Detection of discoloration and decay in living trees and utility poles

A method is described for detecting discoloration and decay in living trees and creosoted utility poles. The method and devices have come from research involving many people over a seven-year period. A probe was inserted into a 3/32-inch (2.4 mm) diameter hole made by drill bits 8 inches (20.32 em) and 12 inches (30.48 cm) long mounted in a portable, light-weight, battery-operated drill. The probe was attached by a flexible cable to a portable, light-weight, battery-operated meter, a "Shigometer", that delivered a pulsed electric current and measured resistance to it. As the probe was inserted into the hole, the meter measured in ohms the resistance of the wood in contact with the probe tip. As the probe was pushed inward, if the tip contacted only sound tissues, slight changes in resistance were measured. When the probe tip passed from sound wood to discolored or decayed wood there was an abrupt decrease in resistance. The magnitude of the decrease in resistance indicated the degree of discoloration or decay. The depth of the probe when the needle on the meter began to decrease indicated the position of the discolored or decayed wood. D ISCOLORATION and decay are major action can be made: remove the tree or pole, causes of damage to living trees, utility lower the timber value of the tree, increase poles, and wood products throughout the world. Too often the defects are not detected until i t is too late: a tree falls on a house, car, power line, or person; a bridge collapses; a tree that appeared valuable for timber turns out t o be valueless because of discolored and decayed wood on the inside; or a utility pole falls during a storm or while being climbed. The wood has been weakened by decay. Discoloration and decay of wood are caused by bacteria and fungi that digest wood inside of trees and poles, hidden from view. In a living tree, wounds start the processes; microorganisms dften invade the exposed wood and discoloration and decay may follow when conditions are proper (for details on discoloration and decay processes see Shigo and Larson 1969). In utility poles, decay microorganisms are sometimes active in the poles before they are put in service, or microorganisms may invade a t any time later when conditions are proper (for details on decay process in poles see Eslyn 1970). In North America, nine species of fungi cause most of the decay in utility poles (Eslyn 1970). I n living trees wounds should be prevented. When wounds are inflicted they should be treated properly (Shigo and Wilson 1971 ) . Poles should be treated properly with preservatives to prevent decay. But many times even when proper measures are taken for prevention, some microorganisms still invade and discoloration and decay develop. Then early detection of discoloration and decay become all-important. The earlier discoloration and decay are detected, the earlier a decision on tree vigor by pruning, fertilizing, watering, etc. The need for a method of detecting decay in trees and utility poles has been long recognized and research has been done with X-ray units (Eslyn 1959), ultrasonics (Miller et al. 1966), and a needle that measures resistance to pressure (Zycha and Dimitri 1962, Eslyn 1968). Eslyn (1 968) reviews other methods for detecting decay in utility poles. The methods and equipment now available have not been accepted widely and put into practice, especially in living trees. The equipment is either too expensive, not easily portable, or not accurate, or the methods require a high degree of training. And, a t best, they detect advanced decay and not incipient decay and discoloration. A new method of detecting discolored and decayed wood in living trees was described by Skutt et al. (1972). The basic information for the method came from research on the electrical properties of wood (Lin 1965, 1967) and the pioneering work on electrical properties of trees by Fensom (1957, 1960, 1963, 1965). The new method is based on two principles: resistance to a pulsed current decreases as concentrations of cations increase in wood; and as wood discolors and decays the cations potassium, calcium, manganese, and magnesium, increase (Shigo and Sharon 1970, Tattar et al. 1972, Shortle and Shigo 1973, Safford et al. 1974). As wood decays, cations increase and resistance decreases. Skutt e t al. (1972) and Tattar et al. (1972) showed that the method detected discolored wood and decayed wood in living trees when the wood was MATERIALS AND METHODS above the fiber-saturation point (approximately 30 percent W/W) .The method not only detected discolored and decayed wood but indicated the degree of tissue deterioration. Skutt et al. (1972) reported these results from experiments that used a meter first constructed by Ronald M. Lessard.l The measurements were made with steel nails insulated except for their tips. As two nails were driven parallel a t 2 cm apart into a tree, the resistance to a ~u l s ed current of the wood between the nail tips was measured. Measurements were also made on freshly cut wood sections with the nails and with needle probes of the type used for making moisture readings in wood." Although the reports on the method showed that discolored wood and decayed wood could be detected accurately in living trees, two important weaknesses kept it from being accepted for wide use in the field: only expensive, fragile laboratory models of the meter were available, and the nail probes and other probing methods were not practical. This paper reports a method of detecting discolored and decayed wood in living trees and creosoted utility poles that uses a relatively inexpensive, durable meter with a printed circuit, manufactured by Northeast Electronics Corporation, Concord, New Mamphire,^ and an inexpensive, single probe developed by the second author.": The method and devices have been developed through the efforts of many people over a 7-year period. The Shigometer The meter manufactured by Northeast Electronics Corporation has a circuit similar to that described by Skutt et al. (1972). The meter is small and light in weight (fig. 1). The printed circuit makes it reliable and durable for field use. I t is powered by six 1.4 volt batteries. (Newer models will use 1.5 volt batteries also). I t has scales of 50 and 500 K ohms. Both scales and zero can he adjusted by front panel knobs." Figure I .-Pulse resistance meter, "Shigometer," twisted wire probe, and drill for detection of discolored and decayed wood in trees and utility poles.