Unveiling New Zealand's Battle Against Weedy Invaders


In the heart of New Zealand's forests, a silent war rages. The combatants? Invasive weeds, formidable adversaries threatening the very fabric of native ecosystems. In a recent radio interview, Aaron delved into this ecological struggle alongside experts Geoff Reid and Pete Russell, shedding light on the insidious threat posed by these botanical invaders.

“There's a myth out there that if we just let nature take its course, that the natives will eventually win the war against the weeds… But this is not the case. If we let nature find a balance, we're going to lose a lot of natives in that process,” says Pete.

Pete and Geoff are dedicated to shedding light on the plight of environmental weeds in our forests and other ecosystems, emphasising that this effort goes well beyond tackling creeping vines alone. Tree weeds, ground cover, and exotic ferns are all significant contributors to the threat our native forests face. The pair underscored the urgency of the situation, warning that neglecting our forests could result in the irreversible loss of entire ecosystems.


“Sometimes we look at a forest and it's got the understory smothered out by weeds which means that any seeds from the big tuakana trees, the bigger older trees that land and want to grow to replace the next generation of the forest, are not there,” says Geoff.

Delving deeper into the issue, Geoff dissects the proliferation of environmental weeds, noting how species like old man's beard have entrenched themselves in the wild over decades, spreading like wildfire and asserting themselves over native counterparts. Since the 1960s, the spread of these invaders has accelerated, with exotic plants being sold in garden centres and many escaping from the confines of gardens and towns to colonise our native forests.

Species like monkey apple hedges, some palms and macho ferns often sold as landscaping or indoor plants have the potential to wreak havoc once they have spread into our native bush.

“There's an estimated 30-40,000 species of exotic plants in New Zealand, compared with about 2500 native plants. But we're not saying that all 30-40,000 of those need to be removed. Only about 2-3000 of those have gone wild and maybe 4-500 of them are a problem. 

“So it's not that we're against all exotic plants, or even all exotic plants that have gone wild. It's just those that are super invasive that really present a threat to the native vegetation and habitats that we're concerned about,” says Pete.

In terms of conservation efforts, the pair say that protecting key areas from invasive species is crucial. While large infestations may seem like the most urgent targets, focusing on smaller, scattered outbreaks can have a greater overall impact. 

These patches, often found in hinterlands between urban areas and natural habitats, serve as breeding grounds for invasive species. By addressing these smaller infestations first, we can disrupt the spread and distribution of weeds more effectively. 

The degree of isolation from weed sources also plays a significant role, which is clearly evident on isolated sites like islands or forest reserves surrounded by grazed pasture. These environments act as natural buffers, hindering the spread of weeds. 

“Grazed pasture is very hard for environmental weeds to spread across, because any seeds that drop into the grass are eaten by livestock. There's a few exceptions to that, but by and large, environmental weeds can't handle that kind of environment,” says Pete.

Targeting specific spots within these landscapes, even less than 5% of an area within 500 metres of a reserve, can create meaningful buffers against invasive species, offering protection to vulnerable ecosystems and native species. 

“A buffer of 50 metres is an advantage, so it's not like you have to have several kilometres.”

To effectively manage invasive species, the pair say that conducting thorough surveys is essential. Utilising tools like iNaturalist makes it easy to identify and map weeds, aiding conservation efforts. Focusing on high biodiversity areas and establishing weed-free buffer zones around them, as well as containment zones for severe infestations, are key strategies. 

Learning about weeds and their management is an ongoing process and resources like the Weed Busters website can be invaluable for expanding your knowledge. While not everyone can become an expert, community efforts can still make a significant difference. 

Occasionally, enlisting the help of experts for initial surveys, like one recently conducted in the Bay of Plenty, where 155 out of 200 identified weed species were found, can provide crucial insights. Community involvement is often essential, as most weeds thrive in areas where people frequent, creating opportunities for community-led control. 

In our local Whāingaroa catchment, Geoff and Pete warn that riparian planting areas can act as weed corridors if the weeds aren’t kept in check. Pete says that these scattered, sun-drenched vegetation patches are particularly vulnerable to weed colonisation, acting as attractive targets for invasive species. Adding that it's essential to implement effective weed management strategies to preserve the integrity of these restored habitats and sustain their ecological value.

“We can't afford to let those weeds eventually reach places like Mount Karioi because once they get into that bush, it's gonna be a hell of a lot more expensive -  and time consuming - to control them,” says Pete.

Geoff says that while they're hesitant to use herbicides due to concerns about their impact on health and the environment, sometimes it's necessary to address severe weed infestations like climbing asparagus, which can smother native seedlings and has already been found on Karioi. It's akin to choosing a harsh treatment for a serious illness; although not ideal, it may be the best option for preserving biodiversity.

While the threat of weed invasion seems daunting, the weedbusting duo say that by taking action in your own backyard and collaborating with others, you can contribute to effective weed management efforts in the community and make a positive impact on your environment.

For more information you can contact Whaingaroa Weedbusters FB Group, or Friends of Kaitoke Walkway - a group that meets every 1st and 3rd Saturday of the month. Email Leanne on whaingaroaweedbusters@gmail.com.