A new WILDCARD study published in the European Journal of Soil Science highlights the important role that natural vegetation recovery on abandoned agricultural land can play in climate change mitigation across Europe. The review paper, “Soil Carbon Sequestration Following Natural Vegetation Recovery on Abandoned European Lands: Review and Research Needs”, brings together evidence from 36 studies to better understand how soil organic carbon (SOC) changes after farmland abandonment.
Led by Mohammad Tahsin Karimi Nezhad and co-authored by Domagoj Gajski, Clara G. Jeanroy, Peter H. Verburg, Giorgio Alberti, and Pavel Šamonil, the review demonstrates that abandoned croplands undergoing natural regeneration can become valuable carbon sinks over time. In particular, croplands transitioning into mixed and broadleaf forests showed strong increases in SOC, especially in Mediterranean regions and in soil groups such as Regosols, Cambisols, and Calcisols.
The study also reveals important knowledge gaps. Most available research is concentrated in Mediterranean Europe, while regions such as Central France, Germany, Poland, the Baltic states, the Balkans, and the United Kingdom remain underrepresented. The authors stress the need for more long-term studies across different climates, soil types, and vegetation systems to improve understanding of soil carbon dynamics at the continental scale.
Importantly, the paper emphasizes that natural vegetation recovery should not be viewed as a blanket recommendation for widespread cropland abandonment. Instead, land-use decisions must balance ecological, economic, and societal considerations alongside climate benefits.
The findings provide valuable guidance for researchers, land managers, and policymakers working to strengthen nature-based solutions and soil carbon monitoring across Europe.
Reference: Karimi Nezhad, M. T., Gajski, D., Jeanroy, C. G., Verburg, P. H., Alberti, G., & Šamonil, P. (2026). Soil Carbon Sequestration Following Natural Vegetation Recovery on Abandoned European Lands: Review and Research Needs. European Journal of Soil Science. https://doi.org/10.1111/ejss.70333
Across Europe, something quiet but powerful is happening. As people leave rural areas, forests are coming back, slowly reclaiming former meadows and pastures. At first glance, this seems like good news. More forests mean more carbon stored and, potentially, more biodiversity. But is it really that simple?
In our recent study across Italy, we followed this process from North to South, tracking how ecosystems change over time as forests naturally regenerate. By comparing sites at different stages, from open grasslands to forests up to 75 years old, we were able to reconstruct what happens when trees return.
The first answer is clear: carbon storage increases steadily. As forests grow, trees accumulate large amounts of carbon, becoming the main storage pool. In the oldest stands, carbon stocks can reach very high levels, highlighting the strong potential of natural reforestation for climate mitigation. But there is another side to the story: As forests close, light becomes scarce. Many herbaceous species that thrive in open habitats start to disappear. Across most of our study sites, plant diversity peaked in meadows and early stages and then declined as forests matured. In other words, gaining carbon often meant losing plant diversity. Yet, the picture is not entirely uniform. In the southernmost site, under Mediterranean conditions, plant diversity initially declined as forests became denser, but partially recovered again in the oldest stands, suggesting that mature forests can recreate suitable conditions for a richer understory vegetation. This suggests that, in some contexts, forests may eventually host both high carbon stocks and a richer understory. These findings highlight an important message for rewilding and land management: natural forest expansion is not automatically a win-win solution. It can involve trade-offs between climate mitigation and biodiversity conservation.
The challenge, moving forward, is to understand where and when these trade-offs can be reduced. Under the right conditions and given enough time, forests may offer opportunities to balance both goals. Until then, letting forests return remains a powerful tool, although it needs to be used with awareness of what we gain, and what we might lose along the way.
References: Orzan, L., Tomao, A., Antoniella, G., Bonari, G., Casolo, V., Chiti, T., Cingano, P., Foscari, A., Incerti, G., Panico, S. C., Piazza, N., Trotta, G., & Alberti, G. (Year). As forests reclaim the land: Latitudinal variations in carbon-biodiversity trade-offs under natural forest expansion in Italy. Forest Ecology and Management, Volume 605, https://doi.org/10.1016/j.foreco.2026.123527
Last week, our second annual WILDCARD meeting of took place in Freising from February 25–27, 2026. The three-day event brought together consortium partners to reflect on progress and shape the next phase of research on rewilding, forest dynamics, and climate resilience across Europe.
Hosted by Technical University of Munich, our exchange opened with field visits to the Echinger Lohe experimental site and Freising Forest, where our colleagues joined experts from the Bavarian State Institute of Forestry for an exclusive tour of a strict forest reserve, exploring long-term monitoring, nitrogen deposition impacts, ash dieback, and lasting legacies of historical land use. Our group also engaged with the WILDCARD Art Exhibition – an inspiring reminder of the importance of connecting science and society.
Artwork of Diana Takacsova (photo: Evgenia Emets)Artwork of Angelina Kumar (photo: Fabio Castelli)Group entering the foest (photo: Evgenia Emets)
Back on campus, discussions focused on advances across different work streams: biodiversity and carbon monitoring, economic and policy integration, and communication and management. In dedicated modelling sessions our colleagues highlighted progress with LandClim, FlamMap, and ForClim, strengthening links between disturbance dynamics, proforestation and afforestation pathways, and large-scale scenario development. Strong emphasis was placed on harmonising dendrometric, biodiversity, soil, and remote sensing datasets, and on integrating above- and belowground processes.
The Young Researchers’ Spotlight showcased cutting-edge studies on rewilding perceptions, drought resilience in unmanaged forests, agroforestry optimisation, microbial–carbon trade-offs, LiDAR-based structural indicators, and tree-related microhabitats – demonstrating the scientific depth and interdisciplinary strength of the consortium.
The meeting concluded with strategic discussions on policy briefs, cross-WP integration, and future milestones. Together, we reaffirmed WILDCARD’s shared ambition: delivering robust, policy-relevant science to support biodiversity recovery, climate mitigation, and resilient European landscapes.
Europe is unique. Within a relatively small geographical area, an extraordinary diversity unfolds: landscapes, climates, forests, and species form a natural treasure of remarkable richness. This biodiversity is one of Europe’s greatest strengths – but also one of its greatest challenges. Protecting and understanding biodiversity is not a one-time task; it is a continuous effort that can only succeed if we work together.
Diversity, by its nature, brings complexity. This is true not only for Europe’s ecosystems but also for the way we observe and measure them. Forests do not stop at national borders, yet the methods used to monitor them often do. While standards for forest inventories exist, each country or institution has developed its own dendrometric survey methods (the measurement of tree and stand characteristics such as tree diameter, height, volume, and growth), shaped by national priorities, management objectives, and historical tradition. As a result, long-term forest information has traditionally been built for regional or national analyses rather than for a harmonised European perspective.
And yet, within this diversity lies a hidden treasure. Across Europe, enormous amounts of valuable data already exist. The key question is: how can we bring this information together? How can we harmonise these datasets to unlock their full potential and create a “golden state” of knowledge that allows us to address pressing issues such as how to store carbon efficiently, reduce biodiversity loss, and understanding and responding to the impacts of climate change? Achieving this requires not only technical solutions, but also time, expertise, and resources to build and maintain a shared database capable of supporting a wide range of scientific and policy-driven questions.
Dendrometric survey (photo @Wevell v. Krüger)
What Is dendrometric data and why do we need it?
Dendrometric data form the backbone of forest monitoring. They include measurements such as tree diameter, species, height, volume, and deadwood – key indicators for forest structure, growth, and carbon stocks. Collecting such data is not new. In many countries, dendrometric measurements have been part of National Forest Inventories (NFIs) for centuries, providing invaluable long-term records.
In strict forest reserves (designated areas of forest set aside e.g. for conservation or research purposes), however, systematic dendrometric monitoring often started much later. One can imagine the current situation as a large puzzle: countless pieces collected over decades, sometimes centuries, using different shapes and scales, all in different countries. Today’s challenge is to fit these pieces together into a coherent European picture that allows us to understand past developments in forest reserves and respond effectively to current and future environmental challenges on a wider scale.
Lots of deadwood in the site Bechtaler Wald (photo @Lucia Seebach)
How we tackled this challenge in WILDCARD
Within WILDCARD, we addressed this challenge step by step. Firstly, we established a dedicated data taskforce to work on harmonisation issues and to develop a common data template. This meant dealing with very practical issues, such as different names for the same information, varying definitions, and how to handle tricky variables like deadwood.
The first harmonisation trials were carried out with internal project partners across a limited number of sites. Once the approach proved workable, we extended it to external partners within the European Forest Reserve Initiative (EuFoRIA) network, significantly increasing the number of contributing sites. The result is a unique and growing database that will serve as a valuable resource for future research and collaboration across Europe.
Recyling in site Schwarzahalden (photo @Lucia Seebach)
Data heroes behind the scenes
None of this would have been possible without the dedication of the project’s “data heroes.” Harmonising diverse datasets is demanding work, requiring both technical expertise and deep knowledge of forest monitoring practices. Key challenges included dealing with different levels of detail in the data and reconciling fundamentally different monitoring methods – for example, in deadwood assessment, where approaches can vary greatly between countries and institutions. But thanks to the commitment of colleagues of the institution Výzkumný ústav pro krajinu (VUK) in the Czech Republic, these challenges were overcome. VUK, a Public Research Institute dedicated to studying landscapes and their ecosystems, helped to compile dendrometric datasets from more than 800 forest sites all across Europe and harmonized the data within one database. This database ensures that Europe’s diverse forest data can now speak a common language.
In the end, WILDCARD shows that diversity is not a barrier but a strength – if we manage to unite it. By bringing together Europe’s rich and varied forest data of these valuable forest reserves, we are turning a hidden treasure into shared knowledge for the benefit of science, policy, and future generations.
Featured image: forest reserve „Siedigkopf“ in the Black Forest in Germany (photo @Alexandra Kage)
We are living in a decisive moment, facing two connected global challenges: the loss of biodiversity and climate change. As rising temperatures accelerate the disappearance of species, it is clear we need to rethink how we live with nature and how we manage our land. Traditional conservation efforts have had mixed success, and more and more attention is turning to restoration – bringing nature back – as a lasting solution.
The UN Decade on Ecosystem Restoration and the EU Nature Restoration Law both urge member states to “prevent, halt, and reverse” ecosystem degradation. In Friuli Venezia Giulia (FVG, Italy), a WILDCARD Case Study, nature is already making a comeback: over the past 50–60 years, forest cover has nearly doubled (from 160.000 to over 300.000 ha), now covering around 40% of the region. Much of this change has happened quietly as old pastures and terraced fields were left to rewild, with a warming climate helping forests spread higher up the mountains, as shown in a research by Valentina Olmo (University of Trieste) and a team of researchers from different countries, including WILDCARD Coordinator Giorgio Alberti. Across the EU, the story is similar: since the 1990s, forested areas have increased by about 14 million hectares, clear evidence that passive rewilding is already reshaping the landscape.
Example of the recolonisation of abandoned meadows by forest vegetation in the municipality of Tapiana, Udine (Credits: Luca Cadez)
Pros and Cons of Rewilding
Olmo and her team caution that more trees do not always mean more biodiversity. Their initial findings have shown that the trajectories of plant and microbial biodiversity in the soil (fungi and bacteria) and those of carbon do not always coincide or are not always positive. Moreover, numerous national and international projects are investigating not only the impacts of natural reforestation on carbon stock dynamics in the various components of the ecosystem and on plant, animal and microorganisms’ biodiversity, but they are also verifying the level of acceptability of these rewilding processes by local populations and the possible economic tradeoffs.
The purple line in the four graphs shows the trends in the abundance (number of species) of the herbaceous plants, woody plants, fungi and bacteria as carbon accumulated in forest stands of different ages, originating from abandoned agricultural land. It can be seen that the number of species, particularly plants and fungi, increased with the increase in accumulated carbon (and the age of the stand) up to a certain point and then decreases. As of bacteria, however, there is an almost linear growth in relation to accumulated carbon. This suggests that ecosystems with greater carbon accumulation are not always the most favourable for biodiversity conservation, and that this relationship depends on the organisms considered (Credits: Lorenzo Orzan)
Proforestation: Letting Forests Mature
A complementary approach, proforestation, simply suspends timber management to let stands age naturally. Accumulating deadwood boosts carbon storage and creates microhabitats for fungi, insects, and cavity-nesting birds. The Wildcard project and the newly established Italian National Registry of Old-Growth Forests are studying how unmanaged stands handle climate stress, fire risk, and pests. Whereas scaling proforestation more widely must also weigh timber, water regulation, soil protection, and tourism values. Achieving such a balance will require dialogue among scientists, planners, and stakeholders.
Letting forests regrow naturally or leaving them unmanaged, can help tackle biodiversity loss and climate change. Europe’s restoration policies show how abandoned farmland has turned into forest and weigh the benefits and trade-offs of these approaches for carbon storage, biodiversity, and local economies.
To learn more about it and the case of Friuli Venezia Giulia (FVG), read the article by clicking on the link below (only in Italian):
Carbon storage is one of the most important ecosystem services provided by forests to society. However, methods to monitor and report forest carbon stocks are still poorly understood. A new paper by WILDCARD researchers of the Universities of Turin and Udine, in Italy, compares different methods to estimate carbon stocks in old-growth forests of the Dinaric Alps in the Balkans, finding that direct and indirect methods result in significantly different carbon estimates.
The paper compares direct carbon assessment methods, such as field measurements, with indirect approaches, such as IPCC standard methods, finding that the latter tend to underestimate and overestimate carbon stocks, depending on the site considered. It also revealed that a few large trees (5%) concentrate a high amount of carbon stock (36% of carbon) in the study areas, which store a total of 507 Mg C ha−1. The results indicate that old-growth forests in the Dinaric Alps are the largest forest carbon sinks in Europe.
The paper “The largest European forest carbon sinks are in the Dinaric Alps old-growth forests: comparison of direct measurements and standardised approaches” was co-authored by researchers from the Universities of Montenegro and Banja.
Old-growth forests continue to disappear in Europe, with many being logged before their identification and protection. To help map these important ecosystems for conservation and research, a new paper by WILDCARD researchers uses rigorous criteria to identify old-growth mountain forest stands in Bosnia-Herzegovina and Montenegro that have reached their last stage of ecosystem dynamics.
Co-authored by WILDCARD researchers Renzo Motta (University of Turin), Giorgio Alberti (University of Udine) and Davide Ascoli (University of Turin), the paper looks into a network of four mixed montane old-growth forests in the Dinaric Alps of Bosnia-Herzegovina and Montenegro, one of the few regions in temperate Europe that still holds old-growth forests. Strict indicators were applied to investigate forests characterised by structure, disturbance history and processes typical and exclusive of the last stage of the forest dynamic.
The researchers found that the studied old-growth sites harbour a high amount of living biomass, including ample presence of trees larger than 1 meter at breast height and older than 400 years. The sites were also found to have a high biomass of wood from dead trees. This results in the highest forest carbon sink at the continental level in Europe, totalling 398-484 Mg C ha-1. The Dinaric old-growth forest network presents robust indicators of old-growthness, similar structure, and dynamic processes across all four investigated sites, representing high-priority sites for forest protection.
Although the EU Biodiversity Strategy for 2030 provides a broad definition of old-growth forests, using strict indicators to map specific old-growth forest areas is important for both forest conservation and research, as it contributes to the establishment of conservation priorities, offers reliable reference sites for ecosystem restoration, and helps to further ongoing research on the structural differences between managed and unmanaged forests.
In most EU countries, very few old-growth forests remain and they are typically small and isolated. While the EU Biodiversity Strategy mandates their legal protection, old-growth forest loss continues unabated, with less than 1.5 million hectares of old-growth forests remaining in Europe.
