Caloric Content Influences Litter Decomposition and Flammability – A Test on 10 Bark-Shedding Species in Sydney Region

Abstract

Leaves and bark are important components of the litter in the Sydney area. This litter is prone to physical degradation, microbial decomposition or can get burnt. Many factors affect the rate, at which the burning or decomposition occurs. Amongst those, the chemical composition of litter and environmental factors play a significant role in regulating litter burning or decomposition. This study aimed to gain insight into the differences in caloric content in leaf and bark for different species. Moreover, the study examined the impact of caloric content on litter decomposition and flammability (time to ignition, flame duration and smouldering duration). Furthermore, the study wanted to understand how different chemicals contribute to interspecific differences in caloric content for both leaves and bark. To explore this, leaves and bark were collected from ten bark-shedding species around the Sydney region. Oxygen bomb calorimetry was performed on leaves and bark to get the caloric contents. The calorimetry results were then combined with already existing datasets on flammability, chemical analysis and decompositions to analyse interactions and responses of flammability and decomposition with changing caloric content. Leaf litter had a higher caloric content, averaging 21.8MJ/Kg whilst bark litter had a lower caloric content, 19.25MJ/Kg. On average, bark had nitrogen concentrations of 0.14%, while leaves had 0.4%. Bark had higher concentrations of lignin (35.6%) than leaves (19.8%). Consequently, more decomposition occurred in leaves than in bark. In addition, fuel with high caloric content ignited more quickly than fuel with less caloric content. Henceforth, this work concluded that higher caloric content results in slower decomposition and higher ignitability of fuel loads. These findings will aid in crafting informed fire predictions and management decisions for forests that deposit considerable fuel and pose higher fire risks.