Theo E. W. Linders and Peter Manning
Senckenberg Biodiversity and Climate Research Centre, Frankfurt am Main, Germany
An increasing body of literature describes the many impacts that alien invasive trees have on both ecosystems and humans. A challenge in assessing these impacts is that some invasive alien species generate conflicts-of-interest, as they provide some benefits, while simultaneously having negative impacts on other ecosystem services. A multifunctionality approach, which assesses multiple impacts simultaneously, is therefore helpful in drawing informed conclusions about net impacts. Additional challenges in assessing impacts are that simultaneous positive and negative impacts can be separated in space and the people who are affected positively are not necessarily those who are impacted negatively. Furthermore, it is often unclear how impacts on the ecosystem properties translate into impacts on ecosystem services. To address these challenges, we propose a multifunctionality approach that helps bridge the gap between the assessment of invasion impacts and the development of sustainable management options.
We use Prosopis juliflora in Eastern Africa as a case study to understand how an invasion affects ecosystem service multifunctionality for different stakeholder groups. To achieve this goal we combined plot level data on the ecological impact of P. juliflora on multiple biodiversity and ecosystem service indicators, with quantitative stakeholder surveys. In the latter, we assessed the relative importance of ecosystem services for different stakeholder groups, as well as the benefit they gain from different supply rates of ecosystem services. Ecological- and stakeholder preference data are integrated with current and projected P. juliflora distribution maps to create landscape-scale multifunctionality maps for a range of stakeholder groups. This mapping procedure forms the basis of several future scenario simulations, in which different scenarios regarding invasive species management and P. juliflora spread are tested. Mapping the effect of an invader on current and future ecosystem service multifunctionality will highlight which ecosystem services are crucial to retain and in which areas management priorities are highest.