Genetic consequences of forest population dynamics influenced by historic climatic variability in the western USA

We review recent advances in climate science that show cyclic climatic variation over multiple time scales and give examples of the impacts of this variation on plant populations in the western USA. The paleohistorical reconstructions we review and others indicate that plant species track these cycles in individualistically complex ways. These dynamic histories suggest that genetic structures are in a non-equilibrium state, with populations constantly lagging their environmental optima. Such dynamism may serve to maintain genetic variation in populations, which may be a hedge against rapid environmental change. We also discuss how population history affects the way we analyze and interpret genetic data and, conversely, the way genetic theory affects historical reconstructions.