Almost 50 years ago singer Joni Mitchell wrote a song lamenting that "they paved paradise and put up a parking lot." Since then, we've torn out trees to build roads, to build housing subdivisions, and, yes, to build parking lots.
A developer once told me that land without something built on it was "wasted land that's not contributing anything."
Back then, tearing out trees was simply making room for "progress."
That attitude is pretty well gone now, but we still need to persuade people to plant more trees. Better yet, we need to start thinking of urban trees as part of the urban infrastructure.
What's the value of urban trees?
A recent study published in the journal Ecological Modelling reported that in the 10 megacities studied, tree-based ecosystem benefits had a median annual value of US$505 million. That's about US$1.2 million per square kilometre of trees. From another perspective, the value was US$35 per capita for the average megacity resident.
The study's lead author, Theodore Endreny, of the College of Environmental Science and Forestry, in Syracuse, N.Y, says the value of trees' services could easily be doubled by simply planting more trees.
"Megacities can increase these benefits on average by 85 per cent," he says. "If trees were to be established throughout their potential cover area, they would serve to filter air and water pollutants and reduce building energy use, and improve human well-being while providing habitat and resources for other species in the urban area."
The megacities studied were Beijing, Buenos Aires, Cairo, Istanbul, London, Los Angeles, Mexico City, Moscow, Mumbai and Tokyo.
The researchers estimated the benefits of tree cover in reducing air pollution, stormwater runoff, energy costs associated with heating and cooling buildings, and carbon emissions.
"Trees have direct and indirect benefits for cooling buildings and reducing human suffering during heat waves," Endreny says.
"The direct benefit is shade which keeps the urban area cooler, and the indirect benefit is transpiration of stormwater which turns hot air into cooler air."
Most people are unaware of the services provided by urban trees. These include removal of airborne particulate matter by capturing it on leaves, lower cooling costs in the winter and lower heating costs in the summer. They also sequester carbon.
All this fits in nicely with another recent study, this one by The Nature Conservancy.
That study, called Funding Trees for Health, notes that "as city populations grow, urban trees cannot be viewed as a luxury. Trees are an essential component of a livable community and core strategy for improving public health."
It then goes on to make a business case for urban trees.
The study covers some of the same ground as the megacities study, but its primary concern is urban trees in the United States.
It cites, among others, a study in California showing that for every one dollar spent on tree planting and maintenance, urban trees deliver $5.82 in benefits.
It says that street trees can have "phenomenal" rates of return, "exceeding in many cases the return on investment typical in many for-profit business sectors."
Yet another study of 10 U.S. cities found that urban trees remove enough particulate matter to reduce annual health impacts significantly, with reductions of $1.1 million (in Syracuse) to $60.1 million (in New York City).
Most American cities spend less than one-third of one per cent of their budget on tree planting and maintenance. As a result, cities are losing four million trees per year.
A lot of attention has been paid recently to the link between trees and public health, a link that is both robust and economically significant. That's why I'll return to the subject next week.
In the meantime, readers wishing to see the Nature Conservancy report can download a free copy at http://bit.ly/2hyrpvf
Korky Koroluk is an Ottawa-based freelance writer. Send comments to firstname.lastname@example.org.