No man, that's okay - that's why I'm here debating all this stuff. The war/fighting part of the book is the backdrop and I could get away with a "here's just how it is" kind of a treatment, but in my opinion the better the backstory, the better the plot. Your points about fire and the effect of our weapons on trees is well taken.

It would be easy to get into a conversation like the zombie one going on elsewhere, right, where if you apply too much logic the whole thing falls apart. I cannot get away from the fantasy aspect of this story - trees taking on human form. There is no logical explanation for that behavior. But, I'm attempting to make everything else as logical as possible. In this case, the trees themselves are not animated. They can "put out" a human being who is free to move around, under the terms and conditions that apply to any other human being, for a period of about three months before needing to go back to its tree and renew for awhile. Kill the human part, the tree will survive, and could use some of its energy/mass to put out another version of the same person. Kill that version and the next and the tree's going to die, as well.

Kill the tree, and its person has the remainder of its three-month term, maybe a couple extra days, and then it, too dies. Again, these are just the rules - not logic.

So, the US army would be taking on a "human" army, but killing a soldier once doesn't necessarily mean you won't be facing that same soldier again once or twice.

The front story line, the catalyst for the change in the status quo, is that (to be all dramatic): the impossible has happened - a tree/human hybrid has appeared, whose tree and human parts can exist perfectly separately. Lots of different parties, for different reasons, are after this mother and child. The plot is both character and action driven.

Now, I've driven through forests after fire has gone through them where literally everything was dead. I've also toured through redwood forests, however that are inherently made to withstand fire, so it looks like I've got some research to do in that direction. It made sense to me that once the human armies understood where their enemies were coming from, that they would take the fight directly to the trees.