I believe in leaving the trail as you found it, as much as possible.
Its what they teach here in Norway / Scandinavia.
However, if there is a road blockage due to landslide, tree fall, etc. then its fair game to make adjustments.
That is allowed over here, as many roads and trails do experience frequent landslides.
Below is a photo from end 2016 in Iceland, when we encountered a rock fall landslide across our road.
(No, I wasn't strong enough to move the boulder !!!)
You can see the extent of this road damage (1:30 into the film) in the YouTube Video we released on this day trip called "Mountain Solitude"
Typically these landslides are quickly dealt with, and the road / trail relatively quickly reopened.
Authorities are well set up for this action over here.
Use the winch to pull the blockage out of the way (boulder or tree) if mounted / stored on / in the vehicle at the time.
However, we are not allowed to drive with winches mounted on normal roads in Norway - that's the law unfortunately.
So you have to have the winch in the back, and mount it when the occasion demands.
I agree that some tree branches can grow over the road / trail and impact the vehicle.
In these case, we tend to cut as little as possible, and rather drive through slowly and carefully.
If the condition is bad, its good to report it the authorities, who should make the necessary adjustments.
We all impact the environment, whatever we do.
So it good to minimise our impact here, wherever possible.