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University of Arizona ecologists and others say mesquite trees are replacing Southwestern grasslands, since the trees are better able to handle shifts toward higher temperatures and sporadic rainfall.

“Due to the mesquite’s ability to put down deeper roots and access groundwater resources ... it responds better across a whole wide range of temperatures,“ says USDA Research Hydrologist Russell Scott, co-author of the study published in the scientific journal Global Change Biology.

Some mesquite roots can reach down to 160 feet, tapping into groundwater not accessible to plants with shallow root systems, Scott says.

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Photo: Robert Rappaport

Velvet Mesquite at Joseph Wood Krutch Garden, University of Arizona

The study, led by UA Biosphere 2 Associate Research Professor Greg Barron-Gafford, shows grasses blanketed much of Arizona’s landscape of the past century, but that has diminished because of cattle grazing. Woody plants, like mesquite trees, now hold dominance over the area, the study says.