Restoration of natural herbaceous vegetation and spatial variability of forest structure by gradual removal of Scots pine from former plantations

We tested the effectiveness of the gradual removal of Scots pine (Pinus sylvestris L.) in former plantations of this species in Roztocze National Park (SE Poland) to support the restoration of natural herbaceous flora and forest structure. We compared 0.5-ha study plots subjected to selective removal of pine trees with control plots excluded from any kind of human intervention for half a century. The observed changes in forest floor vegetation in the converted plots showed naturalization towards habitat-specific species. However, differences in the spatial distribution of trees between the treatment and control plots showed no universal pattern and revealed subtle but positive shifts from regular to random or clustered patterns. The mean tree diameters were higher in plots subjected to Scots pine removal, which resulted from the vigorous growth of tree species, consistent with habitat types. We conclude that forest restoration through the removal of planted trees can support the naturalization of former Scots pine plantations in protected areas. However, the selection of an appropriate method and its intensity are of vital importance. Methods that resemble typical management practices, such as selection thinning, are not always the best approach, as they may preserve or even increase the regular distribution of trees. Therefore, for restoration purposes, we recommend testing other methods that increase spatial heterogeneity, including systematic cutting or emulating natural disturbances. In addition, low-intensity thinning may not be sufficient to support the restoration of natural forest floor vegetation and the variability in forest stand structure.