Influence of species identity and charring conditions on fire-derived charcoal traits

Fire is a major disturbance worldwide, and it produces significant amounts of wood-derived charcoal. There is increasing evidence that the key properties (“traits”) of charcoal vary greatly, with consequences for ecosystem processes, but how the key factors drive variability of charcoal traits, i.e., species identity and charring conditions, remain poorly understood. Here, we experimentally produced charcoal from three common boreal tree species under six charring conditions representing those encountered during boreal fires and then analyzed their structural and chemical traits. Overall, we found that species identity affected charcoal traits more than did charring conditions. Among the structural traits, density and microporosity varied among tree species, and density decreased with increasing temperature. Among the chemical traits, electrical conductivity, total nitrogen (N) and phosphorus (P) contents, and phosphate concentration differed among species, whereas pH, total N content, and ammonium concentration responded to charring conditions. No traits except nitrate concentration responded to the interactive effect of species identity and charring condition. Our results reveal that traits of charcoal, and potentially its ecological functions, are driven by a combination of fire behavior and tree species identity; such information is relevant for understanding ecological consequences of altered fire regimes due to the changing climate and to forest management.