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Bush Encroachment

De-Bushing on Okonjima

by Wayne Hanssen

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.

Wayne demonstrates bush encroachment problem toby header

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.

thick bush toby thickbushopened areas

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.

clearing bush by handdebush handdebush hand

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.

debush handdiggersgehl machine

Ultimately, 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!

wayne debush1wayne debushtoby thorn removed lefteyetoby 330pxtoby at vet checktoby 3rd eyelid sewn toplid

In April 2011, Toby, a rehabilitated , captive cheetah released into the Okonjima Nature Reserve in 2010, had to be brought in after an injury to his right eye, which recovered well and Toby was able to go back to hunting again. However, on 24th October 2011, Toby was found again with a teary eye and this time it was his left eye. He was darted and brought back to AfriCat's Carnivore Care Centre, with the piece of thorn still stuck inside his cornea. It was carefully removed - two pieces of one of our invader thorn-bushes – the Dichrostachys cinerea - more commonly known as the 'sickle bush'.

Note from Dr Gerhard Steenkamp after viewing images of Toby's second injury: "There was a penetrating corneal foreign body in Toby's left eye. Around this foreign body there was oedema (that is the 'blueish' opaque discoloration around the thorn). The foreign body was removed and was a thorn of the Dichrostachys cinerea bush. The thorn luckily only penetrated very shallow and none of the deeper structures of the eye was damaged."


Bush encroachment is a problem in the Okonjima Nature Reserve, as it is across most of Namibia, because of damage caused to the land by a combination of farmers over-stocking their land and failed farming methods, a lack of natural bush-fires and many years of low rainfall. This has now become the environment where the cheetah, who is a sprinter - has to hunt to survive. The Cheetahs' speed and binocular vision gives them the ability to spot prey from afar before giving chase, which, in perfect conditions gives them an advantage over their competitors. They therefore prefer open plains without the visual and physical obstructions of thick bush/acacias. A more open habitat also gives them a chance to spot predators like lions and leopard sneaking up on them and killing them.

tobys eye cyclopscyclops in the reserve

Toby was following his natural instincts and would not have known better than to give chase to prey which unfortunately led to both his eye injuries. His misfortune was a combination of bad luck and bush encroachment.

eye close ups



Major Achievements 2010 - 2014:

  • International recognition in a joint study where AfriCat and scientists from South Africa and Australia demonstrated very little body temperature rise during cheetah hunts. These results were in contradiction to a paper written in 1973[1] that suggested that hunting may be a thermally limited activity through a heat storage activity. The 'thermal regulation' research project took place in the Okonjima Nature Reserve, using previously captive cheetahs that had been successfully rehabilitated, as research subjects.[2]
    Taylor, CR & Rowntree, VJ (1973)
    [1] Temperature Regulation and heat balance in running cheetahs: a strategy for sprinters? Am J Physiol 224, 848-851.
  • Successfully opened 400ha of new plains (2013), by removing invasive bush, as part of a 7000ha project to re-introduce springbok, which once roamed this area.
  • Purchasing a 'Skid Steer Loader' with circular blade (GEHL) was purchased, to cut down invasive vegetation, without destroying sensitive grassland.
  • Opening up of a further 15kms of 'bush-tracks' to gain access to drainage lines that are frequented by leopards and cheetahs (Total road infrastructure in the park = 300km)

Constraints and Challenges:

  • Finding and or developing a way to de-bush denuded farmland that will not cause erosion or the invasion of other weed and bush species.
  • Finding a practical solution to help maintain the grasslands in a natural way i.e controlled burning programme.
  • Finding the most sustainable way of re-seeding the grasslands with perennial climax veldt, e.g Alan Savory’s holistic farm management programme.

 Future Plans:

  • Introduce springbok, which once roamed this area. This will greatly improve the prey-base for the AfriCat Rehabilitation programme.
  • To open up 1/3 of the 50 000acre Nature Reserve. Opening 1/3 into mixed woodland and leaving 1/3 bushveld thickets i.e +- 20 000 acres of de-bushing to be done and we have currently managed +- 1000acres.
  • Constructing the +- 320km of road works in such a way that will minimise erosion and maximise the utilisation of the park.
  • Combating erosion in all the denuded areas, which has taken place over the past 50 years.


AfriCat founder, Wayne Hanssen talks 'Grassland-science'!
FILMED AND EDITED BY ITV, UK - © itv 2010. Taking Care of the Land: Wayne Hanssen leads the Okonjima team in a tourism venture that offers their guests 'authenticity' and 'luxury'. Funds are used for 'conservation', 'environmental education' and 'social responsibility'.
HIS PASSION: Is grassland science.
HIS DREAM: To turn Okonjima's 55 000acres of Nature Reserve into what it once looked like, before man destroyed it due to a lack of understanding the fragile nature of our environment.
HIS WISH: Is for the next generation that hold the future of this land in their hands, to learn from our mistakes and to 'BE the change they wish to see' in this beautiful country, Namibia!




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