Today, the Karner Blue has disappeared from most of its former range. Many of its savanna habitats have been destroyed, or become overgrown because fires and other natural disturbances that kept them open have been suppressed. Wisconsin now supports the world's largest remaining populations of the Karner Blue. The largest and most numerous populations are found in and near Fort McCoy. The Karner Blue has an unusual ecology that may account for its present rarity.
Lupine is a shade-intolerant herb, and can be rapidly overtopped and excluded by shrubs or trees.
Thus, no one population of the Karner Blue may be able to persist indefinitely in isolation. For such a flickering mosaic of populations to persist in a landscape, the frequency of fire must be high enough to maintain suitable habitat for lupine, but low enough that the Karner Blue, lupine, and plants that provide nectar to the butterfly can recover before the next fire or other disturbance. In addition, lupine patches must be close enough to each another, and be connected by open, appropriate habitat, to allow butterflies to fly between patches and invade those recently disturbed. Today, many Karner populations occur along powerlines or trails where occasional mechanical disturbance maintains open microsites in a fire-suppressed landscape. Considerable uncertainty remains as to the optimal frequency and size of prescribed burns, and whether fire or mechanical disturbance is best.