National and global greenhouse gas dynamics of different forest management and wood use scenarios: a model-based assessment

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Abstract

An increased use of wood products and an adequate management of forests can help to mitigate climate change. However, planning horizons and response time to changes in forest management are usually long and the respective GHG effects related to the use of wood depend on the availability of harvested wood. Therefore, an integral long-term strategic approach is required to formulate the most effective forest and wood management strategies for mitigating climate change.

The greenhouse gas (GHG) dynamics related to the production, use and disposal of wood products are manifold and show a complex time pattern. On the one hand, wood products can be considered as a carbon pool, as is the forest itself. On the other hand, an increased use of wood can lead to the substitution of usually more energy-intense materials and to the substitution of fossil fuels when the thermal energy of wood is recovered. Country-specific import/export flows of wood products and their alternative products as well as their processing stage have to be considered if substitution effects are assessed on a national basis.

We present an integral model-based approach to evaluate the GHG impacts of various forest management and wood use scenarios. Our approach allows us to analyse the complex temporal and spatial patterns of GHG emissions and removals including trade-offs of different forest management and wood use strategies. This study shows that the contributions of the forestry and timber sector to mitigate climate change can be optimized with the following key recommendations: (1) the maximum possible, sustainable increment should be generated in the forest, taking into account biodiversity conservation as well as the long-term preservation of soil quality and growth performance; (2) this increment should be harvested continuously; (3) the harvested wood should be processed in accordance with the principle of cascade use, i.e. first be used as a material as long as possible, preferably in structural components; (4) waste wood that is not suitable for further use should be used to generate energy. Political strategies to solely increase the use of wood as a biofuel cannot be considered efficient from a climate perspective; (5) forest management strategies to enhance carbon sinks in forests via reduced harvesting are not only ineffective because of a compensatory increase in fossil fuel consumption for the production of non-wooden products and thermal energy but also because of the Kyoto-“cap” that limits the accountability of GHG removals by sinks under Article 3.3 and 3.4, at least for the first commitment period; (6) the effect of substitution through the material and energy use of wood is more significant and sustained as compared with the stock effects in wood products, which tend towards new steady-state flow equilibria with no further increase of C stocks; (7) from a global perspective, the effect of material substitution exceeds that of energy recovery from wood. In the Swiss context, however, the energy recovery from wood generates a greater substitution effect than material substitution.

Introduction

Wood as a CO2-neutral natural material and energy resource plays an important role in the discussion on the mitigation of climate change (IPCC, 2000). Long-living wood products in particular can contribute to the mitigation of climate change in many ways. First, wood products with long service life act as a carbon (C) stock during their service life, as they prevent sequestered C from returning to the atmosphere as CO2. Second, wood products can substitute for more energy-intense products made out of ‘conventional’, non-wooden materials. Third, after service life, they can substitute for fossil fuels if they are incinerated in adequate installations. In addition, wood can be used as a biofuel to substitute for fossil fuels, either directly from forests or as industrial residual or waste wood.

The most important basis for the fulfilment of the CO2-reduction commitments defined in the Kyoto Protocol (KP) is well-founded knowledge of the efficacy of the measures that may be implemented to improve the national CO2 balance. This is particularly relevant for issues related to forestry (Nabuurs et al., 2007) and to a less extend related to residential and industrial building construction (Levine et al., 2007), as strategic decisions for a considerably long time span have to be taken.

In recent years, the political debate in the forestry and timber industry has been strongly focused on the fact that in the first commitment period of the KP (2008–2012) forests can be accounted as a C sink or source in accordance with Articles 3.3 and 3.4 of the KP. On international level, negotiations are going on about accounting for harvested wood products (HWP) in subsequent commitment periods of the KP: wood products act as C stocks during their lifetime. In this way, they extend the residence time of the C stored in the wood and thus prevent it from returning to the atmosphere as natural CO2 for a certain time period. Several studies have tried to quantify these stocks and stock changes for some countries, and specifically for their building sector (e.g., Winjum et al., 1997, Pingoud et al., 2001 and literature stated there). As opposed to this, the increase of growing stock in forests is curbed through the use of wood and the sink effect is reduced. If harvesting exceeds net increment, average growing stocks are decreasing and the forest becomes a source of CO2 (see e.g. Liski et al., 2005, Sedjo, 1989, Thompson and Matthews, 1989, Marland and Marland, 1992, Karjalainen, 1996, Matthews et al., 1996, Fischlin et al., 2006).

However, as a renewable CO2-neutral raw material and energy source, harvested wood can make a far more significant contribution to the reduction of national CO2 emissions through the substitution of (a) more energy-intensive materials and construction methods (e.g. Koch, 1992, Marcea and Lau, 1992, Buchanan and Honey, 1994, Suzuki et al., 1995, Buchanan and Levine, 1999, Pingoud and Lehtilä, 2002, Sedjo, 2002, Gustavsson et al., 2006, Werner et al., 2006, Werner and Richter, 2007) and (b) fossil fuels by the energetic use of wood (e.g. Marland and Schlamadinger, 1998, de Jong et al., 2007).

All of these climate-relevant aspects of forests and wood are interconnected on various complex temporal and spatial scales, which have been addressed with different scopes and approaches (e.g., in Fischlin, 1996, Matthews et al., 1996, Skog and Nicholson, 1998, Niles and Schwarze, 2001 or Eriksson et al., 2007).

However, one strategically important aspect has been disregarded in all these studies: the geographical location of the GHG effects in terms of national and international CO2-balances. Foreign trade causes the transfer of emissions generated by the production and disposal of wood products and of their substitutes (for Switzerland, see BAFU, 2007) from one country to another. In the case of imported goods, the emissions arising from their production arise in the country in which they were produced (abroad), and, conversely, in the case of exported goods, the emissions caused by production are attributed to the producing country. Furthermore, the import and export of wood products leads to a transfer of the C stock stored in these products. Thus, in order to assess the efficacy of national and international climate-policy measures, the effect of cross-border goods traffic on the national greenhouse gas balance must be taken into account.

This paper provides an integral view on all relevant GHG effects of different forest management and wood use scenarios, while distinguishing between national effects and effects occurring abroad. Thus, the main aim of this paper is to demonstrate the connections of these GHG effects over a strategically relevant timescale with the help of models based on various wood harvesting and wood use scenarios. It provides bases for demonstrating the possible utility of the forestry and timber industry in relation to the reduction of CO2 emissions in Switzerland in a long term and strategic perspective beyond current Kyoto ruling. Although the case is made for Switzerland, we believe that the modelling approach is generally applicable and that the conclusions on global scale are fairly representative for many European countries, whereas the relative importance of the investigated GHG effects on national level can differ considerably for each country.

This paper is largely based on an extensive study report (Taverna et al., 2007), from which complementary information can be gained.

Section snippets

System boundaries and reference situation

The study incorporates the greenhouse gas dynamics generated by different forest management and wood use scenarios in Switzerland and abroad. The following C pools and fluxes are included:

  • -

    changes in the five C pools, i.e. above- and belowground, litter, dead wood and soil organic carbon in the Swiss forest1;

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    changes in the C stocks in the civilization cycle, i.e.

Scenarios on future forest management and use of wood

The adopted scenarios represent realistic options for future forests management and wood use. They differ on the basis of forest yields and the use made of the harvested wood, whereas the selected average yields are always smaller than or equal to increment.

Scenarios of forest development are simulated with the forest model MASSIMO and the soil model YASSO as described in Section 2.3. The changes from the previous harvesting methods to new forms of intervention and management intensities are

Resulting GHG dynamics

In this section, global effects and in-country effects of the scenarios are distinguished. The in-country effects reflect GHG emissions and resulting substitution effects as well as changes in carbon pools (incl. wood products) that occur within Switzerland; the global effects are the sum of the in-country GHG effects and the GHG occurring abroad, e.g. due to changes in production and transport and related fossil fuel consumption in Switzerland (as GHG emissions related to the extraction and

Discussion and conclusions

The comparison of the scenarios clearly shows that different strategies produce very different effects. Moreover, the short-term effects can differ significantly from the long-term effects.

The Reduced Forest Maintenance scenario shows that large volumes of CO2 can be sequestered initially. In the medium to long term, the effect is reversed, however, as the forest's C pool becomes full and decomposition gradually commences. Furthermore, this scenario poses the greatest risks to forest stability.

Acknowledgements

This research was financed by the Federal Office for Environment (FOEN). The authors acknowledge the technical assistance by Dr. Hans-Peter Bader and Ruth Scheidegger, Department of System Analysis, Integrated Assessment and Modelling, EAWAG, Dübendorf during the modelling of wood flows in SIMBOX. We thank also Dr. Klaus Richter, Wood Laboratories, Empa, Dübendorf for his support in the early phase of this project. We are particularly grateful for the thorough and valuable input by three

Frank Werner is an environmental scientist and has his PhD on modelling problems in life cycle assessment. He is the owner of a small environmental consulting company, dedicated to life cycle assessment, material flow analysis and the sustainable use of forestry and wood products in the context of climate change.

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  • Cited by (0)

    Frank Werner is an environmental scientist and has his PhD on modelling problems in life cycle assessment. He is the owner of a small environmental consulting company, dedicated to life cycle assessment, material flow analysis and the sustainable use of forestry and wood products in the context of climate change.

    Ruedi Taverna is a rural engineer with specialization in dynamic substance flow analysis. He works in a small environmental consulting company, dedicated to themes in forestry, waste management, resource management, environment and construction-related ecology and water balances.

    Peter Hofer is a forest engineer and graduate in business administration and economy. He was during 20 years head of the marketing organization Lignum in Switzerland. He is joint owner of a consulting company, specialized in resource management (forest and timber industry, waste- and water-management).

    Esther Thürig is a natural scientist with a PhD in forest growth modelling and carbon sequestration. She works for the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) in Zurich.

    Edgar Kaufmann has a master degree in forest science and is specialized in forest inventories and empirical models for forest management and forest development. He works as a team leader of the research group “Resource Analysis and Prediction” at WSL, Zurich.

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