After the last Ice Age, temperate European trees migrated northward, experiencing genetic bottlenecks and founder effects, which left high haplotype endemism in southern populations and clines in genetic diversity northward. These patterns are thought to be ubiquitous across temperate forests, and are therefore used to anticipate the potential genetic consequences of future warming. I examined whether these patterns do indeed hold across various taxa between two continents, Eastern North America (ENA) and Europe. Unlike their European counterparts, ENA trees do not share common southern centers of haplotype endemism and they generally maintain high genetic diversity even at their northern range limits. Differences between the genetic impacts of Quaternary climate cycles across continents suggest refined lessons for managing genetic diversity in today’s warming world.