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High rates of species extinction have been predicted for the next century as a consequence of climate change. Although species range shifts have been widely reported, evidence of changes in species frequency linked to recent climate change is scarce. Moreover, studies have mainly focused on mountainous ecosystems and species. There is thus a clear lack of understanding of the recent changes in species frequencies linked to climate change across their whole range. Using a large forest vegetation-plot database, we investigated changes in cold and warm-demanding forest plant species frequencies between the periods 1914-1987 and 1997-2013 in French lowlands and highlands. Changes in frequencies were assessed for 185 lowland (warm-demanding), 135 sub-montane (intermediate) and 104 montane (cold-demanding) forest plant species. Observed changes were compared to predicted changes derived from species distribution model predictions. The frequency of montane and sub-montane species strongly declined, whereas the frequency of lowland species remained steady in lowland areas. In highlands, the frequency of lowland, sub-montane and montane species increased, remained steady and decreased, respectively. Predicted and observed trends of changes in the frequency of forest plant species were in agreement. These results clearly show that cold-demanding species are currently declining in lowlands that correspond to their warm range margins, whereas warm-demanding species are expanding in highlands that correspond to their cold range margins. These trends can be seen as early signs of future regional extinction and reshuffling of the spatial presence of species due to climate warming.