English: The moss on a tree trunk is NOT often an indicator of direction. The above statement is a common urban mistake and you are just as likely to get lost as find you direction.

In regions with a prevailing wind direction moss may grow better on the side less exposed to the wind or it may grow better on the opposite side as the wind delivers more rain to this side.

In the northern hemisphere the northern side of the trunk (left picture) is more shadowy and therefore: damp. Dampness favours the growth of mosses. The southern side of the same trunk (right) is sunnier and drier and has less moss.