I'd leave the rocks because I think they're shatpank for sure. Perhaps a bit of work, but I'd keep them relatively the same. The trees are real good, but I see your point with the flatness a bit. They're still awesome though.
Swamp Pok?mon... Mudkip yes.... Wurmple possibly. Lotad, Gulpin, Surskit, possibly Barboach in the water, Treecko if you're REALLY desperate. That's Hoenn anyway.
I'll have a shot at Kanto too
Weedle, Bellsprout, Poliwag, Grimer possibly, Tangela, maybe Paras, Nidorans if you're in need, and as mad as it sounds I can see Farfetch'd in there too :D