Wednesday, December 6, 2023

Forest slash levels low in Hawke’s Bay debris

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Particular forestry debris ‘unfairly’ blamed for most of the downstream damage after Cyclone Gabrielle.
Cut pine or ‘slash’ formed only a single digit percentage of the forest waste surveyed in the Hawke’s Bay region.
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Despite the frequent use of the term, forest slash has proven to be a minimal part of the waste wood that was left in Cyclone Gabrielle’s wake throughout the Hawke’s Bay region.

A research report commissioned by Hawke’s Bay Regional Council found pine comprised the majority of the timber type strewn across the region’s water courses. Overall, on average pine comprised 53%  of the wood debris across the 15 sites, and was up to 90% in some spots.

The researchers split the pine into debris type to better identify its source, defining the pine as “pine pieces”, “long residence pine”, “windthrow pine” and “cut pine” (slash).

They found it was predominately present as “pine pieces” in the 15 sites analysed. Pine pieces are defined as pieces of timber that have no evidence of cuts on them to indicate they may have recently been harvested. 

On average they comprised 37% of the debris total, trailed by long residence pine forming only 7%, and cut pieces from slash sites averaging only 3%. The maximum contribution of cut pine was 9% at one site.

With pine averaging just over half the debris source, the other species identified were poplar, willow and “other” species.

The sites identified with the greatest proportion of pine in debris included the Wairoa and Waikare river mouths, with 90% pine in the debris. 

The areas with the lightest amount of pine were sites at Tutaekuri and Ngaruroro at 5% and 30% respectively.

Data released by the Gisborne District Council in late February found that pine constituted about 70% of the debris on beaches around the city, and was as high as 80% in the Ūawa-Tolaga Bay district.

However, the figures gathered by Gisborne District Council have been challenged by the Forest Owners Association for the methodology used.

Association spokesman Don Carson said the group feels the Hawke’s Bay research is statistically sound, however, and accepts the findings.

“But what it also highlights is that for the past several months the finger has been unfairly pointed at forestry practices around slash management, and in the Hawke’s Bay at least this is not well founded.

“Trying to address slash in this region is creating a solution for a problem that does not exist.”

He said given that the ministerial inquiry into forestry management is focusing only on the Te Tairāwhiti region down to Wairoa, it begs the question how Hawke’s Bay’s unique set of circumstances will be reviewed.

“You have two very different environments with different soils in both and a huge flood plain with high value crops in Hawke’s Bay that differs from Gisborne with its greater reliance upon hill country farming and forestry.”
The Hawke’s Bay report recommends identifying the amount of land in each catchment with the potential to contribute to woody debris. It also acknowledges that while cut pine or slash volumes were recorded as low, a review of slash trap installation, performance and maintenance should be undertaken in the region.

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