Year

2009

Degree Name

Doctor of Philosophy

Department

School of Biological Sciences - Faculty of Science

Abstract

There is growing interest in the contribution of native plantations to biodiversity conservation in a variegated landscape. Eucalypt plantations are expanding rapidly in Australia; they provide conservation potential through afforestation, but their real value for native fauna requires investigation. The relative conservation value of eucalypt plantations was investigated through assessment of avifauna richness, abundance and composition with transect surveys incorporating point counts in five broad habitat types – dryland forests, riparian forests, dryland plantations, riparian plantations, and riparian pastures. A total of 73 species were recorded during formal surveys. Species richness and abundance were comparable among all habitat types except dryland plantations, which supported fewer species and in lower numbers. The avifauna assemblage differed according to broad habitat types. Forest habitats (dryland and riparian) harboured more forest- and woodland-dependent species, and a greater abundance of nectarivores and insectivores. Riparian plantations supported a similar number of forest- and woodland-dependent species to forest habitats, but also retained many open-country species. Riparian pastures had the highest cumulative species richness, reflecting a diverse mix of forest- and woodland-dependent birds and open-country species. It was the preferred habitat type for granivores and vertebrate eaters. Dryland plantations were dominated by common species and omnivores, and supported fewer forest- and woodland-dependent birds, insectivores and frugivores compared to other habitat types. The presence of riparian strips in plantations and pastures markedly increased habitat value for a wide range of avian species. The importance of riparian habitats needs to be recognised and incorporated into management policies if biodiversity conservation is to be an objective of plantation establishment. In order to determine the conservation value of native eucalypt plantations compared to regrowth forests for insectivorous birds, habitat structure variables and time budgets were quantified for two species of insectivore. In comparison to eucalypt plantations, regrowth forests supported a wider range of tree sizes, and a greater percentage cover of canopy, shrub and litter layers. Although a similar amount of native vegetation was retained in riparian and dryland plantations, there were more large, mature trees retained in riparian strips. Both the eastern yellow robin (Eopsaltria australis) and the white-browed scrubwren (Sericornis frontalis) exhibited some behavioural flexibility in response to changes in habitat structure. The eastern yellow robin utilised rough-barked trunks and stems as perches in forest habitats, switching to branches in eucalypt plantations where vertical perches were few. The white-browed scrubwren also utilised habitat-specific substrates in accordance with availability – logs in forest habitats, and grass, ferns and shrubs in plantations. Scrubwrens spent more time calling and less time actively foraging in riparian plantations than in forest habitats, suggesting differential predation risks in the different habitat types. Although the time budget for both species was similar among habitat types, dryland plantations had fewer birds. Frequent absence of both ground-foragers from dryland plantations suggests that behavioural changes cannot accommodate the absence of essential habitat features and resources in dryland plantations. This study also compared the territory size, shape and usage of an area-sensitive forest-dependent songbird, the eastern yellow robin, in four habitat types – dryland forests, riparian forests, dryland plantations and riparian plantations. Territory size and shape did not differ significantly among forest and plantation habitats; however, territories in dryland habitats were more variable in size than their riparian counterparts. The core area of concentrated activity (50%) comprised approximately 13% of the total size of robin territories. No significant differences in edge indices were found amongst habitat types; however, riparian habitats exhibited greater variability in territory shape. Within plantation habitats, territory occupation was closely related to the distribution of remnant and/or riparian vegetation: the eastern yellow robin showed significant preference for remnant and riparian vegetation over plantation trees. This pattern was especially pronounced in riparian plantations, as riparian vegetation on average comprised over half of the area of robin territories, and almost 75% of the core area, amounts highly disproportionate to the percentage cover of riparian vegetation. This study suggests that plantations have the potential to provide significant conservation benefit for the avifauna of cleared and variegated landscapes. However, this benefit will be substantially increased through retention of old-growth vegetation patches and corridors within plantations, and management of the ground layer to prevent the dominance of weeds.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.