Measuring leaf area index of plant canopies with branch architecture

Radiation transmission through plant canopies is shown to be determined not only by the geometry of the foliage elements (leaves), but also by the geometry of foliage clumps. When the geometry of tree branches (thin slabs of foliage in which leaves are confined) was considered with a Poisson model, it was found that beam transmission measurements at a 62° rather than a 57.5° incident angle can provide a good estimate of the effective leaf area index (Le). The values of Le calculated from the model were approximately 55–65% of the actual leaf area index when the branches were assumed to consist of one layer of randomly dispersed leaves. The calculated results are consistent with experimental data obtained from a Douglas-fir forest stand, which was largely composed of near-horizontal branches.