First 50 hectares of mānuka planted on erosion-prone land behind Mārahau, near Nelson

The first 50 hectares of mānuka seedlings have taken well on erosion-prone land behind Mārahau, about 64km north-west of Nelson.

Planted at a density of 1000 stems per hectare over the winter of 2019, the mānuka trees are permanent replacements for commercial radiata pine on land in the Mārahau catchment that is at high risk of slips and erosion.

They are the first 50,000 seedlings of 114,000 mānuka trees that are to be planted in the area over four years – a programme of work known as the Mārahau-Otūwhero mānuka reversion project.

Mayor Tim King said it was good the initial plantings had taken well. It was a case now of finishing the planting, waiting and monitoring how effective the switch was from pine to mānuka.

“The key thing is what happens when it rains and particularly when it rains heavily,” King said.

READ MORE:
* Erosion-prone land behind Mārahau to be switched from pine to native forest
* Big budget announced to combat erosion
* Sedimentation degrading Kaiteriteri, Otūwhero estuaries
* Building ban and stronger forestry rules possible for slip-prone Tasman catchments

Intense rain that arrived with ex-Tropical Cyclone Gita in February 2018 caused multiple slips across Tasman district including on the forestry land behind Mārahau, which was returned to iwi in 2014 as part of a Treaty settlement.

The replanting project has been designed to help mitigate the effect of adverse weather in areas with highly erodible soils known as Separation Point granite, which is a strip of granitic bedrock about 10km wide that extends more than 100km south, from Separation Point in Abel Tasman National Park to Mt Murchison. It is deeply weathered at the surface, can be several metres deep and readily breaks down to form a coarse sand. It is sand derived from these rocks that form the golden beaches of Abel Tasman National Park.

A partnership between iwi and the council is driving the replanting in the Mārahau catchment in an effort to manage sediment and land disturbance. Ngāti Tama ki Te Waipounamu Trust, Ngāti Rārua Settlement Trust and the council attracted $144,000 from the Ministry for Primary Industries’ Hill Country Erosion Fund as a grant for the project.

That MPI grant is to be topped up by $140,000 each from the council and iwi. Tasman Forest Management is managing the planting operation, from mānuka procurement through to site preparation, planting, release spraying, fertilising and wilding pine pulling.

King said the information learnt from the project, which he described as a trial, would be shared. Replanting mānuka instead of pine could be “another tool in the toolbox” for landowners and forestry companies to manage erosion. They might also use other tools such as harvesting methods and harvesting schedules to meet the requirements of the National Environmental Standards for Plantation Forestry and the council rules.

There was “quite a large area” of plantation forestry on Separation Point granite, King said.

Another 22ha of the land in the Mārahau catchment is due to be replanted in mānuka over winter 2020 as part of the project, followed by 32ha during winter 2021 and the final 10ha over winter 2022.

A council staff report says the ultimate aim of the project is to assist in building resilient forestry systems for highly erodible land.