Spatio-temporal dynamics of soil physico-chemical properties in <i>Quercus</i> dominated forests of Arunachal Pradesh, Eastern Himalayas

Background: This study examines the spatiotemporal variability of soil physicochemical properties along an altitudinal gradient and soil depth in natural Oak (Quercus griffithii Hook. f. & Thomson ex Miq.)-dominated forest stands in western Arunachal Pradesh. Soil samples were collected from five sites at varying elevations (1,693-1,801 m) across three seasons (winter, summer, and rainy) and three depth intervals (0-10 cm, 10-20 cm, and 20-30 cm). Key soil properties, including bulk density (BD), porosity, water-holding capacity (WHC), soil moisture content (SMC), pH, soil organic carbon (SOC), and nutrient availability (nitrogen [N], phosphorus [P], and potassium [K]), were analyzed. Results: Soil properties exhibited significant (p < 0.05) variation with altitude, season, and depth. BD increased with decreasing altitude and depth, with the lowest elevation site (1,693 m) exhibiting the highest BD (1.30 g cm-3) in deeper soil layers. Conversely, porosity, WHC, and SOC were highest at higher elevations and in the surface soil (0-10 cm), likely due to reduced decomposition rates, greater organic matter accumulation, and improved aeration. SMC was higher at lower elevations and in surface layers, reflecting enhanced moisture retention. Soil pH varied significantly with altitude and depth, with more acidic conditions observed at higher elevations and in surface layers, possibly due to increased organic matter decomposition. Nutrient availability, particularly N and P, was strongly correlated with SOC and pH, with higher concentrations in surface soil at higher elevations. Seasonal variations indicated that SOC and nutrient levels were highest during the rainy season, reflecting increased biological activity. Correlation analysis revealed strong negative relationships between BD and porosity (r = -0.998) and positive correlations between SOC, SMC (r = 0.760), and available N (r = 0.671). Conclusions: These findings underscore the significant influence of altitude, soil depth, and seasonal dynamics on soil properties, offering valuable insights for sustainable forest management and soil conservation strategies in western Arunachal Pradesh. Given the potential impacts of climate change on forest ecosystems, understanding these soil-environment interactions is critical for maintaining soil health and ecosystem stability.