Repeated grazing of a salt marsh grass by moulting greylag geese Anser anser– does sequential harvesting optimise biomass or protein gain?

Abstract

The effects of simulated goose grazing on common saltmarsh‐grass Puccinellia maritima plants were tested on a Danish salt marsh during the flightless moulting period of greylag geese Anser anser (3–21 June 1998). Plants in an area exclosed from the influence of grazing and the nutrient effects of goose faeces were subject to removal of youngest lamina at 3‐, 6‐, 9‐ and 18‐day intervals during this period. Average biomass and protein accumulation between harvests was highest at defoliation intervals of 9 days or more. Field observations from two separate study areas demonstrated geese returned to regraze the Puccinellia sward after 6–8 days and oesophageal contents from feeding geese showed selection for lamina lengths consistent with the results of clipping every 6 days. Geese therefore regrazed Puccinellia patches at shorter intervals than expected were they to maximise their intake of biomass or protein at each visit. However, total cumulative lamina elongation, equivalent to the long term gain during the entire moult period, showed no significant difference between the three most intensive defoliation treatments, which were significantly greater than those of plants defoliated at 18 day intervals. Highest overall lamina protein levels were maintained at 6‐ and 9‐day defoliation intervals. This suggests geese regrazed Puccinellia patches at a rate that maximised their number of harvests during the flightless period, but maintained highest protein levels and overall biomass in the sward. This suggests, in line with earlier studies, that moulting greylag geese combine dietary selection, reduced nitrogen excretion and regrazing patterns to meet protein demands during regrowth of flight feathers.