Global change is triggering an identity switch in grasslands
Grasslands make up more than 40% of the world's ice-free land and have sustained humanity and thousands of other species for eons. In addition to providing food for cattle and sheep, grasslands are home to animals found nowhere else in the wild, such as the bison of North America's prairies or the zebras and giraffes of the African savannas. Grasslands also can hold up to 30% of the world's carbon, making them critical allies in the fight against climate change.
Climate change is causing grasslands to shift beneath our feet, putting these benefits at risk. Global change — which includes climate change, pollution and other widespread environmental alterations — is transforming grasslands and the plant species in them. A new study from researchers at Michigan State University shows what these changes to grassland plant communities look like, and reveal they are not always in ways scientists expect.
“Here in the Midwest, grasslands have been reduced to less than 1% of what they were at the time of European settlement and understanding what drove these changes is important to managing and restoring these systems” said Kay Gross, a plant ecologist at MSU’s Kellogg Biological Station, or KBS, and one of the authors of the study. “Our research at the KBS Long Term Ecological Research site and Allegan State Game Area had provided important information on these processes, but including our data into this larger synthesis reveals insights that are not apparent in site-specific research.”
The new paper, published in the Proceedings of the National Academy of Sciences, offers the most comprehensive evidence to date on how human activities are changing grassland plants.
The team looked at 105 grassland experiments around the world, including other sites from the National Science Foundation’s Long Term Ecological Research program and other research done at KBS. Each experiment tested at least one global change factor — such as rising carbon dioxide, hotter temperatures, extra nutrient pollution or drought. Some experiments looked at two or more of these factors. The team was led by Kimberly Komatsu, a grassland ecologist at the Smithsonian Environmental Research Center, and included researchers from around the world—including former KBS graduate students Emily Grman and Greg Houseman. Team members contributed data from a wide range of grasslands, and developed analyses to determine whether global change was altering the composition of grasslands, both in the total number and kinds of plant species present.
They discovered grasslands can be surprisingly tough — to a point. And it can take time for these changes to be detected. In general, grasslands resisted the effects of global change for the first decade of exposure. But after 10 years of exposure to a climate change factor, species began to shift. Half of the experiments lasting 10 years or more found a change in the total number of plant species, and nearly three-fourths found changes in the types of species. By contrast, only 20% of the experiments that lasted less than 10 years picked up any species changes at all. Experiments that examined three or more aspects of global change were also more likely to detect grassland transformation.
“I think grasslands are very, very resilient,” said Meghan Avolio, co-author and assistant professor of ecology at Johns Hopkins University. "But when conditions arrive that they do change, the change can be really important.”
To the scientists' surprise, the identity of grassland species can change drastically, without altering the number of species. In half the plots where individual plant species changed, the total amount of species remained the same. In some plots, nearly all the species had changed.
For the team, this is a sign of hope that most grasslands could resist the experimentally induced global changes for at least 10 years. And that maybe grasslands are changing slowly enough that we can prevent catastrophic changes in the future.
However, time may not be on our side. In some experiments, the current pace of global change transformed even the “control plots” that were not exposed to experimentally higher global change pressures. Eventually, many of those plots looked the same as the experimental plots.
“Working collectively to understand how climate change is affecting grasslands is critical so that we can better restore and manage this important habitat that we and many other species depend on,” Gross said. “Long-term experiments and data sets are crucial for these efforts.”
(Note for media: Please include a link to the original paper in online coverage:https://www.pnas.org/content/early/2019/08/14/1819027116)