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Silent assasins

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Some time ago I read a fascinating book entitled BEYOND SUPERNATURE by the South African botanist, zoologist, biologist and anthropologist Lyall Watson. Watson, who died in 20018, wrote 25 books and tried to make sense of natural and supernatural phenomena in biological terms. He was born in Johannesburg and at one time served as director of the Johannesburg Zoo.

In BEYOND SUPERNATURE Watson tells of an unusual incident that took place in the early 1980s in what was then the Northern Transvaal Province of South Africa and where there had been a prolonged and extremely severe drought. This drought had a devastating effect on the local fauna and flora but wildlife management officers were surprised to learn from farmers in the area that large numbers of Kudu were dying. This was unusual as the Kudu is one of the more drought-resistant wild animals. Kudu are not gentle feeders and strip leaves and bark from branches while also breaking the surrounding twigs.

Scientists went to have a closer look. They found that although the vegetation was sparse it was by no means so poor as to cause Kudu to die of starvation. In fact, most of the dead animals had adequate quantities of leaves in their digestive tracts. Upon analysis of these leaves it was discovered that they contained extremely high levels of "tannins" which are chemicals that prevent leaves from being digested by turning off the microbes that encourage normal digestion. These tannins also create a bitter taste in the leaves that usually force the browsing animals to move to another tree after a short time.

What was happening was that the leaves that the Kudu were eating were passing straight through their intestines without being digested. The animals were thus burning their own body fats and this was leading to their deaths. Why though, was there such a high concentration of tannins in the leaves? And why were the Kudu eating such large quantities of the contaminated leaves?

Biologists have long known that trees and browsing animals coexist by the animals not over-browsing. Farmers in the area though, had begun erecting formidable fences on their farms to protect their game from straying into areas where they might be poached and this restriction was forcing the Kudu to over-brows. The acacia trees that the Kudu browsed on didn’t like this and began to put up their chemical defences by producing the deadly tannins to discourage the browsing animals.

To test this theory the scientists quietly approached selected trees and removed some of their leaves. The chosen trees were then subjected to a "beating" with sticks and whips, damaging and stripping the leaves where-after more leaves were harvested from the hapless trees. The chemical content of the harvested leaves were then analysed. The results of this analysis showed that the leaves removed after the "beatings" contained up to 94% more tannins than those collected before the "beatings".

The scientists repeated the experiment and removed samples of leaves from the trees surrounding those that had been "beaten" and even these were found to have had a similar reaction. The scientists were thus able to conclude that the over-browsed trees were "defending" themselves by producing the tannins that give their leaves a bitter taste and cause browsing animals to move to another tree after a short time. Unfortunately, because their freedom to browse had been restricted by the farm fences the Kudu were forced to over-browse and the overload of tannin in the leaves was killing them.

So, don’t turn your back on the plants that you’ve just pruned or think for a moment that trees and shrubs are as helpless as they appear to be.

Oliver is a freelance writer, book illustrator, cartoonist and artist in Gauteng, He has published 20 e-books consisting of fiction novels, children’s picture books, golf instruction books and a book on wild animals and birds in South Africa. More of his writing and art can be seen at oliverspedding.blogspot.com and www.southafricanartists.com/home/OliverSpedding.

 


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