Unlocking the secrets of forests as carbon sinks: innovative tools to measure forests’ climate mitigation potential

By Sofie Van Winckel & Arne Van Wolputte

How can we maximise the carbon stocks and carbon sequestration potential of forests – by managing or not managing them? And how can carbon Monitoring, Reporting and Verification (MRV) be made effective and affordable as part of the proposed EU Carbon Removal Certification Framework (CRCF) regulation? KU Leuven’s MSc students Arne and Sofie are on a journey to answer these complex questions using different high-tech tools, including the Arboreal App, an iPad with LIDAR and a computer model based on satellite and field data. Read on and join them in uncovering the secrets of climate mitigation in INFORMA’s case studies!


Picture this: as the first light of dawn gently spills over the horizon, you emerge from your tent to behold a breathtaking panorama – a lush valley stretching out beneath the canopy of a verdant forest. We are two Belgian students, Arne and Sofie, and this was one of the captivating scenes that greeted us during the fieldwork of our master’s thesis in the Catalan INFORMA demo site, near the majestic Pyrenees. Energized by a nourishing breakfast, we geared up, laced our hiking boots, and set off eagerly into the wilderness to uncover its mysteries.

Walking in the forest, everyone observes different things. Maybe you notice the different bird songs, the cool temperature in summer, or the beauty of spring flowers. However, even far beyond the experiential wonders, the forest offers us a multitude of services. Climate regulation is one of those services that is especially crucial in current times of climate warming. Excessive emissions of greenhouse gases, like carbon dioxide (CO2) by fossil fuel combustion, deforestation and forest degradation, are disturbing the natural cycle of carbon. Its heat-trapping properties cause an increase in the earth’s temperature at such a high speed that you can notice the differences even within the timespan of your own life. It is in this context that forests can come to the rescue, as so-called ‘nature-based solutions’. Trees and other plants take up atmospheric carbon in the form of CO2 through photosynthesis. In this way, they store the carbon in their biomass; this process is called ‘carbon sequestration’. Like that, forest ecosystems can absorb about 27% of the annual fossil fuel emissions worldwide, while they store already 45% of the terrestrial carbon.

The amount of carbon that is stored in a forest depends on complex relationships between species composition, the disturbance history of the site, the tree age, forest structure etc. Notice that we can influence all these parameters through forest management! This is especially the case for above-ground biomass, which includes stems, branches and leaves of trees. Through our research at KU Leuven, we want to answer the following research questions:

  1. How might the LiDAR scanner included in recent iPad devices be leveraged to assess above-ground biomass?
  2. What is the influence of forest management on the above-ground carbon stock in a forest?
  3. What is the influence of forest management on the above-ground carbon sequestration in a forest?

The first research question is the focus of Arne’s research, while Sofie tries to find an answer to questions 2 and 3.

Carbon markets as a climate mitigation tool

To answer the first research question, Arne has to study the economic context of his work. Carbon markets offer potential for mitigating climate change, but their reliability depends on effective measuring of carbon. Unfortunately, that’s the crux of the matter. Making Monitoring, Reporting and Verification (MRV) more affordable while maintaining sufficient reliability is therefore imperative.

In the quest for more effective climate action, the European Commission has proposed the Carbon Removal Certification Framework (CRCF) regulation. This framework aims to address the current lack of a robust certification scheme by laying down rules for MRV based on four key quality criteria: quantification, additionality, long-term storage, and sustainability (QU.A.L.ITY). While the CRCF sets out to improve transparency in carbon markets, challenges persist, particularly in establishing cost-effective monitoring methods. Although the framework isn’t expected until May 2025, the technical readiness for MRV is essential for stakeholders investing in climate solutions.

A novel app-based approach, called Arboreal Forest has potential to fulfill this call. The Swedish app can be installed on any mobile device with a built-in LiDAR, such as the iPhone 13 Pro and the iPad Pro. Armed with both traditional tools – a trusty tape measure and vertex – and the cutting-edge application, Arne ventured into Belgium’s Brabants Wouden National Park and the forests surrounding the Segre-Rialb basin, in the Spanish Pyrenees. The goal was clear: to determine the accuracy and cost efficiency of inventorying with the Arboreal Forest app, using conventional forest biomass assessment as a benchmark.

Carbon stocks vs. carbon sequestration

While Arne was focusing on the first Research question, Sofie investigated the second and third.  These may look similar, but there is an important difference stock and sequestration. In unmanaged forests, stands typically consist of older trees compared to a managed forest, where trees are harvested when they reach a certain age or size. Young trees grow faster, and in this growth process they sequester carbon faster than old trees. However, this sequestered carbon does not stay in the forest, but leaves the forest as wood products. In an unmanaged forest, the carbon remains stored in the trees until they degrade.

This logic reflects the scientific consensus that existed for a long time: carbon sequestration rates are higher in managed forests, carbon stocks are higher in unmanaged forests. During the last decades however, several studies countered this idea with several findings. Unmanaged forests would still continue to sequester carbon, because they keep growing even at an older age. Moreover, their young trees would grow at a speed surpassing the rate of decay observed in older ones. Forest management can also be seen as an opportunity to optimize carbon stock in a forest by choosing specific species and reducing competition among trees. Moreover, it can protect the forest for climate change related disturbances like wildfires thus avoiding potential massive releases of carbon. Until now, a lot of controversy exists about the subject; the INFORMA Forest Management Platform, a large European dataset of unmanaged forest patches, paired with nearby managed patches, to be launched soon on the INFORMA website, will offer opportunities to obtain clarity.

To manage or not to manage? That is the question

Sofie is comparing carbon stock and sequestration between managed and unmanaged patches from the INFORMA Forest Management Platform, more particularly in  the Brabantse Wouden NP (Belgium) and the Segre-Rialb Basin (Spain). She calculates the carbon stock from the tree stem diameter and the tree height, measured in the field, using so-called ‘allometric relationships’. Using these field data, she can calibrate a model using open access Sentinel-2 satellite images to estimate above-ground biomass in unmeasured forest areas. The above-ground biomass is then directly related to the above-ground carbon stock. By comparing the stock over a time period since 2015 (when the Sentinel-2 mission was launched), she will derive the sequestration rate. To manage or not to manage: that is the question that this study will help to solve in regard to climate mitigation.

Between August and October 2023, with the valuable aid and support of Centre de la Propietat Forestal (CPF) and our mentors at the KU Leuven, we conducted the field measurements, and final results of the research are expected in May 2024. These results will guide policy makers and forest managers in using the full potential of the forest as a nature-based solution to climate warming. By embracing innovative, technological approaches, we are paving the way for a more sustainable future. Imagine the impact of streamlined biomass assessment on conservation efforts, forest management, and climate change mitigation! Together, let’s explore the possibilities and strive for a world where technology works hand in hand with nature to safeguard our planet’s precious resources.

Looking into the past and future of Flanders’ ancient woodlands: the Woods of Brabant

Forest management is under continuous evolution in Flandres’ Woods of Brabant. These multifunctional woodlands of high conservation value are home to important species such as the honey buzzard and the middle-spotted woodpecker, while also providing a source of wood and recreational sites for the publicSustainable forest management plays a crucial role in balancing ecological, societal and economic priorities, but is becoming more challenging as climate change increases the occurrence of windstorms, drought, pests and diseases.

INFORMA’s mission in the area is to propose management options that cater for different needs, expectations and pressures in future climate scenarios. Read on to find more about our case study in Belgium!

Among the most beautiful and oldest forests in Belgium, the Woods of Brabant (Brabantse Wouden) are characterised by more than 10,000 hectares of Atlantic and Subatlantic forest, abundant in oak and beech trees, with an admixture of maples and pines. The larger areas of Meerdaal, Halle and Sonian forests alternate with smaller forest patches, open fields and urban areas, creating a mosaic in the landscape.

The forests are partly under strict protection (about 600 ha of strict reserves plus smaller set-aside patches), while other sections are managed for multiple purposes. In the managed areas, small-scale close-to-nature management is the rule, but patches with more intensive management, mostly for the conversion of conifer to broadleaved forest, are also present. The management aims to ensure that the woods retain their beauty, ecological functionality, and wood production capacity in times of climate change. In order to do  so, management practices are adapting to account for more frequent windstorms, drought, pests, and diseases.

All of the forests in the Woods of Brabant have a high natural value: They are ancient woodland sites with rich fauna and flora. The term “ancient woodlands” refers to the fact that they have been permanently forested, at least since their oldest topographic map of 1770, but most probably since the early Middle Age, a reason why they are all included in the Natura 2000 network of European protected areas.

As currently the woodlands are located within a highly urbanised landscape, recreation plays an important role in these forests, receiving over 2 million visitors per year. Management planning and infrastructure therefore need to cater for this high recreational pressure.

Satellite view of the Brabantse Wouden. In white, from left to right: Hallerbos, Sonian, and Meerdaal-Heverlee forests, surrounded by dense urban infrastructure and intensive agriculture in their immediate surroundings. Source: Google Maps.

Forest management history and practice

The forests of Hallerbos, Meerdaal, and Sonian Forest are all public forests, managed by the regional forest management service. They are shaped by many centuries of intensive but sustainable forest management, interspaced with periods of instability and plundering.

The Hallerbos and Meerdaal forests were traditionally managed as mixed coppice-with-standards forests, dominated by oak. The Meerdaal forest was gradually transformed into a high forest over the last century, mainly of oak and beech, with many of the old oaks still preserved and reaching the age of 200-250 years. Hallerbos was heavily impacted by fellings during the First World War and completely replanted with stands of beech and oak in the 1920s. On sandy outcrops, stands of pine and larch were planted in both forests.

The Sonian forest has a long tradition as a high forest, mainly of beech. The forest has been renowned for its high-quality beech trees. Over the last 150 years, managers have been reluctant to perform final harvesting due to visitor protests and political pressure. This explains the high density of old and impressive trees. While the even-aged structure was long considered a problem from a silvicultural point of view, the old beech stands are now seen as recreational and ecological assets of the forest.

Over the last decades, these forests were mainly managed through selective high thinnings. Final harvest was mainly done in small group cuttings. In the conifer stands, some larger final fellings were performed. Also, some larger fellings were done in beech stands both in the Meerdaal and Sonian forests, in both cases because of the conversion of the stands to other dominant tree species (e.g. oak and lime) in order to enhance the diversification of the forest.

A forest stand in Tranendal, Hallerbos. When bluebells are flowering, large numbers of visitors from far and wide come to see this natural spectacle. Source: hallerbos.be

Challenges for conservation and recreation

Counting among the richest and most valuable oak and beech forests in Flanders, the Woods of Brabant harbour a rich typical fauna and flora of Atlantic beech and oak forests. The sites are important habitats for species such as the honey buzzard, middle-spotted and black woodpeckers and bats, while the stag beetle has some of its last populations in Flanders in the edges of these forests.

Apart from the legal protection under the Natura 2000 network, there is also a strong commitment to nature conservation in their management planning. Strict reserves and smaller set-asides have been designated to protect a representative network of the oldest stands in the forest, and within the managed stands, efforts are made to conserve habitat trees, old trees, and increase the amount of deadwood. This already resulted in the return of species like the middle-spotted woodpecker. The reserves within the Sonian Forest form part of the UNESCO World Natural Heritage Site “Ancient and Primeval Beech Forests of the Carpathians and other parts of Europe”.

Important challenges to the conservation efforts are the strong fragmentation of the forests, surrounded by intensive agriculture and infrastructure (e.g. roads, railways, and built-up areas), and related atmospheric deposition. These depositions have diminished over the last decades, resulting in a slow but gradual recovery of the natural vegetation.

Another challenge for forest managers is pressure from the public. These forests have very high visitor numbers, coming from the close by cities. They need to be catered for, and streamlined, by providing parking areas, hiking, and biking trails etc. This public also became more empowered and informed, so sometimes also criticises the management of the forest, even up to challenging certain harvests in court. To prevent conflicts with the public, forest management avoids interventions with strong ‘visual’ impact, such as large final fellings and organises public hearings and excursions to explain the management approach.

INFORMA contributions to the management of Brabantse Wouden

INFORMA’s research activities in the area are led by two institutions: the Research Institute Nature and Forest (INBO) and KU Leuven.

INFORMA’s activities will contribute to the sustainable management of these forests in several ways. First of all, a better understanding will be gained about the differences between managed and unmanaged forest stands in terms of carbon sequestration, biodiversity conservation and other ecosystem services. Second, new modeling tools will become available to monitor and predict the ecosystem services flow to be expected from these forests in times of climate change. And third, new cost-efficient monitoring tools will be developed to monitor and possibly certify  the carbon sequestration in these forests, as an important contribution to climate mitigation.