Macrofossil and Pollen Representation of Coniferous Trees in Modern Sediments From Washington

Pollen and conifer needle macrofossils were collected from surface sediments in 30 ponds near Mount Rainier to study representation of forest trees in data from modern sediments. Percentages of major taxa calculated from these data were compared with basal area measures of forest composition within 30 m of each pond. Macrofossil percentages of Abies amabilis, Abies lasiocarpa, Pseudotsuga menziesii, Tsuga heterophylla, and Tsuga mertensiana were significantly correlated with their basal areas in nearby forests; none was greatly over— or underrepresented. Macrofossil assemblages were similar in replicate samples from surface sediments, as well as from parallel cores spanning 6000 yr. Fossil needle assemblages can therefore provide estimates of past species composition in coniferous forests in the Pacific Northwest. Also, widespread distribution of pollen was demonstrated by high pollen percentages of taxa that were absent from the flora at the samples sites, such as Alnus rubra. Pollen of Pinus and Tsuga heterophylla was overrepresented, whereas that of Abies and Tsuga mertensiana was underrepresented. Pollen percentages of most conifer taxa were twice the values reported in another study from Mount Rainier using moss polsters. Comparisons between the macrofossil and the pollen data indicate that conifer macroffossil assemblages more accurately reflect forest composition near sample sites, and also provide greater taxonomic resolution.