Macrofossil presence/absence maps and isopoll maps in 3000-year intervals show how ranges and abundance maxima for 12 eastern North American tree and shrub taxa (Picea, P. glauca, P. mariana, Larix laricina Abies balsamea, Tsuga canadensis, Pinus strobus, P. resinosa, P. banksiana. Betula papyrifera, B. alleghaniensis, B. Series Humiles) have changed from the last glacial maximum to the present. The macrofossil maps corroborate patterns shown by the isopoll maps and provide spatial detail and taxonomic resolution. The macrofossils confirm the inference from pollen data that unglaciated southeastern North America was cooler during the last glacial maximum (18 and 15 ka) than simulated by the COHMAP experiments with the NCAR CCM0 general circulation model. The geographic distribution of macrofossil occurrences during the Late glacial (12 and 9 ka) indicate that migration lag of boreal species did not occur at regional to subcontinental scales, and that pollen assemblages lacking modern analogs resulted from climate gradients lacking modern analogs. Early Holocene (9 and 6 ka) macrofossil maps show rapid northward expansion of tree species ranges into deglaciated regions. The data also show modest contractions of northern range limits of temperate species and expansions of southern range limits of boreal species in response to cooling trends during the late Holocene (3 and 0 ka). Comparison of modern macrofossil maps of nine of these taxa with corresponding range maps confirm that the macrofossils record the geographic ranges accurately. Comparison of the modern macrofossil maps with maps of tree growing-stock volume shows that for some taxa (Abies, Tsuga) macrofossil occurrences were most frequent in regions of maximum tree abundance. Comparison of modern isopoll maps with the modern range and growing stock volume maps indicate that, in contrast to the macrofossil data, the pollen data provide poorer resolution of range limits for most taxa, but better indications of abundance maxima and minima within the ranges.
ASJC Scopus subject areas
- Earth-Surface Processes