Cyclone Gabrielle exposed the risks of forestry slash. New research suggests little has changed

When Cyclone Gabrielle tore through New Zealand’s Tairāwhiti region in 2023, it left behind more than silt and floodwaters.

Rivers were choked with forestry debris, beaches littered with logs, and homes, bridges and farmland buried under tonnes of forestry slash swept down from hillsides.

The scale of the impacts – to infrastructure, livelihoods, ecosystems and to Māori kaitiakitanga (guardianship), and the loss of life – triggered widespread public outrage, with a ministerial inquiry launched soon after.

This led to new rules requiring foresters to better manage harvest debris on steep slopes and reduce the risk of slash being swept away in floods.

Now, the rulebook is being rewritten again, with the government proposing changes to the National Environmental Standards for Commercial Forestry (NES-CF).

This would allow foresters to leave more slash in areas considered lower risk.

Detailed government guidance on managing slash risk is still being developed, in a process which will limit opportunity for public input. At the same time, the reforms curtail councils’ ability to impose tougher restrictions to address the risks of slash.

This all points to an obvious question: have Gabrielle’s lessons for forestry management been learned? Our newly published research suggests that, even before these latest policy changes, they have not.

Little evidence of clear-cut limits

When the ministerial inquiry’s findings were released in May 2023, large clear-cutting – felling all trees in one area at once – was singled out as being a key driver of damage from slash and erosion.

The inquiry recommended limits of 40 hectares per harvest, a five-year “green-up” period between neighbouring sites and no more than 5% of a catchment harvested each year.

The then Labour-led government agreed to these measures, tasking officials to work with Gisborne District Council to review existing resource consents and hasten changes to strengthen the Tairāwhiti Resource Management Plan.

However, no change was made to the NES-CF itself to reduce the size of clear-cutting. It was instead left to regional councils to make more stringent rules to protect downstream communities.

To understand how the inquiry recommendations were implemented in Tairāwhiti, we obtained all Resource Management Act (RMA) consent applications for forestry harvesting, along with council decision documents, from the time of the inquiry through to July 2025.

This period ended just before the coalition government halted most council plan changes in August 2025, ahead of its planned RMA reforms.

In particular, we examined whether forestry operations and council decisions were actively limiting clear-cut size.

This was important as large, contiguous harvested areas – which can span hundreds or even thousands of hectares – are especially prone to erosion and landslides. The risk is highest during the “window of vulnerability” – or the period after mature trees are removed but before new seedlings can stabilise the soil.

This was illustrated when scientists mapped more than 116,000 landslides after Cyclone Gabrielle. They found that steep slopes harvested three to five years earlier experienced significantly more landsliding than other forested areas.

Of the six consent applications and decisions we analysed, only one partially limited the harvest area – and that was because it formed part of a water supply catchment. The remaining five imposed no explicit restrictions and did not require neighbouring areas to green up before harvesting continued.

We also examined whether particularly high-risk areas, such as headwater basins and gully systems, were being excluded from harvesting.

These areas are especially vulnerable, as rainfall funnels into gully systems where many landslides begin. Slash left there can become a hazardous mass of debris during heavy rain.

In Washington State in the United States, such areas have long been recognised as requiring specialist geotechnical oversight and are often excluded from harvesting to maintain slope stability.

In contrast, none of the consent documents we reviewed excluded these high-risk areas in Tairāwhiti, from ridge tops down to riverbanks.

Under current national standards, slash can still be left in these zones if it’s deemed by foresters to be unsafe or impractical to remove.

Why the risk remains

Our findings may provide context for why Gisborne District Council raised concerns about slash volumes and locations in many catchments after an aerial survey in late 2024. The potential for future risks clearly remains a concern.

The council is now seeking an exemption from the government moratorium on council plan changes, allowing it to introduce stricter regulations for steep land areas.

At the same time, the government has declined to fund a transition away from clear-felling in highly erosion-prone areas, leaving the council to regulate on a case-by-case consent basis rather than through a strengthened regional plan.

Changes to the NES-CF have also limited councils’ ability to set stricter protections for freshwater ecosystems, except in the most severely erodible soils.

These are so narrowly defined, that most of the country are excluded from tougher rules to protect freshwater ecosystems from damaging sediment loads after rain.

This also raises questions about whether these changes will reduce the national risk of slash-laden debris flows, as foresters may still clear-fell steep gullies without limits on harvest size.

New Zealand could choose a different path. This could include amending the NZ Emissions Trading Scheme to address legacy plantings on unstable steep land.

But as it stands, and as climate impacts hit home, regional communities and taxpayers are likely to continue bearing the cost.