Unique Trees of North Texas:
Live Oak
(Quercus virginiana or Quercus fusiformis)
By Eugene Gehring
You may be asking how one of the most popular and common tree species in North Texas could be considered unique. The fact that it is so popular and common is one of the reasons I think it is unique. Live oaks will grow in almost any soil type. Quercus virginiana (coastal or Southern live oak) is native from Virginia down the Atlantic coast to Florida and across the southern states to somewhere west of Houston. Quercus fusiformis (plateau or escarpment live oak) is native west of I-35 down into the hill country and North in a 3-5 county band to just north and west of Fort Worth. Live oaks are found in the transitional counties. Whether they are “Southern” or “Escarpment” is a good question. The primary morphological difference is the shape of the acorn. The escarpment live oak acorn is fusiform, or more constricted at the base. After 30 years working with live oaks, I still don’t have a clue what that means.
Live oak typically have long, extending branches that give the tree it’s unique shape.
Live oaks are different from the other oak species in several ways. They are evergreen or semi-deciduous. They drop their leaves in February/March instead of the fall. Their leaves are simple nondescript ovals, 1-4” long with an entire margin. White oaks have rounded lobes, while red oaks have points or stipules on their lobes. Based on leaf morphology, live oaks fit more with the white oak group. Live oaks can be more than twice as wide as they are tall with long graceful branches. White oaks tend to be about as wide as they are tall, and red oaks tend to be taller than they are wide.
The wood of most oak species is ring-porous. They lay down different size vessels and cells depending on the season. Live oaks are diffuse-porous. There is not a seasonal variation in the size of the vessels or cells. One of the major differences between white oaks and red oaks is tyloses within the vessels of the wood. In white oaks tyloses occur naturally, while in red oaks they do not. That is why whisky barrels are made of white oak. Live oaks do not have tyloses naturally in their wood, putting them in the red oak group.
Unlike most oaks, live oaks are prolific at sprouting from their roots. This characteristic, along with readily forming root grafts, allows live oaks in a given stand to share their roots. This is one of the reasons live oaks are considered drought hardy. It is also why oak wilt is so devastating to live oaks. During the drought of 2011 – 12 I witnessed live oaks in the Hill Country that bloomed or tasseled in the spring of 2011, but did not leaf out until it rained in the fall of 2012.
Live oaks have a unique ability to adapt and grow in a variety of environments. The exception being they do not tolerate extended periods of saturated soils. They will grow in the 100 year flood plain, but not in areas subject to regular flooding or standing water. In the late 1990s, there was a flood event on Lake Travis where mature live oaks were almost completely submerged and survived because it was a short duration. The same event killed live oaks on Stillhouse Hollow Lake because the water was not lowered as quickly.
Live oak growing in an old cemetery. Although live oak can live an extremely long time, they also grow rapidly when young which often leads to the age being overestimated. A live oak can grow to over 20″ diameter in just 30 years.
Live oaks are hardy to the 7b/8a zones of North Texas. I think the escarpment live oak is somewhat hardier than the Southern live oak. The 60 degree swing in temperature in January 2108 caused damage to the leaves on some live oaks in North Texas. They were not prepared for the extreme change in weather. When I first moved to the DFW metroplex, I was told there were live oaks with basal cankers caused by the cambium freezing during one of the cold winters in the 1980s.
Another unique characteristic of live oaks is that they will grow in almost any soil type. They thrive equally well in the sandy acidic soils of East Texas and the alkaline limestone based soils of Central Texas. Although they are not native to the heavy clays of most of North Texas, they grow and thrive there as well.
Climate change is probably responsible for the split between Southern live oak and Escarpment live oak. At a warmer period in time water covered a lot of North Texas as evidenced by ammonite fossils in Parker County. As the climate cooled and the water receded live oaks were pushed south and the split occurred.
Live oaks have long been valued as landscape trees. Some of the oldest planted can be found at Oak Ally Plantation in Louisiana. They were thought to have been planted around 1710. In North Texas, they can be found in almost every neighborhood. Most of the older planted live oaks are probably Southern live oak because they would have come from nurseries in East or Southeast Texas. As the population in Central Texas increased, more tree nurseries were started in the 70s and 80s resulting in more escarpment live oak in the industry. That is not to say there were not wild trees dug in Parker or Hood counties and planted in Fort Worth or Dallas. There were also nurseries, like O. S. Gray in Arlington, that may have grown escarpment live oak.
A little known fact is that live oak was used in the construction of the USS Constitution (“Old Ironside”). Live oak branches were used to form the ribs of the ship. They used the natural curves of the branches for added strength.
I have had a love/hate relationship in the more than 30 years I have worked with live oaks. I have seen them survive the extremes of drought, flood, tornadoes and hurricanes. I have seen them growing in practically solid rock, sugar sand, black gumbo clay, from East Texas to Midland/Odessa, from Lubbock to Houston to Corpus Christi. More than half of the trees in “The Famous Trees of Texas” are live oaks. The species has been witness to treaties, hangings, fights, marriages and everything in between. I think live oaks are unique because of their strength, adaptability, and mystic.