Doctor of Philosophy (PhD)
School of Renewable Natural Resources
Restoration of floodplain ecosystems relies on identifying the most crucial hydrologic process which has been altered by human and climate. Flooding is a well-known dominant hydrologic process for floodplain ecosystems, but surprisingly little is known about drought's role in structuring ecosystems. In addition, several issues remained uncertain, such as the nature of drought within floodplains and the sensitivity of floodplain species-specific growth to climate. These gaps of understanding have in common in missing observations of mechanistic pathways of vegetation response to water deficits at multiple scales in time and space.Generally, this research contributed to floodplain management by expanding our understanding of the space-time response of floodplain vegetation to soil water deficits by addressing specific objectives. Firstly, results from the sensitivity analysis of species-specific growth to climatic and hydrologic conditions indicated species dependence and hydrologic dependence of the five species, mainly green ash and the site-dependence of climatic-growth relationship which the effects of climate are more critical than rivers on driver sites. Secondly, the utilization of widely used climatic indices and remote sensing-based indicators to capture drought footprints in three floodplain forests are proven beneficial in applications for characterizing drought conditions, specifically, the water balance in SPEI and the water loss estimated by the ESI. Tree rings in green ash were the most consistently affected by drought across floodplains and were the most closely correlated with meteorological indices and remotely sensed indicators. Thirdly, the variation in water and energy availability among and within the floodplain can be explained through the variation of the energy limitation coefficient (characterizing the watershed energy limits), the water availability factor and the plant water availability factor (explaining the vegetation control water limits within the floodplain) via an extended water balance in the humid environment to explain floodplain hydrology changes at a grid-base and monthly time scale. Our study utilized multiple-source data fusion, both remote sensing and field data, from low to high resolution and frequency to create the connection in plot scale data, extrapolating to regional and watershed scale. Despite limitations, our findings widened ecohydrology research and opened more questions about ecohydrological relationships in floodplain forests.
Nguyen, Nga Thanh, "Floodplain Forests Vegetation Dynamics Driven by Water Deficits Across Scales" (2021). LSU Doctoral Dissertations. 5680.
Keim, Richard F.