Carbon balance for wood production from sustainably managed forests

doi:10.1016/j.biombioe.2016.05.025

Biomass and Bioenergy

Volume 93, October 2016, Pages 1-5

https://doi.org/10.1016/j.biombioe.2016.05.025 Get rights and content

Highlights

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The models suggested for carbon analyses are based on the well-known models in use in forest management.
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The approach includes the factor “forest vitality status”, e.g. the age dependent rate of capability of a forest stand to absorb CO₂.
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When analyzing “climate neutrality” of biomass fuels, real empirical values and data should be applied, both for biomass and for substituted fossil fuels.
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Biomass from sustainable forestry could be regarded both carbon neutral and climate neutral.

Abstract

This Short Communication Paper approaches the CO₂ emissions from forest biomass produced in sustainable managed forests from aspects related to photosynthesis and variations in vitality and capability of CO₂ uptake, depending on i.a. different rotation periods and management regimes. These aspects are ignored or diminished in most other analyses on the subject as those analyses typically are based on simplified rigidly structured models. This Short Communication Paper suggests application of more relevant methodologies closer to actual real conditions. Two CO₂ issues are covered; the CO₂ balance between growth and harvesting of biomass in sustainably managed forests, and combustion of woody biomass in comparison with fossil fuels with regard to CO₂ emissions. The analysis of the first issue leads to the conclusion that biomass harvested from sustainably managed forests should be regarded as “carbon neutral” as the vitality and CO₂ absorption is sustained and kept on the same (or better) level. Moreover, to transform old pristine forests to young vigorous forests would be an effective (long term) means of reducing atmospheric CO₂.

Regarding the second issue, we notice that some other authors of papers on bioenergy claim that biomass would not be “climate neutral” when used for energy as, for generation of a given energy amount, more fixed carbon is released from biomass than from fossil fuels. In our opinion, authors of these papers apply obsolete, too general or sometimes illogical default values. This Short Communication Paper suggests that emissions from combustion of forest biomass should be compared with emissions from coal as it is the most common and relevant fuel to replace. Also additional emissions from mining/harvesting, transport, leakage, etc. should be included both for biomass and for reference fuels like coal, gas, and oil. The comparison should also be based on state-of-the-art technology, which for biomass would mean i.a. flue-gas condensing and efficient fuel treatment. Under these conditions, typical biomass applications for energy would be both carbon neutral and climate neutral.

Section snippets

CO₂ neutrality of forest biomass

After having been highlighted at the “Rio Conference” 1992, the interrelations between vegetation, biomass fuels, and climate change became subject to analyses and modeling, e.g. those developed within the IEA Bioenergy Program [1], [2], [3], [4]. While these early models were based on simplified and standardized assumptions, they have been used as bases for further elaborations up till now. In recent years a number of studies on bioenergy and related CO₂ emissions have been carried out.

Conclusions regarding CO₂ neutrality for forest biomass

Regarding the issue of CO₂ neutrality for biomass from sustainably managed forests, the following aspects would be taken into considerations:

Lengthening the rotation periods leads to:

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Temporary short-term increase of total CO₂ uptake in the forest as the not harvested mature parcels (stands) would have higher CO₂ uptake compared to the alternative: newly planted parcels (The argument is valid only for a limited period of time and is not valid for over-mature stands, e.g. pristine old forests.

Biomass neutrality and climate neutrality with regard to CO₂ and energy generation

A comprehensive presentation of the two concepts can be found in reports from IEA Bioenergy T38 [14]. For generation of a given energy quantity, the CO₂ emissions varies between different fuels. Fossil natural gas has typically a carbon intensity of 15 GJ⁻¹, compared to less efficient oil at21 kg GJ⁻¹, and steam coal at 27 kg GJ⁻¹. In addition to these values, the emissions from mining, transport, leakage etc. should be added to arrive at values for the total emissions. For traditional

Summary and conclusions; assuming sustained forest management

Biomass harvested under sustained forest management is CO₂ neutral (or better). Prolonged rotation periods in order to store more carbon would not lead to long term reduction of the atmospheric CO₂, as the total capacity of the forest to take up CO₂ decreases.

In comparison with combustion of coal, biomass may also be regarded as climate neutral, provided that the comparison includes also additional emissions from mining/harvesting, transport, leakage, etc., and state-of-the-art production and

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Diverging results in the literature on the specific extent and role of wood-based energy in climate change mitigation have generated a bitter and wide-ranging debate which is still on-going (see e.g. Refs. [5–12]). Results range widely, with studies concluding that forest-bioenergy increases GHG emissions compared to fossil fuels over a timescale of decades, centuries, or even indefinitely, whilst others concluding that significant emission reductions can be achieved within reasonably short timeframes (see e.g. Refs. [13–23]). This divergence is largely due to different sources of biomass considered, as well as modeling methodologies and assumptions [13,24–28].
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In contrast to more comprehensive forest C assessments, those that do not include post-harvest utilization of biomass for products and energy tend to conclude that the greatest C benefits come from forest preservation, reducing management intensity, and extending harvest rotation lengths (Stoy et al., 2008; Raymer et al., 2011; Creutzburg et al., 2016). Forests used as sources of biomass that replace fossil fuels have long-term C benefits when they are sustainably managed (Zanchi et al., 2012; Hektor et al., 2016). Fossil fuel conversion efficiencies and alternatives to which forest-based products are compared also influence net C benefits (Butarbutar et al., 2016; Pingoud et al., 2016; AiXin et al., 2017; Taeroe et al., 2017).
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Forests may mitigate climate change through extraction of biomass that substitutes fossil fuels and fossil fuel intensive materials (Haus et al., 2014; Gustavsson et al., 2017), or through buildup of carbon pools in biomass and soil (Schulze et al., 2012). The positive effect of substitution versus forest carbon storage is an intensely debated trade-off (Duncker et al., 2012; Seidl et al., 2007; Hektor et al., 2016). Calculated carbon parity times vary in the literature, due to differences in the analyzed situations (Helin et al., 2013; Ter-Mikaelian et al., 2014), but also between studies that analyze seemingly comparable situations, for example due to choice of calculation framework and scale (Bentsen, 2017; Buchholz et al., 2016; Lamers and Junginger, 2013).
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Short communicationCarbon balance for wood production from sustainably managed forests

Highlights

Abstract

Section snippets

CO2 neutrality of forest biomass

Conclusions regarding CO2 neutrality for forest biomass

Biomass neutrality and climate neutrality with regard to CO2 and energy generation

Summary and conclusions; assuming sustained forest management

Biomass Bioenergy

Biomass Bioenergy

Biomass Bioenergy

Biomass Bioenergy

Biomass Bioenergy

For. Ecol. Manag.

Bioenergy and land use change—state of the art

WIREs Energy Environ.

The ‘debt’ is in the detail: a synthesis of recent temporal forest carbon analyses on woody biomass for energy

Biofuels, Bioprod. Biorefining

Fixing a critical climate accounting Error

Science

Short communication
Carbon balance for wood production from sustainably managed forests

CO₂ neutrality of forest biomass

Conclusions regarding CO₂ neutrality for forest biomass

Biomass neutrality and climate neutrality with regard to CO₂ and energy generation