Grazing effects of black swans Cygnus atratus (Latham) on a seasonally flooded coastal wetland of eastern Australia

  • Published source details Smith A.N., Vernes K.A. & Ford H.A. (2012) Grazing effects of black swans Cygnus atratus (Latham) on a seasonally flooded coastal wetland of eastern Australia. Hydrobiologia, 697, 45-57.


This study is summarised as evidence for the following.

Action Category

Exclude wild vertebrates: freshwater marshes

Action Link
Marsh and Swamp Conservation
  1. Exclude wild vertebrates: freshwater marshes

    A replicated, controlled study in 2007 in a freshwater marsh in New South Wales, Australia (Smith et al. 2010) found that plots fenced to exclude black swans Cygnus atratus contained a greater biomass and density of dominant spikesedge Eleocharis equisetina, than plots left open to swans. After 20 weeks, fenced plots contained more spikesedge biomass (above-water: 540 g/m2; above-sediment: 1,200 g/m2) than open plots (above-water: 3 g/m2; above-sediment: 580 g/m2). Fenced plots contained 64–130 spikesedge stems/m2 compared to 1–15 spikesedge stems/m2 in open plots (statistical significance not assessed). Methods: In February 2007, ten 4-m2 plots in a freshwater marsh (occasionally brackish) were fenced (5 cm wire mesh) to exclude black swans. The whole study area was also fenced to exclude cattle. Vegetation was sampled in the 10 swan exclosures, and five nearby plots grazed by swans, until July 2007. Emergent spikesedge stems were counted. All spikesedge material above the sediment was cut, dried and weighed. This summary does not include data (a) for five open plots that were not grazed by swans in 2007, and (b) for exclosures after July, because some exclosures were corroded and grazed by swans.

    (Summarised by: Nigel Taylor)

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