The effect of thinning intensity on some litter and soil properties and fine root biomass in young scots pine (Pinus sylvestris l.) stands

This study investigates carbon dynamics in pole-stage Scots pine (Pinus sylvestris L.) stands situated on upper slopes in Gümüşhane-Torul region. Using a holistic approach, the research evaluates the impacts of aspect (sunny vs. shady) and thinning intensity (control, moderate, heavy) on carbon stocks—specifically within soil, forest floor, and fine root biomass—as well as on soil respiration. Ecosystem carbon and nitrogen pools, alongside seasonal dynamics, were monitored through periodic measurements over a two year period. Results identified aspect as the primary environmental driver of carbon storage. While shady aspects exhibited nearly double the soil organic carbon storage capacity (79.54 t/ha) compared to sunny aspects (37.96 t/ha), an inverse trend was observed for forest floor carbon stocks, where sunny aspects (8.73 t/ha) exceeded shady ones (5.81 t/ha). The higher C/N ratio observed in sunny aspects increased resistance to decomposition; when combined with arid microclimatic conditions, this accelerated forest floor accumulation. Conversely, shady aspects facilitated mineralization and subsequent soil carbon storage due to lower C/N ratios and favorable moisture conditions. Although thinning intensity alone did not significantly alter soil and root carbon stocks, seasonal interactions proved determinant. Notably, heavy thinning increased forest floor and soil carbon stocks via additional organic matter input from logging residues. Regarding soil respiration, values peaked in control plots (4.80 g C m⁻² day⁻¹). Thinning reduced total respiration by increasing evaporation (moisture loss) through canopy opening and decreasing root biomass (autotrophic respiration). Seasonally, respiration maximized during the optimum temperature-moisture conditions of late spring/early summer but declined sharply with the onset of summer drought, particularly in sunny aspects where moisture became a limiting factor. Consequently, moderate thinning is recommended as the optimal strategy for sustaining carbon sequestration in similar young Scots pine stands. This approach preserves critical soil moisture in drought-prone sunny aspects while supporting stand development in shady aspects without compromising their high carbon storage potential. A key limitation of this study is its focus on short-term ecological responses. Future research should prioritize long-term monitoring and provide a deeper mechanistic understanding of the carbon cycle by partitioning soil respiration components (autotrophic vs. heterotrophic) and analyzing microbial community structures (e.g., PLFA or DNA analysis).