Potential distribution of hawthorn in New Zealand

Abstract

Hawthorn (Crataegus monogyna), a bird-dispersed, introduced shrub, is becoming increasingly weedy in parts of New Zealand, North America, Australia and elsewhere. In order to identify areas threatened by this species, an eco-climatic model for its potential global distribution was constructed using CLIMEX software. The model was based on the native range of hawthorn in Europe and validated against the invaded range elsewhere in the world. It suggests that hawthorn could potentially invade most lowland and montane areas of New Zealand. In lowland areas, invasion is likely to be limited by grazing pressure, but changes in the management of South Island montane grasslands as a result of the current tenure review process may favour hawthorn invasion in some areas. Pre-emptive action to identify and remove infestations from montane grasslands is recommended.