Much ado about nothing

In the communities living around our northern harbours few issues can raise as much passionate argument as mangroves. Should they stay or should they go? By David Brooks.

The debate about cutting down our native forests was settled in favour of conservation decades ago, but arguments over our native mangroves won’t be  going away soon. 

One reason for this is that mangroves are spreading and some see them as a weed – albeit a native one – rather than the foundation of a valuable ecosystem.

“A lot of these arguments, because they involve small communities, can be very divisive,” says Forest & Bird Seabird Conservation Advocate Karen Baird. 

Karen has experienced these bitter arguments first hand through her work trying to protect mangroves at Mangawhai Harbour in Northland and at Whangateau, north of Auckland, where she lives.

She treasures the mangroves that start at the end of her back lawn. “I canoe through those mangroves and come out into the estuary. It’s a marine forest, it’s beautiful, you get all this dappled light coming through and weirdly twisted trees and further down you get these quite deep channels. You see schools of fish swimming around and you can hear banded rails calling from the mangroves, which is really cool,” she says.

Mangroves have been in New Zealand for 19 million years but their spreading in recent decades appears to be happening where land clearance and harvesting of plantation forests have increased the amount of mud flowing towards coastlines. 

It settles in relatively sheltered harbours and estuaries, creating the perfect habitat for mangroves.

Forest & Bird North Island Conservation Manager Mark Bellingham says the expansion of mangroves may have accelerated in the last few decades because government agencies and councils have discouraged farmers from grazing cattle and sheep in the mangroves.

Grazing has declined and coastal subdivisions have in many cases taken the place of farm land on the water’s edge.

Waikato Regional Council Harbour and Catchment Management Co-ordinator Emily O’Donnell says many harbour residents want mangroves cleared for several reasons. Among these are the rate mangroves are expanding, the resulting impacts on open-water views and recreational use of harbours, as well as the perceived or actual decline in harbour health.

Ecological values, flood control and impacts on other habitats are also taken into account by the council.

Forest & Bird has opposed proposals for largescale mangrove removal in several harbours, including Whangamatä, Mangawhai and Tauranga. The circumstances vary in each case but the underlying concern is that mangroves provide valuable habitat for native species.

Mangroves are crucial for banded rails, which have all but in the communities living around our northern harbours few issues can raise as much passionate argument as mangroves.

Mangroves are crucial for banded rails, which have all but disappeared from the inland wetlands they used to inhabit throughout New Zealand because of introduced stoats and ferrets. “Around 95 per cent of all the banded rails in New Zealand are found in mangroves in the northern harbours.

Research I’ve done shows they spend about three-quarters of their time feeding in the mangroves and they retreat into the rushes at high tide,” Mark Bellingham says.

Forest & Bird has also been active in opposing plans to clear mangroves at Mangawhai Harbour because of their importance for one of the world’s most endangered shorebirds, the fairy tern, of which 43 individuals remain.

“We have done work on rails and fairy terns but I suspect there are other links to mangroves in the extended food web. Mangroves also provide an important wildlife corridor for birds moving between patches of bush, and some bush birds nest and feed in mangrove forests,” Mark says.

Marine biologist and photographer Roger Grace says mangroves support juvenile populations of fi sh including parore and yellow-eyed mullet. Flounder are also found among the trees, along with shrimps, triplefi ns, gobies, oysters, barnacles, snails and other creatures. “There is no way it can be called an impoverished environment, as some people like to argue,” he says.

Forest & Bird is not always opposed to mangrove clearance but sometimes the way they are cleared is one of the main problems. The Bay of Plenty Regional Council in 2010 started mechanically removing and mulching mangroves in parts of Tauranga Harbour. The mulch was left on the flats in the expectation the tide would carry it away but that generally failed to happen, says Forest & Bird Central North Island Field Offi cer Al Fleming.

NIWA has been investigating the results and preliminary findings show that 15–21 months after mulching much of the waste has failed to clear and there has been little sign of recovery in the marine life, partly due to poor oxygen levels in the mulch and mud below.

“I think the regional council should take a deep breath and take notice of NIWA and hold off on any further mechanical removals. Research undertaken by regional council staff concluded that at one mulched site there has been a change over time towards restoring bare sandfl ats. This is contrary to NIWA’s findings over several sites within the harbour. By and large, what I’m seeing is a muddy mess,” Al says.

The real answer is to stop silt from catchments flowing into harbours – a solution generally accepted by all sides.

Emily O’Donnell says the Waikato Regional Council sees mangrove management as just one small part of harbour and catchment management. “The council, through the harbour and catchment plan process, now takes a more hands-on approach – mangrove management has become part of our

Mangroves also provide an important wildlife corridor for birds moving between patches of bush, and some bush birds nest and feed in mangrove forests. 

The council, through the harbour and catchment plan process, now takes a more hands-onapproach – mangrove management has become part of our river and catchment management role, we are working in a more holistic way with all the affected stakeholders and the different teams within our own organisation,” she says.

“By looking at the bigger picture, by looking at and addressing the causes of mangrove expansion, that will help find a solution,” she says, adding that more scientific research is needed to help inform future decision making.

In Whangamatä, the decade-long deadlock over mangrove management – which resulted in illegal clearances by residents in 2005 – has ended after Forest & Bird and the council came to a compromise in which clearances will be confi ned to areas of lower ecological value. “I said I don’t want them cleared in the upper harbour where the best wildlife values are. I’m a bit more relaxed about some other areas because they will probably be cleared illegally anyway,” says Mark Bellingham, who negotiated the deal on Forest & Bird’s behalf.

He says Forest & Bird has never advocated conserving all mangroves everywhere. “From early on we’ve said if there’s a problem with infrastructure – jetties, drains and so on – some clearing should be allowed. That includes plucking seedlings, because in the longer term we want the catchment sediment issues settled. I hope in the medium term we will see a collaborative approach with foresters and farmers in the same room as coastal communities and Forest & Bird.”