Savannah Ecosystems in Danger
Few of the world's ecosystems are more iconic than Africa's sprawling savannahs home to elephants, giraffes, rhinos, and the undisputed king of the animal kingdom: lions. This wild realm, where megafauna still roam in abundance, has inspired everyone from Ernest Hemingway to Karen Blixen, and David Livingstone to Theodore Roosevelt. Today it is the heart of Africa's wildlife tourism and includes staunch defenders such as Richard Leakey, Michael Fay, and the Jouberts. Despite this, the ecosystem has received less media attention than imperiled ecosystems like rainforests. But a ground-breaking study in Biodiversity Conservation finds that 75 percent of these large-scale intact grasslands have been lost, at least from the lion's point of view.
"These savannahs conjure up visions of vast open plains. The reality is that from an original area a third larger than the continental United States, only 25 percent remains," co-author Stuart Pimm, with Duke University, said in a statement. Currently around 30 percent of the world's rainforest remains.
The study's authors write that while "global assessments of how much tropical moist forest remains are made routinely, and, in the case of the Brazilian Amazon, monthly [...] comparable assessments of tropical dry woodlands and savannahs are few."
In order to determine how much intact savannah remains, the study took a "lion's view." In other words they focused on habitat that would be intact enough for the region's top predator, the African lion (Panthera leo leo), to survive.
"If areas retain lions, the continent’s top predator, they are likely to be reasonably intact ecosystems," the scientists explain in their paper. "By considering the size of savannah Africa from the lion's perspective, we can assess how much of it remains in large, relatively intact areas, not yet heavily modified by human influence. Clearly, smaller areas will still support less complete sets of species."
Researchers then used high-resolution satellite imagery to measure the extent of Africa's grasslands, defined as areas that receive 300 to 1,500 millimeters of rain annually.
"Based on our fieldwork, we knew that most of the information out there from low-resolution satellite-based studies was wrong," explains lead author Jason Riggio of Duke University’s Nicholas School of the Environment. "Existing global maps are quite coarse and show large areas of African woodlands as being intact. Only by utilizing very high-resolution imagery, were we able to identify many of these areas as being riddled with small fields and extensive, if small, human settlements that make it impossible for lions to survive."
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Savannah image via Shutterstock.