The species richness pattern exhibits a strong altitudinal dependence which may be altered under the influence of land use-related disturbances. The Beskid Niski Mountains are part of the northern Carpathian Mountains – an area that saw a large-scale relocation of certain ethnic groups after World War II. The subsequent rapid decline in the human population level was the main factor shaping the environment in this area, and contributed to a rapid increase in the forest area, also introducing changes in its functioning. The increase in the forest area was not evenly distributed, showing the largest values at higher locations. The present study is focused on changes in the species richness of the Carpathian fir forests along the altitudinal gradient, in relation to socio-economical transformations. The changes indicated an overall decrease in species richness, especially at higher locations. The main reason for these changes seemed to be forest management-related, causing an increase in the share of blackberry, fern and grass species, as well as the disappearance of species diagnostic of the ancient forests, which led to homogenization of vegetation. The increase in the mountain forest area has proven to be insufficient to secure the species richness of forests.