Carbon and Climate: Key Factors for the Future of Forests

French forests are at the heart of climate issues: various government initiatives in recent years confirm this. In 2020, the update to the National Low-Carbon Strategy (SNBC) focused on increasing the use of wood in construction and boosting the carbon sequestration capacity of forests and wood as a carbon sink. At the same time, a roadmap was published for adapting forests to climate change.^[1]. That same year, the Recovery Plan included support for adapting forests to climate change^[2] through the restoration of damaged stands, the adaptation of vulnerable stands, and the improvement of poor-quality stands (for example, by converting coppice to high forest). Finally, the RE2020 regulations for the building sector aim to steer new construction toward greater use of wood by 2028.^[3].

To fully understand the implications of these various initiatives, let’s take a closer look—through a series of articles—at the carbon challenges facing the forestry and wood products sector—specifically, the current state of emissions and carbon sequestration by French forests, the consequences of varying levels of forest management intensity, and on the compatibility between the SNBC’s objectives and the current structure of the forestry and timber sector.

Introduction

With 76% of greenhouse gas emissions removals recorded in 2020 in the latest National Inventory Report (NIR) prepared by CITEPA for the United Nations Framework Convention on Climate Change (UNFCCC)^[4], Forests are by far the leading source of carbon sequestration in France. The goal of the National Low-Carbon Strategy (SNBC) is to double carbon removal by 2050 compared to 2015.
What is the status of current and past emissions from French forest areas? Where do we stand in relation to the guidelines set forth by the SNBC?

When we talk about forests, what are we talking about?

According to the Food and Agriculture Organization (FAO), a forest is defined as an area containing trees that meet four criteria. The first three are physical:

• Potential height > 5 m (as opposed to maquis and other garrigue vegetation)
• More than 10% ground coverage
• Area > 0.5 ha

The final criterion relates to how the trees are used: they must grow in an environment that is neither agricultural nor urban—unlike, for example, an orchard or an urban park.

CITEPA uses these criteria to characterize greenhouse gas (GHG) emissions associated with forested areas (included in the “Land Use, Land-Use Change, and Forestry ” (LULUCF) sector of the national greenhouse gas inventory). Various GHG fluxes occur within these areas and are taken into account to characterize the emissions or removals associated with forested areas. These fluxes are shown in Figure 164 of the NIR.

It is also important to note that the Definition of Forest Management, a definition that objectifies the relationship between humans and the forest.
"A forest is considered to be managed within the meaning of the UNFCCC when it is subject to forest management operations aimed at managing its ecological, economic, and social functions. The term 'forest management operation' covers logging and forestry operations, as well as forest planning, public access to forests, and the protection of forest ecosystems. ” As noted in the CITEPA report, under this definition, all French forest areas are considered managed, because even if they are not harvested, these areas are governed by specific regulations, such as those for National Natural Parks.
Although the forest existed before us—and was the first to shape our way of life—this definition reflects the way humans have appropriated forest areas. The forest has, in fact, always been a space cherished by humans, used for recreation (such as walking or hunting), as a source of inspiration, or as an environment teeming with resources (timber harvesting, grazing land in the Middle Ages, the presence of species used in the pharmaceutical and cosmetics industries, etc.). This ecosystem provides numerous services.

In France, carbon sequestration has been declining since the 1990s

The latest CITEPA report does not bring good news regarding the carbon sequestration capacity of French forests: although French forests are growing in both area and volume, their carbon storage capacity (in ktCO2e) fell by 25% in 2019 compared to 1990 and by 50% compared to 2010. (Figure 163 of the NIR). One-off disturbances may explain sharp variations in carbon uptake (such as the 1999 storm), but more structural causes account for the long-term decline in carbon uptake: the effects of droughts and water stress, pest outbreaks (such as the bark beetle epidemic affecting spruce trees), slower growth, and increased harvesting. CITEPA highlights the sharp increases in stand mortality since 1990, despite only a slight increase in harvesting (Table 175 of the NIR).

The results are all the more striking because they were unexpected. The level of carbon uptake had been estimated for the 2016–2019 period to be close to that of the 1990–1995 period, as if the forest’s carbon sequestration potential had stabilized following various disturbances. However, analysis of the latest data has ultimately shown that carbon uptake did indeed continue to decline through 2019, and mainly due to the increase in tree mortality.

Please note that we are referring here to a slowdown in the annual rate of carbon sequestration, not a reduction in forest carbon stocks. France’s forest carbon stock continues to grow (with a net positive balance between emissions and removals), but its absorption capacity—which offsets the emissions generated by human activities each year—is weakening (see chart below).

Before the summer, the High Council for Climate (HCC) warned about the delays in carbon sequestration^[5] compared to the targets set by the SNBC. As a reminder, the target set by the SNBC is for the entire UTCATF sector to maintain carbon sequestration at approximately 40 MtCO2e per year between 2015 and 2030, increasing to 67 MtCO2e by 2050, by gradually redistributing carbon flows: wood products will sequester more carbon at the expense of forested areas, and other lands—which are currently net emitters of 20 MtCO2e—will become carbon sinks by 2050. The national strategy therefore anticipates a decline in carbon absorption by forested areas. However, while the strategy projected a decline of -2% per year, a decline of -8% per year was actually observed between 2015 and 2020. Furthermore, the carbon stock of short- and long-lived wood products from French forests (used in France or exported), which was expected to increase by 3% per year between 2015 and 2030, has actually decreased since 2015 (-1% per year) (Table 213 of the NIR).

More frequent and intense disturbances in an already weakened French forest

Last summer, numerous wildfires ravaged French forests, affecting 66,000 ha—seven times the average observed over the past 15 years^[6]. These disturbances are an example of the consequences of climate change, which could become increasingly frequent and exacerbate the decline in forests’ carbon sequestration capacity.

Climate change does indeed have a direct impact on the increased vulnerability of trees and forests:

•  Water stress : A hydraulic failure can lead to cavitation and, consequently, damage to the sap-conducting vessels as well as the gradual drying out of the leaves. Trees can prevent this failure by closing their stomata. However, closing the stomata leads to a decrease in carbon assimilation and, consequently, reduced tree growth as well as increased photorespiration.^[7].
• Spread of Pests : Species (bacteria, viruses, fungi, predators) that are expanding due to an imbalance in their ecosystem are hindering tree growth. Forest insect pests are shifting northward, and their populations are expanding due to increasingly mild winters (which reduce mortality and extend growing seasons).
  Water stress, exacerbated by climate change, weakens trees’ defense mechanisms and thus increases their vulnerability to these pathogens (for example, bark beetles, which feed on soft wood, spread more easily when the tree can no longer produce resin to harden the wood).
• Forest fires : The fires will most likely intensify^[8] and increase tree mortality rates. There are also factors that increase the likelihood of fires (natural climate variability, such as El Niño events in the tropics; deforestation and the draining of peatlands; the expansion or abandonment of agricultural activities; and the accumulation of fuel).
• Shifts in Climate Zones : The ranges of tree species are affected by shifts in climate zones^[9]. The slow rate of species migration will prevent all species from adapting to the new distributions of climate zones^[10].

In France, the primary causes of the increase in mortality are droughts and die-offs associated with pathogens (ink disease, canker, chalarosis, bark beetles, etc.).^[11]. Chestnut, spruce, and ash are tree species that are particularly vulnerable to these various diseases. The causes and mortality rates vary by region, depending on the tree species present and how the stands are managed.

In addition to these various factors, forests are becoming increasingly vulnerable due to human activity, caused by forestry practices such as soil compaction, clear-cutting, or monoculture.

In some cases, the type of silviculture practiced may have influenced the extent of the damage observed. The Landes Forest, the main victim of the fires of summer 2022, is a monospecies forest dominated by maritime pine. Napoleon III’s decision in the 19th century to turn it into an industrial forest certainly made it more vulnerable to climate-related hazards. This vulnerability has been observed in the past, as the Landes forest lost nearly half of its area in 1949 following devastating fires.

As mentioned above, the forest is susceptible to many diseases. Studies show that Mixed forests are believed to be more resistant and resilient to disturbances than monocultures, and less susceptible to pests.^[12] and sometimes more productive^[13]. It is conceivable that, in the case of the Landes region, trees’ defense strategies against these pathogens are no longer sufficient when climatic conditions change (intensity of climate-related hazards and isolation of the species). This is the case for species such as Dothistroma septosporum and Lecanosticta acícola, which are already present in forested areas and have become more virulent against pine trees. We should not jump to conclusions about the elimination of single-species plantings, which in some cases may be well-suited to the geological and climatic context, but it is necessary to anticipate the risks to which forests are exposed and to ensure the quality of tree mixtures. This is all the more important during reforestation. It would be absurd to repeat the same mistakes of the past by replanting an identical forest, as was done in the Landes region, or worse, to resort to using even more chemicals—whose production is highly carbon-intensive—to combat certain pests.

Deforestation, the leading cause of land-use emissions worldwide

On a global scale, forests are also the primary source of carbon sequestration on land. However, Carbon sequestration by the world's forests is significantly reduced by human-caused disturbances, primarily deforestation : With 12.5 GtCO2e sequestered by unmanaged lands each year, compared with 5.9 GtCO2e released by managed lands (excluding agricultural emissions) over the 2010–2019 period, the land sector absorbs an average of 6.6 GtCO2e per year^[14]. The graph below shows that only Europe—and, to a lesser extent, North America—has managed lands that sequester carbon. However, it is precisely on managed lands that carbon sequestration must increase in order to limit global warming to less than 2°C, according to the IPCC’s recommendations in its AR5 report.

Analyses by Global Forest Watch, which specifically examine forested areas regardless of their management practices, show that even though, over the 2001–2019 period, the forests in every major region of the world remained net carbon sinks, large areas of forest are still net emitters: among the three largest forest areas—the Amazon Basin in South America, the Congo Basin in Central Africa, and Southeast Asia—only the Congo Basin has a net carbon sink ^[15].

Forest areas continue to decline in two of the world’s six regions: Africa and South America^[16]. Illegal logging (the cutting and harvesting of timber in violation of laws and regulations) and overexploitation of timber are leading to the degradation of tropical forests and mangroves. These deforestation practices serve to supply the market for products such as meat, cocoa, coffee, palm oil, soy, timber, and rubber. Beyond the climate disruptions that could further threaten the sustainability of forest ecosystems, The first global challenge, therefore, is the fight against deforestation. A change in practices regarding the products mentioned—most of which result from deforestation—is inevitable.

The stakes are clear, and the challenge is all the greater: forests, the primary source of carbon sequestration in France and around the world, are at the heart of carbon-related issues, and the trends observed by national and international organizations must be reversed. How, then, can we best manage forests to maximize carbon uptake, while limiting losses caused by increasingly frequent climate-related disturbances, ensuring the use of the resources provided by forests, and continuing to benefit from the many services provided by forested areas (biodiversity, the water cycle, recreation, landscape, etc.)?

This issue will be the focus of our next article on carbon-related challenges in the forestry and wood products sector.