Adding 10 more trees per average city block has the effect of making residents feel seven years younger or $10,000 richer annually, says research published in the Scientific Reports journal on Thursday.

The study, which surveyed about 31,000 residents of Toronto, Canada, found that people who lived in areas with higher street tree density had a far better perception of their own health.

Residents also reported fewer conditions of obesity and hypertension compared with residents living in areas with fewer trees.

"We basically found that if you put 10 more trees in a city block on average, people feel that they're healthier, and it's also improving their objective cardio-metabolic health. Those extra 10 trees are equivalent to increasing their income by $10,000 or moving them to a neighbourhood with a median income $10,000 higher than the one they live in," said University of Adelaide study co-author Lyle Palmer.

He said the results could be used to inform city planning in Australia and the kinds of neighbourhoods needed to improve the health outcomes of Australians.

The study said it was unclear why exactly trees had such an effect on people, although the effect itself was "clearly very strong".

And Professor Palmer said the cost of planting and maintaining street trees would be far outweighed by the health benefits they provide.

"The cost would be minimal versus treating people in emergency, treating people in hospitals, which is clearly extensive. It's hard to know but thinking about it in a commonsense sort of way, it must be highly cost-effective compared with any other form of intervention," he said.

The study was controlled for other factors that could influence health, such as age and affluence. The benefits of more trees were observed for areas within a five-kilometre radius.

So how does Australia's canopy coverage measure up? A 2014 UTS study analysed the tree canopy cover of every urban local government area in Australia.

Using 2009 data for Sydney, it found we have one of the lowest canopy covers of the major Australian cities, with just 15 per cent of the city covered. The highest percentages were in Hobart with 59 per cent and Brisbane with 49 per cent.

That study's co-author, Dr Brent Jacobs, said there were limited opportunities for planting trees in the city and the council would need to create green walls and roofs instead.

"Trees are fantastic because they provide shade for anything underneath them and they transpire moisture, they cool the environment down. Green walls and green roofs cool the building underneath them but don't offer shade to the street," he said.

In the suburbs, there were more opportunities for putting trees into verges and private property, Dr Jacobs said.

The City of Sydney council plans to grow the city's total canopy coverage from 15.5 per cent in 2013 to 23.25 per cent by 2030 as part of its Urban Forest Strategy.