These individuals, who create their own legacy, have proved to be powerful advocates for urban greening, typified by Michael Bloomberg in New York City (www.nyc.gov) and Richard Daley in Chicago (www.cityofchicago.org) slugging it out to see who will get a million trees planted first.
Raw political instinct told them that people like trees - and happy people equals votes. This is not hard to work out, but it takes leadership and vision to put the principle into practice.
In contrast, UK Government tree policy is a shambles, staggering from one crisis to the next, blunder after blunder, stumbling on into a hot and uncomfortable future. With 27 degsC highs in mid April, climate change is starting to bite and Londoners are glimpsing the peril to come.
The inevitable prolonged repetition of these conditions in midsummer will see the weak and vulnerable dying in their thousands. It may be a few years away yet, but such events will come, along with the questions: What could have been done? How much would it have cost? Why didn't our leaders see it coming?
Well, one has. Although not on the US-scale, the mayor of London has nonetheless taken the first steps towards a legacy that could be green and see him remembered as the first leader to take street trees seriously.
In its latest report, Branching Out - The Future for London's Street Trees, the London Assembly environment committee (www.london.gov.uk) has published its assessment of the state of the capital's trees. It reports that the mayor is making progress, but that "while Londoners continue to value their street trees, they face an uncertain future".
The assembly acknowledges the potential of the mayor's new city-greening campaign, "RE:LEAF London", but it also warns that he "needs to support a few vitally-important measures".
The detail is interesting, but the strategic nature of what London is doing is the jewel. Of course, it is not enough and it is probably too late, but it has to be recognised as the vision that the rest of the country has yet to even think about, let alone implement. Well done, London.
Jeremy Barrell is Managing Director of Barrell Tree Consultancy.