The ecological significance of cultural parks and protected areas, such as battlefields, has frequently been overlooked. Yet small cultural parks with rare populations can provide refugia and colonists for re-establishment elsewhere, and thus are likely to become increasingly important as climate change leads to range shifts and accelerated population declines. We estimated the abundance of the regional endemic plant Lemhi penstemon (Petistemon lemhiensis) in Big Hole National Battlefield in western Montana. We estimated during 2009 and 2010 that approximately 1500 adult plants occurred in two subpopulations clustered on steep south-facing slopes where down-slope soil movement is highest. Results from 2011 provided evidence for an increase to approximately 3000 adult plants. The battlefield contains the largest reported population of this geographically restricted species and is, therefore, a globally-significant reserve for Lemhi penstemon. However, inflorescence rates were lower and the mean number of basal rosettes per plant, a proxy for plant age, was greater than reported elsewhere. Lemhi penstemon requires open soil microsites for regeneration and appears vulnerable to land- use change, particularly when it involves disruption of fire regimes. Spotted knapweed (Centaurea stoebe) abundance is also increasing in the study area, presenting another threat. Managing Big Hole Battlefield to simultaneously reflect a fixed historic period and support Lemhi penstemon will be a persistent challenge that will require a more active, adaptive management strategy. Our study has helped to integrate cultural and natural resource management in the Battlefield and provides a model for conservation in other cultural parks. © 2013 Natural Areas Association. Abstract reproduced by permission.