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

SpeciesDiameters
#10.2, 0.3, 0.1 cm
#20.2, 0.3, 0.1, 0.4, 0.2 cm
  
  
  
  
  
  
  
  

Sample #: 2

SpeciesDiameters
#10.2, 0.2 cm
#20.3, 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 cm0.0314 cm2
0.30.0707
0.10.0079
0.20.0314
0.20.0314

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 cm0.0314 cm2 
0.30.0707
0.10.0079
0.40.1257
0.20.0314
0.30.0707
0.40.1257
0.40.1257

 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

Sample data calculation using Microsoft Excel