After calculating the site index of each sample plot, the
Chapman–Richards growth function (Eq. (2)) was fitted to the
data set of average dominant height, site index and age through
Gauss–Newton non-linear least squares regression analysis
(Daniel and Wood, 1980) executed by SAS statistical analysis
software NLIN procedure (SAS Institute Inc., 1989). In order to
test if the dominant height growth patterns are polymorphic, we
parameterized the full Chapman–Richards model with parameters
k and r depending on site index (Eq. (3)).