concept

Leaf area index

The total area of leaves stacked above one unit of ground — a number for how "thick" a forest's foliage is. The higher the leaf area index, the denser the canopy, the more light it intercepts up top and the less it lets through below. It is the way to quantify why a closed forest floor is so dark: light is absorbed layer by layer as it passes down through stacked leaves, in a steady decline.