I really dig the theme of reforestation for a faction! Permanent buildings are a very interesting concept.
I'd be a little worried if opponents would ever even let you get there - given that you can only ever have one 'actual' warrior to defend them and permanently blocking building spots + passive scoring is quite scary. On the other hand, the chance to use matching cards as mini-ambushes to add 'temporary' warriors for protection is neat. I'd be curious to see if this is enough defense for your trees, especially once they are on the verge of becoming permanent. Maybe as an alternative Public Support could add warriors of other factions present in the clearing to the defenders, or work like WA's Guerilla War at the price of a matching card? The way it is, it might also need some clarifications (do you actually place a warrior there? What if there are none in the supply? How do you deal with snares or the keep? And does this (I assume) ignore the restriction that you can only have 1 warrior per clearing?)
But I definitely think you have some nice ideas in there, like having more seedlings/saplings than mature trees in order to spread out the opportunities to grow them, or the way you incorporate the swarming theme in the attack mechanism.
I'm a big fan of the notion of evolving buildings, well incorporated!
Overall, a really good idea, seems like an interesting faction to play with the restrictions and opportunities they offer! Good job