- 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 case.)

- Depending on how you measured the trees,
you should

- 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.

Point | Quarter |
Species | Distance (m) | DBH
(cm) | DBH
(cm) | DBH
(cm) | DBH
(cm) |

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.

- PDF file of Quantitative Analysis by the Point-Center Quadrat Method
written for the
Hobart and William Smith Colleges
and Union College
Partnership For Global Education: Queensland Term

- An eccology field exercise on Sampling the Tree Stratum at another college which includes using importance values.

Author: Kevin Mitchell (mitchell@hws.edu)

Hobart and William Smith Colleges and Union College

Partnership For Global Education: Queensland Term

Copyright © 1998-2001

Last updated: 17 July 2001

Hobart and William Smith Colleges and Union College

Partnership For Global Education: Queensland Term

Copyright © 1998-2001

Last updated: 17 July 2001