Does the Type of Disturbance Matter When Restoring Disturbance-Dependent Grasslands?

Authors

  • Andrew S. MacDougall,

    Corresponding author
    1. Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
    2. Present address: Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
      Address correspondence to A. S. MacDougall, email amacdo02@uoguelph.ca
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  • Roy Turkington

    1. Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
    2. Biodiversity Research Center, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
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Address correspondence to A. S. MacDougall, email amacdo02@uoguelph.ca

Abstract

The reintroduction of burning is usually viewed as critical for grassland restoration; but its ecological necessity is often untested. On the one hand, fire may be irreplaceable because it suppresses dominant competitors, eliminates litter, and modifies resource availability. On the other hand, its impacts could be mimicked by other disturbances such as mowing or weeding that suppress dominants but without the risks sometimes associated with burning. Using a 5-year field experiment in a degraded oak savanna, we tested the impacts of fire, cutting and raking, and weeding on two factors critical for restoration: controlling dominant invasive grasses and increasing subordinate native flora. We manipulated the season of treatment application and used sites with different soil depths because both factors influence fire behavior. We found no significant difference among the treatments—all were similarly effective at suppressing exotics and increasing native plant growth. This occurred because light is the primary limiting resource for many native species and each treatment increased its availability. The effectiveness of disturbance for restoration depended more on the timing of application and site factors than on the type of treatment used. Summer disturbances occurred near their reproductive peak of the exotics, so their mortality approached 100%. Positive responses by native species were significantly greater on shallow soils because these areas had higher native diversity prior to treatment. Although likely not applicable to all disturbance-dependent ecosystems, these results emphasize the importance of testing the effectiveness of alternative restoration treatments prior to their application.

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