Jaime Duberstein

Ph.D. Candidate, Clemson University

Conference Travel Grant Type 2 (Society of Wetland Scientists)

Effects of microtopography on transpirational characteristics of baldcypress in a tidal freshwater swamp

“Tidal freshwater swamps generally occur in coastal floodplains of the US near the upper reaches of tidal influence. These swamps experience freshwater flooding once or twice daily depending upon river discharge and site tidal regime. Many tidal freshwater swamps have a microtopographical mosaic consisting of the base elevation of the swamp (hollow) interspersed with elevated islands (hummocks) that exceed the height of most floods. There is growing evidence that the diversity and distribution of wetland trees is largely influenced by site microtopography, with hummocks providing necessary sites for respiration while hollows remain flooded. We hypothesized that hummocks play a role in the physiology of tidal freshwater trees during flood stage of a tidal cycle and this role can be detected by measuring the amount of water transpired by the trees. Thermal dissipation probes were installed on 22 baldcypress trees in a South Carolina tidal freshwater swamp, half in hollows and the other half on hummocks, to record the amount and timing of water flowing through the active sapwood. We also measured water level, air temperature (base of crown), and humidity at 15-min intervals concurrent to sap flow. Rates of sap flow for trees on hummocks and hollows were compared during periods when hollows were inundated by tidal waters, hummocks remained unflooded, and vapor pressure deficits were high enough to ensure that trees were transpiring. Our data provide evidence that baldcypress maintain broad tolerance to flooding on these sites; differences that were detected between hummocks versus hollows were small.“