Lesson 6 spacer Advanced Options for Growth Intercept
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Lesson 6

Lesson Objectives

Advanced Options for Using GI Method

Measuring More Than One Sample Tree Per Plot

Estimating SI from Partial Growth

Determining Age by Counting Branch Whorls

Assessing the Reliability of the SI Average

Building a Growth Intercept Table

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Lesson Objective

Learn some advanced options for the GI method.

Advanced Options for Using GI Method

The GI method allows for some advanced options that surveyors may find useful. The following options allow surveyors some flexibility in using the GI method.

Measuring More Than One Sample Tree Per Plot

In order to reduce between plot variation, surveyors may wish to measure more than one GI sample tree per plot. Surveyors must increase plot size in order to collect more than one sample tree per plot. The following stipulates the appropriate plot radius for the corresponding number of sample trees:

  • 1 tree 5.64 plot radius
  • 2 trees 7.99 plot radius
  • 3 trees 9.74 plot radius

To compile data when more than one sample tree per plot is measured, SI is estimated for each tree and the SI values are averaged.

Estimating SI from Partial Growth

It is possible to estimate SI from a portion of the total growth above breast height if the SI species has distinct annual branch whorls. This method is less accurate than the method based on ring count and total height. However, it can be used during the growing season. It is suitable for quick reconnaissance work.

To estimate SI from partial growth, surveyors follow these five steps (Figure 6.1):

  1. Locate breast height.
  2. Select an annual branch whorl below the leader. If the survey is conducted during the growing season, surveyors should measure up to the annual whorl below the currently growing leader. This whorl is called the upper measurement point.
  3. Measure the tree height from the ground to the upper measurement point.
  4. Determine the number of years growth between breast height and the upper measurement point.
  5. Indicate that the measurement is for partial growth on the data collection card.

Estimating SI from partial growth
Estimating SI from partial growth

Figure 6.1. Estimating SI from partial growth.


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