Ecobot follows the rules as outlined for the 50/20 rule in USACE's Regional Supplements to determine if a species is dominant.
The calculator in Ecobot that determines the dominance of a species adheres to the logic of the 50/20 rule as outlined by US Army Corps of Engineers in the Regional Supplements to the 1987 Wetlands Delineation Manual.
The rule is defined as follows:
Dominant species are chosen independently from each stratum of the
community. In general, dominants are the most abundant species that
individually or collectively account for more than 50 percent of the total
absolute coverage of vegetation in the stratum, plus any other species that,
by itself, accounts for at least 20 percent of the total.
Ecobot follows the protocol in the following order:
1. Estimate the absolute percent cover of each species in the first stratum.
Since the same data may be used later to calculate the prevalence index,
the data should be recorded as absolute cover and not converted to relative
cover.
2. Rank all species in the stratum from most to least abundant.
3. Calculate the total absolute coverage of all species in the stratum (i.e., sum
their individual absolute percent cover values). Absolute cover estimates
do not necessarily sum to 100 percent.
4. Calculate the 50-percent threshold for the stratum by multiplying the total
cover of that stratum by 50 percent.
5. Calculate the 20-percent threshold for the stratum by multiplying the total
cover of that stratum by 20 percent.
6. Select plant species from the ranked list, in decreasing order of absolute
coverage, until the cumulative coverage of selected species exceeds the
threshold representing 50 percent of the total coverage for the stratum. If
two or more species are equal in coverage (i.e., they are tied in rank), they
should all be selected. The selected plant species are all considered to be
dominants. All dominants must be identified to species.
7. In addition, select any other species that, by itself, is at least 20 percent of
the total percent cover in the stratum. Any such species is also considered
to be a dominant and must be accurately identified.
8. Repeat steps 1-7 for any other stratum present. Combine the lists of
dominant species across all strata. Note that a species may be dominant in
more than one stratum (e.g., a woody species may be dominant in both the
tree and sapling/shrub strata).