Doctor of Philosophy (PhD)
Renewable Natural Resources
In forested wetlands, the biotic and abiotic consequences of water level variability is not well understood. The effects of flooding on carbon and water exchanges are important knowledge gaps where progress could benefit management of natural resources and predicting of changes in surface geophysical cycles. Two specific needs are a better understanding of (1) wetland tree responses to hydrologic variations, and (2) the effects of the forest and associated tree stressors on surface energy and water fluxes. Objectives were to determine effects of flooding on evaporation rates and energy dynamics, tree water use and growth responses to river-floodplain connectivity and water level variability, and interactions between tree-level and site-level effects of flooding. Energy-balance measurements in the understory of a permanently flooded swamp showed nearly all energy was partitioned to latent heat, yielding evaporation rates of 0.9-2.0 mm day-1 among months assessed; the seasonal pattern of canopy senescence superimposed upon the pattern of heat storage in the floodwater resulted in highest evaporation rates in October and November, out of phase with above-canopy solar forcing. Evaporation from open water was similar to that from floating vegetation. Tree sapflow measurements in a floodplain forest showed increased transpiration in response to a late season flood pulse at a more flooded site, while, concurrently, transpiration declined at a drier site. The more flood tolerant species (Quercus lyrata) benefited more from flooding than did the less tolerant species (Celtis laevigata), but neither species showed flood stress. To examine radial growth responses to water levels in forested wetlands, a model (VSL-Wet) was developed and calibrated across six baldcypress chronologies. Best model fits were obtained with parameters that suggest permanently flooded trees may benefit from deeper flooding. Last, measurements across differently flooded sites showed that more flooded sites had sparser forests but with higher growth efficiency trees, demonstrating the need to consider tree-level responses separate from stand-level patterns. Consistent with common assumptions, this work shows that abiotic and biotic parameters of forested wetlands, including carbon and water fluxes, are influenced by hydrologic variations; however, consequences of hydrologic influences are not universal across scales.
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Allen, Scott Thomas, "Ecological-Hydrological Feedback in Forested Wetlands" (2016). LSU Doctoral Dissertations. 433.
Keim, Richard F