I think it’s a very good idea, and I can’t see any obvious disadvantages except, perhaps, the loss of posting and comment history from the currently existing communities.
Maybe also consider merging !foodporn@lemmy.world ? That one seems to be quite general too, and posts often become discussions of how to cook the showcased dish (plus I really dislike the name of the community).
Spinney is a nice word for a smallish gathering of trees, alongside copse, coppice, etc. I’m not aware of a term for one specifically in an open field, though.