Integrating flood rings and false rings to reconstruct seasonal flooding in Southeastern U.S. coastal plain rivers

Summary Flood rings and false rings are complementary anatomical proxies that record hydrological disturbances at different points in the growing season. This study integrates flood rings in Quercus lyrata (overcup oak) and false rings in Taxodium distichum (baldcypress) from four sites within two coastal plain river systems, the Pascagoula River (Mississippi) and the Altamaha River (Georgia) to reconstruct seasonal flood variability across the growing season. Superposed epoch analysis confirmed statistically significant Hyporheic Connectivity Index (HCI) anomalies during flood/false ring years at both sites, with flood rings linked to elevated spring HCI in March–April during earlywood vessel formation, and false rings associated with elevated July–August HCI during the late growing season. Binary logistic regression models achieved area under the curve (AUC) values of 0.736–0.858 for flood rings and 0.735–0.747 for false rings, demonstrating moderate predictive skill across both systems. The co-occurrence of both anatomical features in 14 years at Pascagoula and four years at Altamaha identifies exceptional hydroclimatic events, including strong El Niño years in which flooding disrupted cambial activity during both earlywood and latewood development within a single season. Comparison with standardized ring-width chronologies shows that false rings frequently develop independently of above-average radial growth, confirming that conventional ring-width methods underrepresent late-season flooding. Together, the two proxies provide a more complete and seasonally resolved paleoflood record, with multi-century chronologies extending flood histories beyond the instrumental period.