University of Auckland biology senior lecturer Margaret Stanley says it will take years before new trees provide mental and physical health benefits.

Auckland is a city divided by trees.

Auckland Council data shows across the city urban trees cover on average 18 per cent of land. But depending on the suburb that figure can fluctuate between 8 per cent and 74 per cent.

Māngere, Ōtāhuhu, Ōtara, Papatoetoe, Manurewa and Papakura have an average of 10.5 per cent tree coverage, while central areas like Waitematā, Whau, Albert Eden, Puketāpapa and Ōrākei averaged 19.3 per cent - almost double the amount of trees.

SUPPLIED Auckland councillor Alf Filipaina says future tree planting should happen in poor suburbs.

Across the harbour Upper Harbour, Kaipatiki and Devonport Takapuna averaged 24.6 per cent tree coverage.

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Earlier this month Auckland Council approved a strategic plan to plant trees and bolster coverage, favouring native species and promoting ecological corridors and urban forests on private and public land.

SUPPLIED A map of Auckland's urban tree coverage.

But University of Auckland biology senior lecturer Margaret Stanley said it would take years before new trees would provide the sparsely covered areas with mental and physical health benefits.

The disparity reflects inequity in Auckland, Stanley said.

"People in those low socioeconomic areas are less likely, if they're working two jobs, to worry about tree protection in their neighbourhood and planting trees," Stanley said.

"If you've got reductions on trees it has bad flow on effects for lives of residents in those areas - for their mental and physical well being."

Benefits like carbon storage, canopy shading, reduced air pollution and flooding mitigation came from trees more than eight metres tall, and newly planted trees would take years to reach that height, she said.

It was widely recognised that mental health improved with more trees in urban areas, she said.

A study based in London, which has about 20 per cent of its total land area covered in urban forest, shows less antidepressants were prescribed to patients who live in more leafy suburbs.

In the United States city of Portland, Oregon the city council cut rates for property owners who had large trees on private properties, to recognise the stormwater and pollution benefits, Stanley said.

Auckland Council chief sustainability officer John Mauro said there were a number of factors accounting for different tree coverage, including land ownership, land use, geography and legal protections.

A suburb's age was also a factor. Trees planted close to the city centre in the early days of Auckland's development had now matured, like in Ponsonby, Mauro said.

More recently, some legacy council areas had active tree planting programmes, while others didn't, he said.

According to an Auckland Council report a 20 metre tall tree provided between three and seven times the benefit of a 10 metre tall tree.

Auckland councillor Alf Filipaina, who represented Manukau for 14 years, said he was shocked and never had any idea such a discrepancy between areas existed.

"It's crazy," he said.

South Auckland communities had to be considered first for future planting, he said.