Recovery of Potamogeton pectinatus L. stands in a shallow eutrophic lake under extreme grazing pressure

Published source details Hilt S. (2006) Recovery of Potamogeton pectinatus L. stands in a shallow eutrophic lake under extreme grazing pressure. Hydrobiologia, 570, 95-99.
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Summary

Action: Exclude wild vertebrates using physical barriers

A replicated, paired, controlled study in 2001 in a freshwater lake in Germany (Hilt 2006) found that fencing to exclude birds and/or fish sometimes increased the biomass and length of sago pondweed Potamogeton pectinatus shoots, but had no significant effect on shoot density. After two months, pondweed shoot biomass was greater in fully fenced plots (birds and fish excluded; 14–23 g/m²) than in open areas (1–5 g/m²). Partly fenced plots (only birds excluded) had a statistically similar shoot biomass (2–11 g/m²) to the open areas. Meanwhile, pondweed shoots were longer in both fully fenced plots (22–25 cm) and partly fenced plots (11–13 cm) than in open areas (6–7 cm). Pondweed shoot density did not significantly differ between treatments (fully fenced: 340–1,690; partly fenced: 190–1,400; open: 190–1,670 shoots/m²). Methods: In April 2001, sixteen 1-m² exclosures (2 cm mesh) were established in sago pondweed stands in two shallow-water sites (0.5 m deep). In each site, four exclosures were fully fenced (mesh extending to sediment surface, excluding waterbirds and large fish) and four were partly fenced (25 cm gap between bottom of mesh and sediment surface, excluding birds but not fish). Vegetation was surveyed in June 2001: one sample/exclosure and four samples/site outside the exclosures. Biomass was dried before weighing. This study used two of the sites from Körner & Dugdale (2003).