THE EFFECT OF DEFOLIATION BY DIDYMURIA VIOLESCENS (PHASMATIDAE) ON THE GROWTH OF ALPINE ASH

Abstract

Moderate defoliation of pole-stage alpine ash by the phasmatid, Didymuria yiolescens (Leach), during summer 1962–63 had no significant effect on diameter increment during the period of attack. Its effect was most pronounced during the period of late-wood production in the following autumn and winter, when the diameter increment was only 11 per cent, of that in controls. There was a good recovery of crowns during the following summer (1963–64), when phasmatids were very scarce, but the diameter increment was reduced by about 50 per cent. Saplings of alpine ash that were artificially defoliated by hand, in January and May. at two different intensities, showed that the diameter increment decreased with increasing defoliation, and defoliation in January resulted in greater tree mortality.