The decline of the Frosted elfin butterfly (Callophrys irus (Godart)) population in the Rome Sand Plains (RSP) of central New York is directly related to loss of its host plant, Wild blue lupine (Lupinus perennis L.), as Eastern white pine (Pinus strobus L.) invades the open sandy habitats where lupine grows. A Frosted elfin (New York threatened) population remains where lupine is the densest. We tested the hypotheses that tree canopy hinders lupine performance and restricts elfin behavior. Removal of white pines in experimental plots resulted in dramatic increases in canopy openness. Lupine flowering stems and lupine cover increased significantly in the tree removal plots and remained constant or declined in the control plots. The total number of lupine stems decreased, however, in both control and cleared plots. Observations of butterflies in the experimental plots increased significantly after tree removal, and male elfins, which form mating territories in sandy areas at the edges of lupine patches, established new territories in open patches where trees had been removed. Several new territories have been used each year since tree removal. This rapid response by the butterflies reflects their behavioral preferences for open areas near lupine patches. Selective tree removal at the RSP has benefited individual lupine plants and increased habitat for Frosted elfin butterflies, but more extensive habitat manipulation may be necessary to increase lupine population numbers.