There are several limitations to the site index estimates provided in the SIBEC guide.
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).
For this application (i.e., estimating mean site index for a group of stands), the BEC method can achieve a high level of accuracyassuming correct site identification and no bias.
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:
If you collect data suitable for the SIBEC database, you are requested to:
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.
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.