Successional Trajectories Of Coastal Forested Floodplains Wetlands Along The River Continuum

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About the Webinar

Coastal floodplain forests (CFFs) exist across the riverine-tidal coastal river continuum; however internal ecological succession has been historically studied as distinct systems—riverine and tidal. This can be attributed to the differences in environmental tolerances (riverine: shading and flooding; tidal: salinity) that regulate their respective canopy structure and composition (e.g. diversity, basal area, stem count). Importantly, climate change-driven alterations to hydrology and water quality (i.e. saltwater intrusion, sea level rise, and shifting precipitation trends) across the riverine-tidal continuum poses a significant threat to internal ecological succession. In this work, we unify the riverine and tidal CFF literature to develop and test a comprehensive CFF ecological succession framework that uses species level environmental tolerances to inform how climate change will affect canopy community structure and composition along the riverine-tidal gradient. We leveraged a historical, spatially rich dataset on community structure and composition in the forested floodplains of the Lower Suwannee River (Florida, US) to quantify ecosystem response to 20 years of sea-level rise, saltwater intrusion, and freshwater flow variability. In alignment with existing literature, we found that average diameter-at-breast height (DBH) and stem count were inversely related on the riverine-tidal gradient with DBH, growth rate, and size class recruitment being significantly greater at the most upstream transect. Species richness and diversity declined along the riverine-tidal gradient with a few species at each transect holding a disproportionate share of importance value (IV; a metric that captures both structure and composition). Finally, principal components analysis (PCA) and hierarchical clustering on principle components (HCPC) were used to identify and define three unique species clusters (Riverine, Transitional, and Tidal) based on species-level environmental tolerances to shading, flooding, and salinity. Spatiotemporal trends in average cluster IV over the riverine-tidal continuum were used to assign each cluster to a distinct part of the river with the Riverine cluster being defined by shade and salinity intolerance and the Tidal cluster being defined by salinity tolerance. Importantly, a Transitional cluster (intermediate tolerance to shading, flooding, and salinity) was found to best represent canopy structure and composition of the mid-river. In total, this work presents a comprehensive framework for CFF ecological succession across the riverine-tidal continuum that can be used to inform a nuanced understanding of structural and compositional shifts in the context of climate change. By linking successional trends directly to environmental variables, these findings can lead to improvements in species distribution models and aid land managers in understanding species transitions in the context of climate change.

 About the Presenter

Elliott White Jr. is an Assistant Professor of Earth System Science in the Stanford Doerr School of Sustainability. He is a coastal ecosystem scientist who leverages his domain expertise in wetland sciences with interdisciplinary training in remote sensing and ecohydrology to investigate climate change-related challenges on coastal socio-ecological systems. He has ongoing research projects that are partnering with community-based organizations to 1) leverage wetlands as a form of flood protection, 2) create access points to carbon markets, and 3) linking hydrology directly to swamp canopy health. At Stanford, he is an affiliate of the Center for Comparative Studies on Race and Ethnicity and a center fellow, by courtesy, of the Woods Institute for the Environment. Elliott has a PhD in Environmental Engineering Sciences from the University of Florida and a BS in Biology and Animal Ecology from Iowa State University.

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