Yonghe Wang

Modified site index equations for major Canadian timber species

Abstract Modified site index equations for major Canadian timber species were developed based on constrained biological and the Weibull-type growth functions. The resulting equations satisfy the definition of site index, height being exactly equal to site index at index age, with only slight loss of accuracy compared with the unconstrained model used previously. Direct estimate of site index from stand height and age is accomplished through numerical method rather than by a separate regression equation, as was done earlier.

A bi-segmental curve fitting approach to improve the accuracy of site index equations

Abstract Following Newnhams suggestion, Payandeh and Wang remondified Eks base-age specific site index equation so as to satisfy the definition of site index, i.e. to meet the condition of H = S at index age. However, imposing such a constraint adversely affects the accuracy of the parameter estimation of the model, i.e. it results in a larger sum of squared error. A bi-segmental curve fitting procedure is proposed here to improve the accuracy of Payandeh and Wangs model when fitted to stem analysis data.

A base-age invariant site index model for aspen stands in north central Ontario

Abstract A time series version of the Chapman-Richards function was used to develop a base-age invariant site index model for aspen ( Populus tremuloides Michx.) stands in north central Ontario. The model developed was compared with a base-age invariant and a base-age specific site index model. It proved to be superior to both for estimating the height at Age 40 years from all other heights, but somewhat less accurate than the base-age specific model for estimating all other heights from the height at Age 40 years. The time series version of the Chapman-Richards function described here may be used to develop base-age invariant site index models for other species.