Foliage distribution in old-growth coniferous tree canopies

Abstract

The vertical distribution of foliage for several old-growth trees is discussed and modeled. The data include the foliage distribution of nine Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) crowns, the foliage distribution of a sugar pine (Pinuslambertiana Dougl.) crown, and the foliage distribution of a composite of the nine Douglas-fir trees which represents the stand canopy. The data show that the foliage is distributed asymmetrically in the crown with the maximum amount often located at a height approximately equal to 80% of the tree height. The data further show that the crown base is 9–30 m above the ground. Five different mathematical models of the foliage distribution (a normal distribution, a chi-square distribution, a beta distribution, a difference of exponentials, and a chi-square-like distribution) are fitted to the data and compared. The beta distribution and the chi-square distribution appear to fit the data slightly better than the others; but the differences in r 2 between all the models are often small. The normal distribution has the advantage that it shows the least variability from one tree to the next; however, it also has the disadvantage that it is significantly different from zero at the top of all the tree crowns modeled here.