Canopy structure and radiation environment metrics indicate forest developmental stage, disturbance, and certain ecosystem functions
Geoffrey
Parker, Smithsonian Environmental Research Center, parkerg@si.edu
David
Roy
Fitzjarrald, Atmospheric Sciences Research Center, fitz@asrc.cestm.albany.edu
(Presenting)
The structural and environmental complexity of a forest is the compound result of a development sequence overlain with perturbations. To date, these complexities have been poorly quantified. Here we introduce some potentially useful metrics derived from measurements of canopy structure and radiation environment and discuss known and potential implications of these measures for understanding forest developmental stage, disturbance intensity, and some ecosystem functions.
Common summaries of forest structure include maximum height, and overall surface area density and cover. However, these measures are inadequate characterizations and provide little indication of forest state or function. High-frequency first-return LIDAR measurements obtained from forest floor or from aircraft can yield summary and distributional measures that are interpretable in terms of whole canopy structure and function.
Most canopy volumes are dominated by open space; various sorts of "porosity" may be defined and specific classes of interior environments may be recognized. The shape of the spatially averaged vertical profile of surface is also a useful descriptor. "Heaviness" is the relative height of median canopy surface. In "top-heavy" canopies ,the majority of surfaces are near the top, whereas "bottom-heaviness" indicates a distribution skewed toward the forest floor. The outer canopy surface is the primary interface interacting with the free atmosphere - its texture is important. Various measures of the complexity of its shape may be defined, including the variability in its shape ("rugosity"). The overall canopy gap fraction is likely less important than the distribution of openings penetrating to the ground ("gappiness"). The balance of large and small gaps is described by the slope of the gap-size distribution function.
We discuss how these measures alone and in combination can be used to indicate developmental stage, degree of disturbance or intervention, and some aspects of ecosystem function, including potential growth, radiation balance, the coupling with atmosphere, mixing, storage, and the spatial distribution of sources and sinks of energy and carbon.
Submetido por David Roy Fitzjarrald em 24-MAR-2004
Tema Científico do LBA: CD (Armazenamento e Trocas de Carbono)