Efforts to maximize or restore ecological function on floodplains impacted by dam construction have increasingly focused on river flow management. Few studies, however, consider floodplain hydrogeomorphic position and annual climatic variation in dam impact assessment. The Savannah River, a large river ecosystem in the Southeastern United States, was impounded in the 1950's. Our study objectives were: (1) Characterize hydrology in floodplain areas containing Taxodium distichum, and determine how it has been affected by dam operations; (2) Identify basal area increment (BAI) response of Taxodium to annual flooding and climate (dry, average, wet) conditions; (3) Assess BAI response to dam-induced hydrologic changes. Levee and backswamp sites were significantly drier in the post-dam era, and trees at these sites showed a significant post-dam increase in BAI. Low-elevation river sites did not show significant hydrologic differences between pre- and post-dam eras, but BAI was significantly higher in dry years and significantly less sensitive to hydroperiod in the post-dam era. All trees demonstrated a significant quadratic BAI vs. hydroperiod relationship. This study demonstrates that annual productivity of Taxodium trees can be reduced by either drought or flood stress. It also suggests that climate and hydrogeomorphic location mediate dam impacts and productivity-flooding relationships in Taxodium.