First-year post-fire alterations of Scots pine forest: composition, relationships, ecological consequences

Forest fires are key ecological factors affecting pine forests globally. Understanding impacts of varying fire intensities on forest ecosystem components is crucial for predicting recovery and informing management. This study aimed to assess effects of different surface fire intensities on structural components of pine forests, including tree canopy, herbaceous layer, and surface soil horizons, and identify relationships between fire intensity and ecosystem parameters. The study examined three areas with different fire intensities (severe, moderate, mild) 1 year after a surface fire in Ukraine's Volyn-Polissia region, using vegetation surveys, soil analyses, and statistical methods. Fire intensity significantly influenced tree mortality and the vitality structure of Pinus sylvestris stands. Scorch height correlated strongly with stem diameter in mild and moderate intensity zones (P < 0.0001). Herbaceous layer composition showed significant variations in all life-form traits across different fire intensities. Species diversity, dominance, and evenness indices varied with fire intensity, as did species distribution by ecological strategies. Soil physicochemical properties, including surface layer density, ash content, moisture capacity, and pH, also changed. Correlations were found between the condition index of P. sylvestris and soil pH, as well as between herbaceous cover dominance/evenness indices and P2O5 content in surface soil layers. Weaker associations were identified between herbaceous cover diversity and soil density/hygroscopic moisture. The study was conducted over a 1-year period following the fire event, focusing on the short-term responses of vegetation and soil properties. Surface fires of varying intensities alter multiple forest ecosystem components. Severely damaged areas may require restoration efforts, including active interventions such as artificial reforestation or other measures to accelerate recovery processes. Moderately and mildly affected zones, on the other hand, show potential for natural self-regulation. These findings have important implications for post-fire forest management strategies.