Calculating Importance Values
Using the Point-Center Quarter Method
- If you are not familiar with importance value calculations, you should first read the
PDF file of Quantitative Analysis by the Point-Center Quarter Method.
- Each point in your sample will generate four quarters. In each quarter record in
the appropriate columns
- the sample point and quarter numbers;
- the species of the tree nearest the sample point;
- the distance of this tree to the sample point (in meters);
- the diameter at breast height (DBH) or the circumference at chest height (CCH)
of this tree (in cm).
- Depending on how you measured the trees,
you should select either DBH or CCH at the head of the third input colum.
- Note that some trees may have more than one
trunk at this height. Measure each diameter or circumference separately. (See Point 2, Quarter 2 below for such a
- Enter the data into the calculator in the same manner.
- Press the "Do Calculations" button at the top of the calculator.
- The mean basal area, number of trees per hectare, the relative density, relative cover (also known
as the relative dominance), the relative frequency, and the importance value (sum of the last three
items) for each species will appear at the bottom of the input table.
- Estimates of the mean distance between trees (without regard to species) and the absolute density
of all trees are also calculated.
Format of Data Table
|1||1||Acacia||1.1||6|| || || |
|.||2||Eucalyptus||1.6||48|| || || |
|3||Casuarina||2.3||15|| || || |
|4||Callitris||3.0||11|| || || |
|2||1||Eucalyptus||2.8||65|| || || |
|2||Acacia||0.9||8||6|| || |
|3||Casuarina||3.7||16|| || || |
|4||Casuarina||2.2||9|| || || |
|3||1||Acacia||2.8||4|| || || |
|2||Acacia||1.1||6|| || || |
|3||Acacia||3.2||6|| || || |
|4||Acacia||1.4||5|| || || |
|4||1||Callitris||1.3||19|| || || |
|2||Casuarina||0.8||22|| || || |
|3||Casuarina||0.7||12|| || || |
|4||Callitris||3.1||7|| || || |
|5||1||Acacia||1.5||7|| || || |
|2||Acacia||2.4||5|| || || |
|3||Eucalyptus||3.3||27|| || || |
|4||Eucalyptus||1.7||36|| || || |
- You need not type the entire species name; any (unique) alphanumeric abbreviation will do as
long as the same abbreviation is used consistently.
- The results list the number of points used in the analysis. Make sure that this coincides with the
data you entered. The applet assumes that the data ends when the first empty species cell in the
first quarter of a point is encountered.
Links to Related Materials