NE-FIA Tree Taper Study:
Current Status and Future Work
James A. Westfall, Research Forester
Forest Inventory and Analysis
Northeastern Research Station
Newtown Square, PA 19073
Phone: (610) 557-4043
Fax: (610) 557-4250
Email: jameswestfall@fs.fed.us
ABSTRACT
The northeastern unit of the Forest Inventory and Analysis program (NE-FIA) is engaged in an ongoing
project to develop region-wide tree taper equations. Sampling intensity is based on NE-FIA plot data and is
stratified by species, diameter class, and height class. Tree form measures are obtained with a Barr &
Stroud optical dendrometer. Data collected to-date permits some research on taper model development.
Thus far, this research has largely been aimed at evaluation of existing model forms (and hybrids thereof),
and incorporation of mixed-effects parameters to account for correlations among measurements. During
the upcoming leaf-off season, additional taper data will be collected in the northeast region.
Due to the nondestructive nature of data collection, only outside-bark diameter (dob) measures are
accessible. However, NE-FIA has traditionally reported tree volumes based on inside-bark diameter (dib)
values. To facilitate these calculations, bark thickness estimates are being developed from wood utilization
studies. These data and results from other studies indicate that bark thickness is highly correlated with
outside-bark diameter (dob). For some species, this results in a relatively constant dib/dob ratio along the
length of the bole. However, in other species, the ratio of dib/dob decreases as dob gets smaller, suggesting
that the application of ratios may not be suitable for all species. When fully implemented, the bark
thickness/taper equation system will provide a wide range of analytical flexibility for tree species occurring
in northeastern forests, and may reduce or eliminate the costs of collecting merchantable heights.