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Effects of cattle grazing on food patch choice of brown hares on the salt marsh of Schiermonnikoog

Beek, P. (2002) Effects of cattle grazing on food patch choice of brown hares on the salt marsh of Schiermonnikoog. Master's Thesis / Essay, Biology.

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Abstract

Nitrogen input by clay sedimentation has been shown to be the driving force behind plant species replacement in the Wadden sea salt-marsh system. Old successional stages are dominated by the superior light competitor, Elymus athericus, and suitable grazing sites for the brown hare (Lepus europaeus) dissappear. Consequently hare densities increase with age of the salt marsh, but seem to increase again at salt-marsh areas which are grazed by cattle. This study discusses the effects of cattle grazing on hare grazing on the grazed salt marshes of Schiermonnikoog, one of the barrier islands in the Dutch Wadden Sea. The effects of cattle grazing on the vegetation and subsequent on hare feeding patch choice in short-term and long-term will be discussed. Short-term effects are defined as within a season and are monitored by measuring quality and biomass. Long-term effects accumulate over multiple years and can be seen in influences on succession. In the short term cattle grazing is predicted to decrease the biomass of Festuca rubra, which has been shown to be the hares preffered forage. However, cattle grazing is also expected to increase the quality of Festuca rubra. These two effects can be termed as direct competition and facilitation, respectively. In the long term, cattle grazing is predicted to increase the availability of Festuca rubra, by decreasing abundance of light's shading, dominant plant, Elymus athericus. This long-term effect can be described as indirect facilitation. Diet analyses were performed on hare faeces, collected from grazed and ungrazed salt marsh areas, and, taken together with vegetation measurements, showed that hares actively select for Festuca rubra both in presence and absence of cattle grazing. An experiment manipulating forage quality and blomass was set up, in order to find the preference hares have when choosing their grazing site. Manipulations of quality and biomass were intended to mimick the effects of cattle grazing within a season, i.e. short-term effects of cattle grazing. Neither quality nor biomass manipulations of Festuca rubra caused the hares to show significant preference, neither in the early growing season, nor later in the season. Long term effects on the vegetation by cattle grazing were studied by using exclosed areas. There was one exclosure that had been excluded from grazing for 4 years and five exclosures which had been excluded from grazing for 30 years. After 4 years of excluding cattle, a higher biomass and a taller vegetation was found and the composition of the vegetation was changed. Later successional species were abundant in the ungrazed area, which indicates that cattle grazing impedes plant species replacement and thus retards vegetation succession. Furthermore Festuca rubra was equally abundant inside and outside the exciosure. Hares did not show a clear preference for the grazed or the ungrazed areas. Areas which had been excluded from cattle grazing for 30 years, characterised by old successional stages, exhibited very little to no hare grazing. The abundance of Elymus athericus appeared to be the most important factor which deters hares. Extremely low hare grazing intensity was found in vegetation with more than 30% of Elymus athericus coverage and the highest dropping densities were found on sites where Elymus athericus was lacking. Abundance of Festuca rubra cannot explain the hare grazing density results. Therefore it seems that the hypothesis discussing the indirect facilitative effect of cattle grazing on hare grazing, concerning the availability reduction of Festuca rubra due to shading by the strong competitor Elymus athericus, must be discarded. Another possible hypothesis is that structural plants, such as Elymus athericus, may effect hare grazing density.

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/9172

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