White Forest is an area exclusive to Pokémon White. Unlike its Black counterpart, Black City, the area focuses on nature and wild Pokémon, although there are a couple of trainers to battle. It's a tranquil woodland filled with ivy, flowers and cobblestones. Pokémon from regions outside of Unova can be found here.
The population plays an important part in the growth of the forest, the Pokémon residing within it, and items dropped. In order to expand the forest and get more Pokémon and items, you'll need to use the Entralink to visit another player's Black City or White Forest (depending on which version you're playing) and invite characters over. At maximum population (ten characters), White Forest has lush tall trees, abundant grassland, and gleaming water surfaces. When very few people are around, the grassland is sparse, there are fewer, smaller trees and fewer or no water surfaces.
The Mayor's house is here, no matter what the population is. If you visit the Mayor, he'll ask to see a certain Pokémon and hand over a Berry when you show it to him.
The Pokémon available to catch varies depending on which characters are currently in the forest. To catch the Pokémon you want, make sure to invite the right people through the Entralink. All wild Pokémon in the White Forest are at level five.
Characters also have an impact on the dropped items you could find; it's important to note that these items are not guaranteed to be dropped, just that there is a chance of finding them when a certain character is in the forest.