Future-proofing weed management for the effects of climate change: is New Zealand underestimating the risk of increased plant invasions?

Climate change may exacerbate the impacts of plant invasions by providing opportunities for new naturalisations and for alien species to expand into regions where previously they could not survive and reproduce. Although climate change is not expected to favour invasive plants in every case, in Aotearoa-New Zealand a large pool of potential new weeds already exists and this country is predicted to be an ‘invasion hotspot’ under climate change. In particular, ornamental garden plants originating from warmer native ranges are likely to naturalise and become invasive when climatic constraints are lifted. This forum article synthesises research on potential synergistic effects of plant invasion and climate change and discusses the general implications for management of weeds under climate change in New Zealand. A comprehensive assessment of three recently naturalised subtropical species (Archontophoenix cunninghamiana, Psidium guajava and Schefflera actinophylla) illustrates the potential risk of invasions by such species arising with climate change. Despite two recent Department of Conservation reports giving policy recommendations for conserving biodiversity under climate change, in which the potential of new weeds was highlighted as one of the most imminent threats, very little action has been taken. We argue that climate change needs to be accounted for in current weed management policies. Specifically, prediction of potential new weeds needs to be improved, considering up-to-date research and using best-practice modelling tools. Better surveillance for new infestations through spatial prioritisation by habitat suitability and use of well-managed citizen science projects is required. Education campaigns to raise awareness of climate change effects and new weed threats are essential. With an ever-increasing number of potential weeds but limited resources available, it is crucial that more preventative management is taken. Conservation managers, scientists and the general public need to combine their efforts to future-proof New Zealand weed management for the effects of climate change.