sea of trees; dense forest expanse
Evokes a vast, unbroken stretch of forest, often with a poetic or slightly ominous feel. Frequently associated with Aokigahara (青木ヶ原樹海).
A vast sea of trees spreads out at the foot of Mount Fuji.
It's easy to lose your sense of direction in a sea of trees.
Compound of 樹 (ju, 'tree') and 海 (kai, 'sea'), literally 'sea of trees'. The term is a relatively modern coinage, likely from the early 20th century, used to describe vast forested areas.