A Million Trees is the perfect group to get behind this Arbor Day and really any day that you feel like making this city a better place. They have one goal:
To plant and care for one million new trees across the City's five boroughs over the next decade. By planting one million trees, New York City can increase its urban forest—our most valuable environmental asset made up of street trees, park trees, and trees on public, private and commercial land—by an astounding 20%, while achieving the many quality-of-life benefits that come with planting trees.
There's also an LA branch.