Foliage randomness and light interception in 3-D digitized trees: an analysis from multiscale discretization of the canopy.
Sinoquet H., Sonohat G., Phattaralerphong J., Godin C.
Author Affiliation: UMR PIAF INRA-UBP, Site de Crouelle, 234 Avenue du Brézet, 63039 Clermont-Ferrand Cedex 2, France.
Plant, Cell and Environment 28 : 1158-1170
Abstract : A study was conducted to assess the effect of 3 possible sources of non-randomness in tree canopies on light interception properties. Three-dimensional (3-D) digitized walnut, mango cv. Nam Nok Mai and peach cv. August Red trees and 4 theoretical canopies (one random and 3 built from fractal rules) were used to compute canopy structure parameters and light interception, namely the sky-vault averaged silhouette to total area ratio (STAR). STAR values were computed from images of the 3-D plants and from a 3-D turbid medium model using space discretization at different scales. For all trees, departure from randomness was mainly due to the spatial variations in leaf area density within the canopy volume. Indeed STAR estimations, based on turbid medium assumption, using the finest space discretization were very close to STAR values computed from the plant images. At this finest scale, foliage dispersion was slightly clumped, except one theoretical fractal canopy, which showed a marked regular dispersion. Taking into account a non-infinitely small leaf size, whose effect is theoretically to shorten self-shading, had a minor effect on STAR computations. STAR values computed from the 3-D turbid medium were very sensitive to plant lacunarity, a parameter introduced in the context of fractal studies to characterize the distribution of gaps in porous media at different scales. 3-D turbid medium models based on space discretization are able to give correct estimation of light interception by 3-D isolated trees, provided that the 3-D grid is properly defined, that is, discretization maximizes plant lacunarity.