Abstract
The influence of winter foraging pressure by Bewick's Swans Cygnus columbianus on rhizomes, on the aboveground biomass the following summer, of Zizania latifolia, was investigated at Sugao Marsh, Ibaraki Prefecture, central Japan, from 1998 to 2004. An experimental area was covered with netting to prevent Bewick's Swans from grubbing up Z. latifolia rhizomes during winter. The dry weight of aboveground stalks was measured from quadrats inside and outside the experimental area the following autumn. From the second year, after preventing swans from foraging, the aboveground biomass of Z. latifolia in the experimental area declined, and was lower than the aboveground biomass of Z. latifolia outside the experimental area. Thus, the foraging pressure of swans on Z. latifolia rhizomes in winter positively impacts Z. latifolia growth aboveground during the subsequent growing season.
