Earth Notes
5:00 am
Wed March 7, 2012

Earth Notes: Blackbrush

What can a small, inconspicuous shrub tell us about climate change in the Southwest? That’s the question researchers are asking about blackbrush.

Most people don’t take a second glance at this compact, slow-growing shrub bristling with spiny, gray-black branches. Yet it grows across several million acres in the Mojave Desert and up onto the Colorado Plateau, sometimes in nearly pure stands. You can see extensive swaths in Arches and Canyonlands, and over the Tonto Plateau in Grand Canyon.

Blackbrush bears small yellow flowers from March to May, and shows off a mass of blooms when winter moisture is good. In those years, the plants can produce a bumper crop of seeds, which kangaroo rats and pocket mice harvest and stuff underground. Those seeds sprout successfully only during the occasional years that bring adequate spring and early summer moisture.

Occupying a transition zone between hot and cold deserts, the shrub makes a good subject for climate studies because it tolerates only a narrow range of environmental conditions.

U.S. Forest Service research ecologist Rosemary Pendleton and colleagues think blackbrush will move higher and northward as the Southwest becomes hotter and drier. Blackbrush is also susceptible to burning, especially if surrounded by nonnative cheatgrass. Once wiped out by fire, it rarely recovers.

For that reason, successful reproduction is key. To give blackbrush a nudge, scientists are mimicking the work of the small rodents. At selected locations in the Mojave, they’re carefully burying blackbrush seeds so that the plants have a chance to germinate and grow.

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