. Department of Agriculture Miscellaneous Publications.