Treeline elevation is rising in alpine areas throughout the world. Encroachment of forest into alpine areas is predicted to isolate and reduce the area of habitats above treeline, such as mountain-top meadows. These changes potentially threaten organisms endemic to these habitats. However, not all area above treeline is necessarily suitable for forest. Since many of these areas contain resources necessary for endemic alpine species, there is the possibility that these species may be able to persist for considerable time, despite broad changes in the elevation of treeline. We will investigate encroaching forest and its effects on the Rocky Mountain Apollo butterfly, Parnassius smintheus, an alpine meadow specialist, at three sites in the front ranges of the Canadian Rocky Mountains that have experienced considerable forest encroachment over the last 60 years. Using a combination of aerial photography, habitat mapping, and tree ring dating, we will determine areas above treeline that are not subject to forest encroachment as well as a time frame over which such chnages may occur. We will parameterize and optimize metapopulation persistence models for the butterfly using 14 years of exisitng population and dispersal data and additional data collected during this study. Using habitat areas not subject to forest encroachment, these persistence models will allow us to predict if forest encroachment will impact P. smintheus and if so when populations will be affected.