In the absence of fire, Pinus palustris (Longleaf Pine) ecosystems in the southeastern United States are vulnerable to successional change including mesophication, a process where increases in the importance of mesic and fire-intolerant species reduce biodiversity and thwart efforts to restore these systems. To determine the degree and nature of this successional trajectory at a local scale, we examined changes in species composition of a montane Longleaf Pine ecosystem in northwest Georgia using modern vegetation surveys and historical “witness tree” data. We also determined historical fire frequency using fire scars within Longleaf Pine stumps cross-dated to extant Longleaf Pine trees. Modern forest composition contained significantly more fire-intolerant taxa than the historical forest due to increased abundance of mesophytic species, especially Acer rubrum (Red Maple) and decline of Pinus spp. (pines) and some pyrophytic Quercus spp. (oaks). Counter to expectation, there were few differences in species composition between northeastern- and southwestern-facing slopes in modern or historical data. Fire scars indicated a historical mean fire-return interval of 5.5 years and suggest that without the reintroduction of more frequent prescribed fire, regeneration of montane Longleaf Pine is unlikely. Additional restorative techniques may also help these stands support greater biodiversity over time. For instance, co-dominance of pines and oaks in the historical forest suggests that fire-tolerant oaks should be retained in montane restoration efforts.