Every time I cut down a tree it's really annoying to have to wait for all the leaves to break (breaking them myself only helps so much). On multiplayer, forest are slowly destroyed by people not replanting.

A possible solution would be to have samplings plant themselves a fifth of the time upon landing. Sadly nothing's perfect, so this would have some unintended consequences. Chiefly it would allow for fully automatic tree farms, but by stipulating that only natural saplings (saplings falling from decaying leaves) replant themselves they could be kept impractical. Because there isn't a guaranteed replanting, eventually such a system would grind to a halt.

In brief: saplings from decaying leaves falling on dirt plant themselves some of the time.