Researchers from the University of Exeter and the University of Trnava in Slovakia writing in the April 2015 edition of Landscape and Urban Planning have released more evidence to show that there is a strong association between urban green space and mental health and wellbeing, and that street trees specifically are critical in keeping us happy.

The team of researchers looked at the levels of anti-depressent prescriptions across a range of London boroughs and then matched those to the density of trees in that area. After correcting for other factors such as income levels, they found a direct link between the number of trees in a given area and the number of anti-depressents prescribed by local GPs.

The places with higher tree densities had lower prescription rates: For every additional tree per sq km of street, the researchers found 1.38 fewer prescriptions in the population.

In their study they found an average of 40 trees per sq km across the boroughs of London, with antidepressant prescriptions ranging from about 358 to 578 per 1,000 people, but the places with higher tree densities had lower prescription rates: For every additional tree per sq km of street, the researchers found 1.38 fewer prescriptions in the population.

The study follows another green space study from the Exeter team in 2011 which examined 18 years of data covering almost 10,000 people living in urban areas. Through annual surveys they found that as green space increased within a 2.5-mile radius of where someone lived, overall well-being increased proportionally. Specifically, life satisfaction increased by two per cent and psychological distress decreased by four per cent.

So are well served in Greater Manchester with a happy-making urban canopy?

The Greater Manchester Tree Audit, which was co-ordinated by Red Rose Forest in 2011, estimates that there are 12 million trees in Greater Manchester covering on average 16 per cent of our land area on average, just above the national average. The tree-cover winner of the AGMA boroughs is Stockport with an impressive 25 per cent cover while Oldham could do better with just 9.2 per cent cover.

An earlier audit by Red Rose Forest, however, shows that there are big discrepencies between different electoral wards and that particularly when council-run parks are taken out of the mix, some areas are very poorly served in terms of street trees: Manchester city centre for example, as well as Harpurhey and Moss Side all have tree cover levels at around just five per cent.

If tree cover levels are patchy between different parts of the city region there’s also the very real concern of tree disease taking a significant toll on our urban forest. Around 20 per cent of the trees audited across Greater Manchester are ash, for example, and as Ash Dieback continues to spread across the country we could have around two million trees at risk if rates of tree mortality follow those seen overseas.

So with fresh evidence showing street trees giving a boost to mental health, and with a host of studies showing that they provide urban cooling in the face of climate change, a lift to property prices and can be helpful in reducing flood risk, that old adage remains true: the best time to plant a tree was 20 years ago; the next best time is today.