Use of Growth Rings to Determine Past Phasmatid Defoliations of Alpine Ash Forests

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Abstract
The characteristic pattern in the composition of the growth rings of alpine ash which defoliation by the phasmatid Didymuria violescens produces is used to estimate the past occurrence and severity of defoliation by the phasmatid in 25,000 acres of alpine ash at Bago State Forest. Growth rings in discs cut from 157 sample trees located throughout the ash area indicated that defoliation had occurred every two years, beginning as a small discrete patch in 1951, extending over the whole forest by 1961, and contracting rapidly in 1963 and 1965. The effect of the defoliation on current annual radial increment ranged from an estimated reduction of one per cent in 1951 to 56 per cent in 1962, and averaged 20 per cent over the outbreak period of 16 years.