Glyphosate helps killing the willows

Lake Waihola Waipori Wetlands Society chairman Robert Girvan says that glyphosate spraying to...
Lake Waihola Waipori Wetlands Society chairman Robert Girvan says that glyphosate spraying to kill crack willows in the wetlands has allowed native species to make a comeback. Photos by Hamish MacLean.
Lake Waihola Waipori Wetlands Society chairman Robert Girvan shows the leaves of the invasive...
Lake Waihola Waipori Wetlands Society chairman Robert Girvan shows the leaves of the invasive crack willow.
Many people who drive by the Lake Waihola Waipori Wetlands do not know the extent of the wetlands...
Many people who drive by the Lake Waihola Waipori Wetlands do not know the extent of the wetlands, Mr Girvan says. The remaining glyphosate-sprayed willows were in a position that have made their extraction difficult.
Lake Waihola is a shallow, tidal lake that makes it susceptible to reduced water flow and...
Lake Waihola is a shallow, tidal lake that makes it susceptible to reduced water flow and sedimentation.
Channels throughout the Lake Waihola Waipori Wetlands have opened up since spraying commenced...
Channels throughout the Lake Waihola Waipori Wetlands have opened up since spraying commenced four years ago, Mr Girvan says.

Dead and dying willows on the shores of Lake Waihola are signs of progress in the battle to improve the quality of the lake. Hamish MacLean reports on the struggle, which is being led by the local community.

From the roadside, passersby can see stands of dead crack willows as State Highway 1 traces the eastern edge of Lake Waihola.

Robert Girvan, the chairman of the Lake Waihola Waipori Wetlands Society, said he knew the stand of dead trees that lined the edge of the lake and the railway was not the most attractive feature of the wetlands but that stand of dead trees symbolised a lot of work done to bring the wetlands back towards a state of health.

''It's not a good look, but they're not doing any harm,'' he said.

''Everybody asks: 'When are those willows going to go?'

''It's going to take time.''

Crack willows were introduced to the wetlands in 1875, but it was not until more recently that their impact on water levels and sediment movement were realised.

Willows are deep rooting, and in Lake Waihola they had choked out channels feeding into the shallow tidal lake. Sedimentation occurred and water quality suffered.

Four years ago, work began, and since then 600ha of the invasive tree species had been sprayed with a glyphosate herbicide from helicopters.

He said the society had spent ''well into the hundreds of thousands of dollars'' on the willows.

Some areas of dead trees had been cleared. Ground that was hard allowed a digger to collect trees, which were then turned into firewood.

But a lot of the work to remove the remaining treeswould be done by volunteers with chainsaws, clearing trees from areas that diggers could not access, he said.

Volunteers with backpack sprayers would need to ensure that the trees did not return.

Mr Girvan said it can be hard to find volunteers for the project with alternative volunteer conservation work available.

''It's not a beach, it's not a mountain, it's not a forest. It's not that sexy,'' he said.

The Lake Waihola Waipori Wetlands is a 2157ha bird habitat that includes two lakes and about 1000ha of wetlands.

Mr Girvan said he has seen more native fernbirds, more pukeko, more shags in the wetlands.

There are royal spoonbills, white faced herons, and Australasian harriers.

Residents of the area, he said, would at times catch a glimpse of a white heron as well.

Planting of native shrubs and trees had begun, but to keep the health of the wetlands improving, required vigilance and a commitment from volunteers.

Earlier this month, Mr Girvan stood beside a chest-high crack willow that had sprouted since an area had been sprayed and cleared.

He said it could be 4-5m high in a couple of years.

''In a flood, one plant becomes 10 and goodness knows [floods] happen here,'' he said.

''There's always going to be one stick that was missed, one branch hiding under a plant,'' he said.

He said that keeping on top of the willows at the wetlands was similar to any farmer keeping on top of gorse.

When one or two remain in an area, it could be a problem.

Unchecked, the few plants would multiply rapidly.

''You turn your back on them and they're everywhere again.''

hamish.maclean@odt.co.nz

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