noun
overstory; canopy layer; tree stratum
Technical term in forestry and ecology for the uppermost layer of vegetation formed by tall trees.
この森林の高木層は主にブナで構成されている。
The overstory of this forest is mainly composed of beech trees.
高木層が発達すると、下層の植物に届く光が減る。
When the canopy layer develops, less light reaches the understory plants.
草本層 is the herbaceous layer on the forest floor, below the shrub and tree layers.
Compound of 高木 (こうぼく, 'tall tree') and 層 (そう, 'layer, stratum').