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Herbivory in Australian Rain Forests, with Particular Reference to ...

Herbivory in Australian Rain Forests, with Particular Reference to ...

Herbivory in Australian Rain Forests, with Particular Reference to

Herbivory in Australian Rain Forests, with Particular Reference to theCanopies of Doryphora sassafras (Monimiaceae)Margaret D. LowmanBiology Department, Williams College, Williamstown, Massachusetts 01267, U.S.A.ABSTRACTHerbivory in the canopies of Australian rain forest trees was measured from 1979-1988, and their associated leafgrowth dynamics quantified. Levels of defoliation were compared on several spatial scales: within and among canopiesof one species (Doryphora sassafras Endl.) (Monimiaceae), between species, and among sites, light, and height. Sassafraswas distributed throughout all rain forest formations in New South Wales, from the upper elevation cool temperatesites to the warm temperate and lowland subtropical sites. In addition, two methods of measuring herbivory werecompared. One method (long-term observations) measured losses up to four times greater than estimates obtainedby the second and more conventional technique of harvesting leaves to measure missing surface areas (discretesampling). Leaf area losses in Australian rain forests averaged between 14.6 percent and 27 percent, ranging from3.3 percent to 41 percent with species and site. The factors contributing to this variability within Australian forestsand compared to studies elsewhere are discussed.Key words:Australia; Dotyphota; herbivory; leaf area; leaf growth; rain forest; tropics; patchiness.THE RESOURCE AvAILABILIn of green foliage for herbivoresin forests appears enormous, particularly inrain forests, with their tall trees and multilayeredcanopies. But, while it is clear that different treespecies differ in quality of resource for herbivoresand in herbivory rates (e.g., Coley 1982, Lowman1986b), the variation in both availability and utilizationof this resource within and among canopiesof different rain forest trees has not been quantifiedother than by general, short-term surveys (e.g., Odurn& Ruiz-Reyes 1970, Leigh & Windsor 1982, Proctoret a/. 1983). Most studies have involved thediscrete harvest of lower canopy leaf samples andsubsequent measurement of missing surface area, afairly simplistic approach to a complex interaction.The variability of biological and environmental conditionsthroughout the complex vertical distributionof rain forest foliage may affect leaf palatability.These factors include light, height, aspect of canopyregion, age, species of tree, elevation, and other siterelatedcharacteristics. Some of these factors (e.g.,height, light, species) may also act as constraints tothe distribution of herbivores.In this study, spatial and temporal factors affectingherbivory and related leaf growth dynamicswere quantified over ten years, a relatively longtermstudy in scientific terms, albeit short in termsof rain forest phenology. Several questions wereaddressed, in particular: How is the apparent vastgreen resource of leaves partitioned among herbivores?What factors contribute to the patchiness inherbivory of one species in particular (D. sassafras)both within and among different Australian rainforest canopies?My results indicate that general surveys of leafarea losses in tree canopies may seriously underestimatethe actual herbivory, due both to the logisticalproblems of reaching upper foliage and to thetime constraints of field research. This long-term,comprehensive study attempts to quantify inter- andintraspecific variability in herbivory of some Australianrain forest trees, and also to compare theseresults with other short-term studies.METHODSSITES AND SPECIES s~~~c~ro~.-Research was conductedin the three major types of rain forest inNew South Wales: subtropical, cool temperate, andwarm temperate. Two sites of each formation werecompared between the northern (Dorrigo or NewEngland National Parks) and southern (Royal NationalPark) regions of the state. Site descriptionsand profile diagrams are listed elsewhere (Lowman1986a). Five species of canopy trees were measuredfor both leaf growth dynamics and herbivory from1979- 1988, including Doryphora sassafras Endl.(Monimiaceae), Dendrocnide excelsa (Wedd.) Chew(Urticaceae), Nothofagus moorei (F. Muell.) (Fagaceae),Toona australis (F. Muell.) (Meliaceae), andCeratopetalum apetalum D. Don (Cunoniaceae).

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