The June 2014 issue (page 9) has an article by Robert Lichvar and Jennifer Gillrich. Mr. Lichvar is the fellow who also leads the species update program for the National Wetland Plant List (NWPL). The article topic is the use of the HCL (described below) as a replacement for Dominance and Prevalence. I like it, although it will require a new version of the Wetland Data Form and of course I will need to change all the Desktop and Android Software I have developed for the current forms.
Bottom line I think is that you only need to make one list of species regardless of strata, sum up cover for all the FAC and wetter species, then divide by the total cover for all species x 100. If the percent is greater than 50% then the vegetation is Hydrophytic.
Seems totally reasonable to me. Any thoughts especially any criticisms?
From the article:
" the Hydrophytic Cover Index (HCI), the Dominance Ratio (DR) and the Prevalence Index (PI) - were tested and compared using a large national dataset of delineation data (Lichvar and Gillrich 2014a). The HCI was recommended by the National Techni¬cal Committee for Wetland Vegeta¬tion (NTCWV) in light of recent work showing that up to 20% of determina¬tions made using the DR are biased (Lichvar et al. 2011) and that up to 14% of determinations made using the PI are incorrect (Lichvar and Gillrich unpublished data). The national dataset is from nine Corps regions collected during the development and field testing of the Regional Supple¬ments to the Army Corps of Engineers Wetland Delineation Manual (Berkowitz 2011). It consists of data from 637 plots at 232 sites. For each site, nested circular sample plots with 9 m and 2m radii were located on each side of the wetland boundary or along a wetland-to-upland transect. The HCI, the PI, and the DR were calculated for each plot in the national data set (n = 637), and the number of plots containing hydrophytic vegetation were tallied for each method. The HCI was calculated using wetland ratings and the percent cover data from each plot, as follows:
HCI = (Σ COBL + Σ CFACW + Σ CFAC)/( Σ COBL + Σ CFACW + Σ CFAC + Σ CFACU + Σ CUPL) × 100
where Σ is the sum and C is the cover – the percent areal cover for species represented by each of five wetland indicator status ratings."