The bright edges on the trees are the rimshine / rimlighting + fresnel working together to add depth to the trees. In photography you have a key light & fill light that light up the subject and provide shadowing on the front surface of it. But, you also have a backlight that's used to provide a slight light "outline" on an object to help it standout from the background. That's the goal of rimlighting. The PBR BRDF already does a decent job of edge lighting. But, the rimlight adds extra light / edge highlighting to help things pop a bit more. The trees and vehicle are allowed to have a bit of specular light (and rimlight) occur in shadows. Hence, the very large, dark tree behind the vehicle still has faint rimlighting. (Fresnel lighting also helps with this, but the rimlighting sets it off more.) AO softening now only impacts the AO trees generate under them. So, the AO spot under vehicles will still be dark. This helps vehicles stand-out while also making it easier to soften shadows and especially tree shadows that have under-tree AO that likes to keep them dark.