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Bush Encroachment

DE-BUSHING ON OKONJIMA by Wayne Hanssen and AJ Rousseau

Over the past hundred years, commercial farming has probably caused the most damage to Namibia's natural habitat. Due to over grazing and controlled natural fires, certain bush species were able to get the upper hand and resulted in the majority of Namibia's open plains becoming thorny thickets.

On Okonjima we are trying to reclaim the grass-land and turn it back to what it looked like before man interfered. The two main bush species causing encroachment in our area are the Blackthorn (Acacia mellifera) and Sicklebush (Dichrostachys cinerea). The problem is that in the areas where these two species have taken over, it also causes an imbalance in the ratio of grasses to bush and in turn, a decrease in the biodiversity of the Reserve.

The Cheetah's preferred habitat is open plains. Here, their speed and binocular vision give them the advantage over their prey and competitors. In areas where the bush has become too thick, the cheetah is suddenly at a disadvantage. Other predators, like leopards, can very easily sneak up and kill a cheetah as the cheetah cannot see the other cat approaching. Also, it forces the cheetah to hunt in areas which are typical leopard habitat.

So, on Okonjima where AfriCat is trying to rehabilitate captive cheetahs, the issue of bush encroachment is a major priority. The aim for the Reserve is to create more open plains which then might create natural habitat boundaries between the different predators, where cheetahs should stay more in the open plains and the leopards more around the riverine thickets. But then again, this is only a theory.

Mechanical removal of bush is preferred. Where there are fewer or no good grasses amongst the encroached bush, this is the faster and more productive way of clearing invader bush.

The down-side is that the machines can cause a lot of damage to the soil as they can take out many of the remaining grasses as well as the bush. In areas where the invasive woody species represent more than 90% of the flora, Mechanical removal of bush is the best option. Being able to clear 7 ha per day will enable you to open up large areas in a relatively short period of time, but at a cost of N$ 2,500.00 per day, it can become a very expensive operation.

The labour-intensive, 'hand-method' is a preferred means to clearing invader bush especially in areas where selective de-bushing is needed; high grass cover must not be disturbed and it's a method of creating employment for many Namibians. Although this method takes a very long time, the impact on the land is much less.

To recap – the first stage of clearing the bush in the Okonjima Reserve is mechanical or by hand.  

The second stage is controlling the re-growth by hand.

The third stage is going back to Mother Nature's way, i.e. controlled fires at the right time of the year.

But, by this time we hope to have enough combustible material (plus minus 2500kg/ha), i.e. much higher density of grass/ha to induce a hot burn every 8 to 10 years, to control the re-growth.

ltimately, we are hoping to have the reserve's habitat in such a condition that it can be divided into thirds: one third being open plains, one third being woodlands and then one third to be left as riverine thickets. This will be no easy task and at the moment we are working on a 10-year plan. Even though one might have cleared an area before, one will have to come back to the same area again in 2 – 3 years, to take out bush that has grown again. During this time we will be using more controlled burning as this will also promote the natural growth cycle of the new grasses.

The next couple of years are going to be a tough fight, but at the end we are certain that we will be able to win the fight against bush encroachment. The result will hold positive benefits to both fauna and flora within the Reserve.

If you think about it, humans caused the problem… It is our duty to rectify it!

 

 

Article posted: 2012-01-01 06:01:10

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