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Giraffes and other African hoofed animals are only slowly returning to the former grounds of the Mkwaja Ranch. (Credit: Judith Sitters / ETH Zurich)

ScienceDaily (June 30, 2010) — The Swiss wanted to rear cattle in Tanzania and in so doing completely disturbed the ecosystem: the example of the Mkwaja Ranch shows how dependant agriculture is on a functioning ecosystem. And what a serious effect its encroachment can have on a sensitive balance.

Giraffes and other African hoofed animals are only slowly returning to the former grounds of the Mkwaja Ranch (picture: Judith Sitters / ETH Zurich) (more pictures)

After the Second World War a practical experiment was carried out in Tanzania, which provided deep insights into the diversity of ecosystems. The Mkwaja Ranch was founded in the 1950s by the Anglo-Swiss sisal producer Amboni. Here, in the savannah of western Tanzania, the company wanted to rear cattle in order to be able to provide the workers on their sisal plantations with good meat. The ranch was built near the coast over an area of 400 square kilometres. Using native Zebu cows and Boran bulls from Kenya, Swiss farmers bred fast growing and robust high-performance cattle. In contrast to the European standard of breeding, the animals were initially reared in the African manner. They were allowed to graze during the day and spent the night in protective enclosures, so-called bomas or kraals.

Tsetse flies out of control

The experiment started successfully, the cattle thrived and the ranch management was satisfied. Then, however, the cattle started to be affected by diseases which were transmitted by ticks and tsetse flies. The farmers tried, unsuccessfully, to get the fly situation under control by using fly barriers and sterilised males, and for decades they concentrated on medical treatment and prophylaxis. While the ranch management were busily concentrating on fighting the diseases, they overlooked the beginning of a subtle and disastrous development: bushes were growing on the grassland.

The appearance of bushes became the biggest problem of this practical experiment. It was the reason why the experiment ultimately failed. The general economic and political conditions of Amboni also changed, sisal production was no longer profitable for them and as a result they gave up the ranch in 2000. The land was turned into a national park.

Even in the early 70s, the farm management had already realised that the situation was in danger of running out of control and got help from ETH Zurich. In 1973 Frank Kloetzli, a titular professor emeritus for plant sociology and botany, began to work out a scientific basis for a change of strategy by the management. He found out that the redistribution of nutrients, which was being caused by the large amounts of manure in the bomas, could be reduced by rotational grazing.

Kloetzli used goats to prevent the growth of bushes, a measure which was successful for a while. The wide range of problems caused by the interventions in the complex savannah ecosystem, however, eventually became too much for the farm management. "The cultivation of the ranch was becoming increasingly expensive," explains Peter Edwards, Professor of Plant Ecology at ETH "and so it had to be closed in the end." From 1998 onwards Edwards has continued research on the ranch. To date he has led three research projects to discover what influence cattle breeding has on the savannah ecosystem.

Chain-reaction of cattle breeding

In the first phase the plant ecologist and his team examined what effects cattle rearing had on the ecosystem of the ranch area. At its peak, there were some 15,000 cattle here. They displaced the local wildlife such as antelopes and giraffes, which used to shape the vegetation through their grazing. Without the grazing of native wildlife the original savannah with its open grassland and permeable tree population changed, with tall grassy vegetation arising in its place. And instead of trees, which were unable to stand the grazing pressure of the cows, bushes grew.

This finding was linked with another: the redistribution of nutrients in the ground due to the high amount of livestock made the animals more susceptible to diseases. In addition some invasive plant types took root, spreading quickly across the area which was rich in nutrients. It is not fully clear whether biodiversity suffered over the 50 years of cattle grazing, says Edwards. "We can say for sure that the quality of the biodiversity is worse and therefore that the ecosystem has been damaged. It is, however, virtually impossible to measure whether the overall biodiversity has worsened."

But the ecosystem itself has suffered severely. "Due to the loss of natural hoofed animals, the area cannot even be called a real savannah anymore" says the biologist. And the displaced wildlife is only slowly moving back to the area, as Edwards and his team were forced to recognise in a second research project. The transition from an area used for cattle-grazing to a natural ecosystem will therefore take a while.

Edward's latest research project, which he is carrying out together with the wildlife biologist Werner Suter from the Swiss Federal Research Institute for Forests, Snow and Agriculture (WSL), should now show what effect the returning wildlife is having on the ecosystem. It is still too early for specific results, says Edwards. A few conclusions can, however, already be drawn: "We observed very diverse feeding behaviour amongst the different hoofed animals." For example some, such as the bushbuck, a small antelope, feed very selectively and on a small area. "This produces a positive reaction, as on this area the vegetation is changing and the quality of nutrition for this species is therefore improving. The animals thereby create conditions in which they are able to live."

An ecosystem without animals

What findings can be deduced from this practical experiment in Tanzania for other ecosystems? According to Edwards, "We are getting a much better understanding of how the savannah system functions. Here we can see quite clearly, what an important role hoofed animals play." We can also see from this example that recreating an ecosystem is not easy. "The example of the Mkwaja Ranch also clearly shows that the ecosystem is completely different without animals," continues Edwards. Specific measures are probably going to be necessary to get the wildlife to return within a useful period.

The findings from Edward's research are very helpful, particularly for Africa, as poaching has severely reduced wildlife stocks in many savannah areas, and the relocation of wild animals is problematic. Edwards: "Bringing an ecosystem back to life without animals is a great challenge."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by ETH Zurich.

Journal Reference:

  1. Gross M, Hoffmann-Riem H, Krohn W. Practical experiments. Ecological structuring processes in the knowledge-based society. Science Studies, 2005. 234 p

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