Northland pays the price when poplars lose their ground

NRC staff member Doug Foster is dwarfed by a roughly 70-year-old poplar which fell into a stream in the Okaihau area.

Old poplars planted in Northland to control erosion and prevent waterways from blocking are contributing to rather than preventing the problem.

The Northland Regional Council (NRC) actively promotes, and even subsidises, landowners planting modern varieties, but decades old trees, some at the end of their natural lives, have caused headaches.

Council member Justin Blaikie, who represents the Hokianga-Kaikohe constituency, said the council supports using poplars for erosion control, but promotes smaller varieties like kawa on hill country.

They should not be planted on riverbanks, where the NRC recommends willows like matsudana.

"Unfortunately, however, between the 1920s and the 1960s, relatively large numbers of Aspen poplars - which can grow more than 30 metres tall, with trunks more than a metre thick - were planted to thwart streamside erosion all over Northland,'' Mr Blaikie said.

''Some of those surviving trees are now seriously big and as they begin to succumb to old age, disease or storms, floods and other adverse events are increasingly having a negative and costly impact on the very environments they were originally planted to protect.''

The trees can stretch across waterways when they topple, causing dams and making flooding, erosion and other problems worse. They can also cause costly damage to electricity lines, roading and other infrastructure.

The council has removed two large Aspen poplars that recently fell into the Waihou River in Rahiri Settlement Rd, near Okaihau. Both trees fell only metres from a road bridge and power lines.

Mr Blaikie said the cost of removing them could be as much as $10,000. The NRC is responsible for river and catchment management but landowners are responsible for ''normal'' maintenance of waterways on or around their properties.

"[The] council does undertake removal of major blockages and obstructions that effect public infrastructure, effectively footing the bill for the wider public good.''

Landowners should check their properties to ensure problem trees are dealt with before difficulties arise.

"Fortunately, timber from poplars – especially well-formed Aspen – does have some commercial value," Mr Blaikie said.

The NRC offers landowners kawa poplar poles grown at its plantation in Flyger Rd, Mata.
For river-related advice, including erosion control and gravel removal: www.nrc.govt.nz/rivermanagement; for information about establishing poplars and willows: www.nrc.govt.nz/poplars