Needles District of Canyonlands National Park, with continuous biocrust in the foreground. (Courtesy Bill Bowman, University of Colorado.)
By Chris Mooney September 14
Virtually every ecosystem of the world — from forests to the oceans — raises concern about the toll that a warming climate will take. There’s one type of landscape, though, that doesn’t get talked about very much in this context — so-called “drylands,” a grouping that includes arid and semi-arid regions ranging from many deserts to grasslands. Drylands are one of the more important ecosystems in the world, comprising fully 40 percent of the Earth’s land surface. And now, an alarming new study in the Proceedings of the National Academy of Sciences says the impact of a warming climate on these ecosystems could be much worse than expected — comparable to humans trampling the landscapes underfoot or driving off-road vehicles across them. “Contrary to our expectations, experimental climate change and physical disturbance had strikingly similar impacts,” wrote the researchers, led by Scott Ferrenberg of the U.S. Geological Survey’s Southwest Biological Science Center in Moab, Utah. Ferrenberg conducted the work with two Geological Survey colleagues….
et al PNAS Sept 2015 doi: 10.1073/pnas.1509150112
In drylands worldwide, where plant cover is sparse, large amounts of the ground surface are covered by specialized organisms that form biological soil crusts (biocrusts). Biocrusts fix carbon and nitrogen, stabilize soils, and influence hydrology. Extensive physical disturbance from livestock/human trampling and off-road vehicles is known to destroy biocrusts and alter ecosystem function. More recent work also indicates that climate change can affect biocrust communities. Contrary to our expectations, experimental climate change and physical disturbance had strikingly similar impacts on biocrust communities, with both promoting a shift to degraded, early successional states.
These results herald ecological state transitions in drylands as temperatures rise, calling for management strategies that consider risks from both physical disturbances and climate change.