Description

Monoecious evergreen trees up to 30 m tall and 100 cm dbh. Trunk can be straight, but is often bent and twisted. Crown usually columnar to irregular. Bark on mature trees gray, fissured and cross-checked into elongate, irregular, scaly plates, lacking resin pockets, about 6-8 mm thick; it resembles red oak bark, and is unlike any other pine in the region. On younger trees and branches, the bark is smooth and gray. Branches whorled, spreading to ascending; twigs slender, purple-red to red-brown, occasionally glaucous, aging gray, smooth. Buds ovoid to ovoid-cylindric, red-brown, 5-10 mm, slightly resinous; scale margins finely fringed. Leaves 2 per fascicle, spreading to ascending, persisting 2-3 years, 4-8(-10) cm × 0.7-1.2 mm, pliable, slightly wavy, slightly twisted, dark green, stomata in lines on all surfaces, margins finely serrulate, apex acute; fascicle sheath 5-10 mm, base persistent. Pollen cones long cylindric, 10-15 mm, purple-brown. Seed cones maturing in 2 years, shedding seeds soon after, persisting a year or more, spreading to recurved, nearly symmetric, long-ovoid before opening, ovoid-cylindric when open, 3.5-7 cm, red-brown, aging gray, on peduncles 1-10 mm long. Cone scales lack contrasting border on adaxial surfaces (as in P. echinata); apophyses slightly thickened and raised; umbo central, depressed, unarmed or with small, curved, weak, deciduous, short-incurved prickle. Seeds deltoid-obovoid; body ca. 6 mm, brown, mottled darker; wing to ca. 12 mm. 2n=24 (Kral 1993, Mark Brian email 2006.12.31). See García Esteban et al. (2004) for a detailed characterization of the wood anatomy.

Also see the Key to the Pines of the Southeastern United States.

The shoots and leaves resemble P. echinata but cones are less prickly, leaves are a deeper green, and the bark lacks resin pockets (Kral 1993).

Life History

Trees begin producing cones at about age 10 and reach full production potential at 20-40 years. Seed cones are borne in upper crown, pollen cones somewhat lower. Receptive seed cones appear in February-March depending on local climate. Seed cones mature in September-October of the second growing season, and seeds are released in November. Seed germination is not reported, but studied pines in the Taeda clade germinate in early spring following seed release, and do not form a seed bank. P. glabra seedlings can germinate and grow on organic-rich substrates beneath a hardwood (or pine) canopy; they form a wide-spreading, lateral taproot near the surface before penetrating deep into the soil. Trees grow rapidly (heights of 11.6 to 14.9 m reached in 15 years) and reach maximum height at about 60-75 years of age. There seem to be no data on potential maximum ages (Koch 1972, Kossuth and Michael 1990, and sources therein).

Distribution and Ecology

USA: South Carolina, Georgia, Florida, Alabama, Mississippi & Louisiana on sandy alluvium and mesic woodland in the Atlantic and Gulf coastal plains, at 0-150 m elevation (Kral 1993). It is most abundant in S AL and S MS (Koch 1972).

The climate features hot, humid summers and mild winters. Annual rainfall is about 1270 mm, distributed throughout the year. The growing season is about 240 days and the average annual temperature is about 16°C. Predominant soils are acidic sandy loams high in organic matter, and the pine grows well on poorly drained sites that are intermittently waterlogged, such as in riparian areas or on rich moist hummocks (Kossuth and Michael 1990, and sources therein).

Distribution data from USGS (1999).

Spruce pine is the least fire-adapted pine in North America, and is almost unique among the temperate pines in being able to establish on heavily shaded sites beneath a hardwood canopy, and thereafter to grow into the forest canopy and become an emergent tree (some white pines also have this potential) (Kral 1993). It will also establish beneath a pine canopy, and this has particularly been observed with establishment beneath lobolly pine (P. taeda) that have invaded abandoned agricultural fields (Farjon 2010). It will regenerate prolifically following destruction of a hardwood canopy by a windstorm (usually a hurricane), and virtually all of its native range is at least occasionally affected by such storms (Batista and Platt 2003); consequently, the age structure of a forest with spruce pine tends to reflect that dates of past hurricanes (Hirsh and Platt 1981). I suspect that prevalence of stand-destroying disturbance by windstorms was one of the primary selective pressures leading to the development of this ecologically unique pine. Surprisingly, it is the least wind-resistant of all southern pines; it breaks readily due to the brittle wood (Mitchell and Andreu 2024). Perhaps this means that affected emergent trees are broken off rather than windthrown; the same thing happens to the emergent Taxodium distichum.

This species occurs mainly in forest cover types Loblolly Pine-Shortleaf Pine, Loblolly Pine, Loblolly Pine-Hardwood, Slash Pine, and Slash Pine-Hardwood. Regeneration typically occurs beneath overstory species such as magnolia (Magnolia spp.), gum (Nyssa spp.), hickory (Carya spp.), beech (Fagus spp.), and oak (Quercus spp.). Other associated trees include various species of Pinus, Ulmus, Ilex, Prunus, and Crataegus, along with shrubs and woody vines such as Callicarpa americana Myrica cerifera, Ilex glabra, Clethra alnifolia, Berchemia scandens, Vaccinium spp., Toxicodendron radicans, Smilax spp., Rubus spp., and Vitis spp. (Kossuth and Michael 1990).

A variety of pests and pathogens affect P. glabra, but since it rarely occurs in pure stands, they seldom have a substantial impact at the population level. The pests include southern pine beetle Dendroctonus frontalis, gall mites Trisetacus floridanus, and sawflies Neodiprion spp. Unlike several other southern pines, spruce pine is resistant to fusiform rust Cronartium quercuum. The principal cause of mortality is neither pest nor pathogen, but is lightning, which particularly affects emergent mature trees (Mitchell and Andreu 2024).

Spruce pines are heavily utilized for winter roosting by turkeys, since they are often the only cover in the bottomlands in the winter (Mark Brian email 2006.12.31). Northern bobwhite and squirrels eat spruce pine seeds (Van Dersal 1938). Although pines in the SE US generally provide both food and cover for wildlife, the matter seems to have been little investigated for spruce pine.

Pinus glabra has been assessed as of "Least Concern" for conservation due to its very extensive range, with many discrete populations and little evidence of long-term decline.

Remarkable Specimens

A tree near Alachua, FL; 110 cm dbh, 35.7 m tall, with a 15.5 m crown spread, when measured in 2016 (American Forests 2021). This is also the tallest extant tree recorded. A previous champion near Norwood, LA was 129 cm dbh and 34.14 m tall (American Forests 2000); since this was a larger tree, it has presumably died. The height record is matched by a tree in Moody Tract Natural Area, GA; it is 35.63 m tall (Rucker 2003). Dial et al. (1976) cite a tree on Mt. Holly Plantation near Mt. Holly, SC that it measured 38.1 m tall and 107 cm dbh.

Ethnobotany

Spruce pine was used very heavily by the Cherokee people. All recorded uses were medicinal, applied both externally and internally and used nearly all parts of the plant: foliage, resin, bark, and roots (Native American Ethnobotany Database 2025). No uses are reported for peoples other than the Cherokee, but this is unlikely; many tribes lived within the range of spruce pine, and many of them likely put it to similar uses.

Pinus glabra has occasionally been used for its lumber, which is reported to be brittle and not decay-resistant. It is suitable for pulp, but not widely used (Kossuth and Michael 1990). Due to radically different drying rates, spruce pine cannot be intermixed with other southern pine species in lumber manufacturing. It can be made into lumber, but it must be dried separately. It is often used for large timbers and beams (Mark Brian email 2006.12.31). It is also grown sometimes as a Christmas tree. When grown in full sunlight, spruce pine boles/stems typically grow twisted, crooked, and more compact. For this reason, it is not grown on a significant scale in a plantation setting, but it does confer a certain ornamental value (Kossuth and Michael 1990, Mitchell and Andreu 2024). It is hardy to Zone 8 (cold hardiness limit between -12.1°C and -6.7°C) (Bannister and Neuner 2001).

Observations

Spruce pine is common along the trails of Torreya State Park in Florida. Hurricane Michael hit the park on October 10, 2018. Most of the pines (except P. palustris) and other trees in the forest were snapped off. When I visited the site in early 2024, P. glabra was one of the most abundant regenerating species, with many individuals already 4-5 m tall. This area was also hit by Hurricane Helene in 2024, though, but as of early 2025 no damage assessments have been reported.

The species is also common in the San Felasco Hammock Preserve State Park in Florida, particularly along the popular trail system in the southern part of the park. This area holds the largest known spruce pine in Florida. Exceptionally large trees can also be seen in a floodplain setting at the Edisto River preserve just E of Jacksonboro, SC. An interpretive trail provides access.

An interesting mixed stand with loblolly pine is at Bluff Lake within the James Webb Wildlife Center, also in SC. Spruce pine can also be found mixed with loblolly pine in Congaree National Park.

Stalter and Dial (1986) describe 9 sites they found throughout the range of the species to characterize it at "maximum development". If these sites still exist, they would be worth checking out. They found a nearly pure stand at a site "located in Pearl River County, Mississippi, just east of the Pearl River".

Remarks

The epithet glabra refers to the smooth bark ("cortice glabro", Walter [1788]) found on young trees, which commonly resembles the bark of neighboring hardwoods.

There has been remarkably little study of Pinus glabra, considering its broad distribution within a densely-populated area.

Citations

American Forests 2000. The National Register of Big Trees 2000. Washington, DC: American Forests.

American Forests 2021. 2021 National Register of Champion Trees. Washington, DC: American Forests.

Batista, William B. and William J. Platt. 2003. Tree population responses to hurricane disturbance: syndromes in a south-eastern USA old-growth forest. Journal of Ecology 91(2):197-212.

Cruz-Nicolás, Jorge, Juan Pablo Jaramillo-Correa, and David S. Gernandt. 2024. Stochastic processes and changes in evolutionary rate are associated with diversification in a lineage of tropical hard pines (Pinus). Molecular Phylogenetics and Evolution 192:108011, https://doi.org/10.1016/j.ympev.2024.108011.

Dial, S. C., Batson, W. T., and Stalter, R. 1976. Some Ecological and Morphological Observations of Pinus glabra Walter. Castanea 41(4):361–377.

Hirsh, Donald W.; Platt, William J. 1981. Dynamics of regeneration within a spruce pine population in a beech-magnolia forest in north-central Florida. Bulletin of the Ecological Society of America. 62: 71-72. Abstract.

Koch, P. 1972. Utilization of the southern pines. U.S. Department of Agriculture, Agriculture Handbook 420. Washington, DC. V.1, p.32.

Kossuth, Susan V. and J. L. Michael. 1990. Spruce pine, in Silvics of North America, V.1, Conifers. USDA Agriculture Handbook 654. Available: https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_1/pinus/glabra.htm, accessed 2025.03.27.

Mitchell, Allie M. and Michael G. Andreu. 2024. Pinus glabra Walt., Spruce Pine. FOR405/FR476. https://doi.org/10.32473/edis-fr476-2024.

Native American Ethnobotany Database. 2025. Results of search for "Pinus glabra". Available: http://naeb.brit.org/, accessed 2025.03.28.

Stalter, R., and Dial, S. C. 1986. Some observations on Pinus glabra Walter (Pinaceae). SIDA, Contributions to Botany 11(3):325–328.

Van Dersal, William R. 1938. Native woody plants of the United States, their erosion-control and wildlife values. Washington, DC: U.S. Department of Agriculture. 362 p.

Walter, T. 1788. Flora Caroliniana. London: J. Fraser. p. 237. Available: Biodiversity Heritage Library, accessed 2025.03.27.

See also

The FEIS database.