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Novel light regimes in European forests

Nature Ecology & Evolution volume 8, pages 196–202 (2024)Cite this article

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Abstract

Tree canopies are one of the most recognizable features of forests, providing shelter from external influences to a myriad of species that live within and below the tree foliage. Canopy disturbances are now increasing across European forests, and climate-change-induced drought is a key driver, together with pests and pathogens, storms and fire. These disturbances are opening the canopy and exposing below-canopy biodiversity and functioning to novel light regimes—spatial and temporal characteristics of light distribution at forest floors not found previously. The majority of forest biodiversity occurs in the shade within and below tree canopies, and numerous ecosystem processes are regulated at the forest floor. Altered light regimes, in interaction with other global change drivers, can thus strongly impact forest biodiversity and functioning. As recent European droughts are unprecedented in the past two millennia, and this has initiated probably the largest pulse of forest disturbances in almost two centuries, we urgently need to quantify, understand and predict the impacts of novel light regimes on below-canopy forest biodiversity and functions. This will be a crucial element in delivering much-needed information for policymakers and managers to adapt European forests to future no-analogue conditions.

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Fig. 1: Drought in Europe and the unique position of drought compared with other forest disturbances.
Fig. 2: Examples of canopy opening across Europe resulting in novel light regimes below the canopies.
Fig. 3: Schematic representation of novel light regimes in European forests.

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Acknowledgements

I thank my colleagues at the Forest & Nature Lab and J. Lenoir, F. Zellweger, R. Seidl, T. Jucker, F. Rodríguez-Sánchez, Ø. Opedal, S. Caluwaerts, M. Baele, D. Miralles, K. Calders and H. Verbeeck for extensive discussions and comments on earlier versions of this idea and/or manuscript. I also thank K. De Pauw, C. Greiser, W. Maes, T. Nagel, F. Selvi, F. Rodríguez-Sánchez and P. Sanczuk for help with the figures. I received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (ERC Starting Grant FORMICA 757833).

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  1. Forest & Nature Lab, Ghent University, Gontrode, Belgium

    Pieter De Frenne

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Correspondence to Pieter De Frenne.

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Extended data

Extended Data Fig. 1 Conceptual diagram showing how novel combinations of levels of light, and frequencies, return intervals, extent, and durations of high light lead to novel light-regimes.

In this example, the high-light return interval (X-axis) and size of the area of high light (Y-axis) increase when entire regions are hit more frequently by summer droughts due to anthropogenic climate change leading to large-scale tree defoliation and mortality. The zone of novel light regimes is shaded in green. Similar examples can be made with other spatial and temporal characteristics of light distribution at forest floors not found previously.

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De Frenne, P. Novel light regimes in European forests. Nat Ecol Evol 8, 196–202 (2024). https://doi.org/10.1038/s41559-023-02242-2

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