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The impact of goose foraging on Spartina anglica: Plant performance under field- and laboratory conditions

Siepel, A. (1998) The impact of goose foraging on Spartina anglica: Plant performance under field- and laboratory conditions. Master's Thesis / Essay, Biology.

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Abstract

Since 1991, Greylag Geese use the island of Schiermonnikoog as an autumn and winter staging area. In the season of 1995-1996, approximately 700 Greylags wintered on the island. The Greylags were mainly found in two areas. A brackish Scirpus maritimus marsh served both as roosting- and foraging area. The salt marsh served as a day-time foraging area. In the salt marsh, Greylags foraged on the below-ground parts of Spartina anglica. In contrast to Scirpus maritimus, goose foraging on below-ground parts of Spartina anglica has only rarely been described. The effects of goose grubbing on Spartina anglica, a relatively new species, are largely unknown. On Schiermonnikoog, we studied the impact of Greylag foraging on stands of Spartina anglica. In a greenhouse experiment, we determined the effects of shoot removal, an aspect of goose grubbing, on the recovery and survival of Spartina anglica under both flooded and dry conditions. Spartina anglica was found as a wide belt of vegetation in the lower salt marsh between the third and the fourth creek. Greylags grubbed for rhizomes on both the northern and the southern edges of these stands. They foraged on the below-ground parts of Spartina anglica only in areas where it was present in clones, surrounded by bare soil, and that were waterlogged or regularly flooded. The below-ground parts of Spartina anglica can probably only be extracted by Greylags in these particular areas. The Greylags preferred grubbing for rhizomes of isolated Spartina anglica shoots, which are relatively easy to extract. This enables them to maximise their foraging efficiency. Greylag foraging pressure on Spartina anglica was very low. In the most intensively used area, less than 2% was removed. The greenhouse experiment showed that Spartina anglica could survive and recover from shoot removal under dry soil conditions. Under flooded soil conditions, both above- and belowground survival and recovery of Spartina anglica plants was poor, unless the flooding ceased. Shoot recovery in clipped pots was much faster in the dry- than in the flooded treatment. Many new emerging shoots died in flooded-clipped pots, while shoot death was negligible in dry-clipped pots. In only two flooded-clipped pots, shoots could eventually recover after flooding had ceased. In all treatments, the soil was virtually anoxic 1 mm below the soil surface. Greylags preferably grubbed for Spartina anglica rhizomes in flooded areas. Especially in these areas, Spartina anglica is most vulnerable. Hence, foraging Greylags could potentially eliminate large parts of the Spartina anglica stand on Schiermonnikoog. In our field season, however, goose grazing pressure on Spartina anglica was very low. This was mainly caused by the fact that the main food of wintering Greylags was formed by Scirpus maritimus tubers. Only when the Scirpus marsh will be depleted by grubbing geese, Greylags are expected to intensify their use of the salt marsh as a foraging area. This might eventually result in a significant damage to the Spartina anglica stands on Schiermonnikoog.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Biology
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 07:31
Last Modified: 15 Feb 2018 07:31
URI: http://fse.studenttheses.ub.rug.nl/id/eprint/9238

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