Does Soil Application of Bioenergy Wood Ash Emulate Natural Wildfire in Boreal Forests?.

Wood ash from bioenergy production is almost exclusively treated as a waste product in Canada. Disposal of ash in landfills presents a significant cost to forest companies, energy producers and the public at large. In Europe, wood ash is applied to forest soils as part of standard forest management practices. In general, ash applications are used to reduce soil and surface water acidification caused by acid rain, as a liming substitute to raise soil pH and to provide nutrient compensation where intensive forest harvesting has taken place. In most Canadian forests, fertilization is not an approved management practice and emulation of natural disturbance (END) is the emerging paradigm for ecosystem-based forest management. In the case of the boreal forest, wildfire is the predominant disturbance agent.  During wildfires, forest floor horizons are partially or completed consumed, and ash is distributed across the soil surface within the boreal landscape.   

Combustion temperatures vary among wildfires and bioenergy boilers.  Given that each element volatilizes at a different temperature, this may result in differences in resultant ash chemistry. We contrasted the chemistry of wood ash produced in Canadian bioenergy boilers with ash produced during wildfires. We also compiled the results of studies that measured soil chemistry after ash applications and wildfire. Most studies showed increased pH and exchangeable base cation concentrations in the forest floor and upper mineral soil after both ash applications and wildfire.  However, this depended to some degree on the intensity of the wildfire, ash application rate and whether the ash was applied in a loose or hardened form. We conclude that wood ash applications from bioenergy production can be used to emulate the effects of wildfire on some soil chemical properties.