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Sycamore trees are in the crosshairs of Dunedin city councillors, who have asked council staff to identify the implications of registering them as a noxious plant.
Councillors also supported, in principle, initiatives to control and eradicate the trees on all public land, including roadsides and rail corridors.
The decision was taken by councillors considering the 2013-14 annual plan.
Although the matter is not one that has any funding allocated in that year, there were several submissions concerned about the extent of sycamores seeding and growing around the city.
Councillors said they understood the trees were presenting a real problem around the city and a way to deal with it needed to be found.
But it was a tricky area because it was generally difficult to get plants registered as noxious, registration could have major financial implications for the council, and the trees were also growing on New Zealand Transport Agency, KiwiRail and private land.
Parks and recreation services manager Mick Reece said addressing the issue would require partnerships with community groups if the eradication effort was to be sustained over the long term, as it would be too costly for the council to manage by itself.
He said the council was slowly killing sycamores in Dunedin's Town Belt and that programme seemed to be working well, but limits on funding meant it could not do any work on the sycamores in the Port Chalmers town belt at present.
Cr Kate Wilson initially proposed to have staff work to have the tree registered as a noxious plant, but then backed down over concerns about the cost implications for the council.
But Cr Andrew Noone said having it registered gave all landowners the responsibility for controlling it on their land, and it was a step the council would have to take if there was to be a permanent solution.
The resolution was amended to identify the implications of registration, which satisfied the concerns of councillors.
Those concerns included that there was a tendency to want to have plants registered as noxious when, in some circumstances, they might have a viable use.
That also meant other authorities would be involved in the discussion, Mayor Dave Cull said.