Homoclime analysis and the prediction of weediness

Summary: Homoclime analysis of three weed species of potential significance to agriculture in New Zealand was undertaken. Using the Bio‐climate Prediction System computer program (BIOCLIM), climatically suitable regions in New Zealand were estimated for Homeria flaccida Sweet, Chondrilla juncea L. and Emex australis Steinh., on the basis of their respective distributions in Australia. These estimates indicated that the current eradication campaign for Homeria is warranted, owing to the existence of extensive areas with a suitable climate on both of New Zealand's main islands. For Homeria , most of the known occurrences fell within regions predicted to be climatically suitable. For Chondrilla , only very small areas were predicted to be climatically suitable, due to the generally low temperatures that prevail during its reproductive period. This suggests that the designation of Chondrilla as a quarantine pest may be unwarranted. Much of the land in the interior of the North Island was estimated to be climatically suitable for Emex. However, invasion has not occurred, despite the presence of this weed in New Zealand for over 100 years. The failure of Emex to invade perennial pastures is probably a result of its poor competitiveness, since climatic and edaphic characteristics appear to be suitable over large areas. It is concluded that homoclime analysis can be used to identify regions at risk of invasion by a species which has been weedy elsewhere, when potentially modifying factors such as soils, land use/management practices and competitive interactions are taken into account.