Predicting the dominance of planted and invading trees using site index curves

Abstract

We predicted the dominance of planted and invading trees using the site index and site index curves. The study area was Compartment No. 25 in the University of Tokyo Forest in Chichibu, Japan. Sixty 10×10 m plots were established in a plantation of hinoki cypress (Chamaecyparis obtusa). Six factors were calculated from a digital elevation model (DEM): altitude, slope angle, flow accumulation, the wetness index, shaded relief, and curvature. The maximum heights of hinoki cypress and invading hardwood trees were classified as explanatory variables by regression trees with these factors. The Richards function was fitted to the tree height growth of them from the tree analysis data. The site index curves for them were drawn for the values of the site index classified from the regression trees, setting the tree height growth curve expressed by the Richards function as a guide curve. Comparing all combinations of the site index curves for them, we showed how many years after invasion hardwood trees take to exceed the height of hinoki cypress.