Oakwald Forest is a forest west of Adarlan. It is Brannon's forest. Fae used to live there but were believed to be extinct after the king of Adarlan came to rule. At least one Dryad, The Lord of the North, lives there.
In Throne of Glass, Celaena warns the guards taking her from Endovier not to speak ill of the forest because she "wouldn't be surprised if some of the trees remember him." Brannon's forest is described as beautiful and jewel-like, despite the "ravages of conquest."