Future climates are predicted to alter the potential distributions of non-native conifer species in New Zealand

Non-native conifers constitute a significant threat to the ecology and biodiversity of many of New Zealand’s native ecosystems and species. From the top down, the potential distributions of non-native conifer species are governed by climate suitability, which alongside variables such as the availability of suitable habitats and a source of propagules determines whether an area of land will be susceptible to invasion by a given species. Here, we undertook a novel study to quantify potential distributions as defined by climate suitability for all 55 non-native conifer species in New Zealand using ecological niche modelling. Using current and future climate data, we then predicted how climate change may affect the potential distributions of these species. For most conifer species currently of concern from a management perspective, the total potential distribution is predicted to decline in future climates, with the largest reductions occurring for Pinus contorta. However, the climatically suitable land area for species such as Pinus pinaster and Pinus patula is predicted to increase in the future, while for species such as Pinus radiata future losses of suitable climate space in the North Island are approximately balanced by gains in the South Island. Although there is a great deal of variation at the individual species level, the vast majority of New Zealand will have climate suitable for a non-native conifer species both now and in the future. While data and methodological limitations associated with ecological niche modelling means we are more confident about increases than decreases in potential distributions, our results can be used to guide the management of non-native conifers in New Zealand and contribute to invasion risk assessments for these species. Our data and methodology can also be used to contribute to invasion risk modelling in other areas of these conifer species’ introduced ranges throughout the Southern Hemisphere.