According to Assmann (1970) volume increment results from the combined effects of basal area increment, height increment and also a change in the form factor. However, for Norway spruce at greater ages he found the form height (product of breast height form-factor by total tree height) to remain constant. For the sample trees

we plotted AVI versus the annual basal area increment (ABAI) on a double logarithmic scale and found a strictly linear relationship which significantly differed between the plots. Total tree height from the end of the period (h) could significantly improve this relationship. Hence we found a separate log-linear equation of the form ln (AVI) = α  0 + α  1 · ln(ABAI) + α  2 · ln(h) for every plot that explained 93.5–98.2% of the variation in ln(AVI). For the back-transformation to the non-logarithmic-form PCI-32765 datasheet AVI = exp  α0 · ABAIα1 · hα2 a plotwise correction factor λ = Σ (AVIobserved  )/Σ (AVIpredicted  ) had PI3K inhibitor to be applied. Total height, height to the base of the live crown and dbh (outside bark) were measured from every tree at the end of the period. Also every tree got cored and the 5 year radial increment was measured in the laboratory. With these measurements we could calculate ABAI from every tree, however first

we had to establish an equation to calculate the bark thickness (BT) for every tree, which had to be deducted twice from the dbh (outside bark). We used the data from the stem discs at 1.3 m height, Niclosamide where bark thickness was also measured, and fitted a nonlinear equation of the form BT=0.589+0.157RoB, with the bark thickness (BT) and the radius outside bark (RoB) (R2 = 0.768). Comparing

AVI for the thinned and the unthinned treatments in each pair of plots showed no significant difference in variances for the mature and the immature stands, but significant differences for both pole-stage pairs. However, a two sample Welch t-test, which allows for unequal variances, showed significant differences for all pairs, with the thinned treatment showing a higher mean AVI than the unthinned treatment. Maestra, a three-dimensional array model which couples stomatal conductance, photosynthesis, and light absorption provided the mathematical modelling framework (Wang and Jarvis, 1990a). In this study, only photosynthetically active radiation absorbed by individual tree crowns was critical, where Maestra uses an array of tree crowns to calculate radiation absorption from leaves by considering direct beam, diffuse, and scattered beam irradiance (Norman and Welles, 1983). The radiation submodel of Maestra has been validated successfully for Sitka spruce (Picea sitchensis (Bong.) Carrière) and Monterey pine (Pinus radiata D. Don) ( Wang and Jarvis, 1990b) and also applied to Picea abies in several studies ( Jarvis, 1999, Medlyn et al., 2005 and Ibrom et al., 2006).