Given that Namibia (Figure 20.1a) is one of the driest African countries south of the Sahara, this chapter may seem out of place in a book on invasive plants in forest ecosystems. However, based on the Food and Agriculture Organisation of the United Nations’ (FAO) definition of a forest as "an area covered by at least 10% canopy cover of trees higher than 5 meters and extending for more than half a hectare" (FAO 2000), slightly less than 10% of the country is estimated to be covered by forest (Mendelsohn and el Obeid 2005). This figure excludes numerous riparian forests along perennial and ephemeral rivers.