2004 Ton Damman Award Recipient

Jason McLachlan has won the 2004 Ton Damman award for his paper The importance of small populations in the postglacial dynamics of eastern forests, co-authored by J. S. Clark and P. S. Manos of Duke University and presented at the 2004 ESA meeting in Portland. The paper was based on Jason's research at Duke. He currently is a postdoc at Harvard forest, where he is studying climate and land use effects on forest population dynamics. Here is the abstract of Jason's winning paper: The importance of small populations in the postglacial dynamics of eastern forests. J. S. McLachlan, J.S. Clark, and P.S. Manos. Duke University.

The postglacial dynamics of temperate trees are understood primarily based on paleoecological range reconstructions. These reconstructions suggest that many eastern North American species expanded rapidly from glacial refuges in the south during the early Holocene. The concept that trees are able to accommodate rapid environmental change through range shifts has subsequently been widely accepted by ecologists and conservation biologists. We show that pollen and macrofossils in modern sediments poorly represent the ranges of species when they are rare. Fossil data, by extension, run the risk of grossly underestimating the past ranges of species that are rare over much of their range. We reconstructed the postglacial history of a suite of common eastern tree species based on genetic data that are independent of the fossil record. We surveyed chloroplast DNA variation throughout the modern distribution of these species. Our molecular data show that fossil based reconstructions have indeed underestimated the importance of small populations in the dynamics of postglacial recolonization. Combining fossil and molecular data leads to the following revised scenario of postglacial spread: The late glacial ranges of many species was extensive south of the Laurentide Ice Sheet, though population densities were low everywhere. Deglaciated terrain was colonized by advance populations near the ice sheet, rather than by rapid
long distance migration from southern refuges. Northern populations of these species today are consequently more genetically diverse than equivalent European populations, which experienced more severe postglacial bottlenecks. Projections of contemporary climate change indicate that these populations will have to spread more rapidly in the near future than did equivalent populations during the early Holocene.