Burning Prairie to Restore Butterfly Habitat: A Modeling Approach to Management Tradeoffs for the Fender's Blue

Authors

  • Cheryl B. Schultz,

    1. Department of Zoology, University of Washington, Box 351800, Seattle, Washington 98195-1800, U.S.A.,
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  • Elizabeth E. Crone

    1. Department of Zoology, University of Washington, Box 351800, Seattle, Washington 98195-1800, U.S.A.,
    2. Current address: Ecology Division, Biological Sciences Department, University of Calgary, Calgary, Alberta T2N 1N4, Canada
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Abstract

Designing strategies to manage rare species’ habitats may involve tradeoffs that include negative short-term impacts to achieve positive long-term success. In managing grasslands, fire is a powerful tool to control invasive weeds and stimulate native plant growth, but it may decimate the invertebrate fauna. To rank potential burn strategies for Icaricia icarioides fenderi (Fender's blue butterfly) habitat, we present an empirically based mathematical model. Parameter estimates are based on experiments conducted by Wilson and Clark from 1994 to 1997. Potential strategies include combinations of times between burn (1, 2, 3, 4, or 5 years) and fractions of a habitat to burn in each fire (1/8, 1/4, 1/3, or 1/2), as well as a strategy of never burning. Burning one-third of the habitat every year maximizes the average annual population growth rate, but, based on maximum likelihood parameter estimates, 8 of 21 strategies led to 95% of simulated butterfly populations persisting for 100 years. In simulations based on the parameters’ lower confidence limits, however, there were some cases in which no strategies led to populations persisting 100 years. In this uncertainty analysis—the effect of changes in parameters based on our confidence in them—we also investigated the rank order of the strategies. This uncertainty analysis indicated that the rank order of burning strategies is most sensitive to our confidence in rates of habitat change after a burn (number of “good” years after a fire and time for habitat to return to pre-burn conditions). Surprisingly, however, the rank order of strategies changes little over a wide range of butterfly demographic rates. Better knowledge of rates of habitat change after a burn would improve our ability to make management decisions substantially more than better knowledge of the butterfly's vital rates.

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