We compared shade tolerance of maple, ash and beech in the sapling stage from two sites with rich soils differing in water supply, growing in dense thickets underneath a beech shelterwood of varying canopy densities. Shade tolerance was described by two components: mortality in shade and height growth in high light. At low light, beech showed the least mortality, maple the highest and ash in between on both sites. The decline with increasing light was steepest in beech and more gradual with ash and maple. At ~ 15 per cent above canopy light, all three species approached zero mortality. Beech as the most shade-tolerant species had the highest survival rate under low light and the least length growth rate under high light (>17 per cent). Ash had a lower survival rate at low light than beech and a highest growth rate at high light. Maple showed a bit weaker trade-off with the lowest survival rate but a growth rate inferior to ash. On the better water-supplied site, height growth was signifi cantly superior in all three species only under high light. On the basis of these results, silvicultural conclusions are drawn with respect to appropriate light levels and cutting types.

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In a field study, we measured saplings of beech, ash and maple growing in a fairly even-aged mixed-species thicket established by natural regeneration beneath a patchy shelterwood canopy with 3-60% of above canopy radiation reaching the saplings. Under low light conditions, maple and ash showed a slight lead in recent annual length increment compared with beech. With increasing light, ash and maple constantly gained superiority in length increment, whereas beech approached an asymptotic value above 35% light. A suite of architectural and leaf morphological attributes indicated a more pronounced ability of beech to adapt to shade than ash and maple. Beech displayed its leaves along the entire tree height (with a concentration in the middle crown), yielding a higher live crown ratio than ash and maple. It allocated biomass preferentially to radial growth which resulted in low height to diameter ratios, and expressed marked plagiotropic growth in shade indicating a horizontal light-foraging strategy. In addition, beech exhibited the highest specific leaf area, a greater total leaf area per unit tree height, a slightly greater leaf area index, and a greater plasticity to light in total leaf area. Ash and maple presented a ''gap species'' growth strategy, characterized by a marked and constant response in growth rates to increasing light and an inability to strongly reduce their growth rates in deep shade. In shade, they showed some plasticity in displaying most of their leaf area at the top of the crown to minimize self-shading and to enhance light interception. Through this, particularly, maple developed an ''umbrella'' like crown. These species-specific responses may be used for controlling the development of mixed-species regeneration in shelterwood systems. Keywords Shade tolerance Á Juvenile growth Á Mixed species broad leaf stand Á Tree architecture Á Leaf morphology Á Light availability Communicated by R. Matyssek.

ABSTRACT:The formation, size distribution and percentage of gaps in two virgin deciduous forests are presented in two case studies. Gaps are defined as openings in the canopy above 2/3 of stand height. These gaps comprise 16% of the forest area in Havešová Reserve and 14.6% of the forest area in Kyjov Reserve. The estimated turnover time is 220 years. More than half the gaps were caused by the death of one tree, and 80% of the gaps were due to the death of up to 3 trees. The largest gap in Havešová Reserve was 0.40 ha, resulting from the death of 56 trees over the last 40 years. The area of the largest gap in Kyjov Reserve was 0.44 ha. It was caused by the death of 80 trees over the last 40 years. Such large gaps are scarce. 85% of the gaps are smaller than 250 m². A correction of the bias towards the over-abundance of large gaps by line-transect sampling was made by estimating the percentage area of gaps of different size from the percentage length along the transects. In Havešová an attempt was made to date the death of trees that were still visible in the gaps. 1/5 of the trees initiated gaps by their death, while 4/5 of the trees extended gaps. While uprooted trees dominate in Havešová, breakage is most common in Kyjov.

Zusammenfassung: Anhand von Vollaufnahmen des lebenden und toten Derbholzbestandes auf mehreren Hektar großen Untersuchungsflächen wird die Waldstruktur von drei albanischen Buchenurwäldern analysiert. Ergänzend werden die Ergebnisse einer stichprobenweisen Verjüngungsinventur vorgestellt. Die Urwälder zeichnen sich durch hohe Derbholzvorräte, eine starke Durchmesserdifferenzierung und hohe Verjüngungsvorräte aus. Sie werden sowohl im Derbholzbestand als auch in der Verjüngung von Buche dominiert. Die Lücken im Kronendach liegen im Mittel unter der Größe einer Altbuchenkrone und entstehen daher überwiegend durch den Ausfall einzelner Bäume. Die kleinflächige Lückenbildung geht mit einem kleinflächigen Wechsel der Waldentwicklungsphasen einher. Ein wichtiges Strukturelement sind Altbäume über 80 cm Brusthöhendurchmesser, die in geklumpter‐zufälliger räumlicher Verteilung vorkommen. Auch liegendes und stehendes Totholz ist ein typisches Kennzeichen der Urwälder. Dessen Anteile liegen jedoch am unteren Ende der für naturnahe Laubwälder der gemäßigten Zone bekannten Werte. Dies wird auf die vergleichsweise rasche Zersetzung des Buchentotholzes zurückgeführt. Der Anteil liegenden Totholzes liegt deutlich über dem des stehenden Totholzes. In den Schlussfolgerungen für eine naturnahe Buchenwirtschaft wird die Bedeutung punktueller, an Stelle flächendeckender Eingriffe und die Bedeutung von Altbäumen und Totholz betont. Zielkonflikte können sich aus der Forderung nach gleichzeitig naturnahen und gemischten Buchenwäldern ergeben.