Did tree removal really trigger the Mauao landslide?

Tuesday, 27 January 2026

Last week’s landslide at Mount Maunganui Beachside Holiday Park killed six people and left Tauranga reeling.

On social media, some blamed the tragedy on the removal of large trees from Mauao in 2022-23.

Some people claimed trees were removed by the council with the support of the Mauao Trust to restore native vegetation, protect archaeological sites and phase out exotic species.

Prime Minister Christopher Luxon condemned the claims and called the posts unhelpful.

Experts, however, say it’s more complicated than that.

Can a few trees really hold back a disaster this big?

Dr Andrew Stolte, senior lecturer at the University of Auckland’s department of civil and environmental engineering, says tree roots play a key role in stabilising near-surface soil.

“They help limit erosion and keep shallow slopes intact,” he said.

But did the 2022-23 tree removals trigger last week’s deadly landslide?

“Not really,” said Stolte.

Tree roots may not be deep enough to control a deep, fast-moving slip like this, he said.

“Removing trees could contribute, but can I point my finger and say this caused it? No. It’s not like these trees were removed and the landslide happened immediately. It’s a lot of factors adding up,” he said.

Stolte said the role of extreme weather could be far bigger factor.

“Unprecedented rainfall and susceptible soil conditions are some of the big factors,” he said.

“Water is a big thing that can drive these failures. It temporarily reduces the strength of the soil. It also increases loading on the slope decreasing strength and getting closer to what can be a landslide.”

Emeritus Professor Euan Mason from the University of Canterbury’s School of Forestry agrees.

Mature forest, whether native or exotic, generally reduces landslide risk, which is very well documented in the scientific literature, he said.

“Having trees on sloping land where the soil is prone to erosion is known in the scientific literature to reduce the likelihood of landslides. With grass or recently harvested forests, there would be a greatly enhanced risk of landslide,” Mason said.

However, he says the removal of trees in 2022-23 may not be the sole reason for this tragedy.

“This particular event was caused by a large rainstorm so I wouldn’t say it’s just because of tree removal.

Mason said how closely trees are planted and how old forest canopies were are other important factors in preventing landslides.

Robinson, a senior lecturer at the University of Canterbury’s School of Earth and Environment, told The Post the sheer size and depth of the recent landslide meant trees alone wouldn’t have stopped it.

He said the site has a history of slips, pointing to a major one in 1977, and said heavy rainfall played a key role in the disaster.

“I’m not sure trees would have made any difference,” he said.

What puts Mauao at risk of landslides?

Mauao, a volcanic cone and taonga for local iwi, has a mix of regenerating forest, scrub, shrubland, grazed pasture and scattered patches of native vegetation.

Last week’s landslide struck at the tail end of a weak La Niña system, which typically brings wetter conditions to northern New Zealand, and warm seas added extra moisture leading to unusually heavy downpours.

On Thursday, some areas recorded more than 200mm of rain in 24 hours, well above the thresholds known to trigger landslides.

Experts point to a mix of unprecedented rainfall and the mountain’s history of slope failures as key factors.

A landslide map of Mt Maunganui from 1943 to 2011 shows widespread slope movement across the maunga, highlighting its long record of instability.

Professor Martin Brook of Applied Geology at the University of Auckland, wrote in The Conversation that Mt Maunganui’s slopes carry a long memory of past landslides.

Brook explained a 2024 LiDAR-based digital elevation model strips away vegetation to reveal the bare land highlighting countless landslide features across the slopes.

“Many cluster along the coastal cliffs, but two particularly large ancient landslides can be seen directly above the holiday park,” he wrote.

“These older slips left behind prominent head scarps - steep, crescent-shaped breaks in the hillside - indicating where large volumes of material once detached and flowed downslope onto flatter ground below.”

Brook also pointed out a 2000 geotechnical survey near the campground’s northern toilet block found a 0.7m layer of colluvium - loose debris left by earlier landslides and erosion - buried beneath the surface.

Investigations under way

Tauranga City Council launched an independent review into the events leading up to the landslide.

Council’s emergency operations centre controller Tom McEntyre said all relevant matters relating to the lead-up to this tragic event will be considered as part of the independent review.

“The detailed scope, timeframes and personnel involved in this independent review process are currently being worked through and will be communicated publicly as soon as finalised,” McEntyre said.

Tauranga mayor Mahé Drysdale said the council had cut down trees on Mauao “a few years ago” but he was unsure if that was in the same area as the landslip.

Local iwi Ngāi Te Rangi say they are seeking a thorough investigation into the cause of the slip.

Mauao Trust chair Matemoana McDonald said the trust would refrain from any interviews or public statements until all the loved ones of the grieving families have been recovered.

In 2007, the three principal iwi of Tauranga Moana - Ngāi Te Rangi, Ngāti Ranginui and Ngāti Pūkenga - reclaimed ownership of Mauao from the Crown, returning it to iwi stewardship.