An Assessment of Techniques for Measuring Herbivory: Is Rainforest Defoliation More Intense Than we Thought?

Abstract

Amounts of leaf material grazed by insect herbivores in Australian rainforest canopies were measured over 3 yr and 2 methods of assessment were compared. Long-term observations of labeled leaves and shoots measured losses up to 5 times larger than estimates obtained by the more conventional technique of measuring missing leaf area on single occasions. Long-term observations gave higher but more accurate rates since they incorporated a temporal component to grazing activities and also accounted for leaves totally eaten. Annual leaf area losses of 26, 22 and 14.6% were measured in Australian cool temperate, warm temperate and subtropical rainforests, respectively. Grazing in some plant communities may be higher than previously recorded from discrete measurements of missing-leaf area, resulting in an underestimation of the impact of herbivory.