What do you imagine when you think of a tropical ecosystem—lush rainforests or maybe coral reefs teeming with life? Whatever you’re picturing, it probably doesn’t involve too much grass. But tropical grasslands and savannas, including Africa’s Serengeti and Brazil’s Cerrado, are also important tropical ecosystems. They are home to many of the world’s large mammals and they provide important livestock grazing lands and sources of food for vast numbers of people. These grassy ecosystems are also key players in the global carbon cycle.
Despite their importance, tropical grasslands and savannas tend to be ignored or completely misidentified when it comes to conservation priorities and climate change efforts, argues a new paper published in the April Trends in Ecology & Evolution. “These tropical grass biomes have essentially been neglected,” says Catherine Parr, a researcher at the University of Liverpool’s School of Environmental Science and the lead author of the paper. “They’ve been misclassified…. They’ve been really misunderstood,” she says.
Tropical grassy ecosystems can be difficult to categorize in part because their appearances can vary widely, ranging from virtually tree-free grasslands to savannas with extensive tree cover. The Food and Agriculture Organization of the United Nations (FAO) defines forests based solely on percentage of tree cover, tree height and area, leading to the classification of many savannas with some trees as forests or degraded forests in need of reforesting. But those classifications are incorrect, Parr says. Tropical grasslands and savannas are “very different [from] forests, and they contain immense amounts of biodiversity…. They’re not these anthropogenic degraded lands,” she says.
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Neglect and lack of understanding of these grassy ecosystems is contributing to their decline. In some cases mismanagement is to blame. Grasslands and savannas require periodic fires to keep out forest species, but land managers often suppress fires to promote the growth of more trees. “Where fire is taken out, you can get a rapid shift…from savanna to forest,” Parr says, with implications for both biodiversity and the livelihoods of people living nearby.
Even programs that are meant to protect biodiversity and the climate can end up harming these grassy ecosystems. The United Nations’ Reducing Emissions from Deforestation and Forest Degradation in Developing Countries (REDD+) program, along with its Framework Convention on Climate Change Clean Development Mechanism (CDM), which aim to reduce carbon emissions through reforestation and the prevention of deforestation, rely on the FAO’s definition of forests. This can lead to “reforestation” of healthy grasslands or savannas that were not forests to begin with, says Parr. REDD+ and CDM reward this conversion because it results in increasing measurable aboveground carbon in the form of new trees. But those trees come at the expense of an existing, biodiverse grassy ecosystem.
Agricultural development is also destroying grasslands, such as the Cerrado. And many parts of the Serengeti are overgrazed by livestock.
Tropical grasslands “deserve more research and conservation attention than they currently receive,” Parr and her co-authors conclude. They must be considered “biomes in their own right,” she says, with unique ecologies, plants, and animals.
