Forest is the primary biome. The islands with the Forest biome are Forest Island, Forest Village, Plains, Pirate Village and Dungeon Entrance.
You can get Spruce Saplings, Oak Saplings and Blueberry bushes, as well as Sunflowers and Firemone, here. Cows, Sheep and Rabbits can also be found in the Forest biome. Zombies and Zombie Archers spawn at night.
The Plains have fewer trees than the Forest Island.
Each Forest Village has an entrance to the Forest Caves.
The Pirate Captain can be found here. The Pirate Recruits will attack you as soon as you get close to their village. If you move significantly away from the village, the pirates will not chase you. The pirates and the Pirate Captain do not respawn after being killed.
The Dungeon Entrance is guarded by either Vampires or Void Apprentices. They do not respawn after being killed.