Origin

The character 森 is built by stacking two simpler tree-related characters. The bottom part, 林, itself means "woods" or "thicket" and is made from two 木 (tree) characters side by side. By adding a third 木 on top, the character shows an even denser collection of trees — moving from "a few trees" to "many trees," which represents a forest. So the visual idea is that more trees piled together make a bigger forest.