Height growth and site index of trembling aspen in north central Ontario

Abstract

Height-growth and site-index curves were developed for estimating site quality of trembling aspen {Populus tremuloides Michx.) in north central Ontario. These curves were developed from stem analysis data of dominant and codominant, uninjured aspen trees obtained from 89 plots covering a wide range of site quality in north central Ontario. The actual height-growth patterns were modelled using several non-linear biological growth models: Chapman - Richards function, modified Weibull function, Monserud logistic function and an expansion of the Chapman - Richard function. In addition, a new height-growth model was developed using a similar approach to that of Cieszewski and Bella. Height-growth patterns of aspen varied with level of site-index. Height growth curves show an almost linear growth pattern for poor sites (SI < 16 m) to a highly curvilinear pattern on good sites (SI > 24 m). Medium sites (S116-24 m) show a rapid linear surge of height growth before 40 years followed by a slowing curvilinear pattern. Height-growth curves, site-index curves and a site-index prediction equation were constructed from trembling aspen stem analysis data. Goodness of fit tests were computed using a modified Chi-square test. In addition, the accuracy of the height-growth curves, site-index curves and site-index prediction equation were tested using independent stem analysis data from 19 plots supplied by the Ontario Ministry of Natural Resources. Comparisons with the independent data source shows close agreement; the 95% site index error prediction interval for the site-index curves and the site-index prediction equation are 0.19 ± 1.37 and 0.21 ± 1.35 respectively.