A civilization flourishes when people plant trees under which they will never sit.
If someone has enough money to donate to the poor, hungry, or homeless, they most likely will never be in that situation. We should be green but only the next generations will relax under that "tree." If we give without asking for anything in return, you give up the "shade" so they can enjoy it and then pass it on.
[What kind of society would we have if everyone followed this proverb?]
We would have a giving society today, with a better world for the next generation.