Weeding out our future?
2050… exotic palms have replaced nikau groves; native forest remnants are being strangled by old man’s beard, banana passionfruit and Japanese honeysuckle; wilding pines and Scotch broom have changed the panoramic tussock grasslands of the central plateau and the southern high country. Demented vision or potential reality?
The indisputable fact is that weeds are a rapidly increasing threat to New Zealand’s natural ecosystems. In the 200 years since European colonisation, at least 25,000 exotic species have been introduced to New Zealand. One of these exotics establishes a self-sustaining wild population (naturalises) about every 40 days. We now have more naturalised species than native species. In a short time our flora has doubled.
Currently about a quarter of the naturalised flora are weeds, with 200 species controlled under legislation. These weeds are costly— losses to agricultural and forestry production exceed $1 billion annually. Environmental damage is incalculable—one estimate suggests more than $2 billion annually. We are in danger of losing our special landscapes and biodiversity.
Why is our weedy 50-year vision so pessimistic? Firstly, few naturalised species have reached their potential range and abundance in New Zealand. Even long-established species like gorse and broom are still spreading. Secondly, long-lived exotic species can take 10s to 100s of years to realise their weedy potential. Thirdly, we do not learn from our own mistakes. For example, climbing spindleberry was known from only one locality in 1988, but no proactive action was taken—it spread widely and the opportunity for eradication was lost. Fourthly, we are our own worst enemies—most new environmental weeds are garden escapees.
About every 40 days, a new weed establishes in New Zealand.
Research can help prevent this weedy vision becoming reality. Stopping new weeds is a priority. We need to get better at predicting potential weediness, understanding how and where weeds are spreading, and assessing the likely impacts of new weeds. We need to raise awareness among nurseries and the gardening public. Eradication of established weeds is rarely feasible. Biological control may be the only answer for many species, especially in environmentally sensitive areas, and where herbicide use is unacceptable.
This scenario, developed by Lynley Hayes, Peter Williams and Peter Bellingham, was one of several developed as part of our 50-year visioning exercise. The information is factual.
Further information is available in the weeds section of our website.
The potential for a future weed “explosion” of exotic plants in New Zealand, many in ordinary gardens, has been on Manaaki Whenua’s “radar screen” for some time. Our weed research complements other critical biosecurity and pest management research in Manaaki Whenua—improving management and control of vertebrate animals that are already well-established and recognised as pests in New Zealand; strengthening border biosecurity and risk management for unwanted invertebrates and micro-organisms known to be problems overseas; and assessing the environmental risks of GM crops.