Rio de Janeiro in Brazil has 2 huge forests in the middle of the city, Tijuca Forest and Pedra Branca Forest, and I am pretty sure Tijuca Forest was hand-planted as a reforestation project in the late 19th century. It is far from difficult to pull off if a country like Brazil could do it, you just have to be willing to give up huge amounts of what could be prime real state areas and be willing do have your city spread out around it. The only bad side is that Rio ended up being too large so some people have to commute for 2/3 hours (one way) every day if they don't live close to central Rio where most jobs are and are not fortunate enough to find jobs close to their neighborhoods. This problem can be solved with a decent metro system which Rio almost lacks.
Talking about trees importance is the height of foolishness of Intelligence people we all know tree and plant gives us life but in the name of developments burnt all tress. Now they want to go back in the name of Urban forests...
