Forest Shuffle: Alpine
Buy this firstBGG rates it 8.2 from 3,642 ratings, the highest of the three. It is the expansion used in the online BGA arena play, per a BGG poster, and shuffles straight into the deck.
Needs: Just the base game
Adds: 36 multifunctional cards, including two new tree species, that you shuffle into the base deck; some cards add rule twists.