Forest

Particularly dense forests, such as rainforests, have a canopy level above the ground. A creature trying to reach the canopy or travel along it must Climb. Swinging on vines and branches usually requires an Acrobatics or Athletics check. A canopy provides cover, and a thicker one can prevent creatures in the canopy from seeing those on the ground, and vice versa.

While trees are omnipresent in a forest, they typically don't provide cover unless a character uses the Take Cover action. Only larger trees that take up an entire 5-foot square on the map (or more) are big enough to provide cover automatically.