Hybrid sweetgum volume equations for a north Louisiana afforested site following herbicide applicationThis article is part of a larger document. View the larger document here.
Investigating the suitability of hybrid sweetgum (Liquidambar formosana x styraciflua) as a biomass feedstock for Western Gulf forest industries requires information on stand yields. Using data from 2-year-old (1-0 seedling stock) hybrid sweetgum trees, equations were developed to estimate stem volume, comprising both wood and bark, on an afforested site in north Louisiana. Dummy variable statistical analyses concluded all data could be pooled across herbicide and varietal treatments to produce a single model system. Eighty-eight trees were measured for stem diameter at 1-foot increments from the groundline, and total stem height was determined from pole measurements. The volume of each section was calculated using Smalian’s formula
and summed to provide total stem volume. Eighty trees served as a model development set, with eight trees randomly withheld for validation. The square of groundline diameter (DG2) alone was determined to sufficiently predict stem volume, which could save managers time and effort when constrained by scarcity of resources at this stage of stand development. The validation set suggested our model over-predicted stem volume of smaller trees and under-predicted larger trees. Mean absolute deviation was 0.003 cubic feet, or 17 percent. Including tree height, form, and/or other variables as age increases will likely improve upon these estimates over time.