Effects of Forest Surface Fuel Bed Structure on Flame Residence Time

Flame residence time (FRT) is an important indicator of flaming duration and is closely related to local heat release and associated ecological effects. However, the intrinsic mechanisms through which fuel bed structure affects FRT remains insufficiently understood. Clarifying how fuel bed structure affects FRT under flat, wind-free conditions is important for prescribed burning and ecological restoration. This study investigated surface fuels from typical forest types in southwestern China through controlled laboratory experiments conducted under flat, wind-free conditions, with moisture content, loading, thickness, and bulk density systematically varied. The driving mechanisms of fuel bed structural characteristics on FRT were systematically analyzed. Coniferous forests and moso bamboo had significantly lower FRT than broadleaved forests. Moisture content was the most influential factor, followed by thickness and bulk density, whereas loading had a relatively limited effect. Prediction models developed using machine learning methods significantly outperformed traditional regression approaches. Fuel bed structure is a critical factor controlling FRT. The high-accuracy prediction models established in this study enhance the mechanistic understanding of FRT. The findings provide a theoretical basis and practical support for prescribed burning and fire behavior modeling and may contribute to improved forest fire management.