In this study, we focused on the diversity and abundance of Carabidae in the Somosierra forest in Madrid, Spain. This forest is atypical for the Mediterranean region due the presence of birch. Collection of 13 monthly samples yielded 29 635 specimens, including 4829 imagos of 21 Carabidae species. The dominant species was west European chorotype of Calathus (Amphyginus) rotundicollis. There was a high proportion of endemism of Iberian species, and considerable seasonal variations in the activity of different species. A wing development assessment indicated that most species were brachypterous (i.e., with reduced wings). This feature restricts the carabid dispersal suggesting high environmental stability in the forest. Overall, our study supports the uniqueness of the study forest and that stable environments support species that are highly vulnerable for anthropogenic disturbances.