Circular utilization of urban tree waste contributes to the mitigation of climate change and eutrophication

Abstract

Substantial urban tree waste is generated and underutilized in the US. Circular utilization of urban tree wastes has been explored in the literature, but the life-cycle environmental implications of varied utilization pathways have not been fully understood. Here we quantify the life-cycle environmental benefits of utilizing urban tree wastes at process, state, and national levels in the US. Full utilization of urban tree wastes to produce compost, lumber, chips, and biochar substantially reduces nationwide global warming potential (127.4–251.8 Mt CO2 eq./year) and eutrophication potential (93.9–192.7 kt N eq./year) compared with landfilling. Such benefits vary with state-level locations due to varied urban tree waste availability and types. Process-level comparisons identify the most environmentally beneficial combination as using merchantable logs for lumber and residues for biochar. The results highlight the climate change and eutrophication mitigation potential of different circular utilization pathways, supporting the development of circular bioeconomy in the urban environment.