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The effects of vertebrate herbivore grazing on the alpine vegetation of the Eastern Central Plateau, Tasmania

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Bridle, Kerry Lynn (2000) The effects of vertebrate herbivore grazing on the alpine vegetation of the Eastern Central Plateau, Tasmania. PhD thesis, University of Tasmania.

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Abstract

This thesis examines the relative influences of domestic stock, rabbits and native
vertebrate herbivores on alpine and treeless subalpine vegetation on the Eastern Central
Plateau Tasmania, with special reference to tall alpine herbs.
Results from 25 year old grazing exclosures on Liawenee Moor indicated that domestic
stock had a much greater impact on the vegetation than rabbits and native vertebrate
herbivores. Vegetation cover was greatest and structure was most complex in the
ungrazed exclosure, whilst vegetation cover was least in the sheep, rabbit and marsupial
grazed control area. Aerial photographic analysis showed that, over a 19 year period,
regeneration in these exclosures was most successful in the ungrazed exclosure, whilst
bare ground increased in the sheep grazed area.
Most plant species that were present in the grazing exclosures were also present in
sheep grazed areas. However, sheep grazing had a dramatic impact on flowering
success of many tall alpine herbs, with significantly more herbs flowering in the rabbit
and native vertebrate herbivore grazed plot and the ungrazed exclosure than the sheep
grazed area. A few tall herbs were tolerant of grazing by rabbits and native herbivores
as there was no significant difference in flowering success between the two exclosures
(the ungrazed exclosure and the rabbit plus native herbivore grazed exclosure). Vegetation cover in 23 year old plots at Liawenee and Augusta tended to increase at
approximately 1% per year, whether grazed by domestic stock (Liawenee) or not
(Augusta). Regeneration at Liawenee was dominated by shrubs and grasses. Shrubs
were the most important recolonisers of bare ground at Augusta. Regeneration occurred
at a slightly faster pace at Augusta, despite its higher altitude.
At other sites, where domestic stock grazing ceased 6 years before the study
commenced, the average annual increment in vegetation cover was also approximately
1%. The greatest increase in vegetation cover was found in the ungrazed exclosures,
followed by the rabbit grazed exclosures, whilst the rabbit plus native vertebrate
herbivore grazed controls had the lowest increase in vegetation cover. Flowering success at these sites was greater for some tall herb species in the ungrazed
exclosures, but differences were less marked than at Liawenee. There were very few
differences in flowering success between rabbit grazed exclosures and those areas that
were open to rabbits and native vertebrate herbivores, indicating that rabbits may have a
larger impact on flowering success than native herbivores.
Naturally ungrazed areas, small islands in a fast flowing stream, were dominated by tall
alpine herbs and palatable grasses, which were non-existent or sparse on the native
vertebrate herbivore grazed banks. Tall herbs were dominant on the upstream ends of
these islands, which experienced physical disturbance from fluctuating stream levels.
These islands had very little bare ground other than that created by stream erosion.
A major implication of this study is that the continuation of domestic stock grazing in
treeless subalpine environments will contribute significantly to the deterioration of the
landscape through a decrease in vegetation cover in exposed sites, a reduction in the
structural diversity of the vegetation, a loss or reduction of some palatable plant species
(mainly tall alpine herbs), the reduction of flowering of some tall herbs, and the
maintenance of bare ground patches. Sheep plus rabbits and marsupial grazers have a
much greater impact than rabbits and natives alone. Rabbits in their present numbers,
may be considered to be an additive effect to native vertebrate herbivore grazing as
recovery is slower under combined grazing (rabbits and native vertebrate herbivores)
than under rabbit grazing alone. Rabbit grazing substantially affects the flowering
success of some tall herb species. It is estimated that most of the Eastern Central Plateau will regenerate naturally within
50-80 years. Tall herbs are more prevalent where bare ground is less than 20%, but are
not the dominant lifeform in areas that are grazed. Tall herbs may dominate in naturally
ungrazed environments (islands) but only where physical disturbance of the ground has
occurred.

Item Type: Thesis (PhD)
Keywords: Grazing
Copyright Holders: The Author
Copyright Information:

Copyright 2000 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Includes notes in back pocket. Thesis (Ph.D.)--University of Tasmania, 2000. Includes bibliographical references

Date Deposited: 25 Nov 2014 00:50
Last Modified: 21 Jun 2016 01:33
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