Ecological history of a long-lived conifer in a disjunct population

1. In northern Idaho (USA), more than 100 vascular plant species are disjunct <200 km from their main distribution along the Pacific Northwest coast. It remains unclear whether most species within this interior forest disjunction, including Tsuga mertensiana, survived the last glacial period in a north-Idaho refugium or whether these species colonized the region via long-distance dispersal during the Holocene.
2. Sediment cores were extracted from three mid- to high-elevation lakes within T. mertensiana dominated forests in the Northern Rocky Mountains of Idaho. Pollen and macrofossils were used to reconstruct forest composition, determine the timing of T. mertensiana establishment, examine the hypothesis that the region was a glacial refugium, and contrast how climate, competition and/or dispersal limitation has influenced its modern distribution.
3. The modern distribution of T. mertensiana was analyzed by constructing a range map and modeling the potential species distribution. ...