Effect of trunk circumference on resonance of trunk with the vibration resonance measuring device for five tree species

Abstract

Resonance measurement is considered to be available method for non-destructive diagnosis of trunk with no visual injury. Recently, the vibration resonance measuring device was developed, however, suitable trunk size for the device is not known. Then, relationship between circumference and vibration level at resonance of trunk was investigated for 14 individuals of five species (Betula platyphylla, Thuja occidentalis, Ginkgo biloba, Metaseqoia glytostroboides and Castanea crenata). Data were obtained by FFT analysis of vibration that occurred in the trunks with excitation. The vibration peak with requirement of 3 parameters (-90° < phase < 35°; vibration level > 12 dBV; lowest frequency) was designated as the resonance. Regardless of species, trunk circumference was inversely correlated with vibration level at the resonance (vibration level at resonance ＝ 41.52-19.32 × circumference: r ＝ 0.890), and was measured from 0.47 to 1.85 m. Thus, providing that vibration level at resonance is 0, the circumference is ca. 2.2 m. It is suggested that the vibration resonance measuring device used in the present experiment can measure trunks from 15 to 60 cm, but not larger than 70 cm in diameter.