Soil health: exploring horizons, biodiversity and forest soil monitoring across Europe

Soils are living systems that sustain life on land, and perform many important functions, including sustaining forest ecosystems. Soils store the largest terrestrial carbon pool (Lal 2007) and play a crucial role in achieving global commitments, such as the Sustainable Development Goals (FAO 2020) and the European Green Deal (European Commission 2020a). 
Soils provide essential services vital to human well-being and environmental sustainability, such as regulating climate and sustaining agriculture and forestry. Soils act as natural filters, purifying water and influencing the balance of water and nutrient availability (Tóth et al. 2013). Also, they contribute to biodiversity as the habitat for many organisms (Aksoy et al. 2017).
Yet, soil degradation in Europe is taking a heavy toll. Over 60% of all soils in the EU are unhealthy (Arias-Navarro et al. 2024; European Commission 2020b), and 35% of European forest soils are considered degraded (EUSO Soils Degradation Dashboard).
The main drivers of soil degradation are a combination of natural processes and human activities, for example, unsustainable land use practices, climate change, urbanisation and land use change. To understand how to keep soils healthy, we need to understand what soil is and how it functions.

What is soil? 

Soil is made up of a mixture of many components, including living organisms, organic material (such as plants and animals in various stages of decomposition), minerals (clay, silt, and sand), water and air.
As we dig into the soil, we observe changes in its properties, which appear as distinct layers, or ‘horizons’, each exhibiting different colours and/or characteristics.

In Europe, there are more than six main soil types, exhibiting a range of features, including characteristic texture, structure, chemical properties, and vegetation cover.

FISE

Soil health and forests 

Soils and trees have a deeply rooted connection. Forest soils are home to diverse organisms, and key among them are fungi that form symbiotic (mutually beneficial) relationships with roots. In fact, a study found that ectomycorrhizal fungi can be considered the primary drivers of forest growth in Europe (Anthony et al. 2022). Forest soils are the locus of some of the plants’ vital gas exchanges via root respiration. And forest soils retain water, which roots use for growth and other processes, as well as nutrients.
In return, trees protect and enriches their soil through its extensive root systems. The roots grow through the soil, keeping its particles together and reducing the risk of erosion (Burylo et al. 2011; Baumert et al. 2021).
Tree roots also facilitate water infiltration and retention, as well as improve aeration by opening space in compacted forest soils, processes that are evident in agroforestry systems (Mitrova et al. 2025).
Additionally, leaves, branches and twigs fall to the forest floor and decompose. This is beneficial for forest soils as they receive nutrients and other chemicals back from this organic matter – including carbon, which forest soils store in large amounts. One study quantified that the nutrients obtained are about 80 kg of fertiliser per hectare per year in European forests (Neumann et al. 2018).  

This mutually beneficial relationship between soils and forests is evident in many forest management practices and in the capacity of forests to restore soil functions following disturbances: Site preparation in forest management can reduce forest soil erosion to about 30% of potential erosion (Figueredo et al. 2012). Closer-to-nature and continuous-cover forestry managements are also beneficial for soil health, as these systems can maintain soil fungi and soil chemical properties similar to those of unmanaged forests in boreal forest ecosystems (Kim et al. 2021) and increase nematode abundance and biomass in pine plantation (Renco et al. 2024). These management approaches aim to mimic natural disturbances and reduce  harvest-induced tree cover loss through low-impact single tree selection cutting or group harvesting, thereby protecting soil and biodiversity. 
Alternative management approaches, such as agroforestry can reduce soil erosion and nutrient loss compared to traditional agricultural practices (Moreno et al. 2018).
Moreover, forest disturbances, like forest fires or deforestation, impact soil properties and the microorganisms in the soil, be they natural ones like forest fires or human-caused ones like timber harvesting or deforestation to clear land for agricultural use. 
In response to forest fires, sustainable post-fire management strategies in Mediterranean forests can help in the recovery of soil function. Plants growing in the burned area can help in the recovery of soil diversity (Garcias-Pausas et al. 2022). The remaining ash (Sanchez-Garcia et al. 2023) and burned wood are rich in nutrients that can fertilise the soil, accelerating microbiological processes (Marañón-Jiménez et al. 2012). Additionally, deadwood can serve as a barrier against erosion (Pagter et al. 2023) and facilitate seedling survival (Lingua et al. 2023). 

Soil under pressure 

Still, forest soils can become degraded if forest management does not consider the impacts of machinery use, harvesting intensity, and other key drivers of soil degradation.
Heavy machinery, such as tracked or wheeled skidders (D’Acqui et al. 2020), used in forestry operations negatively impacts soil properties and, consequently, ecological processes. The main variables affecting soil compaction are machine size, traction type, tyre size, axle load, and the total number of passes (Labelle et al. 2022).
Studies have proposed strategies to mitigate those effects, for example, by adding steel flexible tracks (SFT) to forwarders, reducing tyre inflation pressure, or adding pendulum arm technology to forwarders (Labelle et al. 2022). These technical features were found to reduce compaction.
While specially designed machinery and limiting the loads carried can alleviate the problem (Riggert et al. 2016), the transit of a machine causes soil compaction, i.e. reduces the porosity of the soil in the forest (D’Acqui et al. 2020). These pores normally contain water and serve as the path for fine roots to access nutrients and water essential for their growth. 
When the forest soil is compacted, there is less water and air, and that has negative consequences for methane absorption. A study found that compacted forest soils in temperate Europe lose the ability of the soil to absorb methane (Frey et al. 2011). When forest soils lose their ability to absorb methane, their role shifts from carbon sinks into carbon sources, worsening global warming and air quality (European Environment Agency 2022).
Climate change also causes further problems for forest soils: nearly all chemical and biological processes in the soil, like nutrient cycling, plant growth and transpiration, rely on its water content. 
Moreover, climate change is one of the primary drivers of soil degradation (Arias-Navarro et al. 2024). In fact, more frequent droughts, heatwaves, and extreme rainfall can accelerate soil erosion (Panagos et al. 2021) and increase salinisation. Limited information is available on the impacts of climate change on soil biodiversity (Hamidov et al. 2018), but soil biodiversity is affected by multiple global stressors linked to climate change (Delgado-Baquerizo et al. 2025). However, drought experiments have been shown to shift soil fungal community composition in boreal forests (Koelemeijer et al. 2025) and to reduce total nematode (roundworms) abundance in Mediterranean ones (Homet et al. 2023). 

Forest soil monitoring: from knowledge to action 

The need for an improved local understanding of the current state of forest soil health and its vulnerability to degradation is crucial, as forest management practices and soil recovery occur over long timescales, making long-term forest soil monitoring essential also to subsequently take action (Wellbrock et al. 2024). 
As well as the environmental impacts mentioned earlier, the call for forest soil monitoring has received political backing in recent times. Overall soil degradation in the EU also has economic consequences, costing over EUR 50 billion annually, which includes loss of soil organic carbon, erosion, compaction, salination, sealing and land take and loss of soil capacity of water retention (European Commission 2023). However, the sum excludes the costs of soil contamination (EUR 3.4–292.4 billion alone). 
It is a concern that is not only financial and environmental but also social, as this transboundary issue impacts human well-being and food security (Panagos et al. 2021). To tackle it, European farmers, foresters, researchers and policymakers are working to prevent the situation from worsening. 
The European Council and the Parliament have adopted on 23 October 2025 the Soil Monitoring Law, setting out measures to achieve healthy soils by 2050. This legislative initiative aims to establish a framework to monitor, assess, and improve the resilience of soils across all EU Member States, as well as manage contaminated sites. 
A harmonised EU soil monitoring system will help land owners, managers, and policymakers to make informed and appropriate decisions, enabling actions to support sustainable soil management (Panagos et al. 2025). Using harmonised sampling and assessment of forest soils across the EU will allow consistent reporting and help the EU track the condition of a wide range of soils over time. 
This harmonised EU soil monitoring system rests on existing soil monitoring networks, such as the long-term series of the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) and the LUCAS top soil survey (van Leeuwen et al. 2017). 
In addition, the soil monitoring initiative is complementary to the Common Agricultural Policy (CAP), which incentivises the protection and sustainable management of soils (Manzoni et al. 2025). For example, soil conservation measures from CAP reduced soil and water loss by 9.5% and 20% respectively, for agricultural lands (Panagos et al. 2015).
The EU is also investing in finding better "soilutions" for the future more broadly. The EU Mission Soil and Horizon Europe grants are funding soil science and real-world experiments so that policy incentives and practical soil protection measures rest on scientifically sound, regionally relevant research.
A dedicated sampling and analysis protocol for the monitoring of forest soils across Europe has been developed by the EU-funded HoliSoils project (Mäkipää et al. 2025; Makowski et al. 2023). 
In addition, the EU Mission Soil aims to promote soil health through a EUR 1 billion investment in research and monitoring. By 2030, the Mission Soil will have 100 Living Labs (sites where research and innovation are tested) and Lighthouses (forests, farms, industrial sites, and urban city green areas) for demonstration of solutions and achievements, to support the transition towards healthy soils in rural and urban areas (European Commission 2024).

Unearthing the path forward 

Soil is a crucial natural resource essential for life on Earth. It supports biodiversity, agriculture, forestry, and human populations. However, climate change, more frequent and extreme wildfire, intensive management, land use change, and other key drivers of forest soil degradation are degrading forest soils. 
Managing forest soil sustainability and restoring degraded lands is vital. Therefore, regular soil monitoring is necessary to inform policies, to support soil health and resilience, and allocate funding for research and innovation. 
The new EU Soil Monitoring Law aims to ensure that Member States rely on trustworthy, comparable soil data for decision-making. A central, accessible digital soil health data portal will support policymakers, scientists, and soil experts, including those advising farmers and foresters, in adopting evidence-based soil management practices. This initiative enhances knowledge, transparency, and action, helping Europe progress toward its climate, biodiversity, and land-restoration goals by 2050.

Useful resources from an EU-funded project:  

One of the Horizon Europe projects is HoliSoils. Running from 2021 to 2025, it investigated which forest soil management practices can be used to mitigate climate change and enhance ecosystem services. The project provided insights into soil health, carbon storage, biodiversity, and degradation risks in European forest soils.
Dedicated summaries tailored to the interests of different target groups are available for forest managers, policy makers, scientific experts, forest sector professionals, learners and educators in relevant disciplines and the general public.  

Selected important results of HoliSoils are: 

• A proposed harmonised methodology to assess soil nutrient stocks, organic matter properties, biomass of soil organisms, and biodiversity in European forest soils (Makowski et al. 2023);
• An outline and illustrations of complex soil processes;
• A multi-model ensemble tool to simulate soil organic carbon and greenhouse gas fluxes at site scale based on parameters of soil function and properties across different European countries;
• Predictive yield and resilience scenarios combining different climate pathways with different forest management approaches;
• Data on European soils’ vulnerability to degradation and carbon loss;
• A web portal providing policymakers, practitioners, researchers, and the general public with access to information on forest soils across Europe, such as charts, infographics;
• A number of important policy recommendations regarding forest management for soil health.

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