Towards a holistic understanding of non-native tree impacts on ecosystem services : A review of Acacia, Eucalyptus and Pinus in Africa

Fast-growing, stress-tolerating tree species belonging to the genera Acacia, Eucalyptus and Pinus have historically been introduced to many tropical and sub-tropical regions to support various economic and environment-regulating functions. While these non-native tree (NNT) species are often highly useful, many are simultaneously invasive, generating negative environmental impacts. Current knowledge regarding the impacts of these NNTs on the ecosystem services (ES) that affect human well-being is largely informed by South African research, which inhibits a broader understanding of the contributions of these trees to those services. Acacia, Eucalyptus and Pinus have been widely introduced globally, yet very little is known about their contribution to ES in many locations. Here, we aimed to summarise the evidence for Acacia, Eucalyptus and Pinus as generating benefits and harm to ES, focusing on sub-Saharan Africa outside of South Africa. We conducted a literature search using the ISI Web of Science, which yielded 125 relevant publications. Although the three genera were reported to affect key ES in sub-Saharan Africa, the data were limited in geographic scope, with a strong bias towards East Africa as well as biases towards certain species and ecosystem service. The benefits of these NNTs relative to their costs are context dependent and may not reflect their actual impacts on ES in sub-Saharan Africa. Our review highlights the need for more systematic research from a broader perspective to manage potential conflicts and guide better management prioritisation.