First of all, the woodland creatures must have something like human intelligence in order to stand a chance against a determined human assault. This is because they need to recognize what's at stake, remain focused, and adapt to changes in the invaders' behavior.

Given this, I think that you can get some good inspiration from Tucker's Kobolds.

Tucker's Kobolds came about when a D&D game referee by the name of Tucker took the puniest sentient monster in the game—a monster that starting players can one-hit most of the time—and made use of strategy, battlefield control, etc. to turn it into a holy terror, even to player characters who have gone up against dragons, greater demons, etc.

The essence of their tactics was to allow the players to advance to a certain area of the dungeon, where the attack would begin, and from which every avenue of escape involved running a gauntlet of snipers, traps, hit-and-run attacks, etc., slowly wearing down the party.

First of all, the woodland creatures must have something like human intelligence in order to stand a chance against a determined human assault. This is because they need to recognize what's at stake, remain focused, and adapt to changes in the invaders' behavior.

Given this, I think that you can get some good inspiration from Tucker's Kobolds.

Tucker's Kobolds came about when a D&D game referee by the name of Tucker took the puniest sentient monster in the game—a monster that starting players can one-hit most of the time—and made use of strategy, battlefield control, etc. to turn it into a holy terror, even to player characters who have gone up against dragons, greater demons, etc.

The essence of their tactics was to allow the players to advance to a certain area of the dungeon, where the attack would begin, and from which every avenue of escape involved running a gauntlet of snipers, traps, hit-and-run attacks, etc., slowly wearing down the party.