As part of efforts to address the root causes of climate change and non-renewable resource depletion, many regions in the world are considering sustainable biomass feedstocks for renewable energy production. Prior to making such large-scale shifts in primary energy feedstocks, location-specific research is still needed to understand the environmental impacts and benefits of biomass associated with its many potential applications. The objective of this study was to evaluate environmental and energy impacts associated with generating 1 MJ of thermal energy from direct combustion of short rotation willow (SRW) pellets for 2 purposes: to determine where improvements could be made in the life cycle of SRW bioenergy to reduce impacts, and to compare SRW bioenergy to fossil fuel (light fuel oil and natural gas) for thermal energy. Life cycle assessment (LCA) was conducted using primary data on SRW biomass production collected from field trials at the Guelph Agroforestry site in Guelph, Ontario, Canada, as well as carbon sequestration rates modeled based on local conditions. Results showed that direct combustion of SRW pellets reduced global warming potential (GWP) by almost 85% relative to the fossil fuels. However, relative to fossil fuels, SRW energy had higher impacts in certain categories (e.g. eutrophiEation and respiratory effects), due to biomass combustion and N inputs (inorganic fertilizer and SRW leaf inputs) for biomass production. Soil nitrous oxide emissions, from the N inputs, dominated the GWP, but a sensitivity analysis showed that soil carbon sequestered by SRW biomass during growth could reduce the GWP by 23%. Pelletizing the SRW biomass prior to combustion affected the energy ratio and accounted for almost 85% of non-renewable energy use in the life cycle of bioenergy. Location specific factors that affected environmental performance of the bioenergy system included agro-climatic conditions, management practices, and conversion technologies. Nevertheless, most of the impacts associated with SRW thermal energy generation can be minimized through better fertilizer management, by using alternate sources of fertilizer, by improving yields, and by the use of cleaner wood combustion technologies with emissions controls. (C) 2017 Elsevier Ltd. All rights reserved.