Vegetation Dynamics in Seasonally Grazed Upland Systems
dc.contributor.advisor
Legg, Colin
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dc.contributor.advisor
Waterhouse, Tony
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dc.contributor.advisor
Atkinson, David
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dc.contributor.author
Pollock, Meg L
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dc.date.accessioned
2006-01-05T15:28:05Z
dc.date.available
2006-01-05T15:28:05Z
dc.date.issued
2003-07
dc.description.abstract
This thesis addresses the effects of seasonality of grazing on vegetation dynamics.
Background to the thesis is provided by the Hill Sheep and Native Woodland (HSNW)
project, a system-scale experiment with the long-term aim of integrating upland sheep
husbandry within native woodlands. Sheep husbandry in the HSNW project has
involved a change from year-round grazing to off-wintering (grazing on upland areas
from April to October only). The potential impact of this change on individual plants,
plant communities and the landscape is evaluated.
A cutting experiment was run to simulate herbivory in different seasons at the level of
the individual plant. In grassland communities, where most species are wintergreen
graminoids, interaction between species and seasons in response to cutting was
minimal. In mire communities, where species with a range of life-forms and
phenologies are present, there was considerable interaction between species and lifeform
in response to cutting in different seasons. Non-wintergreen graminoid species
recovered more rapidly than wintergreen graminoid species following cutting in
spring, but the reverse occurred following cutting in autumn. Dwarf shrubs and forbs
were slow to recover from cutting in all seasons in both mires and grasslands.
The impacts of three grazing treatments in the HSNW project (unchanged year-round
grazing, change to off-wintering, and change to zero grazing) on sward structure and
species abundance were monitored. Sward height increased in the ungrazed treatment,
but changes in species relative abundance were minimal in the short time-scale of the
study.
Literature suggests that change in plant species abundance in grazed systems is driven
by herbivore selection preference for (or avoidance of) plant species and plant
responses to grazing. Experts were interviewed to generate a set of seasonal data on
herbivore selection preferences and plant responses, and levels of agreement between
experts were assessed. Information was also collated on plant response to herbivory
from the cutting experiment (above) and plant trait information from the literature. A
qualitative model was developed to predict change in species abundance. It was used
to: i) explore patterns of interaction between herbivore preferences and plant responses
to grazing; ii) compare short-term predictions of change in abundance made using each
of the information sources available; iii) make longer-term predictions using plant trait
information. The short-term predictions were tested against the small changes in
species abundance that had occurred in the HSNW project. Predictions made with the
plant trait information were more accurate than those made with other information.
A study of levels of browsing on regeneration was carried out in mature sheep-grazed
birch woodlands. It was rare to find regeneration at sites grazed only by sheep, but
tree regeneration did occur in the presence of sheep. Seasonal variation in browsing
was found to be more related to the presence of cattle than to the presence of sheep.
Finally, the findings are collated to make management recommendations for the
HSNW project and other systems where seasonal grazing regimes could be beneficial.
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dc.identifier.uri
http://hdl.handle.net/1842/856
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dc.publisher
University of Edinburgh; College of Science and Engineering; School of GeoScience
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dc.subject
vegetation dynamics
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dc.subject
Hill Sheep and Native Woodland project
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dc.subject
Grazing
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dc.subject
Global Change Research Institute
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dc.subject.other
vegetation dynamics
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dc.subject.other
Hill Sheep and Native Woodland project
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dc.subject.other
Grazing
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dc.title
Vegetation Dynamics in Seasonally Grazed Upland Systems
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dc.type
Thesis or Dissertation
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dc.type.qualificationlevel
Doctoral
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dc.type.qualificationname
PhD Doctor of Philosophy
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