The spatial genetic structures of three French natural beech stands were analysed using polymorphic enzyme loci. Two methods were used: F-statistics and spatial autocorrelation statistics. Within these stands where self-fertilization rate is 0, a low heterozygote deficit was observed which may be due to a moderate level of mating between relatives. However, no increase of this deficit was observed from one generation to the next. The spatial genetic structuring was low. Within one open stand composed of several patches, founder events are invoked to explain a significant autocorrelation. Within the two other stands, both dense, results are similar to those produced by simulations of an isolation by distance model. The genetic structure seems not to be stable in space and time which may be due to (i) a limited number of generations; (ii) an effective gene flow less limited than hypothesized; and (iii) fertility differences or phenological incompatibilities between individuals.

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Variation at 12 polymorphic isozyme loci was studied in the European beech on the basis of an extensive sample of 389 populations distributed throughout the species range. Special emphasis was given to the analysis of the pattern of geographic variation on the basis of two contrasting measures of genetic diversity, gene diversity (H) and allelic richness, and to their relationship. Measures of allelic richness were corrected for variation in sample size by using the rarefaction method. As expected, maximum allelic richness was found in the southeastern part of the range (southern Italy and the Balkans), where beech was confined during the last ice age. Surprisingly, H was lower in refugia than in recently colonized regions, resulting in a negative correlation between the two diversity measures. The decrease of allelic richness and the simultaneous increase of H during postglacial recolonization was attributed to several processes that differentially affect the two diversity parameters, such as bottlenecks due to long-distance founding events, selection during population establishment, and increased gene flow at low population densities.

Summary — The mating system of beech (Fagus sylvatica L) was investigated using polymorphism at 4 allozyme loci and the multilocus model of Ritland and Jain (1981). Beech appears to be a highly outcrossing species: the outcrossing rate ranges from 0.94 to 1. No significant differences were found in outcrossing rates according to