Ancient Live Oak Forests Vital Habitat for South Texas Wildlife

Scattered throughout deep South Texas along the coastal plains are ancient oak forests, and some of the oldest trees are likely to have been growing before Columbus sailed to the Americas in the late1400's. These groves of live oaks are called mottes, and a few individual trees may be approaching 1,000 years old.

"I think the history of them is pretty interesting when you read some of these accounts of early travelers in South Texas," said Dr. Tim Fulbright with the Caesar Kleberg Wildlife Research Institute at Texas A&M University in Kingsville. "The impression that you get is that the live oaks were a lot less abundant back in the 1830's, 1850's. In fact the Spaniards used the live oaks as boundary markers."

The Coastal Sand Plain covers 2 million acres in southern Texas, stretching from the Laguna Madre west to Jim Hogg and Starr Counties. Live oak forests are a unique and ecologically important part of the region, but oak mottes are relatively small covering only some 72,000 acres. "They are an ancient feature of the landscape with some individual trees being hundreds of years old," Fulbright said.

The largest and perhaps oldest live oak in Texas is found on the Lamar Peninsula of Aransas County in Goose Island State Park. The ancient oak has a circumference of more than 35 feet and is estimated to be a 1,000 years old.

I know of one venerable oak on the Encino Division of the King Ranch that has a girth of some 25 feet, and it too may be approaching the 1,000 year milestone. "I think about some of these trees and what they have witnessed over time. You know, here I am standing by a tree that native Americans stood under possibly before they ever saw Europeans," Fulbright said.

While oak mottes make up only a small percentage of the coastal plains they are vital wildlife habitat. "Those oaks have a number of ecological functions," Fulbright said. "One thing they do is add to the diversity of the landscape, and they help to stabilize sand dunes. You see areas particularly on the Norias Division of the King Ranch or the Kenedy where sand dunes have run into a live oak motte, and that is where it stops."

"The diversity of wildlife that utilizes the live oaks is amazing, and if you didn't have those live oak habitats you wouldn't have all the different bird species like pygmy owls," Fulbright said. "Live oak mottes are particularly important for migrants that come across the Gulf and make landfall. They have to have trees to land in. There are a number of warbler species that migrate thru and use these live oaks and a number of species that nest in the live oaks. The ferruginous pygmy owl is a species that uses the live oaks predominantly, and studies have shown that more than 80 percent of red-tailed hawks nest in the tops of oaks."

Oak mottes are also used by bobwhite quail for cover and food, particularly at the edges of woodlands. The canopy provides cover which allows quail a place to hide from hawks. The acorns produced by live oaks are also eaten by quail.

Live oak woodlands provide vital roosting habitat for wild turkeys. Some of the taller trees tower more than 70 feet, and the turkeys are safe from most predators in the uppermost branches. In addition to providing roosts, live oaks also afford important thermal cover for turkey, quail, deer and other species. Most of the wild turkeys that have been monitored during an ongoing study by the Caesar Kleberg Wildlife Research Institute use the oaks during hot periods to stay cool in the shade, and in winter the woodlands provide shelter on wet and cold days.

When there is a good acorn crop, and this year promises to be a bumper crop, acorns become a primary food for whitetail deer. "When acorns are available, they may compose almost half of white-tailed deer diets," Fulbright said. "Acorns are particularly important because they are produced during autumn when deer are accumulating body fat in preparation for breeding. Poor body condition could result in lower fawn production and lower survival of bucks after the breeding season."

Live oaks are hardy, and they are well adapted to the extremes of South Texas weather from frigid northers to scorching heat. Those oaks closest to the coast often develop a sculpted look as they have been artfully pruned by the strong prevailing southern winds.

"One way they have survived the hurricanes and the droughts and so forth is that they have a very broad lateral root system that helps anchor them in the ground," Fulbright said. "Oaks are root sprouters so you may see a large stand of oaks, and they are basically all clones."

"There was a ranch west of Highway 77 that in the 1980's applied a chemical known as "spike" with the intention to kill live oaks in strips," Fulbright said. "But they did not take into account that the roots of all the plants on the edges went into the entire motte, so they wound up with about an 80 percent kill."

South Texas is one of the most biologically diverse regions in the world, and the impressive stands of live oaks are a vital part of that diversity. The area is sometimes referred to as the "Last Great Habitat," because it is one of the last regions in the state that contains extensive tracts of contiguous wildlife habitat.

The ancient oak forests that have endured for centuries on large well managed private property like the King Ranch are vital to the preservation of native wildlife and many migratory bird species. In Texas, where the vast majority of remaining natural habitat is on private land, good stewardship is essential for the continued existence of our natural heritage, and hopefully the venerable live oak woodlands of southernmost Texas will thrive for generations to come.


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Copyright 2007 Richard Moore