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11 de febrero de 2019

About Live Oaks

This is Quercus fusiformis:

Q. fusiformis in Bexar County, Texas

Quercus fusiformis is the common live oak found in the wild in central Texas. It is more drought-tolerant and cold-hardy than Q. virginiana, which it is sometimes considered a variety of, and is becoming more commonly used as a landscape tree.
Habitat is one of the best ways to distinguish between the two in the wild.
Quercus fusiformis is typically found growing on dry sites, unlike Q. virginiana, which prefers moister conditions and is found along the coastal areas of the southeastern United States. Q. fusiformis is generally accepted to be the hardiest evergreen oak, able to tolerate winters to USDA zone 6a. It has become a popular landscaping tree for its stately form, ability to endure urban conditions, and general hardiness. It is prevalently used for these purposes in Texas and southern Oklahoma, and use is becoming more widespread into the Western US.

Q. fusiformis can appear as a thicket forming shrub or be a large spreading tree that is identical to Q. virginiana. Q. virginiana is known as Coastal Live Oak, or Southern Live Oak. Q. fusiformis is known as Escarpment Live Oak or Texas Live Oak.


Q. fusiformis in Bell County, Texas


Q. fusiformis in Travis County, Texas


Q. fusiformis in Real County, Texas


Q. fusiformis in Tarrant County, Texas


Q. fusiformis in Stephens County, Texas

In it's western range, Q. fusiformis tends to be more easily distinguished from Q. virginiana. But in it's eastern range the differences are less apparent. The state record Q. fusiformis (Ht. 63', circ. 342") is larger than the state record Q. virginiana (Ht. 61', circ. 338"), in height and circumference, but they have the exact same size index of 427 due to the Q. virginiana tree having a greater width.


Note the dotted line along the Balcones Escarpment.

Some authors recognize as distinct species the forms others consider to be varieties of Quercus virginiana. Notably, the following two taxa, treated as species in the Flora of North America, are treated as varieties of southern live oak by the United States Forest Service: the escarpment live oak, Quercus fusiformis (Q. virginiana var. fusiformis) and the sand live oak, Quercus geminata (Q. virginiana var. geminata).
Matters are further complicated by Southern live oaks hybridizing with both of the above two species, and also with the dwarf live oak (Q. minima), swamp white oak (Q. bicolor), Durand oak (Q. durandii), overcup oak (Q. lyrata), bur oak (Q. macrocarpa), and post oak (Q. stellata).

Hybrids & Cultivars - Live oak forms a number of hybrids with other oaks. Cataloged hybrids include crosses with: Q.bicolor (= x nessina); Q. durandii; Q. fusiformis; Q. lyrata (= x comptoniae -- a fast growing tree with goodcold tolerance for hardiness zones 7-9); Q. macrocarpa; Q. minima (= x succulenta -- a Quercus geminatacross); and, Q. stellata (= x harbisonii).In addition to hybrids, there are a number of live oak cultivars: Boardwalk ‘FBQV22’ with a pyramidalshaped crown, a strong central leader, and perpendicular branch angles; Cathedral ‘SDLN’ (PP#12,015) witha dense canopy, a strong central leader, and evenly spaced branches; Grandview Gold (gold colored foliage);Highrise ‘QVTIA’ (PP#11,219) with a strongly upright / columnar crown and dominant leader; Millennium‘CLTF2’ (PP# 11,097) with large dark green leaves, and strong stem and branch taper; Parkside ‘FBQV1’with a dense canopy broadly pyramidal in shape and with perpendicularly attached branches; and,Shadowlawn. Not all cultivars listed in the literature can be found currently in the commercial nursery trade.

According to Turner's Atlas of the Vascular Plants of Texas, Vol. 1, in Texas Q. virginiana occurs only as far west as eastern Williamson County and eastern Bell County. The majority of the occurrences are east and south of Bell County, mostly clustered along the Gulf Coast. Quercus fusiformis, on the other hand, occurs mainly west of the line of counties including McLennan, Bell, Williamson, Travis, Hays, Comal and Bexar—generally, the Edwards Plateau. There is also a grouping in the southern tip of Texas in the South Texas Plains. Additionally, there is an eastern line of counties (including Goliad, DeWitt, Lavaca, Colorado, Fayette, Bastrop, Washington and Brazos) where Q. fusiformis and Q. virginiana overlap. In its eastern range and especially where the two overlap, is where the confusion abounds. Robert Vines in Trees of Central Texas says about Q. fusiformis:
"Although it appears distinct in the western part of its distribution (beyond the Edwards Plateau area and into Mexico), on its eastern range it seems to pass into Q. virginiana with many intermediary variants."
Benny Simpson says this about Q. fusiformis:
"Escarpment Live Oak grows in mottes, attaining heights of 50 feet (72' has been recorded) on almost any alkaline to slightly acid, well-drained soil. It is rather rare on the the true Blackland Prairies, possibly because of the poor internal drainage of those soils, but it does occur in the West Cross Timbers and Grand Prairie, west and north of the Balcones Escarpment on the Edwards Plateau, and, to a lesser degree, east of the Balcones Fault Line on the Blackland Prairies. It grows in hybrid swarms of Quercus virginiana x Q. fusiformis from the Balcones Escarptment to the coastal area and then eastward to the Brazos River, where, on the east side, more or less pure forms of Q. virginiana are encountered."

From Flora of North America:
"The difficulty in distinguishing Texas populations of Quercus fusiformis from Q . virginiana is reflected in a variety of taxonomic treatments, including reducing Q . fusiformis to varietal rank under Q . virginiana . The latter disposition is problematic, however, because Q . fusiformis in northeastern Mexico is amply distinct from Q . virginiana and appears to be more closely related to Q . brandegei Goldmann, an endemic of Baja California, Mexico. Thus, here we assume that the intergradation of Q . virginiana and Q . fusiformis is a result of secondary contact, and is not primary clinal variation. Under this interpretation, Q . virginiana in typical form extends into Texas only as far west as the Brazos River drainage along the coast from there to the escarpment of the Edwards Plateau; most populations elsewhere are either intermediate between the two species or show greater affinity with Q . fusiformis . On the Edwards Plateau, the live oak populations are small trees forming rhizomatous copses (shinneries) and having mostly acute acorns."

Quercus fusiformis was described and the name validly published by John Kunkel Small in 1903.

John Kunkel Small, 1869-1938

From 1897-1933, Small split Q. virginiana into several additional species (e.g. Q. minima (Sargent) Small, and Q. fusiformis). However, Charles Sprague Sargent disagreed with Small and reduced Q. fusiformis to a varietal rank under Q. virginiana.

Charles Sprague Sargent, 1841-1927

In 1961 Cornelius Muller supported species recognition for Q. fusiformis. Muller reported acorn morphology as the major separation between Q. virginiana and Q. fusiformis. Muller also reported morphological integration between Q. virginiana and Q. fusiformis.

Cornelius Herman Miller, 1909-1997

Kevin C. Nixon reported that populations of Q. virginiana were limited to south and east Texas, whereas Q. fusiformis populations were generally located in the central area of Texas from the coastal plain to the Edward’s Plateau. He further reported introgression between Q. fusiformis and Q. virginiana on the Edward’s Plateau that resulted in populations that consist of complex mixes of hybridization between the two species. “The populations of live oak that occur in the area bounded by Columbus, Austin, and San Antonio, Texas can all be considered morphologically intermediate between the populations of Quercus fusiformis that occur on the Edward’s Plateau and Quercus virginiana of coastal southeastern Texas”.

Kevin C. Nixon, Cornell University

Previous research using hybridization studies between Q. virginiana and Q. fusiformis was conducted by H. Ness and by James Hardin. They both concluded that Q. virginiana and Q. fusiformis were one species that adopted different growth patterns in different environments. Presently Q. fusiformis and Q. virginiana are treated as two separate species with the ability to freely hybridize.

James Walker Hardin, North Carolina State

Q. fusiformis in Young County, Texas

Q. virginiana in Aransas County, Texas

Historic Tragedy - Live oaks have dense, hard, and strong wood which is resistant to weather, water, and mechanicalstrain. The massive, low, curved branches and sweeping stems were useless for straight-grained, dried lumberas made from other trees. But the natural growth pattern of live oak made the perfect structural components forwooden sailing ships. Live oak forests first seen by Europeans were storm pruned, extensive, and containedmany massive individual trees. Commerce and war of the 1700’s generated demand for this premium wood forship hull ribs, knees, and support parts. The old growth live oak forests were decimated by European nations,colonists, and early acts of our new nation. “Live-oaking” was a way of life for Northern ship builders. Live oaks accessible to water transportwere targets. Large trees were first cut to see if they were sound, and then divided into the largest and mosteffective parts for use in ship design. Many trees damaged by centuries of storms, were cut only to reveal theywere internally decayed and would not meet the stringent specifications of New England, Atlantic Canadians, orEnglish shipwrights. These cut trees were left to rot. No new trees were planted nor sprouts conserved.Sustainable forest management was nonexistent.Hired gangs of loggers and carpenters from all over were dispatched to hunt and convert live oaks intowooden ship components. The new United States of America federal government attached preserves, laws andbounties to live oak trees. Tree poaching, timber theft on public and private lands, federal agent corruption, andtimber pirates were so common (and results so lucrative), only the demise of easily accessible live oaks and ironboat hulls halted live oak tree slaying and forest destruction. Major parts of the Atlantic coast old-growth liveoak forests were gone by 1870. The Gulf coast live oaks were conserved more effectively for a longer periodof time.

Thinking Big - We today cannot imagine the tree sizes, numbers, and distribution of live oak forests of the 1700’s.What is lost cannot be recreated except through our appreciation of history and a celebration of some of theremaining tree giants (i.e. survivors). See Appendix 1. Live oaks are today visible pillars, ceilings, and walls ofold Southern coastal landscapes and line older streets, squares, and parks, while large wooden sailing ships ofcommerce and war are but a romantic memory.
Although the current accepted scientific name of Texas live oak is Quercus fusiformis, there is no full consensus among taxonomist concerning the taxonomic status of Texas live oak. Some still consider it to be a varietal cline of Quercus virginiana (called variety fusiformis). Moreover, to add to the name confusion in central Texas Q. fusiformis is known to readily hybridize with Q. virginiana. One thing we do know for sure is that Texas live oak is dense wooded and will buckle concrete.

Historical note: Quercus are concentrated in the Northern Hemisphere and number about 600 species. Quercus belongs to a genus steeped in prehistory of Europe and well known to Linnaeus who named it Quercus. This is from the fact that the ancient tree-worshipping tribes often queried very large old oak trees they believed contained powerful spirits that could foretell the future. Live oaks (evergreen oaks) are considered one of the noblest trees in the world and is virtually an emblem of the 'Old South' United States. Consider the following written by Dr. Oliver Wendell Holmes:

"There is a mother-idea in each particular kind of tree, which, if well marked, is probably embodied in the poetry of every language. Take the Oak, for instance, and we find it always standing as a type of strength and endurance. I wonder if you ever thought of the single mark of supremacy which distinguishes this tree from all our other forest trees? All the rest of them shirk the work of resisting gravity: the Oak alone defies it. It chooses the horizontal direction for its limbs, so that their whole weight may tell, and then stretches them out fifty or sixty feet, so that the strain may be mighty enough to be worth resisting. You will find that, in passing from the extreme downward droop of the branches of the weeping willow to the extreme upward inclination of those of the poplar, they sweep nearly half a circle. At ninety degrees the Oak stops short: to slant upward another degree would mark infirmity of purpose: to bend downwards, weakness of organisation."

Ingresado el 11 de febrero de 2019 por lanechaffin lanechaffin | 1 comentario | Deja un comentario