PERSPECTIVE Species Invasions and the Limits to Restoration: Learning from the New Zealand Experience

Species invasions impose key biotic thresholds limiting the success of ecological restoration projects. These thresholds may be difficult to reverse and will have long-term consequences for restoration because of invasion legacies such as extinctions; because most invasive species cannot be eliminated given current technology and resources; and because even when controlled to low levels, invasive species continue to exert substantial pressure on native biodiversity. Restoration outcomes in the face of biological invasions are likely to be novel and will require long-term resource commitment, as any letup in invasive species management will result in the loss of the conservation gains achieved. Recent theoretical advances have empha-sized thresholds and alternative stable statesas key drivers influencing the outcomes of ecological restoration (1). One consequence of these emerging perspectives is the recognition that restoration must address not only the degrading factors but also the altered feedbacks that lead to self-perpetuating novel ecosystems—ecosystems that are different from those that would have existed be-fore human impacts, especially as the impacts of cli