PATTERNS IN VERTICAL-DISTRIBUTION OF FOLIAGE IN YOUNG COASTAL DOUGLAS-FIR

Total amount and vertical distribution of foliage represent important aspects of forest stand structure and its influence on dry matter prod uctivity, forest microclimate, watershed properties, and habitat struc ture. Variation in foliage distribution was analyzed on trees and plot s in a series of even-aged Douglas-fir (Pseudotsuga menziesii (Mirb.) France) stands scheduled for management under a wide range of silvicul tural regimes. Branch-level foliage mass and foliage area equations we re developed from a sample of 138 branches. These equations were appli ed to 27 trees on which the diameter and height of all live primary br anches were measured, allowing estimation of both the total amount of foliage and its vertical distribution. A beta-distribution was fitted to data describing the vertical distribution of foliage on each tree, and the resulting parameter estimates were modelled as functions of tr ee height, diameter at breast height, crown length, and relative heigh t in the stand. Foliage area distribution tended to be shifted downwar d relative to foliage mass because of the expected increase in specifi c leaf area with depth into the crown. Similarly, the relative foliage distribution in terms of both mass and area was shifted downward as t he tree became more dominant, or as relative height in the stand incre ased. In contrast, foliage on trees of similar relative height was shi fted upward in response to the lower stand densities imposed by precom mercial thinning. On the stand level, relative vertical distribution o f foliage in the canopy was more peaked than would be implied by assum ing a constant leaf area/sapwood area ratio throughout the composite t ree crowns. Between-stand variation in vertical foliage distribution w as dictated by differences in stand top height, height to crown base, and number of trees per hectare.