When the going gets tough, the plants keep growing.
A new study has found that various communities of plants around the world, from forests to grasslands, all are more drought resistant than previously thought. As rainfall decreases, plants use water more efficiently. But they also approach a point of "diminishing returns" beyond which their efficiency plummets, and they become more likely to die out, said University of Arizona researcher Guillermo Ponce-Campos.
Several important grasslands in the American Southwest and western Australia, which support large numbers of cattle and other important animals, appear close to reaching this threshold after years of extended drought, Ponce-Campos said.
Perhaps surprisingly, even in drought years plant communities like grasslands can maintain the same level of productivity as in wet years by becoming more efficient, said Ponce-Campos, a co-author of the study, which was published recently in the journal Nature. When nature's cup floweth over and floods come, however, plants respond by becoming a little lazy and using water less efficiently.
"Plants can adapt to extremes in water availability, such as drought and flood," Ponce-Campos said. "But this ability to cope with these extreme patterns may be tested by future climate change."
That's because most models of future climate predict more extreme weather, both of the extremely wet and dry variety, he added.
He and other researchers are currently working to better understand what exactly these thresholds are, and how land management practices could help avert some of the worst-case scenarios like desertification.
Grasslands are particularly at risk from global warming, as they make due with little precipitation to begin with. They are vital to preserve since they support such a wide variety of animals, from North American bison to the lions of Africa's savannahs.
Ponce-Campos' group regularly works with land managers, ranchers and policy makers to help them make ecologically sound decisions; for example, they advise cattlemen to make changes in grazing policy that prevent animals from foraging in certain areas at specific times.
The study examined 29 sites with different ecosystems around the world, in the United States, Australia and Puerto Rico. Satellite imagery allowed the researchers to calculate plant productivity by measuring the amount of foliage produced, and precipitation measurements were taken at each of the sites. This helped the scientists figure out how efficient the thirsty plants were.
Some of the measurements were taken at the Santa Rita Experimental Range, the longest operating site of its kind in the world, which takes up 80 square miles on the western side of the Santa Rita Mountains south of Tucson.
The study took place from 2000 to 2009, which incidentally were the ten warmest years since 1880, according to the study. American heatwaves in 2005, 2006 and 2007 also broke all-time records for high maximum and minimum temperatures, and drier than average conditions were recorded in more than half of the continental United States during five of these years. Down under, the wide-ranging drought from 2001 to 2007 is considered the most severe in Australia's often hot-and-dry history, the study noted.
If conditions like these become more common, as they are expected to, it's important to know what various plant communities can handle—and if there's anything that can be done to avert the worst-case scenario, Ponce-Campos said.