Cool sandbox game :D I got a Kraken, Mummy, Goat, Giant, Kangaroo, Crab, Koala, and of course, Buffalo. Lots of Buffalo. Neat little game, reminds me of those Doodle God games where you have all the elements, but you need to figure out a way to combine them. I'm a little annoyed that I couldn't fill the entire island with grass (the grass tiles disappeared too fast).
Maybe if you added onto the game, you could have rain make forests on grass. Or when lake tiles are surrounded by lake, they turn into ocean and can spawn fish and stuff. Just some ideas :)
Edit: Saw the screenshots for the game and saw forests... I guess you're already one step ahead of me!