Trees are resource objects placed randomly on meadows. Chopping a tree down requires an axe, and will give 1 wood unless you have the Saw perk which gives you an additional piece of wood when you chop down tree.
Minions with axes will automatically move to trees to chop them down. It will take 3 hits to fell a tree, and an additional 3 chops to make it drop wood. Birds fly away from the tree when it falls.
Like most other resources, trees regrow when clouds rain on their meadows.