Mangrove removal work gets underway

 

It’s generally conceded that the harbour is the jewel in Mangawhai’s crown either from a fishing point of view or simply as the glowing foreground to the pearly white sand dunes that frame it.
 

Under constant pressure to keep it that way since the Big Dig of 1991 removed the silt build-up which was unable to be flushed by tides, Mangawhai Harbour Restoration Society (MHRS) also purchased a dredge to continue maintenance of this earlier work.

 

More recently however, attention has moved to the on going issue of the invading mangroves which, with their increasing growth and spread have gradually trapped and built up sediment in Mangawhai waterways,

limiting access and impeding water flow.
 

Following years of debate, court action and appeals costing around $400,000 and involving Forest and Bird, DoC, Northland Region-al Council and several environmental experts, agreement was finally reached earlier this year allowing the MHRS to remove up to 16 hectares of the invader.

 

The area targeted runs from near the Lincoln St reserve, around to Moles-worth Causeway and the Insley St inlet.

Work began on the removal a few weeks ago with contractor Dave Smith’s digger alternating between digger bucket and claw to see which was the more effective.

Mangrove plants generally don’t need to come out by the roots – when they break off down low the outer protective seal is broken and, as the salt water of each tide gets in, the stumps will rot in time negating regrowth. Options on controlling seedlings are being investigated with possibly volunteers coming forward to pull them out or using an adopt-a-beach system by groups who will keep them at bay.

“It’s great to see the operation under way at last,” says MHRS Chair-man Trevor Downey.

 

“The object is to take only mangroves and preserve the rush marsh. We have a window from now through until August to do the job depending on the weather.”

The cost of the removal is estimated at around $10,000.

The waste is currently being stockpiled with disposal undecided.

“When dry the mangroves burn very hot and leave little ash,” says Mr Downey “but we have had enquiries from people willing to try the waste as mulch which is a good option.” Given their salty environment they may contain a lot of useful garden nutrients.

Coastal Consultants and Ocean Engineers, Andre and Robin La Bon-te have overseen a similar 27 hectare sustainable management project operation at Pahurehure on the Manukau Harbour and have supported this project all the way.

“This is a joint effort between the NRC and MHRS and is the first permit in New Zealand allowing the removal of whole trees so is a partial experiment but one that will be will be closely monitored.”

Mangrove removal work gets underway  24th March 2014

By Rob Pooley

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