Year of Award


Document Type


Degree Type

Master of Science (MS)

Degree Name

Resource Conservation

Other Degree Name/Area of Focus

Forest Biometrics

Department or School/College

College of Forestry and Conservation

Committee Chair

David L.R. Affleck


biomass, crown mass, prediction bias


University of Montana


Several crown biomass equations have been developed for local, regional, and national scale biomass estimation across the United States. The prediction equations most commonly used were developed by Brown (1978) and Jenkins et al. (2003). Because of the widespread application of these equations for managerial and scientific use in the inland northwest, USA, crown mass data for several important conifer species were collected and used to examine the direction and magnitude of bias associated with predictions made from the diameter-based equations of Brown (1978) and Jenkins et al. (2003). A total of 140 trees of 4 different conifer species were sampled, delivering 725 individual unbiased estimates of total crown mass. Regression analyses were run on differences between crown mass estimates and the Brown (1978) and Jenkins et al. (2003) equation predictions to determine whether any bias was present. Results of the regression analysis determined that bias was present in both equation sets. Brown’s (1978) equations were found to over-predict the crown mass of ponderosa pine (Pinus ponderosa) and western larch (Larix occidentalis), and under-predict the crown mass of Douglas-fir (Pseudotsuga menziesii) and lodgepole pine (Pinus contorta). Further, it was found that the magnitude of the bias increased with diameter at breast height (DBH) for all species but western larch. The Jenkins et al. (2003) equations were found to over-predict the crown mass of Douglas-fir and western larch, but under-predict for ponderosa pine, while no significant bias existed for lodgepole pine. Again, the magnitude of bias was found to increase with DBH. Bias correction models are presented which, if used within the inland northwest, could potentially increase the accuracy of these equations.



© Copyright 2012 Brian Robert Turnquist