New Zealand is one of the weediest countries in the world!

• “Rampaging weeds pose a deadly threat to our native ecosystems by smothering, outcompeting and preventing regeneration of native plants,”

• “Some plants that have naturalised here threaten to smother native ecosystems and prevent the regeneration of native plants. If left to their own devices, these weeds will transform our natural environment beyond recognition”.

For an island nation, New Zealand has a very high number of naturalised exotic plant species – it stands out globally in this regard. Over the years, humans have introduced more than 25,000 exotic vascular plant species to these islands, and nearly 3,000 of them have been found growing in the wild. Some do more than merely survive. Almost 1,800 exotic plant species are now considered naturalised. In other words, they have escaped cultivation and are successfully maintaining populations in the wild without human help. To put this botanical invasion in perspective, a recent study found that both the North Island and South Island have more naturalised plant species than almost any other island in the world.

On the other side of the botanical ledger, there are about 2,300 native vascular plant species growing in New Zealand. This means that for every four native plant species growing here, there are roughly three naturalised ones also growing in the wild. There are plenty of potential places for these naturalised plants to thrive. Widespread clearance of native forests has created a porous front that opens the remaining native ecosystems to invasion from naturalised plants.

These botanical incursions come not just from plants associated with production systems but also from urban development and sprawl. Many thousands of ornamental and horticultural plants have been brought here to look at and admire or eat. Problems arise when they escape their fields and gardens to spread across the landscape with unintended impacts in new settings.

This wave of leafy exotic invasion has not yet peaked. It is estimated that 20 new exotic plant naturalisations occur each year.6 Many of these are garden escapees. Without intervention, harm to native ecosystems will increase, not only as the existing naturalised invaders we know about continue their spread but as they are joined by these new ‘escapees’ that start to move away from where they have been deliberately planted.

New Zealanders have a responsibility to protect the native plants, animals and other life forms that are unique to Aotearoa. Nearly 80 per cent of the native plants found here are found nowhere else. If we do not care for them, no one else will. There is no doubt that some of the exotic plant species that have naturalised here pose a serious risk to some of our unique species and ecosystems – they are native ecosystem weeds.

The message is that we need to protect our native ecosystems from invasion by weeds

Have have a look at the report of the Parliamentary Commissioner for the Environment on the extent of weed problems and suggestions for how we might begin to address that.