European beech (Fagus sylvatica L.) is the most abundant tree species in Serbia and is highly interesting for economic and ecological reasons. Today, forests are subject to various environmental stresses that lead to the overproduction of reactive oxygen species in plants. Existing beech forests in Serbia are exposed to stressful environmental conditions since they are living under ecological conditions barely within the limit of their requirements, and with the predicted climate change it will become endangered. The present study was designed to define and compare antioxidant capacity of beech populations from three localities (Kopaonik, Tara and Stara Planina) in order to assess their adaptability to oxidative stress caused by specific ecological conditions during investigated period. Total phenols, tannins, flavonoids and proanthocyanidins contents, proline, total protein, soluble protein, and pigment content were analyzed. Lipid peroxidation and protein oxidation intensity were also determined as indicators for oxidative damages. The antioxidant activity was investigated by using ferric reducing power, permanganate reducing antioxidant capacity and ^•OH, ^•NO, O₂^•- and DPPH^• scavenger activity. The extract from Kopaonik contained the highest amount of phenols, flavonoids, tannins and proanthocyanidins and had lowest malondialdehyde (MDA) and protein carbonyl accumulation. The highest accumulation of proline and high accumulation of MDA were observed in the extract from Tara, the locality with the highest temperature. In the present study, extract from Kopaonik exhibited the highest reducing ability and DPPH^• scavenger activity. The relatively high antioxidant capacity may be a determinant for beech acclimation processes, what could be an important tool for the improvement of breeding strategies and reforestation programmes for European beech.

Keywords: antioxidant activity, Fagus sylvatica L., lipid peroxidation, oxidative stress.