noun
subcanopy tree; understory tree; semi-tall tree
Ecological term for a tree that grows beneath the main canopy but above the shrub layer; used in forestry and vegetation surveys.
この森では亜高木層にカエデ類が多い。
In this forest, maples are abundant in the subcanopy layer.
低木 are shrubs or low-growing woody plants, shorter than 亜高木.
Compound of 亜 (a, 'sub-') + 高木 (kōboku, 'tall tree'), literally 'sub-tall tree'. The exact historical derivation is uncertain; the spelling is conventionally associated with the ecological meaning.