Stem growth and epicormic branch formation in understorey beech trees (Fagus sylvatica L.)

A study of the formation of epicormic branches on suppressed beech trees revealed developmental sequences that had not hitherto been studied in depth. By combining architectural analysis and anatomy, it was possible to trace the history of the plant and thus fully understand the ontogenesis of the individuals studied. The main sequences observed were: (1) the formation of moribund trees that were gradually covered in epicormic branches from the base of the stem to the crown following gradual forest closure; (2) the formation of this new crown of epicormic branches was combined with a very sharp reduction in stem cambial activity (partial rings, if any) and modifications to the ligneous sections; and (3) resumed girth increment following the establishment of epicormic branches. After describing in detail the methods and individual variation, we highlight the spatial and temporal patterns of the phenomena observed. Lastly, we put forward functional hypotheses with a view to setting these results against a background of forest tree ontogenesis in general.