Temporal and spatial variability in insect grazing of the canopies of five Australian rainforest tree species



Herbivory was measured monthly for 2 years on leaves of permanently marked replicate branches in the canopies of five Australian rainforest tree species. Variability in insect grazing activities was evident with respect to several factors:

  • 1leafage — young leaves were preferred over older leaf tissue:
  • 2height — leaves closer to ground level were more heavily grazed:
  • 3light — shade leaves were preferred to sun leaves:
  • 4time — grazing was intense during spring and summer months, and almost negligible during autumn and winter, but was cumulatively similar between the 2 years:
  • 5space — grazing was extremely variable on small spatial scales such as between individual leaves and branches, but similar where hundreds of leaves were pooled on larger scales between individual canopies and among geographically different sites:
  • 6tree abundance — grazing was heavier at sites where a tree species was common than where it was rare:
  • 7host tree species.

Long term observations resulted in higher but more accurate estimates of herbivory since it was possible to quantify losses of leaves totally eaten, an event not accounted for infield methods of discrete sampling whereby leaves are merely harvested and measured for area missing. Variability in herbivory is discussed in terms of plant-insect phenologies, plant defences, successional status of tree species, and insect behaviour.