Regional Stem Taper Equations for Eleven Conifer Species in the Acadian Region of North America: Development and Assessment

Abstract

Taper models to predict upper stem diameters, as well as total tree volume, are presented for 11 major conifer species in the Acadian Forest Region of North America. The Kozak (2004. My last words on taper equations. For. Chron. 80:507‐514) Model 02 taper equation was used as the base model form. A nonlinear mixed-effects modeling approach was used to account for autocorrelation present among multiple stem analysis observations collected from the same tree. Results show that fitted taper equations can accurately predict both stem form and volume across a range of conditions. The taper models generally had slightly lower bias and root mean square error than the commonly used regional Honer refitted volume equations (1965. A new total cubic foot volume function. For. Chron. 41:476‐493). The mean absolute bias was reduced up to 28% for certain species using the fitted taper equations compared with the refitted Honer (1965) equations, although the refitted Honer's models are also quite accurate where total stemwood volumes are needed. Independent validation data sets were used to further confirm reliability and accuracy of fitted taper models in predicting tree volume. These data sets indicated that the equations performed well, in general, but were slightly biased in certain thinned stands and in some New Brunswick ecoregions. Additional data are needed to confirm this and potentially improve model behavior. Overall, the models will be useful for predicting both stem form and merchantable and total volume.