https://www.youtube.com/watch?v=DNqmrLSt-BA&feature=youtu.be
(Full Screen For Best Effect)
The "Weeping Willow" like trees in Shadowfen seem to have a bug in their Alpha Channels for the the branches which hang down. On pretty much every "weeping" branch there's a rogue leaf at the bottom which floats randomly in the air. My assumption is that that there's something with the alpha channels that has a big of extra leaf data at the bottom, and it should be a simple fix as far as checking with the texture. The video shows the effect in motion and lets you see the visual issue more clearly (and it has a location of the tree right off, too).
It's, admittedly, probably the single-most minor issue in all of ESO across the board, but it also could potentially be a super easy fix (e.g. if it's is an alpha layer issue just clean up the alpha, 30 seconds, texture is good to go and happy again)