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 the related source population of the wind-pollinated forest tree Nothofagus menziesii (Hook. f.) Oerst. in the upper Taramakau catchment, South 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 populations had distinctly lower levels of heterozygosity. Correlation between expected heterozygosity and effective population size and between genetic and geographical distance was poor. Unusually high frequencies of some alleles in the pioneer populations had been determined by the 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 towards that of the (seed) source population, presumably as a result of gene flow via long-distance pollen dispersal. It is estimated that initial genetic divergence of N. menziesii pioneer stands can be adjusted within 2000 - 4000 years by gene flow through pollen dispersal from their source population, even over distances of several kilometres.