Restoring Pipiroa Wetland and its Watershed

Pipiroa coastal wetland and its largely vegetated catchment

Image:  Pipiroa Wetland and Watershed, February 2017 (Dean Wright Photography)

Near the southwest corner of the Russell Peninsula in the Bay of Islands is Pipiroa Bay. Your topographic or Google-Earth map shows a narrow sandspit containing a mangrove estuary backed by saltmarsh and a freshwater wetland mosaic with drainage from two largely bush-clad valleys to the east.

This drone-shot shows the sandspit with the estuary outlet at its northern (left-hand) end. Although it seems to be a relatively intact watershed and wetland complex, appearances can be deceptive. Over one hundred years ago the (then) owner flood-gated the outlet, drained the wetland, cleared most of the trees and attempted to develop a dairy farm. He persevered for 50 years in the face of storms driving saltwater over the spit into his pasture. Finally a storm smashed the concrete buttress of his floodgate and he abandoned the farm.  Council later seized the land in lieu of unpaid rates.

Since then, natural processes have helped to regenerate the mangrove forest and saltmarsh, both of which are fairly resilient to weed invasion. However, the freshwater wetland and fertile valley-floor and slope forests are great habitats for alien pest plants, possums and predators, so native recovery is having serious competition from the invaders.

When the local community developed a Walkway from Okiato (starting with the boardwalk across the wetland at the bottom right corner of the photo) through the forest and coastal areas to Russell, it discovered the amazing pre-settlement remnants of native forest and wetlands. In the Pipiroa wetland were a few small groves of kahikatea, but these were no longer linked to the majestic stands of pukatea-kahikatea forest on the valley floor, nor the kauri-podocarp-broadleaved forest of the hill-slopes.

In the neighbouring Te Wahapu watershed to the north, similar sequences of hill-slope and valley floor forest, freshwater wetland, saltmarsh and estuarine /sandspit habitat did remain. These were also impacted by invasive plant and animal pests, and similarly some erosion arising from poorly managed stormwater generated from roading and residential development.

Living Waters BOI (the catchment working group of Bay of Islands Maritime Park Inc) and Pacific Eco-Logic recognised the ecological value and educational/advocacy potential of restoring the integrity of these two coastal wetlands and the whole watersheds upon which they depended. Vicky Froude prepared an Ecological Restoration Plan for the 100 ha of Scenic and other reserves administered by the Far North District Council, which make up the core of the two watersheds.  This facilitated core funding from the Community Board, supplemented with donations and lots of volunteer hours.

Efforts during the first year of the programme (2016-17) have concentrated on plant pest, predator and other pest control to protect habitat for threatened wildlife including kiwi, weka, bittern, marsh crake, spotless crake and fernbird. The plant pest control has focussed on bindweeds, blackberry, banana passionfruit, honeysuckles, pampas, gorse, woolly nightshade, Taiwan cherry and mountains of 40 year old wild ginger.

The predator control has focussed on the stoats, weasels, rats and possums that threaten both our wildlife and the native vegetation that supports it. This is being managed by the Russell Landcare Trust which undertakes monthly servicing of the pest control lines.

Revegetation has focussed on re-establishing the kahikatea forest margin to the Pipiroa wetland and reconnecting it to the valley-floor forest. Hundreds of locally sourced kahikatea seedlings have been planted, along with flax, cabbage trees, manuka and other wetland species.

The big challenge over summer was a rampant expansion of the pink bindweed Calystegia sepium, crushing plantings to their bamboo stakes, and smothering the wetland with a cover up to 70cm depth.  Weedbusters advice was to hand-release the plantings the spray with Trichlopyr. Eventually it worked, with the sedges, rushes and other monocots flourishing.

The senescent wattle forest was cleared from the eroding hillside adjoining the lower wetland and replanted it with pioneer species of native trees to quickly establish a weed-resistant closed canopy (see top end of boardwalk).

Despite the severe drought this summer, most of the autumn 2016 plantings survived, due partly to the use of moisture retention crystals in the base of the hillside planting holes, and partly through our hand-watering of the plantings on the drier flats.  In autumn 2017 some infill planting will be undertaken and the wetland planting extended.

There are some other challenges to address. Recent consents granted by the District and Regional Councils have approved mangrove clearance and reclamation of part of the estuary for a pole-house on a small privately owned lot near the middle of the sandspit (see photo). Developing and servicing this site required establishment of a road along the sandspit, which will be threatened by sea-level rise, storms and tsunami.

Chris Richmond