The three dimensional structure of canopy trees: how to model crowns for light-driven growth.
Wolosin, Michael1, Clark, James1, Dietze, Michael1, Chakraborty, Sukhendu2, Agarwal, Pankaj2, 1 Duke University, Durham, NC2 Duke University, Durham, NC
ABSTRACT- The relationships between adult canopy tree growth rate, canopy shape, and light availability are explored using a combination of remote sensing and field data from four hectares of mixed pine-hardwood forest in the North Carolina Piedmont. High-resolution aerial videography provides the raw materials for a variety of crown shape reconstructions using standard stereo analysis. These crown models are placed in a ray-tracing computer simulation, and parameters for absorptance in each model are estimated by fits to both individual tree growth and to below-canopy light levels. A conceptual model of crown shape, location, and internal structure guides the choice of crown models tested, and standard model selection tools guide the choice of the "best" models for particular purposes. Results show that the relationship between canopy light availability and growth varies between species - providing evidence that large trees do experience resource response trade-offs. Simple models of crown shape were adequate for the purpose of forest simulation modeling when crown location was allowed to vary from stem location due to local light competition. The benefits of including complex shapes or internal structure were small in the context of community modeling compared to the extra computing costs, but might be useful in answering some ecophysiological questions.
Key words: crown competition, light absorptance, 3D remote sensing
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