Protected Area Soils as Natural Laboratories: Topographic Controls on Soil Carbon Storage and Nutrient Stoichiometry for Sustainable Ecosystem Management

There are 266 nature parks in Türkiye, including Aşıkpaşa Nature Park, covering a total area of approximately 109,023 ha; however, information regarding soil organic carbon stocks (SOCS), soil nitrogen stocks (NS), and nutrient stoichiometry in these protected forests remains limited. This study evaluates the influence of tree species, altitude, aspect, and soil depth on nutrient stocks and stoichiometry using a 3 × 2 × 3 × 3 factorial experimental design. The findings indicate that mixed stands (Black Pine + Cedar) significantly optimize nutrient storage, reaching peak N (3.531 ± 0.115 t ha−1) and P (0.948 ± 0.016 t ha−1) stocks. SOC and N stocks reached 66.34 ± 1.86 t ha−1 and 4.032 ± 0.123 t ha−1, respectively, along the altitudinal gradient. Soil pH exhibited a steady rise with altitude (from 7.86 to 8.15), contrary to typical leaching patterns, while bulk density varied depending on Altitude × Aspect × Depth interactions. Stoichiometric analyses revealed that Cedar stands maintain higher C:K ratios (3.457 ± 0.258), reflecting superior nutrient use efficiency. Furthermore, sunny aspects prioritized nitrogen mineralization (N:P ratio: 4.540), whereas shaded aspects facilitated phosphorus retention. These results prove that soil fertility and carbon sequestration are modulated by complex topographic–biotic interactions, suggesting that preserving mixed forest structures is of vital importance for ecological sustainability and forest resilience.