Canopy Structure in a 650-Year Douglas-Fir Chronosequence in Western Washington: Distribution of Canopy Elements and Open Space

Abstract

Abstract Using within-canopy, side-viewing light detection and ranging (LiDAR), we measured canopy structure in a Douglas-fir (Pseudotsuga menziesii) chronosequence. We present foliage profiles, canopy composition, and a new metric quantifying the vertical distribution of open space, supporting and extending results from other structural studies. Foliage distribution shifted from vertically uniform in the youngest stand (50 years), to a canopy surface peak in mature forests (100–160 years old), to a near-ground maximum in old-growth (650 years). Leaf area index in old-growth and mature forests was similar but was smaller in young forest. Canopy composition changed with age: relatively more dead elements in young, boles in mature, and diversity in old-growth canopies. Older forest had greater mean and variance in open space than younger forests. Open space was vertically uniform in young, unimodal in mature, and greatest in the upper canopy in old-growth forests. Our results provide an integrated description of canopy structure over more than half a millennium, highlighting solid structure and its complement, open space. The unique element we present—open space—provides novel insights into the assessment of forest structure. This study provides a means to compare forests across ages, from immature to old-growth, with an additional canopy variable available for developing relationships between canopy structure and function.