Development of branch, crown, and vertical distribution leaf area models for contrasting hardwood species in Maine, USA

Abstract

Branch, crown vertical leaf area distribution models were developed for naturally regenerated hardwood species and planted hybrid poplar clones. Species-specific differences were found at all levels of investigation. Coexistence in mixed-species stands is strongly influenced by species differences in leaf area production and distribution. The majority of leaf area models in the literature are focused on conifer species, which have substantially different crown forms than hardwood species. Therefore, the goal of this investigation was to develop branch, crown, and vertical leaf area distribution models for various hardwood species that accounted for their greater crown complexity. A nonlinear model including branch diameter, branch tip height, and height to the start of the foliage was the best fit for branch leaf area. Branch leaf area ranged from 0.05 to 0.37 m2 for Populus grandidentata and Betula populifolia for an averaged sized branch, respectively. The best fit model for crown leaf area was a nonlinear form accounting for stem diameter and crown length. Crown leaf area ranged from 3.26 to 9.85 m2 for Populus tremuloides and Betula populifolia for an averaged sized tree, respectively. Vertical leaf area distribution was best fit by a right-truncated Weibull distribution and showed a peak in the middle third of the crown for most of species. In addition, leaf area production varied among four hybrid poplar clones in plantations, suggesting a strong genetic control over crown form. Overall, leaf area varied among species at all levels of investigation, suggesting that coexistence of hardwood saplings in this investigation was strongly influenced both by inherent species-specific leaf area production and vertical distribution.