| Southern live oak | |
|---|---|
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| The Volusia Oak on theSt. Johns River inVolusia, Florida. | |
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| 1812 illustration[1] | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Fagales |
| Family: | Fagaceae |
| Genus: | Quercus |
| Subgenus: | Quercussubg. Quercus |
| Section: | Quercussect. Virentes |
| Species: | Q. virginiana |
| Binomial name | |
| Quercus virginiana | |
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| Synonyms[4] | |
List
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Quercus virginiana, also known as thesouthern live oak, is anevergreenoaktree endemic to theSoutheastern United States.[5] Though many other species are loosely calledlive oak, the southern live oak is particularly iconic of theOld South. Many very large and old specimens of live oak can be found today in theDeep South region of the United States.[6]
Althoughlive oaks retain theirleaves nearly year-round, they are not trueevergreens. Live oaks drop their leaves immediately before new leaves emerge in the spring. Occasionally,senescing leaves may turn yellow or contain brown spots in the winter, leading to the mistaken belief that the tree hasoak wilt, whose symptoms typically occur in the summer.[7] A live oak's defoliation may occur sooner in marginal climates or in dry or cold winters.[8]
Thebark is dark, thick, and furrowed longitudinally. The leaves are stiff and leathery, with the tops shiny dark green and the bottoms pale gray and very tightlytomentose, simple and typically flattish with bony-opaque margins, with a length of 2–15 centimetres (3⁄4–6 inches) and a width of1–5 cm (3⁄8–2 in), borne alternately. The male flowers are green hangingcatkins with lengths of 7.5–10 cm (3–4 in). Theacorns are small,1–2.5 cm (3⁄8–1 in), oblong in shape (ovoid or oblong-ellipsoid), shiny and tan-brown to nearly black, often black at the tips, and borne singly or in clusters.[9][8]
Depending on the growing conditions, live oaks vary from a shrub-size to large and spreading tree-size: typical open-grown trees reach 20 m (66 ft) in height, with a limb spread of nearly 27 m (89 ft).[10] Their lower limbs often sweep down towards the ground before curving up again. They can grow at severe angles;Native Americans used to bend saplings over so that they would grow at extreme angles, to serve as trail markers.[citation needed]
The southern live oak has a deeptaproot that anchors it when young and eventually develops into an extensive and widespread root system. This, along with its low center of gravity and other factors, makes the southern live oak extremely resistant to strong sustained winds, such as those seen in hurricanes.[11]
Quercus virginiana is placed in the southern live oaks section of the genusQuercus (sectionVirentes).[12]
A large number of common names are used for this tree, including "Virginia live oak", "bay live oak", "scrub live oak", "plateau oak", "plateau live oak", "escarpment live oak", and (inSpanish) "roble". It is also often just called "live oak" within its native area, but the full name "southern live oak" helps to distinguish it from otherlive oaks, a general term for anyevergreen species of oak.[13]
This profusion of common names partly reflects an ongoing controversy about the classification of various live oaks, in particular its near relatives. Some authors recognize as distinct species the forms others consider to be varieties ofQuercus virginiana. Notably, the following two taxa, treated as species in theFlora of North America, are treated as varieties of southern live oak by theUnited States Forest Service: theescarpment live oak,Quercus fusiformis (Q. virginiana var.fusiformis) andthesand live oak,Quercus geminata (Q. virginiana var.geminata).
Matters are further complicated by southern live oakshybridizing with both of the above two species, and also with thedwarf live oak (Q. minima),swamp white oak (Q. bicolor),Durand oak (Q. durandii),overcup oak (Q. lyrata),bur oak (Q. macrocarpa), andpost oak (Q. stellata).
Live oak can be found in the wild growing and reproducing on the lower coastal plain of theGulf of Mexico and lowerEast Coast of the United States. Its native range begins in southeastVirginia, and then continues south in a narrow band throughNorth Carolina along the coast to the interiorSouth Carolina coast, where its range begins to expand farther inland. The range of live oak continues to expand inland as it moves south, growing across southernGeorgia and covering all ofFlorida south to the northernmost Florida Keys. Live oak grows along the Florida panhandle toMobile Bay, then westward across the southernmost two tiers of counties inMississippi. Live oak grows across the southern third ofLouisiana, except for some barrier islands and scattered parts of the most southern parishes. Live oak's range continues intoTexas and narrows to hug the coast until just pastPort Lavaca, Texas.[9]
There is a misconception that the southern live oak reaches its northwestern limit in the granitemassifs and canyons inSouthwestern Oklahoma.[citation needed] However, this actually belongs to the closely related and much more cold-hardyEscarpment Live Oak (Quercus fusiformis), a rare remnant from the lastglaciation also found aroundNorman, Oklahoma.[14]
Along the coastal plain of the Gulf of Mexico and south Atlantic United States, live oak is found in both single and mixed species forests, dotting the savannas, and as occasional clumps in the grasslands along the lower coastal plain. Live oak grows in soils ranging from heavy textures (clay loams), to sands with layers of organic materials or fine particles. Live oak can be found dominating some maritime forests, especially where fire periodicity and duration are limited. Live oak is found on higher topographic sites as well as hammocks in marshes and swamps. In general, southern live oak hugs the coastline and is rarely found more than 90 m (300 ft) above sea level. Live oaks grow across a wide range of sites with many moisture regimes – ranging from dry to moist. Live oak will survive well on both dry sites and in wet areas, effectively handling short duration flooding if water is moving and drainage is good. Good soil drainage is a key resource component for sustained live oak growth. The usual precipitation range is 650–1,650 millimetres (25–65 in) of water per year, preferably in spring and summer. Soil is usually acidic, ranging betweenpH of 5.5 and 6.5. A live oak on Tyler Avenue inAnnapolis, Maryland or one on Cherrywood Lane in Bowie, Maryland is the northernmost known mature specimen, although a number of saplings can be found growing around nearbyTowson. Multiple healthy young examples can be found in theBolton Hill neighborhood ofBaltimore.[15]
One source states that the southern live oak responds "with vigorous growth to plentiful moisture on well-drained soil."[8][16] They tend to survive fire, because often a fire will not reach theircrowns. Even if a tree is burned, its crowns and roots usuallysurvive the fire and sprout vigorously. Furthermore, live oak forests discourage entry of fire from adjacent communities because they provide dense cover that discourages the growth of a flammable understory.[citation needed] They can withstand occasional floods and hurricanes, and are resistant to salt spray and moderatesoil salinity. Although they grow best in well-drained sandy soils and loams, they will also grow in clay.[17]
The branches frequently support other plant species such as rounded clumps ofball moss (Tillandsia recurvata), thick drapings ofSpanish moss (Tillandsia usneoides),resurrection fern (Pleopeltis polypodioides), and parasiticmistletoe.
Southern live oak is cultivated in warmer climates as a specimen tree or for shade in the southern United States (zone 8 and south),Nuevo León andTamaulipas states in Mexico, and in the warmer parts of the United States, Europe, and Australia. Cultivation is relatively simple, as southern live oak seedlings grow fast with ample soil moisture. Planting depth has little effect on the success of the tree.[18] After a few years live oak needs only occasional supplemental water. Southern live oak is very long lived, and there are many specimens that are more than 400 years old in the deep southern United States. The southern live oak is reliably hardy to USDA Hardiness Zone 8a, which places its northern limit for long-term cultivation inland aroundAtlanta,Memphis, andWashington, D.C.
Live oak wood is hard, heavy, and difficult to work with, but very strong. In the days of wooden ships, live oaks were the preferred source of the framework timbers of the ship, using the natural trunk and branch angles for their strength. The frame ofUSS Constitution was constructed from southern live oak wood harvested fromSt. Simons Island, Georgia, and the density of the wood grain allowed it to survive cannon fire, thus earning her the nickname "Old Ironsides".[19] Even today, theU.S. Navy continues to own extensive live oak tracts.[20]
The primary uses for southern live oaks today are providing food and shelter for wildlife. Among the animals for which live oak acorns are an important food source are thebobwhite quail, thethreatenedFlorida scrub jay, thewood duck,yellow-bellied sapsucker,wild turkey,black bear, various species ofsquirrel, and thewhite-tailed deer. The tree crown is very dense, making it valuable for shade, and the species provides nest sites for many mammal species. Native Americans extracted a cooking oil from the acorns, used all parts of live oak for medicinal purposes, leaves for making rugs, and bark for dyes.[21] The roots of seedlings sometimes form starchy, edible tubers. People in past centuries harvested and fried these tubers for human consumption much as one might use a potato.[13]
In 1937, the southern live oak was designated the officialstate tree of Georgia (U.S. state).[22]
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