Patterns of natural regeneration of pine forests in the Left-Bank Forest-Steppe of Ukraine

The study of natural regeneration in pine stands, widespread in the Forest-Steppe of Ukraine, is crucial for transforming forest management towards sustainable, close-to-nature practices. This study aims to reveal the features of the natural regeneration of pine stands in the Left-bank Forest-Steppe of Ukraine, based on data from sample plots in Kharkiv and Sumy regions. Natural regeneration in pine-dominated stands is characterized by an age of 4–8 years and a low number of plants per hectare (1,000 [500–2,000]), with few plots containing enough regeneration (over 3,000 plants per hectare) to form a new forest stand without additional planting. The regeneration in the plots varies by species composition: pure Scots pine (Pinus sylvestris L.), pure English oak (Quercus robur L.), pine-oak mix in different proportions with accompanying species (Silver birch (Betula pendula Roth.), Small-leaved lime (Tilia cordata Mill.), or Scots elm (Ulmus glabra Huds.) or without any accompanying species. A statistical analysis revealed that only vegetation cover significantly influences the presence of regeneration: at lower vegetation cover, the occurrence of natural regeneration is significantly higher. No significant correlation was found between the amount of renewal and the relative density of parent stands. No significant correlation is found between the density of regeneration and the relative density of stocking, and ground vegetation cover. A significant difference in the density of regeneration depending on its species composition was shown: the lowest number was observed in pure pine regeneration biogroups, slightly higher in pine regeneration with the admixture of other broadleaved species (without oak), and the highest number was in the most diverse regeneration, containing a mixture of pine, oak, and other broadleaved species. A significant decrease in the number of naturally regenerating plants was revealed during the observation period at the monitoring sites.