Abstract
We examined the effect of a low-cover stratum—woody vines—on 1) the outcome of vegetation determinations made using the Prevalence Index (PI) and the Dominance Ratio (DR), and 2) agreement between vegetation and soils during wetland delineations in the United States. Different vine abundance measures—stem counts vs. percent cover—had no effect on the percentage of hydrophytic vegetation determinations made by either formula. Artificial increases and decreases to the woody vine stratum’s minimum cover threshold of 5.0% also had no effect. However, in plots that contained borderline hydrophytic/nonhydrophytic vegetation, the percentage of hydrophytic vegetation determinations made by the DR decreased significantly when vine indicator status was artificially increased (p = 0.048). The PI produced significantly fewer hydrophytic determinations in plots with nonhydric soils than in plots with hydric soils (p < 0.001). The DR produced large percentages (81.8–100%) of hydrophytic determinations, regardless of soil type. Plots in which the DR and the PI differed had many commonalities, including nonhydric soils, nonhydrophytic PI/hydrophytic DR values, borderline hydrophytic vegetation, and an odd number of dominant species. During wetland delineations, the PI should be used in plant communities with low-cover strata, high species richness, or a high frequency of hydrophytes.
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