Author: Harald Mauser (EFI)
Contrary to the still ongoing deforestation at global level (FAO, 2020), forest area and growing stock in the EU 27 (EU in the following) have expanded continuously since the 1950s (Mauser, 2022) and impacted on the carbon sequestration and storage dynamics of forests. This document provides information on the development of the forest carbon sink and stock in the EU. It also discusses the outlook for the main drivers for this development. The findings presented build on quantitative analyses of data sourced from official databases as well as from scientific publications and publicly available documents (see Methods and Data used).
Highlights
- Forests and harvested wood products in the EU have acted as an annual net carbon sink over the last seven decades.
- The forest-based carbon sink in 2020 was about 3.7 times larger than in 1951.
- Carbon stock in forests was more than twice as large in 2020 compared to 1950.
- EU climate policy today benefits from the development of the forest carbon sink and stock as it helps to reduce the size of the current mitigation challenge.
- The main drivers for the increase of the forest carbon sink and stock in the 20th century may be weaker in the 21st century. To assess their future dynamics, comprehensive regional analyses integrating natural, socio-economic and cultural aspects are needed.
1 Development of the forest carbon sink and stock in the EU since 1950
1.1 Development of annual CO2 removals in the EU by forests and harvested wood products 1990-2020
Since 1990, EU countries annually report their greenhous gas emissions and removals by forests and harvested wood products under the United Nations Framework Convention on Climate Change (UNFCCC). Consequently, time series are available for all 27 EU member states on the forest-related carbon removals for the period 1990-2020, the latest year with actual data. Forest land and harvested wood products in the EU have acted as a net carbon sink and have removed CO2 from the atmosphere over the past three decades, albeit with some variation between years (Figure 1). The sink peaked in 1999. In 2020 it was about 5% smaller than in 1990.
Figure 1: Annual CO2 Removals by Forest Land and Harvested Wood Products 1990-2020 in the EU (in Mt CO2/year, data from the 2022 EU submission to the UNFCCC).
1.2 Development of the annual CO2 removals in the EU by forest land and harvested wood products 1951-2020
In the EU, the emissions of CO2 from fossil sources started to grow remarkably since 1950 (see Figure 4), contributing to the climate change mitigation challenge of today. It is therefore interesting to see also the development of the forest carbon sink over this extended period. The combination of data from Nabuurs et al. (2003) for the period 1951-1999 and the time series presented in section 1.1 shows that the annual net carbon sink in forests and harvested wood products grew since 1951 (Figure 2. Please note that sinks are expressed with a negative sign according to international convention). After about five decades of continuous growth, the sink has been fairly stable between 1999 and 2013. The sink in 2020 was about 3.7 times bigger than in 1951.
Figure 2: Annual CO2 Removals by Forest Land and Harvested Wood Products 1951-2020 and CO2 Content of Annual Roundwood Production 1961-2020 (both in million tonnes CO2) for the EU. Removals are based on Nabuurs et al. (2003, scaled to EU 27 by growing stock 1990/2000) and UNFCCC data. Please note the different scales and signs for carbon removals and roundwood
Recent years with decreases indicate first signs of sink saturation. The forests are reaching a dynamic equilibrium with the current intensity of management, tree species and age-class distribution (Nabuurs et al., 2013) as well as due to other reasons including climate change impacts. The reduction of the sink in recent years must be seen in the light of the long-term increase in the decades before, also considering the main drivers for this development and their future prospects, like changing afforestation rate, diminishing effects of nitrogen deposition, increasing disturbances or adaptive forest management (see section 3).
Combining information on the carbon sink development with a time series on the CO2 volume of annually harvested roundwood (data available from 1961 onwards, Figure 2) shows that roundwood production and carbon sink increased simultaneously for many decades. However, between 2013 and 2020, the sink decreased stronger (-24%) than the roundwood production increased (+10%), indicating to the other reasons for sink saturation mentioned above.
The differences in the years 1990 to 1999 between the two time series on the carbon removals in Figure 2 are due to the use of different methodological approaches, changes in definitions and data collection. Another reason may also be the approach to scale the results from 30 European countries in Nabuurs et al. (2003) to the EU 27 (described in Data and Methods used). However, these differences do not change the general result of a clear growth of the forest-related net carbon sink in the EU since 1951.
1.3 Development of the volume of carbon stored in living biomass in forests and of round wood production in the EU 1950-2020
Acting as a net carbon sink (volume of carbon sequestered in a year), forests in the EU have built up a growing carbon stock (the total volume of carbon accumulated up to date in forest ecosystems).
The analysis of combined data from Kuusela (1994), Nabuurs et al. (2003) and FAOSTAT (2022) shows that the volume of carbon stored in living biomass in forests more than doubled between 1950 and 2020 (Figure 3), while the roundwood production increased by about 97%. In the EU, the volume of carbon stored in forests increased with a higher rate than the volume of roundwood production at the same time.
Figure 3: Development of Carbon Stock in and Roundwood Production from Forests in the EU since 1950 (in % compared to starting year 1950).
Due to different conversion factors and to avoid methodical constraints, a second approach was used to verify the results. This was done by combining two series on forest growing stock data for 20 EU member states for the period 1950-2000 (Verkerk, 2015. Country list see Data and Methods used) and 1990-2020 (FAO FRA, 2021). The growing stock data were converted to volumes of carbon stored in living biomass in forests with the same factors (see Data and Methods used). The carbon stock in living biomass in forests of the 20 EU countries analysed by this approach results in 3,736 million tonnes of carbon in 1950 that grew by 2.7 times to 10,233 million tonnes in 2020. Roundwood production in 2020 for these 20 EU countries was about 87% bigger than in 1950. These results confirm those of the previous approach.
The presented increase in carbon stock in forests in the EU for the period 1950-2020 is in line with previous findings. Ciais et al. (2008) reported for the period 1950-2000 for 15 EU countries, excluding Luxembourg, plus Norway and Switzerland an increase in the biomass carbon stock per hectare of forests by a factor of 1.75. Since then, forest area and growing stock has increased further.
2 Relevance of the forest carbon sink and stock development for EU climate policy
The annual emissions of CO2 from burning fossil fuels for energy generation and industry in the EU increased steeply since the 1950s (Figure 4) and peaked in 1979 with 4.11 billion tonnes. In 1990 (3.86 billion tonnes), the volume was 2.9 times bigger than in 1950 (1.28 billion tonnes). Until 2020 the number went down (2.6 billion tonnes) but was still twice as big as in 1950.
Figure 4: Annual CO2 Emissions from Fossil Fuels and Industry in the EU (land use change is not included). Source: Our World in Data (2022) based on the Global Carbon Project.
The capacity of forests to sequester and store carbon is an important contributor to the EU’s climate change mitigation endeavour, characterized by a strong increase in the forest carbon sink and stock in the past decades.
For the period 1951-2020, Figure 5 combines the development of the annual CO2 emissions (enlargement from Figure 4) and the net forest carbon sink. Substitution effects by wood-based products and energy are impacting on the volume of annual CO2 emissions. There are no data available for substitution effects, consequently they cannot be separately visualised in this illustration.
Figure 5: The Annual CO2 Emissions from Fossil Fuels and Industry and the Forest Carbon Sink (including harvested wood products) in the EU for the Period 1951-2020.
From 1951 to 1979, the EU contributed to the global surge of CO2 in the atmosphere by sharply increasing emissions from burning fossil fuels. Already in this period, the growth of the annual forest carbon sink compensated for some of these emissions by storing continuously more carbon in forests and harvested wood products. At that time, this was neither a political nor a forest management objective.
The forest carbon sink increased until 1999, was rather stable until 2013, slightly decreased since then, but remained a net sink that in 2020 was 3.7 times bigger than in 1951. This means that EU forests mitigated climate change over more than 70 years. They did by no means contribute to climate change by CO2 emissions. In theory, the sink could have been larger if forest managers and policy makers had prioritized this goal in the past, albeit with the need to manage trade-offs with other forest-related objectives. However, this does not change the fact that forests in the EU continuously acted as a net carbon sink over the past seven decades.
Despite the sink decrease in recent years, the volume of the carbon stock in forests is still expanding. This carbon is not in the atmosphere for several decades. Today’s EU climate policy is benefiting from the past growth of the forest carbon sink and stock as it has helped to reduce the size of the current mitigation challenge and the cost related to mitigation measures.
One important aim of current EU climate policy instruments, in particular the LULUCF Regulation (EU, 2018a), is to make the forest sector comparable to other economic sectors. That regulation does not take into account the mitigation benefits forests have already provided in the past. It is very likely that the EU’s aim of carbon neutrality by 2050 will not be reached without phasing out fossil-based material and energy, and simultaneously increasing the forest sink. Therefore, policies that help boost this sink will be needed. When designing such policies, it is important to understand the main drivers for carbon sink and stock development (see section 3) and the way those can be governed. One of the drivers has been improved forest management to meet the growing demand for forest products and services. The higher carbon uptake of forests in the EU, to some extent, has been a co-benefit of this management and related investments.
3 Drivers for the evolution of the forest carbon sink and stock in the EU
The development of the forest carbon sink and stock in the EU has been due to several drivers (Mauser, 2022) that resulted in the expansion during the 20th century presented above. However, this past development cannot be extrapolated to the 21st century, because of various changes of relevant drivers. Their power and direction of impact in the future will differ between regions, depending on the natural, socio-economic and cultural conditions as well as land-use history:
- Forest expansion and afforestation will depend on available land that is not claimed for other land-use interests. The need to strengthen domestic agricultural production in the EU and to increase areas for nature conservation of open habitat types, as well as limitations on tree growth due to climate change, will limit the land area available for natural forest expansion and afforestation. On the other hand, land abandonment is still continuing in several EU regions for different reasons (Schuh et al., 2020). This offers opportunities to expand forest areas (Biodiversa, 2020), adapted to local/regional social and ecological situations (Frei et al., 2020). To avoid leakage effects when serving the growing biomass demand for the substitution of fossil-based and climate unfriendly materials and energy, increasing domestic forest production may be needed. The decision to accept natural forest expansion or to undertake afforestation is made by landowners who will have to consider incentives and risks. In addition, the EU has set targets for planting new trees and forests (EU, 2019; EU, 2020; EU, 2021b).
- Forest age structure development may be associated with a decreasing increment in several EU regions. Many forests were established in the first half or middle of the 20th century. They are entering or will soon enter older age classes with slower growth rates (Nabuurs et al., 2013). Pilli et al. (2022) found a decreasing net biomass accumulation rate with increasing age of the forests, confirming the findings of Valade et al. (2017). They see the ongoing aging process of the European forests as one of the main drivers of the long-term dynamics of the forest carbon sink. Biomass productivity may regain pace later as better adapted provenances or tree species of newly planted forests enter development phases with higher growth, but this also depends on future disturbance risks (see below). In several regions, disturbances in recent years reduced the share of older coniferous stands. Some species, such as beech and douglas fir maintain quite high growth rates also in older ages.
- Recovery of forest soils - the long-lasting nutrient depletion due to past land uses ended in the first half of the 20st century, and will have a diminishing influence (Gimmi et al., 2012) or finally no effect at all on the future biomass productivity. However, the uptake of carbon in the soil can continue and improve the total carbon stock in forest ecosystems over a longer period (Gleixner et al., 2009). The conversion from coniferous to mixed and broadleaved forests can increase carbon uptake in forest soil (Labeda and Kondras, 2020) or reduce it (Galka et al., 2014).
- Effects of the increasing CO2 concentration in the atmosphere, nitrogen deposition and global warming on forest biomass productivity will level off or turn negative as there are tipping points in the fertilising effect of nitrogen deposition (Etzold et al., 2020). Forests already nitrogen-saturated can suffer from excess nitrogen deposition (Högberg, 2007). The fertilisation effect of CO2 and nitrogen may decrease as other nutrients and water availability will become limiting factors. Enhanced growth at elevated CO2 may cause trees to proceed faster through their lifecycle, increasing biomass turnover rates and therefore limiting any CO2-driven enhancement in the carbon sink (Pugh et al., 2019). However, the future CO2 effect is unclear as there are opposing results and many uncertainties (e.g., Sperlich et al., 2020; Wang et al., 2020; Zhu et al., 2021; Chen et al., 2022). Also, global warming is likely to lead to increasing drought and water stress impacts, in particular in the second half of the 21st century. On the other hand, rising temperature and prolonged growing seasons can still foster forest growth at higher elevations and latitudes if there is sufficient precipitation (Sperlich et al., 2020). Generally, forest growth and tree species composition in Europe is likely to change due to climate change, but the location, amount and partly even the direction of this change is hard to predict (Lindner and Verkerk, 2021) due to many uncertainties regarding growth dynamics and mortality in the future (Sperlich et al., 2020).
- Forest management must consider the adaptation of forests to a changing climate (see below), the growing demand for wood-based and non-wood forest products in the transition to a circular bioeconomy, and the growing demand for other ecosystem services including carbon sink and storage or biodiversity conservation (Muys et al., 2022). Changing market requests and legal frameworks will pose incentives and limitations for this endeavour. Climate Smart Forestry aims to connect climate change mitigation with adaption measures, enhance the resilience of forest resources and ecosystem services, and meet the needs of a growing population and expanding middle class (Nabuurs et al., 2015; Verkerk et al., 2020). Many regions have been applying improved forest management approaches since the last century, while others are lagging behind. There, forest productivity can be increased by applying state-of-the-art silvicultural practices. On the other hand, there are first signs of carbon sink saturation in Europe (Nabuurs et al., 2013). Research and innovation will be needed to support the development and application of adapted forest management approaches (e.g., close-to-nature-forestry (Larsen et al., 2022)), tree breeding, silvicultural measures and harvesting technologies that balance productivity and resilience of forest ecosystems (FTP, 2019).
- Adaptation of forests to changing climate conditions and disturbance regimes will become a core task for forest management. Within the framework of Climate Smart Forestry (Verkerk et al., 2020; Bowditch, 2020; Hetemäki et al., 2022), specific management practices and tools need to be applied to maintain or improve the capacity of forests to produce biomass and provide all their services under changing climate conditions. This includes not only forest management at stand level, but also more integrated landscape management, promotion of good practices, and knowledge exchange beyond the forest community (EIP AGRI, 2019). In particular mitigating risks from disturbances, e.g., forest fires, pests and diseases (see below), will need active management interventions (EFI, 2015). The use of more deciduous tree species with slower growth dynamics than the previously used softwood species could lead to a lower forest carbon sink for the next decades (Nabuurs et al., 2018) as long as their higher wood density does not compensate for lower volume increment rates. After that, biomass productivity will possibly grow above the current level with a lower risk of mortality and growth depression due to disturbances.
- Privately owned forests in the EU amount to 60%. Fragmented and small-scale ownership structures dominate, consisting of quite diverse categories of forest owners regarding their motivation and objectives for managing forests (Weiss et al., 2019). It is hard to predict the net impact of changes in forest owners’ attitudes as it is not known how many owners will see more opportunities and therefore continue or improve their management activities, or how many see increasing risks or are already affected by negative impacts of climate change and therefore want to reduce their engagement in forestry. It is an open question if rising timber prices will convince forest owners to invest into their forest resource to maintain or increase it. Reduced management and forest abandonment may result in more or less biomass productivity, depending on the natural growth conditions and disturbance regime in a given region.
- Demand for wood-based products is likely to increase (UN, 2021), offering incentives for active forest management to maintain or increase forest productivity. An increase in demand would be due to a growing world population and wealth levels, the need to replace finite, fossil-based and climate unfriendly materials with more climate friendly and renewable biomaterials, and in general with the development of new bioeconomy products. However, Hurmekoski et al. (2018) and Hetemäki et al. (2020; 2022) point out factors that will reduce the demand for roundwood in the future and see the net impact on wood demand as still unclear. Tendencies towards decreasing wood demand include the decline of communication papers and, in the longer-run, most likely declining demand for forest biomass for energy purposes. Also, some new products do not necessarily generate new demand for roundwood, since they are based on forest residues and side-streams of current products or post-consumer wood, i.e., resource efficiency and circularity are also increasing.
- Harvesting rates might increase due to salvage logging after disturbances and to serve the growing material demand of the circular bioeconomy. On the other hand, new policy priorities and legislation (e.g., EU, 2018a; EU, 2020) might reduce harvesting rates. In most regions, they will continue to stay below the annual increment, but possibly not at the low levels seen during the final part of the 20th century. However, a moderate increase of harvesting volumes in the EU would use only a small share of the wood and biomass volume that was built up over the last decades, to some extent specifically for the purpose of increasing future harvesting potentials.
- Reduced potential for imports from third countries might impact on the domestic sourcing of wood in the EU. The import volumes of round wood and semi-finished wooden products to the EU could decrease for several reasons, e.g., continued global deforestation, reduced forest growth in third countries due to climate change, growing demand in sourcing countries for domestic markets and exports of value-added products to other regions, export bans and restrictions. Of particular importance will be the development in Russia (Hetemäki et al., 2022), also in view of the consequences of the recent Russian invasion of Ukraine on future economic and trade relationsships. All these reasons could trigger forest management in the EU to improve productivity and/or increase harvesting levels to compensate for reduced imports, in order to meet the raw material demand of the wood processing industries in the EU.
In addition, some new drivers will also impact on the future development of the carbon sink and stock in the EU:
- Recent and future forest disturbances triggered by climate change will reduce biomass production in existing forests in some regions. The disturbance regimes of Europe’s forests are changing with increasing disturbance frequency, more variable disturbance patch sizes and decreasing disturbance severities (Senf and Seidl, 2021). There is likely to be an increase in disturbances from fire, insects and pathogens in particular (Seidl et al., 2017). While the majority of Europe’s forest area can be considered highly resilient to the currently prevailing disturbance regime, critical resilience states were found for the Iberian Peninsula (Senf and Seidl, 2022). At regional scales, climate change induced negative impacts on gross terrestrial primary production may effectively counteract positive CO2 fertilization effects (Gampe et al., 2021). The EU experienced in recent years some severe forest disturbances that will have consequences on the mid- to long-term development of forest growth and tree species composition in the regions affected. In particular this includes the drought of 2018 and the following bark beetle infestation in parts of Central and Eastern Europe (Schuldt et al., 2020), as well as the forest fires in Southern Europe and several storm damage events in other regions. Mitigating the risks of disturbances will be a key element of managing forests in the future.
- Loss of forest areas due to climate change is likely to occur in some regions, in particular in the Mediterranean (Penuelas and Sardans, 2021). Reduced water availability, more often and severe heat and drought episodes, and more wildfires will increase the risk of terminating the existence of forests that currently are already at the limits of living conditions for native tree species. This also affects regeneration of forests as very young plants are particularly susceptible to water stress and heat impacts. Such areas are under risk to shift from Mediterranean forest to shrubland and semi-arid steppes (Penuelas and Sardans, 2021). Spain, Greece, Bulgaria, Italy, Romania and Portugal were identified as European hotspots of the desertification threat (Pravalie et al., 2017). Portugal and Spain were found to be in a critical state with regard to disturbance resilience as disturbances occur faster than forests can recover, increasing the risk of forest loss (Senf and Seidl, 2022). Active migration with better adapted provenances and tree species and adapted land-use planning could mitigate the effect of this driver. This would impact on the development of forest resources only after some decades, when planted trees have successfully survived the critical starting phase.
- Growing demand for non-wood products and other ecosystem services provided by forests, amongst them carbon sequestration and biodiversity conservation, will offer forest owners alternative income sources and might reduce their interest to rely on revenues from selling wood. This could result in forest management approaches that focus less on biomass productivity and wood production. Reduced timber harvesting would result in growing biomass volumes and carbon stocks if disturbances do not counteract this, but also could result in other effects (see below).
- An evolving EU policy framework relevant for forest management and the use of wood is addressing the needs originating from climate change mitigation and adaptation (Verkerk et al. 2022), from the transition to a more sustainable, climate and environmentally friendly economic model in the form of a circular bioeconomy, from higher ambitions on protecting and restoring natural resources, and to ensure vibrant rural communities in the EU (EU, 2018b; EU, 2019; EU, 2021a; EU, 2022). On the one hand prioritising carbon sequestration in forest ecosystem and biodiversity conservation through EU policy instruments (EU, 2021b) could affect wood production, resulting in a decreasing domestic wood supply and increasing imports of roundwood, semi-finished and final wood products with related risks of leakage effects (Dieter et al., 2020). On the other hand, productivity can be intensified in other parts of forests with no or limited constraints regarding their wood and biomass provisioning services. The overall impact of recent and upcoming EU policies on forest productivity and consequently on forest carbon sinks and stock dynamics remains still unclear.
Available assessments on the future development of the forest carbon sink address some of these drivers. In a recent analysis of the impacts of climate change and forest management on the long-term evolution of the EU27+UK forest carbon budget, Pilli et al. (2022) found a decreasing trend in the forest sink until 2050. Uncertainty about the future evolution of environmental variables and their impact on forest growth resulted in a wide range of future sink volumes in the different scenarios they analysed, and between different parts of Europe. Also, Valade et al. (2017) point to the uncertainty in whether climate change will enable forests to maintain the current carbon sink. Verkerk et al. (2022) synthesised scientific literature on the mitigation potential provided by forest-based activities in the EU-27, Norway, Switzerland and the United Kingdom. Their findings suggest that it will be challenging to achieve the EU’s climate targets for the LULUCF sector by 2035 and the higher removals needed in 2050 (EU, 2021c) to reach climate neutrality.
The outlook on the possible future development of drivers and the available assessments indicate that achieving EU policy ambitions regarding the forest carbon sink will be challenging. Even maintaining the current sink capacity might be difficult, at least for some regions. Therefore, comprehensive, region-specific analyses of all relevant drivers and their impacts on the future development of the forest-based carbon sink and stock in the EU are important to be able to design targeted EU and national policy measures to maintain or increase the forest carbon sink and stock. These assessments have to address natural, socio-economic and cultural aspects as well as land-use history by interdisciplinary approaches.
Information on data and methods
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