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RESPONSES OF SALT-MARSH VEGETATION TO GRAZING BY LESSER SNOW GEESE (Anser caerulescens caerulescens).

RESPONSES OF SALT-MARSH VEGETATION TO GRAZING BY LESSER SNOW GEESE (Anser caerulescens caerulescens).

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Title: RESPONSES OF SALT-MARSH VEGETATION TO GRAZING BY LESSER SNOW GEESE (Anser caerulescens caerulescens).
Author: Bazely, Dawn R.
Abstract: SUMMARY:
 
1. The mechanisms by which grazing by lesser snow geese bring
about an increase in cumulative net above-ground primary
production (NAPP) of salt marsh vegetation at La Pérouse
Bay, Manitoba were investigated.
 
2. In the absence of grazing, cumulative NAPP was approximately
80 g m-2 in swards dominated by Puccinellia phryganodes in
1982 and 1983. Grazing by snow geese resulted in increases
in cumulative NAPP of 46% in 1982 and 106% in 1983. These
increases were significant (p < 0.05).
 
3. There was a significant correlation between values of leaf
Brea index and live standing crop in grazed and ungrazed
sites (p < 0.05).
 
4. Grazing stimulated tillering in P. phryganodes. This
increase in axillary shoot production accounted for the
increase in cumulative NAPP of grazed sites compared with
ungrazed sites in 1982 and 1983.
 
5. The rate of appearance of leaves and the rate of death of
leaves was similar on main shoots of P. phryganodes in both
grazed and ungrazed sites. However, the total number of leaves
produced on axillary shoots of grazed plants was substantially
higher than that of ungrazed plants. The average age of a
leaf when grazed was 14 days, whereas the mean age of ungrazed
leaves was 35 days.
 
6. Significant increases in live standing crop were observed in
exclosed plots fertilised with fresh snow goose drqppings
compared with that in control plots which received no droppings
(p < 0.05).
 
7. Rates of nitrogenase activity, measured by acetylene reduction,
were consistently greater in grazed than in ungrazed sites
in 1983.
 
8. Grazing maintained the total nitrogen content of P. phryganodes
at a level of 2.4% on a dry weight basis, while that of
ungrazed shoots of P. phryganodes declined by 30% two weeks
after hatch.
 
9. In the absence of snow geese, over a period of four years plant
species diversity increased in exclosures while live standing
crop declined and litter accumulated. The soil environment
of ungrazed sites was cooler than that of grazed sites.
 
10. It was concluded that the intensive grazing activities and
colonial feeding behaviour of snow geese result in higher
nitrogen availability for plant growth in grazed sites, and
the maintenance of better quality forage as a result of
the higher nitrogen content. Nitrogen is supplied from goose
droppings and increased rates of nitrogen fixation in grazed
sites. P. phryganodes, a grass, is able to withstand
heavy grazing, and plants respond by producing tillers so
that the amount of forage 13 increased significantly.
 
Subject: Herbivory
Wapusk National Park
Churchill
Manitoba
La Pérouse Bay
Plant-Herbivore Interaction
Nitrogen Cycling
Type: Thesis
Rights: Attribution-NonCommercial-NoDerivs 2.5 Canada
http://creativecommons.org/licenses/by-nc-nd/2.5/ca/
URI: http://hdl.handle.net/10315/18772
Citation: Thesis (M.Sc.) - University of Toronto.D. R. Bazely: Theses Canada, 1984. (AMICUS No. 36132274)
Date: 1984

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Attribution-NonCommercial-NoDerivs 2.5 Canada Except where otherwise noted, this item's license is described as Attribution-NonCommercial-NoDerivs 2.5 Canada