Dormant season submergence as a predictor of forest seedling survival in a connected floodplain

Abstract

Hydroperiod predicts forest species composition within floodplains, which influences productivity of connected ecosystems and supports people through critical ecosystem services. Therefore, understanding tree species responses to changes in hydroperiod is critical for maintaining these systems. Trees are most vulnerable to stressors during their seedling stage, and the seasonality of floods can influence their response. Many species are considered tolerant of dormant season floods, but some experience reduced productivity and survival, which can influence competition and species composition. In lower elevation swamps of the Apalachicola River floodplain (Florida, USA), anthropogenically altered hydroperiod may predict observed species composition shifts from more flood-tolerant species, such as water tupelo (Nyssa aquatica) and pop ash (Fraxinus caroliniana) to less flood-tolerant competitors, such as water hickory (Carya aquatica) and overcup oak (Quercus lyrata). In a controlled experiment, we tested the hypothesis that dormant season seedling submergence affects survival and leaf flushing rates of these species differently and that shorter durations of seedling submergence allow increased survival of the less flood tolerant species, potentially increasing competition in floodplain swamps. We observed no differences in survival or rates of leaf flush among species after all treatment durations ranging between one and four months. Seven-month-old seedlings of these common competitors are similarly tolerant of dormant season flood events, when the Apalachicola floodplain is connected, and water conditions are aerobic. High water events are poor predictors of survival for established seedlings, but further investigations of tolerance to aerobic and hypoxic conditions by younger seedlings may reveal differing species adaptations.