Effects of Forestry Transformation on the Species Level of Biodiversity in Poland’s Forests

Forest biodiversity is of particular importance for the world’s natural resources and for humans, so it is essential to observe the impact of forest management on its state. In this paper, the effects of Poland’s forestry evolution after 1945 on the forest biodiversity at the species level are interpreted based on four indicators (deadwood, species composition of forest stands, introduced tree species, and common forest bird species) and considering the two politically and economically different eras. In the era of socialism (1945–1989), the area share of broadleaved tree species increased intensively, with a steady predominance of single-species stands, the ongoing removal of deadwood, and a relatively slow increase in the area occupied by alien tree species. In the era of democracy (ongoing since 1990), there was a less intensive increase in the proportion of broadleaved species, an intensive increase in the stock of deadwood, an increase in the area of multi-species stands over that of single-species stands, as well as an increase in the value of the Forest Bird Index. However, an intensive increase in the area occupied by alien tree species, especially invasive ones, which negatively impact native wildlife, was also noticeable in the era of democracy. The dilemmas and problems related to the amount of deadwood in forests; the continued conversion of stands towards more complex ones; the presence of other invasive species; the consequences of climate change; the reduction in migration barriers for forest animals; and the provision of funding for biodiversity conservation activities need to be discussed and resolved or implemented further.