- Old-growth grasslands contain multitudes of unique species – including underground trees that may be thousands of years old.
- Researchers say that a lack of study may have led to the mislabeling of many ancient tropical grasslands as artificially cleared landscapes, making them prime targets for reforestation activities.
- They urge the need for more research and better technology that will help distinguish old-growth from secondary grasslands.
New commitments coming out of December’s COP21 in Paris set their eyes on forests as a way to curb global warming. But a recent article published in Science warns that these forest expansion goals could put the world’s grasslands at risk.
Forests are great at keeping carbon out of the atmosphere, which is why countries are banding together to reforest 1.5 million square kilometers by 2020. By doing so, scientists say global warming can be limited to less than 2 degrees Celsius, thus curbing the worst consequences of climate change.
But in the clamor to save and spread the world’s forests, are grasslands getting the short end of the stick?
In a recent issue of Science, William Bond, a grasslands researcher and professor at the University of Cape Town, writes that “old growth” grasslands around the world are threatened by the purposeful planting of forest where none was before – a process called “afforestation.” This differs from “reforestation,” in which trees are planted in a previously deforested area.
Has that grassland always been there?
A big issue at play here is the lack of research on tropical grassy ecosystems, Bond writes. He’s concerned that not all of the land presumed deforested has actually been artificially cleared, and that planned reforestation efforts could actually be accidental afforestation – destroying native grasslands in the process.
“Vast areas of open grassy vegetation have been identified as suitable for reforestation,” Bond writes in his paper. “But are all these grasslands secondary products of deforestations? Recent research shows that grasslands are often ancient and highly biodiverse, but it remains difficult to distinguish between primary and secondary grasslands on a large scale. Reforestation efforts thus risk converting ancient tropical grasslands to plantations.”
This, Bond says, could not only be bad for the grasslands themselves and the wildlife that inhabit them, but also for the global climate. He points to the albedo – solar reflection – ability of grasslands. He writes that while forests sequester carbon and help keep it out of the atmosphere, their dark canopies absorb solar radiation, which in turn warms the air. Light-colored grasslands, on the other hand, reflect that radiation back towards space.
Grasslands – tropical grasslands, in particular – have high levels of biodiversity and are home to multitudes of species, many which depend on their ecosystems’ unique conditions to survive. North America’s Atlantic coastal plain holds an estimated 6,000 kinds of vegetation, amounting to almost a third of the continent’s plant biodiversity; 29 percent of these species are endemic, meaning they are found nowhere else in the world. South Africa’s native grasslands contain around 4,000 plant species, as well as 15 of the country’s 34 endemic mammals, 22 percent of its 195 reptile species, and 10 of its globally threatened bird species.
Yet, Bond says, official protections for South Africa’s old-growth grasslands don’t seem to match up with their biological significance.
“In South Africa, the grassland biome has the smallest proportional area formally conserved of all the biomes in the country,” Bond told Mongabay.
Of particular conservation importance and concern is the once-vast Cerrado savannah of central and southern Brazil. Historically accounting for more than 20 percent of the country’s land area, the Cerrado (which also includes some forest) has been whittled away, leaving less than 40 percent remaining. This conversion largely happened over just the past two decades, after Brazil’s agronomists figured out that by adding lime, they could make the region’s acidic soil conducive to growing crops. Today, the cerrado is responsible for 70 percent of the country’s agricultural production. Of its grasslands’ estimated 6,000 plant species, 645 are threatened with extinction.
One big reason why the Cerrado has been the target of such heavy conversion is the protection of forest elsewhere. Namely, the Amazon rainforest. As Brazil cracked down on deforestation in the Amazon, the region’s soy and cattle industries had to shift their attention to another venue. Luckily for them, the cerrado was nearby – and it had relatively few restrictions for its new tenants. Of its 1.2 million square miles of area, less than 2 percent of the cerrado is officially protected.
Bond and other grasslands experts lament what they see as a lack of appreciation and prioritization for the world’s grassy biomes, particularly in the wake of programs aimed at expanding forests.
“In the subtropical grasslands in Brazil there are huge areas being converted into pine and eucalyptus plantation, because people think they need to do “reforestation” in the Pampas! And pine trees, as we know, are aggressive invasive species, particular in grassland areas (which is also happening in the Cerrado – mostly in wet grasslands),” said Alessandra Fidelis, an ecologist with Brazil’s Universidade Estadual Paulista.
Many of the world’s grasslands have been assumed deforested at some point in the past, according to Bond. In Madagascar, he writes, ecologists once thought that the grassy plains that stretch across most of the island were the result of human immigration to the island that began millennia ago. But when scientists did finally survey their biodiversity, they found that these grasslands contained around 230 endemic grass species – among the most in the world. Since it would take quite a long time for so many unique species to evolve, this indicates that Madagascar’s grasslands are indeed a native biome.
Madagascar was lucky: the antiquity of its grasslands was recognized before reforestation projects started converting them. But South Africa was a different story.
“In South Africa, extensive forestry plantations were established in old growth grassland which, at the time, were assumed to be produced by deforestation when farmers first moved into the area in the past two millennia,” Bond told Mongabay.
This mistaken reforestation not only displaced what turned out to be native, old-growth grasslands, but also wreaked havoc on ecosystem functions that had evolved in-concert with grasslands for millions of years.
“Hydrology experiments (paired afforested versus grassland catchments) showed that the plantations (mostly conifers) reduced streamflow relative to grasslands and, since this is a water scarce country, further afforestation was then subjected to rigorous control depending on downstream water needs,” Bond said. “There has been very little recent afforestation because of the water issue and the realisation that the grasslands are rich in endemic species of both plants and animals.”
What makes a grassland a grassland?
Grass is fairly new on the scene in terms of plant evolution, appearing around 66 million years ago, according to some estimates. In comparison, flowering plants as a whole (the group to which grasses belong) emerged about 100 million years before that. However, it wasn’t until around 25 million years ago when the vast grasslands as we know them entered the picture, encouraged by rising mountains, retreating glaciers, and a warming and drying climate. Fossil and genetic evidence indicate that many modern grassland species are younger still, with some species emerging as recently as 2.5 million years ago.
Most grasslands are “natural-burn” ecosystems that have evolved, in essence, to be destroyed. Grasses are unique from most “leafy” plants in that their growth centers lie close to or under the ground. This lets the plant live on and regrow even after its entire aboveground portion is eaten by a grazing animal or burned in a fire.
Grasslands don’t just contain grasses. They’re also home to a variety of other plants like forbs such as milkweed and sunflowers, and even underground trees. Yes, underground trees. This poorly understood group of plants is found in the grasslands of South America and Africa. They can be massive, but most of their structure – their branches and roots – exists underground. All that can be seen of them aboveground are short stems with little leaves, flowers, and seeds poking up from the soil.
Little seems to be known about underground trees. However, studies in the Cerrado indicate that some may be very, very old.
“They are thought to be old but dating these structures is difficult,” Bond told Mongabay. “A recent (the only?) attempt for a Jacaranda in Brazil produced an estimated age of 3,800 years!!” The Jacaranda referenced by Bond is Jacaranda decurrens, a tree that can grow to be 22 meters (72 feet) across.
Old-growth grasslands take a long time to grow back
Underground trees, grassland forbs, grasses themselves: they’ve all evolved to withstand the destructive force of fire. So what happens when old-growth tropical grasslands are afforested? Can they bounce back from that like they do after a natural burn?
Not necessarily, say the experts. While certain species can come back after a converted area is restored, this is far from a hard-fast rule.
“I can tell about some subshrubs in the Cerrado that could survive and resprout after 60 years of pine cultivation (e.g., Eugenia arenosa, Peritassa campestris, Andira humilis, Anemopaegma arvense),” said Giselda Durigan, researcher with the São Paulo state government’s Forest Institute.
According to Bond, native grasslands can completely change when afforestation comes into play. As humans plant trees and suppress fires so that those trees can grow, a factor suddenly appears that many grassland plants aren’t equipped to deal with: shade.
“Fire-suppression experiments have led to the elimination of long-lived forbs as a result of shading by an accumulation of dense undecomposed grass litter,” Bond writes. “Old-growth grassland plants…are eliminated by forest expansion or afforestation with pines and eucalypts.”
The “secondary grasslands” that pop up after conversion of an area by humans are completely different than old-growth grasslands, favoring less biodiversity; a previous study coauthored by Bond found that even after restoration, grassy ecosystems in South Africa contained 50 percent to 75 percent fewer plant species. Indeed, research indicates that it may take decades, even centuries, for native grasslands to completely recover after afforestation.
Must reforestation come at the sake of grasslands?
This lack of resilience isn’t the main issue that has Bond and his colleagues worried about the future of the world’s native tropical grasslands. The big problem, he writes, is that many old-growth areas remain unstudied or misidentified as secondary growth – and thus are at particular risk of afforestation. He points to AFR100, a plan launched during December’s COP21 climate conference in Paris by the World Resources Institute (WRI) that aims to restore 100 million hectares of African degraded lands by 2030. So far, 10 countries have officially signed on, together committing to restore than 30 million hectares.
“If you set fixed targets like this, I don’t see how you can be appropriately cautious about planting up ancient grasslands,” Bond said. “What if only 5 million hectares are obviously secondary grasslands produced by deforestation? Will the countries not be paid? I think it is a recipe for future disaster.”
However, WRI disagrees with Bond that their restoration proposals will harm grasslands. The organization’s representatives write in a response letter to Bond’s Science article that their approach, called Forest and Landscape Restoration (FLR), “does not call for increasing tree cover beyond what would be ecologically appropriate for a particular location, nor should it cause any loss or conversion of natural forests, grasslands, or other ecosystems.
“Rather, FLR is a process that seeks to regain the ecological integrity and enhance human well-being in deforested or degraded forest landscapes. The FLR approach includes a wide range of sustainable land management practices applicable to both forest and non-forest ecosystems. A fundamental first step in the FLR process involves understanding the ecosystem at the landscape level, including its historical and cultural values, before making decisions on a restoration approach. FLR under this definition would promote exactly the same conservation of ancient grasslands that Bond advocates.”
In its response letter, WRI acknowledges that some of areas highlighted in their Atlas of Forest Landscape Restoration Opportunities include sparse forest that overlap with grasslands.
“These mosaic areas require individual assessment — including identifying the natural level of tree cover — before deciding on the appropriate management approach,” its authors write.
But the issue remains that there is no easy way to figure out, on a large scale, which grasslands are old-growth and which are not.
“We need better technology and lots of ground work,” said Geraldo Wilson Fernandes, an ecologist at Federal University of Minas Gerais. He and his research team are in the process of developing a system to differentiate grassland types via their distinctive light reflectance patterns – or “spectral signatures.”
In the meantime, Bond urges caution when it comes to ambitious reforestation projects while remaining optimistic that there is potential to conserve both forests and grasslands.
“There has been considerable progress in identifying old-growth grasslands and their ecological requirements,” he writes, “and this bodes well for restoring forests and the services they provide while also maintaining ancient tropical grassy ecosystems.
“It would be a travesty if ancient grasslands are replaced by ill-conceived forest plantation projects because of misconceptions about the origins of tropical grassy systems.”
- Bond, W. J. (2016). Ancient grasslands at risk. Science, 351(6269), 120-122.
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