other towns. But the cardoon (Cynara cardunculus) has a far wider range: it now occurs in these latitudes on both sides of the Cordillera, across the continent.
1
Introduction: the many aspects of the invasive alien species problem ODD T. SANDLUND, PETER J. SCHEI and ASLAUG VIKEN
Norwegian Institute for Nature Research (NINA), Directorate for Nature Management (DN), Norwegian University for Science and Technology (NTNU), Trondheim, Norway
The problem "Near the Guardia we find the southern limit of two European plants, now become excessively common. The fennel in great profusion covers the ditch banks in the neighbourhood of Buenos Ayres, Montevideo, and other towns. But the cardoon (Cynara cardunculus) has a far wider range: it now occurs in these latitudes on both sides of the Cordillera, across the continent. I saw it in unfrequented spots in Chile, Entre Rios, and Banda Oriental. In the latter country alone, very many (probably several hundred) square miles are covered with one mass of these prickly plants, and are impenetrable by man or beast. Over the undulating plains, where these great beds occur, nothing else can live. Before their introduction, however, I apprehend the surface supported as in other parts a rank herbage. I doubt whether any case is on record, of an invasion of so grand a scale of one plant over the aborigines." (C. Darwin 1839. Voyage of The Beagle). When Charles Darwin in the 1830s observed two European plant species that had established and dominated in seminatural and urbanized habitats over large areas in South America, he considered it quite remarkable. Today, this is a general phenomenon in many parts of the world. In most countries, the number and proportion of alien species in the flora and fauna are frightfully high, so that seminatural ecosystems may be dominated by non-native species. This has devastating effects on native biodiversity, and introductions of alien invasive species is one of the four members of Jared Diamond's (1985) "evil quartet" of major threats to native biodiversity. Moreover, with the present development in international trade and travel, the transport of species, and thereby the risk of introduction into new areas is bound to increase (Jenkins, Ch. 15). Thus, we are in an urgent need for 0. T. Sandlund et al. (eds.), Invasive Species and Biodiversity Management, © 1999 Kluwer Academic Publishers. Printed in the Netherlands.
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0. T. Sandlund, P.J. Schei & A. Viken
Introduction
tools and methods to reduce this threat to natural biodiversity. The tools be based on understanding the invasive species and the invasible ecosystem , and the processes involved in invasions. We need to develop predictive models for invasions, and practical ways and means of stopping or reducing invasions. _ _ _ _ During the negotiations of the Convention on Bwlogical_ Diversity (CBD) the threats to indigenous biodiversity posed by ahen mvas1ve species were highly recognized. Most biologists consider this the second most important threat factor after habitat destruction. Therefore the obhgations laid down in the Convention are quite extensive and demanding. Article 8 h of the Convention states: "Prevent the introduction of, control or eradicate those alien species which threaten ecosystems, habitats or species" The complex, difficult and global nature of this task indicates the need for a thoroughly planned worldwide strategy and action plan or the f prevention of invasions and the management of invasive species. An important element is the cooperative development and use of new, innovative tools in this struggle. A global strategy 1s now underway, partly as a follow-up to the conference in Trondheim in 1996 (Mooney, Ch. The third Conference of the Parties (COP-3) of CBD in Buenos Aires in 1996 gave its full support to this initiative and the support has later been reinforced by CBD's Subsidiary Body for Scientific, Techmcal and Technological Advice (SBSTTA) at its third meeting in Montreal in 1997 · The expert group on marine and coastal diversity which was established _ under SBSTTA in 1995 has also emphazised the imp ortance of a global alien species strategy. _ It may be noted that the CBD applies the expression ahen species to denote any species which is introduced into new habitats by human intervention; i.e. a process considered different from the naturnl process of literature specie s migrating and e stablishing in new areas. In the biological we find several different words for this phenomenon. Introduced species, non-native species, and exogeneous species are mo re or less synonymous and means any species which has been established after hum_an-mo derated introduction to the habitat. Alien species as a threat to native b1olog1cal diversity implies a more restricted concept, and is commonly called invasive or aggressive species. In this book we have accepted the terminology preferred by the individual authors, as the meamng emerges clearly regardless of words. In any case, it is probably a futile effort to try to develop a standard terminology on this subject. "Species" in CBD's _article 8h must also be understood to include any ahen stock, population or subspecies.
must
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The human dimension of alien species: across disciplines and sectors The problems related to the invasion and spreading of unwanted organisms are obviously not restricted to the seminatural and urbanized habitats as observed by Charles Darwin in South America more than 160 years ago. Organisms which employ humans as their habitat, or which inhabit domesticated food producing species or food products are on the same bandwagon of increased transport across oceans and continents, as demonstrated by, e.g., Skjerve and Wasteson (Ch. 17), Jenkins (Ch. 15), and Bryan (Ch. 11) in this vo lume. This impose a major threat to human and animal health, and agricultural production. Disease organisms like the tuberculosis bacterium, which were considered close to extinction, are apparently increasing in frequency and area of occurrence. This is a combined result of resistant strains of bacteria and an increased frequency and distance of migration by peo ple who may carry the disease organism. Diseases and parasites of domesticated food-producing animals and cultivated plants are in many cases increasing, mainly due to liberalized trade and related reduction in quarantine restrictions. The spreading of alien invasive species which may do harm to human, animal and plant health as well as to the native biodiversity in our environments is a problem handled by agencies responsible for many of s ociety's sectors. An important aim of this volume is to demo nstrate that the various sectors of society, e.g., environmental management, human health, agriculture, and veterinary medicine may benefit greatly from sharing their experiences and learning from each other. Holt (Ch. 5) provides an excellent example of cross-sectorial collaboration on alien species management in Hawaii. The numerous dilemmas inherent in alien species management is amply demonstrated by the fact that most of the food production of the world is based on a great reshuffling of species through agriculture (McNeely, Ch. 2). We are not able to imagine the present level of global food production without this reshuffling. More than 90 % of the world's agricultural production is based on less than 20 plant and 6 animal species. These few species presently have a nearly global distribution, while their areas of origin are restricted to a few "Vavilov centers" (Smith, 1995). Fortunately, most of the dominating domesticates do not invade natural or seminatural habitats. However, the transport of seed material and products from agriculture pose a serious and continuing threat by bringing unintentionally weeds, parasites and disease organisms. Intentional introductions of alien species most often happens because management institutions or individuals expect to gain some short or long
4
Introduction
0. T. Sandlund, P.J. Schei & A. Viken
term benefit (McNeely, Ch. 2). The expected benefits are commonly economic, but individual or public demand for an enjoyable environment is also a common motivation for introductions. Thus, the objectives might be to, e.g. increase biomass production in fisheries, agriculture or forestry (Huntley Ch. 24; Richardson, Ch. 16) or to create nice garden or park sceneries by planting alien species of ornamental and garden plants. However, the efforts to reach laudable objectives have often resulted in serious side effects (Oguto-Ohwayo, Ch. 4) or outright disasters (Huntley, Ch. 24). Both Oguto-Ohwayo, and Shiva (Ch. 3) also points to the cultural, socio-economic and social impacts often experienced from introductions with otherwise laudable intentions. All these cases highlight the dilemma that faces the informed manager in most, if not all, cases where an introduction is the proposed action. Your action may give some benefit, but will at the same time cause environmental damage. It may be said, however, that the problems we face today in many instances are the results of the action of uninformed managers or the general public, e.g. in the shape of tourists bringing ornamental plants back to their garden, or families emptying their aquarium into the nearest pond or river before leaving for a holiday.
The ecology of introductions: do we understand it? Although much scientific work has been performed on the ecology of invasions since the subject was highlighted by Elton (I 95 8) fourty years ago (cf. Drake et al., 1989), our understanding is still quite restricted. What is clear is that there is a series of steps in the process from an organism is introduced into a non-native habitat until it is established in numbers to give major effects on the new habitat. The trajectory taken by this process depends on characteristics of the introduced species as well as the conditions of the receiving ecosystem (Rejmanek, Ch. 6; Hengeveld, Ch. 8). Empirical evidence shows clearly that many introduced species may stay passive for a long time. Many generations may be spent in a non-expanding state, until suddenly the species becomes invasive and "aggressive", and expands to dominate the environment (Crooks and Soule, Ch. 7). The reasons for this phenomenon are poorly understood. There is obviously a great need for predictive models to describe the invasive process, but the models presently available mainly enable us to see what factors might be important (Hengeveld, Ch. 8). The most devastating effects of introduced species have been observed on islands (Strahm, Ch. 22; Clout, Ch. 23). While freshwater systems have been subject to extensive introductions, with a larger number of introduced
5
than native species in some regions, the ecosystem and species diversity effects often appears small (Moyle, Ch. 12). However, in lakes with a high number of endemic species, the effects of introductions appear similar to what is observed on islands with high endemism (Oguto-Ohwayo, Ch. 4; Clout, Ch. 23; Huntley, Ch. 24). Ecosystems modified by man generally appears more receptive to alien species than undisturbed ecosystems. Although this may also be related to the higher number of anthropogenic introductions into these habitats (cf. Williamson 1996), it appears natural that global change processes, e.g., climate change, will seriously influence the impact of alien species on ecosystems (Mooney and Hofgaard, Ch. 9). The process where man seeks to cultivate natural populations or ecosystems to increase the yield of some desired product commonly involves introduction of genetically different individuals to strengthen populations. This has been common practice in forestry and inland fisheries. One fairly well studied example is the domesticated or semi-domesticated escapees from salmon culture which pose a serious threat to natural Atlantic salmon stocks (Hindar, Ch. 10). Research on this problem may also bring important understanding of the potential impacts from introduction of genetically modified or engineered organisms (GMOs, GEOs) into the environment. As Bryan (Ch. 11) demonstrates, the spreading and re-emergence of human diseases may be better understood if analysed as ecological processes, whereas the often well documented epidemiology and migration of various human diseases may teach environmental researchers and managers many lessons regarding pathways, mechanisms and population variations in invasives.
International pathways The globalization trends in the world's trade, tourism and migration, offer unrestricted opportunities for unintentional introductions of invasive alien species. This includes, but also adds to sea transport, which has been an important pathway for both aquatic and terrestrial species for several hundred or even thousands of years. Sea transport continues to be a dominant agent in what might be called the internationalisation of coastal marine fauna (Carlton, Ch. 13). Sea transport is also an important indirect cause for the spreading of catastrophic human disease organisms; witness for example the Yersinia-infected Norway rat (Rattus norvegicus) brought by ships to the American west coast in 1899 (Bryan, Ch. 11). Significant changes in the marine biota are also brought about through technical
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0. T. Sandlund, P.J. Schei & A. Viken
development schemes. The Suez Canal is one eloquent example (Boudouresque, Ch. 14). Sea transport is but one agent in the global trade systems of today. As pointed out by Peter Jenkins (Ch. 15), the galloping liberalization of world trade is accompanied by transport and introduction of an ever increasing number of alien species among all the world's regions. The reduction in quarantine regulations resulting from trade liberalization also negatively impacts human and animal health (Skjerve and Wasteson, Ch. 16). The important economic activity of forestry has been a dominant agent in reshaping many of the world's terrestrial biota. Several temperate and subtropical tree species have been extensively planted over large areas in many biogeographic regions (Richardson, Ch. 17). Considering the major effect of forest trees on both biotic and abiotic environmental parameters, it is disturbing that this activity is still going on at a large scale, while our understanding of the effects on biodiversity, soil chemistry etc. from the planting of alien tree species is poorly understood (Huntley, Ch. 24).
Management tools: can we learn from experience? Considering the impacts of alien invasive species, and the difficulties m predicting effects of any new introduction, it appears that the only solution would be to put a stop to introductions of aliens. As this is clearly not a feasible solution, management institutions in most of society's sectors are in dire need of effective management tools. Legislation and regulations to restrict the movement of unwanted organisms are clearly very important (Bean, Ch. 18). Experiences from the trade on agricultural products like live animals and animal products before the present trade liberalization seems to indicate that application of strict regulations is a very efficient tool (Skjerve and Wasteson, Ch. 17). Prevention of introductions is clearly more cost efficient than eradication or control of an invasive once it is established (Westbrooks and Eplee, Ch. 19). This is clearly the case both in plants, insects (Samways, Ch. 20), and disease organisms (Skjerve and Wasteson, Ch. 17). Once an invasive species is established, introducing some biological control agent may be the only possible way out (Oduor, Ch. 21; Pech, Ch. 25). This solution often, however, involves its own risks of unforeseen negative effects.
Introduction
7
Where do we go from here? With international agents being instrumental in the steadily increasing movement of species around the world, international agreements and protocols are obviously needed to reduce the pressure of invasives on natural ecosystems, cultivated lands and human and animal health (Glowka and de Klemm, Ch. 26). At the same time, a concerted effort is needed in a Global Strategy for dealing with Alien Invasive Species (Mooney, Ch. 27). The development of new and innovative preventive tools is badly needed, and the sharing of experiences and knowledge across borders and disciplines will be an important element in this global effort. Acknowledgements
We thank the Conference Committee and the International Advisory Group to the second Trondheim Conference on Biodiversity for their essential contributions to a successful conference in 1996. Thanks are also extended to all the contributors to this volume for their efforts to enable us to keep to schedule, and to the peer reviewers for their assistance in the development of the chapters. Ms. Synn0ve Vanvik and Mr. Knut Kringstad, at NINA, have helped us with the word processing and graphics, respectively. Dr. Bob Carling, formerly of Thomson Science, helped develop this into a book project.
References Diamond, J.M. 1985. Introductions, extinctions, exterminations, and invasions, in Community Ecology, (eds T.J. Case and J.M. Diamond), Harper & Row, New York, pp. 65-79. Drake, J.A., Mooney, H.A., di Castri, F., Groves, R.H., Kruger, F.J., ReJmanek, M. and Williamson, M., eds ( 1989) Biological Invasions. A Global Perspective. John Wiley, Chichester, UK. Elton, C.S. ( 1958) The Ecology of Invasions by Animals and Plants. Methuen, London, UK. Smith, B.D. (1995) The Emergence of Agriculture. Scientific American Library, W.H. Freeman & Co, New York. Williamson, M. (I 996) Biological Invasions. Population and Community Biology Series 15, Chapman & Hall, London, UK.
