Example Calculations
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.
Raw Data Table
Sample #:1
| Species | Diameters |
| #1 | 0.2, 0.3, 0.1 cm |
| #2 | 0.2, 0.3, 0.1, 0.4, 0.2 cm |
Sample #: 2
| Species | Diameters |
| #1 | 0.2, 0.2 cm |
| #2 | 0.3, 0.4, 0.4 cm |
Density
The formula for density is:
Density = Number of Individuals
_________________
Sum of all plot areas
Equation #1 For species #1, this becomes:
Density (Species #1) = 5 individuals
_________________
0.2 sq m.
= 25 individuals/m2
Density (Species #2) = 8 individuals
_________________
0.2 sq m.
= 40 individuals/m2
Dominance
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 cm2 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 m2, 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 cm2 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
Frequency
The equation for calculating frequency is:
Frequency = Number of plots which have at least 1 individual
____________________________________
Total number of plots sampled
Equation #3 For species #1:
Frequency (species #1)= 2
___
2
= 1
Frequency (species #1) = 2
___
2
= 1
Relative Density
The equation for calculating relative density is:
Relative Density = density/total density of all species Equation #4
Relative Density (species #1) = 25
______
25 + 40
= 0.385
Relative Density (species #2) = 40
______
25 + 40
= 0.615
Relative Dominance
Relative Dominance = dominance/total dominance for all species Equation #5
Relative Dominance (species #1) = 0.0000864
__________________
0.0000864 + 0.000295
= 0.227
Relative Dominance (species #2) = 0.000295
__________________
0.0000864 + 0.000295
= 0.773
Relative Frequency
Relative Frequency = frequency/total frequency of all species Equation #6
Relative Frequency (species #1) = 1
__________________
1 + 1
= 0.5
Relative Frequency (species #2) = 1
__________________
1 + 1
= 0.5
Importance Value
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
Electronic Spreadsheets
Click a link below to see how these data are entered into the electronic spreadsheets. Be sure to read the instructions for using these spreadsheets before using them to analyze data.
Instructions for using the electronic spreadsheets to analyze plot sampling data