| The overall research topic addressed in this dissertation is the relationship between canopy microclimate and scalar sources (or sinks) and how such relationship varies with structural and functional attributes of forested ecosystems. Towards this end, I decomposed my research thrust into two elements: the first deals with describing mass and energy exchange rates on short-time scales assuming that the structure of the canopy is held constant or entirely specified. The second, which is still in a developing stage, deals with these processes but at time scales relevant to stand development. Both these questions are high priority in the US global climate change programs for carbon and water, and it is not possible to address all their aspects in a single dissertation. Hence, it is necessary to focus on a subset of questions whose solution provides new insights to pursue more broadly these elements. Namely, my dissertation addresses two key scientific questions: (1) How well can we estimate forest-atmosphere mass and heat exchange rates from temperature and/or concentration profile measurements within the canopy knowing the turbulent transport processes (the inverse problem)? Here the structure of the canopy is prescribed. (2) How can current “state of the science” forest growth models predict forest response (i.e. fluxes) to changes in climate (mainly elevated CO2) at different time scales?; To summarize, for shorter time-scale, where turbulence is the major exchange mechanism, we addressed the first question in two stages. First, we demonstrated that knowledge of the canopy microclimate (i.e. mean concentration profiles) and dispersion mechanics are sufficient to infer scalar sources and sinks without any knowledge of the canopy functional attributes. This demonstrates the strong coupling between the biological active scalar sources and sinks and the canopy microclimate. Second, we demonstrated that if the radiative, drag, and ecophysiological properties (i.e. canopy functional properties) are known, it is possible to infer sources, sinks, and fluxes as well as the mean concentration. We also showed that the computed sources and sinks from these two approached are in good agreement thereby providing satisfactory answer to the first question.; For longer time scales, where stand development is crucial to forest productivity, existing models tend to reproduce the overall annual trend of forest growth but they clearly miss the monthly variations in biosphere-atmosphere mass and energy exchange rates. (Abstract shortened by UMI.)... |
