Global Efforts to Limit Australian Acacia Invasions

Diversity and Distributions, (Diversity Distrib.) (2011) 17, 1030–1046 S BIODIVERSITY Risk assessment, eradication, and PECIAL ISSUE REVIEW biological control: global efforts to limit Australian acacia invasions 1,2 2,3 2 John R. U. Wilson *, Carla Gairifo , Michelle R. Gibson , Margarita :H Arianoutsou4, Baki B. Bakar5, Ste´phane Baret6, Laura Celesti-Grapow7, Joseph M. DiTomaso8, Jean-Marc Dufour-Dror9, Christoph Kueffer10, 11 12 12 Christian A. Kull , John H. Hoffmann , Fiona A. C. Impson , Lloyd L. UMAN Loope13, Elizabete Marchante14,He´lia Marchante15, Joslin L. Moore16,17, 18 19 20 21 Daniel J. Murphy , Jacques Tassin , Arne Witt , Rafael D. Zenni - MEDIATED INTRODUCTIONS OF and David M. Richardson2 1South African National Biodiversity Institute, ABSTRACT Kirstenbosch National Botanical Gardens, Claremont 7735, South Africa, 2Centre for Invasion Biology, Aim Many Australian Acacia species have been planted around the world, some Department of Botany and Zoology, Stellenbosch are highly valued, some are invasive, and some are both highly valued and University, Private Bag X1, Matieland 7602, South Africa, 3Departamento de Engenharia Florestal, invasive. We review global efforts to minimize the risk and limit the impact of Instituto Superior de Agronomia da Universidade invasions in this widely used plant group. 4 A Journal of Conservation Biogeography Tećnica de Lisboa, Portugal, Department of Ecology and Systematics, Faculty of Biology, University of Location Global. Athens, Athens 15784, Greece, 5Institute of Biological Sciences, University of Malaya, 50603 Kuala Methods Using information from literature sources, knowledge and experience Lumpur, Malaysia, 6Parc national de La Reúnion, of the authors, and the responses from a questionnaire sent to experts around the 112 rue Ste-Marie, 97400 St-Denis, Reúnion, France, world, we reviewed: (1) a generalized life cycle of Australian acacias and how to A 7Department of Environmental Biology, Univ Roma USTRALIAN ACACIAS La Sapienza, I-00185 Rome, Italy, 8Department of control each life stage, (2) different management approaches and (3) what is Plant Sciences, Mail Stop 4, One Shields Ave., required to help limit or prevent invasions. University of California, Davis, CA 95616, USA, 9Environmental Policy Center, Jerusalem Institute for Results Relatively few Australian acacias have been introduced in large numbers, Israel Studies, Jerusalem, Israel, 10Institute of but all species with a long and extensive history of planting have become invasive Integrative Biology, Plant Ecology Group, ETH somewhere. Australian acacias, as a group, have a high risk of becoming invasive Zu¨rich, CH-8092 Zu¨rich, Switzerland, 11School of Geography and Environmental Science, Monash and causing significant impacts as determined by existing assessment schemes. University, Melbourne, Vic. 3800 Australia, Moreover, in most situations, long-lived seed banks mean it is very difficult to 12Department of Zoology, University of Cape Town, 13 control established infestations. Control has focused almost exclusively on — Rondebosch 7700, South Africa, U.S. Geological widespread invaders, and eradication has rarely been attempted. Classical Survey, Pacific Island Ecosystems Research Center, A GLOBAL EXPERIMENT IN BIOGEOGRAPHY PO Box 246, Makawao, HI 96768, USA, biological control is being used in South Africa with increasing success. 14Department of Life Sciences, Centre for Functional Ecology, University of Coimbra, Apartado 3046, Main conclusions A greater emphasis on pro-active rather than reactive 3001-401 Coimbra, Portugal, 15Department of management is required given the difficulties managing established invasions of Environment, Centre for Studies of Natural Australian acacias. Adverse effects of proposed new introductions can be Resources, Environment and Society, Escola Superior Agra´ria de Coimbra, 3040-316 Coimbra, Portugal, minimized by conducting detailed risk assessments in advance, planning for 16Australian Centre of Excellence for Risk Analysis, on-going monitoring and management, and ensuring resources are in place for University of Melbourne, Parkville, Vic. 2010, long-term mitigation. Benign alternatives (e.g. sterile hybrids) could be developed 17 Australia, Australian Research Centre for Urban to replace existing utilized taxa. Eradication should be set as a management goal Ecology, Royal Botanic Gardens, Melbourne, c/o School of Botany, University of Melbourne, Vic. 3010, more often to reduce the invasion debt. Introducing classical biological control Australia, 18National Herbarium of Victoria, Royal agents that have a successful track-record in South Africa to other regions and and Distributions Botanic Gardens Melbourne, Birdwood Avenue, identifying new agents (notably vegetative feeders) can help mitigate existing South Yarra, Vic. 3141, Australia, 19UPR 105, Cirad, Campus International de Baillarguet, 34398 widespread invasions. Trans-boundary sharing of information will assist efforts to Montpellier Cedex 5, France, 20CABI Africa, PO Box limit future invasions, in particular, management strategies need to be better 633-00621, Nairobi, Kenya, 21Department of Ecology evaluated, monitored, published and publicised so that global best-practice and Evolutionary Biology, University of Tennessee, procedures can be developed. Knoxville, TN, USA *Correspondence: John Wilson, Centre for Keywords Invasion Biology, Department of Botany & Australian weed risk assessment protocol, biological invasions, classical Zoology, Stellenbosch University, Private Bag X1, biological control, eradication, invasion debt, Racosperma. Matieland 7602, South Africa. Diversity E-mail: [email protected] DOI:10.1111/j.1472-4642.2011.00815.x 1030 http://wileyonlinelibrary.com/journal/ddi ª 2011 Blackwell Publishing Ltd Pro-active management of Australian acacias Interestingly, the known invaders are also the most heavily INTRODUCTION traded taxa (Fig. 1a, Griffin et al., 2011). For those Australian It is still unclear to what extent biological invasions, and any acacias that are invasive, there are also substantial differences impacts they might cause, can be predicted (e.g. Williamson, between the extents of invasions in different regions; for 1999). This is in part because of the many ways in which an example, eleven Australian acacias in South Africa are amongst invasion could arise (Blackburn et al., 2011). This creates a the most widespread invaders in the region, while other species conflict in natural resource management – what should be are invasive (or only naturalized) at only a few sites (Fig. 1b). done to minimize the costs of biological invasions without Again there is a strong correlation between history of usage unduly limiting the potential benefits derived from introduced and the extent of invasion (van Wilgen et al., 2011). This is organisms. Progress towards predicting future invaders has similar to Pinus (Proches¸et al., 2011), where the amount of been made by focussing on particular taxonomic or functional planting is closely correlated with extent of invasions, at least groups (Paynter et al., 2003; Richardson & Rejmańek, 2004; in South Africa. Harris et al., 2007). Similarly, although invasions are context Two plausible explanations can account for these correla- dependent, valuable insights into management have been tions. First, those species that are most likely to become gained from different parts of the world (Richardson et al., invasive are also those most suited for utilization, and so are 2008; Simberloff et al., 2010). For best practices to be those that humans have spread most widely. Alternatively, developed and implemented, the successes and failures of invasiveness in this group is mediated by propagule pressure, different management actions need to be documented and and so the extent of invasions is the result of greater shared, see Richardson et al. (2008) and Simberloff et al.(2010) introduction and dissemination efforts. Even if the former for relevant insights regarding Pinus species. Developing were true, and managers needed to concentrate only on general management guidelines for a particular taxonomic existing known invaders, Australian acacia invasions are still group across different biogeographical regions can potentially likely to increase in global extent over the next few decades save resources by focussing attention on the most critical (Richardson et al., 2011). Within invaded ranges, species are aspects required for successful management. spreading further; some species that are known to be Australian acacias (also termed ‘wattles’; here defined as the widespread invaders have not yet been introduced in signif- 1012 species formerly placed in Acacia subgenus Phyllodineae icant numbers to all suitable regions around the world, and we DC. that are native to Australia; see discussion in Richardson expect that some species currently at low densities will become et al., 2011; Murphy et al., 2010; Miller et al., 2011) are a widespread invaders in future simply because of population group of leguminous woody plants that include some of the growth and spread. In short, there is a significant invasion debt most important plant invaders globally (Richardson & in the group (sensu Seabloom et al. 2006). Reducing this debt Rejmańek, 2011). They are a model group for studying the will require management strategies that focus on multiple ecology, management and biogeography of plant invasions fronts and at all stages of the introduction-naturalization- (Richardson et

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