ak. Heide Baas and her husband Siggi Baas started to deal with bush encroachment since 2002 after recognizing, that also in years with a higher average of rain they were not able to build up a pasture reserve and thus having to reduce the cattle stock. On Thursday 14 September 2006, she presented a lecture at the Scientific Society Windhoek about "Arbitrariness of the Rain - bush control a necessity" and by this shared her knowledge, acquired on their farm in the southeast of Windhoek with about 50 farmers and other interested guests.

In 1992, Heide Baas and her husband, who both grew up on a farm acquired their own 4700 hectare farm Ombuerendende, which would theoretically be an ideal piece of farmland if not having the problem with bush encroachment, Heide Baas pointed out. But what is bush encroachment? In the case that on an originally open piece of land where 2 to 3 species of bush occur another bush, such as the Acacia mellifera (Black Thorn Bush) grows profusely this is than called an intruder bush. Should 600 bushes per hectare be found than the stage of bush encroachment has been reached, Heide Baas explained. In the north of Namibia some areas, which were used as pastureland some years ago are now absolutely unusable for this purpose, due to 2000 to 4000 trees per hectare today. But also the south is no longer spared. Thus approximately 26 million hectare of former pastureland in Namibia is now unusable. According to Heide Baas, this decrease of pastureland caused an enormous decrease in cattle farming and leads to an annual loss of about N$700 million.

The bushes consume vast amounts of water, for example a 2 m high Black Thorn Bush needs 0,65 litres of water each day, this means that 300 of these bushes need 195 litres per day. By an annual average of 330 mm rain per year sufficient water for all bushes and plants is not available, Heide Baas emphasized. In some regions 80 percent of annual rainfalls are mainly consumed by acacias. Besides the Black Thorn Bush the Bastard Umbrella Thorn (Acacia Luederitzii), Mopane (Colophospermum mopane), Rattle Tree (Catophractes alexandri), Three-thorned Acacia (Acacia senegal) or the Sickle Bush (Dichrostachys cinera subsp. africana) cause major problems. Thus controlling only one of these species is ineffective as wiping out one, the next one spreads. A very good example of such a situation can be seen driving along the road from Windhoek to the Airport. There the thorn bush was demolished chemically but now the Rattle Tree has taken its place, Heide Baas emphasized.

This situation is induced by overgrazing, uninterrupted pasturing, bad farm management, especially in regard to the numbers of animals grazing on one hectare, impeding bush fires (on the one hand bush fire impedes bush encroachment but on the other hand pastureland has a very high value and today hardly any farmer burns down his pastureland), climate changes leading to an increased content of carbon dioxide in the air (acacias need carbon dioxide for development) as well as unbalanced proportions between bush- and grass eating animals (some years ago much more game, e.g. giraffes or rhinos, which ate bushes, occurred in Namibia than today).

Especially during this year, after the good rainy season, the seed of the thorn bush, which can only germinate during one year, is growing very well. But also in years where less rainfalls were experienced the thorn bush proves to be a real artist in survival, e.g. a small bush which is only five to six centimetres high could have a primary root of 2 meters deep, Heide Baas further explained.

An increase of bushes caused a decrease of pastureland as well as pasture capacity, poor soil, erosion, less productivity and proceeds. Due to this development artificial drought occurs because of poor soil, the rain waters flows off and is unable to soak into the ground.

To solve this problem, a mechanical and a chemical method are possible, but both acquire very good planning. It is compulsory to ascertain the number of bushes per hectare and the composition of the soil, especially its clay content. For the chemical method, a growth hormone is disseminated either by hand or by plane. According to Heide Baas a plane is useful when there are 2.500 bushes or more per hectare. Using the mechanical method by plane huge pieces of land can be processed very quickly, but unfortunately a selection is not possible, which means that also useful trees such as the Acacia eriloba (Camelthorn tree) are destroyed. On the other hand disseminating the hormone by hand needs much more time and working forces, because the hormone dissolved into water, has to be dispersed more than once around the bushes but allows a selection between the trees. This hormone, which remains active for three years in the ground, destroys the photosynthesis process of the bushes and thus the plants kill themselves by growing and growing. According to Heide Baas, the whole disseminating process, which has to be executed before the rainy season, needs to be repeated 2 or 3 times. The dried out bushes remain on the fields because young grasses are more protected under this scrub and also the dry wood supplies good humus.

The second way is uprooting the bushes mechanically. Higher trees, whose roots could range 30 meters wide, are uprooted with the help of a special tool on the tractor. For smaller bushes Heide Baas and her husband engaged bush-hackers. Even if this was the most expensive method, after the mechanical method one really has beautiful open fields and meadows, Heide Baas gladly explained. In all cases aftercare measures, which have to be initiated after four or five years, are absolutely important. All in all the Baas family invested about N$700.000 in the last four years in all three methods of bush control, but as Heide Baas emphasized "every cent was worthwhile". Besides the very interesting facts, impressive photos before and after bush control processes were shown during the lecture. According to Heide Baas, the government unfortunately does not encourage or support bush control projects to this day. For reading more about encroachment in Namibia, the book "Bush Encroachment in Namibia" by Nico de Klerk was highly recommended by Heide Baas.