The report from the Environmental Protection Authority - intended to help the government plan for the predicted population explosion across Perth and Peel by 2050 - found that more than 70 per cent of Swan Coastal Plain vegetation had been cleared and the resulting urban heat island effect, along with climate change, was impacting air quality and public health. How your area scores on the tree front. Credit:University of Technology, Sydney But it also said the city could grow without these factors worsening, providing it counteracted the urban heat island effect through methods, including tree preservation. A 2014 University of Technology Sydney report on Australia's urban tree canopy ranked local governments against each other, showing Perth's least-treed was Belmont, with less than 10 per cent cover. Fremantle and Canning were next-worst with just over 10 per cent each.

Best were Kalamunda, Mundaring and Swan, but the western suburbs also scored highly. Mr Cornish said that since he was elected, members of the public had succeeded in getting public trees "topped and lopped" for issues such as magpies carolling in them at night and the trees blocking sunlight from solar panels, despite the trees pre-dating the panels. A financial planner by trade, he said environmental arguments had failed to change the culture and people needed to hear about the money. He referenced a 2013 research paper in the Elsevier Press Landscape and Urban Planning journal on the effect of street trees on Perth property values, in which researchers analysed data on 23 Perth suburbs and found that broad-leaved trees (that is, not palm trees) on verges increased median property prices by nearly $17,000. He said street trees also protected bitumen with their shade, extending its life, and improved "walkability", which in turn improved business trade.

He said it was possible to place a dollar value on trees, giving the example of the Burnley Method, established in the 1980s for matters relating to compensation, litigation, insurance and policy making. The method factored in tree size, life expectancy, form, vigour and location. Alarmed by Bayswater's ranking as Perth's fourth-worst in terms of tree canopy, he is campaigning at both a local and state government level for that to become common practice. "Everyone understands dollars," he said. "Any person responsible for decision making about the destruction of a tree should have included in the information given to them the financial value of that tree. "A councillor would have to think twice about cutting down five trees together worth $100,000 – it's a bit more in-your-face."

Late last year he moved a motion in council that in order to mitigate the urban heat island effect and provide other benefits, that city officers investigate options to increase the city's tree canopy coverage from the current 13.2 per cent to 20 per cent by 2025. City officers are now preparing an Urban Forest Strategy to that effect. But he said changes had already started. From first contact, developers were now being informed that designs must not impact street trees and this had resulted in a dramatic decrease in applications to cut these down. "If a public tree does have to be cut down for any reason, we plant two," he said.

"We are also carrying out mass plantings in the city and the routine pruning of street trees that don't actually need it, which in itself costs money, has stopped. "The officers are embracing it – it's as though they were just waiting for the gun to be fired." Mr Cornish has written to Local Government minister Tony Simpson and Environment minister Albert Jacob urging them to consider laws that any proposals involving the destruction of urban trees should include the monetary value of those trees. Curtin University school of public health director Helen Brown, who has led research into the interactions between health, heat and climate change, said urban heat islands resulted from three factors. First, they had a greater concentration of built materials – bricks, buildings, roads and pavements - all of which tended to trap heat.

Second, people, buildings, cars, air conditioners and other machinery all produced waste heat. Third, the usual consequence of building infrastructure was also to simultaneously remove trees, and trees not only shaded buildings, helping prevent heat trapping, but also carried out the process of "evapotranspiration" – like evaporative airconditioners, they actively cooled the environment. Dr Brown said in Scotland or Russia, urban heat islands would have little importance. But extreme heat was an issue for Perth and heat waves were considered significant natural hazards in Australia, she said, pointing out that the heatwaves after Victoria's Black Saturday bushfires killed more people than the fires themselves. Groups such as the elderly, the very young, outdoor workers were vulnerable to heat stroke and other heat-related illnesses, but so were the poor and the homeless – people without the capacity to choose well-designed housing, or get airconditioning.

Organisations including the WA Council of Social Services and Red Cross were already looking into the potential effects of this development on communities. "The projections are that as a result of climate change, the frequency and severity of heatwaves will increase, the number of days over 35 degrees will increase and we're going to see more temperatures that are record-breaking," she said. "The concern with the urban heat island effect is that it will potentially make that even worse. [The] urban heat island effect is essentially like a local climate change." But, Dr Brown said, though planning decisions in Perth might not have much effect on global climate change, they had complete power over the urban heat island effect. "In a way, [addressing this is] one of the best ways to approach adaptation to climate change," she said.

Dr Brown runs private and public sector workshops on how planners and developers could increase housing density without increasing the urban heat island effects. "Sometimes people see this argument as an argument against higher density and it's not," she said. "It's usually a two-pronged approach; the built materials and also retaining vegetation. "When you go around and you have a look at development, it doesn't seem to happen that way very often." "With infill, quite often what they'll do is they will remove the house and every single thing on the block and they are allowed ... there is no regulation governing existing trees, particularly mature trees.

"We need to have some type of regulation on this and one of the ways of approaching it is to start putting value on trees." Spokespeople for Ministers Simpson and Jacob said Mr Cornish's letters had been received and responded to but neither Minister was contemplating legislation to require financial valuations on trees as part of development applications. Follow WAtoday on Twitter