I have been sent a link by Tom Stuart-Smith to an article in Nature which suggests on the basis of a study in Toronto that proximity to trees is worth the equivalent of an extra $10,000 a year in terms of quality of life (what they call the cardio-metabolic condition).   I thought of this research yesterday morning as I walked across Hyde Park to the dentist and felt my spirits lift in the Spring sun (11 trees per city block is worth $20,000):-