Insect Herbivory in a Eucalyptus maculata Forest on the South Coast of New South Wales

Abstract

In most years between 1977 and 1992, insect defoliation was negligible in a regrowth stand of E. maculata Hook. on the south coast of New South Wales. However, leaf consumption by winter–spring infestations of cup moth larvae accounted for c. 6%, 19% and 4% of the total leaf loss from the canopy in 1989–90, 1990–91 and 1991–92, respectively. During the most serious infestation of 1990, cup moth larvae produced 0.56 t ha^–1 of frass, equivalent to the consumption of c. 0.8 t ha^–1, or c. 0.5 m² m^–2 of eucalypt leaf (c. 12% of winter leaf area index). In early November 1990, shortly after the infestation, an assessment of insect defoliation in the crown of a dominant tree revealed that (i) 47% of the leaf population was damaged, (ii) a larger proportion of older than younger leaves was damaged, (iii) the proportion of damaged leaves increased down the tree-crown profile, and (iv) 13% of the potential leaf area was missing. In the absence of further insect attack, the process of canopy renewal (leaf production and leaf fall) reduced the proportion of damaged leaves to 23% by June 1991.