Compensatory growth responses of Potamogeton pectinatus to foraging by migrating trumpeter swans in spring stop over areas

Published source details LaMontagne J.M., Jackson L.J. & Barclay R.M.R. (2003) Compensatory growth responses of Potamogeton pectinatus to foraging by migrating trumpeter swans in spring stop over areas. Aquatic Botany, 76, 235-244.
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Summary

Action: Exclude wild vertebrates

A replicated, paired, controlled study in 1999 in two ponds in Alberta, Canada (LaMontagne et al. 2003) found that excluding migrating trumpeter swans Cygnus buccinator had no significant effect on the abundance of the dominant submerged macrophyte species. In two of two ponds, the abundance of sago pondweed Potamogeton pectinatus was statistically similar in both plots from which swans were excluded, and plots left open to swan grazing. This was true for both above-ground biomass (exclosures: 48–96 g/m²; open: 51–157 g/m²) and shoot density (exclosures: 22–284 shoots/m²; exclosures: 57–122 shoots/m²). In one pond, the density of small shoots (<1.0 g) was significantly greater in exclosures (18 shoots/0.09 m²) than open areas (7 shoots/0.09 m²). Methods: Five temporary swan exclosures (60 x 60 cm; 0.2 cm plastic mesh) were set up in each of two ponds. The exclosures were set up in spring 1999 before trumpeter swans migrated into the area, the removed in summer after the swans had moved out of the area. Macrophytes were cut from 30 x 30 cm quadrats in August 1999: 3–5 quadrats/pond in the (former) exclosures, and 5 quadrats/pond in adjacent macrophyte patches open to goose grazing. Biomass was dried before weighing.