Special Feature: The Science of Slash

Special Feature: The Science of Slash
     Story: Jim Childerstone

Forestry, a significant New Zealand land-based industry, has become a media whipping boy  in recent times.

Headlines scream: “Pastoral land covered in exotic pine trees”; “Forest harvest slash inundates farmlands, knocks out bridges, destroys buildings and a threat to life and limb”; and “Pine trees invade iconic landscapes”.

Nightly television images depict devastation due to extreme weather events in the Gisborne/Hawke’s Bay regions with comments mostly from environmental groups.

And so on, regularly featured in the mainstream media.

Our exotic pine plantations have reached the bottom rung in popularity among both urban and many rural dwellers.

Yes, many large corporate plantation forests are overseas-owned by up to 37% but there are also many local investors in large-scale plantations, including small-scale farm foresters and Māori interests.  

And most do follow the rules for sustainability and good management under the Forestry Stewardship Council (FSC) certification scheme.

But people in the industry admit they are still learning – particularly with the advent of climate change.

The main concern among pastoral farmers is the more recent advent of permanent forests or “carbon farming”.

Struggling property owners are entitled to either sell up or plant pine trees, which is proving to be more profitable than running livestock.

But it’s the recent extreme weather events and Cyclone Gabrielle that have really put the heat on forestry.

Post-harvest “slash” is in fact a mix of bin wood (offcuts) reject logs, tree tops and branches sitting on skid sites and landings. But also broken branches left on the cutover areas.  In some areas this residue is processed into biofuels.

DCC City Forests’ Grant Dodson, President of the NZ Forest Owners Association, describes this as a “very sensitive” situation. “Forestry companies are working very hard to help their communities but are also suffering a backlash.”

He warns that there are literally billions of dollars at stake and significant impacts on the community infrastructure – as well as some very large investments from New Zealand and overseas. Forestry exports exceed $7 billion annually. 

The future of the industry has to be carefully managed, he believes, and, “be sensitive to the considerable social hardship and damage done by the cyclones”.

Prior to the cyclone and now doubling down on the research are scientists from both universities and Crown research institutes who are working hard on solutions.

This could mean changes to forest management systems.

The NZ Farm Forestry Association (NZFFA) recommends permanent or continuous cover systems on steep slopes. 

Mixed species of both exotic conifers and indigenous species should be part of the solution.

The University of Canterbury’s Forestry School’s Mark Bloomberg is working on small coupe and select tree harvest in several steeper areas, including in Hawke’s Bay.  

This allows continued timber production for local processors and stabilisation of catchments.

The Forestry School’s Campbell Harvey is working on accumulations of residues on steep slope harvest sites.

Meanwhile, a Scion Research team led by Peter Hall has been researching conversion of forest residues into a variety of products such as liquid fuels and processes for heat energy.

However, a significant percentage of New Zealand’s population remains ignorant of our forestry industry,...

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