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Mechanisms regulating Poa pratensis L. and Festuca campestris Rybd. within the foothills fescue grasslands of southern Alberta Open Access


Other title
Invasive species
soil moisture
available nitrogen
Festuca campestris
Poa pratensis
rough fescue
Kentucky bluegrass
Type of item
Degree grantor
University of Alberta
Author or creator
Tannas, Steven Clare
Supervisor and department
Dr. Edward W. Bork (Agricultural, Food and Nutritional Science
Examining committee member and department
Dr. James T. Romo (Plant Sciences, University of Saskatchewan)
Dr. M. Anne Naeth (Renewable Resources)
Dr. Walter W. Willms (Agriculture and Agri-Foods Canada)
Dr. Andreas Hamann (Renewable Resources)
Dr. J.C. Cahill (Biological Sciences)
Department of Agricultural, Food and Nutritional Science

Date accepted
Graduation date
Doctor of Philosophy
Degree level
Invasion of non-native species such as Poa pratensis L. has become a serious threat to the conservation of bunch grass communities including foothills fescue grasslands in Alberta, Canada. Conservation efforts are currently limited by a poor understanding of the ecological mechanisms responsible for regulating resistance of native grasslands to encroachment by P. pratensis. While invasion of P. pratensis has been linked to summer grazing, we lack an understanding of how environmental conditions (light, soil moisture content and soil N) may influence invasion. Four studies were conducted to determine the individual and interactive effects of environmental and disturbance mechanisms on P. pratensis invasion and the associated vigor of foothills rough fescue (Festuca campestris Rydb.). An in-situ field study within a late-seral grassland suggested that conditions favoring F. campestris (i.e. high soil moisture content, abundant litter, winter defoliation, undefoliated conditions) suppressed P. pratensis, while those favoring P. pratensis (i.e. summer defoliation, litter removal, ambient water) reduced the vigor of F. campestris. Further exploration of this relationship in a variable density planting study under fallow field conditions suggested that the vigor and density of F. campestris were important factors regulating P. pratensis invasion. In a parallel greenhouse study using seedlings of both species, increased soil moisture content, defoliation, and ambient soil N, increased the ability of P. pratensis to suppress F. campestris, but this was much more significant with younger F. campestris plants. Finally tillage and litter removal were the most effective methods of suppressing P. pratensis and increasing the vigor of F. campestris within heavily disturbed grassland. In the latter experiment, establishment method was also important (cuttings = plugs > seeding) in determining the vigor of F. campestris plants. Observed responses suggest that maintaining the vigor of F. campestris within existing grasslands is the best method of suppressing invasion by P. pratensis. P. pratensis suppression may be accomplished through winter defoliation, allowing litter accumulation and minimizing soil nitrogen. Age appeared to be important in determining the competitive ability of F. campestris plants with immature plants appearing more likely to be detrimentally impacted by P. pratensis than more mature plants.
License granted by Steven Tannas ( on 2011-08-31T15:06:56Z (GMT): Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of the above terms. The author reserves all other publication and other rights in association with the copyright in the thesis, and except as herein provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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