Research Branch
Contents
• 1. Introduction
• 2. Site Index Basics
• 3. Site Index and Site Factors
• 4. Methodology
• 5. Report Format and Content
• 6. Field Use
• 7. References
• Appendix 1. Species Conversion Tables
• Appendix 2. Resources

Reports
2008 Approximation
• SISU By Region Report (PDF Format)
• SISU By Region Report (Excel Format)
• SISU By BGC Unit Report (PDF Format)
• SISU By BGC Unit Report (Excel Format)
• Custom Reports Web Page
• Comparison Report

Standards
• Sampling and Data Standards Version 5.2

Products
• SIBEC e-brochure
• SIBEC Technical Report

 

 Site Index estimates by Site Series (SIBEC) - second approximation

Using The SIBEC Model To Estimate Site Index In The Field

When required to estimate the site index for a selected species, several methods are often appropriate. These methods differ in their availability throughout the province, their suitability for different stand conditions, and their accuracy. The BEC method is appropriate where:

  • stand conditions are unsuitable for using growth intercept or site index curve methods (see Figure 1), and
  • a correct site identification of the area can be obtained.

Where sample tree conditions are suitable, careful use of either the growth intercept or site index curve methods is generally more accurate than the BEC method. Frequently though, stand conditions are unsuitable for these methods as, for example, in the situations listed below. Under each of these circumstances the BEC method is preferred.

  • uneven-aged stands
  • very old stands (age class 8 and 9)
  • stands where sample trees are very large or rotten at breast height
  • stands where many sample trees have stem damage (forks, broken tops, dead tops)
  • stands with significant forest health problems
  • stands that have received heavy partial cutting
  • stands where treatment has modified sample tree height growth (e.g., fertilization temporarily accelerating height growth, or thinning shock temporarily slowing height growth)
  • stands that regenerated densely, particularly lodgepole pine

A general procedure for applying the BEC method in the field follows. For timber supply review purposes, please contact Forest Analysis Branch for guidance on applying the BEC method.

6.1 Determine site series

The first step in using the BEC method to estimate site index for a stand is to determine the biogeoclimatic unit (zone, subzone/variant) and site series. Ideally, only one site series will exist; however, because of the inherent variability of many sites, a stand may contain more than one site series. For instance, if a surveyor using objectives other than ecological uniformity stratified the stand, more than one site series may result. In cases where stands contain more than one site series, estimate the percentage of stand area by site series.

6.2 Select the site index species

Select the desired site index species for the stand. The site index species is the tree species for which site index is estimated. Generally, site index is required for the leading species on both the inventory and silviculture forest cover map labels. In a forest cover map label, site index refers to the leading species on the particular site. Each species on a site has a unique site index.

When selecting site index species, check the tables in either the Site Index-Site Unit Report by Region or the Site Index-Site Unit Report by Biogeoclimatic Unit to see which species have site index estimates available for the site series in your stand. If the tables do not have entries for the leading species in your stand, consider using a species conversion. An updated species conversion table is provided in Appendix 1. If no conversion is available,often the next best option is to apply the site index of a similar species to the other species.

6.3 Look up the site index value in the Site Index-Site Unit Report tables

Once zone, subzone/variant, site series, and species are identified for the stratum, proceed to the tables in the Site Index-Site Unit Report by Biogeoclimatic Unit to look up the site index estimate. As mentioned above, estimates may not be available for some site series-species combinations.

6.4 Compute average site index

If the stand contains more than one site series, it will be necessary to determine the average site index. To compute the average site index for the stand, average the site indices of each site series in the stand - weighting each value by the amount of the stand area in each site series.