Coastal Restoration Trust of New Zealand

Coastal Dune Ecosystem Reference Database

Assessing the risk to indigenous New Zealand Biota from new exotic plant taxa and genetic material DOC Publication

Williams, P.A.; Nicol, E.; Newfield, M.
Journal / Source
Science for Conservation
Publisher / Organisation
Department of Conservation
invasive weeds, exotic taxa, plant imports, ecological risk, New Zealand
This report describes the potential risks to New Zealand natural areas and indigenous biota from the importation of new plant taxa and additional material of taxa already here. A broad comparison of weed impacts throughout the world with those in New Zealand suggests the impact of new taxa or material is likely to be similar to impacts observed here. The ecosystems most likely to be invaded and the opportunities for novel impacts are described. In the absence of border controls, at least one to two percent of all introductions will become a significant environmental or agricultural weed. Plants arrive in New Zealand via many pathways including different forms of postage, baggage, and with air travellers. The relative importance of these carriers, and their geographical origins, appear to be changing. These trends have implications for detecting potential weeds, especially amongst undeclared imports. Recent experience of screening prospective plant imports suggests the potential weediness of legal imports can be reduced. But this takes no account of illegal imports of which very little is known. The importation of additional material of taxa already here cannot be convincingly demonstrated to pose a high risk other than simply by increasing propagule pressure. Clear exceptions are where it removes a bottleneck in the life cycle of a taxon, such as the introduction of male plants where none were present before. A review of the instances of 'genetic pollution' of native species from introduced taxa shows this is a minimal threat. The threat to conservation values in the medium term of new plant imports is considered to be less than that posed by the large pool of taxa cultivated in New Zealand.