This is what I was going to say as well. Avoid setting up a vertical in a forest if possible. I have never had success with a vertical in a forest; however, as many of the lower summits are wooded in DL, an Inverted-V dipole does not seem to have any issues, so I’m guessing Chris’s Inverted-V EFHW should be fine as well.
Me too, I am a “tree-hanger”. 99% sloping or horizontal. I try to operate at the edge of the forest or outside when still in the activation zone. When inside a dense wood (Lupfen DM/BW-057 comes to mind), I try to be at least at the edges 1-2m away from leaves or ground.
This works for me. The rare times I really want to work W/VE or VK/ZL, I go for a vertical, but in open spaces (Mont Racine HB/NE-001, Selibühl HB/BE-151, Röti HB/SO-003).
I just found this article. The author, Mark K8MSH, appears to be concentrating mostly on vertically polarised VHF transmissions, but it can be a good read anyway: