FORECO: The role of forest recovery from biotic and abiotic threats for risk resilient management
Project overview
The aim of the FORECO project is to provide tools for identifying and operationalizing sustainable and multifunctional forest use and management strategies, which simultaneously consider ecological and economic risks arising from biotic and abiotic threats in the coming decades (i.e., drought, storm, bark beetles) and take into account forest recovery from disturbances. In close collaboration with local, national and EU-level stakeholders, we will identify needs of forest practitioners, advisors and policy makers for evidence to inform adaptation strategies in face of increasing vulnerability of forests and uncertainty about the future.
Thus, the main research questions of our project are:
(1) How vulnerable are European forests to the major biotic and abiotic threats (drought, storm, bark beetle) and how are forest disturbances modulated by forest structure?
(2) How well are European forests recovering from major biotic and abiotic threats, and how is recovery influenced by management strategies?
(3) How should current forest management regimes in Europe be adapted to make stand structures and tree species composition robust to biotic and abiotic threats to ensure sustainable wood production and ecosystem service provisioning?
(4) How does uncertainty about future climate, the impacts of biotic and abiotic threats and timber market prices influence optimal forest management regimes in the coming decades?
The core of our methodological approach is a systematic analysis of remote sensing and ground-based monitoring data, and a process-based modeling platform for managed forests coupled with a multi-objective, risk-sensitive optimization model to schedule potential trends in forest ecosystem functioning, ecosystem service provision and optimal management regimes under changing biotic and abiotic threats and timber markets. At EDFM we will in particular advance the use of optical and active remote sensing for better characterizing forest recovery from disturbances, with a special emphasis on storm and bark beetle disturbances.
The first live meeting of the FORECO project was held from 20th to 21th April, 2023, in Slovenia, organized by the project partners from the Department of Forestry and Renewable Resources of Biotechnical Faculty.
The first day was held at the Department of Forestry in Ljubljana. All the partners presented updates on the progress of the work packages, from ground-based empirical approaches to remote sensing and dynamic global vegetation modelling, and ended the day with a delicious dinner in a local restaurant, tasting Slovenian specialities (Figure 1).
The program of the second day consisted of a field workshop with local stakeholders (Slovenia Forest Service, Slovenian State Forest Company, Slovenian Forestry Institute). Representatives of the local units of Slovenia Forest Service and State Forest Company led the tour in two field sites at different stages of recovery after large and severe disturbances, where the Department of Forestry established study plots to monitor recovery dynamics. These included sites damaged by a combination of ice-storm and bark beetle disturbance in 2014 and windthrow sites from 2008.
We visited disturbed stands in central Slovenia, close to Logatec, where an extremely destructive ice-storm and bark beetle outbreak, which severely damaged spruce trees, was followed by salvage logging and replanting. Here forests are recovering slowly as a combination of shallow soils and heavy browsing by red deer are negatively affecting the regeneration (Figure 2). Our tour featured an overview of the typical small-scale forest management in Slovenia and a glimpse at the forest operators in action. Afterwards, we drove to Črnivec, a pre-Alpine mountain pass in Northern Slovenia, which was hit by a severe windthrow in 2008 and was subsequently salvage logged and replanted. This is a fertile site where regeneration is growing well in the lower part of the slope, but largely hindered by the competition from the herb layer at higher elevations (Figure 3). The workshop sparked many discussions on the management strategies to cope with the consequences of large and severe disturbances and was appreciated by both stakeholders and project partners.
The second live meeting of the FORECO project was held from 13th to 14th May, 2024, in Lund, Sweden, organized by the project partners from the Department of Physical Geography and Ecosystem Science of Lund University.
The first meeting day was held at Lund University. All the partners presented the progress in their respective work packages, including advances on the combined use of remote sensing and ground-based approaches to assess forest recovery after disturbances, updates of LPJ-GUESS and related disturbance submodules, and preliminary results from the optimization of management strategies under the risk of extreme disturbances. Potential synergies between project partners and with other related European projects were further discussed. A representative of FSC also joined the meeting and gave a presentation on the ecosystem services certification procedure.
The program of the second meeting day consisted of an excursion in managed forests of southern Sweden. We were joined by forest managers and other stakeholders, who showed us how they manage forests in light of the risks connected to global change. The field trip sparked discussions about adaptation strategies to the challenges of global change and the role of spruce, a species which will particularly suffer the warmer climate and intensification of disturbance regimes, in the future of forest management in southern Sweden.
The excursion started at Gustafsborg[CM1] , which is an industrial forest owner that also offers services to private forest owners. The company has a strong focus on timber and biomass production, working predominantly with spruce plantations managed with a clearcut system. We proceeded with a guided tour of the Hyltemossa [CM2] research station, which is part of the ICOS (Integrated Carbon Observation System) network, providing standardised measurements of greenhouse gases throughout Europe. The station is located in a spruce forest managed by the Gustafsborg company and features atmosphere and ecosystem flux towers measuring gas exchange at various heights above the ground using eddy covariance [CM3] techniques, besides collecting meteorological data, and monitoring biomass growth, vegetation diversity, and soil characteristics in permanent plots. Finally, we had guided tour of the Fulltofta forest recreation area[CM4] , where timber production is only a secondary goal. We walked through open areas and forest stands, characterized by diverse structures and species compositions. Here managers rely on a variety of silvicultural systems combining planted and natural regeneration, with a strong focus on improving forests adaptive capacity to global change.
[CM2]www.icos-sweden.se/hyltemossa
As a result of climate change, interactions between forest disturbances are becoming more and more frequent. These so-called compound disturbances can alter the dynamics of post-disturbance recovery compared to an individual disturbance alone, leading to unpredictable outcomes, therefore, they represent a threat for forest resilience. A recent example of such interacting disturbances is an extremely severe ice storm[CM1] (i.e. rain at a temperature below 0°C which freezes upon impact with the surface) which happened in Slovenia during the winter 2014. This event was followed by a bark beetle outbreak, which affected spruce trees, and their subsequent salvage logging.
In order to analyse forest resilience to such compound event, we sampled forest stands in central-western Slovenia, which featured a gradient in disturbance severity, mainly due to the varying proportions of spruce in the stands. We assessed multiple dimensions of resilience, including forest structural and species diversity, growth, and post-disturbance regeneration, each with focus on some ecological driver that can be influenced by forest ecosystem management.
The proportion of spruce before the disturbance was the main driver of both structural and species diversity after the compound event, even when accounting for the differences in pre-disturbance diversity. More interestingly, structural diversity abruptly dropped above 50 % of spruce in the stand composition, highlighting the greater resilience of mixed forests in contrast to spruce monocultures.
When comparing radial growth of canopy trees that survived the compound event, we found that their growth over a period of 6 years after the ice storm was equal or greater than in the period before the event. In particular, broadleaf trees with the crown damaged up to 75 % did not show evidence of consistently lower growth than undamaged trees.
Finally, the negative effect of ungulates browsing on post-disturbance regeneration was evident from our exclosure experiment. Regeneration of highly palatable species had significantly lower heights outside the exclosures compared to inside, which underscores that, if we aim to recruit these species into the canopy, thus maintaining species diversity in the stands, interventions to reduce deer abundance are needed in areas with particularly high populations.
For more information check the full article [CM2] published in Forest Ecology and Management:
Cerioni, M., Klopčič, M., Roženbergar, D., & Nagel, T. A. (2025). Multiple dimensions of forest resilience to compound disturbances in a mixed sub-montane forest landscape. Forest Ecology and Management, 577, 122400.
Background
Understanding forest recovery dynamics after disturbances is essential for effective conservation and management, especially as we face a future with more climate extremes. This is particularly relevant in mountainous landscapes like the Alps, where steep terrain and frequent extreme weather can hinder natural tree regeneration. Many existing studies use spectral indices to measure recovery, interpreting decreases in these indices as disturbances and subsequent increases as recovery. However, these indices don't reveal which type of vegetation is driving the post-disturbance recovery. To address this, we propose using tree cover as a tangible and ecologically informed unit for assessing post-disturbance recovery.
Methods
We investigated post-disturbance forest recovery in the Alps using satellite remote sensing from Landsat and Sentinel-2, covering the period from 1990 to 2021. and applying a state-of-the-art technique called temporally generalized synthetic spectral unmixing, which allows to disentangle the land cover types within each pixel, giving us accurate tree cover fractions. We computed recovery intervals for both stand-replacing and non-stand-replacing disturbances using two recovery indicators: baseline-normalized and absolute recovery. Absolute recovery relies on the FAO definition of closed forests, requiring a minimum tree cover of 40%. Baseline-normalized recovery sets the threshold at 80% of the pre-disturbance tree cover, aligning with previous studies. We also calculated recovery intervals using spectral indices like NDVI and NBR to compare our findings with existing research. Additionally, we used bare ground shares, disturbance severity, and pre-disturbance tree cover shortly after disturbance events to predict long-term recovery trajectories. This approach allows us to assess recovery success for recent disturbances without needing long time series.
Results
- Recovery intervals –
For tree cover-based absolute recovery, the mean interval was 5.5 ± 0.03 years (mean and standard error) for non-stand-replacing and 13.4 ± 0.16 years for stand-replacing disturbances. Baseline-normalized tree cover recovery took 6.9 ± 0.04 years and 10.2 ± 0.64 years, respectively. Spectral index-based indicators showed faster recovery: NBR intervals were 3.5 ± 0.01 years for non-stand-replacing and 7.3 ± 0.36 years for stand-replacing disturbances, while NDVI intervals were 1.6 ± 0.006 years and 5.9 ± 0.32 years, respectively. Over the entire observation period of 32 years, nearly all disturbances have recovered, independent from the recovery indicator used. Within 10 years post-disturbance, 61% and 70% recovered by baseline-normalized and absolute recovery, respectively, while 83% recovered by NBR-based and 93% by NDVI-based recovery. Recovery based on spectral indices was thus far more rapid and overestimated the recovery success compared to recovery measured in terms of canopy cover.
- Prediction of long-term recovery success –
We finally predicted the long-term recovery success fitting logistic regression models based on pre- and early post-disturbance characteristics, that is pre-disturbance tree cover, disturbance severity and the bare ground share 3-years post-disturbance. For the absolute recovery indicator, the overall model accuracy was 83%; for baseline-normalized recovery we found an accuracy of 76%. We thus provide evidence that long-term recovery trajectories can be projected based on the signal from just a few years post-disturbance.
Scientific papers published in connection with the project.
- Cerioni, M., Brabec, M., Bače, R., Bāders, E., Bončina, A., Brůna, J., Chećko, E., Cordonnier, T., de Koning, J. H. C., Diaci, J., Dobrowolska, D., Dountchev, A., Engelhart, J., Fidej, G., Fuhr, M., Garbarino, M., Jansons, Ā., Keren, S., Kitenberga, M., … & Nagel, T. A. (2024). Recovery and resilience of European temperate forests after large and severe disturbances. Global Change Biology, 30, e17159. https://doi.org/10.1111/gcb.17159
- Gregor, K., Krause, A., Reyer, C. P., Knoke, T., Meyer, B. F., Suvanto, S., & Rammig, A. (2024). Quantifying the impact of key factors on the carbon mitigation potential of managed temperate forests. Carbon Balance and Management, 19(1), 10. https://doi.org/10.1186/s13021-023-00247-9
- Mandl, L., Viana-Soto, A., Seidl, R., Stritih, A., & Senf, C. (2024). Unmixing-based forest recovery indicators for predicting long-term recovery success. Remote Sensing of Environment, 308, 114194. https://doi.org/10.1016/j.rse.2024.114194
- Gregor, K., Reyer, C. P., Nagel, T. A., Mäkelä, A., Krause, A., Knoke, T., & Rammig, A. (2024). Reconciling the EU forest, biodiversity, and climate strategies. Global change biology, 30(8), e17431. https://doi.org/10.1111/gcb.17431
- Cerioni, M., Klopčič, M., Roženbergar, D., & Nagel, T. A. (2025). Multiple dimensions of forest resilience to compound disturbances in a mixed sub-montane forest landscape. Forest Ecology and Management, 577, 122400. https://doi.org/10.1016/j.foreco.2024.122400
- *Mandl, L, *Cerioni, M., Bače, R., Bončina, A., Brůna, J., Chećko, E. ... & Senf, C. (2025). Mandl, L., Cerioni, M., Bače, R., Bončina, A., Brůna, J., Chećko, E., ... & Senf, C. (2025). The amount of undisturbed forest in proximity of severe disturbance patches enhances their recovery in temperate Europe. Landscape Ecology, 40, 1-15. https://doi.org/10.1007/s10980-025-02231-9 *shared first authorship
- Eckes-Shephard, A.H., Argles, A.P.K., Brzeziecki, B., Cox, P.M., De Kauwe, M.G., Esquivel-Muelbert, A., Fisher, R.A., Hurtt, G.C., Knauer, J., Koven, C.D., Lehtonen, A., Luyssaert, S., Marqués, L., Ma, L., Marie, G., Moore, J.R., Needham, J.F., Olin, S., Peltoniemi, M., Piltz, K., ... & Pugh, T.A.M. (2025), Demography, dynamics and data: building confidence for simulating changes in the world's forests. New Phytol, 248: 2722-2749. https://doi.org/10.1111/nph.70643
FORECO:
PI LSAI: Prof. Dr. Anja Rammig
Staff LSAI: Dr. João Paulo Darela-Filho
Project partner:
- Lund University, Department of Physical Geography and Ecosystem Science: Thomas Pugh, Mats Lindeskog, Per-Ola Olsson, Karl Piltz, Fredrik Lagergren, Annemarie Eckes-Shepard, Haoming Zhong, Anna Maria Jönsson
- Technical University of Munich, TUM School of Life Sciences:
- Institute of Forest Management: Thomas Knoke, Sebastian Kienlein, Reyhaneh Farahani
- Professorship of Earth Observation for Ecosystem Management: Cornelius Senf, Lisa Mandl
- University of Ljubljana, Biotechnical faculty, Department of Forestry and Renewable Forest Resources: Thomas Andrew Nagel, Gal Fidej, Matteo Cerioni
- European State Forest Association (EUSTAFOR)
- FSC International
- EIT Climate-KIC
Time frame: 07/2022 - 01/2026
Funding: H2020 ERA-NET Cofund Action and Fachagentur für Nachwachsende Rohstoffe (FNR)