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The remarkable habitat of the Sand Sheet

Published in the South Texas Chapter, Texas Master Naturalist March 2023 Newsletter

Story and photos by Anita Westervelt, South Texas Border Chapter

I visited a fellow Texas Master Naturalist’s ranch in the far reaches of northwest Hidalgo County, and was awe struck by the contrast between the thorn scrub there and those same familiar species that grow in mid-south Cameron County.

The immediate difference was the soil. My friend said it is alfisol, that the sands were actually deposited over the caliche; she later offered a description from a University of Texas web presentation by Bob Harms on sand sheet plants that explained: "The region is defined by a sheet of eolian sand blown inland from the shoreline of the Gulf of Mexico during Holocene times, a sheet that covers most of Kenedy and Brooks counties as well as the northern tips of Willacy, Hidalgo and Starr counties."

South Texas Chapter of the Texas Master Naturalist covers Nueces, Kleberg, Kenedy and Willacy counties; South Texas Border Chapter covers Starr County; the Rio Grande Valley Chapter includes Willacy County, both chapters share Hidalgo and Cameron counties.

I won’t pretend to be geologically smart. I Googled alfisol and found South Texas Chapter’s USDA Soil Orders for South Texas: Alfisol is fertile. I looked up eolian, which means deposits resulting from wind action. A Google search of Holocene revealed an interesting online Smithsonian Magazine article by Joseph Stromber: “According to the International Union of Geological Sciences (IUGS), the professional organization in charge of defining Earth’s time scale, we are officially in the Holocene ("entirely recent") epoch, which began 11,700 years ago after the last major ice age.”

So, were I to say I gazed upon the austere beauty of this ancient sandscape, I would be relatively correct. Though beautiful, the vegetation appeared to be struggling as we headed through a well-traveled path maintained by her horse and donkey. Caliche boulders poked through sand erosion. We saw traces of javelina destruction on prickly pear cactus pads, and javelina and bobcat scat. We were soon among old friends like black brush, catclaw acacia, wild olive and Spanish dagger in bloom; brasil, granjeno, mesquite, colima, coma and guayacán also sparsely populate the land.

Black Brush in bloom. (Photo by Anita Westervelt)

Vibrant flowering plants unlike those in my Cameron County clayey soils had pushed through dry sand in what seemed an amazing feat: silky evolvulus, Evolvuls sericeus; speedwell, Evolvulus absinoides; bracted fanpetal, sida ciliaris; and taller round head broom, Gutierrezia sphaerocephala.

Tropical speedwell plants of the sand sheets. (Photo by Anita Westervelt)

Sticky florestina, Florestina tripteris, provides numerous blooms despite the drought, attracting many pollinators and nectar insects. Off the track, a pencil cactus, Echinocereus poselgeri, was starting to bloom. Bristleleaf pricklyleaf (tiny Tim), Thymophylla tenuiloba; cow pen daisies, Verbesina encelioides; and lazy daisy, Aphanostephus ramosissimus seemed dwarfed compared to the lusher spring growth I’m used to seeing.

The desire to be good land stewards is at the heart of Texas Master Naturalists; my friend is dedicated to protecting what she has, constructing sturdy, labor-intensive exclosures, by driving four foot galvanized steel t-posts into the ground with a t-post driver and securing Hog Feedlot Panel fencing to the posts with reusable zip ties, keeping rabbits and larger critters from destroying rare yellow flowered alicoche, Echinocereus papillosus Var. angusticeps; and Manfreda maculosa and other plants from becoming extinct.

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