Systematic Error Trends of Existing Crown
Biomass Equations for the Major
Commercial Conifers of the Inland
Northwest
Brian R. Turnquist
M.S. Candidate
University of Montana
College of Forestry and Conservation
What kind of prediction equations are out there?




National, Regional, and Local
Tree and stand level
Predictions for tree-level component weights such as branches, foliage,
stem, stem bark, etc.
Found in research papers, technical reports
 Papers which act as compilations of many biomass equations
 Jenkins et al. (2004), TerMikaelian & Korzukhin (1997)
Weight and Density of Crowns of Rocky Mountain Conifers
Brown (1978)

Describes crown allometries for 11 species

Weighed the entire tree crown, and estimated
component proportions
 Used data from 2 previous studies (Storey
(1955) & Fahnestock (1960))

Produced equations which use DBH, height,
and crown ratio (these variables are
sometimes log transformed)
National-Scale Biomass Estimators for United States
Tree Species
Jenkins et al. (2003)
 Provides prediction equations for
species groupings for use across the
country
 Trees were not sampled, rather a
compilation of prediction equations
was used

Pseudo-data was created,
and regression equations
produced
Methods
Analysis of differences between equation predictions
and RBS estimates
RBS field estimate
Brown’s equation prediction
Jenkins’ equation prediction
Positive differences = under-prediction
Negative differences = over-prediction
Results
Sampling Region
Site Conditions
Ponderosa Pine
Differences between equation predictions and RBS
field estimates for ponderosa pine
Differences from Brown (1978) equation predictions
DF
WL
LP
PP
Differences between equation predictions and RBS
field estimates for ponderosa pine
Differences from Jenkins (2003) equation predictions
DF
LP
WL
PP
Discussion
Differences in Crown and Stem Definitions
Storey et al. (1955)
2 lbs
12 lbs
12 inch
Conclusions




These equations are biased, and shouldn’t be used without these bias correction
models
Some of the bias can be associated with a few differences in sampling methods,
methods of equation creation
The amount of bias present could have immense impacts on management
decisions
Creation of new equations for use in this region is an appropriate next step
Acknowledgments
David Affleck
John Goodburn
INGY members
Spokane Tribe of Indians
Plum Creek
Salish-Kootenai Tribes
Coeur d’ alene Tribes
Joint Fire Science Program
Ryan, Jamie, Kagan, Eric,
Jesse, Shane, Alex
RBS Sampling Schematic
Stem
Diameter
Branch
Diameters
x1,0
x1,2
x1,1
x1,4
x1,3
1 meter