Report

Europe’s forest management did not mitigate climate warming

Science  05 Feb 2016:
Vol. 351, Issue 6273, pp. 597-600
DOI: 10.1126/science.aad7270

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  • RE: Europe’s forest management did not mitigate climate warming. Full stop.
    • Alessandro Agostini, Researcher Italian National agency for new technologies, Energy and sustainable economic development
    • Other Contributors:
      • Jacopo Giountoli, Researcher
      • Luisa Marelli, Researcher

    Naudts et al. presented a clear goal for their study: to assess the climate effects of forest management (afforestation, species conversion and wood extraction) in Europe in the last 260 years. In this context, we may comment that the modelling approach adopted is not fully consistent with the stated goal. A more appropriate goal definition would have been: climate impacts of carbon, water and surface albedo balances of forest management in Europe in the last 260 years.
    The current atmospheric GHG concentration and current state of Earth's climate is the result of historical processes, natural and anthropogenic, including both forest management changes as well as wood products utilization in various sectors of the economy. The study seeks to attribute part of the historical changes in temperature anomaly to forest management changes happening in Europe.
    However, climate is far more complex than CO2 emissions and albedo; although probably these are the most important factors in the forest-climate nexus.
    A large fraction of the biomass extracted from forests is eventually combusted, either directly or at the end of life. Other climate forcers released during the combustion of biomass, such as short lived GHGs, aerosols and non-CO2 long lived GHG, may thus play a non-negligible role in the overall climate impacts of forest management [1, 2]
    In particular, in long term analyses, black carbon and N2O emissions should not be overlooked. Black carbon...

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    Conflict of Interest:
    None declared.
  • Europe’s forest management did not mitigate climate warming”: a correct historical perspective!
    • Roberto Pilli, PhD JRC, Institute for Environment and Sustainability Forest Resources and Climate Unit

    Apart from the technical limitations of the study proposed by Naudts et. al., already mentioned by other comments, the conclusion of this work, that “Europe’s forest management did not mitigate climate warming” seems to be missing a correct historical perspective. Modern Forest Management (FM), as was (and largely is) applied in the majority of European forests, was founded by the German school of Cotta at the beginning of the 19th century (Puettman et al., 2009). As highlighted by the same Cotta in 1816, “There would be … no forest science without deficiency in wood supply. The science is only child of necessity or need”. This statement clearly suggests the “perspective” that inspired FM; i.e., ensured an adequate wood supply, in order to satisfy the increasing demand of wood coming from the second industrial revolution. This is strictly related to the “recognition” of a specific function (i.e., providing a productive service) attributed to the majority of European forests. Largely applied to many other countries, these theories deeply changed the structure and composition of European forests, maximizing timber production at the expense of any other possible forest function. And indeed, thanks to these high-productive management strategies, largely based on the use of pure, even-aged, coniferous species (as highlighted by Naudts et al.), European forests could considerably increase their productivity. Due to the long life cycle of the trees, the biological limits of these...

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    Conflict of Interest:
    None declared.
  • RE: Europe’s forests mitigated climate warming since the 1950’s and could continue to do so in the future!
    • Marcus Lindner, Head of Programme Sustainability and Climate Change European Forest Institute
    • Other Contributors:
      • Frits Mohren, Professor
      • Gert-Jan Nabuurs, Professor
      • Hans Verkerk, Senior Researcher

    Afforestation and forest management are important for mitigating climate change (1). However, by analysing how afforestation and management modified Europe’s forests in extent, stocking and species composition in 2010 as compared to 1750, Naudts et al. (2) recently claimed that ”two and a half centuries of forest management in Europe have not cooled the climate”. Unfortunately, the authors do not consider important aspects in their analysis.

    The major trends in their study period included a decline of forest cover and a change of dominant species from deciduous to coniferous species. Indeed, for centuries to millennia humans have overexploited forest resources. Much of the Mediterranean and central European forests were already degraded or deforested in Medieval times and before (3, 4). In response to degradation, Von Carlowitz (5) published his widely acclaimed “Sylvicultura Oeconomica” in 1713, being the first account of the need for sustainable forest management. With the onset of sustainable forest management after World War II, these trends have reversed. European forest cover has increased by more than 25% since the 1950’s (6) and carbon in forest biomass has accumulated drastically (7, 8). Similarly, the trend in tree species composition has changed since 1990 in many European countries from coniferous-dominated forests to more mixed or deciduous dominated forests (9). Hence, by comparing forest resources in 2010 with 1750, Naudts et al. ignore changes in for...

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    Conflict of Interest:
    None declared.
  • Response
    • Sebastiaan Luyssaert
    • Other Contributors:
      • Aude Valade
      • Kim Naudts
      • Matthew J. McGrath
      • Yiying Chen
      • James Ryder
      • Juliane Otto

    The majority of the critiques on “European forest management did not mitigate climate change” touch on two issues: (a) the suggestion that our study did not or incorrectly accounted for the wood product pools and (b) the omission of wood substitution in our GHG budget calculations.

    (a) Our model-based approach accounts for different wood uses (1). Harvested trees with a diameter above a species-specific threshold are distributed across a short, medium- and long- lived product pools which mimic, for example, paper, particle boards and timber usages, respectively. Trees with smaller dimensions are entirely moved to the short-lived product pool. The lifetime of the short-lived pool was set to 1 year, the medium-lived pool 10 years and the long-lived pool 100 years. We choose a 100-year product pool rather than the present day 50-years, to account for the possibility that historical wood usage was longer lived than present day uses. Our approach is therefore more likely to have overestimated than underestimated the carbon sequestered in the wood product pool.

    (b) Substitution of fossil fuels and energy-intensive materials by wood-based alternatives was not overlooked in our analysis but deliberately omitted because we judged today's concept of wood substitution unfit in a historical context. Calculating wood substitution is meaningful in the context of evaluating voluntary alternative policy scenarios. However, in a historical context there are no well-defin...

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    Conflict of Interest:
    None declared.
  • RE: Europe’s forest management did not mitigate climate warming
    • Lynn Huntsinger, Professor University of California, Berkeley
    • Other Contributors:
      • Tobias Plieninger, Associate Professor
      • Fernando Pulido, Associate Professor
      • Paul F. Starrs, Professor

    Beyond not mitigating climate warming (1), dense conifer forests are highly flammable. In recent decades, traditional European agro-forestry landscapes have lost ground to monocultural pine plantations (2). In California, one hundred years of fire suppression have created dense unhealthy forests loaded with fuel accumulations (3). From 2006 to 2010, wildfires burned more than 2 million ha in Europe’s Mediterranean regions, 65% of that in Iberia (4). More than 800,000 ha burned in California from 2013-2015 (5). By contrast, the agro-sylvo-pastoral oak woodlands of Iberia, with woody and herbaceous plants controlled by grazing, occasional tillage, and clearing, have fewer wildfires (6) and support high biodiversity and multiple diverse ecosystem services at local to global scales (7). In pre-European California, frequent natural and anthropogenic fires reduced fuels and tree density (8), creating more open woodlands and forests that are often higher in biodiversity than dense forests and pine plantations (9). The recent huge wildfires should be seen as a chance to create forests and woodlands for an even warmer future. For example, disturbances by storm, fire, and insects were capitalized on in Germany by converting formerly monospecific pine plantations to diverse forests with native broadleaved species (10). Traditional forest users and residents have controlled tree and shrub growth with livestock grazing, regular burning, cultivation, and hand clearing, limiting the dens...

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    Conflict of Interest:
    None declared.
  • There is no alternative to forest management
    • Bernhard Felbermeier, Senior scientist Institute of Silviculture, Technische Universität München
    • Other Contributors:
      • Michael Weber, Professor, Dean of Studies
      • Thomas Knoke, Professor, Head of the Institute
      • Reinhard Mosandl, Professor, Head of the Institute

    Naudts et al. [1] present a study on Europe’s past forest management (FM) and conclude a climate warming effect. We want to make a point on technical limitations of reconstructing Europe’s FM and on the omission of substitution effects, which severely challenge the conclusions of the study.
    (i) The authors admit in a former study [2] several limitations on the reconstruction of FM: 1) Lack of comprehensive data to parametrize and validate past FM [p4295&p4299]. 2) Reconstruction before 1828 is hypothetical, representing only how much forest would have been required to satisfy the unknown and therefore assumed wood demands [p4291]. 3) Spatial & temporal representativeness remains unknown as the data are mainly based on local case studies [p4310].
    (ii) No information is provided about the important initial stocking (and thus carbon) densities assumed for the forests in 1750 - unmanaged forest as well as widely degraded forest. Paintings at this time indicate low carbon densities (see [3]).
    (iii) Poor representation of forest sites, stand structures, and silvicultural interventions (e.g. only clear cuts) - although decisive for water balances.

    Furthermore it is crucial to make explicit alternatives to FM, which could have satisfied the former raw material demands. For a sound statement on the effects of past FM on mitigation of climate warming the avoided emissions due to the substitution of fossil fuels and of energy intensive materials (e.g....

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    Conflict of Interest:
    None declared.
  • RE: Forests and forest management plays a key role in mitigating climate change
    • Niclas Scott Bentsen, Associate Professor University of Copenhagen, Department of Geosciences and Natural Resource Management, Denmark
    • Other Contributors:
      • Thomas Nord-Larsen
      • Søren Larsen
      • Göran Berndes
      • Richard Birdsey
      • Annette Cowie
      • Claus Felby
      • Martin Junginger
      • Promode Kant, Institute of Green Economy, Gurgaon NCR, India
      • Werner Kurz
      • David Lamb
      • Magnus Löf
      • Palle Madsen
      • Chadwick Dearing Oliver
      • Tat Smith
      • John A. Stanturf
      • Anders Taeroe
      • Lars Vesterdal

    The report by Naudts et al. concludes that forest management in Europe during the last 260 years has failed to result in net CO2 removal from the atmosphere. The authors have reached this conclusion through their failure to consider a key factor in their otherwise comprehensive analysis.
    The authors present an analysis of net carbon emissions from forest, but omit substitution effects related to the link between forest management and the fossil carbon pool. The link between fossil and terrestrial carbon pools is however critical for modelling climate impacts. To conclude as they do, the authors should have asked: What would the GHG emissions have been in absence of forest management in Europe? The services provided by forest management - increased biofuel and materials production – substitute fossil fuels and materials, which are generally GHG-intensive. The report ignores that sustained yield forest management was developed to meet demands for energy and materials for an increasing population and prevented a complete destruction of Europe’s forest. Particularly since 1850, forest management has increased Europe’s forest area and productivity, and thus also the forest carbon pool as also reported by Naudts et al. By ignoring the link between forestry and fossil carbon pools and not considering development in the absence of forest management, there is no accounting for the effect on GHG emissions, and no basis for estimating the contribution of forest management to cl...

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    Conflict of Interest:
    None declared.
  • Europe’s coniferous forest management can mitigate climate warming – an answer to Naudts et al. (2016)
    • Marcus KnaufKnauf Consulting
    • Other Contributors:
      • Arno Frühwald

    In their article Naudts et al. call into question the key contributions made to climate change mitigation by forests through carbon sequestration (Kyoto agreement, COP 21 Paris) and forest management in Europe with the cultivation of coniferous forests. Their conclusions are far-reaching, but have no scientific founding, neither in their methodological approach, nor their results and analysis. The study disregards current scientific research, in particular:

    1. The authors completely ignore or incorrectly assess the historical developments which ultimately led to significant changes in the species composition of Europe’s forests. The deciduous forests did not disappear and transform into managed coniferous forests as a result of forest management, but rather as a consequence of the industrial revolution which devastated Europe’s forests, in particular through agriculture and the exploitation of wood for energy, metallurgy, mining and glassmaking.

    2. The authors only focus on the aspect of carbon storage in forests and wood products, thereby fully neglecting the potentials presented by substitution. At the same time, they overlook the opportunities coniferous forests offer for higher wood productivity and material use.

    3. The study does not include the positive effects of using wood as a substitute for fossil fuels. Thus, no account is made for the effects of material and energy substitution on the CO2 balance. Knauf et al. (2015) have shown that these e...

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    Conflict of Interest:
    None declared.
  • RE: Europe’s forest management did mitigate climate warming
    • Jürgen Bauhus, Professor of Silviculture University of Freiburg, Institute of Forest Sciences
    • Other Contributors:
      • Andreas Bolte, Head - Thünen Institute of Forest Ecosystems
      • Matthias Dieter, Head - Thünen-Institute of International Forestry and Forest Economics
      • Friederike Lang, Professor of Soil Ecology
      • Joachim Rock, Climate Change Researcher, Thuenen-Institute for Forest Ecosystems
      • Hermann Spellmann, Director, North-West German Forst Experimental Station

    In their study, Naudts et al. (1) point out that the conversion from deciduous to coniferous forests in Europe increased summertime boundary layer temperature by 0.08 K and that the reduction in forest C stocks since 1750 resulted in a carbon debt of 3.1 Pg C. We question the conclusion that afforestation with predominately conifer species and harvesting of timber have increased climate warming. Unlike the IPCC has outlined (2), the authors did not fully consider that wood products are an integral part of the forest sector C cycle and contribute through the substitution of fossil energy and energy-intensive products to climate warming mitigation. Using the substitution factors provided by (3) and the average growth rate provided by (4), the positive substitution effect of wood use would have offset the calculated average C debt (ca. 16 t C ha-1) in less than 2 decades. Since a greater proportion of coniferous timber is used in long-lived products and less for direct energy generation when compared to hardwoods, the substitution potential of conifers is substantially higher than that of deciduous tree species (5). This effect, and also the cooling effect of higher emissions of organic vapours from conifers (6) should have been considered to estimate the true effect of species change on the mitigation potential of forests. Further, the reference year 1750 is highly problematic since the majority of forests were still used largely also for agricultural purposes until 1820-185...

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    Conflict of Interest:
    None declared.
  • RE: Comment on the results and the method (Naudts et al. 2016)
    • Pekka Eero Kauppi, Professor of Environmental Science and Policy Dpt Environmental Sciences, 00014 University of Helsinki, Finland
    • Other Contributors:
      • Richard A. Birdsey, Program Manger

    The retrospective study of European forests (Naudts et al. 2016) assesses the long-term impact of forest management on climate by estimating the combined effects of removing CO2 from the atmosphere and altering the energy balance and evapotranspiration. However, the broadly stated headline that forest management may not be an appropriate climate mitigation strategy refers to a historical period that does not represent current forest management objectives and practices. The period from 1750 to present is an inappropriate analog for assessing the post-WW2 trends and the potential of current forest management practices to assist with climate change mitigation. Over the last 70 years, European forests have been managed far more intensively than forests of most other regions while the tree species distribution has remained virtually unchanged and the timber resources have significantly increased. It is very unlikely that European forest management represents a net release of C to the atmosphere especially if the effects of harvesting wood products are fully accounted for.
    The methodology is also seriously flawed. The authors fail to account for the reduced use of fossil fuels when substituting wood products for materials that require high energy inputs to manufacture, such as steel and concrete. And some of the data used or cited in the study is questionable, such as: the exceptionally high rate of forest harvest is not consistent with published data; and the large wa...

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    Conflict of Interest:
    None declared.
  • RE: Europe’s forest management did not mitigate climate warming

    It should not be that surprising that forest management strategies that were not designed to mitigate climate change did not have a positive impact on the terrestrial forest carbon flux. Unfortunately, serendipity does not seem to have great potential as an effective climate mitigation strategy. The analysis would have been more rounded if they had also considered the avoided negative climate impacts if Europeans had not been utilized their forests as intensively, and had instead increased their coal burning for heat and used more Portland cement in buildings. As Bill Gates stressed in at the Paris IPCC meeting we need to invest in innovation since we can not depend on luck to get out of this mess. Looking forward, improvements in system level efficiency of forest harvesting, wood product manufacturing, and society’s use and reuse of products should lead to better overall GHG impacts from managed forests. We must design future forest management strategies for the world’s temperate forests that consider biological richness, forest carbon and harvested wood products that can replace emission intensive substitutes. Ignoring one or two of these goals will shortchange us all.

    Bill Stewart
    Forest Economist
    University of California, Berkeley

    Conflict of Interest:
    None declared.