Effects of grazing on underground parts of marsh plants by wintering Middendorf's bean goose Anser fabalis middendorffii: Its role as a keystone species in plant communities

Abstract

AbstractGeese are known to impact on the species composition and abundance of plant communities, with grazing pressure by flocks negatively affecting various aspects of vegetation and ecosystems. However, positive effects have also been highlighted, including grazing preventing competition among plants and helping to maintain a high level of biodiversity. The Middendorf's bean goose Anser fabalis middendorffii is one waterfowl that winters in the marsh lands of Japan. At the Katano‐kamoike pond, the species main wintering site in central Japan, the effects of goose grazing on the structure of marsh plant communities were investigated by using field observations and experiments. During observations of foraging behavior, A. fabalis middendorffii mainly foraged on underground parts of Zizania latifolia and Bolboschoenus fluviatilis, including rhizomes, roots, and tubers, at the marshlands of the pond. The field census showed the biomass of the underground parts was significantly reduced by A. fabalis middendorffii grazing during winter. Specifically, the biomass of rhizomes in Z. latifolia was drastically decreased. Data collected from exclosure experiments over 5 years suggested that grazing pressure regulated the overgrowth of B. fluviatilis and enhanced the abundance of Z. latifolia. Furthermore, a field census of marsh plants at the Shimofukuda reservoir, where there have been no A. fabalis middendorffii, confirmed that the absence of A. fabalis middendorffii was related to a decrease in the abundance and biodiversity of marsh plants. In the Katano‐kamoike pond, A. fabalis middendorffii may play a key role in maintaining plant diversity.