Impact of underground wildfire on plant roots in peat soil

Peatlands are vital terrestrial ecosystems that support a diverse range of plant species and habitats. Wildfire poses a significant disturbance to the peatland ecosystems, especially when underground fires are burning in the peat soil layer. This study presents a comprehensive investigation on the vulnerability of plant root systems to smoldering peat fires through an integrated laboratory and field experiments. In the lab experiments, controlled smoldering fire spreads over peat soil containing simulated plant root samples, that is, wood sticks with diameters of 1–5 cm. In the field experiments, the peat soil planted with larch trees is ignited to observe fire-induced damage to roots. Laboratory experiments show that, when the peat soil moisture content is below 50 % (dry mass basis), almost all root samples burn to ash after the fire, regardless of root diameter within the test range. As peat moisture content increases above 50 %, a greater proportion of the roots remain with different levels of charring and mass loss. Thinner roots experience faster heating and severer damage than thicker roots. The severity of the smoldering peat fires on root is further quantified by relating temperature and heat flux thresholds to residence time, showing long-lasting thermal impacts. The field experiments successfully reveal similar patterns of root charring and damage, deceasing with the soil moisture content. Furthermore, the underground smoldering fire can also initiate a flaming surface fire to exacerbate the fire impact on the root systems. This study quantifies the damage of underground wildfires on plant roots and provides insights into ecological impact and mitigation strategies of the persistent peatland fire and peatland conservation practices.