The Deciduous Forest, or Birchnut Forest, is a Biome found in the Reign of Giants DLC. It is very similar to the regular Forest biome with the exception that all the trees are Birchnut Trees, which produce Birchnuts, and the ground is covered with Deciduous Turfs. The Deciduous Forest also exclusively spawns Glommer Statues, which spawn Glommers, and Hollow Stumps, inhabited by Catcoons. Catcoons spawn more often here than in other biomes due to the number of Hollow Stumps.
Fireflies are more abundant in the Deciduous Forest than in any other biome, so much so that any section of the forest will likely have two or more patches.
This biome is a great source of Mushrooms. In fact, all mushrooms (Red, Blue, and Green) can grow here, exclusively making this biome the only surface biome that is capable of having all three types.
In Don't Starve Together, the Loot Stash can spawn in the Deciduous Forest during Winter, although it may spawn in the Mosaic biome as well. It despawns as soon as Winter ends. In some worlds, Twiggy Trees and Juicy Berry Bushes replace Saplings and Berry Bushes respectively, including in the Deciduous Forest. No-Eyed Deer also spawn in this biome.
A Deciduous Forest as seen on the Map.