Okay, I know it was scanlated within the last year, and as said in the topic, it has tree mecha. Though it was greater than 80 pages, it wasn't a one-shot.
The plot is along the lines of forests are encroaching on civilization, destroying all in their path. They have a laboratory and are trying to create children who have the ability to talk to and control the trees in order to halt their advance. The protagonist goes and frees these children, though he dies in the process. A tree revives him, giving him the power to control it. That is the general outline anyway. Ring any bells?

Verdant lord?

Yup, that's it, thanks a ton.