A NOVEL METHOD FOR IDENTIFYING REFUGIA IN THE FOSSIL RECORD

Refugia are localities where a population is sheltered from extirpation during periods of adverse conditions. Environmental conditions within a refugium should promote the population’s re-expansion after the adverse conditions pass. If conditions are not amenable to re-expansion, then it may become a refugial trap, where the population declines and is eventually extirpated, or a disjunct population, where the population remains stable within the geographic limits of the former refugium. Distinguishing between these three states is critical for conservation, particularly when choosing the location of future protected areas. Data including the baseline, disturbance, and recovery of prehistoric ecosystems can facilitate this conservation by providing testable examples. We propose a novel empirical method for identifying and discriminating among refugia, refugial traps, and disjunct populations in both the Recent and deep past. The method is tested using pollen preserved in lake cores from northern Alaska, USA over the past 20 kyr, which includes the end of the last glacial maximum and the onset of the present interglacial interval. Northern Alaska was unglaciated throughout the last glacial interval, so it provides an excellent region to observe plant responses to climate change without glacial interference. Lake core data were procured from the Neotoma Database (Williams et al., 2018). Heat maps were constructed using pollen from three ecologically divergent tree taxa – spruce (Picea spp.), willow (Salix spp.), and aspen (Populus spp.) – to visualise changes in their geographic distribution in response to climate change. This method provided a sufficient sampling grain to identify the geographic contraction, preservation, and subsequent re-expansion that distinguishes refugia from refugial traps and disjunct populations. Although pollen is used as a case study, the general approach is applicable to any assemblage of taxa, and any ecosystem for which sufficient geographic, population, and temporal data are available. Identifying fossil refugia is critical to understanding patterns of survivorship that can help manage for successful protected areas now and in the future.