Weeds such as Russell lupins are picturesque and are favoured by some landowners for their ability to fix nitrogen, but are also an invasive weed, a new report says.
Parliamentary Commissioner for the Environment Simon Upton says the Government must lift its game to better protect native ecosystems from the thousands of exotic plants spreading throughout New Zealand.
If not, forests risk being overrun in a silent invasion by weeds such as wild ginger, old man’s beard and climbing asparagus, Upton says in a new report on how NZ manages pest plants that threaten native ecosystems.
Russell lupins are carpeting braided rivers and wilding conifers are covering hillsides.
“If left to their own devices, these weeds will transform our ecosystems beyond recognition,” Upton said.
The report explained that protecting native ecosystems from being overrun by weeds not only helps native plants, but also saves crucial habitat the fauna needed to survive.
Māori brought about a dozen new plants with them to Aotearoa. But since European colonisation, more than 25,000 plant species have been introduced. Over 1800 of these exotic plants now survive in the wild without human help and are joined by about 20 new ones each year. Most are escapees from gardens.
The risks they pose will only rise as climate change increases the area over which many of them can spread and conquer.
“We cannot rid New Zealand of every single weed. There are simply too many. But we can be smart about which ones we choose to tackle, have a clear outcome in mind and make sure we coordinate our actions,” he said.
“Weed management programmes need to be achievable and sustainable over time – potentially a very long time.
“There is no point removing one species and creating an expensive ‘weed-shaped hole’ waiting to be reinvaded. Knowing what comes next is critical.”
The report detailed how land-use change continued to be a major driver of weed invasions.
Clearing land, whether for planting or harvesting exotic plants or expanding built environments, provided ample opportunities for weeds to invade and spread. The disturbances that land-use change brings create a never-ending supply of ‘weed-shaped holes’, the report said.
It also called out cultivation as a major source of risk for new plant naturalisations in NZ.
It examined the impact of afforestation could have on weed invasions, saying this will depend on the type of new forests being created and how they are established and managed.
“Simply removing livestock from marginal pastoral land in the hope that it will revert to permanent native forest will bring its own weed management challenges – but so too will planting new exotic plantation forests,” he said.
The commissioner made several recommendations to improve weed management, including better leadership from the MPI, DoC and the Ministers of Biosecurity and Conservation, to help coordinate action on which plants to manage, where and how they are to be managed and by whom.
“Our biosecurity system is very good at protecting our borders from exotic plants and looking out for farming and forestry interests,” he said.
“But protecting native ecosystems from plants already established here does not get the same attention.”
He also recommended better monitoring and surveillance of exotic plants, including establishing an emerging risks team to scan for new escapees that could harm native ecosystems.
A single, publicly accessible database of all exotic plants in NZ should also be developed and maintained so everyone has a better idea of which plants are in the country and where they are, the report said.
Upton says the report’s recommendations would back up existing community-based efforts.
“A better focused and coordinated system would give these groups the support they need to make progress and hold onto it,” he said.
“With massive land use and climatic change in the offing, that will be harder than ever to achieve. We need to lift our game.”
