VARIABLE-FORM TAPER FUNCTIONS FOR 4 ALBERTA TREE SPECIES

The variable-form taper function was tested on a data set of 5074 tree s, consisting of jack pine (Pinus banksiana Lamb.), lodgepole pine (Pi nus contorta Dougl.), white spruce (Picea glauca (Moench) Voss), and t rembling aspen (Populus tremuloides Michx.), from Alberta. When compar ed with the results of tests performed on the same data using the vari able-exponent function and the segmented polynomial model, the variabl e-form model was found to be superior (based on residual mean squares) for estimating both upper stem diameter ratios and total stem volumes . The two pine species could be combined and a single taper function u sed without significant loss of accuracy. Stem form in two of the volu me sampling regions was significantly different from that in other reg ions of the province, but this may have been because the samples were not representative of the two regions. The variable-form function gave accurate and unbiased estimates of both merchantable height and merch antable volume.