The recent increase of red deer (Cervus elaphus) population and the consequent damage caused by their herbivory impact increasingly concern foresters and farmers in Slovakia as well as in other European countries. A key challenge for wildlife management in order to manage the population effectively is a reliable quantification of available plant biomass, to determine diet composition and the assessment of damage to economically important tree species. Using data from 320 sampling plots, we estimated the overall availability of all forage items seasonally consumed by red deer in the commercial Carpathian forest and we identified the main factors affecting the forage availability in summer and winter. The seasonal diet variability was evaluated by microhistological analysis of 103 samples of red deer faeces from the Kremnica Mountains. The intensity and the degree of damage caused by red deer on economically important tree species were evaluated, in relation to the growth phase and the tree species diversity of the forest. We found that cutblocks were the most productive habitats throughout the year irrespective of the site quality. We found summer forage biomass peaked at ≈8 years and winter forage biomass at ≈10 years following felling, then slowly declined as the cutblocks aged and the canopy increased. However, after two decades after felling forage abundance was still 5 – 8.5 times higher compared to mature forest. Further, ground forage production in mature forest was determined primarily by the light availability, as the major driving factor of the vegetation growth in the closed-canopy forest ecosystems, and to a lesser extent by the site quality. It is suggested that traditionally used site quality is not an efficient indicator of the forage availability for red deer and estimations of the forage potential of hunting grounds should incorporate the developmental stage of the forest as well as the degree of the canopy closure. Our results from microhistological analysis confirmed that European Red Deer is concentrate selector throughout the year. The majority of the red deer diet was composed by herbs, grasses and genus Rubus during the vegetation period. Grasses, bark and wood, needles and genus Rubus were the main components during the winter period. We found significant differences in winter diet composition in habitats in lower altitudes (< 700 m a.s.l.) compared to habitats in higher altitudes (>700 m. a.s.l.). The winter diet in low-altitude habitats mainly consisted of grasses, wood and bark and leaves of wood, with a minimum proportion from supplementary feeding 21.4%. The winter diet in high-altitude habitats mainly consisted of wood and bark, needle and genus Rubus with significantly lower proportion from supplementary feeding 3,1%. The analises of damage of economically vaiuable trees has shown that fir, maple and ash are the most attacted by ungulates since advance growth stage. Spruce was also significantly damaged in older growth stage. Beech was the least damaged tree species. Our results confirmed that the intensity and degree of damage were higher in high diversity forest stands in term of tree species compared to low diversity ones. Our research show that recent numbers of ungulates will likely lower the occurrence of valiuable tree species such as fir, maple and ash, causing decrease ecologycal diversity and stability of forests ecosystems.