An empirical approach to the analysis of forest stratification

Natural forest communities are made up of different overlapping elementary subpopulations consisting of individuals of different species and ages. To stratify the individuals of a forest stand into elementary subpopulations by using tree height records, a graphical method was empirically proposed employing a derivative of Pearson's type VII distribution as a basis. Arranging all of the individual trees in a stand in the descending order of their height (x), and introducing the rank (N) of any individual in the ordered ranking ofx, finite difference (n) ofN and three values ofx, i.e.,x(N), x(N−n), andx(N+n) labelled byN, N−n, andN+n, respectively, the proposed method used the linear relation betweenx(N) and [x(N−n)+x(N+n)]. On thex(N) vs.[x(N−n)+x(N+n)] diagram, the relation between both the variables could be approximated by a few segmental linear relations and used for stratifying the individuals of a forest stand into subpopulations. The method was applied for analyzing the vertical stratification in forest stands of different forest formations in Japan, Southeast Asia, Africa, and South America. The conclusions on stratification which resulted from the proposed method corresponded well to the conclusions on stratification from profile diagrams.