The small mammal community of an air pollution affected area of the Beskydy Mts was studied over a seven-year period. Highest dominance and population density values were found in the field vole (Microtus agrestis) and its feeding ecology and negative impact on reforestation have been evaluated. The vegetative parts of plants, particularly those of monocotyledons, were dominant in vole diets, mainly as the area is largely occupied by the invasive plant genus Calamagrostis. In early spring (i.e. before the growing season started) grasses predominated in the field vole's food (74 % of volume, v). Bark was also consumed to some extent - its importance index value (I) was 4 %. In spring (i.e. after the growing season started) grasslike species were again preferred (v = 57 %) but flowers of Vaccinium myrtillus were also consumed (v = 20 %). Even in autumn grasslike species prevailed (v = 36 %), however, the diet was more diverse and seeds and fruits (v = 30 %) were also eaten. of these the basic food items were those of V. myrtillus (v = 16 %) and of herbs and ferns (v = 16 %) including Oxalis acetosella (v = 14 %). An increase in fungi in the diet was found in autumn. Diet availability and early spring and spring diets ere highly correlated, but this was not the case in autumn. The extent of vole damage to tree regeneration in 3,027 saplings was studied. The frequency of damage was significantly greater in deciduous tree species (15 %). Coniferous tree transplants were attacked only rarely (1.4 %), and usually when the tree was already in poor condition. The greater degree of damage caused to natural and artificial forest regenetarion can only be associated with high vole population densities.