Impacts of Invasions by <i>Prosopis</i> Species on Rural Livelihoods: The Human Dimension

Abstract

Prosopis juliflora and other Prosopis species were introduced into eastern Africa for their presumed benefits to people and the environment. However, P. juliflora became invasive, spreading across valuable ecosystems on which rural communities rely for their livelihoods. This chapter reviews the impacts of P. juliflora on rural livelihoods, with a focus on people’s perceptions, costs and benefits to households, and willingness to pay for managing P. juliflora invasions. About 70% of the population of eastern Africa are rural, and more than half (>60%) of them are directly dependent on ecosystem services. Prosopis trees generate benefits as well as negative impacts, and people’s perceptions of the net value of these trees vary considerably with the regional context and stage of invasion. Importantly, the net value (benefits minus costs) does not change in a linear fashion, but starts off being positive, then becomes increasingly negative at an exponential rate as the cover of invasive trees increases. People’s perceptions of the potential or actual impact of these invasions are not always aligned with ecological evidence and change relatively slowly in comparison with the growth of impacts. Despite this, 98% of 503 surveyed households were willing to pay between USD 38 and 50 per year towards managing invasions. This would amount to annual investments of USD 4.2 million and USD 6.3 million in Baringo County, Kenya, and Afar region, Ethiopia, respectively. The current estimated economic costs of Prosopis invasions could grow to USD 375 million/yr in Ethiopia, Kenya and Tanzania jointly if all suitable habitat becomes invaded, suggesting a net present cost of USD 7 billion over the next 30 years. By recognizing the potentially significant future costs and allocating appropriate amounts to control and containment efforts now, it would be possible to avoid much greater social costs in the future.