Many high-altitude summits across the boreal forest zone of Quebec are colonized by tundra vegetation. In this study, the origin and plant composition of these remote, isolated tundra summits have been documented to link their nature and floristic diversity to several potential causal factors. Analysis of spruce macrocharcoal pieces distributed at the soil surface indicates that wildfire is the chief factor behind the creation of the tundra summits across the boreal forest zone. All of the summits were deforested by fire during 2 main periods of the Holocene, around 100–500 cal y BP and 1150–1600 cal y BP. However, fire activity seems to have little influence on vegetation composition and diversity of post-fire tundra summits; latitudinal position and surface area are the main driving factors influencing floristic diversity. Given the remoteness of the sources of the arctic—alpine flora and young age of tundra summits associated with recent deforestation, only a small number of arctic—alpine species are colonizing the sites. Because of the regional dominance of boreal flora composed of common and widespread species adapted to nutrient-poor soils, it is probable that arctic—alpine species located on the tundra summits will go extinct in a warmer world promoting forest recovery.