An equation for irregular distributions of leaf azimuth density

The von Mises equation was modified to describe numerically irregular distr ibutions of leaf azimuth density. The new equation has three indexes: T (de scribing distribution elongation), S (describing number of azimuth preferen ces), and R (describing general canopy azimuth position). The equation was tested on two contrasting canopies: sunflower and maize. In 1998, the diurn al variation of leaf azimuths was measured weekly beginning 66 days after p lanting for 5 weeks. The equation was tested again in 1999. The equation ch aracterised the leaf azimuth densities accurately (mean absolute estimation error of 0.05). For sunflower, R index was linearly related to sun azimuth , and sunflower generally tracked the sun in the same way for both years be cause they had almost equal R at a given sun azimuth. However, the azimuth density distribution in 1999 was slightly more clumped than in 1998, and th at sunflower canopies in 1998 would fluctuate between one to two azimuth pr eferences, but sunflower in 1999 generally showed one azimuth preference. F or maize, mean T,S and R for 1998 and 1999 were similar to each other These values agreed with field observations, where maize canopies were usually e longated, having two azimuth preferences that were perpendicular to plantin g row direction. Logistic regression showed that these indexes were descrip tive enough to differentiate between sunflower and maize canopies with an a ccuracy greater than 80%. The most important index to differentiate between canopy types was T, S, then R. (C) 2000 Elsevier Science B.V. All rights r eserved.