You'll drive yourself crazy trying to come up with post-hoc justifications that comport with the lore, when the creators didn't do so in the first place.

I try not to go too far down the rabbit-hole of lore in fiction - especially visual arts - because more often than not things look a certain way for aesthetic reasons, and not as entirely logical outgrowths of the world being portrayed. Living trees aren't out in the world, because Bethesda are going for a bleak, scorched wasteland look. Same reason they probably have dead leaves on the ground - because otherwise everything would just be a brown dirt texture. to Missing or Repacked Mod Files, then download Skyrim Flora Overhaul - Version 1. The answer? The dead trees are there, because they look good visually. This mod features designs from 4 regions in Teyvat: Liyue, Inazuma. Animals also wouldn't have mutated so severely in a mere 200 years.

Of course, even the idea that dead tree trunks would still be standing after 200 years, is laughable.

According to the Fallout lore, it wasn't just the nukes that killed everything - it was something like four days of irradiated fallout rain that fell afterward, that devastated the surviving flora and fauna.

Fallout 4 flora mod