Dear Farmers and Resource Managers,

The Decision Support System (EXPERT SYSTEM) booklet is a work in progress. It is not intended to be a definitive authority on how to manage bush encroachment. The EXPERT SYSTEM was originally developed for the Highland Savanna vegetation type of the Khomas Region, and is largely based on a conceptual model for savanna dynamics in this region, developed by Dave Joubert and Axel Rothauge (Joubert, Rothauge and Smit, 2008). The model in turn was largely based on research done on the population dynamics of Acacia mellifera (now referred to as Senegalia mellifera; swarthaak; omusauna) in this vegetation type. We have opted for the retention of the genus Acacia. Although the EXPERT SYSTEM was originally developed for the Highland Savanna type, we believe it has relevance to the Thornbush Savanna and other Savannas which are dominated by fine leaved Acacias and sekelbos, in situations where A. mellifera (S. mellifera) is the dominant encroaching species. Since Dichrostachys cinerea (sekelbos) and other species are different to A. mellifera (S. mellifera) biologically, different management decisions could be necessary in some circumstances. Although bush encroachment is a problem in many places in Namibia, Africa and many other parts of the world, the mechanisms of bush encroachment differ from species to species and climate to climate.

This makes rangeland management (farming) challenging. We believe that: Rangeland management is not rocket science, it’s much more complex! But the expert system makes it much easier.

The EXPERT SYSTEM is divided into two types of decisions:

1. Adaptive decisions (these are opportunistic decisions which would only be relevant and useful during certain circumstances related to periods of exceptionally good rainfall, drought, and after frost (See Figure 1 and Figure 2). Making the right decisions at these times might be crucial in preventing large-scale transitions towards bush thickets (good rainfall), or thinning out of existing mature thickets (drought, after frost). In fact, we believe that removing the opportunities that come with these weather extremes is a major reason for the current encroachment situation.

2. Reactive decisions or decisions to treat the symptoms (these are decisions on whether to and how to, treat existing problems – i.e. areas already under dense cover of bush). The EXPERT SYSTEM includes actual methods of bush control, while recommending that it should be done in contour strips to regenerate water and nutrient cycling. We emphasise though that much of our rangeland is not bush encroached at this stage and can remain this way if ongoing good management and adaptive management are applied.