In addition to site index data available at the 10 sites, we
utilized field measurements of tree heights and total age to
estimate site index from McArdle’s (1961) yield tables on 5263
FIA survey plots in Oregon as described in detail by Swenson
et al. (2005). The FIA plots are not as representative of
surrounding lands as the calibration sites, nor are they as
precisely located, being offset by 1–3 km to satisfy concerns of
private land owners: