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Variations in coniferous wood moisture estimation by electrical techniques

University of British Columbia

Electrical moisture meters have certain advantages over other techniques for determining wood moisture content. Variability associated with such meter measurements has not been thoroughly investigated. This study examined some sources of this variability that arise between species, between trees and within stem which relate to wood electrical properties. Wood samples included portions of seven recently felled full-tree coniferous logs. This provided comparison as: between species (lodgepole pine (Pinus contorta var. latifolia Engelm.), western white spruce (Picea glauca (Moench.) Voss.), Douglas-fir (Pseudotsuga menziesii var. glauca-(Beissn.) Franco) and subalpine fir (Abies lasiocarpa (Hook.) Nuttl.); within species (four lodgepole pine); and within individual stem (four to five in height series, two to five in radial series). In addition, one lodgepole pine stump displaying reaction wood was included. Direct current resistance (Delmhorst RC-1B) and power-loss (Moisture Register, Model L) meters were used to estimate moisture. Radial specimens (2.5 cm x 2.5 cm x 40 cm) were subdivided into four 10 cm lengths and placed side by side to expose radial or tangential faces that accommodated the power-loss meter head. This provided a novel way for collecting and replicating data with regard to position within stem, as well as minimizing the influence of defect. Specimens were tested at 21°C for nominal moisture levels ("green", 19% and 12% for resistance meter, 19%, 12% and 6% for power-loss meter) and meter readings were compared with calculated moistures. Direct current resistance moisture meter measurements did not appear to be related to wood specific gravity. Between tree measurements within lodgepole pine showed less variation than measurements between the four species. Within tree height contributed little to variation, but radial-direction did provide discernible variation, especially at low moisture contents. Precision of the resistance measurements was good, but accuracy was poor. Power-loss type moisture meter measurements were influenced by specific gravity. Regression lines of meter readings and moisture content approached quadratic functions, with the notable exception of Douglas-fir. Regression equations containing moisture content, moisture content squared and specific gravity as independent variables accounted for 92% of the total variability for all seven trees studied, and 96% among the four lodgepole pine trees. Between species variations in power-loss meter measurements were prominent and highly significant. There were also significant differences for between tree measurements. Within tree height contributed little, but radial direction did contribute to variation. Exposure of radial or tangential faces gave significantly different readings. Better understanding of the contribution of such variables could increase usefulness of moisture estimations by electrical meters.

Text

2010-01-29

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http://hdl.handle.net/2429/19346

Forestry

University of British Columbia

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