Marschall et al., 2014
RESEARCH BRIEF 17
For red oak sawlogs, most value loss is due to lumber grade changes, not volume loss.
Expect minimal value loss for red oak sawlogs with fire damage less than 20 inches tall.
Regardless of fire-scar size, red oak sawlogs harvested within 5 years of injury will have little or no value loss.
In this study, researchers sought to determine how timber value was affected by fire damage to the boles of saw-log size trees. The lowest logs of fire injured red oaks were harvested and milled into dimensional lumber. Value losses due to fire injuries were tracked through the lumber grading and valuation processes.
The economic loss due to fire-caused injuries (i.e., fire scars) was measured in terms of volume and value in the butt logs (only) of 88 red oak (Quercus velutina, Q. rubra, and Q. coccinea) trees harvested from prescribed fire units in southern Missouri. Fire scar dimensions and tree sizes (diameter at breast height (DBH)) were measured prior to tree harvest. Trees with varying diameter, external fire damage, and fire-scar residence time (time between fire damage occurrence and tree harvest) were selected. DBH ranged from 9.5 – 24.8 inches; fire-scar heights ranged from 6 to 154 inches; and fire-scar residence time was a maximum of 14, minimum 2 years. The number of logs above the butt log (upper logs) were tallied and the small end diameter measured. Lumber grade changes and volume losses due to firerelated injuries were tracked on individual boards (n=1298, 7754 board feet). Lumber values were assigned using rough, green lumber values reported by the Hardwood Market Report (April, 2011).
Overall, value and volume losses were low. Volume loss per fire-scarred log averaged 3.9%, with the value loss average per butt log at 10.3%. The average value loss decreased to 7.1% if estimated values for the upper logs were considered. A large amount of fire-caused defect was removed incidentally during the milling process (see figure). Statistical models were developed that predict log value loss from tree size, fire scar size, and fire-scar residence time. A reference table (next page) was developed to estimate value loss per butt log from tree size (DBH) and fire scar height and depth. Depending on fire scar height, annual value loss is estimated to range from 0.5% to 1.3%. For example, a fire scar 40 inches in height is expected to lead to about 10.5% value loss to the butt log if the tree is harvested 14 years after the fire damage occurred.
Trees that were mid-sized (i.e., pole size) when injured were most likely to experience higher value loss, while trees that were small or large in diameter at time of injury typically experienced little or no value loss. If fire damage is less than 20 inches in height and/or less than 20 percent basal circumference is injured, then little value loss occurred over 14 years. If these thresholds were exceeded, then value loss was likely. Regardless of fire-scar size, value loss was very low if trees were harvested within five years after fire damage.
Study authors note that Brose and Van Lear (1999) found that implementing relatively simple practices (i.e., directional felling and lopping of excessive fuels near crop trees) in a shelterwood harvest accompanied by prescribed fire can minimize damage to residual trees, indicating that fire-scar heights, and timber quality losses can be effectively minimized.
The findings from the study summarized here are applicable only for red oak trees which are at least 8 inches DBH at time of fire damage and a log grade typical for dimensional lumber utilization (i.e., ‘sawlogs’) as opposed to higher value products such as veneer or staves, and with fire-scar residence times not greater than 14 years.
Percent value loss on standing timber per butt log, based on fire-scar measurements and tree diameter.
Joseph Marschall, Richard Guyette, Michael Stambaugh, Aaron Stevenson (2014) Forest Ecology and Management 15: 182-189
FOR FURTHER READING
Brose and Van Lear (1999) found that implementing P. Brose, D. Van Lear, 1999. Effects of seasonal prescribed fires on residual overstory relatively simple practices (i.e., directional trees in oak-dominated shelterwood stands. South. J. App. For., 23 (2), pp. 88-93.
The Oak Woodlands and Forests Fire Consortium seeks to provide fire science to resource managers, land owners and the public about the use, application, and effects of fire in the region. www.oakfirescience.com
This research brief was funded by The Joint Fire Science Program. www.firescience.gov