Passage III
Leaf area index is a unitless measure of the percent of a rainforest floor that is covered by the leaves
of tall trees. Leaf area index may increase because of an increase in precipitation (measured as
millimeters of rainfall per km^2 per year). Table 1 shows how the leaf area index formed by the canopy
layer (30 to 45 m above the rainforest floor) varies with precipitation in a 1000 km^2 section of the
Amazon Rainforest. Figures 1– 3 show the relative precipitation, RP (the percent below the rainfall
measured on January 1, 1985), and the monthly average leaf area index of the emergent layer (45 to 55 m
above the rainforest floor), canopy layer, and understory layer (0 to 30 m above the rainforest floor),
respectively, from January 1990 to January 2005.
