A Brief History of the Introduction and Management of <i>Prosopis</i> Trees in Eastern Africa

Abstract

This chapter reviews the history of introduction of Prosopis trees to Africa, with a focus on eastern Africa, how their perceived and actual value has changed over time, and how management policies have accordingly been adapted. People were initially encouraged to use Prosopis trees to combat desertification, and as a source of firewood and fodder for livestock. Some Prosopis species, notably P. juliflora in eastern Africa, subsequently became invasive, causing substantial negative impacts. The benefits provided by these trees were initially welcomed but this changed as the negative impacts grew. P. juliflora had thus become a conflict species, in which some people reaped the benefits of the trees while others suffered the negative consequences. This led, in one notable case, to rural communities seeking redress from the Kenyan government in court in 2006. While the realization that these trees were more harmful than useful was slow to develop, several recent studies have clearly demonstrated that the net economic value has become negative, with any value derived from the plants being offset by greater losses in the value of ecosystem services. Management has had to adapt to these new realities. The first policies promoted the active distribution of Prosopis trees. When the trees became invasive and negative impacts became apparent, management switched to policies of control through utilization, mainly in the form of subsidised charcoal production projects. The failure of this approach is now apparent and new initiatives have been proposed. These have been informed by recent transdisciplinary research projects and include spatially explicit management approaches, the use of best management practices (including biological control) and raising awareness. Key challenges remain but the chances of successful outcomes would be increased by embracing biological control opportunities and setting clear and achievable management goals, both of which have been absent to date.