Thresholds of change in decomposition rates along a dune/swale transect on Virginia’s barrier islands

Aboveground and belowground decomposition rates were determined along a barrier island dune/swale transect located on the Virginia Coast Reserve-Long Term Ecological Research Site using litterbags and wooden dowels.  The objective was to determine the influence of fine scale changes in the environment on decomposition. Wax myrtle (Morella cerifera) leaves and dowels of southern yellow pine wood were used as standard substrates to evaluate environmental influences on decay.  Aboveground decomposition was highest in the shrub-dominated swale (44% leaf mass lost after 185 days) and at the edge of the fresh water marsh (48% leaf mass lost after 185 days); and was lowest at high dune elevations (23% leaf mass lost after 185 days) and the lower dune side facing the shrub-dominated swale (21% leaf mass lost after 185 days). Belowground decomposition was quite variable with the highest amount of decomposition found just below the peak of the dune on the shrub-dominated swale side (41% woody mass lost after 185 days) and at the marsh edge (21% woody mass lost after 185 days).  Belowground decomposition was lowest in the marsh itself (10% woody mass lost after 185 days). Aboveground and belowground decomposition increased with decreasing elevations toward both the shrubby and marshy swales, though decomposition was slightly higher in the marshy swale.  Elevation, groundwater level, vegetation composition and soil N-content are being analyzed for correlations with spatial patterns observed in decomposition rates.  The fine scale dynamics of ecosystem processes, like decomposition, merit further investigation in order to determine areas where these processes would be enhanced or restricted and where thresholds of change occur.