For those interested in garden design:
A garden without trees scarcely deserves to be called a garden.
- Henry Ellacombe
For those thinking more in economic terms:
Someone's sitting in the shade today because someone planted a tree a long time ago.
- Warren Buffett
And for those who just like general wisdom:
Character is like a tree and reputation like a shadow. The shadow is what we think of it; the tree is the real thing.
- Abraham Lincoln