Brush Control Will Increase Groundwater Supply

For over 50 years, Hill Country ranchers have been telling tales of springs bursting from the ground after they removed ashe juniper infected areas. Actually, they probably didn’t call it ashe juniper. In Texas, it’s “affectionately” known as cedar. A recent study on 700 acres owned by the state (40 miles north of San Antonio) is giving federal researchers the data to find out just how much water the trees use, and if a massive program to restore grasslands across the Hill Country would result in more water for cities, farms and wildlife.

“Now we are controlling the water with the landscape,” said George Ozuna, the deputy director of the U.S. Geological Survey’s Texas Water Science Center. Until now small-scale studies on parcels up to 50 acres have shown juniper removal from the Edwards Plateau might result in an increase of stream flow and groundwater recharge equal to about 5 percent of annual rainfall.

If proved true on a watershed scale, that would be a significant additional source of water for drought-prone South Texas.
“We would be silly not to try it out,” said Neal Wilkins, with the department of Wildlife and Fisheries Sciences at Texas A&M University.

Ten years ago, the U.S. Department of Agriculture and U.S. Geological Survey designed their study to look at the impacts of removing young junipers — commonly known as mountain cedars — by analyzing two similar-sized and neighboring drainages in the Honey Creek State Natural Area.

After setting up a baseline study of the hydrologic budget of both — the amount of water that falls as rain, balanced with the amount that evaporates, runs into streams or seeps in the ground — they performed brush management practices to remove 75 percent of the junipers from one of the watersheds in 2005. The trees were removed so as not to disturb endangered species.

Five years later, they now believe they have enough data to measure changes to both the water quality and quantity. A paper is expected to be published by the end of the year with the results.

Regardless of the recharge rate, the $300 cost per acre to remove trees is justified by protecting water quality and improving wildlife habitat, said Phillip Wright, a range management specialist with the USDA’s Natural Resources Conservation Service.

The quality and quantity of the water that flows into the Edwards Aquifer and thus out of taps in San Antonio is dependent on the type of land that catches the rainfall.

If the land is covered in native grassland with waist-high grass, the water will be guided into the topsoil and then filtered as it seeps into the aquifer and then via springs into the creeks.

If the land is covered with junipers, some 40 percent of it will be caught in the brushy trees’ thick branches and will evaporate, having never touched the ground.

If the land is covered with pavement and rooftops, the runoff will quickly be moved unfiltered into streams and rivers, often bypassing the aquifer entirely.

“We are really kind of fragile, and it’s really kind of scary because of what is happening in the Hill Country,” Ozuna said.

Overgrazing, fire suppression, land fragmentation and sprawling development, and the construction of vacation and retirement homes have all reduced grassland coverage. In its place: thick stands of junipers and impervious cover.

“The offsite benefits are much greater than the onsite benefits,” Wright said of juniper removal. “We are trying to educate these new landowners that everything they do affects water quality.”

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