Competition‐induced tree mortality across Europe is driven by shade tolerance, proportion of conspecifics and drought

• Published in: Journal of Ecology
• Main Authors: Kulha, Niko, Honkaniemi, Juha, Barrere, Julien, Brandl, Susanne, Cordonnier, Thomas, Korhonen, Kari T., Kunstler, Georges, Paul, Carola, Reineking, Björn, Peltoniemi, Mikko
• Other Authors: Academy of Finland, Agence Nationale de la Recherche, Bundesministerium für Bildung und Forschung
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2023
• Subjects: Arctic
• Online Access: http://dx.doi.org/10.1111/1365-2745.14184; https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2745.14184

Abstract Forest stand densities are increasing in the boreal and temperate biomes, suggesting that tree‐tree competition is intensifying. Anticipating the consequences of this intensified competition is difficult because competition‐induced mortality may depend not only on the occurrence of extreme climatic events such as drought, but also on stand composition, since tree species differ in their ability to compete and tolerate competition. A better understanding of the effects of stand composition and drought on competition‐induced mortality would help to anticipate future changes in forest ecosystems. We studied the tree‐level probability of competition‐induced mortality using National Forest Inventory data from three European countries (Finland, France and Germany), covering a latitudinal gradient from the Mediterranean to the Arctic. We investigated how (i) the proportion of conspecifics, (ii) the shade tolerance (ST) of the focal tree and its competitors and (iii) drought events modify the effect of competition on tree mortality. We used a generalized linear mixed model on a dataset of 461,109 trees representing 39 species on 48,088 individual plots. Competition, measured as the basal area of larger trees, was a stronger driver of background mortality (BM) than tree size and climate. A higher proportion of conspecifics increased the competition effect on mortality, showing that conspecific individuals had a higher competitive effect compared to heterospecific individuals. The competition effect on mortality also increased as a function of the ST of neighbouring trees, suggesting an increased shading effect. A higher ST of a focal tree decreased the competition effect on mortality. Drought anomalies increased the competition effect, resulting in a higher mortality probability for the most suppressed trees. Synthesis . Competition was the main driver of background mortality. Increasing stand density increased competition‐induced tree mortality in both monospecific and mixed stands, but to different extents ...