Appendix 4 spacer Determining a Suitable Site Index Method
Lessons
Lesson 1
Lesson 2
Lesson 3
Lesson 4
Lesson 5
Lesson 6
Lesson 7
Lesson 8
Lesson 9
Lesson 10
Lesson 11
Lesson 12
Appendices
Appendix 1
Appendix 2
Appendix 3
Appendix 4
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1. Who Should Use this Key?

2. Cautions

3. Methods to Estimate Site Index

4. Documents Required

5. Description of Each Box in the Decision Key


Appendix 5
Appendix 6
Appendix 7
Appendix 8
Appendix 9
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This figure is a decision key to select a recommended method to estimate site index for silviculture polygons and strata. The background required to properly use the decision key follows.

Decision key
Decision key
Decision key

1. Who Should Use this Key?

This decision key is provided for silviculture surveyors who must determine site index for silviculture polygons. The key may also assist other users (e.g., inventory or research crews).

2. Cautions

This decision key will recommend a method to use to determine site index. However, operational concerns not addressed by the key may override this recommendation. These additional concerns include 1) the cost of data collection and the available budget, 2) damaging crop trees when determining age, and 3) combining the recommended method with other surveys planned for the block.

3. Methods to Estimate Site Index

For most silviculture polygons (strata), there is more than one method that can be used to obtain site index. These methods differ in their availability throughout the province, their suitability for different stand conditions, and their accuracy. This decision key assists in selecting from four methods: 1) BEC method, 2) growth intercept method, 3) site index curve method, and 4) estimate site class and convert to site index.

BEC method

With the BEC method, site index is predicted from the Biogeoclimatic Ecosystem Classification (BEC) for the stratum. The surveyor determines the biogeoclimatic unit and site series and then obtains a site index estimate for the selected species from the site index—site unit look-up table.

Growth intercept method

With the growth intercept method, site index is predicted from the height and age of sample trees measured on site. The surveyor measures the heights and ages of a number of sample trees in the stratum and obtains site index from a look-up table.

Site index curve method

With the site index curve method, site index is predicted from the height and age of sample trees measured on site. The surveyor measures the heights and ages of a number of sample trees in the stratum and obtains site index from a look-up table.

Estimate site class and convert to site index

With this method, the surveyor estimates site class and uses a table to convert site class to site index.

4. Documents Required

To accurately estimate site index and to properly use the decision key, the following documents are required:

  1. The SIBEC guide (Site Index Estimates by Site Series for Coniferous Tree Species in British Columbia).
  2. FS 415 growth intercept field cards.
  3. A complete set of site index curves and tables.
  4. The table to convert site class to site index.

5. Description of Each Box in the Decision Key

Existing site index

This box questions whether there is a site index value already available for the stratum. Some strata have site index indicated on the forest cover map label; within ISIS, MLSIS, or a licensee's silviculture information system; or on a note in the opening file.

Adequate accuracy

This box asks if the existing site index is accurate for the purpose of the survey. In general, an existing site index is accurate enough for silviculture uses if it was obtained by careful, on-site application of any of the BEC, growth intercept, or site index curve methods. Usually, an existing site index is not accurate enough for silviculture purposes if it was 1) obtained by converting site class to site index, 2) taken from an adjacent stand, or 3) taken from the forest cover map label (since the site index in the label of most young stands was converted from site class and the site index in the label of most old stands is inaccurate).

Use existing site index

To obtain a site index estimate for the stratum, use the existing site index value.

Less than three years growth above breast height

This box questions if dominant and codominant trees of the selected site index species have completed less than three years growth above breast height.

BEC method available

This box asks if the Biogeoclimatic Ecosystem Classification (BEC) method of predicting site index is available. It is available if the species—site unit combination in the SISU tables of the Site Index Estimates by Site Series for Coniferous Tree Species in British Columbia contains an estimate.

Use BEC method

To obtain a site index estimate for this stratum, use the BEC method.

Estimate site class; convert to site index

To obtain site index for this stratum, estimate site class and convert site class to site index.

3-30 years growth above breast height

This box asks if dominant and codominant trees of the selected site index species have completed 3-30 years growth above breast height.

Growth intercept method available

This box asks if the growth intercept method is available for the selected site index species.

Stand suitable for growth intercept

This box questions whether if the stand condition is suitable for the growth intercept method. The growth intercept method is suitable for a stratum if there are enough sample trees, with enough growth, and their growth reflects site potential. Usually, a stand is not suitable if many of the dominant and codominant trees of the selected site index species have been:

  1. overtopped by other trees or brush;
  2. seriously damaged or diseased;
  3. cut out by spacing; or
  4. affected in height growth by treatment (for example, fertilization temporarily accelerating height growth or thinning shock temporarily reducing height growth).

Use growth intercept method

To obtain site index for this stratum, use the growth intercept method.

3-9 years growth above breast height

This box asks if dominant and codominant trees of the selected site index species have completed 3-9 years growth above breast height.

10-30 years growth above breast height

This box asks if dominant and codominant trees of the selected site index species have completed 10-30 years growth above breast height.

More than 30 years growth above breast height

This box asks if dominant and codominant trees of the selected site index species have completed more than 30 years growth above breast height.

Stand suitable for site index curve

This box questions if the stand condition is suitable for the site index curve method. The site index curve method is suitable for a stratum if there are enough sample trees with growth that reflects site potential. Usually, a stand is not suitable if:

  • it is uneven aged;
  • the sample trees have been overtopped by other trees;
  • it has received partial cutting removing the larger trees;
  • many of the sample trees are seriously damaged (for example, broken or dead tops) or diseased;
  • sample trees are very old (age class 8 and 9);
  • sample trees are very large or rotten at DBH;
  • it is a stand that regenerated densely, particularly lodgepole pine.

 

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