Canopy accession strategies reveal much about tree life histories and forest stand dynamics. However, the protracted nature of ascending to the canopy makes direct observation challenging. We use a reconstructive approach based on an extensive tree ring database to study the variability of canopy accession patterns of dominant tree species (Abies alba, Acer pseudoplatanus, Fagus sylvatica, Picea abies) in temperate mountain forests of Europe and elucidate how disturbance histories, climate, and topography affect canopy accession. All four species exhibited high variability of radial growth histories leading to canopy accession and indicated varying levels of shade tolerance. Individuals of all four species survived at least 100 years of initial suppression. Fir and particularly beech, however, survived longer periods of initial suppression, exhibited more release events, and reached the canopy later on average, with a larger share of trees accessing the canopy after initially suppressed growth. These results indicate the superior shade tolerance of beech and fir compared to spruce and maple. The two less shade-tolerant species conversely relied on faster growth rates, revealing their competitive advantage in non-suppressed conditions. Additionally, spruce from higher-elevation spruce-dominated forests survived shorter periods of initial shading and exhibited fewer releases, with a larger share of trees reaching the canopy after open canopy recruitment (i.e. in absence of suppression) and no subsequent releases compared to spruce growing in lower-elevation mixed forests. Finally, disturbance factors were identified as the primary driver of canopy accession, whereby disturbances accelerate canopy accession and consequently regulate competitive interactions. Intensifying disturbance regimes could thus promote shifts in species composition, particularly in favour of faster-growing, more light-demanding species.

Department of Agriculture and Forest Sciences University of Tuscia Via SC de Lellis 01100 Viterbo Italy

Department of Dendrology University of Forestry Sofia Kliment Ohridski 10 Blvd 1797 Sofia Bulgaria

Department of Forest Ecology and Silviculture Faculty of Forestry University of Zagreb Svetošimunska cesta 25 10000 Zagreb Croatia

Department of Forest Ecology Faculty of Forestry and Wood Sciences Czech University of Life Sciences Prague Kamýcka 129 165 21 Prague Czech Republic

Department of Forest Ecology Faculty of Forestry and Wood Sciences Czech University of Life Sciences Prague Kamýcka 129 165 21 Prague Czech Republic; Department of Biology and General Ecology Faculty of Ecology and Environmental Sciences Technical University in Zvolen Masaryka 24 96053 Zvolen Slovakia

Department of Forest Ecology Faculty of Forestry and Wood Sciences Czech University of Life Sciences Prague Kamýcka 129 165 21 Prague Czech Republic; Department of Forestry and Renewable Forest Resources Biotechnical Faculty University of Ljubljana Večna pot 83 1000 Ljubljana Slovenia

Faculty of Forestry Sciences Agricultural University of Tirana 1029 Koder Kamez Albania

Faculty of Forestry University of Agriculture in Krakow Al 29 Listopada 46 31 425 Kraków Poland

Forestry and Forest Engineering Department University of Oradea Oradea Romania

Institute of Biodiversity and Ecosystem Research Bulgarian Academy of Sciences Gagarin Street 2 1113 Sofia Bulgaria

Institute of Forest Management Ukrainian National Forestry University Vul Henerala Chuprynky 103 79031 Lviv Ukraine

PSEDA ILIRIA organization Tirana 1000 Albania

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