'Unhealthy' willow trees removed

Up to 40 ailing willow trees along a Christchurch creek are being replaced with natives to help stabilise the land and reduce sediment build-up.

The project along Kā Pūtahi Creek at Englefield Reserve, Northwood, is being under taken by the city council’s three waters and parks teams.

Some willow trees are considered a pest along waterways, as they can spread and suppress native vegetation. 

They also produce heavy leaf falls in autumn, which can de-oxygenate the water, making it difficult for fish and invertebrates to survive.

The 40 trees to be removed are on the left bank of the creek, which is a tributary of the Pūharakekenui/Styx River. The trees have been deemed unhealthy or structurally unsound. 

About five willows will be retained as they offer nesting areas for wildlife.

The willow canopy is also suppressing the existing native trees, including several kahikatea estimated to be more than 15-years-old.

“Although we will be removing 40 mature willows, the loss of existing tree canopy will be minimal because of this understory,”  said city council community parks manager Al Hardy. The willows bordering the reserve are also unhealthy or structurally unsound.

“As part of the project we will also be planting about 2800 riparian trees along the creek bank, including more than 1000 eco-sourced canopy-forming native trees, which will replace any lost canopy within 20 years.”

Eco-sourcing is when seeds are collected close to where they are going to be planted, meaning the plants will be suited to the conditions and more likely to survive.

The Styx Living Laboratory Trust will also plant a 15m-20m wide area of low-lying, floodplain vegetation between the creek and Englefield Reserve playground. The area, which the city council manages as rough-mown grass, is wet all the year, making it difficult to mow, Hardy said.

The trust will work with TreeTech’s Green Gear company and Trees for Canterbury to supply, plant and maintain additional plants in the reserve as part of Project Kotare, the Ministry for the Environment’s freshwater improvement fund project.

The willows will be removed this month. The bank renewal and stream enhancements will be done next summer. The final riparian corridor replanting will be completed by June next year. 

The work will tie in with the city council’s Styx Vision plan, which aims to establish a spring-fed ecosystem along the river and its tributaries.