H.A. Nix

EFFECTS OF FOREST FRAGMENTATION ON BIRD ASSEMBLAGES IN A NOVEL LANDSCAPE CONTEXT

We report findings of a large-scale study in a 100 000-ha subsection of the Tumut region in southern New South Wales, southeastern Australia. The study was designed to measure the effects of landscape context and habitat fragmentation on forest birds. The study region consisted of a forest mosaic characterized by different landscape contexts: large, continuous areas of native Eucalyptus forest, extensive stands of exotic softwood (radiata pine, Pinus radiata) plantation, and remnant patches of native Eucalyptus forest scattered throughout the extensive areas of radiata pine plantation. A set of 85 eucalypt remnants was randomly selected across several stratifying variables: four patch size classes (1-3 ha, 4-10 ha, 11-20 ha, and .20 ha), two isolation age classes (,20 years and .20 years since fragmentation), and five dominant eucalypt forest type classes. In addition to the 85 eucalypt remnants, a further 80 3-ha sites were selected for study: 40 in large, continuous areas of eucalypt forest and 40 in radiata pine stands. Point-interval counts of forest birds at the 165 sites were conducted in 1996 and 1997. Of 90 species recorded, 23.1 species (95% confidence interval, 22.0, 24.2 species), on average, were present in continuous eucalypt forest, 20.6 (19.5, 21.7) species in patch- shaped eucalypt remnants, 20.6 (19.5, 21.7) species in strip-shaped eucalypt remnants, and 16.7 (15.6, 17.8) species in radiata pine. Strong gradients in bird assemblages were found. These gradients were governed by a combination of landscape context, remnant size, and remnant shape effects, and, in the case of radiata pine sites, the extent of native forest surrounding the pine. These gradients could, in part, be explained by bird life history attributes such as foraging guild and nesting height. For example, birds more often detected in patch-shaped remnants were smaller, produced smaller clutches, were more likely to be migratory, and typically had cup nests or burrows. The results of our study showed that eucalypt fragments of all sizes and shapes have significant conservation value. This is because they contain many native species of birds, some of which are more abundant in fragments than they are in continuous eucalypt forests, and also because they increase native bird populations in nearby non-native pine plantations.

The Nature of Northern Australia: Natural Values, Ecological Processes and Future Prospects

The book offers a synthesis of the natural values and ecology of north Australia together with recommendations for actions needed to maintain these values. The book’s authors, John Woinarski (NRETA), Brendan Mackey (ANU), Henry Nix (ANU) and Barry Traill (Pugh Foundation, formerly The Wilderness Society) have brought together a great deal of recent research in these areas, much of it enabled by the TS–CRC partners, particularly through John Woinarski and NRETA.

The conservation of arboreal marsupials in the montane ash forests of the Central Highlands of Victoria, South-East Australia: III. The habitat requirements of leadbeater's possum Gymnobelideus leadbeateri and models of the diversity and abundance of arboreal marsupials

Factors influencing the presence and abundance of leadbeaters possum Gymnobelideus leadbeateri McCoy and the diversity and abundance of other species of arboreal marsupials in montane ash forests were determined from logistic and Poisson regression analyses. The presence of G. leadbeateri was related to the number of trees with hollows and the basal area of Acacia spp. There was a positive correlation between the abundance of the animal and the number of trees with hollows, the quantity of decorticating bark and a negative correlation with the number of shrubs and the slope of the site. The diversity of arboreal marsupials was greatest on sites with a large number of trees with hollows, a high basal area of Acacia spp., a large quantity of decorticating bark and south- or east-facing sites. A model containing similar variables was developed for the abundance of arboreal marsupials. This model also produced a significant negative correlation with the number of stumps resulting from timber harvesting operations. Our findings highlight the deficiencies of current measures to conserve arboreal marsupials which are dependent on hollows in trees, when these forests are harvested by clear-felling.

Characteristics of hollow-bearing trees occupied by arboreal marsupials in the montane ash forests of the Central Highlands of Victoria, south-east Australia

Abstract A total of 1125 hollow-bearing trees was observed for the presence of arboreal marsupials in the montane ash forests of the Central Highlands of Victoria, south-east Australia. Different species of arboreal marsupials exhibited preferences for hollow-bearing trees with different characteristics. Gymnobelideus leadbeateri (Leadbeaters possum) selected short, fat trees with numerous holes and a large quantity of dense surrounding vegetation. Very large hollow-bearing trees were favoured as nest sites by Petauroides volans. Petaurus breviceps preferred trees with a large number of fissures, whereas trees favoured by Antechinus stuartii were tall and thin. Trees selected as nest sites by Trichosurus caninus were typically short and fat with few holes. Our results provide evidence of resource partitioning of hollow-bearing trees amongst arboreal marsupials. Clear-felling of montane ash forest on an 80–120-year rotation will have a highly detrimental effect on arboreal marsupials by substantially reducing the number and range of types of hollow-bearing trees required to support the complete diversity of species. The 80–120-year interval between logging operations will result in trees being harvested well before they develop characteristics which make them suitable nest sites for arboreal marsupials.

The abundance and development of cavities in Eucalyptus trees: a case study in the montane forests of Victoria, southeastern Australia

Abstract A study of the abundance of cavities in Eucalyptus regnans, Eucalyptus delegatensis, Eucalyptus nitens, Eucalyptus obliqua and Eucalyptus cypellocarpa is described. The investigation used a database of 2315 living and dead trees with cavities, measured on 523 sites each of 3 ha throughout the montane ash forests of the Central Highlands of Victoria, southeastern Australia. Poisson regression analysis was used to examine the relationships between the number and type of cavities and a range of attributes of trees. These analyses demonstrated that, for all species of trees, the abundance of holes, fissures and hollow branches increased with tree diameter. Log-linear analysis of contingency tables demonstrated that various combinations of cavity types typically occur. Patterns of co-occurrence of cavities changed significantly according to the diameter, height and form of trees. The application of restricted maximum likelihood estimation (REML) for examining multi-level data, enabled the relatioships between the number of cavities, tree characteristics and site parameters to be analysed The characteristics of trees that were important were height, diameter and form. Site parameter that had a significant influence on the total number of cavities in trees included slope, latitude and stand age. This highlights the range of factors, at several measured spatial scales, that may influence the development of cavities in Eucalyptus trees. Although the various relationships derived in this study were highly significant, the statistical models had limited predictive ability. Thus for any given tree the development of cavities will be influenced by site and tree attributes as well as highly stochastic episodic events that may occur during its lifetime. The key findings from the study are discussed in terms of their relevance to forest wildlife management.

The conservation of arboreal marsupials in the Montane ash forests of the central highlands of Victoria, Southeast Australia: I. Factors influencing the occupancy of trees with hollows

Abstract A total of 1125 trees with hollows on 152 sites in the montane ash forests of the Central Highlands of Victoria was observed for the presence of arboreal marsupials. One of every 3 trees was occupied by an arboreal marsupial and

Spatial analysis of anthropogenic river disturbance at regional and continental scales: identifying the wild rivers of Australia

A method for assessing anthropogenic river disturbance is described. The grid-based spatial modeling procedure computes indices of disturbance for individual stream sections. These indices rank streams along a continuum from near-pristine to severely disturbed. The method couples geographical data, recording the extent and intensity of human activities known to impact on river condition, with a Digital Elevation Model (DEM) used for drainage analysis. It was developed to produce the first nation-wide assessment of river disturbance from which Australia’s least disturbed or ‘wild’ rivers were identified. A national summary of the extent and the potential impact of human activities is presented, calculated from the disturbance index values computed for more than 1.5 × 10 6 stream sections with a total length of over 3 × 10 6 km. Index values close to the undisturbed end of the continuum are rare, especially among large rivers. Most of the least disturbed streams are predicted to lie within the monsoonal tropical north or the arid/semi-arid center of the continent. The disturbance indices generated provide a comprehensive and consistent characterization of river and catchment disturbance that has applications beyond the identification of wild rivers. These include identification of priorities for rehabilitation and restoration; development of systematic survey strategies for aquatic, riparian and estuarine biota and identification of reserve networks for river systems. However, these applications depend on validating the correlation between river disturbance indices and intensively sampled physical and biological indicators of river condition.

Assessing representativeness of places for conservation reservation and heritage listing

Problems arising from application of the representative criterion for conservation and natural heritage evaluation are discussed. An ecological basis to this criterion is suggested that focuses on those key environmental factors dominating biotic response. A methodology is proposed that utilizes computer-based methods of establishing and interrogating spatial data bases (geographic information systems), environmental modeling, and numeric analysis. An example is presented illustrating some of the advantages and limitations of classification and dimension reduction techniques in both defining bioenvironments and displaying their spatial distribution. The advantages of this method for representativeness evaluation are that it maximizes the utility of available data, is explicit and repeatable, and enables large areas to be analyzed at relatively fine scales.

Assessing the representativeness of the wet tropics of Queensland world heritage property

Abstract An assessment is made of the representativeness of the Wet Tropics World Heritage property of north-east Queensland, Australia. The relevance of this feature to the World Heritage criteria is discussed. Computer-based spatial data sets are used to provide a sample of the distribution of key environmental factors at both continental and regional scales. Numerical classification techniques are applied to generate environmental groups from pattens in the distribution of these environmental factors. An evaluation is presented of the representation of these groups within the World Heritage property, in the context of present and potential tropical forest cover.

Mapping regions climatically suitable for particular species: an example using Africa

Abstract Data from approximately a thousand irregularly spaced meteorological stations were analysed to produce a climatic database for 10 187 points in a regular half-degree grid covering Africa. From the monthly mean values of average daily maximum temperature, average daily maximum temperature and total precipitation, six factors important for tree species selection were calculated for each point. These included measures such as mean annual temperature, maximum temperature of the hottest month, mean annual precipitation and rainfall regime. A microcomputer program was written which enables this database to be interrogated. Maps can be generated which indicate regions climatically suitable for particular species.