FAMILY DIFFERENCES IN EQUATIONS FOR PREDICTING BIOMASS AND LEAF-AREA IN DOUGLAS-FIR (PSEUDOTSUGA-MENZIESII VAR MENZIESII)

Logarithmic regression equations were developed to predict component b iomass and leaf area for an 18-yr-old genetic test of Douglas-fir (Pse udotsuga menziesii [Mirb.] Franco var. menziesii) based on stem diamet er or cross-sectional sapwood area. Equations did not differ among ope n-pollinated families in slope, but intercepts assuming equal slopes d id differ for equations predicting leaf, branch, or bark biomass, or l eaf area. These results may be explained by family differences in part itioning between stemwood and bark and between stem and crown. Predict ions of biomass and leaf area based on equations developed in this stu dy differed from predictions based on equations from other studies by as much as a factor of two, suggesting that discretion is needed when applying equations to other sites at other stages of stand development and with other ranges of tree sizes.