By Mbatjiua Ngavirue WINDHOEK Namibian farmers lose N$700 million a year, or N$110 000 per farmer in the country each year as a result of bush encroachment, according to leading expert Dr Axel Rothauge. He defined bush encroachment as a bush density of anything between 2 000 and 12 000 bushes a hectare, saying that those densities can eventually lead to desertification of the land. Rothauge estimates that at present 20% to 50% of all commercial and communal ranching areas in Namibia are affected by bush encroachment. Studies done by other academics estimate that bush encroachment reduces the grass-based carrying capacity of the land anywhere from 20% to 90%. Put slightly differently, he said, bush densities of 10 000 per hectare could reduce grass coverage on a farm to one tenth of normal. “Namibia can ill-afford this loss since ranching contributes 90% to agricultural production, and agriculture comprises 5.6% of GDP and provides 37% of formal jobs,” he said, quoting figures from the Ministry of Agriculture, Water and Forestry. Rothauge spoke about the subject of bush encroachment in detail at a public lecture at the University of Namibia last Thursday, titled ‘Veld Degradation on Cattle Ranches’. He is currently a Senior Agricultural Training Officer at Neudamm agricultural College. The lecture was based on research that he carried out for his doctoral thesis at the Sandveld Research Station in the Omaheke Region between 2001 and 2003. The study involved carrying out a “bite count” of free-ranging cows at four systematically increasing stocking rates. In practice, this meant observing and counting the bites taken by a total of 1 152 cows when grazing, the type of grass they grazed and also collecting production data on all the animals. The aim was to establish how Namibia’s domestic animals interact with the environment, and to what extent they contribute to landscape level degradation. Rothauge said one third of Namibia has similar conditions to where the research was carried out, and the study is therefore applicable to those areas. The study found that where animals have a free choice, they would rely on only two species of grass for 70% of their diet, in this case borseltjiegras and perennial sand coach. “As stocking rates increase, the competition between animals increases and changes in diet, significantly, also reduce the nutritive value of the selected diet,” he said. There is an increase in less desirable grasses at higher stocking rates, meaning animals increasingly have to rely on poor grasses such as silky bushman grass and krulblaar. He also found that with increased stocking rates, the inter-calving period of animals increased from an average of 420 days to 435. That may not sound like much, but over the average 12-year productive life of a cow, the cow would produce one calf less. A significant finding was that animals select grazing for crude protein and phosphorous content more than anything else, and that calcium content is not a major factor. With increased stocking rates, he also found that animals started grazing close to the roots of the grass, thereby destroying any chance for the grass to regenerate. “Beyond a stocking rate of 45kg per hectare you will get classic bush encroachment, but stud breeders should in any case not exceed 25kg a hectare if they want animals that are rounded off well,” he advised. His most startling conclusion however was that controlled fires be accepted as a legitimate management tool to control bush encroachment, with strong emphasis on the words “controlled fires”. He advocated the opportunistic use of controlled, fierce fires to control bush encroachment, but only when conditions are right. Farmers, he said, can also use chemical and mechanical means of control. Rothauge noted that bush encroachment in Namibia is approximately 30 years old, which coincides with the time when farmers stopped using fires as a management tool. “The use of fire should be circumscribed, but fires are very useful as an aftercare measure to maintain a favourable bush to grass balance,” he remarked. The main causes of bush encroachment by swarthaak are three exceptional rainfall years in succession, which allows seed to germinate and together with the exclusion of fire allows sapling survival. Other factors are reduced competition from grass growth as a result of overgrazing and reduced browsing pressure, especially on seedlings. “We should hope we don’t have another good rainy season because it will be the start of another cycle of bush encroachment,” he warned. Switching to browsing animals such as goats, he added, is not a solution to bush encroachment. Goats are selective browsers and if bush encroachment is already serious, they will only kill off the remaining good bush while doing little to invader bush. Goats, Rothauge explained, are only useful in preventing bush encroachment before it starts. He recommended that bush control should be an ongoing, systematic process and not a one-off measure. Other recommendations are the periodic use of controlled fires as a bush-thinning aftercare measure, and sowing locally extinct preferred forage grasses. Farmers should also use perennial sand coach (Schmidtia pappophoroides) as an indicator species to determine when to reduce grazing pressure. They also need to allow preferred grasses to rest so that they can set seed before they are re-grazed. Finally, he suggests alternative measures, such as establishing cultivated dryland pastures of indigenous grasses to relieve grazing pressure on the veld during the rainy season.