Journal
CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE
Volume 80, Issue 5, Pages 504-511Publisher
CANADIAN SCIENCE PUBLISHING
DOI: 10.1139/B02-032
Keywords
Intermediate Disturbance Hypothesis; diversity; exotic species; grassland
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The Intermediate Disturbance Hypothesis states that the greatest species diversity occurs at inter-mediate levels of disturbance because species coexistence is maintained at a nonequilibrium state and no strong competitor can dominate completely. On the other hand, diversity of exotic species is expected to increase with the disturbance magnitude. These patterns were tested for in this study, The cover of all vascular plants, mosses, and lichens in 1 x 1 m plots across a range of disturbance levels was sampled in 11 remnant grasslands within the Aspen Parkland Ecoregion of central Alberta, western Canada. The Intermediate Disturbance Hypothesis was supported for small-scale within-patch diversity for total species richness and Simpson's diversity index. Lower species diversity was found in undisturbed and lightly grazed as well as in highly disturbed plots. Intermediate levels of disturbance had reduced dominance of Festuca hallii (Vasey) Piper and increased abundance of most other species; this gave the highest species diversity. The species richness and diversity of exotic plant species showed a significant positive relationship with the magnitude of the disturbance. Understanding relationships between disturbance and plant species diversity, especially exotic plants, can influence management decisions on what disturbance regime is conducive to maintaining natural plant communities.
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