The fallout from Cyclone Gabrielle will be massive and long-term. Amid the clean-up, we can expect increased scrutiny on the forestry industry and its practises, with slash being one of several key issues.

What is forestry slash? 

Slash is a waste product from commercial forestry: it is detritus – anything from small branches to whole trees – from logged trees left behind on the land when other wood is harvested. Wood takes a long time to biodegrade, so slash can remain on patches of land for years. 

Why is it such an issue right now? 

When there is high water levels or flooding slash can be a massive problem. The debris is picked up by moving water and can choke rivers, sometimes damming them and causing more flooding when the dam breaks. When rivers full of slash break their banks, land, including farmland, may be covered in the wood, which requires an enormous clean-up effort. The weight of the debris also means that slash can damage infrastructure like fences, gates and roads.

Much of this debris is eventually deposited on beaches, where it’s difficult to remove and can impact the local tourism industry. It can also be dangerous: earlier this summer, a child in Gisborne died after being injured by a log floating in the water. The beach was filled with wood after the calamitous impact of ex-Cyclone Hale. 

Areas of intense commercial forestry are often filled with slash. Fast-growing exotic trees like pinus radiata, commonly used in commercial forestry in Aotearoa and farmed as a monoculture may damage the landscape, especially after clear-cutting leaves behind slash.

Where is it worst? 

Areas of the North Island where forestry takes place, including Coromandel, Wairarapa and Hawke’s Bay, have had issues with slash. And Tairāwhiti has had problems with slash for years, since before the devastating Cyclone Bola in 1988. Further up the East Coast heavy rain in 2017 and 2018 caused forestry offcuts to repeatedly flood Tolaga Bay. Following a $10m cleanup in the affected area, the forestry industry said it would change some of its practices; one of the companies involved was later fined for poor management of forestry sites.

Ex-Cyclone Hale in January 2023 also caused extensive damage from slash across Tairāwhiti. Locals called for change; the debris issue was a saddening “legacy we’re going to pass on to our kids,” Hera Ngata-Gibson told the Gisborne Herald. 

Forestry is a key part of many local economies in Aotearoa, and slash isn’t the only environmental problem caused by the industry. The high amount of sediment created by flooding in cleared forestry sites has a damaging effect, particularly in marine environments. And the impact is huge: satellite images from almost five years ago show the extent of earth exposed by the forest industry in the Tolaga Bay area.

For people living near the East Cape, the slash influx following Cyclone Gabrielle means another arduous cleanup, only a month after they were hit by Cyclone Hale. “Every facet of our home has been hit with the deepest amount of sediment and logging that you could possibly imagine and it just went for hours,” farmer Bridget Parker told RNZ on Tuesday morning. With her husband and son, Parker has been trying clear a route through the debris; much of their land is currently inaccessible, and their kiwifruit orchards have been overwhelmed by maize and sediment. “We’re all struggling to find out why these logs are continuing to be allowed in these forestry estates and strewn over our beautiful properties. It’s just beyond us,” she said, sounding incredibly tired and frustrated.

Rural and isolated communities are particularly vulnerable to the infrastructure damage caused by forestry debris and flooding, and the extensive, expensive cleanups that follow. 

Has Cyclone Gabrielle exacerbated this issue? 

With communications with Tairāwhiti limited, it’s still unclear how much slash has impacted the region after the most recent cyclone. However, in a report from Monday, Nori Parata, Civil Defence deputy officer and Tolaga Bay Area School principal, told Stuff: “it’s quite soul-destroying watching the live webcam of the Hikuwai River and seeing all that wood heading our way.” The high winds created by the cyclone have likely added to the volume of slash since then by breaking branches and moving debris. Woody debris has closed or damaged a number of bridges in the region. 

In two statements on Saturday and Monday, Eastland Wood Council, an association for forestry activities in the Tairāwhiti region, said that they were monitoring Cyclone Gabrielle closely. “Since slash issues in 2018, the industry has changed its practices to mitigate the risks of woody debris flowing. This includes reducing harvest residues left on sites, increasing road drainage structures, lifting construction of infrastructure to a much higher standard to reduce the risk of failure and increasing streamside buffers and re-vegetation with native species to protect waterways.

“However, we cannot control some factors such as the weather and the highly erodible soils we work with in Tairāwhiti,” said chief executive Philip Hope. Contractors had been working to clear debris where possible all weekend. 

Prime minister Chris Hipkins and minister for emergency management Kieran McNulty both acknowledged in press conferences on Tuesday that management of slash may need to be changed following the cyclone.

What are the solutions? 

Following Cyclone Hale, Tairāwhiti locals created a petition calling for an independent inquiry into land use in Tairāwhiti, which was supported by Gisborne councillors, while minister of forestry Stuart Nash suggested that stakeholders meet for a discussion. Members of the forestry industry, including Eastland Wood, said they were supportive of a review but the petitioners insisted the inquiry had to go beyond this, because the “local industry and regulator just reviewing themselves is unacceptable”. 

Keeping debris away from waterways with riparian planting, strengthened roads for debris removal, increasing the volume of native trees and moving slash off site can help reduce the problem of slash, Grant Dodson, the president of the New Zealand Forest Owners Association, told RNZ in January; he said it was possible for slash to be used by the industry as mulch or a source of bioenergy. 

But Gary Taylor, chief executive of the Environmental Defence Society said fixing the problem means going beyond this. In an opinion piece published on Newsroom, he called for a complete review of the rules governing the industry, suggesting new laws include limiting clear felling in favour of continuous cover and incentivising planting permanent native forests on eroded, cleared land.