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

  • Author / Creator
    Tannas, Steven Clare
  • 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.

  • Subjects / Keywords
  • Graduation date
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
  • Institution
    University of Alberta
  • Degree level
  • Department
    • Department of Agricultural, Food and Nutritional Science
  • Supervisor / co-supervisor and their department(s)
    • Dr. Edward W. Bork (Agricultural, Food and Nutritional Science
  • Examining committee members and their departments
    • Dr. Andreas Hamann (Renewable Resources)
    • Dr. J.C. Cahill (Biological Sciences)
    • Dr. James T. Romo (Plant Sciences, University of Saskatchewan)
    • Dr. Walter W. Willms (Agriculture and Agri-Foods Canada)
    • Dr. M. Anne Naeth (Renewable Resources)