Improved resolution of pollen taxonomy allows better biogeographical interpretation of post-glacial forest development: analyses from the North American Pollen Database
*Correspondence and present address: S. A. Finkelstein, Department of Geography, University of Toronto, 100 St George Street, Toronto, Ontario, Canada, M5S 3G3 (tel. +1 416 978 3375; fax +1 416 946 3886; e-mail email@example.com).
- 1Species-level pollen identifications within the genera Acer, Fraxinus and Juglans have the potential to increase the detail available from regional- and landscape-scale studies of palaeo-forest dynamics.
- 2Data from the North American Pollen Database (NAPD) and the North American Modern Pollen Database (NAMPD) for sites in eastern North America for which species-level identifications have been recorded enabled us to consider pollen taxonomy at high resolution.
- 3Species within each of Acer, Fraxinus and Juglans have important differences in habitat, functional type and responses to climatic change. Analysis of the modern distribution of these taxa and their pollen rains confirms that species-level pollen identifications provide detailed ecological information, but the lack of distinction to the species level in many fossil and modern pollen studies renders palaeoenvironmental reconstructions incomplete.
- 4Within each of three selected high-resolution sites, ordinations indicate that individual species of Acer, Fraxinus and Juglans follow different trajectories through the Holocene, showing that analysing only generic categories results in the loss of ecologically valuable information. For example, pollen of Acer rubrum increased in abundance in response to canopy openings in a southern Ontario forest around 500 years ago, while that of A. saccharum declined. Similarly, Juglans nigra pollen percentages increased while J. cinerea decreased at this time.
- 5Regional-scale comparisons of pollen percentage curves indicate that, despite the uncertainties associated with the low temporal resolution and the chronologies, it is reasonable to conclude that individual species of Acer, Fraxinus and Juglans responded synchronously to palaeoclimatic changes within each region.
- 6Taking analyses to the specific level shows that different species followed different tracks in their post-glacial history, a fact previously blurred by less resolved taxonomy. This information is meaningful in biogeographical terms, providing much more specific evidence of how the selected trees behaved in the past.