According to Shaping Tomorrow, Melbourne has set a target for increasing canopy cover from 22% to 40% by 2040, and within that target improving quality and diversity of plants and species. Green roofs are being incorporated into more and more developments. In the process, according to research done elsewhere in the world, they will save lives, carbon and millions of dollars.
When a pest which killed an estimated 100 million trees across 15 states in north western America, there were 6.8 additional deaths from respiratory diseases and 16.7 additional deaths from cardiovascular problems per 100,000 adults: a total of 21,000 deaths. That is because trees help absorb air pollution by up to 30%. In one study of 10 US cities, trees removed between 4.7 and 64.5 tonnes tonnes of particulate matter, with annual economic benefits of between $142,000 per tonne in Atlanta and $1.6 million per tonne in New York. The value of benefits was predominantly related to less illness / fewer deaths.
An important tool in quantifying the economic value of trees is iTree, which was originally developed in 2006 and is in its 5th iteration, with new capabilities being added each wave. In Pittsburgh, they established that their street trees – in pavements and on streets only – provided $2.4 million worth of eco-system services – such as shade, reduced temperature, air quality, aesthetics. That represented a return of $3 for every dollar spent on tree planting and maintenance. A later study, including the cities full tree population, valued their services at between $10 and $13 million per year.
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