Anthropogenic structures introduced into the forest by silvicultural practices may lead to increased floristic diversity of the forest complex. Among artificial structures, ditches play a special role because they cause differences not only in lighting but also in moisture conditions. Species from contrasting habitats can exist together in a relatively small area because of the different conditions found on the bottom and slopes of the ditch. We studied the effect of the presence of three types of ditches (i.e. drainage ditches, road ditches, and war trenches) on the floristic diversity of forest phytocenoses in central Poland. These were managed forests on sites of Vaccinio-Piceetea and Querco-Fagetea phytosociological classes. In addition to measuring species richness, we analyzed the dominance structure, species rarity and ecological indicator values of plants. We have determined that species richness was higher in ditches than in the surrounding forest phytocenoses. Most species in ditches occurred at low frequencies. Based on Shannon's formula, ditches usually had greater diversity; species evenness, however, was variable in ditches when compared with the forest. Plants that occur in the ditches differed from these found in forests in terms of their trophic, humidity and light requirements. It has also become apparent that there are differences between the three types of ditches. Roadside ditches had the highest influence on floristic diversity, and war trenches the lowest.

Key words: floristic diversity, habitat heterogeneity, drainage ditches, roadside ditches, war trenches, managed forests