Contributions Series Nr. 43

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An Atlas of Pollen-Vegetation-Climate Relationships for the United States and Canada
Williams et al.
2006

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Abstract

This atlas displays the distribution of modern pollen abundances in North America, both geographically and relative to various climatic, bioclimatic, and vegetational variables. It is intended to aid analyses of modern pollen-environment relationships as well as the climatic and ecological interpretations of fossil pollen diagrams. The atlas is based upon a recent compilation of pollen samples from surface sediments and polsters that includes 4549 samples, 134 pollen types, and independent climatic and vegetational attributes for all locations. Atlas pages are presented for 106 pollen types, representing all of the major and many minor pollen types found in North America. Ten pollen types are split into eastern and western regional groups, using the corresponding species range maps as a guide. The pages are designed to show in detail the distribution of pollen abundances with respect to key climatic and vegetational variables; each set includes a map of modern pollen abundances plus a series of visualizations of pollen-climate and pollen-vegetation relationships. The relationship between pollen abundances and indices of fractional broadleaf and needleleaf areal cover is consistent with the ecological associations of the plant taxon, and biomes can be distinguished by the characteristic frequencies of various pollen abundances, although abundances for individual taxa may vary widely within a given biome. Pollen-abundance distributions with respect to environmental gradients are usually characterized by an upper-limit unimodal distribution, except where the representation of multiple species by a single pollen morphological type results in multimodal distributions. Consequently, high pollen abundances are usually more climatically informative than low pollen abundances. Although individual pollen types are rarely diagnostic of a particular climatic regime or vegetation type, assemblage-level information about the abundances of many pollen types provides a strong basis for paleoenvironmental inference.