Biogeochemical responses to short-term thinning intensity across contrasting topographic aspects in pole-stage Pinus sylvestris L. stands

Thinning is widely applied to enhance stand resilience, yet its interactive effects with topography on soil biogeochemistry remain poorly understood. This study evaluated thinning intensity (control, 22.1%, and 36.8% basal area reduction) and aspect (shaded vs. sunny) impacts on litter and mineral soil carbon (C) and nitrogen (N) dynamics in high-altitude pole-stage Pinus sylvestris stands. Results indicated that short-term (≤2 years) C and N patterns varied significantly between different aspects, while the short-term impacts of thinning intensity were not statistically detectable. The observed aspect-related differences may concurrently reflect underlying lithological and edaphic contrasts between the sites, as the experimental framework cannot fully separate slope aspect from elevation and parent material effects. Shaded aspects were characterized by higher mineral soil stocks (79.54 t ha −1 C, 3.67 t ha −1 N) and lower C/N ratios (24.1). Conversely, sunny aspects experienced elevated soil temperature and moisture limitations. These localized constraints provide a plausible ecological explanation for the higher forest floor accumulation (17.0 t ha −1 ) on the sunny aspect, serving as a descriptive baseline for organic matter retention patterns rather than a verified functional mechanism. While forest floor mass was higher on sunny aspects, these sites exhibited lower mineral soil nutrient stocks, which was reflected in the PCA space through an orthogonal alignment between variables. These preliminary patterns suggest a degree of structural resilience in the stands during the immediate post-thinning phase (≤2 years). Consequently, uniform thinning prescriptions require long-term verification, as initial canopy reduction could potentially influence early soil moisture balances on sunny aspects during these transitional post-disturbance stages.

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