Hi,
Second shot using Cycles, I find the principled volume quite efficient to create atmospheric ambient.
Not yet very convinced by the displacement, duno if like in Octane, there is a way to not having to add a subdivision modifier first and by the way even with that I don’t find the result as expected.
Edit : The previous image has been replaced
Very good render overall! I liked the lighting and atmosphere of the nature.
I’m a beginner for Octane but according to this manual, displacement is more limited than Cycles (Cycles doesn’t have those limitations mentioned).
It’s good that Octane have option for level of detail in the node without the need for subdivision modifier but I’m not sure if it subdivides the mesh depending on the distance of the object to the camera as Cycles adaptive subdivision does.
If you are not satisfied because of the resolution of displacement, you may want to reduce the dicing scale in the subdivision modifier.
Thanks Filibis,
I had adaptive subdivision in mind indeed but couldn’t find it and never thought about the experimental.
And indeed now I see the things from another angle of view and displacement is much more efficient using it in this way. The only thing that bother me is the fact if the subdivider is not the last in the list of modifier it doesn’t expose the adaptive settings, I may miss something …
Regarding the hash shadows on the trees I’m afraid it’s mainly due to the fact that I used sun for lighting the scene and it produces those hard shadows. I saw that angle parameter may help defining the sun size, which should result in smoother shadows 
