Comprehensive Experimental Studies on Smoldering Characteristics of Forest Soil from pinus sylvestris Vegetation

Smoldering combustion, often linked with forest fires in coniferous forests, pose significant health and environmental risks, particularly in densely populated countries like Germany, where these fires commonly occur in wildland–urban interface (WUI) areas. This study investigates the combustion characteristics of Pinus sylvestris soil, focusing on the underlying processes and thermal behavior. The aim is to provide a comprehensive analysis of smoldering combustion in pine forest soil, with a specific focus on fire-exposed soil horizons. The research integrates soil characterization, elemental analysis, heat of combustion determination, and thermogravimetric analysis (TGA) of pine soil fractions ranging from < 0.063 to > 4 mm, conducted under both air and nitrogen atmospheres. The derivative thermogravimetry (DTG) curves reveal that the fastest mass loss occurs during pyrolysis, with peak temperatures between 240°C and 280°C. Activation energies (E _a ) were calculated using the Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods. The highest activation energies were observed between conversion rates of 0.2 and 0.4. Activation energies at peak temperatures for all fractions were determined using the Kissinger method. Residue analysis reveals significant variations in organic content, ranging from 22.6% to 92.7%. The findings demonstrate that German-typical pine soil is prone to smoldering combustion, highlighting processes determined as preheating, drying, pyrolysis, and oxidation. As part of the German Pilot of the EUs TREEADS project, this study provides essential data for numerical simulations, emphasizing the need to consider both physical and chemical properties of soil fractions to mitigate the impact of smoldering fires in pine forest ecosystems.