In the face of a rapidly changing global environment, detailed research into the actual role of protected areas (PAs) in preventing the destruction of ecosystems and the loss of biodiversity became particularly important. Using 304 phytosociological relevés of oak forests from SW Poland, we monitored their state of preservation reflected by the share of synanthropes (Ws-c index) in relation to (i) duration of protection, (ii) status of protected area, (iii) main topographic factors, and (iv) bedrock type. We show that the Ws-c index of studied forests depends primarily on the habitat conditions, especially bedrock type, while both the duration and status of protection are not relevant. The most disturbed are forests developing on serpentine substrates regardless of whether they are protected or not. Within the rest of the investigated sites, the Ws-c index is significantly lower and does not meaningfully differ between protected and unprotected areas. On the one hand, our results suggest that the fact of establishing protection does not ensure a favourable state of conservation of forest communities. On the other hand, well-preserved forest communities can also be expected outside PAs what makes them an important target for nature protection in the future.