This is a cool RTS, fun to play and requires some strategy to achieve the win condition! I noticed a few minor bugs but nothing particularly game breaking, the capital letters in the text prompts were not showing up when I was playing is the most noticeable thing I found. On a second playthrough I think the letters are showing up they are just not moving with my view but are maybe locked to a global point on the map. Also the green mottled texture that starts as the UI background would migrate onto the map and get stuck there for me, occasionally blocking my view of the map and making it difficult to play.
I was able to destroy the mill however by building on the right side of the map where the texture wasn't blocking any of the view and I had a lot of fun playing. I liked building up the oak walls and positioning the pine tree towers in protected places. I think this could really be expanded out into pretty intense experience with more challenging lumberjack buffs, possibly multiple saw mills around the larger map/maps, and a few more trees with different costs and effects.
I did run into some minor frustration with the pathfinding, but I was able to get around it by being very specific with the move command instructing the wisps where to go very deliberately, they seemed to have some trouble going long distances without getting stuck but the move command worked well as long as there was a direct route to where they were going. Maybe something to address down the road though.
I could see putting some hours in on this game once it is expanded out a little more though, the framework is definitely solid for a fun game. Oh and I love the story as well, I would much rather be a tree fighting the lumberjacks than play as the lumberjacks trying to kill all the trees. I really enjoyed playing from natures perspective.