Foliage distribution in old-growth coniferous tree canopies

The vertical distribution of foliage for several old-growth trees is discussed and modeled. The data include the foliagedistribution of nine Douglas-fir (Pseudotsuga menziesii (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 standcanopy. The data show that the foliage is distributed asymmetrically in the crown with the maximum amount often locatedat a height approximately equal to 80% of the tree height. The data further show that the crown base is 9-30 m above theground. Five different mathematical models of the foliage distribution (a normal distribution, a chi-square distribution, a betadistribution, a difference of exponentials, and a chi-square-like distribution) are fitted to the data and compared. The betadistribution and the chi-square distribution appear to fit the data slightly better than the others; but the differences in r2 betweenall the models are often small. The normal distribution has the advantage that it shows the least variability from one tree tothe next; however, it also has the disadvantage that it is significantly different from zero at the top of all the tree crowns modeledhere.