jouw wetenschapsgids in de hoofdstad

jouw wetenschapsgids in de hoofdstad

Elephants prevent soil depletion in African Savana

Wildlife always has right of way in the savanna, so sometimes you have to wait peacefully while a herd of elephants cross the road. © Judith Sitters

In my previous blog about my job as an ecologist, I took you to the Arctic tundra in Norway. The research I’m about to tell you about now took place 10,000 km to the south, in a savanna in Kenya. I have several research projects in collaboration with a research centre in Kenya (Mpala Research Centre) and American and Kenyan colleagues. As an ecologist who studies the fascinating interactions between large herbivores, plants and the soil, the African savanna is a researcher’s paradise. This is one of the few ecosystems on earth where there is still an enormous diversity of wildlife

Olifanten

In most African savanna wild herbivores need to share their living space with livestock such as cattle. The Kenya Long-term Exclosure Experiment (KLEE) examines the effects of different combinations of livestock and wildlife on processes in vegetation and soil. With this experiment researchers hope to proof that savannas can be sustainably management for both biodiversity conservation and livestock production. © Dino J. Martins.

More than half of Kenya’s wildlife lives outside protected areas, creating conflicts between the needs of wildlife and humans. Wild animals are increasingly displaced by livestock, such as cattle. A pressing ecological issue is whether savannas can be sustainably managed for both the conservation of natural biodiversity and livestock production. To answer this question, the famous Kenya Long-term Exclosure Experiment (or KLEE) was set up in 1995. This experiment examines the effects of different combinations of livestock and wildlife on processes in vegetation and soil. Cattle and wild herbivores, such as elephants or giraffes, are included or excluded from various experimental plots.

KLEE

The KLEE consists of several experimental plots of 200m x 200m where herbivores are either included or excluded. Here you see two of the experimental plots with a fenced plot on the left that only allows cattle to be herded in through the fence, and on the right a plot that only wild herbivores have access to. Here the herders actively ensure that their cattle do not graze. © Judith Sitters

Zebra

One of the fences of the KLEE excluding a zebra from an experimental plot. © Truman P. Young.

kudde koeien

A herd of cattle in one of the experimental plots of the KLEE. The cows are herded in on certain days of the year where they graze for several hours. © Duncan Kimuyu.

For me personally, it was a joy to return to Kenya as I spent part of my childhood there. The African savanna is my favorite ecosystem, and Mpala Research Centre, where KLEE is located, is a great hub for savanna ecology. It is located in the middle of a Kenyan savanna and this offers researchers a ‘living laboratory’ where they can conduct controlled experiments at a landscape level. During my FWO postdoctorate I visited Mpala twice and had a great time there. At Mpala there are always other researchers at work and students following courses. In the evenings we often drank a beer by a campfire under a clear starry sky. Living in the Kenyan bush you also regularly come in contact with the animals there: from the house-dassies that could make a hell of a noise at night, to the elephants who were keen to join a game of soccer. Oh, and the leopard that apparently passed your jogging route often enough …

Buas

Here my field assistant Buas takes soil samples in one of the experimental plots. © Judith Sitters

Olifant

Close encounter. While Buas and I are taking samples in one of the experimental plots, a curious elephant tries to find out if the grass is greener on our side. Fortunately, the fences are electrified! © Judith Sitters

Zebra

The savanna around Mpala Research Centre is beautiful and on the way to the KLEE you often encounter herds of wild animals, such as these zebras. Are you aware that there are two different species of zebra here? Take a closer look at the stripes of the zebras on the left, compared to the one on the right. The left zebras are common zebras, while the one on the right is a Grévy’s zebra, which is an endangered species. Grévy’s zebra are larger than common zebra, have thinner stripes, a white belly, large round ears and a brown nose. © Judith Sitters

For my research in KLEE, I examined the impact of cattle and wild herbivores on the storage of carbon, nitrogen and phosphorus in the soil and vegetation. These are important elements in the optimal functioning of ecosystems. The storage of carbon, for example, is important to buffer climate change, while nitrogen often determines the quality of plants as forage for herbivores. I collected soil and vegetation samples and analyzed them for carbon, nitrogen and phosphorus concentrations. I collected these samples together with my field assistant Buas and we experienced both pleasant and less pleasant moments … While driving in our old Landrover, we were able to enjoy the unparalleled splendor of the savanna, stopping for a herd of elephants crossing the road. We also saw the greatest diversity of animals: from a drinking giraffe in the most unnatural position to the slow march of world’s smallest tortoise. Less pleasant: I did get slightly electrocuted several times by the KLEE fences and you can imagine the shock of a fence that needs to keep out elephants … Elephants are also surprisingly limber as we saw one limbo-dancing under the fence that was supposed to keep him out. This quickly turned into quite a frustration as we had to drive the elephant back out (and all of a sudden he wasn’t a contortionist anymore).

Schildpad

You also come across beautiful little creatures when you spend your days in the field. Look at this mini tortoise! © Judith Sitters

Olifant

At Mpala Research Center, the wild animals also prevail. Here you see one of the house-dassies getting acquainted with some guineafowl. © Judith Sitters

The results of my research indicate that in areas where cattle graze the soil becomes poorer (so it contains less carbon, nitrogen and phosphorus) because the cattle do not sufficiently fertilize the soil where they graze. They mainly drop their dung at night when they are kept fenced-in to protect from lions. This impoverishes the soil, which reduces the productivity and quality of the grass.

However, when elephants are present, this soil depletion does not occur; the soil is even enriched. Elephants bring down trees in the savanna, which accelerates the return of nutrients to the soil. 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 savanna, provided that the largest species such as elephants are protected.

Bodemuitputting

Elephants can reverse soil depletion by livestock, their presence even enriches the soil. They do this through various mechanisms that I have illustrated here. © Judith Sitters

Our research was recently published in the prestigious journal Nature Sustainability. It has been highlighted in the journal’s News & Views and in Science magazine.