"We still get significant emission reductions even after we include all lifecycle emissions of wood pellets, which are produced in the US and exported to Europe, as well as emissions due to market-induced changes in forest management practices and land use," Madhu Khanna of the University of Illinois, US, told environmentalresearchweb.

According to Khanna, the study reveals that wood bioenergy can be used to achieve compliance with the European Union’s Renewable Energy Directive without negatively affecting forests in the southern part of the US.

"The demand for forest bioenergy can create incentives to increase forest land in anticipation of future demand," she said. "The extent to which this occurs depends on the planning horizon that forest landowners use to make forest management decisions; the longer the horizon, the greater the extent to which landowners have an incentive to convert pastureland to forests to meet future wood demand. This creates a carbon credit that offsets some of the reduction in forest carbon stock that occurs due to increased harvest of trees."

To come up with the findings, Khanna and colleagues from the University of Illinois, University of Georgia, and North Carolina State University, all in the US, developed an economic model of the forestry, agricultural, and transportation sectors to look at the greenhouse gas emissions associated with wood pellet production in the US and transportation to Europe from 2007–2032 under scenarios of high and low pellet demand met with pellets produced only from forests or from both forest and agricultural biomass.

Pellets made from a mix of agricultural and forest biomass had a greenhouse gas intensity 28–34% lower than pellets produced from forest biomass alone, Khanna and colleagues found. "Agricultural sources of biomass are able to sequester a considerable amount of carbon in the soil per acre of land – much more than forests – and the greenhouse gas intensity of pellets is lower if you’re able to source it from agricultural biomass rather than just from forests," said Khanna.

For forest-only biomass pellets, 11–26% of the greenhouse gas intensity was due to effects on forest carbon stock caused by changes in harvest rotations, land use and conventional wood production. These greenhouse effects were negative for pellets made from forest and agricultural biomass.

Now the team will focus on analysing the wide range of estimates of the impact of wood bioenergy on greenhouse gas emissions. "We want to undertake a comprehensive review of the existing literature to examine the factors that lead to these widely differing estimates, so that there is a greater transparency and understanding of the role that forest bioenergy can play as a strategy to mitigate climate change," said Khanna.

Khanna and colleagues reported their findings in Environmental Research Letters (ERL).

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