GENETIC-VARIATION, GENE FLOW, AND THE FOUNDER EFFECT IN PIONEER POPULATIONS OF NOTHOFAGUS-MENZIESII (FAGACEAE), SOUTH ISLAND, NEW-ZEALAND

Genetic variation and gene flow in four isolated pioneer stands and th e related source population of the wind-pollinated forest tree Nothofa gus menziesii (Hook. f.) Oerst. in the upper Taramakau catchment, Sout h Island, New Zealand, were investigated by isozyme analysis. Measures of genetic variation were similar to those found in three other South Island populations of N. menziesii; only the two smallest pioneer pop ulations had distinctly lower levels of heterozygosity. Correlation be tween expected heterozygosity and effective population size and betwee n genetic and geographical distance was poor. Unusually high frequenci es of some alleles in the pioneer populations had been determined by t he genotypes of their pioneers and F1 generation trees. Comparison of allele frequencies of the pioneer, F1, and F2 generation trees in one sample stand revealed a gradual adjustment of allele frequencies towar ds that of the (seed) source population, presumably as a result of gen e flow via long-distance pollen dispersal. It is estimated that initia l genetic divergence of N. menziesii pioneer stands can be adjusted wi thin 2000 - 4000 years by gene flow through pollen dispersal from thei r source population, even over distances of several kilometres.