BURNING PRAIRIE TO RESTORE BUTTERFLY HABITAT - A MODELING APPROACH TOMANAGEMENT TRADEOFFS FOR THE FENDERS BLUE

Designing strategies to manage rare species' habitats may involve trad eoffs that include negative shortterm impacts to achieve positive long -term success. In managing grasslands, fire is a powerful tool to cont rol invasive weeds and stimulate native plant growth, but it may decim ate the invertebrate fauna. To rank potential burn strategies for Icar icia 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. Poten tial 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 populatio n growth rate, but, based on maximum likelihood parameter estimates, 8 of 21 strategies led to 95% of simulated butterfly populations persis ting for 100 years. In simulations based on the parameters' lower conf idence limits, however, there were some cases in which no strategies l ed to populations persisting 100 years. In this uncertainty analysis-t he effect of changes in parameters based on our confidence in them-we also investigated the rank order of the strategies. This uncertainty a nalysis indicated that the rank order of burning strategies is most se nsitive to our confidence in rates of habitat change after a burn (num ber of ''good'' years after a fire and time for habitat to return to p re-burn conditions). Surprisingly, however, the rank order of strategi es changes little over a wide range of butterfly demographic rates. Be tter knowledge of rates of habitat change after a burn would improve o ur ability to make management decisions substantially more than better knowledge of the butterfly's vital rates.