Conservation of the Grassy White Box Woodlands: Population Genetics and Fragmentation of Eucalyptus albens

White box ( Eucalyptus albens ) woodlands once covered large parts of the fertile agricultural land of the wheat‐sheep belt of southeastern Australia. Populations of E. albens were almost continuous across much of this region, but clearing has left a mosaic of remnant populations, scattered trees, and treeless pastures or cropland. Using allozyme electrophoresis of remnant populations sampled from across the range of E. albens , we examined patterns of genetic variation in this species and the effects of fragmentation on its genetic diversity. Total genetic diversity in E. albens was higher than reported for any other eucalypt species (H t = 0.306), while differentiation among populations from across its range was one of the lowest for eucalypts (G st = 5.7%). Cluster analysis of the 10 largest populations sampled indicated that patterns of genetic variation in E. albens are generally consistent with geographic relationships, although no major genetic differentiation was detected. The relationship between genetic and geographic patterns was obscured with the inclusion of small populations in the analysis, suggesting a need for caution in the sampling of small populations for genetic studies. There was a significant, log relationship between remnant population size and all genetic diversity measures, with lower diversity in small populations of less than about 500 individuals. Some small populations had higher levels of diversity than would be expected from this simple relationship, and the deviants were best explained by low isolation from larger stands of E. albens (for total number of alleles) or lower than average levels of inbreeding (for observed beterozygosity). We recommend that for maximum conservation of genetic diversity in E. albens at the local scale, populations should either contain greater than 500 individuals or form a closely spaced mosaic to allow gene flow between smaller units. Reconstructed populations should be established from seed collected from local populations of greater than 500 individuals. At the broad scale, conservation of genetic diversity in E. albens would probably be maximized by a wide geographic spread of reserved populations.