THE MAXIMUM DENSITY CONCEPT APPLIED TO UNEVEN-AGED MIXED-SPECIES STANDS

In even-aged pure stands, the relationship between density and quadratic mean diameter of different stands can be described by a hyperbola, the coefficients of which depend allometrically on dominant height (Sterba's modified Competition Density Rule). From the equations describing these relationships the slope of Reineke's maximum density line can be calculated and (for a given data set) tested against the hypothesis that this slope is -1.605. Data from 134 even- and uneven-aged mixed species stands in northern Idaho and northwestern Montana showed that this slope depended on the skewness of the dbh1.5 distribution, which in turn was correlated with structural stand characteristics like ''unevenagedness'' and species mixture. The parameters of the extended Competition Density Rule were simultaneously estimated by nonlinear regression under an assumption relating asymptotic dominant height and maximum basal area by habitat type. Results demonstrated that both the maximum basal area at a given dominant height are higher in even-aged pure stands (with smaller skewness of the dbh1.5 distribution) than in unevenaged mixed stands. Furthermore, the differences in maximum stem number and maximum basal area resulting from differing skewness decrease with increasing dominant height. Large differences in maximum basal area can be shown between different habitat types and any given site index, thus demonstrating that habitat types can be used to distinguish yield levels sensu Assmann.