A tree protection group is calling on Tūpuna Maunga Authority to shelve permanently its plans to rid Tāmaki Makaurau Auckland’s maunga (volcanic cones) of around 2500 exotic trees, saying it would be irresponsible to proceed in the light of severe slip damage recently suffered on several maunga.

The Ōwairaka slip’s progress was stopped by a group of mostly exotic trees, all of which have since been felled. The slip started just below the stumps of trees that were removed many years ago.

Photo: Anna Radford

Ōwairaka Mt Albert, Maungakiekie One Tree Hill and Ōhinerau Mt Hobson all suffered significant slips during the 27 January deluge. Tellingly, all slips occurred on steep bare ground; many would have been even worse had it not been for nearby trees restricting their flow. Ironically, mostly non-native trees prevented further slip damage.

Honour the Maunga spokesperson Anna Radford says mature trees are well known to absorb massive amounts of water and to stabilise soils, as graphically evidenced on those three maunga.

Tūpuna Maunga Authority wants to rid the city’s maunga of around 2500 non-native trees and plant mostly grasses, flaxes and shrubs in their place. Most of these small plantings will be on lower slopes, with the steep upper slopes to be left largely bare.

“The recent floods have dramatically demonstrated the dangerous consequences arising from Auckland’s inadequate stormwater infrastructure.

“Imagine how much extra run-off there will be around all of the maunga if 2500 mature climate managing trees are removed, not to mention the increased soil stabilisation issues that could threaten surrounding homes and properties as was recently seen at Ōwairaka.

Furthermore, non-notified resource consents have been issued for ridding Puketāpapa Mt Roskill, Ōtāhuhu Mt Richmond and Te Tātua a Riukiuta Big King of their exotic trees. None of those consents suggest that either Tūpuna Maunga Authority or Auckland Council have considered questions of stability, hydrology or stormwater runoff issues associated with mass-felling trees on those maunga.

“The Climate Emergency is wreaking havoc and further severe storms are forecast. Mass felling healthy mature trees just because they are not native is not only irresponsible but potentially dangerous because it will likely cause more slips in future,” she says.

“Felling the trees will create a ticking time bomb. Tūpuna Maunga Authority cannot be allowed to proceed with destructive plans put local communities and neighbouring properties at risk.

Ms Radford notes the Authority has said one of the reasons it wants to fell the exotic trees is to protect archaeological features.

“Many shell middens have been exposed by the One Tree Hill slips in particular and are now being washed away. It is clear that trees protect middens and other archaeological features under and around them from erosion-related harm.

Ms Radford says the Authority’s multi-million tree felling budget would be better invested in maintaining the existing trees and new native plantings, and also heavily planting all steep slopes.

At Ōwairaka, for example, the Authority wants to remove nearly half the mature tree cover. Yet there were no new plantings last year and only a handful the year before. Less than half of the intended 13,000 plantings have gone in there and those that haven’t died are nearly all low-growing species. The Authority’s plans show the steep slopes are to be left unplanted. The same plans also show the plantings are to be well away from where the condemned exotics are.

The number of intended plantings for Ōwairaka sounds impressive until compared with the native revegetation project on Tiritirimatangi Island. Taking size differences into account Ōwairaka would need more than 130,000 plantings of mostly trees to come close.

In addition to planting vastly more trees, Ms Radford encourages the Authority to engage expertise to assess water flows on the maunga. The Ōwairaka slip was caused by torrents of water cascading down a paved access road and shooting off the side at a bend and onto steep open ground below, thus destabilising it.

“A modest investment in adequate guttering and drainage could have helped prevent a situation that has badly damaged the maunga, put homes below at risk and will likely cost millions to remediate.”

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