Tuesday, May 21, 2024

A better, cheaper way to plant natives takes root

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More effective method comes in at a third of conventional method’s cost
A report funded by Our Land and Water outlines a cheaper, more effective method of re-populating land into ngahere, or native bush.
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This article was one of the most popular articles on farmersweekly.co.nz in 2023.

For New Zealand to get anywhere near the Climate Change Commission’s recommendation of 380,000ha of native trees planted by 2035, industry and supporters agree the costs need to fall significantly. 

Current estimates of $30,000/ha put native planting beyond the reach of most private landowners, often limiting projects to small-scale woodlot-type areas. 

But a report funded by Our Land and Water outlines a cheaper, more effective method of re-populating land into ngahere, or native bush. It is a method being undertaken by a number of catchment groups around New Zealand, with total costs almost a third of the conventional native-planting method.

Alison Dewes, director of environmental advisory company Tipu Whenua and John Burke have overseen the Tīmata (kickstart) method as a means for catchment groups around the country to get more natives in the ground cheaper and faster.

Dewes said Tīmata is a combination of ideas and techniques for planting bundled together, including methods borrowed from conventional exotic forest planting operations.

The Tīmata report said farm foresters using the method reported establishment costs of $5000-$6000/ha. 

Follow-up weed control on the very worst sites is unlikely to exceed $5000/ha, making the $11,000/ha maximum cost still only 37% of the typical $30,000/ha cost of a high-density planting project – and that cost assumes no additional post-planting costs.

“We are talking a significantly lower cost to the country to meet the aspirations around native plantings. Most farmers you talk to really do want to retire farmland into natives, but simply cannot afford $30,000/ha. 

“It is estimated NZ has about 1 million hectares of land that could be retired into natives. The Tīmata method represents savings of $20 billion across the country in achieving that,” Dewes said.
She said it is critical that weed and pest control are done well at the project’s start, before planting. 

“That may be wholesale spraying out of the land, but even spot spraying prior to planting can be enough,” she said.

The method focuses heavily on taking a “nursery” or colonising forest approach to planting, where kānuka and/or mānuka are the first species planted, acting as a canopy layer to make the establishment of larger podocarp-type trees easier in the future.

“A key difference to conventional planting of mānuka cover using Tīmata is the lower tree density employed. Conventional density can be as high as 4000-4500 trees per hectare, but Tīmata will be far lower, nearer 2500 per hectare.” 

The nursery crop will grow to 6-10m high over 20-plus years, with the wider planting allowing in more diffuse light, encouraging early establishing second-stage podocarp trees to come through and assert their dominance. 

The conventional approach of crowding in more trees has been largely done to try to minimise weed intrusion. However, it does not exclude all weeds, and can prompt die-back due to overcrowding around year 10 that can leave understory soil bare and difficult for seedlings to establish on.

The report also highlights the Tīmata method’s focus on planting trees quicker at the lower densities. Adopting exotic forest planting techniques has planters do away with the wasteful and cumbersome plastic pots native seedlings typically come in. 

Instead, planting teams are able to work with quality forestry-grade propagated mānuka and kānuka seedlings that come in large lots that are easily helicoptered in volume to remoter sites.

A report funded by Our Land and Water outlines a cheaper, more effective method of re-populating land into ngahere, or native bush.

Planting at a lower density does, however,, require good, integrated weed and pest management throughout the forest’s life. 

Dewes lamented that regional councils generally tend to stick with the conventional dense plantings, and said there is a need for greater extension and education to spread Tīmata’s benefits to landowners keen to retire land.

Of the 1.0 million hectares of erodible country suitable for replanting, estimates are this includes 130,000ha in Northland and 200,000ha in Hawke’s Bay.  

Erosion rates in northern Hawke’s Bay alone are estimated to be at an average of 10t of soil per hectare per year.

There are plenty of sites highlighted around the country where the Tīmata method has proven to work, including Burke’s own award-winning property in Bay of Plenty.

Dewes said her greatest concern is not Tīmata’s proven efficacy, but the resources needed to see it adopted wholesale across New Zealand to achieve the country’s reforestation aspirations.

“We simply do not have enough forestry crews to do the work, they are in short supply, not unlike shearing gangs. We are going to need massive teams to do this, but where are they going to come from?”

She said there is also a desperate need for a wider discussion, already highlighted by Parliamentary Commissioner for the Environment Simon Upton, about NZ’s commitment to better pest control and management if native reforestation is to really succeed.

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