It’s a British statistic. But one suspects the same figure, more or less, would probably hold globally.
The same article in the Guardian details how building ‘green services’ into cities with parks and tree dramatically increase quality of life (these bullets are reproduced verbatim):
• Asthma rates for children fall 25% for every extra 350 trees per sq km.
• Money [currently earmarked] for a new Heathrow runway could [could be diverted to] provide 22m street trees.
• 1,000 new parks could help avoid 74,000 tonnes of carbon [dioxide emissions] a year.
• For every 5% of tree cover added, water run-off is reduced 2%.
• A treeless street is 5.5C (10F) warmer than a tree-lined one in hot summers.