Large-scale bioenergy from additional harvest of forest biomass is neither sustainable nor greenhouse gas neutral
I’ve been down and out with the crud this week, so some items I’ve been meaning to post have been stacking up. Researchers from Europe and the United States have ‘collaborated’ on a new study titled, “Large-scale bioenergy from additional harvest of forest biomass is neither sustainable nor greenhouse gas neutral.” Below is the abstract and a snipped portion from the study.
Owing to the peculiarities of forest net primary production humans would appropriate ca. 60% of the global increment of woody biomass if forest biomass were to produce 20% of current global primary energy supply. We argue that such an increase in biomass harvest would result in younger forests, lower biomass pools, depleted soil nutrient stocks and a loss of other ecosystem functions. The proposed strategy is likely to miss its main objective, i.e. to reduce greenhouse gas (GHG) emissions, because it would result in a reduction of biomass pools that may take decades to centuries to be paid back by fossil fuel substitution, if paid back at all. Eventually, depleted soil fertility will make the production unsustainable and require fertilization, which in turn increases GHG emissions due to N2O emissions. Hence, large-scale production of bioenergy from forest biomass is neither sustainable nor GHG neutral.
Homogeneous young stands with a low biomass resulting from bioenergy harvest are less likely to serve as habitat for species that depend on structural complexity. It is possible that succession following disturbance can lead to young stands that have functional complexity analogous to that of old forests; however, this successional pathway would likely occur only under natural succession. A lower structural complexity, and removal of understory species, is expected to result in a loss of forest biodiversity and function. It would reverse the trend towards higher biomass of dead wood (i.e. the Northwest Forest Plan in the United States) to maintain the diversity of xylobiontic species.
Cumulative impacts of bioenergy-related management activities that modify vegetation, soil and hydro- logic conditions are likely to influence erosion rates and flooding and lead to increased annual runoff and fish habitat degradation of streams. Young uniform stands with low compared to high standing biomass have less aesthetic value for recreation and are less efficient in avalanche control and slope stabilization in mountains owing to larger and more frequent cutting. A potential advantage is that younger forests with shorter rotations offer opportunities for assisted migration, although there is great uncertainty in winners and losers (species, provenances, genotypes) in a future climate. Plantations, however, largely contribute to pathogen spread, such as rust disease.
Forests offer several important ecosystem services in addition to biomass and some would be jeopardized by the bioenergy-associated transition from high to low standing biomass. Agriculture provides a visible example for abandoning most ecosystem services except biomass production; communities in intensive agricultural regions often rely on (nearby) forested water sheds for drinking water, recreation and offsetting GHG emissions from intensive agriculture.