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Resilience of European temperate forests to large and severe disturbances – what have we learned from a continental-scale network of regeneration inventories?

As a result of anthropogenic climate change, forest disturbance regimes are also changing, with individual disturbances often becoming larger and more severe. This may slow down the forest recovery process, or in worst cases, especially under a warmer and drier climate, lead to strong shifts in ecosystem dynamics, or in other words: a loss of forest resilience. Though numerous case studies have examined post-disturbance regeneration in Europe, it’s less clear if we can generalize broad patterns of forest recovery across European temperate forests subjected to large and severe disturbances caused by different agents.

A team of forest researchers from the University of Ljubljana, leveraging the networks created under the European projects I-MAESTRO and FORECO, joined forces with several research institutes across Europe to put together numerous ground-based inventories of regeneration after large and severe disturbances in European temperate forests. The goal was to achieve a more robust understanding on their resilience. We aimed at identifying the main environmental drivers affecting resilience, and how people should manage disturbed forests to support the recovery of their pre-disturbance structure and functionalities.

Location of the study sites and respective disturbance agents. The pictures show forests recovering after bark beetles in Czechia (A), wind in Slovenia (B), and fire in Bulgaria (C).
Location of the study sites and respective disturbance agents. The pictures show forests recovering after bark beetles in Czechia (A), wind in Slovenia (B), and fire in Bulgaria (C).

The study, which was the result of a collaboration of more than 50 scientists across Europe, synthesized forest recovery after large and severe disturbances over the past five decades. It also provided a baseline for future assessments of resilience, when climate change impacts, such as heat and drought stress, are expected to increase. When accounting for the differences in time since disturbance across the sites, European temperate forests showed the potential to recover their structure after large and severe disturbances and current climate conditions, although with more difficulty after fires compared with other disturbance agents. A lower recovery potential was found for species composition compared to forest structure, though this pattern was mainly related with the process of natural forest succession, whereby pioneer and early-successional species tend to establish earlier than the species that constitute the largest share of mature forest stands (i.e. late-successional species).

In the case of wind, which was the main disturbance agent represented in the regeneration dataset, the main environmental driver negatively affecting post-disturbance regeneration was increasing elevation, while post-disturbance droughts had little negative effect on regeneration densities, except in the case of pioneer species. A potential explanation of this result is that the role of post-disturbance drought likely differs across sites and disturbance agents, and would be more relevant in more arid locations and particularly after fire disturbances. Concerning post-windthrow management, the execution of salvage logging alone proved to be detrimental to regeneration, particularly in the case of late-successional species, since logging activities could have damaged the regeneration which had already established before the disturbance. On the other hand, intensively managed areas, with planting or tending following salvage logging, did not show consistent benefits to forest recovery compared to unmanaged areas. These results represent a good reminder for us that, currently, forests can be quite resilient (or even more resilient) without our intervention. This also means that allowing natural succession might be a suitable option for forest managers even when the predominant forest function is an economic one.

Effect of post-disturbance management on post-windthrow weighted density of different successional groups. Note that “Salvaged” category refers to plots where only salvage logging was carried out, and “Intensive” category refer to plots where salvage logging and planting or tending were carried out.
Effect of post-disturbance management on post-windthrow weighted density of different successional groups. Note that “Salvaged” category refers to plots where only salvage logging was carried out, and “Intensive” category refer to plots where salvage logging and planting or tending were carried out.

However, more questions on the process and drivers of recovery after severe disturbances remain unanswered, for instance what’s the role of biotic interactions, such as competition from herbs and shrubs, or herbivore browsing, on post-disturbance regeneration? How is the recovery process developing over time, and is it possible to predict the long-term dynamics from an early post-disturbance stage? In the forthcoming years we plan to continue exploring this ground-based European-scale dataset in combination with novel remote sensing approaches, under the European project FORECO, in order to further improve our understanding of the complex process of forest recovery under climate change. Furthermore, more replication is needed for fire and bark beetle-disturbed areas in order to draw robust conclusions about the main environmental and management drivers of regeneration after different agent types. Scientists that have sampled regeneration after such large and severe disturbances, especially in less represented regions of temperate Europe, and are interested in contributing and further explore the recovery dataset are welcome to contact the lead author of the study at matteo.cerioni@bf.uni-lj.si.

For more information check our full article published on Global Change Biology.

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

Acknowledgements: This work was supported by the Slovenian Research Agency (ARIS) (project J4-1765) and the Forest Value projects I-MAESTRO and FORECO.

Cover image: Beech forest reserve recovering after wildfire (Sokolna, Bulgaria); photo by Prof. Momchil Panayotov, University of Forestry (Sofia)

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