Grasslands Build Biodiversity and Resilience Over Centuries
The perhaps underappreciated champions of underground carbon storage and resilience, grasslands can often be found at most latitudes in open, continuous areas. Their grasses grow to between eight inches and seven feet in height with roots that go deep underground, according to NASA Earth Observatory.
The height of the grass depends on soil depth and how much rainfall it receives. Because of these two parameters, trees are rare in the grasslands ecosystem.
New research has found that the biodiversity and resilience of grasslands to events like fire and drought develop over centuries, according to a press release from University of Colorado Boulder (CU Boulder).
“Old growth forests are old/ancient, mature forests that have assembled over centuries mainly undisturbed by humans, composed of large and old trees, large snags and a diverse tree community with structural complexity,” Dr. Elise Buisson, one of the authors of the study and professor at Avignon Université who does research in restoration ecology, community ecology and conservation told EcoWatch in an email. “Similarly, old growth grasslands are old/ancient grasslands that have assembled over centuries, mainly undisturbed by humans, containing long-lived perennial plants and high species diversity with well-developed below ground structure.”
The study, “Ancient grasslands guide ambitious goals in grassland restoration,” was published in the journal Science.
In the last 200 years, a great deal of the world’s ancient grasslands have been converted into farmland or been used to grow trees, the press release said.
“Any activity that disturbs the soil (plowing, mining, quarrying, etc.), and thus the bud and seed bank, destroys ancient grasslands,” Buisson told EcoWatch.
For years prior to the study, it was thought that the regeneration and ecological evolution of grasslands were fast, the press release said. The realization that it’s actually an extremely slow process presents issues for the restoration of grasslands.
“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,” distinguished professor in the Department of Ecology and Evolutionary Biology at CU Boulder Katharine Suding, who was senior author of the paper, said in the press release. “It’s an important reminder that we need to conserve the ancient grasslands that are still intact.”
Suding is a North American grasslands specialist who, with a team of international experts, studied grassland conservation and restoration on a global scale. The research team looked at tropical and savannah grasslands as well as coastal, prairie and arid grasslands.
There are grasslands in different stages of evolution on the planet.
“Most people mix up ancient grasslands, secondary grasslands, derived grasslands, hay meadows, etc. because they look the same (from a non-expert point of view) ” Buisson told EcoWatch. “Because they mix up everything and very often see grazed or mowed meadows, they think that farmers can sow them and install them quickly. Some temperate meadows or prairies which are used to being managed can be restored relatively easily. That’s why people thought it would be the same for all grasslands.”
Buisson contrasted old growth forests and grasslands with secondary forests and derived grasslands.
Secondary forests are those “which have re-grown after being harvested or cleared for agriculture (and then abandoned),” while derived grasslands are in “an early grassy stage in the development of forest after being harvested or cleared for agriculture (and then abandoned),” Buisson said.
According to the press release, almost 40 percent of terrestrial ecosystems on Earth are grasslands — the home to many plants and animals. Grasslands provide benefits to biodiversity and aid in the subsistence of more than a billion people all over the world.
With the rapid pace of climate change, grasslands have the ability to be more hardy than forests.
But grasslands are distinct from forests, and do not represent an early stage in their evolution.
“I think that a lot of ancient/old growth grasslands in the world are in the tropics. These areas were colonized by Europeans, with their vision of European ecological systems and the concepts of succession, climax, etc. Succession stops when the system has reached a steady state which was believed to be mature forests in most cases. This made it generally accepted everywhere that grasslands were successional stages towards forests. This is not true everywhere, and definitely not in ancient grasslands,” Buisson told EcoWatch.
Many grassland and tree species have adapted to fire and other ecological disruptions.
“[T]hey have evolved with them over centuries (sometimes millions of years). African savannas have evolved with fire and species have been selected with fire for 16-20 million years. The Brazilian savanna (Cerrado) between 10 and 5 millions years. That’s huge!!” Buisson said. “Most species are adapted to fire. Savanna trees have thick bark. After fire, lots of species have the ability to resprout from bark-protected buds or underground buds (buds which are protected from fire in the soil), etc. Some species have underground storage organs, with reserves to regrow after fire, etc. They actually need fire.”
The researchers discovered that, although grasslands can be decimated quickly, their recovery time varies, and — for some — recovery is only possible over a long period of time or not at all, which makes it all the more vital to conserve those that remain pristine.
“Not all grasslands are long to regenerate. It depends what kind of grasslands we are talking about. Ancient grasslands take a long time to regenerate because they have assembled over centuries (just like it is really hard to restore ancient forests… only time can do it). Moreover, it seems like in many ancient grasslands, species have a conservative strategy. They are slow growing. They don’t disperse very far. They don’t all produce a lot of seeds,” Buisson told EcoWatch.
The older the grassland biome, the more complex it is, and sometimes recovery may not be possible.
“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,” Suding said in the press release.
One-third of all terrestrially stored carbon lies underground in the roots of grasslands, which can stretch down as far as 20 feet. It is one of the reasons they are so resilient in the face of ecological disruptions like fires.
Compared to forests, grasslands can sometimes be unsung heroes when it comes to carbon storage, since they aren’t as apparent in the landscape.
“Like any other plant, grassland plants store carbon in the soil by providing organic matter (dead leaves, stems, roots), which decomposes; store carbon in alive roots; for some species, store carbon in underground storage organs (particularly common in fire prone ecosystems, thus in grasslands and savannas),” Buisson told EcoWatch.
Transplanting such grassland species isn’t an option, just like it isn’t an effective method for old-growth trees.
“[W]e thought that because grassland plants are smaller than trees they can be transplanted… But as one cannot translocate a tree from an old-growth forest to salvage it, one cannot hope to translocate a grassland species with an underground storage organ (USO). Digging out USO often leads to killing the plant,” Buisson said.
The belowground makeup of old growth grasslands differs from that of less mature grasslands, the press release said. The biodiversity of the old growth grasslands may never be able to be restored, but they can give scientists a restoration blueprint, according to Suding.
Just ten years ago, the restoration of grasslands was centered on the disbursement of seeds with the addition of fire or grazing before leaving the landscape alone to heal over time. However, this has been found to be more complex and require a methodical strategy to be successful.
“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,” Suding said in the press release. “These processes take time.”
The growth of grasses from seeds does better in some geographic locations than others, for instance, and some grasses, such as those in tropical regions, spread through underground tubers and rhizomes, which are significantly harder to restore.
“Some old-growth grassland species do not produce seeds every year or have seeds of low quality. In a stable environment, with just fire that they can overcome by resprouting, there is no real need for these plants to produce seeds. That makes it very complicated for us to collect seeds to be sown or germinate seeds in nursery to later transplant seedlings (as it is done for forest restoration) because seed availability may be low,” Buisson told EcoWatch.
Last year was the beginning of the United Nations Decade on Ecosystem Restoration, the goal of which is to restore the biodiversity of Earth’s ecosystems and to assist in attaining the UN’s Sustainable Development Goals and the objectives of the Paris agreement.
And while tree planting has been seen as a relatively simple and “natural” way to extract atmospheric carbon, it does not work everywhere, the press release said.
“We would lose a huge element of the biodiversity on Earth if we planted trees in old growth grasslands,” Suding said in the press release. “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.”
Suding is concerned that a great number of nations may feel planting trees is enough, even though the United Nations’ drive for ecosystem restoration states that “planting trees on natural grassland may destroy more than it creates,” the press release said.
With their ability to survive with less water, survive fires, store carbon underground and decrease soil erosion, grasslands should be especially revered in places like the Western United States that have been plagued by heatwaves, drought and wildfires due to climate change.
“They’re very resilient to a lot of these threats that we’re increasingly experiencing. Grasslands are resilient and can deliver well in terms of our priorities of carbon storage, water infiltration and soil health,” Suding said in the press release.
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