At the Slovenian Forestry Institute (SFI), monitoring of the forest soils and processes in them has been one of the fundamental threads of our scientific research since its establishment. As early as 1957, a laboratory was established within the Department of Forest Ecology, in which forest soil analyses became part of initially national, and after 1987 international programs, and after 1991 also of research and application projects.
Forest soils are understood as a key dynamic part of the forest ecosystem, which interacts with air, water, nutrients, carbon, etc., biodiversity and thus has a key impact on the resilience of forests to environmental changes, such as climate and (other) human impacts.
40 years of ICP Forests and the role of GIS
In 1985, Slovenia, through the then Institute for Forest and Wood Management of Slovenia, later known as SFI, joined the international program "The International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests" (ICP Forests), which operates under the auspices of the Geneva Convention on Long-Range Transboundary Air Pollution. This placed our monitoring of forest ecosystems and laboratories in the European context of coordinated forest monitoring, of which forest soil monitoring is a part.
On a 16 × 16 km grid of plots (level I), we participated in the first coordinated monitoring of forest soils in Europe (1995/96) and its repetition (2005/06 – BioSoil project) and in the re-sampling and analysis of forest soils on a 16 x 16 km grid, which we are carrying out in 2025 and 2026. Since 2004, we have been participating in the Intensive Monitoring of Forest Ecosystems program, part of which is also monitoring the dynamics of soil processes on 10 selected hectare plots in Slovenia (level II). As SFI researchers, we actively co-developed the ICP Forests guidelines for soil sampling and analysis and participated in ring tests of laboratories and soil analyses for quality assurance, which is a condition for Slovenian data to be equally included in the common European database.
We cooperate with the ICP Forests Soil Coordinating Centre (FSCC) and numerous partner institutions in the EU, which ensures methodological comparability and international recognition of the results.
The four decades of ICP Forests, which the programme celebrates this year, show that long-term and quality-based monitoring of forest ecosystems, including soil, is feasible, cost-effective and directly applicable to European environmental and forestry policy.
Soil research in SFI: from chemistry to biodiversity
Soil knowledge in SFI is now owned, used and upgraded by several departments in the implementation of various programmes and projects. This includes research and monitoring of:
- the circulation of elements in forest ecosystems, including knowledge of soil carbon dynamics;
- soil biodiversity,
- the impacts of pollution, climate change and land use on forest soils,
- the importance of forest soils for water retention and circulation and on the condition of trees (droughts, floods, erosion, etc.),
- forest soils in urban and peri-urban forests,
- the development and adaptation of soil sampling methods for national inventories and special studies.
Examples include participation in projects such as Leachate from groundwater as an untapped source of information on soil biodiversity (ARIS J4-3098), Establishing a Monitoring Network to Assess Lowland Forest and Urban Plantation in Lombardy and Urban Forest in Slovenia (Life+) and current participation in the international project SOIL: Our Invisible Ally (Interreg Alpine Space) as lead partner. SFI researchers are also active in the Slovenian Soil Partnership and the ICP Forests expert groups, strengthening the link between science, policy and practice.
New European Framework: the Directive on Soil Monitoring and Resilience
With the adoption of the Directive on Soil Monitoring and Resilience (Soil Monitoring Law), the EU has for the first time established a comprehensive legal framework for soils, comparable to water and air legislation. In October 2025, the European Parliament approved the Council's position and paved the way for the publication of the directive in the Official Journal.
The Directive builds on the European Green Deal and the EU Soil Strategy to 2030, which recognise that most European soils are degraded and that without systematic monitoring, management and remediation, food security, clean water, climate change mitigation and biodiversity protection cannot be ensured.
Key obligations for Member States (in a simplified summary):
- they must establish national soil monitoring systems in line with EU legislation and use a common European methodology;
- future soil monitoring data will be included in environmental monitoring reporting as part of various reporting obligations under EU legislation (e.g. LULUCF, etc.);
- they must use common descriptive indicators and soil status classes linked to non-binding EU targets and national trigger values, allowing for comparability and prioritisation
- they must establish a register of contaminated sites and establish procedures for risk assessment and remediation;
- they must monitor soil sealing and implement principles for mitigating these pressures;
- reporting to the Commission and the EEA, which should provide a transparent, open and comparable picture of the state of soil in the EU.
For forest soils, the directive means that the work to date – from ICP Forests, the EU soil monitoring programme LUCAS, to national surveys – will need to be integrated into a meaningful whole in accordance with new EU legislation so that it becomes an integral part of a mandatory European system; such monitoring of “soil health” must become EU “good practice”.
This year’s amendments to the Forest Act: legal basis for a national forest soil inventory
A new amendment to the Forest Act (ZG-H), published in the Official Gazette of the Republic of Slovenia, No. 85/2025, significantly supports the systematic collection of forest data. In Article 16a, it introduces the national forest inventory as a large-scale monitoring of the state of forests, forest ecosystems and forest soils, including carbon stocks.
This means that:
- data on forest soils are recognized as a mandatory, no longer additional component of monitoring,
- soil data are part of reporting for the needs of national policy, EU and international obligations (climate, biodiversity),
- conditions are created for the existing ICP Forests network, the national forest inventory and the new required EU soil framework to operate in a coordinated manner.
The role of the Slovenian Forestry Institute
The intertwining of pillars – long-term monitoring of forest soils on GIS, the operation of ICP Forests, reporting from other EU programmes (e.g. LUCAS) and the new European Soil Directive – represents a turning point:
- The data that we have been collecting for decades is becoming the core of the European system for monitoring the state (health) of soils.
- By amending the Forest Act, Slovenia has the responsibility and opportunity to contribute qualitatively to the implementation of the Soil Directive in the field of forests.
- Forest soils are given the status of a strategic natural resource that must be monitored, understood and protected on the basis of internationally comparable measurements.
The Slovenian Forestry Institute will continue to connect forest soil research, method development, national monitoring and international initiatives to ensure that decisions on forests are based on verified data and contribute to soil protection.
Prepared by: dr. Primož Simončič, dr. Aleksander Marinšek, Daniel Žlindra in Andrej Verlič
