While scientific research highlights the threats of invasive alien species (IAS) to the environment and human livelihoods, another voice is rising that recognizes their beneficial impacts. With evidence increasing of the contrasting impacts of some IAS, the lack of communication between science and society makes decision-making processes more complex. Here, we consider the beneficial aspects of invasive alien plant species and take examples from other life forms to argue that, over time and space, the detrimental impacts of IAS might endanger sustainable livelihoods by increasing invasion debt manyfold. We therefore suggest that future studies reporting the positive impacts of IAS and those encouraging the management of IAS through their utilization should include value judgements that acknowledge the potential risks involved in the practice and the scale and context specificity of such studies. Studies highlighting the negative impacts of IAS should also recognize the context dependency of their findings and emphasize the benefits to be gained from the management of the IAS. We provide a more complete picture of IAS impacts that could help to inform management decisions in the face of different potential choices and the possible impacts of these choices on sustainable livelihoods in the long term.

Biological control of parthenium, a major weed in grazing areas in Australia, was initiated in the mid 1970s. Since then, nine species of insects and two rust fungi have been introduced. Evaluation using pesticide exclusion at two sites (Mt. Panorama and Plain Creek) in Queensland, Australia, revealed that classical biological control had a significant negative effect on the target weed, but the impact varied between years. In this study, I quantified the effects of biological control of parthenium on grass production. Grass production declined with the increase in parthenium biomass. Significant increase in grass production due to biological control was observed, but only in 1 of 4 yr at Mt. Panorama and 2 of 4 yr at Plain Creek. At Mt. Panorama, there was a 40% increase in grass biomass in 1997 because of defoliation by Zygogramma bicolorata and galling by Epiblema strenuana. At Plain Creek, grass biomass increased by 52% in 1998 because of E. strenuana and by 45% in 2000 because of combined effects of E. strenuana and the summer rust Puccinia melampodii. This study provides evidence on the beneficial effects of biological control of parthenium in areas under limited grazing.