Pinus clausa (sand pine) description - The Gymnosperm Database

Pinus clausa

(Chapm. ex Engelm.) Vasey ex Sarg. 1884

Common names

Sand pine, spruce pine, scrub pine (Brendemuehl 1990); "sand" is widely used, while "scrub" is applied to a variety of different species, and "spruce" is more commonly used for P. glabra.

Taxonomic notes

Type not designated, but A. W. Chapman first collected this species in May and June 1875 near Apalachicola, Florida; several herbarium specimens survive from his collections (THIS may be the best). Pinus clausa is a representative of Pinus Section Trifoliae subsection Contortae, which also includes P. banksiana, P. contorta, and P. virginiana. The subsection seems to have arisen in the early Miocene (Jin et al. 2021). The four species are united by strong similarities in foliage, seed cones, and ecology; together, they cover most of the forested biomes of North America. Synonyms include:

Pinus inops var. clausa Chapm. ex Engelmann (1877);
Pinus inops subsp. clausa (Chapm. ex Engelm.) Engelmann (1880);
Pinus virginiana subsp. clausa (Chapm. ex Engelm.) Eckenw. (Eckenwalder 2009).

In addition, Ward (1963) described a var. immuginata (syn. Pinus clausa subsp. immuginata (Ward) A.E.Murray) comprised of trees found in the Florida panhandle that bear non-serotinous cones. The non-serotinuous character has real ecotypic significance, but is not necessarily taxonomically significant; an older isozyme study (Parker et al. 1997a) found only weak support for separation of the two varieties. However, due to their ecological differences, it is convenient to discuss them as distinct varieties, and many published works do so. Var. immuginata is also commonly called the Choctawhatchee race, while var. clausa is the Ocala race. My observations of trees representing both races at locations throughout the species' range indicates that both serotinous and non-serotinous cones are common in both races, and in fact at some sites (e.g. Fort Pickens) serotinous cones predominate on Choctawhatchee trees, and at others (e.g. Jonathan Dickinson State Park) non-serotinous cones predominate on Ocala trees. On balance, the existence of two separable varieties is not supported by the evidence, but the terms "Choctawhatchee" and "Ocala" are useful for distinguishing the two ecotypes.

Description

Monoecious evergreen trees to 28 m tall and 65 cm dbh. Usually single-trunked; in dense pure stands the trees are mostly slender, straight and erect, with ascending branches that are slow to self-prune; but on dunes or other poor soils the trees may be short, crooked, much branched, with irregular crowns. Bark first smooth, reddish brown, with age becoming flaky and brown, and later furrowed with narrow, flat, irregular ridges and no resin pockets. Twigs slender, purplish to reddish brown, glabrous, rough with persistent pulvini after fascicles have fallen. Buds ovoid to cylindrical, 5-10 mm long, red-brown, resinous or not, the scales with fringed white margins. Leaves in fascicles of 2 with 4-8 mm long persistent sheaths, (3-)6-9(-10) cm x 1-1.5 mm, straight to strongly twisted, light to dark green, all surfaces with fine, inconspicuous stomatal lines, margins finely serrulate, apex acute, persisting 2-4 years. Pollen cones borne in small spiral clusters at branch tips, short-cylindric, 10-15 mm long, yellow maturing red-brown. Seed cones maturing in 2 years, usually borne along twigs old enough to have lost their foliage, long-persistent, variably serotinous on non-serotinous, solitary or paired, nearly sessile, largely symmetrical, 3-8 cm long, narrow-ovoid when closed, broad-ovoid when open, red-brown. Cone scales thin-woody, stiff, with a dark red-brown, purple, or purple-gray border distal on adaxial surface; apophyses slightly raised, cross-keeled; umbo central, low-pyramidal, tapering to sharp tip or weak, deciduous prickle. Seeds variably brown, obovoid, slightly flattened, 4-6 mm long with a narrow 15-20 mm wing. 2n=24 (Kral 1993, Farjon 2010, and pers. obs. of trees in habitat, spring 2024).

Distribution and Ecology

USA: Alabama and Florida, at 0-60 m elevation (Kral 1993). The largest sand pine concentration is a block of the Ocala race covering about 101,000 ha in Ocala National Forest, an area sometimes referred to as the "Big Scrub." The Ocala race also grows in a narrow coastal strip from St. Augustine south to Fort Lauderdale, and along the Gulf Coast in small tracts scattered from Tampa to Naples. The Choctawhatchee race grows along the coast of the Panhandle from Apalachicola to Pensacola and on into Baldwin County, Alabama; it is most abundant in Okaloosa and Walton Counties, Florida, covering an area of about 40,500 ha. Scattered stands of Choctawhatchee pines can be found 32 to 40 km inland from the coast in this area. Sparse stands of sand pine are also found on many of Florida's offshore islands (Brendemuehl 1990).

Distribution data from GBIF occurrence download https://doi.org/10.15468/dl.buph83, 2024.11.22.

The species grows in pure stands on acid to strongly acid sand soils (Entisols) of marine origin. Beyond that, there are significant differences in habitat and ecology between the two races. The Ocala pines experience hot, humid summers and mild, dry winters. Precipitation averages 1350 mm per year, and varies from 50 to 75 mm per month from October to April, to 200 to 230 mm per month in June, July, and August. The recorded temperature ranges from -11°C to 41°C, with a mean frost-free period of 290 days. The Choctawhatchee pines have a slightly wetter, cooler climate. Precipitation averages 1520 mm per year, and varies from 100 to 110 mm per month from December to May. The recorded temperature ranges from -17°C to 42°C, with a mean frost-free period of 265 days (Brendemuehl 1990). Most authorities report P. clausa as hardy to Zone 9 (cold hardiness limit between -6.6°C and -1.1°C) (Bannister and Neuner 2001), but some sources report hardiness to as cold as Zone 7A, which is consistent with the observed minimum of -17°C.

The Ocala pines form a highly distinctive community amongst areas of predominantly sandhill community dominated by longleaf pine (Pinus palustris), turkey oak (Quercus laevis), and pineland threeawn (Aristida stricta). In these areas, even-aged P. clausa dominates the overstory, while the understory is composed almost entirely of evergreen shrubs 1.8 to 3.0 m tall. There is little or no herbaceous ground cover. Shrubs found in this understory include sand live oak (Quercus virginiana var. geminata), myrtle oak (Q. myrtifolia), Chapman oak (Q. chapmanii), rosemary (Ceratiola ericoides), tree lyonia (Lyonia ferruginea), scrub palmetto (Sabal etonia), saw-palmetto (Serenoa repens), silk bay (Persea borbonia var. humilis), gopher-apple (Chrysobalanus oblongifolius), and ground blueberry (Vaccinium myrsinites). Mats of lichens (Cladonia spp.) are often plentiful on the ground beneath the trees and shrubs. In contrast, the Choctawhatchee pine community of the Florida panhandle grows in uneven-aged stands. The understory in these stands is quite sparse. Turkey oak, bluejack oak (Q. incana), sand post oak (Q. stellata var. margaretta), pineland threeawn, and prickly pear (Opuntia spp.) are the most common understory species (Brendemuehl 1990).

The principal disturbance agents affecting P. clausa include fire, hurricanes, insects, and pathogens. Like the other pines of subsect. Contortae, the tree is strongly fire-successional; it is unlikely to survive even moderate-intensity fire, but its serotinous cones produce profuse seed in the aftermath of fire and the species readily dominates the replacement stand. Hot ground fires will kill it as readily as crown fires, and factors such as long branch retention and a dense understory contribute to a high incidence of crown fires. A unique combination of fuel and weather conditions is associated with crown fires that occur in forests of the Ocala race. The moisture content of sand pine needles is often lowest in March, and their resin and energy contents reach a yearly high from February through May. These fuel properties take on critical importance when they are combined with severe drought conditions and blustery spring weather characterized by unstable air masses, low relative humidity, and high winds. The conditions may result in spectacular crown fires that release seed from the serotinous cones, helping to perpetuate the species in an edaphic fire climax (Brendemuehl 1990). Myers (1990) reports that wildfire in sand pine stands usually exhibits extreme and uncontrollable behavior, relating a fire in Ocala National Forest in 1935 that burned 2,300 ha in 4 hours. However, controlled burning is possible and provides the principal hope for protecting remnant native stands from conversion to oak, which otherwise is the consequence of fire suppression (Carey 1992).

Hurricanes occur throughout the range of P. clausa, but in the more isolated areas supporting Choctawhatchee pines (e.g. barrier islands), fire is rare or absent. Stands of Choctawhatchee pines show all-ages structures typical of non-catastrophic recruitment associated with severe windstorms, while stands of Ocala pines show uniform age structures typical of recruitment after stand-replacing fire; thus hurricanes likely affect all P. clausa populations but their effect is eclipsed by high-severity fire events in areas dominated by Ocala pines (Drewa et al. 2008). Hurricanes are a dominant disturbance factor affecting other Florida pines, as well.

The principal insect pests of P. clausa also attack the other species of pine growing in Florida, and are found throughout the range of P. clausa. They include bark beetles and sawflies, but a variety of lesser insects pests have also been recorded. Bark beetles, primarily Ips calligraphus and I. grandicollis, cause the greatest losses in sand pine, especially among var. immuginata. These attacks are generally associated with stress factors such as severe drought, lightning, fire, mechanical damage, or crowded stand conditions. The sand pine sawfly (Neodiprion pratti) reduces the productivity of affected trees, and afflicts both varieties of P. clausa. Attacks are reported to be most severe along stand edges and in plantations with fewer than 750 trees per hectare (Brendemuehl 1990).

Sand pine varies in its susceptibility to pathogens. Mushroom root rot caused by Clitocybe tabescens is found in natural stands of the Ocala race, but the Choctawhatchee race is considered resistant to this disease. Phytophthora cinnamomi is reported to be a virulent pathogen on seedlings of both races, but there is no conclusive proof that this fungus is a pathogen of P. clausa under field conditions. Eastern gall rust (Cronartium quercuum), which forms spherical galls mainly on twigs and branches of both P. clausa races, is common but seldom a serious problem. Heart rot caused by Phellinus pini has been reported in sand pine but is usually not a problem until the stands are more than 40 years old, a relatively advanced age in this species (Brendemuehl 1990).

The seeds are known to be eaten by the wild turkey (Meleagris gallopavo), bobwhite quail (Colinus virginianus), fox squirrel (Sciurus niger), gray squirrel (Sciurus carolinensis), and mourning dove (Zenaidura macroura) (NCSU Dendrology Project n.d.).

P. clausa is listed as "Least Concern" for conservation due largely to its extensive range and large population sizes. However, much of its habitat has been lost or severely degraded due to development, and the sand pine scrub in particular is of conservation concern because it is used by a wide variety of special-status plants and wildlife. Various programs have endeavored to protect and restore this habitat by restoring natural fire regimes, substituting harvest for fire, controlling invasive species, and restoring or re-creating habitat at mitigation sites (Richardson and Hedgepeth 2020). The sand pine scrub is a structurally diverse habitat; "scrubs dominated by a canopy of sand pine are usually found on the highest sandy ridgelines. The pine canopy may range from widely scattered trees with a short, spreading growth form, to tall thin trees forming a dense canopy of uniform height" (FNAI 2010). The Ocala National Forest contains the largest remaining area of sand pine scrub habitat, about 100,000 ha. The U.S. Forest Service asserts that introducing prescribed fire is impractical because the flammability of the trees and their understory vegetation makes it extremely difficult to control a fire and keep it from burning into adjacent ownerships. Instead, management agencies use harvest and ground disturbance to mimic the effects of fire, treating large patches (hundreds of hectares) and managing the forest to keep it in a relatively young state, with few patches more than 50 years old. This approach is said to be successful at maintaining the sand pine scrub community and the wide variety of shrubs, herbs, and wildlife that depend upon it (Hinchee and Garcia 2017). However, it appears to also be a land management strategy focused on timber production. The Ocala National Forest also includes the Juniper Prairie Wilderness, an unmanaged sand pine forest that in 2006 experienced a 4700 ha wildfire that burned about 80% of the designated wilderness. Study of this area 1 and 2 years after the fire revealed a pattern of heterogeneous postfire recovery influenced by both prefire conditions (sapling, mature or old forest) and fire severity (unburned, low, moderate, or high). Sapling recruitment was highest in mature stands burned with high severity, and was much lower in sapling and old forest stands regardless of burn severity. Thus a highly heterogenous forest developed in response to a superficially extensive severe disturbance (Freeman and Kobziar 2011). These results suggest that some skepticism is warranted when land management agencies state that timber harvest preserves the ecological functions of the sand pine scrub.

Remarkable Specimens

The largest tree on record is an Ocala pine 65 cm dbh and 26.12 m tall with a crown diameter of 8.5 m; height measured by laser; located near Saint Cloud, Florida (Will Blozan email 2009.01.04). I have no data for the Choctawhatchee pines. Two former large trees included dbh 70 cm, height 29 m, crown spread 12 m; also dbh 62 cm, height 30 m, crown spread 13 m; both located in Starkey Wilderness Park north of Tampa (American Forests 1996). These two trees are no longer listed, and have presumably died or been reduced in stature.

This seems to be one of the most short-lived pines. Trees mature and begin to bear cones as early as 5 years (Cooper 1959). Parker et al. (1997b), studying Ocala pines in Jonathan Dickinson State Park, found a maximum age of 71 years (crossdated). Outcalt (1997) cites ages as great as 80 years among old-growth stands of Choctawhatchee pines, but provides no details; likely these ages represent ring counts, and it's worth noting that Parker et al. (1997b) observed numerous false rings in their samples.

Ethnobotany

I have found no documentation of aboriginal use of the species, and it was also not used in the early historical period, likely because the wood was "light, soft, not strong, brittle" (Sargent 1884) and anyway "most of the sand pine stands were so young, as a result of frequent fires, that they were unmerchantable" (Cooper 1959). Commercial harvest of the species on Ocala National Forest (the largest area forested by sand pine) began in 1946, and utilization has been exclusively as pulpwood. The species has low timber value due to numerous persistent dead limbs and often crooked trunks (Kral 1993, Will Blozan e-mail 2009.01.04).

There has been one dendrochronological study, evaluating age structures and fire history in two southern coastal stands of Ocala pines (Parker et al 1997b). Results tended to confirm the hypotheses of rapid postfire regeneration followed by localized episodic mortality in response to windstorms (hurricanes).

Observations

The best occurrence of Choctawhatchee pines that I know of is in the Fort Pickens area of the Gulf Islands National Seashore, where variously-aged trees can be found on a barrier island where the dominant forest tree is Pinus elliottii. The sand pines mostly occur outside the P. elliottii forests, in areas of coastal scrub vegetation. Inland, good stands of old trees are reported to occur at Fred Gannon Rocky Bayou State Park and on Eglin Air Force Base (Outcalt 1997). The state park looks easily accessible, with the best stands around (30.49593°N, 86.43072°W). Members of the general public can get permits to hike the Florida Trail where it passes through Eglin, but I don't know if that accesses the P. clausa stands.

The Ocala pines occur in coastal scrub developed on dry sandy uplands. Forests consisting primarily of dense even-aged stands are widely distributed in Ocala National Forest, but are probably best seen in the Juniper Prairie Wilderness, which experienced a large wildfire in 2006. The coastal scrub is best seen in the coastal dunes at Jonathan Dickinson State Park. The area is very well managed to preserve a natural disturbance regime, and trees of many ages and sizes can be seen here. It's also an excellent place to see P. elliottii and Taxodium distichum, scenic, and with good hiking; and the visitor center provides an excellent museum, interpretive trail, and detailed map of the park's vegetation. Also worthwhile is the Tiger Creek Preserve, where some exceptionally large individuals can be seen growing in mixed stands with P. elliottii var. densa and P. palustris. The Lake Lizzie Nature Preserve south of Orlando also sounds like a good place to see it. This preserve includes the largest known sand pine (Will Blozan email 2009.01.03).

Remarks

The epithet clausa means "closed", referring to the seed cones.

It's not the usual approach to taxonomy, but a study of the ectomycorrhizal communities of the Ocala and Choctawhatchee races found that 300 species of fungi are mycorrhizal on these taxa, and that each race harbors different mycorrhizal species composition and function. A greenhouse experiment found that Ocala seedlings had the same total biomass regardless of soil origin, but Choctawhatchee seedlings had higher biomass when grown in their own soil rather than the soils occupied by Ocala pines (Rúa 2021).

Citations

American Forests 1996. The 1996-1997 National Register of Big Trees. Washington, DC: American Forests.

Brendemuehl, R. H. 1990. Sand pine, in Burns and Honkala (1990).

Carey, Jennifer H. 1992. Pinus clausa. In: Fire Effects Information System, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Available: https://www.fs.usda.gov/database/feis/plants/tree/pincla/all.html, accessed 2024.11.22.

Cooper, R. 1959. Regeneration of sand pine on the Ocala National Forest. U.S. Forest Service Production Research Report 3, Washington DC. 37 p. Available: Internet Archive, accessed 2024.11.22.

Drewa, Paul B., William J. Platt, Charles Kwit, and Thomas W. Doyle. 2008. Stand structure and dynamics of sand pine differ between the Florida Panhandle and Peninsula. Plant Ecology 196(1):15–25. https://doi.org/10.1007/s11258-007-9333-6.

Engelmann, George. 1877. Pinus Serotinae. Botanical Gazette 2(10):125. https://doi.org/10.1086/325077

Engelmann, George. 1880. Revision of the genus Pinus, and description of Pinus Elliottii. Trans. Acad. Sci. St. Louis 4:177. Available: Biodiversity Heritage Library, accessed 2024.11.22.

Florida Natural Areas Inventory [FNAI]. 2010. Guide to the natural communities of Florida - Scrub. https://www.fnai.org/PDFs/NC/Scrub_Final_2010.pdf, accessed 2024.11.22.

Freeman, Johanna E., and Leda N. Kobziar. 2011. Tracking postfire successional trajectories in a plant community adapted to high-severity fire. Ecological Applications 21:61–74. https://doi.org/10.1890/09-0948.1.

Hinchee, Janet K. and Jay O. Garcia. 2017. Sand pine and Florida scrub-jays—an example of integrated adaptive management in a rare ecosystem. Journal of Forestry 115:230-237. http://dx.doi.org/10.5849/jof.15-150

Jin, Wei-Tao, David S. Gernandt, Christian Wehenkel, Xiao-Mei Xia, Xiao-Xin Wei, and Xiao-Quan Wang. 2021. Phylogenomic and ecological analyses reveal the spatiotemporal evolution of global pines. Proceedings of the National Academy of Sciences 118(20): e2022302118. https://doi.org/10.1073/pnas.2022302118.

Myers, Ronald L. 1990. Scrub and high pine. Pp. 150-193 in R.L. Myers and J.J. Ewel (eds.), Ecosystems of Florida. Orlando, FL: University of Central Florida Press.

NCSU Dendrology Project. [n.d.]. Pinus clausa (Chapm. ex Engelm.) Vasey ex Sarg., accessed 2019.02.28.

Outcalt, Kenneth W. 1997. An Old-Growth Definition for Sand Pine Forests. U.S. Forest Service General Technical Report SRS-12.

Parker, Kathleen C., J. L. Hamrick, Albert J. Parker, and Elizabeth A. Stacy. 1997a. Allozyme diversity in Pinus virginiana (Pinaceae): intraspecific and interspecific comparisons. American Journal of Botany 84(10): 1372–82. https://doi.org/10.2307/2446135.

Parker, Kathleen C., Albert J. Parker, R. Matthew Beaty, Mark M. Fuller, and Timothy D. Faust. 1997b. Population structure and spatial pattern of two coastal populations of Ocala sand pine (Pinus clausa (Chapm. Ex Engelm.) Vasey ex Sarg. var. clausa D. B. Ward). Journal of the Torrey Botanical Society 124(1): 22. https://doi.org/10.2307/2996595.

Richardson, Donald, and Marion Hedgepeth. 2020. Ecological restoration of an endangered sand pine scrub community. Florida Scientist 83:98-112.

Rúa, Megan A. 2021. Characterizing ectomycorrhizal fungal community structure and function of two varieties of Pinus clausa that differ in disturbance history. Forests 12(2):219. https://doi.org/10.3390/f12020219.

Sargent, C. S. 1884. Report on the Forests of North America (Exclusive of Mexico). Washington: Government Printing Office. p. 199. Available https://www2.census.gov/prod2/decennial/documents/1880a_v9-03.pdf, accessed 2019.02.28.

Ward, Daniel B. 1963. Contributions to the flora of Florida, Pinus (Pinaceae). Castanea 28:1-10.