Stimulation of boreal tree seedling growth by wood‐derived charcoal: effects of charcoal properties, seedling species and soil fertility

Summary Fire is a major disturbance in many ecosystems world‐wide including the boreal forest, and significant quantities of charcoal can be input to the soil from fire. Some recent studies have provided evidence that wood‐derived charcoal produced by fire can significantly stimulate plant growth. However, the mechanisms by which charcoal affects plant growth are poorly understood, and little is known about how charcoal effects on plant growth are influenced by charcoal type, soil type and plant species. Seedlings from four common boreal tree species, two evergreen gymnosperms and two deciduous angiosperms, were grown in each of two soils of contrasting nutrient availability amended with charcoal with each of nine charcoal types (each produced from wood from a different plant species) in a greenhouse experiment. We also measured several functional traits for each of the charcoal types, as well as of the wood used to prepare the charcoal. Charcoal addition had either positive or neutral effects on seedling growth, with great variability among charcoal types. The charcoal types that had the strongest positive effect were those that had the greatest concentrations of phosphate and total phosphorus and, in some cases, were derived from woods that had the highest total phosphorus concentration. Addition of charcoal on average had a stronger positive effect on plant growth on soil with the lowest levels of phosphate and total phosphorus. Generally, charcoal derived from angiosperms stimulated seedling growth more than charcoal from gymnosperms. Further, angiosperm seedlings were on average stimulated more by charcoal addition than were gymnosperm seedlings. These results indicate that charcoal produced by fire could contribute to the initial dominance of angiosperm trees in post‐fire succession and suggest a possible feedback whereby charcoal from angiosperm tree species favours growth of angiosperm seedlings. This study highlights a new means by which functional trait variation among tree species could potentially exert ‘after‐life’ effects in forested ecosystems through influencing traits (and notably phosphate concentrations) of the charcoal that they produce following wildfire, with potentially important consequences for plant growth and community and ecosystem properties during post‐fire succession.