None of the other variables, age, site index, the dummy variable for thinning, and the measures of stand density were significant. The variances of the random effects were 0.012347 for the stand and 0.118556 for the tree respectively. The random effect of the stand was not significant (p > Wald_z = 0.278). The only stand variable, affecting leaf area turned out to be the dominant height, which can be understood as a compensatory
measure for age and site class, indicating the stage of development of the stand. Thus, we conclude that the stand effect is sufficiently described by the dominant height of the stands. In order PF-02341066 chemical structure to describe and for a better understanding of the relationship between leaf area and crown surface area the final model can Icotinib cell line be rearranged as: equation(15) LACSA=e1.024⋅CSA−0.365⋅dbh0.944⋅hdom−0.840Furthermore,
at a given dominant height, i.e., within a stand, the dbh can be understood as a measure for the social position (crown class) of a tree within the stand, which can be described as hdom/dbh. Inserting the ratio, hdom/dbh, into Eq. (15) results in: equation(16) LACSA=2.784⋅CSA−0.369⋅hdom0.104⋅hdomdbh−0.944now describing the leaf area per crown surface area as a function of crown surface area, dominant height as a compensatory measure for age and site class, and the hdom/dbh, the social position of the tree within the stand. From this equation the sensitivity of the LA/CSA ratio to the independent variables can be easily studied. An increase of dominant STK38 height by 10% leads to an only 1% higher leaf area per crown surface area; an increase of 10% in crown surface area results in a decrease of this ratio by 3.5% and increasing the hdom/dbh ratio by 10% decreases the leaf area per crown surface area by 8.6%. Our findings confirm what many other authors stated, that sapwood area is a very precise measure for leaf area (e.g., Waring et al., 1982, Bancalari et al.,
1987 and Meadows and Hodges, 2002). Within stands, the sapwood area was a better indicator for leaf area, the nearer to the base of the crown it was determined (Table 3). However, the coefficients of the log-linear relationship between leaf area and sapwood area differed significantly between the investigated stands (Table 4). The sapwood area at breast height, which can be more easily determined than those higher up on the bole, exhibited the largest differences of the coefficients between the stands. This result is in line with several other studies where the stand was identified as a driver causing differences in the ratio leaf area to sapwood (Binkley and Reid, 1984, Long and Dean, 1986 and Coyea and Margolis, 1992).