Grasslands – which account for almost 40 percent of land-based ecosystems – provide habitat for a vast diversity of plants and animals, and contribute to the livelihood of over one billion of people all over the world. Moreover, they provide significant carbon sequestration and biodiversity benefits, and can be more resilient to a rapidly changing climate than forests. Unfortunately, during the past few centuries, ancient grasslands worldwide have been largely converted into farmland, used to grow trees, or been replaced by urban areas as citied expanded.
According to a new study led by the University of Colorado Boulder, while the destruction of these pristine grasslands can occur very quickly, the complete recovery of grassland biodiversity and essential ecosystem functions occurs much slower, if at all. These findings contradict prior scientific assumptions that grasslands’ ecological development is quick and their recovery is rapid, posing new challenges to their successful restoration.
“Old growth grasslands have a unique suite of characteristics that develop over a really long time. Recovering grasslands do not have the same species or the same characteristics as they did prior to soil tilling or tree planting, and they take centuries to redevelop,” said study senior author Katharine Suding, a plant community ecologist at CU Boulder.
“If you plant trees in an older grassland or till it for agriculture, you will probably never get many of the unique diversity and belowground characteristics back. It is irreversible. It’s an important reminder that we need to conserve the ancient grasslands that are still intact.”
Compared to newer, younger grasslands, old growth grasslands are unique in their underground structure and biodiversity and need a long time to be restored. “We should think of restoration as more of guiding a trajectory. Some species don’t come in right at the start, and the disturbance that maintains the grassland needs time to grow and be tweaked as these species get established and the soil develops. These processes take time,” explained Professor Suding.
While planting trees has become a popular “natural solution” worldwide to remove carbon from the atmosphere in order to mitigate climate change, many scientists warn than planting trees on natural grassland may create more problems than it solves. “We would lose a huge element of the biodiversity on Earth if we planted trees in old growth grasslands. I think we need to be a little bit more careful about what’s best for the globe, in terms of where to restore what,” warned Suding.
“Viewing grassland restoration as long-term assembly toward old-growth endpoints, with appreciation of feedbacks and threshold shifts, will be crucial for recognizing when and how restoration can guide recovery of this globally important ecosystem,” the authors concluded.
The study is published in the journal Science.