The biodiversity and resilience of grasslands to disturbances such as fire, heat and drought are the result of a slow process over hundreds of years, such as that of old-growth forests, according to new research conducted by the University of Colorado at Boulder.
Published in the journal Science on August 5 2022, as part of a special issue on grasslands, the study contradicts years of assumptions that the ecological development of grasslands is rapid and their recovery is rapid, posing new challenges to their successful restoration.
“Ancient grasslands have a unique suite of characteristics that develop over a very long period of time. Grasslands in recovery do not have the same species or characteristics as before tillage or tree planting, and they take centuries to re-grow,” said Katharine Suding, lead author of the paper. and Professor Emeritus in the Department of Ecology and Evolutionary Biology and the Institute of Arctic and Alpine Research (INSTAAR) at CU Boulder. “It’s a crucial reminder that we need to conserve ancient grasslands that are still intact.”
Skilled in the North American grasslands, Suding has partnered with d other experts from around the world to assess the current state of global grassland science, conservation and restoration – from arid grasslands, grasslands and coastal to those of the tropics and savannahs.
Grasslands, which represent nearly 40% of terrestrial ecosystems, provide habitat for a wide diversity of animals and plants and contribute to the livelihoods of over a billion people around the world. They also offer significant carbon sequestration and biodiversity benefits, and can be more resilient than forests in the face of a rapidly changing climate.
Yet, at Over the past two centuries, ancient grasslands around the world have largely been converted to farmland, used to grow trees, or developed as cities grow.
Researchers have found that while destruction of these pristine grasslands can occur very quickly, full recovery of grassland biodiversity and essential ecosystem functions occurs slowly or not at all. The findings further underscore the importance of conserving the world’s remaining intact grasslands.
“If you plant trees in older grassland or plow it for agriculture, you’ll probably never find much of the exclusive diversity and features below ground. It’s irreversible,” Suding said.
Restoration takes time
Grasslands store most of their material underground, in roots up to 20 feet deep. This invisible physical presence is how they can store a lot of carbon – about a third of all carbon stored on earth – and remain resilient to fire and other ecological disturbances. This is also why grasslands are often underestimated compared to forests. If it’s out of sight, it’s out of mind.
Restoration of grasslands, however, can take a webpage out of the forest playbook.
“’Old growth’ is not just a term for forests, but also applies to grasslands,” said co-author Elise Buisson, who co- writes this discovery in a publication of 40.
Ancient grasslands are unique in their underground constructions and their biodiversity by compared to newer and younger grasslands. And while these old-growth ecosystems can never be fully replicated in modern landscapes, they provide a model for restoration efforts, Suding said.
Ten years ago, grassland restoration focused on distributing the seeds of species across a landscape, adding pasture or fire and withdrawal. The new analysis reveals that it takes more than a hands-off approach to succeed. Instead of throwing all the ingredients into a slow cooker and setting it to high heat, the prairies may need a step-by-step approach to restoration.
“We should be thinking restoring rather than orienting a trajectory. Some species don’t come in early on, and the disturbance that maintains the grassland needs time to develop and change as those species become established and the soil develops,” Suding says. “These processes take time.”
For example, some plants reproduce well from seed in, say, the upper Midwest, but not in Colorado due to the climate drier. Many tropical grasses do not spread by seed at all, but by underground rhizomes and tubers, and are much more difficult to reestablish.
Implications for the policy
The report comes a year after the start of the United Nations Decade on Ecosystem Restoration, which aims to restore degraded ecosystems around the world to increase biodiversity, help achieve the strong development goals and the Paris Climate Agreement. At the same time, planting trees has become a popular “natural solution” around the world for removing large amounts of carbon from the atmosphere.
Yet, so that the UN initiative explicitly states that “planting trees on natural grasslands can destroy more than it creates”, as countries set ambitious targets and commit to restoring ecosystems at the over the course of this decade, Suding worries that for many this means just planting trees.
trees in ancient grasslands,” Suding said. “I think we need to be a little more careful about what’s best for the world, in terms of where to restore what.”
While change climate threatens the American West with drought, heat, and wildfires, grasslands are also a resilient choice for using less water, reducing soil erosion, and keeping carbon in the soil over time. It’s the older, older grasslands that are the most beneficial in this regard.
“They are very resilient to many of these threats that we are increasingly experiencing. Grasslands are resilient and can do well with our priorities of carbon storage, water infiltration and soil health,” Suding said.