Prioritizing scientific data over expert opinion in the valid assessment of Australian Acacia biocontrol success

Invasive species are such a pervasive problem that, in many cases, the management of this global change driver appears close to impossible. Biological control using natural enemies from these invasive species’ native ranges is an attractive option to restore the balance in the invaded environment. The biological control of Australian Acacia spp. in South Africa is a lauded example of textbook biological control of invasive species management. However, we propose that this apparent success of biological control agents in reducing population levels of the alien trees is largely unfounded, as it is not based on ecological data but rather on scientific assumptions by experts. We argue that the fundamental question, “Does biocontrol reduce the impact of invasive tree populations?” is not being asked. Instead, the onus is on researchers to prove that biological control agents do not work. If experts act as reviewers for work that shows the contrary to their expert opinion, we have a potential conflict of interest. The result of this dispute is that contrary empirical data are slow to enter the policy decision-making sphere. The status quo of producing policy recommendations to manage biological invasions is based on expert opinion from the scientists who released the biocontrol agents. We propose that an overhaul of this approach is urgently needed. The scientific burden of proof should not be on whether biocontrol agents are not effective but rather on whether they are effectively reducing the impacts of the host plant. Any corrective management to solve environmental problems should be based on open, multidisciplinary science that provides the necessary supporting evidence. Our case study on biological control of Australian Acacia spp. is an illustrative example of why scientific data should guide decision-making for sustainable environmental management.