Jane Nees BOP Regional Councillor www.janenees.co.nz

Mangroves within the Tauranga Harbour have expanded exponentially during the last 50 years and there is now upwards of 900 hectares of mature mangroves fringing our harbour.

The expansion is due to increased levels of sedimentation in the harbour and a reduction in the frequency of hard frosts.

Mangroves are spread by propagules, germinated seed pods, from mature plants being spread by tides and currents to establish in open, sandy flat areas.

The more mangrove plants we have, the more mangrove propogules are produced – and the faster the spread of mangroves.

We are working on controlling and reducing sedimentation from up in the catchment.

But if we don't want to lose a lot more of our sandy flat and salt marsh coastal fringe to mangrove coverage, we have to address these spreading mangrove seedlings.

The good news is once mangrove seedlings are cut above the roots, they don't regrow, so ‘cutting/mowing' is a good option for control.

Manual removal of mangrove seedlings is a permitted activity under our Regional Policy Statement and Proposed Regional Coastal Environment Plan, but this would take a lot of man-hours to keep on top of the problem.

The Bay of Plenty Regional Council has obtained a consent to allow it to use a machine to ‘mow' seedling-infested areas, providing environmental impacts are minimised.

Tenders for a suitable machine were sought and council has chosen an innovative hovercraft solution, which can cut about 600 hectares of seedlings annually while causing minimal environmental damage.

The hovercraft should leave no discernable footprint on the estuary surface and provide minimal disturbance to birds and benthic animals.

The hovercraft is currently being built and will be trialled – hopefully – before the upcoming bird breeding season when clearance is prohibited.

I look forward to when we have a sustainable way of preventing the on-growing spread of mangroves around our harbour. Addressing the existing mature mangroves is a much harder problem.

If you have any views on this or any other issue, please contact me on neesj@xtra.co.nz or ring me on 07 579 5150. Or you can check out my website at www.janenees.co.nz