Addendum

Deciduous tree monsters look like warriors in summer and wizards in winter, but they're actually rogues. They're just limited in their opportunities.

Nuances of Fantasy Professions

I bet successful lumberjacks are both educated and canny beyond most, what with all those dryads and forest spirits and whatnot that can cause them trouble. If there are outright tree monsters, the lumberjacks must be powerful champions as well.