Via a detailed analysis and review of the currently available literature, this work aims at clarifying the phenomena, physical and mathematical, underpinning the methodologies and results in forest carbon accounting.
The large scale techno-economic models indicate that an increased forest wood removal for bioenergy purposes may cause either a decrease of the forest carbon stock (or a lower increase compared to the BAU) or displacement of wood for products.
The calculation of biogenic CO2 correction factors or carbon debt payback time provides results with a large range of variability that depends on the many different characteristics and assumptions on both the bioenergy system and the reference fossil system such as: the fossil fuel replaced, efficiency of the biomass utilization, the future growth rate of the forest, the frequency and intensity of biomass harvests, forest management, the initial landscape carbon stock. However, in most cases, the bioenergy scenario causes an actual increase in CO2 emissions compared to fossil fuels in the short-term (a decade). In the long-term eventually it may generate GHG savings and become carbon neutral (from several decades to centuries).
It can be concluded also that the carbon neutrality assumption for forest bioenergy is anachronistic and may be misleading and it is fundamental to integrate all the carbon pools in the analysis (above ground biomass, below ground biomass, dead wood, litter, soil and harvested wood products) and their evolution in the time horizon of the analysis for both the bioenergy scenario and the counterfactual. A comprehensive evaluation of the climate impacts of forest bioenergy has to integrate also all of the climate forcers (aerosols, ozone precursors and albedo)