Modeling Neotropical Ecosystems during the Last Glacial Maximum

Rich biodiversity and biogeochemical significance has long motivated research on Neotropical ecosystems, though regionally-focused modeling studies remain relatively sparse and limited in scope. Three individual projects were performed to address potential issues in the modeling of Neotropical ecosystems in past and present contexts with particular emphasis on the Last Glacial Maximum. The first project was focused on discerning the effects of low atmospheric carbon dioxide and temperature on the carbon exchange of a well-watered tropical forest using a canopy-scale ecophysiological model. The radiative transfer regime and canopy energy balance were used to interpret the effect of environmental variables on carbon fluxes, as well as the reproduction of an observed phenomena where leaf temperature drops below air temperature. The second project was an analysis of a four-year data set of ecosystem fluxes designed to assess the seasonal patterns of carbon uptake and the impacts of drought from a tropical dry forest site in Santa Rosa National Park, Costa Rica. A hyperbolic light response function was used to partition net ecosystem exchange into gross primary productivty and ecosystem respiration, while extracting estimates of ecosystem-level photosynthetic radiation and saturated rates of uptake. Bursts of carbon dioxide were observed at the onset of the rainy season suggesting the occurrence of the `Birch Effect' within tropical dry forest ecosystems. The third project was a regional-scale modeling study of vegetation cover in the Neotropics during the Last Glacial Maximum, focusing on the individual and interactive effects of fire and low carbon dioxide on biome distribution and tree cover. Inclusion of fire and the effects of low carbon dioxide improved agreement with pollen records and suggest the past prevalence of grassier, more open ecosystems. Modeling evidence was found to support the existence of hypothesized routes and barriers to dispersal during the Last Glacial Maximum, bolstering theories of range expansion and diversification over Pleistocene climatic oscillations.Ph.D.2020-11-14 00:00:0