Original estimate of extent
Namibia’s bush encroached areas fall mainly within the semi-arid savannas, with rainfall varying from about 300 mm in the west to over 600 mm in the north-eastern parts. It is typically reported that “26 to 30 million hectares of Namibia are encroached”. This figure is based on the map compiled by Bester in 1990, showing the main areas of encroachment (Bester 1990).
Current estimate of extent
The Strategic Environmental Assessment (SEA) on bush thinning and value addition in Namibia (2016) revised the ‘Bester map’ using the field knowledge of a few recognized botanists and bush encroachment experts, to produce the maps shown in below. The individual distribution maps of the six main encroaching species were obtained from the Tree Atlas of Namibia (Curtis & Mannheimer 2005). The distributions were shown in a quarter-degree square grid, with relative abundance in each square. Squares were removed from that map where the species was identified as not encroached. These decisions were based on the team’s field experience and observations. Some areas where the species are dense, were not considered to be encroached if the level of encroachment was thought to be natural i.e. not caused by human interventions (such as overstocking or reduction of fires). This process eliminated the areas where the species was not encroached, to leave the quarter degree squares where the species was known to exist at a relatively high density that has come about in the past 60 years. This process yielded the map below which shows only the extent of encroached bush, not densities. The areas of Prosopis encroachment confined to the main ephemeral rivers in southern and central Namibia. According to this revised map, approximately 45 million hectares of Namibia are bush encroached The map below is based on the distribution of the main encroacher species, and information on where they have shown dramatic increases in density over the past +- 50 years.
Effects on the economy:
Research by the Project on the economics of land degradation in relation to bush encroachment (2016) shows a total net benefit of N$ 48 billion discounted over 25 years, or approximately N$ 2 billion annual could be gained should a national bush control programme be implemented compared to bush thinning. The same assessment has shown that such a national intervention would allow the country to gain between N$ 2.1 billion and N$ 4.2 billion worth of livestock production annually. Bush thinning would generate benefits from livestock production, groundwater recharge, production of firewood and charcoal, and generation of electricity, as well as carbon offsets for electricity. At the same time, bush control/thinning would create an estimated number of 10 000 jobs per annum in mechanical operations, which would contribute to employment and poverty reduction for semi-skilled labourers accounted over the initial round of bush control. There are also many unquantified ecosystem services which would be positively affected by bush thinning, which are not included in the dollar estimates provided