Nairobi, April 7 – As wild herbivores are increasingly displaced by cattle in the African savannah, a new research paper has shown that the livestock only leads to the degradation of the soil while the presence of elephants does the reverse.
The 20-year study by the Vrije Universiteit Brussel in collaboration with Mpala Research Centre in Kenya shows that cattle presence decreased total soil carbon and nitrogen pools, while the presence of mega-herbivores (mainly elephants) increased these pools and even reversed the negative effects of cattle.
The research, published in the journal Nature Sustainability, suggests that a mix of cattle at moderate densities and wild herbivores can be sustainable, provided that the assemblage of wild herbivores includes the largest species.
Cows only drop their dung at night when they are kept fenced-in to protect them from lions. This impoverishes the soil, which reduces the productivity and quality of the grass, according to the study.
However, when elephants are present, this soil depletion does not occur. The soil is even enriched.
“The preservation of these ‘mega-herbivores’ is therefore not only essential for the maintenance of the ecosystem, but also for the food supply of the local population,” said Judith Sitters, one of the scientists who carried out the research.
To examine the impact of cattle and wild herbivores on the soil, the researchers collected soil and vegetation samples in the Kenyan savannah and analysed these for carbon, nitrogen and phosphorus concentrations. Sitters did this in collaboration with Philippe Claeys of the VUB AMGC Analytical, Environmental and Geo-Chemistry Department and in association with American and Kenyan colleagues.
The soil and vegetation samples were collected in the Kenya Long-term Exclosure Experiment (KLEE), which was established in 1995 to examine the effects of various combinations of livestock and wildlife on the ecosystem. Cows and wild herbivores such as elephants and giraffes were included or excluded from experimental plots. This allowed the team to measure the impact of livestock on the native biodiversity and the ecosystem functions (such as the carbon cycle) of the savannah
The research indicates that in areas where cattle and elephants graze together, soil depletion is not only prevented but the soil is even enriched. Elephants bring down trees in the savannah, which accelerates the return of nutrients to the soil.
But more importantly, elephants compete with cattle for the same available food, which results in less grazing by cattle. This also means that cows export less dung away from the place where they graze, while dung deposition of wild herbivores is stimulated, which in turn feeds the soil.
The combination of domestic cattle and elephants can, therefore, be a form of sustainable management for African savannah.
“The largest herbivores of the African savannah, such as elephants and rhino, are threatened with extinction,” said Sitters. “That would first of all be a major loss for diversity in the animal kingdom, but it also has large implications for different ecosystem functions. Our research shows that elephants prevent soil depletion caused by livestock.
“That is good news because soil impoverishment has a long-term negative impact on livestock itself and therefore on the food supply of the local population. Consequently, it is in the best interest of the local population to protect the large herbivores that are threatened with extinction,” she added.
The research was part of the postdoctoral fellowship project from the Research Foundation Flanders (FWO) of Dr Judith Sitters who works at the VUB Department of Biology in the group of Prof. Harry Olde Venterink. For her research, Dr Sitters performed fieldwork at the Mpala Research Centre in Kenya in collaboration with Prof. Truman Young (University of California, Davis, USA) and Dr Duncan Kimuyu (Karatina University, Karatina, Kenya).
