Establishment phase greenhouse gas emissions in short rotation woody biomass plantations in the Northern Lake States, USA

Abstract

Uncertainty exists over the magnitude of greenhouse gas (GHG) emissions associated with open land conversion to short-rotation woody biomass crops (SRWC) for bioenergy in the Northern U.S. Lake States. GHG debts incurred at the plantation establishment phase may delay the climate mitigation benefits of SRWC production. To better understand GHG debts associated with converting open lands to SRWC, we established research plantations with willow ( Salix spp .) , hybrid-poplar ( Populus spp.), and control plots in spring 2010 at two sites in northern Michigan (ES) and Wisconsin (RH). These sites had similar climates, but differed in time since last cultivation: 5 vs. 42 years. To address the short-term effects of plantation establishment, we compared two-year biomass production and GHG emissions. We hypothesized that the long-idle ES site, with higher initial soil C and N stocks, would have higher GHG emissions following conversion compared to the recently-idle RH site, but that this would be balanced in part by greater SRWC productivity at the ES site. As hypothesized, grassland conversion resulted in two-year net GHG emissions due to land conversion of 43.21 and 33.02 Mg-CO 2eq ha −1 for poplar and willow at ES that was far greater than the 4.81 and −1.54 Mg-CO 2eq ha −1 for poplar and willow at RH. Contrary to our hypothesis, we did not observe greater SRWC productivity at ES, which will take longer than RH to reach C neutrality and begin mitigating GHG emissions. Our results show that site-specific soil and management factors determine the magnitude of GHG emissions. • The establishment phase for conversion of open lands to SRWC results in significant GHG emissions. • Site land use history and soil properties appear to play an important role in the magnitude of these GHG emissions. • Large scale models need to account for establishment phase emissions, which will be heterogeneous across the landscape.