Key message Complementarities and/or synergies among different scales of tree architecture enable to achieve different functions simultaneously and/or optimize one function. After trimming, tree reaction occurred in all the scales. Abstract Trees are modular organisms within which each scale has attributes enabling them to optimize different functions. Among these functions, space exploration and light interception are strong determinants of tree productivity and survival. By modifying the crown shape, including foliage dispersion in the 3D space and carbon allocation, tree trimming (i.e. the removal of the higher part of the crown) may largely influence how trees fulfill the space exploration and light interception functions. In this study, we used field measurements of tree annual shoots combined with tree reconstruction from Terrestrial Laser Scanning data to analyze how different scales of the tree architecture complement each other to fulfill different functions simultaneously or combine to fulfill one single function more efficiently. We used morphological and functional variables measured at the annual shoot, axis, and tree scales to compare the architectural and functional strategies of two Fraxinus pennsylvanica cultivars and observe how trimming modifies these strategies. Results show that the two cultivars exhibit different strategies. One cultivar tended to optimize the space exploration function at both the annual shoot and axis scales and to optimize the light interception by displaying a large leaf area at the tree scale. The other cultivar tended to optimize light interception efficiency at both axis and tree levels. In both cultivars, trimming improved light interception efficiency and increased investments into space exploration. Nevertheless, after trimming, the two cultivars maintained their main architectural and functional strategy.