The example below shows how to do the calculations. In order to simplify things for this example, we will use only two samples. In each sample there are two species. We will call these species #1 and species #2.
The formula for dominance is:
Dominance = | Area covered by a species ____________________ Sum of all plot areas | Equation #2 |
Plant diameters in the data table must be converted to metric measure if they were measured in feet or inches. In the table above, the measurements are already in centimeters.
Each diameter must be converted to area. This can be done by using the table provided or by using the formula:
Using the Diameter to Area Conversion table, the areas for each individual of species #1 are:
Diameter | Area |
0.2 cm | 0.0314 cm^{2} |
0.3 | 0.0707 |
0.1 | 0.0079 |
0.2 | 0.0314 |
0.2 | 0.0314 |
The areas listed above are in the same units as the diameters. The diameters were measured in centimeters so the areas are in square centimeters. They can be converted to square meters by dividing by 10,000. The five areas listed above become 0.00000314 m^{2}, 0.00000707, 0.00000079, 0.00000314, 0.00000314.
The sum of these numbers is 0.00001728. The equation for dominance (equation #2 above) becomes:
Dominance (species #1) = | 0.00001728 ____________________ 0.2 | = 0.0000864 = 8.64 X 10^{-5} |
Similar calculations for species #2 are
Diameter | Area |
0.2 cm | 0.0314 cm^{2} |
0.3 | 0.0707 |
0.1 | 0.0079 |
0.4 | 0.1257 |
0.2 | 0.0314 |
0.3 | 0.0707 |
0.4 | 0.1257 |
0.4 | 0.1257 |
Each of these numbers divided by 10,000 become:
0.00000314, 0.00000707, 0.00000079, 0.00001257, 0.00000314, 0.00000707, 0.00001257, 0.00001257
The sum of these numbers is 0.00005892.
Dominance (species #2) = | 0.00005892 ____________________ 0.2 | = 0.000295 = 2.95 X 10^{-4} |
Importance Value = relative density + relative dominance + relative frequency Equation #7
Importance Value (species #1) = 0.385 + 0.773 + 0.5 = 1.11
Importance Value (species #2) = 0.615 + 0.773 + 0.5 = 1.89