concept

Foliage height diversity

A measure of how evenly a forest's leaves are spread across its vertical layers — in effect, how many "floors" the forest has and how evenly they are furnished. In 1961 the MacArthur brothers found this single number predicted the diversity of birds in a habitat astonishingly well: more foliage layers, more evenly filled, meant more kinds of birds. It is the way to quantify the core idea that structure creates room — the more layered a forest, the more life it can hold.