Research updates

Harmonization and variation of deadwood density and carbon concentration

For German forest greenhouse gases reporting, deadwood carbon stock is calculated using volume, deadwood density, and carbon concentration for each decay class. Herrmann et al. developed a method to harmonize data collected from literature to supplement and improve the German data. Their meta-analysis on Central European tree species found the IPCC default value of 50% might under- and overestimate the real carbon concentration of spruce, pine and beech, depending on the decay class, by about 4% at the maximum.

Could changes in forest management regimes enhance carbon sequestration and stock capacity?

Dalmonech et al. used a state-of-the-art biogeochemical forest growth model to simulate the effect of different management practices on productivity and carbon storage in European forests under 20 climate change scenarios. The study findings suggest that the business-as-usual forest management practices may be a close-to-optimum scheme for maintaining both the carbon uptake and woody stocks in forests, even under a changing climate. The results indicate that there is little further leeway to increase the carbon sink capacity in the forests without sacrificing the existing carbon storage. Instead, the authors emphasize that it is today crucial for EU countries to preserve forests’ functionalities under the pressure of the rapidly changing climate conditions, in order to maintain the climate mitigation potential and the supply of wood products and many ecological goods and services. The study highlights the limited potential for simultaneously increasing both net primary productivity (NPP) and potential carbon woody stocks (pCWS) through intensified management practices.

The structure of mountain forests across the Alps and the role of disturbance and recovery

Stritih et al. used spaceborne lidar data to identify forest structure patterns across the European Alps, covering over 10.5 million ha. They identified two alternative states: tall, closed-canopy forests (76%) and short, open-canopy forests (24%). Within 35 years after disturbance, 72% of forests recovered to a closed-canopy state, except in submediterranean forests where recovery is slower. As climate warming increases disturbances and causes thermophilization of vegetation, transitions to open-canopy conditions could become more likely in future. This could pose a challenge for forest management, as open-canopy forests have lower capacities for providing important ecosystem services.

Tree crown defoliation in forest monitoring

Tree crown defoliation is an important parameter in monitoring forests and climate disturbances, eg within the pan-European ICP Forests programme. Defoliation is defined as the loss of needles or leaves compared to a reference tree and serves as an unspecific indicator of tree health and vitality. Bussotti et al. highlight the need to connect defoliation levels with the physiological functioning of trees, as it integrates various intrinsic and extrinsic factors. The authors propose a set of physiological indicators for application in forest monitoring programs, including water relations, photosynthesis and carbon metabolism, growth, and mineral nutrients of leaves. They emphasize the importance of integrating these physiological measurements with traditional visual assessments to improve the prediction of tree mortality and forest decline under changing climatic conditions.

Reporting carbon fluxes from unmanaged forest

Unmanaged land areas are not included in current national reports on greenhouse gas emissions for the Paris Agreement. Nabuurs et al. argue that CO₂ fluxes from all forest land need to be recorded to help track progress towards global climate targets and fill the knowledge gap. They propose a gradual 4-step transition process to start in 2-3 years’ time, including adequate financial support for developing countries to improve their monitoring systems.

Early monitoring of forest wood-boring pests with remote sensing

Remote sensing technology is a powerful tool for monitoring different stages of pest disturbance in a timely manner. Luo et al. evaluate remote sensing platforms, such as ground instruments to monitor needles, unmanned aerial vehicles for stand evaluations, manned aircraft and satellites for larger scales, as well as sensor technology (eg LiDAR, radar) and detection models. Precisely identifying host tree species or differentiating between wood-boring pests causing similar damage is challenging.

A synthesis of multi-taxa management experiments to guide forest biodiversity conservation in Europe

To develop ecologically sustainable forest management practices, it is important to understand the management impacts on forest-dwelling organisms. Tinya et al. study metadata from 28 experimental field studies on the effects of forestry treatments on multi-taxa biodiversity. Based on the results they pose 8 research questions for management- and ecology-oriented studies which could be upscaled to the European level, and set out 11 knowledge gaps which require additional field experiments.

Sustainable economy trade-offs and conflicts in and with the forest

In the transition towards a sustainable economy, forests and their ecosystem services play a vital role. Schulz et al. propose a conceptual framework to describe and classify the potentially competing demands on forests and forest management, and the conflicts that may result. They suggest differentiating between goal conflicts at the policy formulation level, and trade-off situations in forest management and planning. They further distinguish between conflicts and trade-offs that occur “in” or “with” the forest.

Laser scanning reveals potential underestimation of biomass carbon in temperate forest

Accurate assessments of above-ground biomass carbon stocks are needed to quantify the climate mitigation benefits of e.g. forest restoration. Calders et al. use 3D laser measurements across the full range of tree size and shape in a typical UK temperate forest to assess tree size-to-mass allometric models, used since the 1960s for biomass calculation. They find 1.77 times more biomass than expected, due to bias towards small trees in the original models, and more abundant large trees from changes in forest management.

The European forest carbon budget under future climate conditions and current management practices

To meet carbon neutrality goals, the EU27 net carbon sink from forests should increase to −450 Mt CO_2eq yr⁻¹ by 2050. Pilli et al. use a meta-modelling approach to show that if current management practices are continued, the EU27 + UK forest carbon sink would decrease to c. −250 Mt CO_2eq yr⁻¹ in 2050 and −80 Mt CO_2eq yr⁻¹ by 2100. However, climate change adds a considerable uncertainty, potentially nearly doubling or halving the sink associated with management.

Temperature extremes of 2022 reduced carbon uptake by forests in Europe

Van der Woude et al. investigate the impact of the 2022 summer drought in central and SE Europe on carbon exchange between European forests and the atmosphere, using ground-and space-based monitoring platforms. They find a reduction of net biospheric carbon uptake, despite partial compensation by a warm autumn. Comparison to the 2018 drought suggests this is no longer an exceptional situation, and important to factor into Europe’s plans for net-zero greenhouse gas emissions that rely on carbon uptake by forests.

Possibilities of mapping old-growth temperate forests by remote sensing in Europe

The EU Biodiversity strategy for 2030 calls for strict protection for primary and old-growth forests in Europe, leading to more efforts to identify and monitor them. Remote sensing offers a wide range of data and methods which can support the mapping of forests and their properties. Hirschmugl et al. explore parameter-based approaches such as using airborne laser scanning (ALS) data, direct approaches using machine learning algorithms, and indirect approaches via predictions based on existing data.

Where are we now with European forest multi-taxon biodiversity and where can we head to?

Burrascano et al. make extensive and comprehensive data on forest management, structural attributes and multi-taxon biodiversity available in a single, harmonized and publicly explorable platform. They harmonize and merge 34 datasets on forest biodiversity, exploring the links between different forms of sustainable forest management and biological and functional diversity. Knowledge and research gaps include boreal, Mediterranean, thermophilous and floodplain forests.

Harmonised statistics and maps of forest biomass and increment in Europe

A dataset and accompanying article developed in collaboration by the EC’s Joint Research Centre and European National Forest Inventory experts presents harmonized statistics and maps of forest area, biomass stock and their share available for wood supply in the year 2020, and statistics on gross and net volume increment in 2010-2020 for 38 European countries. The work harmonizes the sample-based National Forest Inventory data, generally differing in terms of timing, methods and definitions.

Standardizing forestry terms and definitions across European biodiversity studies

The multitude of forestry terms used in European biodiversity studies hinders comparability and makes the assessment of the impacts of forest management on biodiversity highly context-dependent. Trentanovi et al. developed a harmonized terminology for vegetation and forest management-related information by taking a novel bottom-up and top-driven review process. The standards they propose could be adapted to other geographical areas and extended to other forest interventions.

Continuous forestry can boost carbon sequestration in Finnish peatlands

Widescale drainage of wood-covered peatlands has promoted forest growth but also increased soil greenhouse gas emissions, exacerbated by clearcutting. Lehtonen et al. see continuous cover forestry (CCF) as a promising option for mitigation. They simulated four management scenarios for Finnish forests, including a business-as-usual scenario with clearcutting. Results show CCF has potential for emission reduction without compromising wood production despite the leakage of harvests to sites with mineral soils.

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Trees outside forests contribute to European tree cover and woody biomass

European national inventories assess forest resources, meaning the contribution of urban and agricultural trees to national-level carbon stocks is largely unknown. Using maps from 3-metre resolution nanosatellite imagery across Europe, Liu et al. found that in several countries and regions tree cover outside forests exceeds 15% of national tree cover. Urban areas can have a relatively high tree cover with a considerable contribution to the national aboveground biomass.

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A simple concept for estimating deadwood carbon in forests

While deadwood volume is assessed in forest inventories, data about its carbon and density depending on the extent of decay is limited. Neumann et al. used data collected in Austrian forests to estimate deadwood carbon by measuring deadwood volume and decay classes. They found that decay reduces deadwood density significantly, while the carbon fraction increases moderately with decay. Their method can improve the accuracy of assessment of deadwood carbon content based on forest inventories data.

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Post-fire recovery of soil microbial functions is promoted by plant growth

Increasing evidence shows fires cause a shift in soil microbial communities which play a central role in forest carbon and nutrient cycling. To test how soil heating affects microbial functions, researchers heated a forest soil at 200°C or 450°C. Soil heating temporarily altered microbial functions and reduced soil functional diversity. Heating-induced nutrient availability stimulated grass growth, which increased the response to several substrates and increased functional diversity to values similar to unheated controls.

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Increasing aridity causes larger and more severe forest fires across Europe

In a European-scale analysis of fire activity in response to increasing summer aridity, Grünig et al. used a multi-decadal, spatially explicit dataset of 64,448 fire events mapped from satellite data. They found that consistent climate sensitivity of forest fire regimes across biomes is significant, projecting that potential maximum fire size and maximum burn severity will increase across all biomes of Europe. The authors see a need for improved fire management and firefighting strategies.

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Filling the gap on consistent and spatially explicit insect and disease forest disturbance data

Forest disturbances are increasing in Europe, but geospatial data describing them are often scattered. The Database of European Forest Insect & Disease Disturbances (DEFID2) allows researchers across Europe to share their geospatial reference records of insect and disease disturbances in European forests. Curated by the JRC, DEFID2 currently contains 650,000 harmonized georeferenced records mapped as polygons or points, complemented by the FORWIND database on windthrow events.

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Change of focus in remote sensing science could increase user-uptake in forestry

Remote sensing science often focuses on a particular data source or methodological development rather than the operational use of derived information. Fassnacht et al. see slow user-uptake, technical issues related to forest inventories, and map validation as challenges in using remote sensing in forest inventory and monitoring programmes. They recommend sharing success stories, addressing real-world problems, and promoting best practices to increase the user-uptake of new technologies.

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Examining the environmental and economic complexities that define the forest industry

A deeper understanding of forest ecosystems and their complex interaction with social-economic dimensions and benefits is needed to support forestry and the forest industry to contribute holistically to sustainable development goals. Raihan reviews the ways in which forestry contributes to society economically and explores recent dynamics in European forest resources and European forestry industry trends, as well as the European policy context.

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Capturing the effects of forest management on species richness

The effects of forest management on biodiversity are difficult to measure. However, many forest species rely on specific structures that may be modified by forest management. Zeller et al. analysed 85 studies to identify above-ground structural attributes that could be used to further develop biodiversity monitoring and forest management. Canopy gaps and structural attributes related to old-growth forests (e.g., stand age, share of large old trees) were mostly positively correlated with species richness.

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Further understanding on soil C stabilization process and microbial processes needed

A deeper understanding of forest ecosystems and their complex interaction with social-economic dimensions and benefits is needed to support forestry and the forest industry to contribute holistically to sustainable development goals. Raihan reviews the ways in which forestry contributes to society economically and explores recent dynamics in European forest resources and European forestry industry trends, as well as the European policy context.

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Research updates

May - July 2024

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January 2024