Source: NZ Department of Conservation
Date: 19 June 2025
Royal fern can colonise natural areas rapidly, growing up to 2 m high, and crowding out native species in already pressured wetlands and swamps. A deciduous fern, the bright green paper-thin fronds turn yellow and rusty orange in autumn, and each plant produces thousands of tiny spores easily spread by the wind, birds, and humans.
Surveillance and control work in partnership with iwi, landowners and regional councils is happening in Taranaki, Waikato, Rotorua, and Northland. Susan Emmitt, Technical Advisor at DOC, says despite the intensive work, the fern is still spreading.
“Royal fern is still being found in new places, as the spores disperse over long distances allowing new plants to establish in remote areas,” says Susan.
“The fern has been targeted for eradication in Northland, and is being controlled in the Bay of Plenty, Taranaki, and Auckland. To try and halt its spread, we’ve drawn a containment line roughly halfway down the North Island.
“We’re asking the public to report any sightings of the plant south of this line.”
Royal fern is challenging to remove, as it thrives in wetland sites which are difficult to access on foot.
“It can be dug out, roots and all, but this is slow and very labour intensive. We’re working alongside field teams to find the most efficient control methods.
“It’s very easy to spread the spores around when we’re clearing the area, so we wear gloves and disposable overalls, and carefully double or triple-bag the fertile fronds once they’ve been cut. We also have rigorous decontamination procedures, so we don’t accidentally spread them from one site to another.”
Drones are a valuable tool in the control of the invasive fern.
“The distinct bright green leaves are easily visible from the air in wetlands, so we can use drones to monitor existing or treated sites,” says Susan. “This saves a lot of time and effort, letting us work faster and more effectively.”
Autumn and early winter are the perfect time to spot this plant; royal fern fronds change colour in autumn, making the plants stand out. Members of the public are being asked to report sightings of royal fern from the Bay of Plenty and Taranaki southwards via iNaturalist or info@doc.govt.nz, including a photo and location.
“Nature is in trouble, but all of us can help protect our species and habitats. Reporting royal fern is a small action to make a big difference; thanks to a report at Farewell Spit in March 2024, the site was able to be treated immediately and prevent a potentially catastrophic invasion.”
Background information
Royal fern (Osmunda regalis) is an Unwanted Organism under the Biosecurity Act 1993. This wetland weed has been targeted for eradication in Northland, and is being controlled in the Bay of Plenty and Auckland under the Regional Pest Management plans.
It has spread southwards over the past few decades. Our surveillance operation aims to gain a better understanding of the southern distribution of royal fern with the aim of controlling and containing its spread and protecting high priority sites.
Contact
For media enquiries contact:
Email: media@doc.govt.nz
