Our Mighty Oaks
Photo by Cathryn Hoyt
Photo by Cathryn Hoyt
By Kay Wilde
During the last Ice Age, woodlands covered much of the Chihuahuan Desert region. But as the climate warmed and dried, these trees died back. Some hardy species have hung on though, and among them are several types of oaks. Who are these tenacious survivors? And what desert animals depend on them today?
The 21 oak species in our region assume many forms, with leaves in myriad shapes and sizes. Some oaks here turn brilliant colors and drop leaves in the fall, others wait until spring, and a few are evergreen, shedding and replacing leaves gradually throughout the year. They can be found from mountain tops to desert lowlands, growing as majestic giants or diminutive dwarves.
One such dwarf covers the sand dunes at Monahans Sandhills State Park between Monahans and Odessa, Texas. These three-foot-tall shrubs are Havard oaks, also known as shin oaks. Though small, they form one of the country’s largest contiguous oak forests, stretching across about 40,000 acres from Crane, Texas to Fort Sumner, New Mexico.
Havard oaks sink their roots deep into the sand, helping to stabilize dunes. Their roots grow as long as 90 feet to reach groundwater. As sand blows away, these long roots are exposed, making some Havard oaks look like they’re perched on stilts.
This oak forest provides food and cover from the harsh sun for many animals and insects. Deer and porcupine eat their large acorns. And under their small branches, you might find an ornate box turtle, a jack rabbit, or even a rattlesnake. The endangered sand dune lizard also dwells here.
Another resident of the Havard oak forest is a newly discovered species of stag beetle. M.J. Paulsen, who discovered this beetle in the sand dunes, named it Nicagus occultus. At sunrise and sunset, Paulsen observed hundreds of male beetles burrowed in the sand on dune tops, with only their antennae showing. Hence the name occultus, which means “hidden.” This behavior, known as hilltopping, is something that other male insects do as they wait for females.
Havard oaks aren’t alone in their small stature here. The Hinckley oak rarely grows more than three feet and forms a few dense thickets in the Big Bend. Because its range is so limited, it’s considered endangered. But more than 10,000 years ago, when the climate was wetter, Hinckley oaks were the dominant oak in woodlands that covered what is now Big Bend National Park and Big Bend Ranch State Park.
Larger oak trees live in the Chihuahuan Desert region too. Chinkapin, Gray, Emory and Chisos oaks may tower more than 50 feet and are typically found in moist canyons and on protected mountain slopes. The acorns of these larger oaks provided food to Native Americans, and still sustain many birds, small mammals, and mule deer.
But perhaps no Chihuahuan Desert resident depends on oaks more than the acorn woodpecker. This common bird of western forests spends much of its time collecting and storing acorns. The woodpecker drills many holes in a single tree, called a granary, and deposits an acorn in each hole. Trees are not the only places the birds use as granaries. Telephone poles and fence posts will suffice; even an automobile radiator may be used. Acorn woodpeckers will work cooperatively to fill and defend a granary. One study reported that acorn woodpeckers had stored 60,000 acorns in a single tree.
There is an old saying that “mighty oaks from little acorns grow.” Though many of our region’s oaks are little, they are all truly mighty survivors, having clung to this challenging, changing landscape for millennia.
Guest contributor Kay Wilde is a writer and Texas Master Naturalist in Alpine.
Have a question or comment about this episode? Contact Nature Notes Coordinator Megan Wilde at mwilde [at] cdri [dot] org. Or discuss this episode on Nature Notes’ Facebook page.
References & Resources for Educators
- Havard oak: Lady Bird Johnson Wildflower Center’s Native Plant Database
- Acorn Woodpecker: Cornell Lab of Ornithology’s All About Birds
- Sand dune habitats: from the Sibley Nature Center in Midland
- Monahans Sandhills State Park: Texas Parks and Wildlife Department
- A Field Guide to Texas Trees by Benny J. Simpson (Gulf Publishing Company)
- Trees and Shrubs of the Trans-Pecos and Adjacent Areas by A. Michael Powell (University of Texas Press)
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Nature Notes is sponsored by the Meadows Foundation and the Dixon Water Foundation and is produced in cooperation with Marfa Public Radio.
