Mapping and calibration of modern pollen-vegetation relationships in the southeastern United States

Abstract

We present the first comprehensive evaluation of the quantitative pollen—vegetation relationship for major tree taxa distributed across the southeastern United States. A total of 250 modern pollen spectra (134 spectra contributed by colleagues and an additional 116 spectra that we have collected and counted) provide widespread and relatively uniform coverage across the Southeast. At least one modern pollen spectrum is now available for each 1° latitude by 1° longitude block for the area extending from 29° N to 37°N and 75°W to 95°W. For this region, we have used the most recent Continuous Forest Inventories for merchantable timber to derive estimates of percent growing-stock volume at the spatial scale of both county and larger forest inventory units. For nineteen arboreal taxa, we illustrate contoured maps for precent arboreal pollen (isopoll maps) and percent tree dominance (isophyte maps), as well as scatter plots for pairs of positive percentage values for each taxon. We used geometric-mean linear regression of arboreal pollen percentages against percentages of growing-stock volume to estimate the slope and intercept of a best-fit line and the correlation coefficient of pollen values with tree values. These calibrations are compared with the results of Webb et al. (1981) from the midwestern United States. In these two calibration sets, certain taxa such as Quercus exhibit similar values for both the slope of the regression line and the y-intercept in spite of regional differences in the number and taxonomic composition of Quercus species present. For other taxa such as Pinus, however, the northern and southern groups of species exhibit distinctly different slopes and intercepts. This divergence in calibrations occurs both because different species of Pinus are involved and because pollen productivity of Pinus relative to that of other taxa is different in the two regions. Calibrations of percent arboreal pollen with percent growing-stock volume in the southeastern United States yield new insights that result in a substantive revision in concepts of pollen—vegetation representation.