Cyclone Gabrielle: Are mānuka and other natives the key to restoring Hawke’s Bay’s battered whenua?

Honey bees and mānuka trees near Whanganui. Planting natives could prevent soil erosion during future weather events.

After Cyclone Bola, much of Hawke’s Bay’s steep, erodible land was planted in pine. After Cyclone Gabrielle, pine trees and debris clogged our waterways and covered our beaches. To protect our infrastructure and environment in the future, a regional councillor and advocates suggest planting a different tree. James Pocock reports.

An opportunity to mitigate the scars carved into erodible soil and the piles of silt and wood left in the wake of future severe weather events could lie much closer to home than we think.

Hawke’s Bay Regional Councillor Martin Williams believes farmers retiring their steepest and most erodible land and instead planting natives like mānuka trees and forming wetlands is the solution.

In a Talking Point for Hawke’s Bay Today, Williams writes that decisions to plant steep, erodible land with pine after Cyclone Bola have proven to be a “disaster”, pointing to Hawke’s Bay Regional Council (HBRC) analysis of wood debris after Cyclone Gabrielle which showed whole pine and exotics strewn about.

“Before Cyclone Gabrielle, there was an estimated 250,000 hectares of steep erodible country in Hawke’s Bay. Transitioning this land into native forest through mānuka, and re-establishing natural wetland areas throughout the region, should be the paramount long-term recovery priority,” Williams writes.

“This transition would better hold both land and water in the landscape. It would lessen flooding severity and impact.”

James Powrie, managing director of RedAxe Forestry Intelligence and a consultant for HBRC, said the answer may not be so simple.

About 130 hectares of Tūtira Regional Park were planted with mānuka in 2011, 2012 and 2013 and studied to explore the erosion control potential of the species as a plantation option for soil conservation, and the honey production and high UMF honey potential.

Powrie said parts of the site were damaged after Cyclone Gabrielle and it was difficult to say whether the area fared any better than anywhere else due to factors like different levels of rainfall, but the situation was not as bad as it would have been had the mānuka not been present.

Powrie said about 5000 hectares of mānuka and kānuka, another native, had been planted in Hawke’s Bay over the last 12 years.

“Manuka is a successful local pioneer species for some situations, and provides early groundcover following fires or other traumatic events,” Powrie said.

“Mānuka/kānuka has the benefit of being fairly easy to establish and not too palatable to pests such as goats and deer, which are a huge issue in the Hawke’s Bay landscape for native forest projects, to the extent that without deer fencing and intensive pest control activity, it is easy to fail with most native species.”

He said both trees were part of a tool kit and every plant in a forest had a purpose and gave benefits for the protection of land and water, and the promotion of biodiversity.

Powrie said the cyclone could provide an opportunity to reassess and plant more natives in Hawke’s Bay, but it was an expensive process and pests were another barrier.

Bay of Plenty farmer and kiwifruit grower John Burke has been involved with Tūtira and similar mānuka planting projects across the country, testing a more affordable method of planting, the Tīmata Method.

The Tīmata Method uses wider spacing and “forestry-grade” propagated mānuka and kānuka seedlings for planting, reducing costs from about $30,000 per hectare to about $6000.

Burke said putting “the right tree in the right place” could mitigate floods, creating spongey environments and wetlands that retained water and reduced peak water flow during floods.

He said the Tūtira trial site would have fared even better during Cyclone Gabrielle if it had more time to develop.

“If we had planted it 10 years ago simply for ngahere, or native bush establishment, then we would have kānuka as the primary coloniser species and it probably would have done even better,” he said.

“Because of that, I am pretty happy with how it did.”

Tom Kay, Forest & Bird’s freshwater advocate, said restoring native forests on hillsides with mānuka and other natives was critical to reduce erosion, sequester more carbon, help reduce the impacts of flooding and provide more habitat for native species.

He said “continuous cover production forests” like those used for honey production were a good way to get some of those benefits, but permanent native forest restoration should also be explored.

“These also have plenty of benefits and are the most sustainable option for many places – and landowners can still earn carbon credits from them,” Kay said.