Restoring a Northland wetland illegally drained and sprayed for a watermelon farm will take huge effort and expense, a local expert says.
In a recent Environment Court decision, Paul Harvey and New Zealand Watermelon Distributors were ordered to undertake “immediate remedial work” to undo damage to the protected Kaimaumau Wetland, the largest wetland in Northland and one of the most ecologically significant.
The decision stated that much of a 55 hectare area of wetland at Motutangi, north of Kaitāia, had been cleared, sprayed with herbicide, drained with 600m of illegally-dug channels, and pugged by cattle.
The damage was first discovered by Northland Regional Council hydrologists in 2023, with the council issuing a series of abatement notices. Compliance officers then carried out an inspection, under police escort, in August last year.
Kevin Matthews, a local farmer and expert on the Kaimaumau wetland, said the area could recover “reasonably quickly” — within about 10 years — but only with an ongoing effort to control invasive weeds.
The cost was likely to be “very high”, he said.
The main problem would be controlling Sydney golden wattle, which thrived in acidic wetland soil.
Left unchecked, the weed would quickly dominate the area and prevent the return of native vegetation.
“That’s the biggest problem with the removal of indigenous vegetation on these sites. It comes back like hairs on a dog’s back after ground disturbance,” Matthews said.
The use of herbicide could also delay the return of native plants, although the effect would depend on the type that was used.
Matthews said replanting such a large area would take hundreds of thousands of plants, and the seeds would have to be sourced from the right area.
The best approach could be to allow native vegetation to come back naturally, while keeping on top of weeds such as gorse, hakea and especially Sydney golden wattle.
“It takes a huge amount of manpower to control it, because it has to be hand weeded. There’s no other way of controlling it.”
Matthews said the drainage channels would also have to be filled in, with weirs put in to retain water in the meantime.
“Keeping that water level up is crucial to the to the restoration of the area.”
Matthews said the wetland was a crucial part of the area’s history and ecology, and because the peat in the soil retained so much water, it also played an important — if not fully understood — role in replenishing the underground aquifer upon which the area relied on for water.
Despite that, many people did not appreciate the wetland’s importance.
“Probably one of the biggest problems is that people don’t understand the function of wetlands and what they support. There’s bittern, mātātā or fernbirds, geckos, skinks, mud fish, orchids, and a myriad of insects we probably haven’t even identified yet,” he said.
Only about 5% of Northland’s original wetlands remained, which was even worse than the national figure of around 10%, Matthews said.
“There’s so few of these areas left that if we continue to lose them at the rate we’re still losing them, they’ll soon be a distant memory. Some people don’t care but they’re important … I don’t think we’ve got the right to continue to destroy what we’ve got.”
Orders issued by the Environment Court include filling in all new drains, putting up fencing to keep out stock, and restoring the indigenous shrubland and wetland vegetation.
The landowner would also have to hire a suitably qualified ecologist to prepare a “remediation and mitigation plan” to return the land to the state it was in before September 22, 2022.
Pest plant and animal control in the re-planted area, along with monitoring of plant survival and wetland functioning, would need to continue for at least the next five years.
The landowner would have to cover the regional council’s compliance and monitoring costs resulting from the enforcement order.
A Ministry of Justice spokesperson said the Environment Court could not issue fines as part of an enforcement order.
However, anyone who did not comply with an order could be prosecuted through the District Court, which could result in a significant fine.
In a 2015 study, the Kaimaumau-Motutangi Wetland was ranked as the second most important freshwater wetland in Northland, surpassed only by the Poutu dune wetland system in Kaipara.
At 1860 hectares, it was also the largest.
According to the Department of Conservation, the wetland complex “contains a very high richness of threatened and rare plant species”, including species listed as nationally critical.
The wetland was recovering from a major fire in 2022, caused by a vegetation burn-off that re-ignited in strong winds.
rnz.co.nz
