Variations of organic carbon within the natural Hyrcanian Caucasian oak (Quercus macranthera C. A. Mey.) forests

The unique characteristics of Caucasian oak (CO) stands, located at high altitudes in the Hyrcanian forests, provide valuable insights into the variations of organic carbon (OC) and soil nutrients (NPK), as well as biological and physical changes within these habitats. Understanding these variations is crucial for effective forest management and conservation efforts. To this end, the current study established four 20 x 20 m2 sample plots in each of the CO habitats of Panomehsar in Lavij, Kolanga in Neka, and Tuskestan in Gorgan. Soil samples were collected from two depths (0-15 cm and 15-30 cm) in each plot and analyzed in the laboratory. Biophysical characteristics of trees, such as breast height diameter, total height, average crown diameter, density, and physiographical units, were also recorded.The results showed that OC and nitrogen (N) levels in both soil layers were not significantly different across the study forests (p > 0.05), while available phosphorus (P) and potassium (K) levels varied significantly among them (p < 0.05). There were no significant correlations between OC and N levels in the soil layers, or with the biophysical attributes of the trees based on Pearson tests. The findings indicated that OC and NPK variations were independent of each other, with no significant relationship between them observed in the study sites. Moreover, the nature of OC variations was found to be slow, making it challenging to discern the impact of tree species on these variations within the stands.In conclusion, the study sheds light on the slow nature of OC variations in CO stands and highlights the need for careful consideration of their effects on management and conservation efforts.