STATE PARK WONDER
A Massive Forest of Tiny Oaks
Thickets of shin oak stabilize dunes at Monahans.
Monahans Sandhills State Park is a landscape of shifting sand dunes under a dry West Texas sky. It’s also home to one of the biggest oak forests in North America, but you might not notice that right away.
Many dunes in this park support thickets of Havard shin oak (Quercus havardii), a native tree that usually tops out at 3 feet. Spreading by way of underground stems called rhizomes, the oaks sink roots in the deep sand. They’re most visible on the south side of the park, blanketing dune faces with their brief branches and dark grayish-green foliage.
Shin oak is found in the Texas Panhandle and parts of New Mexico and Oklahoma. Well adapted to a harsh environment, it lives where few other trees will grow. The groves at Monahans are part of a plant community that occupies 40,000 acres of the surrounding sandhill country.
Once described by Texas naturalist Roy Bedichek as “a Lilliputian jungle,” the shin oaks are an essential influence on the local ecology. Their roots and rhizomes stabilize the dunes. Growing close to the ground, they provide nesting sites for scaled quail and cover for the endangered sand dune lizard. Their acorns, measuring up to an inch long and three-quarters of an inch in diameter, provide food for deer and rodents.
Viewed up close, Q. havardii is quite recognizable as an oak. It’s a deciduous species, going dormant in late fall. Leaves are 2 to 4 inches long, generally elliptical in shape and lightly lobed, resulting in a wavy edge. The leaves have a thick, waxy skin to minimize water loss.
Acorns, of course, are the seeds of the next generation but they don’t always get the opportunity to germinate and grow a new tree. In the Texas sandhills, shin oaks are more prone to vegetative reproduction. A group of trees growing close together is likely to be one big clone. Rhizomes may extend 40 feet from the main trunk and can send up shoots anywhere along that length.
Extensive root networks drink up rain that percolates through the sand and may penetrate more than 70 feet in search of groundwater. You could say a shin oak thicket is like an iceberg: up to 90 percent of the biomass is under the surface.
That underground structure enables shin oaks to regenerate after fire, drought and other perils of an unpredictable environment. The root-and-rhizome systems of some thickets are estimated to be hundreds or even thousands of years old.
Think about it. That scrubby 3-foot oak, clinging to the side of a Monahans sandhill, may have grown from an acorn that fell when the Big Tree on Goose Island was just a sprout.
Maegan Lanham | TPWD
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