Threat syndromes and conservation of the Australian flora

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Abstract

The status of the Australian flora was reviewed by compiling published information on all critically endangered and endangered species listed federally in 2004. Threatening processes were categorised and their contributions to past, present and future declines were assessed. The information was cross-referenced against State agency information and field knowledge. Land clearance for agriculture (grazing and cropping) and urbanization have been the primary causes of range contractions and habitat loss in the past, responsible for the current status of the majority of threatened Australian plants. In the future, land clearance will remain important but new issues are emerging. Many species are now at risk from demographic and environmental uncertainty alone. Threats growing in importance include disease, salinity, invasive species and changed disturbance regimes. Many species are subject to common, landscape-level threats. A key issue to emerge from our analysis is that most species are threatened by a number of interacting factors – threat syndromes. Several future risks may be mitigated effectively by simple, low-cost changes in policy, such as more stringent controls on land clearance, strategic fire management, and firmer control on the importation of plant species. Other factors will require greater effort and new strategies to mitigate, including social and legal initiatives in urban landscapes and broad strategies for pathogens, climate change and other landscape-level processes.

Introduction

Many government agencies use lists of threatened species to allocate recovery resources, design reserve systems, constrain development and report on the state of the environment (Possingham et al., 2002a). Threatened species lists are an important part of decisions about conservation priorities (Lamoreux et al., 2003).

Leigh et al. (1981) compiled and subsequently revised lists of threatened Australian plants (Leigh et al., 1984, Leigh and Briggs, 1992, Briggs and Leigh, 1988, Briggs and Leigh, 1996). In several compilations, the most recent in 1996, they included a table summarizing the causes of past, present and future threats to the Australian flora. This table was particularly useful because it provided a continental-scale intuitive overview of the processes affecting the conservation status of numerous vascular plant species. While all lists of threatened species are incomplete and uncertain, Leigh et al.’s summaries represent a substantial sample of species at the threatened end of the conservation spectrum because conservation status reflects the relative likelihood of extinction.

The Australia federal government took up the role of maintaining and publishing the list of threatened Australian plants in 1996. The classification system underpinning the federal list is based broadly on the Red List system devised by the International Union for the Conservation of Nature and Natural Resources (IUCN, 2001). In the Red-listing process, species are assigned to categories including extinct, extinct in the wild, critically endangered, endangered, vulnerable, and near threatened.

Effective conservation involves the identification of the causes of environmental change, and the implementation of practices to manage those changes (Caughley and Gunn, 1996). A threatening process is one that may detrimentally affect the survival, abundance, distribution or potential for evolutionary development of a native species or ecological community. The notion of characterizing and managing threatening processes has been a focus for conservation biology for some time (Falk, 1990, Bradstock et al., 1995), and the Australian Federal Government’s Environment Protection and Biodiversity Conservation Act (EPBC Act, 1999) makes provision for nominating threatening processes. Threatening processes have been identified in many Australian biomes (temperate woodlands, Yates and Hobbs, 1997; riparian and groundwater ecosystems, Boulton et al., 2003; rangelands, Woinarski, 2001). In most assessments of the Australian flora, land clearing, salinity, disease and urban development are prominent. In other places around the world, land clearance is usually the most serious threat to plants, but other threats such as pollution and over-harvesting are also serious (Wilcove et al., 1998). In the face of the enormous number of species that require attention, it will be effective to focus conservation efforts on broad processes that cause population decline (Caughley and Gunn, 1996).

Butchart et al. (2004) devised a robust measure of change over time in the status of threatened species, based on published lists. The method reports the proportion of genuine changes, that is, the number of changes in classification made up of recent genuine improvement or deterioration in status in the period since the previous assessment. The purpose of this paper is to revisit the list of threatened Australian plants and revise the table of past, present and future threats. We intend to create a benchmark for assessing the conservation status of the Australian flora as a whole, so that in several years, the list may again be evaluated and the number of genuine changes in status documented, so that the process of tracking changes in conservation status of the Australian flora over time may begin. The benchmark that we establish will be based on the most important threats that influence the chances of persistence of each listed species.

Section snippets

Methods

The list of critically endangered and endangered species published by the Australian Federal Department of Environment and Heritage in November 2004 contained 524 plant species (Department of Environment and Heritage, 2004). This list differs in part from the latest State lists. All such lists are uncertain, a consequence of observational errors, changes in attitudes to uncertainty and changes in taxonomy (Burgman, 2002). Nevertheless, it contains sufficient taxa for the purposes of the present

Results

The evaluation of the data set and scoring of threats led to explicit definitions for 23 threatening processes (Table 1). After the final iteration, the differences in interpretation between the assessments made by DW and MB were less than 10% of the total number of 1 and 2 scores. Table 2 lists the threats identified in the data supporting listing decisions posted on the federal government web site, and in available publications for the same species. Many of these threats have been identified

Discussion

Sattler et al. (2002) estimated that the most widespread processes threatening Australian ecosystems are vegetation clearing, fragmentation of remnant vegetation, grazing pressure, exotic weeds, feral animals, salinity and changed hydrology, and altered fire regimes. These judgements accord with several of the most important processes in Fig. 1, Fig. 2, Fig. 3, Fig. 4 although they omit disease, especially Phytophthora cinnamomi.

Issues that did not arise in our review, but that have arisen

Acknowledgements

We thank Jan Carey for running the classifications. Comments from two anonymous reviewers and D. Saunders greatly improved the manuscript.

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