Fire, a threatened plant and an endangered butterfly: A study of Kinkaid's lupine and Fender's blue butterfly in Oregon's Willamette Valley

Background/Question/Methods <>Kinkaid’s lupine Lupinus oreganus subsp. kincaidii is a federally listed, threatened herbaceous perennial found in Oregon and Washington. In Oregon’s Willamette Valley, it serves as the larval host plant, and a potential nectar source, for the endangered Fender’s blue butterfly Plebejus icarioides fenderi. The prairie habitat shared by these species has been largely lost to development, agriculture and invasive species. Remaining prairie fragments are threatened by succession in the absence of historic fire. Prescribed burning, a tool used to slow the encroachment of woody plants is also thought to stimulate growth of the Kinkaid’s lupine. Previous studies of butterfly behavior have demonstrated that Fender’s blue females spent a larger proportion of their active time ovipositing in burned habitat and demographic studies indicate that Fender’s blue females lay more eggs on lupine in areas that were recently burned. We explored several possible effects of fire on lupine that may explain these patterns. In this study, conducted during spring 2012, we measured the effects of fire on plant size, flower abundance and flowering phenology. We also collected 480 leaf samples (three leaves each in 20 plots) in each of 4 replicate burned (treatment) and unburned (control) areas. We are using these leaves to determine whether fire affects the water content of lupine foliage, as well as, the nutrient content C, N and total P.

Results/Conclusions<> We found that fire had multiple effects on lupine. Plants in areas burned during the fall of 2011 had more leaves during the spring of 2012. Flowering phenology was also shifted, with lupines in previously burned areas flowering earlier than unburned controls. Analyses of plant water content and foliar chemistry are nearing completion. These data will provide us with a more mechanistic understanding of butterfly oviposition preference. Combined with demographic information, this will allow us to determine if butterflies are actively selecting higher-quality habitat in burned areas and allow us to better estimate the effectiveness of fire as a management tool for Fender’s blue butterfly.

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