Leaf consumption by insects in three Eucalyptus forest types in Southeastern Australia and their role in short-term nutrient cycling.

Abstract

Leaf consumption by insects in three Eucalyptus forest types (E. delegatensis, E. dives and E. pauciflora) in the Brindabella mountains, A.C.T., was studied over a two year period. Foliage consumption was calculated using two methods: (1) sampling of foliage repeatedly through the season and measurement of leaf area loss due to insects and (2) calculation of the mass of leaves consumed, based on frass-fall measurements. Intensive sampling of tree canopies for defoliating insects was also carried out in all three forest types. Defoliation, as estimated by measurement of leaf area loss, did not exceed 10% in any of the forest types except on current year's foliage for two months of one year in the E. dives and E. pauciflora stands. Insect consumption of foliage in all three forest types, as calculated from frass-fall measurements, varied from 2-3% of annual leaf production. The nitrogen, phosphorus, and potassium passing through insect bodies and frass was less than 4% of the total amount falling in other litter. The small amount of leaf consumption occurring in these stands and the small amount of associated nutrient transfer indicate that insect defoliators at low population levels do not affect forest productivity or have significant effects on short term nutrient cycling.