Tree-related microhabitats (e.g. necroses, tree hollows, dead branches) are an important factor affecting biodiversity in forest ecosystems. Among tree-related microhabitats, natural tree hollows are important for many organisms such as birds, small mammals, invertebrates and plants. The aim of the study was to determine what species of trees are associated with natural tree hollows and necroses. In 900 plots (0.05 ha each) located in 100 forest divisions of the Niepołomice Forest, natural tree hollows and necroses were recorded for the most numerous tree groups (pine, oak, lime, alder, hornbeam). Of all the studied tree species, the only species significantly positively associated with natural tree hollows and necrosis was Carpinus betulus. Pinus sylvestris was associated negatively with the occurrence of natural tree hollows. These results signal the very important role of hornbeam in increasing the richness of tree-related microhabitats in managed forests, and point to the need to promote hornbeam as an admixture tree species in managed forests. During forest work it is also important to ensure that a certain number of hornbeams reach old age; it will increase the number of natural tree hollows and consequently biodiversity in managed forest.