Table des matières

Couverture

The forestry & wood sector and climate change mitigation

Preface

Forward

The role of the forestry & wood sectors in mitigating climate change

A global issue

The French forestry & wood sector and its challenges

Forestry mitigation levers

An innovative assessment of the mitigation potential of the French sector

Part I - The current carbon balance of the forestry & wood sector

Chapter 1 - Mitigation capacity of the different segments of the forestry & wood sector

Chapter 2 - The current carbon balance across the French forestry & wood sector

Conclusion of Part I

Part II - The carbon balances and economic effects of three forest management scenarios until 2050

Chapter 3 - Three forest management scenarios to the year 2050

Chapter 4 - Carbon balances of forest management strategies up to 2050

Chapter 5 - Economic barriers and levers for the implementation of forest management scenarios

Conclusion of part II

Part III - Effects of worsening climate change and severe disturbances on the carbon balance up to 2050

Chapter 6 - The effects of worsening climate change

Chapter 7 - Estimating the impacts of severe forest disturbances

Conclusion of Part III

General conclusions

Annex - Determination of the areas to be reforested under the ‘Intensification’ scenario reforestation plan

Choice of areas to be included in a reforestation plan

Allocation of species to classes

References

List of authors and scientific experts involved in this publication

The forestry & wood sector and climate change mitigation

From carbon sequestration in forests to the development of the bioeconomy

Alice Roux, Antoine Colin, Jean-François Dhôte and Bertrand Schmitt, eds

© éditions Quæ, 2020.

ISBN eBook [ePub]: 978-2-7592-3280-2

Éditions Quæ
RD 10
78026 Versailles Cedex

This document is a revised version of the study commissioned by the Ministry of Agriculture and conducted by INRAE and IGN. The contents of the study and of this publication are the sole responsibility of their authors.

The report and its annexes are available on www.inrae.fr/actualites/quel-role-forets-filiere-foret-bois-francaises-lattenuation-du-changement-climatique .

To cite this publication: Roux A. (coord.), Colin A. (coord.), Dhôte J.-F. (coord.), Schmitt B. (coord.), Bailly A., Bastien J.-C., Bastick C., Berthelot A. Bréda N., Caurla S., Carnus J.-M., Gardiner B., Jactel H., Leban J.-M., Lobianco A., Loustau D., Marçais B., Meredieu C., Pâques L., Rigolot E., Saint-André L., Guehl J.-M., 2020. The forestry sector and climate change mitigation: from carbon sequestration in forests to the development of the bioeconomy. Versailles, Éditions Quæ.

www.quae.com
www.quae-open.com/

This eBook is published under the CC-by-NC-ND 2.0 licence.

For any questions, comments or suggestions: quae-numerique@quae.fr

Preface

Climate change, which is already clearly evident around the world, is one of the major challenges facing humanity now and in the decades to come. Mitigating climate change requires that every business sector, production chain, household, consumer and citizen of the world must make significant changes to their production, consumption, lifestyle and use of space in order to reduce greenhouse gas emissions and anthropogenic environmental damage. Faced with these urgent objectives, public policies must define, guide, stimulate and encourage (and, if necessary, force) the societal changes needed to meet this global challenge.

Intergovernmental Panel on Climate Change (IPCC) reports clearly show that limiting the rise in the average global surface temperature to less than +2°C will require not only drastic reductions in human-induced greenhouse gas emissions, in particular by promoting a decarbonised economy, but also an increase in carbon ‘sinks’, which equate to ‘negative emissions’ (IPCC, 2018). Forests have a particular role to play in this context because of their extent, their biological functioning and the services they provide to society. On the one hand, through photosynthesis, forests can fix a proportion of atmospheric CO2 and sequester this captured carbon in the tissues of trees and forest ecosystems. On the other hand, they provide a renewable natural resource conducive to the development of bioeconomies, which have the aim of replacing economies based on non-renewable resources and fossil fuel use, as well as reducing greenhouse gas emissions through product substitution.

While the main challenge in intertropical and boreal regions is tackling deforestation and forest resource degradation, forests and forestry in temperate regions face what may appear to be contradictory goals: to increase atmospheric carbon capture through sequestration in biomass and soils, while providing a growing share of the resources needed to produce essential material goods and energy for human societies as well as gradually renewing forests to enable them to adapt to future climate conditions. Creating a balance between these potentially competing priorities has been the subject of intense societal and scientific debate in recent years, which has prompted us to examine all aspects of these issues in greater depth.

With this in mind, INRAE and IGN, at the request of the French Ministries responsible for agriculture and forestry, have jointly undertaken a scientific assessment to shed light on the details of this debate, using the example of forests and the forestry & wood sectors in metropolitan France. The results of this important exercise are presented in this book.

The aim here is explicitly not to decide between positions, which are sometimes presented in an exaggeratedly disparate manner; rather, it is to enable stakeholders (professionals, the public, and organizations), decision-makers and citizens who feel concerned by this issue to understand the full complexity and uncertainties surrounding the trade-off between carbon sequestration in forests and the development of the bioeconomy. To this end, experts from our two organizations and some of our partners have analysed the various aspects that need to be considered when designing and implementing potential low-carbon strategies for the sustainable management of forest resources and wood-based products.

In restricting the scope of the analysis to the overall forestry & wood sector in France, the experts firstly describe the various components that must be explored in order to produce a comprehensive carbon assessment of the sector. In doing so, they highlight the areas of uncertainty in the current balance estimates, which are related to margins of error in the available data and the difficulties in setting particular coefficients and parameters essential to the establishment of these balances. On that basis, they make projections of this carbon balance up to the year 2050, a horizon that may to some appear remote, but which, on the scale of forest and climate dynamics, is very near. More specifically, these projections examine the potential impacts of three forest management strategies that differ mainly in their levels of resource extraction (and renewal) in order to supply the bioeconomy.

This forward-looking, predictive analysis firstly highlights that, regardless of the chosen option, the carbon balance of the entire forestry & wood sector in France is likely to continue improving. This confirms the major role of this sector in climate change mitigation. However, in addition to the uncertainties already identified for the establishment of the current carbon balance, further uncertainties concern the evolution of particular coefficients and technical parameters that influence the results of the projections. For example, will the growth rate of French forests be maintained as stands age? How might changes occur in the amount of greenhouse gas emissions avoided by using forest products instead of those which today produce more greenhouse gases? While these uncertainties make it difficult to identify a single management strategy with the most favourable outcome in terms of carbon balance, they can, as will be seen in the following pages, guide discussion on wood uses that should be encouraged to improve the carbon balance through strategies to support the development of the bioeconomy.

In addition to analysing the carbon balance, the group of experts chose to add two further dimensions, both of which are original and essential, to better clarify the future role of the sector in mitigating climate change. Firstly, the use of an economic model encompassing the entire French sector allows the identification of economic obstacles that must be removed in order to deploy strategies aimed at increasing harvests. Consequently, as Verkerk et al. (2020) correctly noted, the response of the forestry & wood sector and the management strategies to which they will be subject will be very sensitive to future climatic conditions, as well as to the major biotic and abiotic disturbances that forests will probably experience more frequently over coming decades. Although very difficult to conceptualize and model, especially given their nature and frequency of occurrence, the simultaneous analysis of these two additional dimensions has been attempted here. It provides an initial assessment of the sector’s resilience and carbon balance in the face of such changes and events.

Daniel Bursaux, director general of IGN
Philippe Mauguin, president-director general of INRAE

Forward

This publication is the result of a study carried out by INRA (now INRAE, National Research Institute for Agriculture, Food and the Environment) and IGN (National Institute for Geographic and Forestry Information), at the request of the Ministry of Agriculture and Food and the High Council for Food, Agriculture and Rural Areas. It was conducted by INRAE’s Directorate for Collective Scientific Expertise, Foresight and Advanced Studies (DEPE). As with all work conducted by DEPE, this study was carried out according to the principles and rules for conducting expert assessments and studies laid down by this institution (INRAE-DEPE, 2018). DEPE carries out three types of projects, mostly commissioned by public authorities or external partners.

Collective Scientific Assessments (ESCo) involve the compilation of existing scientific knowledge to highlight achievements, uncertainties and knowledge gaps, and to reveal the latest scientific debates.

When the available literature is unable to precisely answer the questions posed by the public authorities, a multidisciplinary study-type approach is used. These studies are similar to the ESCo, and indeed integrate the ESCo approach, but complement it with the creation of new data (collection, statistical analysis, calculation and simulation).

Prospective studies offer visions of the future (or scenarios) for discussion by exploring, as systematically as possible, hypothetical scenarios based on available scientific knowledge.

The study presented here includes elements specific to each of these three approaches. It examines how carbon balances can be established for the forestry and wood sector - taken here in its broadest sense, i.e. the entire forestry sector system and the activities related to the management, harvesting and value-adding of wood-based products - and their associated uncertainties. Firstly, it adopts an expert assessment approach using a review of the international scientific literature to define and discuss the assumptions and parameters to be adopted for each component along production chains that are likely to sequester or release carbon dioxide (CO2). The detailed results of this first stage were the subject of a first report directed to the ministry responsible for agriculture (Dhôte et al., 2015). This study also considers alternative forest management strategies up to 2050 using a prospective approach, which develops scenarios and seeks to quantify their long-term consequences. Finally, the study quantifies the effects of the scenarios considered using existing simulation tools, which therefore exposes their limitations. The detailed results of the complete study are available in the full report and its numerous annexes (see Roux et al., 2017).

This project was coordinated by the project leader Alice Roux (INRAE-DEPE), and assisted by Marc-Antoine Caillaud and Kim Girard (INRAE-DEPE) who provided logistical and administrative support. The scientific steering was initially entrusted to Jean-François Dhôte (INRAE), with Antoine Colin (IGN) and Bertrand Schmitt, then Director of the DEPE (INRAE), taking over as planned and ensuring the finalization of the study and the coordination of this publication. To carry out this work, a group of experts, comprising researchers and technical experts from a variety of institutional and scientific backgrounds, was formed to cover the various themes addressed in the study. This group was composed of: Alain Bailly (FCBA[1]); Claire Bastick (IGN); Jean-Charles Bastien (INRAE); Alain Berthelot (FCBA); Nathalie Bréda (INRAE); Sylvain Caurla (INRAE); Jean-Michel Carnus (INRAE); Antoine Colin (IGN); Barry Gardiner (INRAE); Hervé Jactel (INRAE); Jean-Michel Leban (INRAE); Antonello Lobianco (AgroParisTech); Denis Loustau (INRAE); Benoît Marçais (INRAE); Céline Meredieu (INRAE); Luc Pâques (INRAE); Éric Rigolot (INRAE); Laurent Saint-André (INRAE). A summary of the expertise and contributions of each of the experts can be found at the end of the book.

The supervision of the study was entrusted to a steering committee which brought together a group of administrative, technical and professional experts around the relevant units of the ministry responsible for agriculture, which commissioned the study. This process ensured constructive exchanges of different perspectives within the French forestry & wood sector. In addition to representatives of the Ministry of Agriculture, participants included: Pierrick Daniel, Lise Wlérick, Frédéric Branger and Florian Claeys (DGEP); Pierre Claquin and Élise Delgoulet (CEP); Sylvie Alexandre (MTES-MCT); Bernard Roman-Amat, then Michel Vallance (CGAAER); Jean-Luc Peyron (GIP Ecofor); Isabelle Feix and Miriam Buitrago (Ademe); Pierre Brender, Joseph Lunet and Elisabeth Pagnac-Farbiaz (MTES-DGEC); Gérard Deroubaix and Estelle Vial (FCBA); Christine Deleuze (ONF); Olivier Picard (CNPF-IDF); Jacques Chevalier (CSTB); Yves Duclerc (MTES-DHUP); Julia Grimault (I4CE).

A first draft of this book greatly benefited from the constructive criticism of Erwin Dreyer (INRAE), Jean-Marc Guehl (INRAE), Mériem Fournier (AgroParisTech) and Jean-Luc Peyron (GIP Ecofor), whose comments were invaluable. Jean-Marc Guehl was also directly involved in the drafting process, helping us to place the approach used within the context of global forest issues in the face of climate change.

Although the following is the sole responsibility of the authors of this publication, the contributions of the members of the steering committee and the scientific reviewers were important, both in the development of the study strategy and in the interpretations of the results. We would like to thank them all for their contributions.

1FCBA, l’Institut technologique Forêt cellulose bois-construction ameublement (The Technological Institute for Forest Cellulose, Timber and Wood Furniture).

The role of the forestry & wood sectors in mitigating climate change

Forest ecosystems are at the heart of major global and climate change issues, in particular due to their major role in the carbon cycle. The scope of this book is limited to the French metropolitan forests and forestry sector. However, in order to fully grasp its scope, it is useful to recall some basic elements concerning forests as a whole, and in particular their sensitivity and importance in the face of current environmental disturbances and imbalances characterizing the ‘Anthropocene’, which Crutzen and Stoermer (2000) define as an ‘epoch characterized by the major impact of human activities on the biosphere and the earth system as a whole’. It is also useful to consider the diversity of contexts across major regions of the globe with respect to changes in carbon budgets and the consequences for atmospheric CO2 levels.

A global issue

The world’s forests cover 4 billion hectares, or 31% of the Earth’s land area. They contain 60-75 per cent of the carbon of the terrestrial plant biomass and 40-53 per cent of the carbon of the terrestrial biosphere, i.e. the total organic carbon contained in vegetation and soils. This represents nearly 860 gigatonnes of carbon (GtC), or nearly 3,150 GtCO2, a level equivalent to that of CO2 currently present in the atmosphere.

Forests make a major contribution to the global natural carbon cycle through highly significant exchanges with the atmosphere. The gross primary production of forests, i.e. the photosynthetic input of CO2 into ecosystems, is estimated at 220 GtCO2/year, i.e. nearly 50% of that of all terrestrial plant cover (Gough, 2011). At the ecosystem scale, this incoming flow is largely offset by a reverse flow of CO2 related to the energy expenditure of plant metabolism and growth, but also of microorganisms associated with plants or involved in the transformation and decomposition of dead organic matter in litter and soil. Wood extraction and natural disturbances (such as storms, biotic stresses, climatic extremes or fires) also contribute to this outgoing flow through the resulting plant mortality or from combustion. However, the positive difference between CO2 inflows and outflows on a global scale means that forest ecosystems are a net carbon sink.

These dual characteristics (their high carbon content and their significant bidirectional exchanges with the atmosphere) imply the existence of strong functional relationships between changes in the carbon stock in forest ecosystems and atmospheric CO2 concentration. Understanding and modelling these relationships requires their consideration in the context of imbalances in the carbon cycle caused by disturbances linked to human activities. In this respect, two main types of factors (extensive and intensive) should be considered:

land use changes, most often transforming areas with high carbon concentrations in biomass and soils (forests, savannahs, grasslands, wetlands, etc.) into crops or plantations, and sometimes into degraded land, have led to a transfer of carbon from terrestrial ecosystems to the atmosphere, resulting in a slow increase in atmospheric CO2 since the 1850s (Le Quéré et al., 2018). This is a source of endogenous CO2, whereby no additional carbon is added to the natural carbon cycle. These practices currently account for 14% of global CO2 emissions (Figure 1.1), with tropical forest clearance and degradation predominant;

CO2 emissions related to the use of fossilised carbon are an exogenous source of carbon. This source currently accounts for 86% of total emissions, at an average of 40.2 GtCO2/year over the last decade (Figure 1.1). They are the predominant source of atmospheric CO2 increases (410 parts per million in 2019, an increase of 50 per cent over the pre-industrial level of 275 parts per million), which have grown exponentially since the 1950s. Various lines of evidence suggest that the terrestrial biosphere has responded to anthropogenic CO2 emissions over the past century by increasing gross primary production in proportion to the increase in atmospheric CO2, primarily through the direct stimulation of photosynthesis (Cernusak et al., 2019). Consistent with this finding, simulation models that quantify carbon fluxes and balances at the continental ecosystem scale indicate that the terrestrial biosphere currently sequesters 11.5 GtCO2eq/yr through carbon accumulation in biomass and soils. This represents 29% of total annual CO2 emissions, thus contributing, along with the oceans (23%), to mitigating the accumulation of CO2 in the atmosphere (Figure 1.1). In the coming decades, the adverse impacts of global climate change (droughts, heatwaves and interactions with biotic stresses) on terrestrial productivity and carbon storage may outweigh the direct positive effects of increased CO2 on photosynthetic activity.

Figure 1.1. Global emissions (sources) of CO2 related to human activities (fossil fuel use and land-use change including deforestation) for the period 2009-2018. Source: Global Carbon Project (Friedlingstein et al., 2019).

44% of total emissions remain in the atmosphere, while 29% of emissions are sequestered in terrestrial ecosystems (mainly forest ecosystems).

The current terrestrial CO2 sink, resulting from the combined effects of these two major factors, is heavily concentrated in forests (Pan et al., 2011). The FAO’s Global Forest Resources Assessments (FRAs) provide estimates of changes in carbon areas and stocks at the scale of major forest regions (MacDicken, 2015), which show highly contrasting dynamics. Overall, forests have suffered a net decrease of nearly 130 million hectares over the last 25 years (-3%). The rate of net deforestation was decreasing until 2015, but the phenomenon remains significant, especially for tropical primary forests, which have been reduced by 222 million hectares (-11%) over the same period. The current terrestrial CO2 sink is ultimately the result of carbon storage by undisturbed or minimally disturbed, temperate or boreal forests (which are increasing in area), but also tropical forests, whose contribution outweighs the carbon emissions from deforestation and forest degradation (Pan et al., 2011).

Figure 1.2. Projected gross CO2 emissions from human activities (fossil fuel use and land-use change) to 2100 based on Shared Socioeconomic Pathways (SSPs), Representative Concentration Pathways (RCPs) and Integrated Assessment Models (IAMs). Source: Global Carbon Project (Riahi et al., 2017; Rogelj et al., 2018).

The thin lines correspond to the results of a set of simulation models for each of the SSP × PCR scenarios (colour coded) with the thick line representing the median. The black line represents observed historical values. The global temperature changes associated with each level of radiative forcing (RCP) correspond to levels of warming for 2100 relative to the pre-industrial baseline (1850-1900). Scenarios limiting warming to +2°C or less (SSP1-2.6, SSP1-1.9 and SSP4-3.4) would require negative net emissions for the second half of the 21st century.

Forest planning and management practices can be used to enhance carbon storage in forests. Stand aging is one option under consideration. Recent assessments have focused on the potential for additional carbon storage through the nature-based solutions[2]...