The purpose of the current project is to continue building SIBEC site index-site unit reference tables in the Okanagan TSA, by increasing sample sizes to the required minimum for second approximation SIBEC (total of 7 trees required in each site series).
SIBEC was initiated in 1994 to fulfill the demand for better site index estimates than those acquired from the forest inventory in old-growth stands. In 2001, at the request of B.C.'s Chief Forester, research was conducted to determine the suitability of PEM site series mapping and Site Index by BEC (Biogeoclimatic Ecosystem Classification) site series (SIBEC) for determination of annual allowable cut (AAC). Results showed first approximation SIBEC estimates were higher than SI estimates currently used by the forest industry. Although the AAC determination results were positive on test locations for the combination PEM/SIBEC approach, substantial additional data were required for priority BEC site series in order to facilitate operational second approximation SI estimates. Subsequent SIBEC second approximation estimates of productivity have commonly continued to be higher than forest inventory estimates of productivity for old-growth stands (Mah and Nigh, 2003).
Site series are, by definition, relatively uniform with regard to climate and soil conditions (Pojar, Meidinger and Klinka, 1991). Individual site series (e.g. ESSFxc2/08 'Bl - Valerian - Globeflower') are thus polygons on the landscape with an overall similar site quality. Since site index, and hence volume or biomass production, tends to be closely correlated with site quality, it follows that site index is predictably similar for a given tree species throughout the distributional range of any given site series, in the absence of localized site quality or biotic impacts (cf. SIBEC sample plot and tree selection criteria).
The sample plot and sample tree selection criteria have been designed to minimize bias, in order to support the development of reliable site index - site series relationships.