From PathfinderWiki

The Berm is a miles-long stand of semi-sentient trees that defend Kyonin's northern border with Razmiran along the Glass River. Nominally part of the northern Fierani Forest, and capable of independent movement, the Berm is greatly feared by the soldiers and agents of Razmir, who have never seen how it travels from place to place. Those who enter the forest are rarely seen again and their blood-soaked clothing is sometimes found downriver. The Berm's sudden morning appearance on what had been gentle plains the day before, is enough to give the stoutest Razmiri pause.12


For the last 50 years, the Razmiri have been hungrily eyeing the fertile plains and lush forests of northern Kyonin. During the middle 47th century AR, they sent raiding parties south in order to annex land in the name of their god. To protect the border, a group of elven druids worked together with the Fierani arboreals to create the Berm in 4683 AR, and they have been mutely standing guard ever since.1