Novel strategies to mitigate GHG emissions from urban forestry waste

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Urbanization affects close to 1.0 x 10^6 km^2 with ~68% of the global population expected to reside in urban areas by 2050. Urban areas are now recognized as hotspots for greenhouse gas (GHG) emissions, accounting for more than half of total estimated GHG emissions globally. While energy use of the built environment and transportation sectors dominates emissions, direct GHG emissions from urban waste streams and soils are also large but poorly resolved contributors; moreover, urban land use can substantially modify energy demand - for example urban trees can mitigate the urban heat island effect and thus reduce energy use. The proposed project will provide data to better quantify GHG emissions from urban forestry waste at processing sites and when used as mulch in three major urban areas in Canada. Our recent studies in log processing sites in operational forestry suggest that large methane emissions are associated with forestry waste material. Targeting reductions in methane emissions is important as methane accounts for ~30% of anthropogenic climate forcing and has a short atmospheric half-life. The study will examine mitigation of GHG emission in this sector through conversion of urban forestry waste to pyrolyzed organic matter (biochar), with a focus on biochar use in urban soils and green infrastructure to enhance C sequestration, reduce substrate GHG emissions (particularly of methane), and increase urban vegetation growth and physiological performance. In collaboration with partners, we will also examine use of innovative biochar-based products, including pelletized biochars and biochar-coasted seeds, in an urban forestry and urban green infrastructure context. Integration, modeling, and life-cycle analysis components of the project will address the potential for novel strategies to generate a "virtuous cycle" in which waste material from urban vegetation is recycled as biochar for use in urban forestry and green infrastructure, with knock-on benefits that include reduced urban energy demand.