© 2007 Heron Publishing—Victoria, Canada
Summary models for light interception and light-use efficiency of non-homogeneous canopies
R. A. Duursma (1,2) and A. Mäkelä (1)
1. Department of Forest Ecology, University of Helsinki, P.O. Box 27, FIN-00014, Finland / 2. Corresponding author (remko.duursma@helsinki.fi) / Received April 12, 2006; accepted August 8, 2006; published online March 1, 2007
Summary
The application of detailed models of canopy photosynthesis rely on the estimation of attenuation of light in the canopy.
This attenuation is readily estimated with the Lambert-Beer law when the canopy is homogeneous. In reality, forest canopies
are far from homogeneous, and this has led to the use of detailed light extinction models that account for grouping of foliage
between and within trees. Because such models require detailed parameterization and fine resolution inputs, they are impractical
in larger-scale applications. Thus, there is interest in simplified models that can be readily parameterized. We developed
two equations that can be used to estimate mean annual light interception by single unshaded trees and by stands of Poisson
distributed trees. Interception by single trees is a function of crown surface area, the ratio of leaf area to crown surface
area, the extinction coefficient in a homogeneous canopy—which can be determined separately—and one empirical parameter that
depends on the mean solar angle. The summary model was tested against a detailed model of interception, and showed good agreement,
although with slight bias. The results showed that crown surface area is a good summary variable for crown size and shape,
because errors are independent of crown shape (ellipsoids, cones and height:width ratios). We also tested whether canopy photosynthesis
is proportional to light interception across canopies differing in structure and leaf area index, and found that light-use
efficiency is influenced by canopy structure. The model is useful in larger-scale applications because it can be parameterized
with available data without the need for additional empirical parameters. It can also be used to study the effect of stand
structure on mean annual light interception and productivity.
Keywords:
canopy light extinction, forest productivity, stand structure.
