The forest is thick and the moss is slippery.

林深苔滑。

《新英汉大辞典》

And in the deep forest, where only the old trees can hear, and the strip of sky see it, he talks with thee, sitting on a heap of moss!

而在深源的树林里，只有那些老树能够听见、只有那一线青天可以看见的地方，他跟你坐在一堆青苔上谈话！

youdao

So it's really the density of very large old trees that are draped in moss that is important at a forest stand level.

因此被苔藓所覆盖的非常古老的树木的密度确实对森林的林分水平很重要。

youdao

Instead of studying, say, a forest, the team looked at moss-covered rocks.

ECONOMIST: Road kill

Then the assailant fled down into the forest, through the wispy tangles of moss that hang from the oaks like a dragon's goatee.

CNN: ASIANOW - TIME Asia

The open valley turns to a forest of tall fir trees, many hung with moss.

BBC: Hiking the Alpine Walserweg trail