Factors influencing electrical resistance in stems of Eucalyptus obliqua, E. globulus ssp. bicostata and E. viminalis.  G. A. Kile, J. D. Kellas and R. G. Jarrett.  August 1983.  12 pp. (unpubl.)

SUMMARY

Electrical resistance (ER) characteristics of the cambial zone tissues of healthy, approximately 30 or 100-year-old Eucalyptus obliqua L'Hérit. (messmate stringybark), E. globulus ssp. bicostata (Maid. et al.) Kirkp. (Gippsland blue gum) and E. viminalis Labill. (manna gum) were determined using a pulsed, direct-current, resistance meter (Shigometer) by inserting insulated or uninsulated stainless steel electrodes through the bark.

Results using both types of electrodes were positively correlated though insulated electrodes were more precise. Mean ER was about 15% and 65% higher in E. obliqua than in E. globulus ssp. bicostata when measured with insulated and uninsulated electrodes respectively. A seasonal pattern of variation in ER was evident in both species and was correlated with growth rate and maximum air temperature on the day of measurement. ER was negatively correlated with diameter, live bark thickness and growth rate. When trees were classified into high- and low-ER classes using the median resistance value, trees in the lower ER class had a significantly faster growth rate and greater live bark thickness. Differences in live bark thickness between trees influenced ER readings with both types of electrodes (even after allowing for differences in diameter), though the effect was

reduced with insulated electrodes, particularly for E. globulus ssp. bicostata.

ER values could be used to estimate live bark thickness and to rank the relative growth rates of trees of these species.

Also published:

Kile, G.A., Kellas, J.D. and Jarrett, R.G. (1982) Factors influencing electrical resistance in stems of Eucalyptus obliqua, E. globulus ssp. bicostata and E. viminalis.  Aust. For. Res. 12: 129-38.