Disentangling competition for light from remaining competition aspects in European beech forests

European beech forests face increasing environmental stress and anthropogenic demands, necessitating an understanding of tree growth and forest ecosystem dynamics to ensure future productivity and stability. Key to this is the disentangling of tree competition for light and edaphic resources to identify growth-limiting factors under different conditions. In this study, we aimed to disentangle the impact of light availability and further aspects of competition on the radial growth of 943 European beech trees across six research sites in Southwest Germany. Using a novel approach combining Terrestrial Laser Scanning and Radiative Transfer Modelling, we conducted a detailed, spatially explicit assessment of potential annual light availability per individual tree, shaped by complex local structures. We compared the predictive importance of light availability on tree growth against common competition indices by contrasting their predictions of basal area increment measurements using Generalized Additive Models. This offered the unique possibility to investigate shifts in importance of competition aspects across annual drought intensities. We observed a positive influence of light availability on general growth levels of European beech (R 2 = 0.67), with a saturation effect at higher light levels. The spatially modelled light availability outperformed a common shading-focussed index (R 2 = 0.47) in describing general growth levels but was explaining less variability than a competition index incorporating both edaphic and light competition (R 2 = 0.72). As expected, the light availability gained relative predictive importance compared to remaining competition for water and nutrients under more humid conditions. Overall, the proposed spatial assessment proved useful to disentangle the competition for light from remaining competition, offering valuable insights for studying, understanding, and modelling competition dynamics. • Detailed, spatially explicit assessment of individual tree light availability. • Light availability promotes tree radial growth, with a saturation at higher levels. • Explicit light resource assessment outperforms indirect shading-focussed index. • Relative importance of light for radial growth rises as drought intensity declines.