Lesson 4 spacer BEC Method
Lesson 1
Lesson 2
Lesson 3
Lesson 4

Lesson Objectives

BEC Method

Old Vancouver Forest Region Format

Old Prince Rupert Forest Region Format

Old Nelson Forest Region Format

New Provincial Format for the BEC Method

SIBEC Guide Tables

Relationships Between SI and Soil Moisture, Soil Nutrients, and Biogeoclimatic Subzone

SIBEC Guide Accuracy and Limitations

Accuracy for Site Index of Single Stand

Accuracy for Mean Site Index of Population of Stands

The SIBEC Program

Local SIBEC Tables

Lesson 5
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

SIBEC Guide Accuracy and Limitations

There are several limitations to the site index estimates provided in the SIBEC guide.

  1. The SI tables do not provide site index estimates for all species and all sites.

  2. The correlation between site index and site units varies from weak to moderately strong across species and sites. As a result, there are inherent limitations to the accuracy that can be obtained when this method is used to determine site index for a given tree species in a given stand.

  3. The right site index estimate cannot be obtained without a correct site identification.

  4. For some species and sites, the site index database is small and therefore the site index estimates given in the tables are imprecise.

  5. The site index database was compiled from sources of varying quality and this contributes to uncertainty in site index.

  6. Site index averages are based on data from naturally established, unmanaged stands and site index estimates for managed stands may be different.

Accuracy for Site Index of Single Stand

For many coastal species and sites, site index on two-thirds of individual sites is within 4 or 5 m of the average provided in the tables. In the interior, site index on two-thirds of individual sites is within 3 or 4 m of the average provided in the tables. For example, the average site index for Fd on the CWHxm/01 is given as 32 m in the SISU table. However, the site index for any individual CWHxm/01 Fd stand can easily be 4 or 5 m above or below the average.

When tested against an independent data set of 706 plots, the SI estimates in the SIBEC book were in the correct SI class 35% of the time. In 80% of the stands, the true SI was in the same class as the SIBEC estimate or one class above or one below (Figure 4.13).

Figure 4.13. Probability that the true stand site index is in the same class as the SIBEC book estimate, or above, or below.

Accuracy for Mean Site Index of Population of Stands

For this application (i.e., estimating mean site index for a group of stands), the BEC method can achieve a high level of accuracy—assuming correct site identification and no bias.

The SIBEC Program

The overall SIBEC program is built around the provincial SIBEC database. One component of the program is SIBEC data collection. SIBEC data collected by ministry staff, licensees and researchers is added to the SIBEC database as it becomes available. Once enough new data accumulates, the SIBEC guide will be revised. The raw SIBEC database is available from:

Del Meidinger
SIBEC Project Leader/Research Ecologist
Research Branch
B.C. Ministry of Forests
Phone: 250-387-6688.

If you collect data suitable for the SIBEC database, you are requested to:

  1. use the data collection standards described in the document “SIBEC sampling and data standards.”

  2. provide your data to the SIBEC database administrator.

Contact Del Meidinger to discuss these issues.

The site index values and reliability codes in the SIBEC guide are available in ASCII file format. Information on the SIBEC Project is available on the Internet at https://www.for.gov.bc.ca/hre/spwg/projects_area_sibec.htm.

Local SIBEC Tables

Several TFL-based SIBEC projects and numerous SIBEC research studies have been completed in British Columbia. These projects provide estimates of average SI for some sites and tree species. Where these estimates are based on an adequate sample and acceptable methods, these local estimates may be superior to the global estimates contained in the provincial SIBEC guide.


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