Three elephants, two buffalo, seven hippos and a few hundred antelope – that’s all that could be spotted in Gorongosa National Park, Mozambique in 1997, when a violent civil war spanning two decades had swept through the nation, imperilling humans and wildlife alike.
In the early 1960s, Gorongosa was a thriving ecosystem – vast numbers of buffalo, hippo, zebra and wildebeest silhouetted the floodplains around Lake Urema. But bounteous days for biodiversity would turn bloody. From 1964, Mozambique entered a turbulent period as it gained independence from its Portuguese colonial rulers. By 1977, an insurgency against the newly formed government ignited a civil war. Caught in the crossfire, 90 to 99 per cent of all mammals in Gorongosa are estimated to have been eradicated.
As herbivore numbers dropped, alien plant species began to spread across the floodplains. Mimosa pigra, also known as the giant sensitive tree, which forms dense, impenetrable thickets, grew unchecked.
Fortunes changed in 2008 when the government of Mozambique and US-based NGO, the Carr Foundation, entered a public-private partnership with a clear mission: restore the ecosystem to pre-war conditions. Since then, species have gradually been reintroduced through a ‘trophic rewilding’ approach, starting with the herbivore species that were historically present.
‘Trophic rewilding is the effort to re-establish a self-sustaining, self-regulating, biodiverse system by ensuring that populations of large animals are healthy,’ explains Robert Pringle, an associate professor at Princeton University and ecologist at Gorongosa. From 2007 to 2018, the park’s rigorous rewilding approach led to a four-fold increase in large herbivore numbers including waterbuck, reedbuck, impala, oribi and buffalo.
With the spotlight on herbivore restoration, ecologists knew that the underlying health of the vegetation would be the real indicator of ecosystem robustness. In a new study, Pringle and his team tracked the growth of the invasive mimosa plant to measure the success of trophic rewilding. ‘The premise of trophic rewilding is that restoration of population numbers will allow the ecosystem to heal itself, but the problem is that its success has rarely been tested,’ says Pringle. His team found that from 2015 to 2017, mimosa progressively declined, eventually matching pre-war conditions. What’s more, mimosa was found across 79-96 per cent of herbivore fecal samples: reintroducing herbivores had restored the ecosystem’s ability to self-regulate.
Some ecologists have raised concern that this kind of rewilding strategy may not be feasible in areas where the altered states of ecosystems – the aftermath of anthropogenic impacts – are irreversible. Yet, in Gorongosa, ten years of rewilding have proved sufficient to counter 35 years of herbivore decline and mimosa growth. ‘Natural processes are taking care of themselves, keeping mimosa under control,’ says Pringle. ‘Establishing robust herbivore numbers has allowed us to start reintroducing carnivores, such as lions and African wild dogs. Fourteen African wild dogs were reintroduced in 2018. Leopards have even returned to the park on their own volition.’
Crucially, rewilding in Gorongosa is uplifting more than just wildlife populations. ‘Sustainable development, women’s education and employment in the communities around the park have all been made possible by the project,’ adds Pringle. ‘If surrounding communities remain poor, there’s little hope for the survival of the national park.