Abstract 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 esti- mated by counting the number of rings at seedling base and by counting the number of GUs along the stem, 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 ac- tively 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 rela- tive to primary growth was only significant when analys- ing annual growth increment (GU length and ring width) and was not statistically significant when comparing seedling final size (total height and basal diameter). Keywords Advance regeneration · Allometry · Fagus sylvatica L. · Shade tolerance · Tree ring Introduction Studies in which the dynamics of tree growth following gap creation in the forest canopy was examined have shown that advance regeneration may contribute signifi- cantly to the future stand composition (Canham 1988; Brokaw and Scheiner 1989). These seedlings have estab- lished beneath a closed canopy and may survive in a sup- pressed state for a few to over 100 years (Merz and Boyce 1956; Tryon and Powell 1984; Poulson and Platt 1989). Once released, they show increased height and diameter growth (Sundkvist 1994; Murphy et al. 1999). However, the ability of advance regeneration to successfully re- spond to canopy release depends on species’ characteris- tics and on individual seedling age, size and vigour (Canham 1989; Loftis 1990; McClure et al. 2000). In mature beech-dominated (Fagus sylvatica L.) stands of western and central Europe, light levels in the understory are typically below 5% of incident radiation (Madsen and Larsen 1997; Emborg 1998). Beech seed- lings are able to persist for prolonged periods of time be- neath the canopy of adult trees (Watt 1923; Oswald 1981) and respond rapidly to canopy release (Newbold and Goldsmith 1990; Peltier et al. 1997). Even severely suppressed seedlings exhibit a rapid increase in diameter and height in response to canopy opening (Collet et al. 2001) and may therefore play a major role in stand re- generation. Numerous studies have shown that beech seedlings growing under low light availability have a reduced growth and exhibit low diameter–height, root–shoot, and branch–stem ratios (Suner and Röhrig 1980; Madsen 1994; Nicolini and Caraglio 1994). However, few studies describing the morphology and anatomy of such seed- lings exist, although it has been shown for other tree spe- cies that severely suppressed seedlings significantly dif- fer from non-suppressed seedlings in anatomical and morphological features (Wang and Lee 1989; Schöne and Schweingruber 1999). The objectives of this study are: (1) to describe the morphology and anatomy of suppressed beech seedlings C. Collet ( ✉ ) · O. Lanter Laboratoire d’Etude des Resources Forêt-Bois, UMR INRA-ENGREF 1092, Institut National de la Recherche Agronomique, 54 208 Champenoux, France e-mail: collet@nancy.inra.fr Tel.: +33-3-83394043, Fax: +33-3-83394034 M. Pardos Departamento de Selvicultura, CIFOR-INIA, Ap. Correos 8.111, 28080 Madrid, Spain Trees (2002) 16:291–298 DOI 10.1007/s00468-001-0159-x ORIGINAL ARTICLE Catherine Collet · Olivier Lanter · Marta Pardos Effects of canopy opening on the morphology and anatomy of naturally regenerated beech seedlings Received: 2 February 2001 / Accepted: 13 November 2001 / Published online: 30 January 2002 © Springer-Verlag 2002