Lesson 5 spacer Growth Intercept Method
Lesson 1
Lesson 2
Lesson 3
Lesson 4
Lesson 5

Lesson Objectives

Growth Intercept Method Notes

How to Use the GI Method

Survey Timing

Number of Plots

1. Pre-stratifying the Opening

2. Select the Site Index Species

3. Collect Growth Intercept Data

4. Summary

Lesson 6
Lesson 7
Lesson 8
Lesson 9
Lesson 10
Lesson 11
Lesson 12
Appendix 1
Appendix 2
Appendix 3
Appendix 4
Appendix 5
Appendix 6
Appendix 7
Appendix 8
Appendix 9
Course Homepage

How to Use the GI Method

Once it has been determined that the GI method is the most appropriate for collecting SI data, there are four steps to the growth intercept method of estimating SI:

  1. Pre-stratify the opening.
  2. Select the site index species for each stratum.
  3. Collect growth intercept data on the site index species in each stratum.
  4. Compute the average SI for each stratum.

Survey Timing

GI data should be collected when the tree is not actively growing. GI data should NOT be collected in the spring or early summer (Figure 5.2). This is especially important for young sample trees.

This limitation can be relieved for species which form annual branch whorls if SI is estimated from partial growth as explained in Lesson 6.

Extra caution is required on GI surveys during growing season

Figure 5.2. Extra caution is required on GI surveys during the growing season.

Number of Plots

As a general rule, surveyors plots should be:

  • stratum >10 ha: 10 plots well spaced across stratum
  • stratum <10 ha: 1 plot/ha.

Within each stratum, survey sample lines should be laid out to achieve uniform coverage of the entire stratum (Figure 5.3).

A sample grid achieves uniform coverage of the stratum

Figure 5.3. A sample grid achieves uniform coverage of the stratum.


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