Photographic method to measure the vertical distribution of leaf area density in forests

Abstract

Many current vegetation–atmosphere models require structural information describing the canopy in order to calculate rates of mass and energy exchange. One of the most important pieces of information is the variation with height in leaf area density, ρ (m 2 leaf area per m 3 canopy volume), but it is notoriously difficult to measure this in forest canopies. Consequently, very few data on ρ exist for tall tropical forests. We describe a relatively rapid photographic method to make this measurement and we demonstrate its use for a rain forest in Cameroon, and two rain forests in Brazil. The method requires an assumption or knowledge of leaf angle distribution, but is relatively rapid and has the benefit of sampling a relatively large volume of canopy. The technique works adequately, especially if the leaf area index of the site is already known; the results agree quantitatively and qualitatively with previous more laborious determinations.