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Abstract. This paper reports application of electric, ultrasonic, and georadar tomography for detection of decay in trees and their comparison with the traditional penetrometer. Their feasibility in arboriculture is also evaluated, critically considering some "open problems." The experiments were carried out in an urban environment on two plane (Platanus hybrida Brot.) trees. Both trees, after felling, showed extensive white rot in the central cylinder. The electric tomography revealed low resistivity zones roughly centered in the trunk. A comparison with the successively cut sections showed a fine correspondence to decayed areas and a strong correspondence between high moisture zones and low resistivity zones. Ultrasonic tomography demonstrated to be a very effective tool for the detection of internal decay, accurately locating the position of the anomalies and estimating their size, shape, and characteristic in terms of mechanical properties. With the georadar technique, the high contrast of electromagnetic impedance measured between the inner decayed section and the outside sound section allowed the detection of the interface between the sound and decayed section of the tree, using radar acquisition in reflection modality. The penetrometer profiles detected the low-resistance areas inside the two trunks.
Key Words. Tree stability; wood decay; tomography; ultrasound; electric; georadar.
The field guide for the visual tree assessment method (VTA) (Mattheck and Breloer 1994) suggests three different tools for detection and quantification of internal defects in trees: a sound impulse hammer, a penetrometer, and a fractometer. The visual tree inspection and its instrumental approach represented, without any doubt, a qualitative leap compared to the old and simple analysis made with the increment borer; in the meantime, the wide, practical use of VTA supported a strong interest in developing and applying more rapid and precise diagnostic techniques to detect defects in wood.
The methods for noninvasive evaluation analyze physical and chemical properties of wood: density (Beall 1996; Sandoz 1996; Bucur and Rasolofosaon 1998; Bucur 1999), electrical resistivity (Dubbel et al. 1999; Weihs et al. 1999), modulus of elasticity (Bucur 1995; Ross et al. 1997; Berndt et al. 1999), ionic concentration and moisture content (Zoughi 1990; Smith and Ostrofsky 1993). In recent years, there has been an evolution of the instruments applying the aforementioned techniques (Nicolotti and Miglietta 1998), often developed for engineering or medical applications,...