Biomass Energy Data Book: Edition 4 - Full Document - Center for ...

Section: Appendix A
Stand Level Biomass Estimation
Biomass estimation at the individual field or stand level is relatively straight forward, especially if
being done for plantation grown trees that are relatively uniform in size and other characteristics. The
procedure involves first developing a biomass equation that predicts individual tree biomass as a
function of diameter at breast height (dbh) , or of dbh plus height. Secondly, the equation parameters
(dbh and height) need to be measured on a sufficiently large sample size to minimize variation
around the mean values, and thirdly, the mean individual tree weight results are scaled to the area of
interest based on percent survival or density information (trees per acre or hectare). Regression
estimates are developed by directly sampling and weighing enough trees to cover the range of sizes
being included in the estimation. They often take the form of:
ln Y (weight in kg) = -factor 1 + factor 2 x ln X (where X is dbh or dbh 2 +height/100) Regression
equations can be found for many species in a wide range of literature. Examples for trees common
to the Pacific Northwest are provided in reference 1 below. The equations will differ depending on
whether foliage or live branches are included, so care must be taken in interpreting the biomass data.
For plantation trees grown on cropland or marginal cropland it is usually assumed that tops and
branches are included in the equations but that foliage is not. For trees harvested from forests on
lower quality land, it is usually recommended that tops and branches should not be removed (see
reference 2 below) in order to maintain nutrient status and reduce erosion potential, thus biomass
equations should assume regressions based on the stem weight only.
Sources:
(1) Briggs, D. Forest Products Measurements and Conversion Factors. College of Forest Resources
University of Washington. Available as of 9/29/2008 at:
http://www.ruraltech.org/projects/conversions/briggs_conversions/briggs_book.asp
(2) Pennsylvania Department of Conservation and Natural Resources. Guidance on Harvesting
Woody Biomass for Energy in Pennsylvania. September, 2007. Available as of 9-29-08 at:
http://www.dcnr.state.pa.us/PA_Biomass_guidance_final.pdf
Biomass Energy Data Book – 2011 – http://cta.ornl.gov/bedb