Managing large ‘problem’ poplars vital; NRC

1 Feb 2018

Huge, decades-old poplar trees planted for streamside erosion control are causing some big headaches for both landowners and the Northland Regional Council (NRC).

Councillor Justin Blaikie (who represents the NRC’s Hokianga-Kaikohe constituency) says the council is a big supporter of poplars for erosion control, but in today’s environment uses them to mainly target erosion-prone hill country, recommending varieties like Kawa, which are smaller when mature.

The council also recommends that willows like Matsudana (and similar) are used near waterways instead of poplars.

“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.  (Lombardy poplars, which can grow to similar sizes, were also popular over that period.)

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.

Councillor Blaikie says the trees are so large that they can stretch right across waterways and when they topple, can have a very effective damming effect, worsening flooding, erosion and other problems.  They can also damage electricity lines, roading and other valuable and costly infrastructure.

As an example, the council is currently arranging the removal of two large Aspen poplars that have fallen into the Waihou River (both just a few metres from a road bridge and power lines) in the Okaihau area, near Rahiri Settlement Rd.

“Removing these two trees alone will be no small feat and is likely to take a number of days and cost up to $10,000; and they’re just two of many problematic trees in the immediate area.”

Councillor Blaikie says while the regional council has overall responsibility for river and catchment management across Northland, landowners are responsible for ‘normal’ maintenance of rivers and streams on and around their properties.

“Council does undertake removal of major blockages and obstructions that effect public infrastructure beyond normal landowner maintenance on a prioritised basis; effectively footing the bill for the wider public good.”

“That’s effectively what’s happening in this case, as these two trees are a major threat to significant public infrastructure, including a bridge, road and powerlines that provide the only access to the Rahiri community.”

However, Cr Blaikie says the council will be approaching both the Far North District Council for help with traffic management and Top Energy for associated electricity control during the work, given they also had a vested interest in it.

“Situations like this are a significant and increasing issue and have some major cost implications for landowners, local authorities generally and our shared ratepayers.”

With very large poplars now causing issues Northland-wide, he says the council is urging landowners to be proactive, checking their properties to ensure problem trees are dealt with – including removal if necessary – well before any difficulties arise.

“Fortunately, timber from poplars – especially well-formed Aspen – does have some commercial value.”  “Provided landowners can collectively provide a fairly large quantity of at least 10 truck and trailer loads or more, they can sometimes offset removal costs by banding together and offering these trees to forest management companies for processing and sale.”

Councillor Blaikie says as well as avoiding potentially much greater problems in future, effective river management makes good sense on multiple fronts.

“By working proactively with Northland landowners on effective river management, we can collectively reduce erosion (protecting valuable soil) and sedimentation (improving water quality) and of course lessen potentially costly flood damage.”

He says the council’s river management team can provide a range of river-related advice (including erosion control and gravel removal) which is also available online at www.nrc.govt.nz/rivermanagement

Information about establishing poplars and willows is also available via: www.nrc.govt.nz/poplars