Waihi Wetland restoration – part 2

Royal spoonbill in the wetland.

In part 2 of the story of how Maketū Ōngātoro Wetland Society (MOWS) rescued Waihī Harbor Wetland, society chairman Julian Fitter describes what happened once the worst of the weeds was cleared and restoration began.

We started work in the Waihī Harbor Wetland in January 2015, so we are now seven years into the restoration project, but we are in no way finished.

At the start of the project the main objectives were clear, but as we have progressed, we have discovered work is much more complex and new issues have arisen.

Ecological restoration – restoring the mauri – is a long-term and complex business. There are four main areas of work:

■ Getting rid of or controlling, pest plant species – weeds.

■ Planting appropriate native plant species.

■ Getting rid of or controlling pest animal species – rats, possums, stoats, etc.

■ Monitoring the results so that you have an idea of ​​your progress.

The Weeds

With this project, the major problem was pampas which completely blocked access to most areas, followed by goris, blackberry and a large number of mature water trees. We have largely dealt with the pampas, gorse and wattles. In the hard to access areas we even used a helicopter to get to the pampas.

You could say that was the easy part and we are now dealing with the tricky ones.

Bittern monitoring in Waihi Estuary Wetland.
Bittern monitoring in Waihi Estuary Wetland.

The biggest and trickiest one is reed sweet-grass Glyceria maxima which looks rather like a small version of raupo, but it is very invasive and is rhizomatous – it spreads underground with a very solid root system. This makes it difficult to deal with, both on the stream banks and inside the wetland.

The other major problem is willows which have developed a very dense thicket in the southeastern corner of the wetland. These two species are the main focus of our current weed control programme.

Planting

We started planting native trees and shrubs in the winter of 2015 once we had finished grassing the cleared areas. We used a fairly small selection of plants, mainly ngaio, taupata, hebe, akeake, manuka and toetoe, planted along the western side where we had a large bund of dead and burnt pampas. This continued into 2017.

We were amazed how quickly the plants grew, particularly the ngaio, which we have also discovered has a slight problem in blowing down. We also realised we had probably planted too many plants, and too close to the trails – we now have to prune the trees, especially if we want to get a larger vehicle down.

Helispraying in the Waihi Estuary Wetland.
Helispraying in the Waihi Estuary Wetland.

One planting project we are proud of is Bolboschoenus fluviatalis, a tall bulb-forming sedge that dies down in winter.

We have a developing erosion issue at the mouth of the Pongakawa stream, so in spring 2019 we obtained some 400 B. fluviatalis and planted them along the banks near its mouth. They liked it immediately and have since spread and started to anchor the banks on both sides of the mouth of the stream. We now have to continue planting further up the stream.

There is still some planting to be done in the southeast corner and we are now looking at increasing the diversity of species.

Aotearoa has an amazing number of native trees and shrubs and if we are restoring the ecosystem, we need to encourage that variety which will, in turn, encourage more invertebrates and more native birds.

In 2019 we started on this by planting a number of fern species to provide some understory. Only one species, the hen and chicken fern, has really prospered, which shows how tricky it is to get it right. There is no simple guide, each location is specific, so what works in one place, might not in another – we just have to keep on trying.

Animal Pests

Unsurprisingly when we first opened up the wetland, we found that we had a significant number of mammalian pest species, pretty much all the usual suspects; Possum, rat, mouse, ferret, stoat, weasel, hedgehog and cat.

But we also knew we had some pretty exciting and important bird species in the wetland – Australasian bittern, banded rail, spotless crake and fernbird.

Once we had done the clearing and the first plantings we set up a pest control system. The main tool was the DOC200 trap, which has two traps in it so can be checked less frequently.

If one trap goes off, there is still another trap set. Additionally, pests are often attracted to another dead pest, so that second trap is really handy. We also used Good Nature automatic traps and A2 traps for possum and feral cats.

Our early records are incomplete, though we did get 22 possums in that first year. In 2016 we caught 128 pests made up of 47 rats, 26 stoats, 23 hedgehogs, 17 mice, 9 weasels, 3 ferrets, 2 cats and 1 possum. And that was just on the western half of the reserve.

Over the years we have continued to catch all of those species.

The reserve is connected to surrounding farmland so there is no inexpensive way of preventing future incursions, so the animal pest control program is ongoing.

We do have other issues not always with alien pest species but related to activities in the catchment streams that flow into the harbor.

One new issue is manawa or gray mangrove Avicennia marina. This saltwater tree is native to northern New Zealand but is spreading south, likely helped by global warming, but also due to the amount of mud or silt being brought into our estuaries and harbors.

”Avicennia flourishes where silt and mud have accumulated and in some harbors, especially those abutting cities it has become a problem species,” says the NZ Plant Conservation Network.

“The increase of Avicennia is however a symptom of a more serious issue, that is the impact of increased sedimentation rates within harbors whose catchments have been seriously degraded and/or deforested.

“It should also be noted that the argument that Avicennia ecosystems in New Zealand are as productive as tropical mangal systems has yet to be demonstrated conclusively. In many places Avicennia has replaced the demonstrably more important and productive Zostera grass beds with potentially serious long-term consequences for our near shore fisheries.”

The good thing here is we now have a catchment management group, Wai Kokopu, part of whose remit is to improve land management practices in the catchment, which should result in a reduced erosion along the streams, and less mud and silt reaching the harbor.

Glenn's fernery in May 2019.
Glenn’s fernery in May 2019.

When we started this project in 2015 there was very little manawa around, now it is increasing rapidly and presents a serious threat to the ecological integrity of the whole harbor.

As I noted at the beginning of this article, restoring the ecology and mauri of the harbor is long-term and complex and many of the issues that you come across along the way, may not be visible at the start.

It is so important to be constantly on the lookout for new threats.

We have such an amazingly rich native biodiversity here in Aotearoa New Zealand, most of our native species are found nowhere else in the world, so we have a duty as kaitiaki, to look after them, not just for ourselves, but for the whole world . We are their guardians.

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