A rare case of natural regeneration in butternut, a threatened forest tree, is parent and space limited

The genetic consequences of natural in situ recovery for rare or threatened species are not as well understood as the impact of population bottlenecks, fragmentation and admixture, particularly the mechanisms by which genetic diversity is lost or preserved as populations recover. Here we examine how mating patterns, dispersal and ecologically constrained regeneration influences genetic diversity and kinship in a naturally regenerating population of a threatened temperate forest tree, Juglans cinerea L. (butternut). Butternut regeneration is now rare throughout the native range due to the butternut canker, a lethal fungal disease from Asia, and land use changes. In this study of one of the only known regenerating patches large enough for kinship and parentage analysis, we used 12 microsatellite markers, direct and inferred parentage analyses and Bayesian clustering of 152 trees to show that natural regeneration at this site resulted in loss of allele richness due to a small number of parents, most of which are spatially proximal to the regenerants. Of the 116 potential parents tested, one contributed 20.8 % and the top four contributed 71.1 % of the gametes in 36 regenerants. Parent-parent and parent-offspring distances revealed limited pollen and seed dispersal (<100 m). Regenerants were highly related and spatially clustered in sibling groups. Proximity to the regenerating patch was the most significant factor in parental success. Our results suggest that in situ regeneration of forest trees with limited propagule dispersal and specific site requirements may be insufficient to preserve native genetic diversity in protected areas with few suitable sites. © 2012 Springer Science+Business Media B.V.