Effects of canopy opening on the morphology and anatomy of naturally regenerated beech seedlings

Beech (Fagus sylvatica L.) seedlings growing under contrasting canopy closure conditions (gaps vs closed canopy) were collected in a naturally regenerating stand of northeastern France. Seedling morphology [total height, basal diameter, number of growth units (GUs), length of GUs] and anatomy (width of the pith and width of the annual rings at seedling base and at various levels along the stem) were described. Seedling ages, as estimated by counting the number of rings at seedling base and by counting the number of GUs along the stern, were compared. Seedling age ranged between 1 and 19 years. The best method for determining the age of seedlings with reduced growth appeared to be GU counting, whereas the best method for determining the age of actively growing seedlings was ring counting. No effect of seedling age on any parameter of seedling growth was found. The degree of canopy closure strongly affected seedling growth. Seedlings sampled in gaps were larger and allocated more biomass to secondary than to primary growth, compared to seedlings sampled under closed canopy. However, the increase in secondary growth relative to primary growth was only significant when analysing annual growth increment (GU length and ring width) and was not statistically significant when comparing seedling final size (total height and basal diameter).