Use of Digital Photography for Analysis of Canopy Closure

Abstract

The relationships between trees and understory crops are very important in agroforestry systems. Also, above ground interactions can be related to canopy structure. However, measurements of canopy structural parameters, either destructive or indirect, are time-consuming or prohibitively expensive. The present work explored the use of digital photography as a simple method to characterise the extent of canopy closure (CC), defined as the area of tree canopies projected onto the horizontal ground surface beneath, and expressed as a percentage of the ground covered. Measurements were made in two Eucalyptus (Eucalyptus nitens, Deane and Maiden) plantations and a subtropical mixed legume woodland dominated by Albizia (Albizia sp), Kidneywood (Eysenhardtia sp.) and Desert Fern (Lysiloma sp.). Images were captured at dawn to minimise light scattering and the number of sunlit foliage elements. Mean CC estimates provided by analysis of images obtained using digital cameras with contrasting performance, a Kodak DC-120 and a Canon EOS D1, were similar in precision and accuracy both between the two cameras and to those provided by a Li-Cor LAI-2000 canopy analyser. Bias between the estimates provided by the Kodak and Canon cameras was –0.02, between the Kodak and LAI-2000 was –0.07 and between the Canon and LAI-2000 was –0.05. Data from a pruning experiment using alder also demonstrated the repeatability of estimates obtained with a photographic method using the Kodak camera. The number of ring sensors within the LAI-2000 used to estimate CC affected agreement between the photographic method and the LAI-2000.