Assessing the geometric structure of a white clover (Trifolium repens L.) canopy using 3-D digitising

Abstract

A method was developed for assessing the three dimensional (3-D) geometric structure of white clover canopies. 3-D co-ordinates of pre-defined points on leaves, petioles and stolons were measured using a Polhemus Fastrak electromagnetic 3-D digitiser. Digitising progressed downwards from the top of the canopy and plant parts were removed after they have been digitised. Leaflets were treated as four quarter-ellipses, and petiole and stolons were treated as cylinders. Leaf dimensions and areas calculated from 3-D co-ordinates were within about 5 % and 20 % of direct measurements made with a ruler and a planimeter, respectively. Special software and freeware POV-Ray were used to reconstruct a virtual canopy from digitiser records and to calculate canopy characteristics such as leaf area index (LAI), petiole intersection area, and profiles of leaflet areas and inclinations with height. It took between 3 and 7 h to digitise 10 x 10 cm stands of clover and the resulting information was considerably more comprehensive and accurate than could have been obtained by the alternative 'point quadrat' or 'stratified clipping' methods. (C) 2000 Annals of Botany Company.