Growth of Fagus sylvatica saplings in an old‐growth forest as affected by soil and light conditions

. Studies were conducted on 41 five yr‐old common beech ( Fagus sylvatica ) saplings collected in an old‐growth beech wood (Fontainebleau forest, biological reserve of La Tillaie, France), under varying humus and light conditions, following gypsy moth ( Lymantria dispar ) caterpillar injuries. Aerial and subterranean parts of each sapling were described by means of 34 parameters and environmental conditions at the microsite, where each sapling was excavated, were characterized by 23 parameters. The development of beech saplings is strongly affected by microsite conditions. An increase in sapling size was associated with darkness of the A‐horizon, typical of zones with poor mineralization of organic matter. Light conditions were more important in influencing the development of the root system than that of the aerial parts. Rooting depth was shallower and rate of mycorrhiza development by the black ascomycete Cenococcum geophilum was lower in microsites receiving incident light during the morning than in those never receiving incident light during this period. Results are discussed in the frame of survival of young beech individuals in varying environmental conditions, when submitted to competition by other vegetation and adverse climate conditions.