Oft-overlooked grasslands build biodiversity, resilience over centuries
Grassland biodiversity and resilience to disturbances such as fire, heat and drought is the result of a slow process over hundreds of years, like that of old-growth forests, according to new research led by CU Boulder.
Publish in the magazine Science on August 5, 2022, as part of a special issue on grasslands, the study contradicts long-standing assumptions that grasslands ecological development is rapid and their recovery is rapid, posing new challenges to their successful recovery.
“Old grasslands have a unique set of characteristics that develop over a very long time. Restoring grasslands do not have the same species or characteristics as before tilling the soil or planting trees, and it takes ages for them to re-develop, said Katharine Suding, senior author of the paper and Distinguished Professor in the Department of Ecology and Evolutionary Biology and Institute of Arctic and Alpine Research (INSTAAR) at CU Boulder. “It’s an important reminder that we need to preserve the old grasslands that are still intact.”
Suding, an expert on North American grasslands, collaborated with other experts from around the world to evaluate the current state of science, conservation and restoration of grassland – from arid, prairie and coastal grasslands to those in the tropics and savannas.
Grasslands, which account for nearly 40% of terrestrial ecosystems, provide habitats for a wide diversity of animals and plants and contribute to the livelihoods of more than 1 billion people worldwide. They also offer significant benefits for carbon sequestration and biodiversity, and may be more resilient than forests in the face of a rapidly changing climate.
But over the past few centuries, ancient grasslands around the world have been largely converted to farmland, used to grow trees, or developed as cities expand.
The researchers found that while the destruction of these pristine grasslands can occur very quickly, full restoration of grassland biodiversity and essential ecosystem functions is slow or not at all. The findings further highlight the importance of preserving the world’s remaining pristine grasslands.
“If you plant trees in an older grassland or cultivate it for agriculture, you probably never get much of the unique diversity and subterranean features back. It’s irreversible,” Suding says.
Recovery takes time
Grasslands store most of their material underground, in roots that can reach up to 20 feet deep. This unprecedented physical presence allows them to store a lot of carbon – about a third of all carbon stored on land – and remain resistant to fire and other ecological disturbances. This is also the reason why grasslands are often undervalued compared to forests. If it’s out of sight, it’s out of mind.
Grassland restoration, however, can take a page out of the forest playbook.
“‘Old growth’ is a term not only for forests, but also for grasslands,” said study co-author Elise Buisson, who co-authored that finding in a publication from 2015.
Old grasslands are unique in their subterranean structures and biodiversity compared to newer, younger grasslands. And while these old-growth ecosystems may never fully replicate in modern landscapes, they provide a model for recovery efforts, Suding said.
Even a decade ago, grassland restoration focused on spreading seed of species on a landscape, adding grazing or fire, and stepping aside. The new analysis shows that it takes more than a hands-off approach to be successful. Rather than throwing all the ingredients in a crockpot and turning it on high, grasslands may need a more step-by-step recipe approach to recovery.
“We should see recovery as more of guiding a trajectory. Some species don’t come in right away and the disturbance that sustains the grassland takes time to grow and adapt as these species establish themselves and the soil develops.” .” said Suding. “These processes take time.”
For example, some plants reproduce well from seed in the upper Midwest, for example, but not in Colorado due to the drier climate. Many tropical grasses do not propagate by seed at all, but by rhizomes and tubers underground, and are much more difficult to recover.
The report comes a year after the start of the UN Decade for Ecosystem Restoration, which aims to restore degraded ecosystems around the world to increase biodiversity, help achieve the Sustainable Development Goals and the Paris Climate Agreement. At the same time, planting trees has become a popular “natural solution” worldwide for removing large amounts of carbon from the atmosphere.
But while the UN initiative explicitly states, “Planting trees on natural grassland can destroy more than it creates,” as countries set ambitious goals and commitments for ecosystem restoration this decade, Suding worries that for many, this is just the planting trees means.
“We would lose a huge amount of biodiversity on Earth if we planted trees in old grasslands,” Suding said. “I think we need to be a little bit more careful about what’s best for the world, in terms of where we can recover some.”
As climate change threatens the American West through drought, heat and wildfires, grasslands are also a resilient choice to use less water, reduce soil erosion and retain carbon in the soil. It is the older, veteran grasslands that are most favorable in this regard.
“They are very resilient to many of these threats that we are increasingly experiencing. Grasslands are resilient and can perform well in terms of our priorities of carbon storage, water infiltration and soil health,” said Suding.
Other authors of this publication are: Elise Buisson, Institut Méditerranéen de Biodiversité et d’Ecologie, Avignon Université, and CNRS, Aix Marseille Université; Sally Archibald, University of the Witwatersrand; and Alessandra Fidelis, Universidade Estadual Paulista (UNESP).
Urgent need for new approach to combat global grassland degradation
Elise Buisson et al, Ancient grasslands lead ambitious goals in grassland recovery, Science (2022). DOI: 10.1126/science.abo4605
Quote: Often overlooked grasslands provide biodiversity, resilience through the ages (2022, August 4), retrieved August 4, 2022 from https://phys.org/news/2022-08-oft-overlooked-grasslands-biodiversity -resilience-centuries.html
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