New research from the University of Auckland shows invasive tropical and sub-tropical plants that displace native species could thrive and spread if global temperatures rise as climate scientists predict.
Plant ecology PhD student Christine Sheppard, from the University’s Centre for Biodiversity and Biosecurity, School of Biological Sciences, used bioclimatic models to investigate future potential distributions of potential new weeds already invasive in other countries: Bangalow Palm, Queensland Umbrella Tree and common Guava.
Field trials with seedlings grown in six sites across the country to test model predictions found introduced plants currently limited to northern New Zealand may not only spread further south, but often grow more vigorously compared to closely-related native plants.
“The results show that we need to worry about the fact that climate change will mean introduced plants, particularly those that have come from tropical or sub-tropical climates, become a bigger problem,” Christine says.
As one of the first studies directly testing bioclimatic models, the results increase confidence in the models’ ability to assess invasion risk, work that could help with the war on weeds.
Around 25,000 plants have been introduced to New Zealand. More than 2,000 of those have naturalised (become self-sustaining populations in the wild).
But Sheppard says that if management measures are taken at an early stage of the naturalisation process, the cost-benefit ratio will be high.
“We can never eliminate all introduced or invasive plants but we can improve the way we manage them and one way to do that is to be able to predict which species will be the next big weed species.”
A native of Switzerland, Sheppard says she feels passionately about New Zealand’s natural environment, the main reason she chose to do her doctoral studies here.
“New Zealand has a major problem with invasive weeds affecting native plants and environments and because I feel passionately about conservation, and New Zealand’s unique environment, then that is what got me started on this research.”
The results of the study, co-authored by Sheppard’s PhD supervisors Dr Margaret Stanley and Dr Bruce Burns, will be published in the journal Global Change Biology.