Potential Environmental Weeds in Australia: Candidate Species For
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NATIONAL WEEDS PROGRAM POTENTIAL ENVIRONMENTAL WEEDS IN AUSTRALIA CANDIDATE SPECIES FOR PREVENTATIVE CONTROL By S. Csurhes and R. Edwards POTENTIAL ENVIRONMENTAL WEEDS IN AUSTRALIA by S. Csurches and R. Edwards Queensland Department of Natural Resources Land Protection, Locked Bag 40, Coorparoo Delivery Centre Qld 4151 Acknowledgments This project was funded by Environment Australia. Considerable information on potential weed species was generously provided by pest management and conservation agencies from around Australia. Assistance with literature searches was provided by Paul Paping. The views and opinions expressed in this report are those of the authors and do not necessarily reflect those of the Commonwealth Government, the Minister for the Environment or the Director of National Parks and Wildlife. ISBN 0 642 21409 3 Published January 1998 © Copyright The Director of the National Parks and Wildlife Biodiversity Group, Environment Australia (formerly Australian Nature Conservation Agency) GPO Box 636 Canberra ACT 2601 Cover design: BH Graphics PREFACE Non-indigenous invasive plants are an insidious, widespread and poorly recognised threat to Australias native plant communities and associated wildlife. To date, at least 2,200 species of non-native plants have naturalised in Australia. Some of these species have invaded native vegetation and replaced native plants. Since additional plant species are imported each year, the invasion process is by no means complete. Over the years, many opportunities to eradicate vulnerable, localised populations of "potential weeds" have been missed. Some species that could have been eliminated quite cheaply when first detected have now spread over many thousands of hectares. We should learn from past mistakes and ensure that opportunities for preventative control are taken wherever possible. A pre- requisite to successful preventative control is the delineation of target species for which eradication may be feasible. This project highlights a number of opportunities for early preventative control that may be taken to protect native ecosystems against further damage by non-indigenous plants. FOREWORD Can weeds be eradicated from Australia? In most cases this is an impossible dream. Controlling environmental weeds is usually an expensive time consuming process and often results in management, not eradication. Occasionally, however, opportunities arise where eradication is possible. These opportunities occur in situations where a weed species is very localised and has not yet begun to spread. Catching a weed before it becomes widespread and well established is perhaps the only chance we have of eradicating some species from Australia. Unfortunately, a lot of these opportunities have been missed in the past. Weeds that could have been eradicated when first detected are now widespread and require continual resources to contain within given areas. There is also the added complication that not all weed introductions have an effect on the environment. Some weed species remain restricted to the location of their release and never spread beyond that. It is critical to identify weeds that have the potential to become problems and, where feasible, to deal with these swiftly while it is still cost-effective and offers the opportunity for complete control. This report identifies potential weeds in Australia, prioritising those that have histories as weeds overseas. Prioritisation was based on their known distribution in Australia and on the feasibility of eradication. I believe this report will be a very useful resource to those agencies and organisations who are interested in taking a proactive role in the management of environmental weeds. Opportunities such as the ones highlighted in this report do not present themselves often - we should make the most of them! G E A H B G CONTENTS 1.0 INTRODUCTION 2.0 REVIEW OF LITERATURE 2.1 Definition of an "environmental weed" 2.2 Impacts of environmental weeds 2.2.1 Impacts on ecosystem function 2.2.2 Spatial and temporal nature of impacts 2.3 Number of environmental weed species in Australia 2.4 Source of environmental weeds 2.4.1 Accidental introductions 2.4.2 Deliberate introductions 2.5 Preventative weed management - early detection and eradication 2.6 Predicting weed potential 3.0 METHODOLOGY 9 3.1 Background considerations 9 3.2 Prioritisation process 9 4.0 RESULTS 12 4.1 Lists of potential environmental weeds 12 4.1.1 Table 1 - Initial list of species nominated as 12 potential environmental weeds. 4.1.2 Table 2 - Potential environmental weed species 20 ( derived from Table 1) that have histories as weeds overseas and are vulnerable to eradication in Australia 4.2 Information on species listed in Table 2 22 5.0 DISCUSSION 63 6.0 RECOMMENDATIONS 65 7.0 REFERENCES 65 8.0 LIST OF CONTRIBUTORS 86 APPENDICES Appendix A - List of native species removed from Table 1 90 Appendix B - Potential environmental weed species that do not have histories as weeds outside Australia 91 Appendix C - Potential environmental weed species that have histories as weeds overseas but are too well established to be eradicated from Australia 134 9.0 INDEX 202 9.1 Species name index 202 9.2 Common name index 205 1.0 INTRODUCTION The aim of this project is to list and describe non-indigenous terrestrial and aquatic plant species considered to have the following attributes: • represent a threat to native terrestrial or aquatic plant communities • a localised distribution • vulnerable to eradication (including species that only exist as cultivated specimens). Pest management and conservation agencies can use the information contained herein to consider eradication, or at least containment, of potentially invasive plant species. Hopefully, this project will facilitate a reduction in the rate at which additional environmental weed species become established in Australias bushland and waterways. 2.0 REVIEW OF LITERATURE 2.1 Definition of an "environmental weed" Humphries et al. (1991) chose to define environmental weeds as "those species that invade native communities or ecosystems - they are undesirable from an ecological perspective, but not necessarily an economic one. Serious environmental weeds are defined as those that cause major modification to species richness, abundance or ecosystem function. Very serious environmental weeds are those that can totally and permanently destroy an ecosystem." The authors pointed out that different categories of environmental weeds could not yet be quantitatively defined. In most literature on environmental weeds, the term "serious environmental weed" is usually assigned to widespread species that have an obvious visual impact on native vegetation ie. appear to dominate native species. As such, authors tend to make qualitative assessments of impact based on visual observations. The time scale of weed problems is problematic as species initially considered to be "minor" weeds can become major problems in the long-term. Environmental weeds have also been defined as "plant species that have established self-propagat- ing populations in native vegetation, terrestrial or aquatic, outside their natural range. " (Csurhes 1995). This definition makes provision for Australian native plant species that have become established in areas outside their "natural" range (eg. species native to the eastern States that have naturalised in Western Australia). The definition is broad however, and includes species that may be restricted to highly disturbed habitats such as roadside vegetation or urban bushland remnants where nutrient input is high or where fire has been excluded. As such, some plants covered by this definition may not necessarily represent a significant threat to native plant communities subject to relatively low levels of exogenous disturbance (eg. in large National Parks and conservation reserves). Swarbrick and Skarratt (1994) defined environmental weeds as "those plants which invade, persist and proliferate within, and cause maintenance, management, aesthetic or other problems in areas which are either set aside for or managed to protect their native vegetation, fauna or other nat- ural or semi-natural environmental values." Perhaps the only criticism is that this definition focuses on conservation areas without acknowledging the capacity for invasive plants to damage native vegetation on land used for other purposes. In the literature, the term `environmental weed tends to be synonymous with several other terms including `invasive plants, `alien plants, `weeds of conservation reserves, bushland weeds, `exotic weeds and ,non- indigenous, naturalised plants. 2.2 Impacts of environmental weeds 2.2.1 I Some impacts on ecosystem function include: a) Competition for resources Environmental weeds can compete with locally indigenous plant species for resources (including sunlight, moisture and nutrients). Many of Australias major environmental weed species were imported without their natural pests/diseases and do not suffer significant damage from Australian insects, fungi or other organisms. For example, one of Australias worst environmental weeds, the Indian blue thunbergia vine (Thunbergia grandiflora), does not appear to suffer any insect or pathogen damage when growing in north Queensland rainforest. Its growth is not kept in check and can be extremely vigorous, enabling the vine to outcompete slower growing native plants for sunlight. As such, freedom from a range of "co-evolved predators and parasites" may provide imported environmental weeds