The Friends of the Urban Forest is a non-profit aimed at helping neighborhoods plant more trees in urban city environments. They have all kinds of plantings scheduled throughout differnt districts, and you can volunteer to be a part of the plantings (and learn about trees and the process of planting and care-taking). The only catch is they only schedule plantings after an agreement has been struck to plant 30 trees in a given area (which can be a bit of a task to organize). Still they are doing great work, so be on the look out!
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