As the desert Southwest becomes hotter and drier, semi-arid grasslands are slowly being replaced by a landscape dominated by mesquite trees, such as Prosopis velutina, and other woody shrubs, a team of University of Arizona researchers has found.
In a "leaf-to-landscape" approach, the team combined physiological experiments on individual plants and measurements across entire ecosystems to quantify how well grasslands, compared to mesquite trees and woody shrubs, cope with heat and water stress across seasonal precipitation periods.
"Our results show that even the smallest mesquites are better adapted for thriving under elevated temperatures and dry conditions the projections for our future climate suggesting that these woody plants are here to stay," said Greg Barron-Gafford, an associate research professor with the UA's Biosphere 2 who led the study, which is published in the scientific journal Global Change Biology.
Over the last century, the face of the Southwest has changed. Before heavy cattle grazing, flowing carpets of grass comprised of, for example, Muhly (Muhlenbergia porteri) or Grama grass (Bouteloua eriopoda) blanketed much of Southern Arizona's open range. Today, woody plants like mesquite trees dominate the landscape.
Native to the region, mesquites have been here for a long time, but not in today's abundance, Barron-Gafford said. "Visitors that see our experimental display at Biosphere 2 are always surprised to hear that the Sonoran Desert in this area used to look very different a century ago."
Scientists have evidence to believe woody plants began displacing grasslands as a result of overgrazing, but has since been propelled by changing climate.
"If there are too many cattle, they have the same effect as a lawn mower," Barron-Gafford said. "They're tilling the soil, and because they don't eat the prickly things, they stay away from the established mesquite trees. But
|Contact: Daniel Stolte|
University of Arizona