Coefficients of Conservatism for the Vascular Flora of New York and New England: Inter-State Comparisons and Expert Opinion Bias

Abstract

The floristic quality index is a widely used method for ecological condition assessments in the United States. The foundation of the index is the conservatism concept, which estimates a species' ecological sensitivity or propensity to occur in areas least altered by humans. Plant species are assigned coefficients of conservatism (CoC) where ruderal and exotic species receive the lowest scores, competitors and matrix species intermediate scores, and remnant-dependent species the highest scores. The method has spread to over half of the United States, but New York and New England still lack CoC coverage. With funding from the Environmental Protection Agency and using nine of the region's most experienced botanists, an effort was undertaken to select CoC for the complete vascular flora of each New England state and New York State. Frequency distributions and rank correlations of CoC varied widely among states, except that each flora contained a large proportion of exotic species. Few taxa were scored with low confidence, although CoC at the extreme ends of the scale tended to be scored with higher confidence than more intermediate CoC. Differences in mean CoC and other summary measures for two botanists working independently on the same state indicate estimator bias in the ranking process, and calls for additional expert opinions, more careful instruction, and calibration of botanists, or the use of objective scoring methods.