Assessment of Soil Carbon Stock and Properties in Different Forest Types of Veun Sai-Siem Pang National Park, Cambodia

Background and Objective: Soil properties play a key role in ecosystem processes and carbon sequestration, but their variation by forest type and depth has not been explored in Cambodia. This study aimed to analyze key soil properties, such as nitrogen (N (%)), pH, organic matter (OM (%)), organic carbon (SOC (%)), and exchangeable hydrogen (H meq/g) in three forest types: Evergreen, semi-evergreen, and deciduous forests. Materials and Methods: Soil samples were collected from three depth intervals (0-10, 10-20, and 20-30 cm) by forest type. Standard laboratory methods were used to determine soil properties, including SOC and OM content, bulk density, and exchangeable hydrogen. Descriptive stats, ANOVA, and Pearson’s correlation (p<0.05) were performed in Excel and R to analyze soil properties. Results: Evergreen forests showed the highest OM (4.0% at 0-10 cm) and SOC (2.35% at 0-10 cm), resulting in lower pH (4.80) and more acidic soils with the highest exchangeable hydrogen (23.57 meq/g). Across all forest types, OM and SOC decreased with depth, reaching the lowest SOC values at 20-30 cm (evergreen: 1.74%, semi-evergreen: 1.65%, deciduous: 1.64%). Bulk density increased with depth, with the lowest values observed in evergreen forests (1.08 g/cm³ at 0-10 cm), indicating better soil structure and porosity. Soil carbon stocks were highest in the 0-10 cm layer (semi-evergreen: 26.07 Mg/ha) and declined at 20-30 cm (semi-evergreen: 19.59 mg/ha). Conclusion: The study revealed a significant effect of forest type and soil depth on soil carbon storage and nutrient accumulation. High SOC and OM in evergreen forests contribute to improved soil quality but also increase soil acidity. These findings provide important insights for sustainable forest management and climate change mitigation efforts, emphasizing the importance of maintaining soil carbon stocks in forest ecosystems.