Undergrowth
Vines, roots, and short bushes cover much of the ground in a forest. A space covered with light undergrowth costs 2 squares of movement to move into, and it provides concealment. Undergrowth increases the DC of Tumble and Move Silently checks by 2 because the leaves and branches get in the way. Heavy undergrowth costs 4 squares of movement to move into, and it provides concealment with a 30% miss chance (instead of the usual 20%). It increases the DC of Tumble and Move Silently checks by 5. Heavy undergrowth is easy to hide in, granting a +5 circumstance bonus on Hide checks. Running and charging are impossible. Squares with undergrowth are often clustered together. Undergrowth and trees aren’t mutually exclusive; it’s common for a 5-foot square to have both a tree and undergrowth.