Analyzing canopy structure in Pacific northwest old-growth forests with a stand-scale crown model

In forests, the canopy is the locale of critical ecosystem processes such as photosynthesis and evapotranspiration, and it provides essential habitat for a highly diverse array of animals, plants, and other organisms. Despite its importance, the structure of the canopy as a whole has had little quantitative study because limited access makes quantification difficult and integration of detailed measures of many individual tree crowns is necessary. A model is presented for simulating the crown architecture of individual trees in the Pacific Northwest to analyze their collective influence on canopy structure at the stand scale. The model uses ground-based measurements of tree height, height to crown base, and crown radii. Crown shapes are modeled as solid geometric shapes based on these measures. Two examples are used to illustrate the model's applications: an estimation of the vertical distribution of foliage in an old-growth Douglas fir/western hemlock forest; and an estimation of understory light conditions in an experimental gap, made by applying ray tracing technology to a model of the overstory tree crowns. Both tramples illustrate how the model can increase detail in the description of canopy structure. Further application and future resting of the model will help refine its precision.