I've been working on a datapack that removes all naturally generated trees with the intention of using/releasing it as a way to add an extra challenge on top of standard hardcore survival worlds. As a part of the datapack, I wanted to be sure that saplings wouldn't drop from leaves, for two reasons:

1. Because the datapack removes trees in small portions to avoid lag (instead of nuking them all at once), there are instances where the leaves left floating in the air decay before they're hit by the next pass of the datapack. It would be nice to ensure that even if sticks and apples still drop, that saplings don't, as it removes a decent part of the challenge if you're just given free saplings.

2. Because a single tree will often provide more saplings than was originally required to plant it, once the player finds even one sapling, the challenge becomes entirely trivial. Ensuring that trees can't drop saplings would make every sapling you find a precious resource.

I'd prefer a solution that still allows players to drop saplings on the ground without them being deleted. I'm open to suggestions that require a bit of complex coding to accomplish, if necessary.