LONG-TERM EFFECTS OF THINNING IN NATURAL PINE FORESTS UNDERGROWTH

Ground cover vegetation is crucial for biodiversity in northern conifer forests, providing habitat, food, and ecosystem functions like seedling regeneration and nutrient cycling. Their composition is shaped by tree species, canopy structure, and environmental factors like temperature, light, water, and soil nutrients. Forest management can modify these processes by increasing light availability, fostering conditions more typical of a natural pine forest biotope, and promoting plant growth. This study aimed to assess whether natural pine forest management influenced ground cover vegetation over 20 years. Six plots across three locations were analyzed. In the studied managed plots, first-story pine trees were thinned by removing second-story spruces between 2004 and 2005. Some plots were thinned (managed), while others remained untouched (control). Initial vegetation assessments recorded species in 10×10m plots before thinning. In 2024, vegetation was reassessed using transects with three 1×1m plots placed along cardinal directions. Vegetation was categorized into trees and shrubs, herbs, mosses, and lichens. The 2024 assessment of managed plots revealed a decline in moss and lichen species, a slight increase in herbaceous species, and a more pronounced increase in tree and shrub species. The opposite trend was observed in control plots. Shannon index values showed significant differences between years (p=0.03) across all vegetation layers but not between management types or factor interactions. Similarly, the total species count varied significantly between years (p=0.02) but not between management types. However, within small 1×1m plots (2024), species count differed significantly between management types (p=0.004). These findings suggest that thinning influences ground cover vegetation composition over time, promoting tree and shrub growth while reducing moss and lichen cover. Species diversity shifts appear more pronounced at finer spatial scales, highlighting the importance of localized conditions in shaping ground cover vegetation dynamics.