What is the extent of the bush encroachment problem in Namibia?
I’ve collected data going to the 1890s. In my opinion, the period from the 1950s to the present has seen the greatest increase in bush encroachment. By 2002, bush encroachment was said to affect some 26 million hectares, mainly in livestock ranching areas, in Namibia. By 2012, the affected area was estimated to have increased to about 29 million hectares. Namibia’s northern parts are the most affected. This is where the savannah-type ecological zone predominates and where valuable livestock and game are ranched extensively.
No economist has ever carried out in-depth research into how this affects Namibia’s economy, but according to the National Development Plan Four, the annual economic impact is ‘big’. It is claimed that bush encroachment, combined with erratic climatic conditions, negatively influences the number of animals marketed. And over the years, this number has dropped, leading to an overall decline in agriculture sector output. In 2012, for example, the decline was 3,7%.
What factors lead to bush encroachment?
One of the main causes is long-term land management that over-exploits the ecological potential of Namibia’s rangelands.
Changing climatic patterns have also greatly influenced bush growth. In consecutively good rainy years, combined with relatively mild winters, vigorous growth and re-growth is noticeable. By contrast, consecutive dry or drought years, as in 1983 and 1984, induce large-scale bush dieback.
Indigenous species include Acacia reficiens (red thorn), Acacia mellifera subsp. detinens (blackthorn acacia), Colophospermum mopane (mopani), Dichrostachys cinerea (sickle bush), Terminalia sericea (silver cluster-leaf) and Rhigozum trichotomum (three-thorn). In southern Namibia, there’s a problem with the alien Prosopis glandulosa (mesquite) and its various types.
How does the problem affect the environment?
Extensive bush encroachment inhibits biodiversity, making the environment vulnerable to erosion and widespread dieback of less dominant and vigorous species. On very densely encroached areas, nothing grows under the bush.
Many browsers – kudu, gemsbok, eland and other large antelope species – cannot enter bush thickets. Even smaller antelope such as duiker and steenbok find it difficult to live in such thickets. As a result, populations of these species in the encroached areas have decreased significantly, while numbers have increased in more open rangeland areas partly due to migration. This leads to biodiversity imbalance.
And what is the effect on livestock?
In general, carrying capacity has decreased substantially since the 1970s. Carrying capacity seems to be directly and inversely correlated with bush encroachment. The extent of this correlation has to my knowledge not been extensively researched. Commercial livestock and wildlife occur on the same land – wildlife is not confined to parks. So, where wildlife can’t roam, livestock’s access to forage and quality browse is also limited.
Many farmers have combined wildlife, including trophy hunting enterprises, with livestock to augment their income. This means that many farms have game-proof fencing. Because wildlife can’t migrate naturally on such farms, animals are under enormous pressure to find suitable forage. If such a farm is also heavily bush-encroached, many animals simply die in a drought. In this case, the farmer first sells off cattle and then takes out wildlife. An example occurred as recently as 2012/2013.
And on water resources?
There are two schools of thought. Extensive bush encroachment increases evapotranspiration per surface area. The vegetation takes up too much groundwater through the root system, which then evaporates through the tree cover. In this way, groundwater drains away. Extensive bush encroachment induces what we call climate change. The increased plant biomass produces more CO2, leading to erratic weather patterns such as shorter but more intense rainy seasons that also contribute to erosion. In addition, longer and hotter dry spells occur between the rains, with drought always a possibility.
What will happen if bush encroachment is left unchecked?
The general belief is that bush encroachment spreads rapidly. But my research shows that it doesn’t seem to spread as quickly as was assumed. I’ve established that, depending on the specific ecological zone, the rate is between 1,5% and 2% per year.
However, because of the lack of concerted efforts to keep encroachment in check in the past, the situation seems to have grown out of proportion. We shouldn’t think that what has grown over several decades can be undone in just a few years with one-off or project-type interventions. We should consider the long-term.
Even with a rather low estimated bush encroachment rate, the demarcated livestock farming area will be encroached with bush within about 50 years if no treatment is carried out. However, this is a very simplified way of looking at it. Proper time-series modelling, as done for climate change time models, would show the true extent.
What are best ways of combating it?
If about 3% to 5% of the bush population is harvested per annum, ‘farming with wood’ could become the most important sub-sector in primary agriculture. I consider this the best approach to deal with bush encroachment. A new industry would be born, securing jobs over many years, driving innovative industrialisation and having the potential to generate forex. Currently, the most common use for Acacia species is making wood pellets for braais or heat, for both local consumption and export (mostly to South Africa and the UK). Some one million tons of this product is produced annually.
Furniture can be made from Prosopis wood, while Terminalia and Colophospermum wood is used as fencing or construction material. Dichrostachys is suitable for animal fodder, but not yet commercially. Rhigozum trichotomum has no commercial value as yet. This approach would need time and detailed planning. It cannot be a one-off, but it’s the most sustainable approach. Over the short-term, alternative solutions such as bush eradication by arboricides or large-scale mechanical removal would render quicker results. But there are substantial risks involved. If applied correctly, arboricides don’t necessarily harm livestock production systems but they cause ecological harm, especially in fragile Namibian soils.
How much progress has been made in combating bush encroachment?
In 2012, great progress was achieved when the government published the National Rangeland Management Policy and Strategy. This declared the agriculture sector a priority, and focused on combating bush encroachment and engaging in activities that would increase productivity. Several interventions to address bush encroachment on a national level are planned.
These include harvesting with the aim of downstream use and animal fodder production. Namibia and Germany have signed an agreement where a four-year project will research the topic in greater depth and engage in various activities that would lead to commercial-scale development projects.
Any final thoughts?
The most successful ways of combating bush encroachment are those where tackling the problem is part of good rangeland management practice. To treat it in a sustainable manner is very costly, but finding a way to generate income from harvested wood with as little effort as possible puts a farmer in a positive cash flow situation. Farmers will engage in activities that control bush encroachment as long as the benefits are greater than the costs and effort involved – the daily operational and technical management, labour management and marketing the wood products.
Phone Dagmar Honsbein on +264 61 290 9208.
This article was originally published in the 3 October 2014 issue of Farmer’s Weekly.