30-Year Changes in Oak-Hornbeam Forest after Windthrow

Hurricane winds are one of the most important abiotic factors in shaping the structure of the forest and the processes that occur in it. The aim of research was to determine regeneration processes and changes in the structure of forest stands caused by the windstorm in 1983. The research, based on stand tables from the years 1982, 1984, 1989 and 2014, was carried out on nine permanent research plots in the Bialowie(z) over dota Forest. The mean number of trees (MNT) taller than 1.30 m decreased by 13.7% after the windstorm. In 2014, MNT increased compared to 1984 (142%) and 1989 (53%). A significant decrease in the share of Picea abies (L.) H. Karst., thicker than 7 cm DBH and a significant increase in the share of Carpinus betulus L. was observed. Species richness for trees thicker than 7 cm DBH indicated a significantly lower species richness in 1982 and 1984 (12 species) compared to 1989 (14) and 2014 (16). The windstorm did not have a direct effect on the species richness, species composition of stands or the distinguished tree layers, except for trees thicker than 55 cm DBH. The observed changes in tree density in the lower layers of the stand prove that the regeneration process does not start immediately and continues even 30 years after the windstorm. Intermediate-severity windthrow accelerated natural changes in the stand structure.