ࡱ> EFBCDܥhW e6tt|||||DDDDD`:DH^|%''';bdƁd*X8H|  %H|||||% " |}||||% PIERRE BINGGELI in association with John B. Hall and John R. Healey OVERVIEW OF INVASIVE WOODY PLANTS IN THE TROPICS TABLE OF CONTENTS Summary 1 Introduction 2 Overview of invasive woody plants and their comparative analysis 2.1 Introduction 2.2 Background 2.3 Invasive Woody Species Database 2.4 Results and discussion 2.5 Future prospects 3 Invasive woody plants in the tropics 3.1 An historical perspective of the introduction of exotics 3.2 Human perception, ignorance and experience 3.3 Invasive tendencies and species biology 3.4 Time-lags 3.5 Management and policy implications 3.6 Research needs 4 Provisional list of woody plant species invasive in the tropics 5 Case histories of highly invasive woody species in the tropics 5.1 Introduction 5.2 Species description 5.3 Species accounts 6 Acknowledgements 7 Bibliography School of Agricultural and Forest Sciences Publication Number 13 University of Wales, Bangor 1998 SUMMARY Using databases and associated literature a review of invasive woody plants in the tropics and sub-tropics is presented. It focuses on information not readily available in published overviews on biological invasions. Using data on 3579 bibliographical references and 653 invasive woody species temporal, spatial, taxonomic and ecological trends and patterns are described. Data for the tropics and sub-tropics are compared to those of the world. The importance of historical and socio-economic factors in the introduction and subsequent spread of exotic species is examined. The difficulty in identifying the taxonomic nature of an introduced plant, ascertaining whether a plant is native or alien and obtaining historical information is stressed. Invasive tendencies of woody species and the predictability of a species becoming invasive are reviewed in relation to species characteristics, disturbance regimes and environmental factors. Time-lags between the introductions of tropical woody plants and their spread are investigated in more detail. Published evidence shows that major changes in a biotic factor (e.g. grazing, pollinator, seed disperser) or an abiotic (e.g. fire, wind, flood, logging) factor determines the duration of time-lag. A list of 235 woody species in tropical and sub-tropical regions is presented with species listed according to life-form and degree of invasiveness. Eighteen species selected from the most highly invasive species category are investigated in greater detail in the form of short species accounts. 1. INTRODUCTION Biological invasions are considered to be one of the major threats to the earth's biodiversity. Many animal and plant taxa are highly invasive and some species dramatically affect the structure and function of ecosystems. During the 1980s the Scientific Committee on Problems of the Environment (SCOPE) programme attempted to draw attention to this major threat as well and summarize the available information. As a result a large number of books and proceedings were published (e.g. Drake et al. 1989, Duffey 1988, Groves & Di Castri 1991, Ramakrishnan 1991). In the plant kingdom a great number of invasive species are woody. However, a perusal of the SCOPE-related literature indicates that no serious attempt was made at gathering, analyzing and interpreting the available information on woody plant invaders. For example, Rejmneck (1989) in his review included only 32 woody species. Whitmore (1991) produced a similar review for the tropics, chiefly based on evidence from south-east Asia, and claimed that all tropical moist forests are resistant to invaders although several cases had been previously reported (Binggeli 1990). The books by Cronk & Fuller (1995), Pysek et al. (1995) and Rejmneck (1996) provide a much broader, but not comprehensive, review of the subject. In this study on woody plant invasions it is intended to: 1. Provide an overview of the literature and of the main taxonomic, biogeographical and ecological attributes of woody invasive plant species with special reference to the tropics and subtropics (including wet, dry and montane regions). 2. Investigate some historical aspects of woody species introductions in the tropics in some detail, 3. Raise some key ecological questions such as the existence of time-lags, the reasons for their existence, and whether we can predict events after a potential introduction, 4. Produce a provisional list of tropical invasive woody plants, and 5. Provide species accounts on a number of highly invasive species and which pay special attention to the autecology of the invaders. An attempt is made to evaluate differences in ecology between the native and invaded ranges in each of these accounts. Much of the information reported in this study is based on a number of databases on invasive woody plants and associated reprint collection. 2 OVERVIEW OF INVASIVE WOODY PLANTS AND THEIR COMPARATIVE ANALYSIS 2.1 INTRODUCTION In this section an overview of woody plant species with special reference to the tropics is presented using the information contained in two databases containing information on, respectively, bibliographical references and information on 653 woody species. This is a preliminary overview, as data on a number of species and ecosystem attributes has yet to be entered in the database and many bibliographical references have yet to be traced. Wherever possible the data from the bibliographical database analyzed in 1994 (up to the year 1992) is compared with the 1998 analysis which includes data until the year 1996. During that period the data set of the bibliographical reference database has roughly doubled. 2.2 BACKGROUND A rapid perusal of the literature indicates that there are hundreds, even thousands, of invasive plant species worldwide. In the plant kingdom a large proportion of invasive species is woody (including sub-shrubs with stems woody at the base). However, it is difficult to gain an overall picture of woody plant invasions because of the limited number of well studied cases and the difficulty in tracing published information on biological invasions. Therefore, only a long-term project can provide the basis to an overview of invasive woody plants. In order to do so, it is essential to gather information on any species exhibiting an invasive tendency as well as information on the biology and ecology of each plant and ecological and environmental information on the native and invaded ranges. This information gathering was initiated in the mid 1980s. To summarize and analyze some of the information gathered a relational database was set up. The Invasive Woody Species Database (using R:Base run on a PC-compatible 486 notebook) was set up between 1990 and 1993 and is based on information gathered over 10 years of literature search. A bibliographical reference database was initiated in 1990 and data entered thereafter. In 1993 a relational database on invasive woody plants was set up and includes a number of species (e.g. life-form, life cycle...) and invaded ecosystem attributes. For practical reasons, mainly as a result of how data was initially entered into the database, sub-tropical areas (up to a latitude 30o) only include Florida, the Indian peninsula, Pacific islands, Northern Africa, South America, but fail to include southern Africa and parts of sub-tropical Australia. 2.3 INVASIVE WOODY SPECIES DATABASE 2.3.1 DATABASE STRUCTURE AND CONTENT The Invasive Woody Species Database (due to lack of computer power) is in two main parts which can easily be connected: the bibliographical reference database (Reference Database) and the invasive plant database (Species Database). The Reference Database is composed of standard fields and contains over 18500 references of which about 6000 pertain to invasive organisms and the majority of the others contain ecological information relevant either to the autecology of these invasive organisms and or the ecology of the native and invaded ecosystems. In this study the term invasive is defined as the establishment of self-regenerating, usually expanding, populations of an introduced species in a free-living state in the wild (Binggeli 1994) and is somewhat different from that of Cronk & Fuller (1995) who do not include species invading man-made habitats. Pysek (1995) reviewed the terminology associated with invasive plants. Each reference record has a number code and a field containing a large number of key words (based on the text rather than the title or the abstract) including species names, geographic areas and life form. The Species Database is relational and consists of four tables, two of which contain information on respectively 42 species attributes and 10 ecosystem attributes. All information entered in the Species Database is linked to a reference in the Reference Database using a number code (where possible a copy of the original publication has been kept in files organised by genera or region). Since the quality and the quantity of the available information are often poor, the various attributes included in the Species Database were necessarily chosen according to the availability of information rather than their importance in generating hypotheses or making predictions. The great majority of biological information is not discrete. To simplify the database much of the information was categorized, often subjectively (for instance life-forms: tree vs shrub; degree of invasiveness). Some of the results presented below may not represent distinct guilds but may prove be part of a continuum when more data has been added. It is intended to continue refining and expanding the species database. This will result in the inclusion of new attributes and possibly the rejection of some existing ones. 2.3.2 DATASET INCLUDED IN PRESENT ANALYSIS 2.3.2.1 Reference Database Bibliographic references entered into the Reference Database have been obtained by scanning Forestry Abstracts, Current Advances in Botanical Sciences, journals' table of contents, floras and bibliographies of a large number of published papers. Any publication which reported the natural regeneration of a woody species outside its natural range was included in the database regardless of its degree of invasiveness or invaded habitats. In order to reduce some degree of bias all references dealing with three species investigated in detail by the author were not included. They are Acer pseudoplatanus L. (184 records), Hippophae rhamnoides L. (25 records) and Maesopsis eminii Engl. (33 records). The total number of references included in the present analysis is 3579, of which notes on or reprints of around 1000 publications are with P.B. Searching has been completed to the end of 1996 as many publications post 1996 publications have yet to be traced and entered. For the 1992 dataset searching had been carried out until late 1994 and includes 1924 records. 2.3.2.2 Species database Published information pertaining to invasive woody plants is often subjective and difficult to interpret. For the purpose of this study, data for a number of attributes (e.g. degree of invasiveness, purpose of introduction and habitat types) have been amalgamated into a small number of broad categories. Wherever possible, invasive events are scored as possibly/potentially, moderately or highly invasive. Introduced species recorded as possibly/potentially invasive are locally regenerating but the extent of spread is not known or is limited. Moderately invasive species are spreading but still occur at low densities and are not considered an immediate problem. Highly invasive species have become dominant or co-dominant in the invaded region and are considered a threat to the native flora and ecosystem. These species are usually subjected to some form of control. Out of 1198 invasive events it has been possible to assess the degree of invasiveness in 1060 cases. Throughout, the data are presented in relation to the degree of invasiveness. As each species can be invasive in more than one region with differing degrees of invasiveness, the highest degree of invasiveness is used for each species in the presentation of the data dealing with species attributes. Results are presented for attributes where data are currently (1/3/1998) available for at least 30% of the species. 2.5 RESULTS AND DISCUSSION 2.5.1 Reference database Temple (1990) remarked that he was amazed that so few papers on exotic organisms were published in Conservation Biology, suggesting a lack of research in this important field of conservation. In fact, the number of references relating to woody invasive plants has steadily increased since the last century with the 1987-1996 period representing nearly half of the total (Table 2.1). The growth in published material on invasive woody plants, both worldwide and in the tropics, exhibit an increase similar to that of publications on African moist forests but compares favourably with the trend for sycamore (Acer pseudoplatanus) (Table 2.1). However, the rate of increase in the number of publications on invasive woody plants appears to have levelled off since 1990 and just over 200 publications have appeared yearly. The three data sets show the same levelling off or even decrease in publication rate associated with the World War II period. It is estimated that around 80-90% of all references published on sycamore, with the exception of those pertaining to suspension cell cultures, have been traced, but out of 2958 references only 30% and 17% are available from, respectively, Forestry Abstracts and Biological Abstracts searches. This clearly indicates that on-line databases only provide a starting point to a thorough literature search. It is estimated that the 3579 references represent no more than about half of all published material on invasive woody plants, although it does probably include the greater majority of key publications. Table 2.1. Comparative increase in the number of references relating to woody invasive species worldwide and the tropics/sub-tropics, African moist forests and sycamore, Acer pseudoplatanus (data expressed as a %) woody invasions African sycamore world tropics forests N 3579 1312 1137 2958 year 1896 0.7 0.6 0.3 5.4 1896-01 0.1 0.1 0.7 1.2 1902-06 0.2 0.2 0.6 1.1 1907-11 0.2 0.2 0.7 1.6 1912-16 0.3 0.4 0.2 1.2 1917-21 0.3 0.3 0.1 0.7 1922-26 0.6 0.5 0.6 1.0 1927-31 0.8 1.1 0.7 1.7 1932-36 0.9 1.0 1.7 1.5 1937-41 0.8 1.0 1.4 1.2 1942-46 0.8 1.1 0.5 1.0 1947-51 1.5 1.7 3.0 2.4 1952-56 2.5 1.9 3.2 5.3 1957-61 2.2 2.0 4.4 4.6 1962-66 3.7 3.6 4.0 4.2 1967-71 4.7 4.4 5.4 8.0 1972-76 6.9 5.9 5.5 10.0 1977-81 8.9 7.2 7.8 11.0 1982-86 15.0 13.5 10.1 11.0 1987-91 22.7 24.6 24.6 14.9 1992-96 26.2 28.7 24.5 11.6 Out of the 3579 references on invasive woody plants, very few (ca <5%) report case histories of biological invasions. The majority mention invasiveness only in passing or in a very descriptive manner. A large number of publications (Table 2.2) are review papers (12.5%) and there was a strong increase in their relative importance during the late 1980s, chiefly as a result of the SCOPE publications. In the 1990s the proportion of review papers still appears to be increasing. Papers on biological control and other forms of control represented respectively 11.5% and 16.6% of the total (note that some references classified under biological control also refer to other means of control). The proportion of publications relating to biological control, in both the world and the tropics, has gone through cycles with peaks around 1950, the late 1970s and 1990s whereas comparatively few publications on biological control appeared in the 1950s and around 1980. Prior to 1976 the proportion of biological publications was much higher in the tropics than worldwide, but since the late 1970s a similar proportion has been published (Table 2.2). The biogeographical origin of the references is in decreasing order of importance from North America, Australia, South Africa, New Zealand, British Isles, Hawaii and tropical Africa (Table 2.3). It is followed by Germany, which in the English-speaking world, is not regarded as a region susceptible to woody species invasions and/or considered to be interested in the phenomenon (Germans scientists were not involved in the SCOPE programme). A comparison of the data for 1992 and 1996 indicate that there has been a relative decrease in the number of publications produced in South Africa and New Zealand. Table 2.2. Changes in the relative importance of review papers and publications on biological control relating to woody invasive species worldwide and in the tropics/sub-tropics. all references general and review biological control references references world tropics world tropics world tropics N 3579 1312 446 171 410 215 % 100 100 12.5 13.0 11.5 15.6 year N N % % % % 1896 26 7 7.7 - - - 1897-01 2 1 - - - - 1902-06 6 3 - - 16.6 33.3 1907-11 8 3 - - - - 1912-16 11 5 9.1 - - - 1917-21 12 4 16.7 - 8.3 - 1922-26 21 6 4.8 - 4.8 16.7 1927-31 28 14 7.1 7.1 14.3 7.1 1932-36 31 13 3.2 - 9.7 23.1 1937-41 29 13 13.8 7.7 10.3 23.1 1942-46 28 14 7.1 7.1 7.1 14.3 1947-51 57 22 - - 5.3 13.6 1952-56 91 25 6.6 8.0 6.6 24.0 1957-61 79 27 7.6 7.4 13.9 25.9 1962-66 132 48 9.1 12.5 12.1 22.9 1967-71 170 58 7.1 6.9 12.3 24.1 1972-76 248 77 5.2 3.9 6.0 10.4 1977-81 319 94 8.8 11.7 8.8 11.7 1982-86 535 177 9.5 7.3 10.5 13.0 1987-91 813 324 16.4 15.7 13.8 16.0 1992-96 936 376 18.2 20.2 13.6 17.8 Table 2.3. Geographical focus of bibliographical references (regions with more than 100 records in 1996 included). Region Year 1996 1992 North America (except Florida) 547 272 Australia 495 202 South Africa 389 248 Hawaii 318 148 British Isles 316 169 New Zealand 309 206 Pacific (other than Hawaii) 224 87 Florida 140 45 Tropical Africa 137 78 Germany 116 59 Islands - world 1276 659 - tropics 617 295 World 3579 1924 Tropics 1312 610 It is worth noting that all the regions with the highest number of references are historically linked with Britain and it is not clear whether this is due to the historical factors such as interest in natural history (chiefly perception of nature) and/or horticultural interest and/or language barriers, or reflect the worldwide pattern and severity of woody invasions. The number of references relating to islands was 1276 (617 in the tropics) and to the tropics was 1312, including 137 for tropical Africa and 140 for Florida. The relative proportion of the figures for 1992 and 1996 are broadly similar. Table 2.4 gives the number of publications in which a genus is given as invasive and includes genera with more than 70 and 20 records in respectively the world and the tropics/sub-tropics. Genera with more than 150 records include two genera each with only one invasive species (Ulex and Lantana) and four with several species (Acacia, Pinus, Psidium and Rubus). Some genera are reported in a large number of publications either in the tropics/sub-tropics (e.g. Psidium, Melaleuca and Chromolaena) or temperate zone (e.g. Pinus, Rubus and Hakea) while others are widely reported in both (Lantana, Acacia and Ulex). Between 1992 and 1996 the number of publications for some genera has increased much faster (e.g. Psidium and Miconia) or much slower (e.g. Ulex) than for the majority of genera. The rapid increase in the number of publications on Miconia and Cryptostegia reflects the rather recent realisation of their invasive potential and impact on native vegetation. Table 2.4. Genera referred to in the largest number of publications. WORLD TROPICS AND SUB-TROPICS Genera Year Genera Year 1996 1992 1996 1992 Lantana 286 137 Lantana 225 100 Acacia 263 189 Psidium 189 83 Ulex 207 155 Mimosa 132 45 Psidium 194 83 Chromolaena 108 53 Rubus 183 113 Melaleuca 106 64 Pinus 172 124 Schinus 78 49 Lonicera 138 64 Acacia 75 34 Mimosa 134 45 Passiflora 72 48 Chromolaena 127 80 Myrica 70 36 Tamarix 124 61 Clidemia 65 32 Melaleuca 106 64 Rubus 61 40 Rhododendron 106 54 Cryptostegia 34 3 Hakea 101 67 Ulex 34 20 Schinus 96 59 Miconia 28 4 Robinia 92 60 Passiflora 79 51 The difficulty in gaining information is illustrated in Table 2.5, where the journal, which published the largest number of papers on invasive woody plants, is noted to contain only 1.2% of the total number of references. Books, including floras and reports, account for 14.1% of the total while chapters in books and conference proceedings represent 19.3% of the total. For the tropics/sub-tropics alone the figures are markedly similar but journals publishing the largest proportion of papers is different. Since 1992 new publications have appeared and others have tended to publish fewer articles on invasive woody plants. The majority of publications relating to invasive woody plants are either not abstracted or make no reference to invasive woody plants in the title, abstract or key words, again highlighting at the difficulty in gathering information. The high ranking of, for instance, BSBI News (not abstracted) in Table 2.5 points out that much of the available information is anecdotal and often collected by amateur botanists. As a result the quantity of information available for a particular species can be very limited. Some genera are widely used in review papers as typical examples of invasive woody plants and some of the species may have be cited in a high proportion of review papers, and this is particularly the case of Myrica and Melaleuca with respectively and third and a quarter of their publications. Table 2.5. Sources of bibliographical references (figures in brackets are %). WORLD TROPICS AND SUB-TROPICS Year 1996 1992 1996 1992 Total 3579 1924 1312 610 (100) (100) (100) (100) Books (including floras 506 264 Books (including floras 201 90 & reports) (14.1) (13.7) & reports) (15.3) (14.8) Chapters in books & 689 423 Chapters in books & 289 141 conference proceedings (19.3) (22.0) conference proceedings (22.0) (23.1) Journals, bulletins & 2384 1237 Journals, bulletins & 822 379 magazines (66.6) (64.3) magazines (62.7) (62.1) Main Journals N.Z. J. Bot. 42 22 Pac. Sci. 27 10 Biol. Conserv. 40 24 Biol. Conserv. 16 13 BSBI News 31 17 Proc. Hawn entomol. Soc. 15 14 Pl. Prot. Quart. 31 6 Monogr. Syst. Bot. MO Bot. Gard. 14 11 US Dept Agric., Agric. Handb. 31 28 Newsl. Hawn bot. Soc. 14 2 Pac. Sci. 27 11 Aliens 13 0 Ecology 26 11 Agnote 11 11 J. Ecol. 26 21 Atoll Res. Bull. 11 1 J. appl. Ecol. 24 14 Pl. Prot. Quart. 11 3 Aliens 21 0 Qld Agric. J. 11 4 S. Afr. J. Bot. 20 17 Entomophaga 10 3 Agric. Ecosyst. Environ. 23 16 Ind. Forester 10 8 S. Afr. For. J. 18 16 Agric. J. (Fiji) 9 6 S. Afr. J. Sci. 16 15 J. Biogeogr. 8 7 Some of the changes observed between the 1992 and 1996 datasets are undoubtedly due to changes in publication rates in various countries, genera and journal/magazine/bulletin, however some of the variation is also due to literature hitherto unavailable or not scanned. 2.4.2 Species database 2.4.2.1 Taxonomy Worldwide 653 woody plant species, belonging to 315 genera and 110 families, have been recorded as being invasive. The Rosaceae and legume families, and to a lesser extent the Pinaceae and Myrtaceae, contain a large number of invasive woody plants (Table 2.6). However most species of the Rosaceae are possibly/potentially or moderately invasive and relatively fewer are highly invasive. On the other hand families such as the Asteraceae, Myrtaceae and Melastomaceae have a number of highly invasive species but few possibly/potentially invasive species and are chiefly tropical/sub-tropical species. Regardless of the degree of invasiveness the Mimosaceae contains the largest number of invasive species in the tropics. Table 2.6. Families with highest number of invasive woody species (Degree of invasiveness (DI): 1 = possibly/potentially invasive, 2 = moderately invasive, 3 = highly invasive, N = no. of species). WORLD Total DI 1 DI 2 DI 3 Family N Family N Family N Family N Rosaceae 98 Rosaceae 34 Rosaceae 50 Mimosaceae 17 Mimosaceae 49 Papilionaceae 12 Mimosaceae 21 Rosaceae 14 Papilionaceae 27 Mimosaceae 11 Myrtaceae 13 Asteraceae 7 Pinaceae 27 Pinaceae 8 Pinaceae 12 Pinaceae 7 Caesalpiniaceae 21 Salicaceae 7 Caesalpiniaceae 11 Myrtaceae 6 Myrtaceae 20 Caesalpiniaceae 7 Ericaceae 11 Papilionaceae 5 Asteraceae 17 Caprifoliaceae 6 Oleaceae 11 Caprifoliaceae 4 Ericaceae 17 Berberidacea 5 Solanaceae 11 Melastomaceae 4 Oleaceae 17 Cornaceae 4 Papilionaceae 10 Solanaceae 4 TROPICS AND SUB-TROPICS Total DI 1 DI 2 DI 3 Family N Family N Family N Family N Mimosaceae 31 Mimosaceae 4 Mimosaceae 15 Mimosaceae 12 Myrtaceae 14 Caesalpiniaceae 3 Rutaceae 9 Myrtaceae 5 Caesalpiniaceae 13 Papilionaceae 3 Caesalpiniaceae 8 Asteraceae 4 Rosaceae 11 Acanthaceae 2 Myrtaceae 8 Melastomaceae 4 Rutaceae 10 Myrsinaceae 2 Euphorbiaceae 6 Rosaceae 4 Table 2.7. Biogeographical distributions of invasive events (DI as in Table 2.6, DI available for 1060 invasive events, N = no. of species). Total DI 1 DI 2 DI 3 Region N N N N Europe 250 107 122 21 Pacific Islands 155 31 83 41 North America 143 37 82 24 New Zealand 134 43 78 13 Australia 88 35 33 15 Indian Ocean Islands 74 9 50 15 Southern Africa 62 13 29 20 Tropical Africa 57 13 32 12 Asia 42 7 22 13 Southern America 27 4 18 5 West Indies 12 1 10 1 Atlantic Islands 11 3 8 - Madagascar 8 - 4 4 Others 2 - 2 - 2.4.2.2 Biogeography In the temperate zone a large number of invasions have been reported from most regions with the exception of Southern America and Asia (Table 2.7). In the tropical zone most invasions are reported from Pacific and Indian Ocean islands, with no records from the Amazon region! Worldwide the same number of invasions of continents and oceanic islands has been reported (Table 2.8). When one takes the degree of invasiveness into account the ratio between possibly/potentially, moderately and highly invasive species is similar on continents and islands (Table 2.8). However, there are relatively few highly invasive woody species on islands situated on continental shelves (e.g. British Isles) than isolated ones (e.g. Hawaii). In the tropics there are relatively fewer invasive species on continents and on continental shelf islands. The relative importance of possibly/potentially invasive species is much lower in tropical regions than for the world but this is probably due to under-recording. Table 2.8. Relative incidence of invasions on continents and oceanic islands (DI as in Table 2.6, DI available for 1060 invasive events, N = no. of invasive events). WORLD TROPICS AND SUB-TROPICS ` DI 1 DI 2 DI 3 DI 1 DI 2 DI 3 N % % % N % % % Continents 529 30 52 18 133 23 56 21 Oceanic islands 531 27 56 17 260 16 60 24 Oceanic islands - isolated 396 22 58 20 247 16 60 24 - continental shelf 135 41 50 9 13 15 70 15 2.4.2.3 Ecology Species attributes Shrubs (height < 5 m) are the commonest invasive life-form followed by small trees (height 5-15 m) and trees (height > 15 m). The relative importance of shrub species is much greater among potentially invasive species than in the other two categories (Table 2.9). There are few invasive woody climbers. In tropical regions the relative importance of possibly/potentially and moderately invasive shrubs is much lower. Table 2.9. Life-forms of invasive woody species (DI as in Table 2.6, N = no. of species). WORLD Height Total DI 1 DI 2 DI 3 N % N % N % N % Trees >15m 166 25 34 20 102 28 30 25 Small trees 5-15m 181 28 32 18 115 32 34 29 Shrubs < 5m 264 41 97 56 125 35 42 35 Climbers 42 6 11 6 18 5 13 11 TROPICS AND SUB-TROPICS Height Total DI 1 DI 2 DI 3 N % N % N % N % Trees >15m 73 30 7 23 51 34 15 24 Small trees 5-15m 90 36 11 35 62 41 17 27 Shrubs <5m 63 26 10 32 29 19 24 38 Climbers 19 8 3 10 9 6 7 11 The relative proportions of evergreen and thorny species increase with the degree of invasiveness, although overall the total number of thorny species is low (Table 2.10). The majority of tropical species are evergreen. Wind-pollination is commoner in possibly/potentially invasive species and insect-pollination more frequent in moderately and highly invasive species and in the tropics the relative importance of wind-pollination increases with the degree of invasiveness (Table 2.10). Some moderately and highly invasive species are amphophilous, bird-pollinated or self-pollinated. A variety of fruit types characterize invasive woody plants including, in decreasing degree of importance, berries, pods, capsules, drupes and cones. Birds are the main dispersal agent followed by wind. The relative importance of wind-dispersed species decreases with the degree of invasiveness (Table 2.10). The relative proportions of fruit types and dispersal agents of tropical species are similar to that of the world, although some fruit types are not represented among the tropical examples. Table 2.10. Various species attributes characterising invasive woody plants (DI as in Table 2.6, in brackets sample size, N = no. of species). WORLD TROPICS AND SUB-TROPICS DI 1 DI 2 DI 3 DI 1 DI 2 DI 3 N % N % N % N % N % N % Deciduousness (383) (112) deciduous 58 57 100 47 27 39 2 18 22 30 3 11 evergreen 36 35 100 47 35 51 7 64 46 63 20 71 semi-evergreen 8 8 12 6 7 10 2 18 5 7 5 18 Thorniness (220) (110) thornless 36 97 114 90 41 73 8 88 62 86 26 70 thorny 1 3 13 10 15 27 1 12 10 14 11 30 Pollinating agent (161) (61) amphophilous - - 3 7 - - 1 5 bird - 1 1 1 2 - - - insect 11 38 57 63 22 54 4 100 32 86 12 60 wind 18 62 32 35 14 35 - 4 11 6 30 self-pollinated - 1 1 1 2 - 1 3 1 5 Fruit type (520) (188) achene 2 1 11 4 7 7 - 4 4 3 6 berry 32 23 59 21 27 27 4 16 21 19 12 23 capsule 20 15 55 19 19 19 5 20 24 21 11 21 catkin 8 6 8 3 1 1 - - - cone 10 7 18 6 9 9 - 3 3 3 6 drupe 17 13 63 22 11 11 7 28 30 27 8 15 follicle 10 7 13 5 1 1 - 3 3 - nut 2 1 6 2 - - - - pod 26 19 37 13 23 23 9 36 23 20 15 29 pome 7 5 7 2 1 1 - 1 1 - samara 4 3 9 3 1 1 - 2 2 - Dispersal agent (287) (117) animal (mixture) 2 3 9 6 4 5 - 3 5 4 10 bird 29 49 71 46 38 49 5 62 27 46 17 43 explosive - 1 1 3 4 1 13 1 2 2 5 insect - - 2 3 - 2 5 mammal - 3 3 5 6 - 2 3 4 10 water 1 2 2 1 3 4 - 2 3 3 7 wind 27 46 65 43 22 29 2 25 24 41 8 20 In the majority of species, fruit size (to the nearest cm) was 1 cm and 3cm with greater variation among pods (1-60 cm) than among other fruit types (1-15 cm). Most fruits contained one or two seeds, but a few had a larger number (up to a thousand). The size of most seeds was between 1 mm and 6 mm with a few reaching 50 mm. The purpose of introduction of species which have become invasive is not known for a large number of invasive events. Introductions for amenity purposes, and to a lesser extent for forestry and agricultural purposes, have been responsible for most reported cases of invasions (Table 2.11). Agricultural introductions result in relatively fewer cases of highly invasive species whereas the reverse is true for forestry introductions. In the tropics the relative proportion of introductions for agricultural, botanical and forestry purposes is greater, however this trend is not observable in highly invasive species rather than amenity purposes. Table 2.11. Main purpose of introductions (DI as in Table 2.6, N = no. of invasive events). WORLD DI 1 DI 2 DI 3 Total N % N % N % N % Agriculture 37 3.5 67 6.3 16 1.5 120 11.3 Botanic gardens 3 0.3 11 1.0 6 0.6 20 1.9 Forestry 27 2.5 70 6.6 34 3.2 131 12.3 Amenity 114 10.8 164 15.5 49 4.6 327 30.9 Landscape 7 0.7 11 1.0 6 0.6 24 2.3 Accidental 1 0.1 - 1 0.1 2 0.2 Unknown 114 10.7 250 23.6 72 6.8 436 41.1 Total 303 28.6 573 54.0 184 16.4 1060 100.0 TROPICS AND SUB-TROPICS DI 1 DI 2 DI 3 Total N % N % N % N % Agriculture 22 5.6 43 10.9 9 2.3 74 18.8 Botanic gardens 3 0.8 9 2.3 4 1.0 16 4.1 Forestry 4 1.0 38 9.7 13 3.3 55 14.0 Amenity 16 4.1 42 10.7 23 5.8 81 20.6 Landscape - 3 0.8 4 1.0 7 1.8 Accidental 1 0.2 - 1 0.2 2 0.4 Unknown 27 6.9 96 24.4 35 9.0 158 40.3 Total 73 18.6 231 58.8 89 22.6 393 100.0 Ecosystem attributes In only half of the reported invasive events is it possible to determine the invaded habitat (Table 2.12). Most invasions occur in forests - both natural and disturbed. The majority of invaded habitats are highly disturbed and in most instances this has resulted from human disturbance. Forests appear to be the natural habitats most susceptible to invasions by woody plants. Results for tropical regions do not differ markedly from world trends. Table 2.12. Habitat types invaded by invasive woody plants (DI as in Table 2.6, N = no. of invasive events). WORLD DI 1 DI 2 DI 3 Total N % N % N % N % Disturbed grounds 35 3.3 71 6.7 36 3.4 142 13.4 Forests - natural 10 0.9 30 2.8 19 1.8 59 5.5 - disturbed 26 2.4 82 7.7 40 3.8 148 13.9 - plantation 4 0.4 7 0.7 3 0.3 14 1.4 Hedges 2 0.2 5 0.5 1 0.1 8 0.8 Grasslands 12 1.1 23 2.1 18 1.7 53 4.9 River banks 9 0.9 23 2.1 10 0.9 42 3.9 Road sides 11 1.0 23 2.1 3 0.3 37 3.4 Swamps 4 0.4 4 0.4 2 0.2 10 1.0 Dunes 5 0.5 8 0.8 3 0.3 16 1.6 Bogs/heathland/fynbos 1 0.1 9 0.9 7 0.7 17 1.7 Cliffs 3 0.3 5 0.5 - 0 8 0.8 Unknown 181 17.1 283 26.7 42 3.9 506 47.7 Total 303 28.6 573 54.0 184 17.4 1060 100.0 TROPICS AND SUB-TROPICS DI 1 DI 2 DI 3 Total N % N % N % N % Disturbed grounds 12 3.0 25 6.4 21 5.3 58 14.7 Forests - natural 7 1.8 17 4.3 13 3.3 37 9.4 - disturbed 9 2.3 45 11.4 15 3.8 69 17.5 - plantation 1 0.3 4 1.0 3 0.7 8 2.0 Hedges - - - - Grasslands 2 0.5 8 2.1 10 2.5 20 5.1 River banks - - 2 0.5 2 0.5 Road sides 1 0.3 5 1.2 - 6 1.5 Swamps 1 0.3 1 0.3 2 0.5 4 1.1 Dunes 1 0.3 1 0.3 1 0.3 3 0.9 Bogs/heathland/fynbos - - - - Cliffs - - - - Unknown 39 9.8 125 31.8 22 5.7 186 47.3 Total 73 18.6 231 58.8 89 22.6 393 100.0 2.5 FUTURE PROSPECTS 2.5.1 CURRENT AND FUTURE PROBLEMS When this invasive woody database was set up it was clear that many problems would arise. Some were predicted. Others have arisen since. Many of the difficulties are linked with our perceptions of nature and difficulties in communicating information. The main problems are: 1. The literature is very scattered. 2. Much more information is available than is currently held in the database. 3. Taxonomic difficulties, including hybridization, are major hurdles for many genera and since this is well-known the reader is referred to other literature for details (e.g. Stirton 1979, Swarbrick 1986). 4. Invasive hot spots have been clearly identified but have yet to be explained. In the literature on biological invasions historical, cultural, social and economic factors associated with humans have received little attention. Do invasive hot spots result from: a. cultural bias in recording, b. high levels of species introductions or c. ecosystem susceptibility to invasions? or a mixture of these and other ecological factors. Above it has been pointed out that most cases of invasions have been reported by, and focus on, countries historically linked with Britain. Therefore, a cultural bias should not be underestimated. 5. Few species and ecosystem attributes have been looked at in any detail. Basic information such as life-history traits (e.g. pollinating agent, seed dispersal) are rarely reported even in case studies. Such information may often be obtained from other sources. A check list of attributes to be answered by workers in the field should be considered, which would provide us with a standardized set of data. 6. The status of some species is unclear, are they biological invasions or the result of natural dispersal? (see section 2 for details) 7. The families with the highest numbers of invasive woody species are given in Table 2.6. However, the invasive potential of a family can only be determined when the ratio of invasive species to the total number of woody species in a particular genera is known. 8. As in all literature based investigations, at least 95% of the data is secondary, dealing with species and habitats unfamiliar to the compiler. 2.5.2 DATABASE USE In addition to the overview of invasive woody plants, the database has two main objectives: 1. To have an easily retrievable source of information on a particular species, including publications relating to it, and information on a number of species and invaded ecosystem attributes, and 2. to use the information to predict the invasive potential of a species in a particular habitat and/or region. For predictive purposes invasive species must be compared with non-invasive species and with a sub-set of local floras for which the same type of information will need to be gathered. Ideally these non-invasive species should be chosen at random, but since information on them will be hard to obtain or unavailable, for present purposes well-documented species will be selected. Invasive woody plants are a minor component of biological invasions. The time, financial resources and effort involved in producing this database, as well as what is still required to make it reasonably comprehensive, indicate that much needs to be done before an overall picture of biological invasions emerges. 3 INVASIVE WOODY PLANTS IN THE TROPICSPRIVATE  This section collates and summarizes relevant information not readily available elsewhere for an illustrative set of tropical species. Several major publications on invasive species have appeared in recent years (e.g. Drake et al. 1989, Ramakrishnan 1991, Cronk & Fuller 1995, Pysek et al. 1995, Carey et al. 1996, Sandlund et al. 1996, Williamson 1996). However there is need for a focus using, for each species, a set of headings covering life cycle attributes, consequences of invasive behaviour and integration into the invaded vegetation. Eighteen accounts are presented here on this basis. As a broader context four issues are discussed below. The first is the historical perspective. The second issue is how this relates to human aspirations, perceptions and actions. The biological basis of the contrast between extremely widely planted species apparently with no or minimal invasive tendencies and others which rapidly become problematic is the third issue. The final issue is possible future trends. 3.1 AN HISTORICAL PERSPECTIVE TO THE INTRODUCTION OF EXOTICS Numerous woody species have been moved around the world, but the timing and the purpose of introductions, the species involved is poorly known. What remain of these introductions are agricultural, horticultural and forestry crops as well as invasive woody plants. Nevertheless, Spongberg (1990) has provided such an overview for North America. For most tropical regions such information has yet to be presented - but see Harris (1962) for the Leeward Islands, Duffey (1964) for Ascencion, Corlett (1992) for Hong Kong and Singapore, and Strahm (1993) - even though a foundation was laid long ago in the work of de Candolle (1860). Subsequently, Guppy (1917), Ridley (1930) and Sauer (1988) made significant advances in information collation and review where seed dispersal and plant migration are concerned. Crosby (1986) has related the pattern of introduction of plants, but particularly herbaceous agricultural weeds, to the European conquest of the world. A conspicuous omission from the studies carried out in the past has been the African situation. In this brief review we have therefore included a preliminary review for tropical Africa. For the purpose of woody plant introductions into tropical Africa four main phases may be recognized: . early exploration and slave trade, . early colonial period, . colonial exploitation, and . post colonial development Early exploration and slave trade Europeans first settled in the Gulf of Guinea in the late 15th century. By the 18th century a number of French and English forts were scattered along the Golden Coast. These forts were involved in the slave trade and each of them had a gardens in which a number of crops, including many tropical American and Asian fruit trees, were grown (Juh-Beaulaton 1994). These included Anacardium occidentale, Citrus spp. and Psidium guajava. A number of weeds were accidentally introduced when American crops were brought to Africa (Wild 1968). Early colonial period In Tanzania, non-indigenous plants were introduced to the experimental gardens of the Bagamoyo Mission shortly after its inception in 1869. From 1893 273 species of mostly tropical plants, including many ornamental and forest trees, such as Acacia spp., Cinchona spp., Delonix regia, Eucalyptus spp. and Terminalia catappa, were tested in an experimental nursery at Dar es Salaam which functioned as a seed production and distribution centre. Large quantities of seeds of various timber species were distributed to private planters and government stations. By 1903 a total of 118 indigenous and exotic timber species were under cultivation in the Lushoto District (Schabel 1990). Following the closure of the Kwai Agricultural Station, founded in 1896, a station was established in the East Usambaras at Amani in 1902 as an experimental site for field testing of exotic species (Iversen 1991). It included a botanic garden of ca 750 acres, including ca 500 acres of plantations, spreading between 400 and 1100 m (Fernie 1948). Nearly all species were introduced from other continents because they were either potential cash crops or known to be fast growing and useful in reforestation of steep mountain sites. Although the Amani forests contain several quality hardwood species, the research station was built with timber imported from Germany - it was cheaper to do that than to utilise local woods (Joelson 1928). Ornamentals, including temperate species, were introduced and it was the Director's (Prof. A. Zimmerman) hobby to collect plants from all over the world and try them out at Amani (Joelson 1928). Amani became a major distribution centre for seeds and seedlings in Tanzania and the tropics (Anon 1930, Schabel 1990). Other botanical and experimental gardens in Africa were established from about 1890 including in Cameroon (Limbe, formerly Victoria, 1891) by the Germans, in Guinea (Fouta-Djalon) by the French, in Zaire (Eala) by the Belgium and in Lagos (1887) and Calabar (1893), both in Nigeria and Uganda (Entebbe, 1898) by the British. Colonial exploitation Soon after World War II a number of large-scale forestry plantations were established in order to enhance timber production. These plantations consisted of introduced species including Eucalyptus spp., Gmelina arborea, Maesopsis eminii and various conifers, especially Cupressus and Pinus. A number of agricultural crops were widely planted. Post colonial development In the last 20 years an increasing diversity of non-indigenous germplasm has been introduced to Africa as it has been to other tropical regions (Hughes 1994). Hughes documents in some detail the increase in the trade including increases in the number of species and provenances distributed as well as the number of planting locations. In other parts of the tropics similar patterns of species introductions, particularly in relation to crop plants, forestry and ornamental woody species, have occurred. Tropical botanical gardens were set up in more places around the tropics, including several small oceanic islands (Pamplemouses, Mauritius; St Vincent, Caribbean), Asia (Bogor, Indonesia; Calcutta, India; Peradeniya, Sri Lanka; Singapore), Australia (Darwin) and South America (Rio de Janeiro). Botanic gardens on islands were created as early as the 18th century whereas those on the continental land masses, particularly mainland Africa, much later (Cronk & Fuller 1995). The importance of Bogor (formerly Bruitenzorg) in Indonesia has been emphasised by Bouvier (1946). The main purpose of these gardens was to introduce exotic seeds and plants (e.g. Darwin, Miller & Lonsdale 1987) and usually to assess the commercial potential of a variety of crops. The name given by the Germans to what is now known as the Limbe Botanic Gardens, was the 'Research Institute for Land Improvement' (Timler & Zepernick 1987), and clearly indicates the original purpose of the gardens. A lack of knowledge of the local timber trees was often the reason for introducing exotic tree species. During the early years of these tropical gardens the botanical interest was secondary. However, many differences in the patterns of introductions, resulting chiefly from different colonial histories and geographical locations, are likely. It is known that Polynesians introduced a large number of woody plants to the Hawaiian islands prior to European colonisation (Wagner et al. 1990, Bevacqua 1994). Botanical gardens were established in settled areas - the easily accessible or climatically ideal regions near coasts or in cooler upland areas. Large areas of South America were devoid of settlements and thus botanic gardens and forestry trial plots until comparatively recently. The colonial powers had different routes for the introduction of plant material. Often plants were first transported to Europe (e.g. to Kew, Bruxelles, Berlin-Dahlem for respectively Britain, Belgium and Germany) and then disseminated to tropical gardens in their respective colonial territories. During the past hundred years Africa has probably been subjected to less introduction of ornamentals than economically more advanced areas such as Australia and Hawaii which have developed major horticultural industries. 3.2 HUMAN PERCEPTION, IGNORANCE AND EXPERIENCE Nearly all introductions of woody plants, which have become invasive, have been introduced intentionally by horticulturalists, botanists, foresters or gardeners. The bibliographical data showed that as early as last century a number of authors realised the regeneration potential and sometimes the invasive potential of introduced woody plants. These problems having been known for quite some time, it is then important to investigate how aware practitioners of introductions were of the potential problems associated with species introductions. Botanists, conservationists, foresters, agroforesters and horticulturalists have, and often still are, to varying degrees, responsible for the introduction and planting of woody species. While there was awareness of invasive potential and related environmental impact, it appears that often it has been considered that introduction of potentially invasive species would do more good than harm. A number of examples are given below to illustrate the problem. In our view, many more cases could also be documented. The French botanist Auguste Chevalier (1952) recommended the introduction of Chromolaena odorata to West Africa to control Imperata spp. and other coarse grasses despite the fact that he regarded the species as a weed (Chevalier 1949) and much earlier had published a paper on man's role in the dispersal of tropical plants (Chevalier 1931). A number of species introduced to tropical botanical gardens have become invasive but there is no evidence to show that scientists responsible for their introductions were aware of the potential problems. The appearance of articles warning that tropical botanical gardens could be the source of invasive species is a very recent development (Sheil 1994). However, Miller & Lonsdale (1987) have shown that the weedy nature and associated problem of introduced species at the Darwin Botanic Gardens was recognised early this century, but the botanists still failed to foresee the implications for the vegetation of the Darwin region. During the 1980s it was realised that a number of introduced trees were spreading in the logged and natural forests of the East Usambaras in Tanzania (Binggeli & Hamilton 1990). Because the biological importance of the East Usambaras and the threat posed by logging, deforestation and invasive species an IUCN project was initiated to help in the sustainable management the mountains. One aspect of the programme consisted in rehabilitating or demarcating Forest Reserves to prevent forest encroachment. In order to make the demarcation noticeable exotics including species known to be invading the natural forest, such as Cedrela odorata, were planted. The original vegetation, rich in endemic species, of the isolated Atlantic island of St Helena has almost entirely been destroyed. These changes have been induced by browsing, grazing, wood harvesting, forest clearance and plant introductions (Cronk 1989). On many parts of this rugged island this has resulted in severe soil erosion. In the early 1990s a sustainable development strategy was initiated by Overseas Development Agency to address St Helena's environmental problems. In their final report Spooner et al. (1993) give a list of exotic species colonising eroded areas which they classify as useful, neutral and some which may lead to resource degradation. The latter group include a species which may have adverse effect on soils and another is an unpopular weed. The colonisation potential of other introduced species is not discussed and assumed to be positive. It is even stated that Acacia used in afforestation "are growing well, but there is limited seedling colonisation outside the planted zones" indicating that the lack of natural regeneration is considered to be a negative feature and concluded that "a high research priority should be given to identifying the regeneration requirements and constraints of the different colonists." Although new species have been recommended for introduction, Spooner et al. (1993) give no clear justification for new imports and trials of Leucaena for fodder and Casuarina equisetifolia currently under way, two species well known for their invasive potential. There is evidence from the temperate zone that some woody species (e.g. Ulex europaeus, Lupinus arboreus) facilitate the establishment of native forest. However this evidence is entirely lacking for the tropics and it is generally accepted that invasive plants displace rather than facilitate succession on tropical oceanic islands. Thus nitrogen-fixing plants such as Acacia and Casuarina spp. main be successfully used to prevent soil erosion but there is, at present, no evidence that they will eventually encourage the regeneration of native plants and that of endemic plants in particular. Until recently foresters have expressed little concern about the invasive potential of introduced trees. In 1980, a book (Anon. 1980, 1983) on the choices of species to be used for fuelwood production globally and their silviculture was produced by BOSTID (Board on Sciences and Technology for International Development). For most species the ease of natural regeneration is discussed without indicating the geographical areas where prolific regeneration could lead to a weed problem. In fact about half of the species included are known to be invasive and some being serious pests in parts of the world. The authors were aware of the invasive problem but simply dealt with it by inserting a "warning" on the page facing the table of contents consisting of a single paragraph. In recent years all foresters have been aware of the invasive potential of some of their introductions and some have now started to confront the problem (e.g. Hughes & Styles 1986, Hughes 1994). In India, due to its prolific natural regeneration Leucaena leucocephala, is generally considered to be a weed, yet it was planted, mainly as a fodder crop, in the Karnataka region in early 1980. Within ten years Patil & Kumar (1990) reported that the species had become a problematic weed in cultivated land, even today, new introductions of Leucaena germplasm are proceeding. With respect to invasive species, little information from horticulture is readily available in the literature. Yet most invasive species have been introduced for ornamental purposes and this area necessitates much more attention. In many countries the introduction of species for ornamental purposes is subject to little regulations and is under-reported. A perusal of the B&T World Seeds Master List (Anon. 1996) indicate that seeds of around 50% of the species included in the Species Database can be readily ordered. As B&T World Seeds can supply reproductive material for around 35,000 species or cultivars the potential for the introduction of known and potential invasives is enormous. A major source of ambiguity in many references to invasive species is taxonomic instability. This is compounded by poor historical records, uncertainty of the sources of introductions and frequent use of local rather than scientific names. Species have sometimes been wrongly identified. For instance, In Hawai'i Melaleuca quinquenervia was formerly referred to as M. leucadendron which is not synonymous (Little & Skolmen 1989). Species identification can be difficult as a number of species hybridize readily. These taxonomic difficulties have been dealt with in some detail by a number of authors including Stirton (1979) and Swarbrick (1986). In many cases taxonomically difficult groups are involved. Species of the genus Cecropia have been introduced to many parts of the tropics and are spreading spontaneously. Cases reported include C. peltata in Malaysia, Cameroon and Ivory Coast (Putz & Holbrook 1988, McKey 1988, Ake Assi 1979), C. leucocoma in Zaire (Lonard 1951) and C. schreberiana in Madagascar (C.C. Berg pers. comm. 1995). However, there is confusion about the identity of the various invading populations. Species in the genus Cecropia have strong morphological similarities but have somewhat distinct geographical and/or ecological ranges. The species C. peltata s.s. (central America), C. pachystachya (southern America) and C. concolor (Amazon basin) can be regarded as C. peltata s.l. The names given in the literature are sometimes inaccurate. Only when the origin of the material is known, is it possible to identify the specimen with confidence. Thus, in Madagascar C. schreberiana (native to the Caribbean) has often misidentified as C. peltata, although clear morphological differences exist between these two species. The Cecropia species reported from Zaire as C. leucocoma and from Malaysia as C. peltata have both recently proved to be C. pachystachya. The identity of the further African material remains unclear (C.C. Berg pers. comm. 1995). In Hawaii C. obtusifolia has also been erroneously identified as C. peltata (Wagner et al. 1990). Details of early introductions are often vague in the extreme. Some species are initially described as native and only much later is their true origin discovered. For instance Ocotea angustitepala (Lauraceae), collected in 1912 in undisturbed forest (Robyns & Wylczek 1950), was described from Cameroon as a new species. It was later discovered to be a neotropical plant (Ocotea patens) introduced to the Victoria (Limbe) Botanic Gardens (Rowher 1989). Evidently, the species started to spread into natural forests soon after its introduction. Its current status in native vegetation is unknown. For a number of species which have been clearly shown to be spreading it is difficult, if not impossible, to determine whether they result from natural or human dispersal. These species reached new areas prior to the 19th century. Uncertainty concerning their status arises from the dearth of historical records. For instance, in the tropics it has been suggested that Hibiscus schizopetalus (Malvaceae) in Tanzania (Hawthorne 1993) and Ceiba pentandra (Bombacaceae) in Africa (Irvine 1961) are invaders, whereas Mora excelsa (Caesalpiniaceae) in Trinidad migrated naturally (Beard 1945). The status of Mimosa pigra in the tropics is a good illustration of the difficulties in establishing the introduction and spread of a woody invasive plant. M. pigra originated from tropical America and was apparently widespread in tropical Africa by the mid 19th century. It has been suggested that its seeds floated across the Atlantic ocean, however as the seed-pod sections float by surface tension rather than buoyancy they are unlikely to travel such a long distance. Therefore the introduction to and the widespread distribution of M. pigra in Africa remains a mystery (Lonsdale et al. 1989). It was originally thought that M. pigra had been introduced to Northern Australia in the late 1930s but subsequent detailed investigations of photographs and grey literature by Miller & Lonsdale (1987) suggest that the shrub was introduced prior to 1891. Early accounts referred to M. rubicaulis, a misnomer for M. pigra or simply as mimosa and already referred to the species weediness. The case of M. pigra clearly shows that painstaking investigations are necessary to unravel some of the historical aspects of an invader. Woody plant species introduced for crop purposes usually have a set of characteristics which include very fast growth, ease of propagation (including suitability for aerial seeding), were often nitrogen fixers and resistant to a variety of biotic and abiotic agents such as pests and diseases, aperiodic drought, inundation and fire (e.g. Maydell von 1989, Hughes 1994). The view is bluntly expressed by Vietmeyer (1986) writing about the Casuarina invasion of Florida where, in his view, the tree's "aggressiveness is a threat, not a benefit" he adds: "But isn't an unstoppable tree just what we need? in our deforested world the whole idea of a 'weed tree' seems like a paradox. If anything, weed trees are vital to the planet's future. Adaptable, resilient, irrepressible, resistant to disease - what could be more vital for Ethiopia, Chad, Nepal, Haiti, and the other bedrock spots of environmental degradation where the people are too busy trying to survive to worry about nurturing trees?" In parts of semiarid western Africa the local population's main reasons for preferring Azadirachta indica for single tree planting is a combination of good availability of seedlings and the ease of vegetative propagation, fast growth and low risk as well as shade and insect repellence (von Maydell 1989) . 3.3 INVASIVE TENDENCIES AND SPECIES BIOLOGY In the Invasive Woody Plant Database the purpose and date of the original introduction are included. However, the database does not contain any information on secondary introductions or plantings or on the use of a species for other purposes than the original introduction. The original introduction is usually limited to a very small number of plants often in a botanic garden or an experimental plot or a private garden. A close look at many cases of invasive species show that secondary introductions or plantings were usually carried out on a very large scale much later than the original introduction. In Hawaii seeds of many tree species introduced for ornamental purposes prior to or around 1900 were aerially sown in the 1920s and 1930s for forestry purposes (Little & Skolmen 1989). Similarly in Tanzania Maesopsis eminii was widely planted 50 years after its original introductions (Binggeli 1989). This has several implications including: artificial dispersal to new sites and rapid build up of a very large population of seed producing trees. This might explain the time-lag (see below) observed between the introduction and the start of the invasion of some woody species. It has been estimated that only about 1% of introduced species become invasive (e.g. Groves 1986). The reasons why most introduced species do not become invasive are not known. Suggestions for a certain number of species can be made which apply to the tropics but may be less relevant to the temperate zone. In tropical regions most widely introduced species have some sort of commercial value whereas potentially valuable species, ornamentals or botanically interesting plants have been introduced rather locally in a few botanic gardens. Cecropia peltata is an escape from the Limbe Botanic Gardens (Cameroon) and is now competing with Musanga cecropioides in secondary vegetation (McKey 1988). This species was also introduced to the Amani Botanic Gardens (Tanzania). However, Fernie (1948) reported that only one tree survived at Amani, and as the species is dioecious, it cannot spread even with suitable environmental conditions. A number of fast growing introduced tropical trees have exhibited invasive tendencies. Janzen (1986) has argued that many of these species, including a large number of legumes, are the sort of species which can become invasive and have a strong impact on the rate of succession and the species composition of the vegetation. However, species of extensively planted genera such as Eucalyptus and Tectona have caused few problems. In the Sierra of southern Peru Eucalyptus globulus is the dominant tree at most altitudes and essential to the local economy (Dickinson 1969). Yet, it does not regenerate. Although a few hundred species of Eucalyptus have been introduced and often extensively planted throughout the world (Penfold & Willis 1961), few instances of invasions have been reported and, those which have, tend to be relatively minor (Kirkpatrick 1977). Abandoned logged Eucalyptus tereticornis in the Western Ghats (India) show that although the species fails to regenerate, its coppicing ability allows it to remain dominant in the secondary regrowth (George et al. 1993) but the understorey species composition suggest that the typical complement of native species will eventually dominate the canopy. Kirkpatrick (1977) identified the poor dispersal ability of Eucalyptus combined with scattered distribution of suitable habitats for seedling survival as the reason for the very slow spread of Eucalyptus species in California. Seedling establishment is only successful in areas more or less free from plant competition. The observed limited spread has occurred despite various species being widely used for timber, windbreak and ornamental purposes. Until recently the problem of invasive woody plants has been publicized principally in relation to oceanic islands such as Hawai'i (e.g. Stone et al. 1992), Rodrigues (Strahm 1989), Runion (Macdonald et al. 1991) and Madagascar (Sussman & Rakotozafy 1994). In recent years a number of invasive species have been reported from Africa (Binggeli & Hamilton 1993, Sheil 1994), Australia (Swarbrick & Skarrett, 1994) and India (Saxena 1991). It has now been realised that biological invasions may become a serious and ever-increasing problem in some continental regions. Below a number of reasons are given for tendencies for such species to become increasingly problematical. These reasons are mainly related to increasing direct and indirect human induced disturbance and to human ever-increasing use of nature. Some evidence supporting some of these views have recently been reported. . Large gaps created by logging operations appear to be more readily invaded by exotics than natural tree fall gaps. The shrub Chromolaena odorata is readily found in selectively logged forests of the Western Ghats (India) but absent from natural forest (Chandrashekara & Ramakrishnan 1994). The reason for this is probably due to the fact C. odorata seeds are usually locally wind-dispersed but can be readily transported by vehicles (see species account). In heavily exploited and degraded forests of lowland of southwestern Sri Lanka Alstonia macrophylla (Apocynaceae) is commonly found in large gaps but appear to be absent from unlogged forest. In Tanzania Maesopsis eminii becomes dominant in logged forest but is capable of regenerating in natural forests in large treefall gaps. In the same forests the shrub Clidemia hirta is also becoming quite common in natural forest gaps. . Why do exotics matter in the general context of conservation of biodiversity? Increase in turn-over rate has been observed (Phillips & Gentry 1994; Phillips et al., 1994), potential rapid climatic change should result in increased intensity of disturbance, increased human pressure for firewood and forest products will all lead to conditions more favourable to known invasive woody species. Most of these species require a substantial amount of disturbance to spread extensively. . If climate changes many areas of natural vegetation are isolated and species will fail to move to other islands. . The conservation of biodiversity becomes increasingly significant in disturbed areas as areas of natural or semi-natural vegetation steadily decrease. In an overpopulated and resource hungry world secondary vegetation will become more and more important to the conservation of biodiversity. For instance in the British Isles motorway verges, railway embankments and abandoned quarries are now important assets to nature conservation. . Susceptibility of natural areas to invasions is higher if a large seed source is available around it. The smaller the area of natural vegetation the more likely it is to be invaded. . Data available from the tropics and sub-tropics on the incidence of invasions clearly show a higher reported number of cases in areas with more advanced economies and standards of living. This is probably not coincidental and rather reflects the large number of plants introduced and distributed in large numbers over wide geographical range for ornamental purposes. Assuming that the less developed world will increase its standards of living an ever increasing number of exotics species will be introduced to regions hitherto not widely affected by invasive species. A combination of isolated natural areas surrounded by large tracts of potentially invasive species, higher human disturbance, higher natural disturbance, increased movement of exotic plants and potential impact of rapid climatic change (more important in areas without climatic gradients) will undoubtedly lead to an increased threat by introduced species. 3.4 TIME-LAGS The populations of introduced species often remain small and localized for long periods of time before they exhibit very rapid expansion. Until very recently little evidence was available to support a number hypothetical explanations for these observed time-lags or lag phases. The reasons for these time-lags are threefold (Hobbs & Humphries 1995): - genotypic adaptations - cyclical disturbance or a combination of environmental conditions - species, with exponential growth, not observed until the population reaches a critical size. The time between the introduction of a species and its first record of spread and pest status in tropical invasive woody species varies, respectively, from 3 years to around 50 years and from 4 years to around 90 years (Table 3.4.1). Most woody plant species were introduced between 1838 and 1937 with a peak in the late 19th century. No obvious differences are observed when the degree of invasiveness is taken into account. This data further supports the view that the existence as well as the duration of time-lags is highly variable. A species may quickly become highly invasive (DI = 3) even after it has already been present for a long-time in a particular region. In the tropics time-lags appear to be much shorter (Table 3.4.1) than those observed in temperate species. Kowarik (1995) reported that in the German Brandenburg province the average duration of the time-lag between the introduction and the initiation of an invasion was 131 years and 170 years for, respectively, shrubs and trees. FACTORS DETERMINING TIME-LAGS For a number of the more comprehensively documented species reasons for the observed time-lags have been inferred and sometimes demonstrated (Table 3.4.2). All reported instances show that major changes in biotic and abiotic factors determine the duration of time-lags. Abiotic factors include wind, flooding and deforestation. In the case of Acacia nilotica in Australia the time-lag resulted from a series of above average wet years in the early 1950s. In Florida Casuarina equisetifolia started spreading following the disturbance caused by two hurricanes. Cecropia peltata was introduced to south western Ivory Coast as a shade tree in coffee plantations in 1910. By the late 1950s the species had spread by 20 km. However, following the destruction of most of the remaining forest the rate of spread increased markedly in the 1960s: the species had reached sites 100 km away from where it was introduced. The introduction of pollinators, marked changes in grazing and trampling intensities are examples of biotic factors determining the duration of time-lags. The sudden introduction of a pollinating agent is one of the main biotic factor determining some time-lags. For instance, Ficus microcarpa widely planted as an ornamental in Florida only became a pest about 45 years after introduction, when its natural pollinator - the fig wasp (Parapristina verticillata) was introduced. Although no evidence for the existence of genetic adaptations in determining time-lags is available for the tropics, limited data from the temperate zone indicate that this factor is probably of some importance in tropical regions too. It has been shown for the Chinese ornamental tree, Ailanthus altissima, introduced to and widely planted in North America, that native and introduced populations are genetically different although their genetic variability is the same. However, it has been argued that the differences are the result of human selection rather than adaptation to local environmental conditions. A number of other biotic and abiotic factors may also affect time-lags and are well-known to produce marked increases in woody plant population sizes including drought, frost, human-induced disturbance, hybridization and diseases. It is often difficult and even impossible to judge if there is a time-lag or simply marked increases in population size resulting from various biotic and abiotic factors - examples are given in Table 3.4.2. In the case of Pittosporum undulatum spread into the natural forest only started after hurricane disturbance, although it had already invaded disturbed forest. Table 3.4.1. Duration (in years) of known time-lags between the introduction and first spread and pest status in tropical invasive woody plants. _______________________________________________________________________ Year of noticed Perceived as initial after problem/pest Region introduction (yrs) after (yrs) _______________________________________________________________________ Acacia nilotica N. Australia ca 1900 ca 50 ca 57 Casuarina equisetifolia Florida ca 1900 ca 56 ca 65 Cecropia peltata Ivory Coast 1910 <48 69 Cameroon ca 1910 ca 23 ca 36 Zaire 1911 19 40 Malaysia 1953 19 35 Chromolaena odorata Ivory Coast ca 1955 ca 7 ca 20 Cinchona succirubra Galapagos 1946 26 40 Lantana camara Galapagos 1938 32 40 Maesopsis eminii East Africa 1913 14 65 Miconia calvescens Hawaii ca 1975 ca 16 ca 16 Mimosa pigra N. Australia ca 1880 ca 36 ca 90 Pittosporum undulatum Jamaica 1883 ca 60 105 Psidium guajava Galapagos 1858 ? < 90 Rubus sp. Galapagos 1983 3 4 Schinus terebinthifolius Florida 1898 50 75 _______________________________________________________________________ In many cases the original introduction of a woody species was limited to one or a few individuals, but a number of subsequent introductions, usually consisting of many individuals, were made for a different purpose. For instance, in Hawaii and Florida a few individuals of some tree species were planted as ornamentals but decades later the same species were either widely planted in forestry plantations or large quantities of seeds were aerially Table 3.4.2. Biotic and abiotic factors known to influence or determine the time-lag and marked population increase of invasive woody plants in the tropics. ____________________________________________________________________ time-lag marked population increase ____________________________________________________________________ ABIOTIC FACTORS Logging/deforestation Cecropia peltata Maesopsis eminii Wind - hurricane Casuarina equisetifolia Pittosporum undulatum - treefall Passiflora mollissima Flooding Acacia nilotica Mimosa pigra Fire Chromolaena odorata Pinus pinaster Nutrient enrichment Schinus terebinthifolius BIOTIC FACTORS Pollinator Ficus microcarpa Grazing Ulex europaeus Disperser Psidium guajava Digging by mammals Clidemia hirta Passiflora mollissima Trampling by mammals Ulex europaeus ____________________________________________________________________ Table 3.4.3. Age (years) of first reproduction of tropical invasive woody species. ____________________________________________________________________________________ Age 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 no data Frequency 8 6 3 1 4 - 1 - - 3 - - - - 1 218 ____________________________________________________________________________________ sown. Some of these species were observed to spread only following these secondary introductions. In areas where monitoring is not regular some time-lags will be an artifact of erratic recording interest. SUCCESSIONAL STATUS AND DISTURBANCE Most short time-lags (i.e. <10-15 years) are caused by a lack of seed production resulting from the juvenile state of the plants. Although limited, the available data indicate that under favourable conditions most species start sexually reproducing by the time they are 10 years old (Table 3.4.3). Longer time-lags, observed in a number of species, are essentially consequences of major, and often dramatic, disturbance events (e.g. hurricane, flood, fire...) which create the conditions favouring prolific regeneration (invasion windows). When an introduced species requires a particular form and/or intensity of disturbance occurring at irregular intervals the time-lag is variable. Early successional species, which exhibit early and yearly fruiting and efficient dispersal, and/or massive seed banks, are able to exploit invasion windows created by exceptional disturbance events. Species with irregular fruiting and no seed bank will often fail to regenerate every time suitable conditions arise and one or more invasion windows may be necessary before the species spread. Considering that the majority of tropical woody species have been introduced within the last hundred years and included relatively few late-successional tree species (usually not used in amenity planting and forestry) it is not surprising that few of these species have been reported as invading tropical regions. In the temperate zone several late successional species are now spreading into semi-natural vegetation (e.g. Quercus rubra, Prunus serotina and several conifers). The duration of the phase between the introduction of a species and its spread being so variable it is not possible to be certain that a species, although present for several decades, will not spread. For any particular region it is essential to understand the long-term disturbance regime as well as the autecology (inclusive of reproductive biology and regeneration requirements) of introduced species before any predictions can be made. Otherwise close monitoring of natural and semi/natural vegetation, particularly after exceptional disturbance events, is necessary for the early detection of new invasions. 3.5 MANAGEMENT AND POLICY IMPLICATIONS Although much information has been gathered on biological invasions (e.g. Drake et al. 1989), our ability to identify potential invaders has been doubted (e.g. Crawley 1987). Willis (1991) in his review of Drake et al. (1989) suggested that some general pointers to the probability of a successful invasion: e.g. high habitat disturbance and broad ecological amplitude, short generation time, high reproductive output, high diffusivity and high numbers of invading individuals. However, these pointers do not explain why a species is a successful invader, although they may suggest factors which regulate the speed and extent of an invasion. Indeed, experimental work by Bergelson (1994) shows that fecundity may not be a useful predictor of invasiveness. A number of diverging views concerning the invasive potential of various plant species exist. For instance, Swarbrick (pers. comm. 1994) suggested that any species given the right location, climate and environment is potentially invasive, whereas it is often considered that pioneer and not 'climax' spp can become invasive (e.g. Whitmore 1991). In Southern Africa, several biological invasions have proved problematical, Richardson & Cowling (1992) have offered a tentative flow diagram to distinguish between species with low and high probabilities of becoming invaders in the fynbos biome. Other work recently carried out on the subject of predictability has been carried out on plants introduced to North American and Australia and on the genus Pinus. Reichard (1994) compared 235 invasive plant species with 114 introduced species which have failed to spread and found that the best single predictor for invasiveness was the behaviour of the species in other regions where it has been introduced: once an invasive, often an invasive. Using multiple logistic regressions Scott & Panetta (1993) found that for agricultural weeds introduced from southern Africa to Australia the highest level of variation was explained by weed status in native region. Using their regressions Scott & Panetta (1993) predict the future weed status of a number of recently arrived or not yet introduced species. However no suitable predictor of invasive plants (environmental weeds) were identified. Rejmnek & Richardson (1996) by using a discriminant function, conclude that invasiveness in the genus Pinus can be predicted from three characteristics: mean seed mass, minimum length of the juvenile period and mean interval between large seed crops. They found that short juvenile phase, small seed mass and short intervals between large seed crops are predictive traits of invasive pine species. They then suggest that their discriminant function derived from demographic parameters of pines can be used as a general screening tool for the detection of invasive woody seed plants. Using their discriminant function they correctly classified 38 out of 40 invasive species as invasive. As the two exceptions were due to efficient vertebrate dispersal and concluded that this factor should be taken into account. They then tested cultivated but non-invasive plants which were all correctly classified as non-invasive. However out of 13 species or genera thought to be non-invasive by Rejmnek & Richardson 6 are recorded as potentially or moderately invasive in the Invasive Woody Plant Database! Clearly further work needs to be carried out to extend Rejmnek & Richardson's pine predictions to other woody plants. One major difficulty is that one of their predictors, interval between seed crops, is generally poorly known or unknown. This characteristic has not been included in the Invasive Woody Plant Database due to the scarcity of reliable information. Although included in the database, information on the age of first reproduction (phase change) is available for fewer than 50 of the invasive woody plants. At present the database cannot be used to test the applicability of Rejmnek & Richardson's predictions to other woody plants. Vegetative propagation is the main, if not the only, mean of spread of a number of invasive woody plants and this is ignored by Rejmnek & Richardson. It is likely that Rejmnek & Richardson criteria will eventually proved not to be applicable to most woody plants and that families and even genera will need to be investigated independently. At present, species known to be invasive elsewhere in the world under similar climatic conditions is still the best predictor of invasiveness. Considering the difficulty in predicting the invasive potential of introduced species, it is therefore essential to look at the reasons and justifications for introducing plant species. Hughes (1994) has extensively discussed the pros and cons of species introductions and provided guidelines for the introduction or non-introduction of non native species. Carter (1994) has suggested that "all plant introductions should be presumed weeds until proven otherwise" and that a plant introduction protocol should be set up, based on the methodology used in the introduction of biological control agents. In case the introduction of a new species is the only mean to satisfactorily fulfil a long-term need, Hughes (1994) suggested that it is then essential to make that its invasive potential will be as limited as possible. Procedures to reduce the risk of introducing a potentially invasive species should include extensive information searches prior to the proposed introduction and the establishment of limited trial plantings. All introductions of non-indigenous plant species should be screened with great care in a process which considered the status in the native range and at other points of introduction. The following points require particular attention and should rapidly provide a clear indication to the introduced species invasive potential. a/ Has the species or a related species has been reported as invasive elsewhere? b/ How similar is the site of the proposed introduction to that of the species in its native and invaded regions? This includes comparisons of soil, climate, disturbance (both in terms of intensity and periodicity including that of fire, wind, flood) and human disturbance. Conditions favouring or limiting the species spread should be identified. c/ Knowledge of the species reproductive biology is important and in particular that of seed production, seed longevity, and dispersal ability. d/ Susceptibility of young individuals to grazing (e.g. whether the plant is thorny or not), e/ Assessment of practical and effective methods of control in the case of weediness problems. The economics of control must be carefully considered. If the above points indicate that the proposed species has no invasive potential an introduction may be considered. On the other hand if the proposed species exhibits invasive tendencies a strong justifications will have to be made for its introduction. If a species introduction is initiated following the assessment of its invasive potential, then tests trials should be carried out. These trials should be established at some distance from natural vegetation and have a clear buffer zone. This buffer zone . The field trials would assess the following parts of the plant's reproductive cycle over a few years after the species has started producing viable seeds: - seed production. - germination requirements under varied environmental and climatic conditions. - seedling establishment in a number of habitats and disturbance regime. It is also important to establish why an introduced species fails to produce any seeds. This might be due to the absence of pollinator (see the case of Ficus above) or a period of unusual unfavourable climatic conditions. Carter (1994) identified a number of difficulties with screening of plants in this way. These include: - unpredictable behaviour of the introduced species after removal from native pathogens, insects and browse animals, - unpredictable behaviour under new climatic, management and fire regimes, and - genetic drift or hybridization which may change the character of the plant introduced. Thus it is essential that, once species are introduced, there should be: - Long-term and regular monitoring (problems may not show for 100 years, see time-lags above), and - rapid action if weediness appears a problem. Case studies reported by Waterhouse (1994) on Chromolaena odorata in Northern Australia, Loope et al. (1992) on Miconia calvescens in Hawaii and Wester & Wood (1977) on Clidemia hirta in Fiji and Hawaii clearly show that in the case of highly invasive species, eradication is possible if the invader is controlled at a very early stage of the invasion. Once a plant has become a weed it is usually impossible to eradicate it (Carter 1994). The following points are essential in detecting the early stages in an invasion: 1/ awareness that the species is a problem in another region where climatic and environmental factors are similar, 2/ first-hand knowledge in identifying and recognizing the species in the wild is essential, and 3/ active governmental or voluntary organisation in the field of plant invasions is necessary to provide background response. The above three points require resources, a good and extensive higher level educational system, good environmental awareness (particularly of biological invasions) as well as an efficient information system. At present the information system is a problem worldwide and the setting up of database(s) on invasive species is being considered or set up by various national and international bodies . Awareness exist in regions where many highly invasive species have already altered the ecosystem structure and function. Resources and to an extensive education system are only available in richer countries. The problem of invasive plants is more likely to become more severe rather than recede in the coming decades. At the same time resources available to deal with the problem of invasive plants are unlikely to increase significantly. Only by using resources, not just financial but also intellectual, more efficiently will be there be more progress made to control invaders. Muniappan & Viraktamath (1993) have pointed out that the effort to control invasive plants in India has been sporadic and uncoordinated. They stress that to deal with the problem of invasive plants cooperative projects must be undertaken by researchers with a variety of scientific backgrounds. In fact Muniappan & Viraktamath's remarks do not just apply to India but is highly relevant to scientists worldwide. As plant introductions and invasions are a global problem coordination and communication must be tackle with on a global scale. 3.6 RESEARCH NEEDS One of the main problems relating to invasive woody plants and plant introductions is a lack of fundamental knowledge of the basic characteristics of woody plant species as well as the lack of an efficient and easily accessible international information system. Furthermore the type and amount of information required by various professionals varies immensely. INFORMATION SYSTEM There is a need for an efficient information system which should provide the following information: a/ current distribution, habitat type and degree of invasiveness of woody plant species. b/ bibliographical resources including the supply of relevant literature. c/ control methods including by mechanical, chemical and biological means. d/ directory of people and organisations involved in the study and control of particular woody species. e/ provide species accounts on all highly and a number of moderately invasive woody species FUNDAMENTAL RESEARCH The assessment of the invasive potential of a species and the control of invaders can only be successful if detailed knowledge of the autecology of the invader and the invaded ecosystem is available. This information is either not available or difficult to obtain. The following areas of research require special attention: a/ species autecology with special reference to the reproductive cycle including dispersal ability. Studies must be carried out in both the native and invaded regions. b/ ecosystem dynamics but particularly the variation in space, time and intensity of disturbance and its impact on species composition and population densities. c/ impact of potential climate change on invading species and on introduced, but non invasive, species. Further work on prediction of invasibility is required. d/ The characteristics of invasive species need to be investigated in more detail and should be compared to control groups such as a sub-set of local floras and to introduced but non-invasive plants. Stratification of the data based on lifeform and uses may proved advantageous. e/ more efficient control procedures and field methods need to be designed. 4 PROVISIONAL LIST OF INVASIVE WOODY PLANTS IN TROPICAL AND SUB-TROPICAL REGIONS Provisional list (1 / 6 / 1997) of woody plant species invasive in the tropics and the sub-tropics. Species are listed according to life form and degree of invasiveness (DI). Species with an * are dealt with in detail in the species accounts. Nomenclature follows mainly Mabberley (1987). The information included below is based on the original papers and the taxonomic status has been updated whenever possible but undoubtedly errors remain (P. Binggeli, p.binggeli@ulst.ac.uk, would appreciate any critical comments and suggestions in order to upgrade the list). The most exhaustive list of weedy plants, containing over 16,000 records, has been produced by Rod Randall. This weed list is complimentary to the one given here. It includes woody and non-woody plants worlwide but its coverage of Australia is more comprehensive than that of the rest of the world. http://www.agric.wa.gov.au/progserv/plants/weeds/weeds/weedlist.htm (Degree of invasiveness (DI): 1 = possibly/potentially invasive, 2 = moderately invasive, 3 = highly invasive, see section 2.3.2.2 for details). TREES >15m tall GENUS SPECIES AUTHORITY FAMILY DI      Acacia auriculiformis A. Cunn. ex Benth. Mimosaceae 3 Acacia dealbata Link Mimosaceae 3 Acacia mearnsii De Wild. Mimosaceae 3 * Acacia nilotica (L.) Del. Mimosaceae 3 * Casuarina equisetifolia L. Casuarinaceae 3 Casuarina glauca Siebold ex Sprengel Casuarinaceae 3 * Cecropia peltata L. Cecropiaceae 3 Litsea glutinosa (Lour.) C.B. Robinson Lauraceae 3 * Maesopsis eminii Engler Rhamnaceae 3 * Melaleuca quinquenervia (Cav.) S.T. Blake Myrtaceae 3 * Pinus patula Schlecht. & Cham. Pinaceae 2 Pithecellobium dulce (Roxb.) Benth. Mimosaceae 3 * Pittosporum undulatum Vent. Pittosporaceae 3 Ravenala madagascariensis Sonnerat Musaceae 3 Acacia confusa Merr. Mimosaceae 2 Albizia falcataria (L.) Fosb. Mimosaceae 2 Albizia lebbeck (L.) Benth. Mimosaceae 2 Aleurites moluccana (L.) Willd. Euphorbiaceae 2 Araucaria angustifolia (Bertol.) Kuntze Araucariaceae 2 Azadirachta indica A. Juss. Meliaceae 2 Bauhinia monandra Kurz. Caesalpiniaceae 2 Bischofia javanica Blume Euphorbiaceae 2 Blighia sapida Knig Sapindaceae 2 Broussonetia papyrifera (L.) Vent. Moraceae 2 Cassia siamea Lam. Caesalpiniaceae 2 Cedrela odorata L. Meliaceae 2 Cinnamomum camphora (L.) Nees & Eberm Lauraceae 2 Cinnamomum zeylanicum Breyn Lauraceae 2 Colophospermum mopane (Benth.) Lonard Caesalpiniaceae 2 Eucalyptus camaldulensis Dehnh. Myrtaceae 2 Eucalyptus deglupta Blume Myrtaceae 2 Eucalyptus robusta Sm. Myrtaceae 2 Ficus microcarpa L.f. Moraceae 2 Ficus religiosa L. Moraceae 2 Flindersia brayleyana F. Muell. Rutaceae 2 Fraxinus uhdei (Wenzig) Lingelsheim Oleaceae 2 Gmelina arborea Roxb. Verbenaceae 2 Grevillea robusta Cunn. Proteaceae 2 Harungana madagascariensis Lam. ex Poiret Guttiferae 2 Heliocarpus popayanensis HBK. Tiliaceae 2 Ilex aquifolium L. Aquifoliaceae 2 Litsea monopetala (Roxb.) Pers. Lauraceae 2 Mangifera indica L. Anacardiaceae 2 Manilkara zapota (L.) P. Royen Sapotaceae 2 Melia azedarach L. Meliaceae 2 Melicoccus bijugatus Jacq. Sapindaceae 2 Milletia dura Dunn Papilionaceae 2 Ochroma pyramidale (Cav. ex Lam.) Urban Bombacaceae 2 Pandanus tectorius Park Pandanaceae 2 Paraserianthes falcataria (L.) I. Nielsen Mimosaceae 2 Phoenix dactylifera L. Arecaceae 2 Pinus lutchuensis Mayer Pinaceae 3 Pittosporum viridiflorum Sims Pittosporaceae 2 Pongamia pinnata (L.) Pierre Papilionaceae 2 Prosopis pallida (Humb.&Bonpl. ex Willd.) HBK. Mimosaceae 2 Rhizophora mangle L. Rhizopharaceae 2 Samanea saman (Jacq.) Merr. Mimosaceae 2 Spathodea campanulata Beauv. Bignoniaceae 2 Swietenia mahagoni (L.) Jacq. Meliaceae 2 Syzygium jambos (L.) Alston Myrtaceae 2 Tabebuia pallida (Lindley) Miers Bignoniaceae 2 Tamarindus indica L. Caesalpiniaceae 2 Terminalia catappa L. Combretaceae 2 Terminalia myriocarpa Van Heurck & Mll. Arg. Combretaceae 2 Toona ciliata M. Roemer Meliaceae 2 Trema orientalis Blume Ulmaceae 2 Achras zapota L. Sapotaceae 1 Albizia chinensis (Obseck) Merr. Mimosaceae 1 Ceiba pentandra (L.) Gaertn. Bombacaceae 1 Cocos nucifera L. Palmae 1 Enterolobium saman Mimosaceae 1 Eucalyptus torelliana F. Muell. Myrtaceae 1 Inocarpus fagiferus (Park.) Fosberg Papilionaceae 1 Swietenia macrophylla King Meliaceae 1 SMALL TREES 15m< >5m GENUS SPECIES AUTHORITY FAMILY DI      Acacia decurrens (J.C. Wendl.) Willd. Mimosaceae 3 Acacia saligna (Labill.) H.L. Wend. Mimosaceae 3 Cinchona succirubra Pavon ex Klotzsch Rubiaceae 3 * Leucaena leucocephala (Lam.) De Wit Mimosaceae 3 Ligustrum robustum Blume Oleaceae 3 * Miconia calvescens DC. Melastomataceae 3 * Mimosa pigra L. Mimosaceae 3 * Myrica faya Ait. Myricaceae 3 Parkinsonia aculeata L. Caesalpiniaceae 3 Psidium cattleianum Sabine Myrtaceae 3 * Psidium guajava L. Myrtaceae 3 Schefflera actinophylla (Endl.) Harms Araliaceae 3 * Schinus terebinthifolius Raddi Anacardiaceae 3 Sesbania punicea (Cav.) Benth. Mimosaceae 3 Solanum mauritianum Scopoli Solanaceae 3 Syzygium malaccense (L.) Merr. & Perry Myrtaceae 3 Tibouchina urvilleana (DC) Cogn. Melastomataceae 3 Acacia catechu (L.f.) Willd. Mimosaceae 2 Adenanthera pavonina L. Mimosaceae 2 Aleurites fordii Hemsley Euphorbiaceae 2 Anacardium occidentale L. Anacardiaceae 2 Annona squamosa L. Annonaceae 2 Ardisia humilis Vahl Myrsinaceae 2 Caesalpinia pulcherrima (L.) Sw. Caesalpiniaceae 2 Carica papaya L. Caricaceae 2 Chrysobalanus icaco L. Chrysobalanaceae 2 Cinchona officinalis L. Rubiaceae 2 Cinchona pubescens Vahl Rubiaceae 2 Citharexylum caudatum L. Verbenaceae 2 Citrus aurantiifolia (Christm.) Swingle Rutaceae 2 Citrus aurantium L. Rutaceae 2 Citrus limon (L.) Burm. f. Rutaceae 2 Citrus reticulata Blanco Rutaceae 2 Citrus sinensis (L.) Osbeck Rutaceae 2 Coccoloba uvifera (L.) L. Polygonaceae 2 Coffea arabica L. Rubiaceae 2 Cordyline fruticosa (L.) A. Chev. Agavaceae 2 Corynocarpus laevigata Forster & Forster f. Corynocarpaceae 2 Cyathea cooperi (Hook. ex F.Muell.) Dom. Cyatheaceae 2 Cyphomandra crassicaulis (Cav.) Sendtn. Solanaceae 2 Dalbergia latifolia Roxb. Papilionaceae 2 Dalbergia sissoo Roxb. ex DC. Papilionaceae 2 Delonix regia (Hook.) Raf. Caesalpiniaceae 2 Eriobotrya japonica (Thunb.) Lindley Rosaceae 2 Flacourtia indica (Burm. f.) Merr. Flacourtiaceae 2 Grevillea banksii R. Br Proteaceae 2 Hibiscus schizopetalous (Masters) Hook. f. Malvaceae 2 Hibiscus tiliaceus L. Malvaceae 2 Hovenia dulcis Thunb. Rhamnaceae 2 Jacaranda mimosifolia D. Don Bignoniaceae 2 Leptospermum scoparium Forster & Forster f. Myrtaceae 2 Manihot glaziovii Muell. Arg. Euphorbiaceae 2 Melaleuca leucadendron L. Myrtaceae 2 Melochia umbellata (Houtt.) Staf. Sterculiaceae 2 Mimosa albida Rudd. Mimosaceae 2 Mimosa nilotica (L.) DeLisle Mimosaceae 2 Mimosa sepiaria Mimosaceae 2 Morinda citrifolia L. Rubiaceae 2 Moringa oleifera Lam. Moringaceae 2 Muntingia calabura L. Elaeocarpaceae 2 Olea europaea L. Oleaceae 2 Ossaea marginata (Desr.) Triana Melastomataceae 2 Persea americana Miller Lauraceae 2 Phyllanthus acidus (L.) Skeels Euphorbiaceae 2 Pinus caribaea Morelet Pinaceae 2 Pithecellobium unguiscati (L.) Benth. Mimosaceae 2 Pittosporum ferrugineum Pittosporaceae 2 Poncirus trifoliata (L.) Raf. Rutaceae 2 Prosopis juliflora (Sw.) DC. Mimosaceae 2 Rhizophora stylosa Griff. Rhizopharaceae 2 Sambucus nigra L. Caprifoliaceae 2 Schinus molle L. Anacardiaceae 2 Syzygium cumini (L.) Skeels Myrtaceae 2 Terminalia arjuna (Roxb.) Beddome Combretaceae 2 Trema micrantha Blume Ulmaceae 2 Vitex glabrata R.Br. Verbenaceae 2 Vitex trifolia L. Verbenaceae 2 Bixa orellana L. Bixaceae 1 Bruguiera gymnorhiza (L.) Lamk. Rhizophoraceae 1 Cassia spectabilis DC. Caesalpiniaceae 1 Cassia suffructicosa Koenig Caesalpiniaceae 1 Cordia sebestena L. Boraginaceae 1 Ilex paraguariensis A. St-Hil. Aquifoliaceae 1 Rhododendron arboreum Sm. Ericaceae 1 Sambucus mexicana K. Presl ex A. DC Caprifoliaceae 1 Sesbania sesban (L.) Merrill Mimosaceae 1 Tecoma stans (L.) Kunth Bignonaceae 1 Ziziphus mucronata Willd. Rhamnaceae 1 SHRUBS <5m GENUS SPECIES AUTHORITY FAMILY DI      Bambusa sp. Poaceae 3 * Chromolaena odorata (L.) King & Robinson Asteraceae 3 Clerodendrum japonicum (Thunb.) Sweet Verbenaceae 3 * Clidemia hirta (L.) D. Don Melastomataceae 3 Cordia macrostachya Roem & Schlucht. Boraginaceae 3 Desmanthus virgatus (L.) Willd. Mimosaceae 3 Homalanthus populifolius Graham Euphorbiaceae 3 Ipomoea fistulosa Mart. ex Choisy Convolvulaceae 3 Jatropha curcas L. Euphorbiaceae 3 Jatropha gossypiifolia L. Euphorbiaceae 3 * Lantana camara L. Verbenaceae 3 Melastoma malabathricum L. Melastomataceae 3 Pluchea odorata (L.) Cass. Asteraceae 3 Rhodomyrtus tomentosa (Ait.) Hassk. Myrtaceae 3 Rubus alcaefolius Poir. Rosaceae 3 Rubus argutus Link Rosaceae 3 Rubus moluccanus L. Rosaceae 3 Rubus rosifolius Sm. Rosaceae 3 Solanum torvum Sw. Solanaceae 3 * Ulex europaeus L. Papilionaceae 3 Wikstroemia indica (L.) C.A. Meyer Thymeliaceae 3 Acacia farnesiana (L.) Willd. Mimosaceae 2 Atriplex lentiformis (Torr.) S. Wats. Chenopodiaceae 2 Bocconia frutescens L. Papaveraceae 2 Buddleja asiatica Lour. Buddlejaceae 2 Carica pubescens Lenn & K. Koch Caricaceae 2 Citrus medica L. Rutaceae 2 Clerodendrum quadriloculare (Blanco) Merrill. Verbenaceae 2 Colubrina asiatica (L.) Brongn. Rhamnaceae 2 Cordia myxa L. Boraginaceae 2 Eugenia uniflora L. Myrtaceae 2 Flacourtia jangomas (Lour.) Ruschel Flacourtiaceae 2 Furcraea hexapetala (Jacq.) Urban Agavaceae 2 Linoceria intermedia Wight Oleaceae 2 Melastoma decifidium Roxburgh Melastomataceae 2 Mimosa acantholoba (Willd.) Poir. Mimosaceae 2 Piper adancum L. Piperaceae 2 Pluchea indica (L.) Less. Asteraceae 2 Punica granatum L. Lythraceae 2 Rubus ellipticus Smith Rosaceae 2 Rubus glaucus Bth. Rosaceae 2 Rubus sp. Rosaceae 2 Senna alata (L.) Roxb. Caesalpiniaceae 2 Senna didymobotrya (Fresen.) H. Irwin & Barneby Caesalpiniaceae 2 Spiraea cantoniensis Lour. Rosaceae 2 Triphasia trifolia (Burm. f.) P. Wilson Rutaceae 2 Ardisia crenata Sims Myrsinaceae 1 Ardisia crispa (Thunb.) A.DC. Myrsinaceae 1 Cassia auriculata L. Caesalpiniaceae 1 Elaeagnus umbellata Thunb. Elaeagnaceae 1 Fuchsia boliviana Carr. Onagraceae 1 Glycosmis parviflora (Sims) Little Rutaceae 1 Indigofera suffruticosa P. Miller Papilionaceae 1 Rubus niveus Thunb. Rosaceae 1 Rubus racemosus Roxb. Rosaceae 1 Tephrosia candida DC Papilionaceae 1 SUB-SHRUBS some parts somewhat woody GENUS SPECIES AUTHORITY FAMILY DI      Ageratina adenophora (Sprengel) King & Robinson Asteraceae 3 Mimosa invisa C. Martius Mimosaceae 3 Sida acuta Burm. f. Malvaceae 3 Gossypium hirsutum L. Malvaceae 2 Ricinus communis L. Euphorbiaceae 2 VINES GENUS SPECIES AUTHORITY FAMILY DI Caesalpinia decapetala (Roth) Alston Caesalpiniaceae 3 Cardiospermum halicacabum L. Sapindaceae 3 Cryptostegia grandiflora R.Br. Asclepiadaceae 3 Ipomoea carnea spp fistulosa (Martius ex. Choisy) Austin Convolvulaceae 3 Lonicera japonica Thunb. Caprifoliaceae 3 * Passiflora mollissima (H.B.K.) Bailey Passifloraceae 3 Passiflora suberosa L. Passifloraceae 3 Anredera cordifolia (Ten.) Steenis Basellaceae 2 Aristolochia littoralis Parodi Aristolochiaceae 2 Hedera helix L. Araliaceae 2 Hiptage benghalensis (L.) Kurz Malpighiaceae 2 Merremia tuberosa (L.) Rendle Convolvulaceae 2 Mikania scandens (L.) Willd. Asteraceae 2 Passiflora edulis Sims Passifloraceae 2 Passiflora ligularis Juss. Passifloraceae 2 Derris elliptica (Wallich) Benth. Mimosaceae 1 Thunbergia alata Boj. ex Sims Acanthaceae 1 Thunbergia grandiflora Roxb. Acanthaceae 1 HOW REPRESENTATIVE IS THE INVASIVE WOODY PLANT DATABASE? Although the data presented in this report are preliminary and therefore not comprehensive it was difficult to estimate how representative the dataset is. When the report was near completion a search of Forestry Abstracts for 1995 yielded a reference of a report on naturalized exotic tree species in Puerto Rico by Francis & Liogier (1991). The authors list and rate the invasive potential of 118 introduced tree species. This information could not be included in the database but can be used to estimate the coverage of the Invasive Woody Plant Database. Out of Francis and Liogier's 118 species only 42% are included in the database and two (1.7%) are recorded as invasive in Puerto Rico. They identified 16 species as widespread and competing in primary and secondary forests and a second group of 16 species able to regenerate and spread in forests which they forecast as becoming common or abundant within 100 years. The respective percentage of species not held in the database are 31% and 58%. Highly and moderately invasive species in Puerto Rico not held in the database and not found in Table 5.1 are listed in Table @xx. The percentage of possibly/potentially, moderately and highly invasive species is 72%, 14% and 14% respectively. The relative proportion of these three groups of invasive species in Puerto Rico is markedly different from the database figures of 16%, 60% and 24% (Table 8) indicating that possibly/potentially invaders are under reported. Table 5.1. Invasive woody plants reported by Francis & Liogier (1991) not found in the Invasive Woody Plant Database. "Species common or abundant, widespread, "Species that have been able to regenerate and and competing in primary or secondary compete in forests stands and are likely to forests stands" become common or abundant within the next century" ............................................................................................. Ardisia solanaceae Roxb. Albizia adinocephala (D.Donn. Sm.) Britt & Rose Artocarpus altilis (S.Park.) Fosb. Castilla elastica Cerv. Muntingia calabura L. Haematoxylon campechianum L. Senna siamea (Lam.) Irwin & Barnaby Hibiscus elatus Sw. Thespesia populnea (L.) Soland ex Correa Lysiloma latisiliqua (L.) Benth. Mimosa arenosa (Willd.) Poir Pterocarpus macrocarpus Kuez Senna mutijuga (L.C. Rich.) Irwin & Barneby Senna spectabilis (L.C. Rich.) Irwin & Barneby Simaboura amara Aubl. Sterculia apetala (Jacq.) Karst. ............................................................................................. 5 CASE HISTORIES OF HIGHLY INVASIVE WOODY SPECIES IN THE TROPICS 5.1 INTRODUCTION The Invasive Woody Plant Database, like any ecological database, can be used to provide an overview of invasion by woody plant species as presented in the previous section. However, information on a ecological database cannot provide a comprehensive picture of the complex interactions of ecological, environmental and historical factors affecting plant invasions. Here, to provide further insight into the subject we present a series of case histories of woody plant invasions. Due to the limited number of well investigated cases only a small subset of the species found in the Invasive Woody Plant Database can be reported in detail. Cronk & Fuller (1995) give detailed accounts on six species dealt with here, namely Clidemia hirta, Lantana camara, Melaleuca quinquenervia, Mimosa pigra, Passiflora mollissima and Pittoporum undulatum as well as another tropical woody plant Psidium cattleianum. Cronk & Fuller have used a different approach to produce their account focusing more on the control and management of the species, botanical description as well as reported cases of introductions and invasions. In Australia, substential accounts of Acacia nilotica (Mackey 1996a), Cryptostegia grandiflora (Mackey 1996b), Prosopis spp. (Csurhes 1996) and Senna obtusifolia (Mackey et al. 1997), with special refrence to Queensland, have been produced. The Department of Primary Industry and Fisheries of the Northern Territory publishes 'Agnote' which consists in a large number of short accounts on weeds of the Northern Territory and include a number of invasive woody plants (e.g. Prosopis limensis (Gracie 1992), Mimosa pigra (Smith & Miller 1991)). Other useful species accounts may be found in Anon. (1980, 1983) and Holm et al. (1977). 5.2 SPECIES DESCRIPTIONS In each species account information on a number of species attributes and on various environmental and ecological characteristics of the native and invaded ranges is reported. Each account is divided into five main sections and the details are given below. Wherever necessary, assumptions made, limitations to information supplied and required explanations are indicated. Species characteristics Synonyms of botanical names are included only if they have been used in TREE-CD over the past five years. Life form, size, lifespan Taxonomy, variation and plasticity Reproductive biology Resilience and resistance This section focuses on the species ability to respond to physical damage, fire, drought, flooding, pests and diseases Environmental requirements and successional status Products and uses Status in native range Range and abundance Climate Site requirements Weediness Pests and diseases Status in invaded regions In this section all information given refers to the most highly invaded region unless stated otherwise History of introductions and intensity of invasions Patterns of invasion and time-lag Site and climate Floristic region and vegetation types Pests and diseases Impact on ecosystem Impact on humans and related activities Control Ecological differences Existence of ecologically equivalent species and competitive interactions in invaded regions Ecologically equivalent species should exhibit great similarities in species attributes (e.g. lifeform, size, lifespan, fruit type, dispersal agent), in site and climatic requirements as well as in successional status. Only detailed investigations can differentiate ecologically equivalent species. A good example is provided by the two European timber trees Acer pseudoplatanus L. and Fraxinus excelsior L. which differ mainly in terms of duration in seed dormancy, tolerance to flooding, susceptibility to grass competition and variation in latitudinal and altitudinal distributions (Binggeli 1992). Another example is the case of Quercus robur L. and Q. rubra L., the latter invading forests dominated by the former, reported by Barkman (1988). Differences in status and ecology between invaded and native ranges Selected references Up-to date key references on the ecology of a species in its native and invaded ranges as well as key references on other subjects such as botanical description, taxonomic treatment, species bibliographies, diseases and biological control are given. Each reference is annotated as follows: * reference on invasion, ** key reference on invasion; ( reference on native range, (( key reference on native range; # references on other subjects relating to the species including: botanical description, pest and diseases, reviews etc... 5.3 SPECIES ACCOUNTS The species accounts of 18 tropical invasive woody plant are available and are listed in Table 5.1. Table 5.1. Woody plant species for which a detailed account is available (S = shrub, sT = small tree, T = tree and V = vine). SPECIES FAMILY LF Native region Invaded regions Habitat invaded ____________________________________________________________________________________________ Acacia nilotica Mimosaceae T Africa-India Australia, Indonesia grassland Casuarina equisetifolia Casuarinaceae T Australasia Florida coastal sands Cecropia peltata Cecropiaceae T neotropics Africa, Asia disturbed areas, forest gap Chromolaena odorata Asteraceae S neotropics Africa, Asia fallow, logged forest Clidemia hirta Melastomataceae S neotropics Oceanic islands disturbed areas, forest Lantana camara Verbenaceae S neotropics tropics pasture, plantations Leucaena leucocephala Mimosaceae sT C. America Pacific islands disturbed areas Maesopsis eminii Rhamnaceae T Africa East Africa natural & secondary forest Melaleuca quinquenervia Myrtaceae T Australia Florida swamp Miconia calvescens Melastomataceae sT neotropics Pacific islands forest Mimosa pigra Mimosaceae sT neotropics Australia, Thailand flood plain Myrica faya Myricaceae sT Atlantic Isl. Hawaii lava flows Passiflora mollissima Passifloraceae V neotropics Hawaii forest Pinus patula Pinaceae T Mexico East Africa forest, grassland Pittosporum undulatum Pittosporaceae T Australia Jamaica forest Psidium guajava Myrtaceae sT neotropics Pacific islands pasture, forest Schinus terebinthifolius Anacardiaceae sT S. America Florida disturbed areas, grassland Ulex europaeus Papilionaceae S W. Europe mountain tropics pasture ____________________________________________________________________________________________ 6. ACKNOWLEDGEMENTS This document is an output from a project funded through the Forestry Research Programme of the UK Department for International Development (DFID) for the benefit of developing countries. The views expressed are not necessarily those of DFID. Project R4742 Forestry Research Programme. Over the years financial assistance for the setting-up and management of the databases and reprints' aquisition has been provided either directly by Berthe Guillod-Blanchard and Max Wirz or indirectly in the form of flexible painting and decorating jobs provided by Curt and Charlotte Binggeli, Siv Gunnarsson and several work agencies while subsistence and rough lodgings have been supplied by a wide number of people. Many thanks to many individuals who willingly or unwittingly bent the rules to facilitate a world review of invasive woody plants. The assistance of Curt Binggeli in setting up the database was essential. Long-term intellectual support and encouragement by Alan Hamilton, Amyan Macfadyen and Brian S. Rushton made this project possible. Library facilities were kindly provided by The University of Ulster at Coleraine (special thanks to Linda Southall), Bibliothque Cantonale et Universitaire de Lausanne, Dpartement de Gobotanique de l'Universit de Lausanne, Queen's University of Belfast, University of Oxford, University College North Wales and Brian S. Rushton. Numerous colleagues kindly supplied reprints of their publications and others provided essential feedback on some species accounts. 7. REFERENCES Ak Assi, L. (1979) Cecropia peltata L. (Moraces): ses origines, introduction et expansion dans l'est de la Cte d'Ivoire. In Kunkel, G. (ed.) Taxonomic aspects of African economic botany, pp. 140-145. Anon. (1930) Plant and seed list. East African Agricultural Research Station, Amani Tanganyika Territory Anon. (1980) Firewood crops: shrub and tree species for energy production, Vol. 1. National Academy of Sciences, Washington. Anon. (1983) Firewood crops; shrub and tree species for energy production, Vol. 2. National Academy of Science, Washington. Anon. (1993) Harmful nonindigenous species in the United States, OTAF565. U.S. Congress, Office of Technology Assessment, Washington. Anon. (1996) B&T master seed list. B&T World Seeds, Bridgwater. Barkman, J.J. (1988) Some reflections on plant architectyre and its ecological implications  A personal view demonstrated on two species of Quercus. In Werger, M.J.A., Art, P.J.M. van der, During, H.J. & Verboeven, J.F.A. (Eds) Plant form and vegetation structure, pp. 17. SPD Acad. Publ., The Hague. Beard, J.S. (1945) The Mora forests of Trinidad, British West Indies. J. Ecol. 33, 173-192. Binggeli, P. (1989) The ecology of Maesopsis invasion and dynamics of the evergreen forest of the East Usambaras, and their implications for forest conservation and forestry practices. In Hamilton, A.C. & BenstedSmith, R. (Eds) Forest conservation in the East Usambara Mountains, Tanzania, pp. 269-300. IUCN, Gland. Binggeli, P. (1990) Maesopsis eminii invasion of the evergreen rain forest in the East Usambaras (Tanzania). In The biology and control of invasive plants, pp. 1-7. British Ecological Society, Cardiff. Binggeli P. (1992) Patterns of invasion of sycamore (Acer pseudoplatanus L.) in relation to species and ecosystem attributes. D.Phil. Thesis, The University of Ulster. Binggeli, P. & Hamilton, A.C. (1990) Tree species invasions and sustainable forestry in the East Usambaras. In Hedberg, I. & Persson, E. (Eds) Research for conservation of Tanzanian catchment forests, pp. 39-47. Uppsala Universitet Reprocentralen HSC, Uppsala. Binggeli, P. & Hamilton, A.C. (1993) Biological invasion by Maesopsis eminii in the East Usambara forests, Tanzania. Opera Bot. 121, 229-235. Bouvier, R. (1946) Les migrations vgtales. Flammarion, Paris. Candolle, A. de (1855) Geographie botanique, Tome 1 & 2. Masson, Paris. Carey, J.R., Moyle, P.B., Rejmnek, M. & Vermeij, G.J. (1996) Invasion biology. Biol. Conserv. 78, 1-214. Carter, J.O. (1994) Acacia nilotica: a tree legume out of control. In Gutteridge, R.C. & Shelton, H.M. (Eds) Forage trees as legumes in tropical agriculture, pp. 338-351. CAB International, Wallingford. Chandrashekara, U.M. & Ramakrishnan, P.S. (1994) Successional patterns and gap phase dynamics of a humid tropical forest of the Western Ghats of Kerala, India: ground vegetation, biomass, productivity and nutrient cycling. Forest Ecol. Mgmt 70, 23-40. Chevalier, A. (1931) Le role de l'homme dans la dispersion des plantes tropicales. Rev. Bot. appl. Agric. trop. 11, 633-650. Chevalier, A. (1949) Sur une mauvaise herbe qui vient d'envahir la S.E. de l'Asie. Rev. Bot. appl. Agric. trop. 29, 539-537. Chevalier, A. (1952) Deux Composes permettant de lutter contre l'Imperata et l'empchant la dgradation des sols tropiquaux qu'il faudrait introduire rapidement en Afrique noire. Rev. Bot. appl. Agric. trop. 32, 359-360. Corlett, R.T. (1992) The naturalized flora of Hong Kong: a comparison with Singapore. J. Biogeogr. 15, 421-430. Crawley, M.J. (1987) What makes a community invasible? In Gray, A.J., Crawley, M.J. & Edwards, P.J. (Eds) Colonization, succession and stability, pp. 629-654. Blackwell, Oxford. Cronk, Q.C.B. (1989) The past and present vegetation of St Helena. J. Biogeogr. 16, 47-64. Cronk, Q.C.B. & Fuller, J.L. (1995) Plant invaders: the threat to natural ecosystems worldwide. Chapman & Hall, London. Crosby, A.W. (1986) Ecological imperialism: the biological expansion of Europe, 9001900. Cambridge University Press, Cambridge. Csurhes, S. (Ed.) (1996) Mesquite (Prosopis spp.) in Queensland. Department of Natural Resources, Coorparoo. Denslow, J.S. (1987) Tropical rain forest gaps and tree species diversity. Ann. Rev. Ecol. Syst. 18, 431-451. Drake, J., di Castri, F., Groves, R., Kruger, F., Rejmnek, M. & Williamson, M. (Eds) (1989) Biological invasions, a global perspective. Wiley, Chichester. Duffey, E. (1964) The terrestrial ecology of Ascension Island. J. appl. Ecol. 1, 219-251. Duffey, E. (Ed.) (1988) Biological invasions of nature reserves. Biol. Conserv. 44, 1-135. Fernie, L.M. (1948) The Amani plantations. E. Afr. agric. J. 14, 86-93. Francis, J.K. & Liogier, H.A. (1991) Naturalized exotic tree species in Puerto Rico. General Technical Report  Southern Forest Experiment Station, USDA For. Serv. SO82, 1-12. Frost, H.M., Terry, P.J. & Bacon, P. (1995) A feasability study into the creation of a database on weeds and invasive plant species. Proc. Brit. Crop. Prot. Council Symp. 64, 35-49. George, S.J., Mohan Kumar, B. & Rajiv, G.R. (1993) Nature of secondary succession in the abandoned Eucalyptus plantations of Neyvar (Kerala) in penninsular India. J. trop. Forest Sci. 5, 372-386. Goodall, D.W. (1954) Vegetational classification and vegetational continua. Angew. PflSociol., Aichinger Festwchr. 1, 168-182. Gracie, A.N. (1992) Prickly acacia (Acacia nilotica). Agnote 525, 1-2. Greenway, P.J. (1934) Report of a botanical survey of the indigenous and exotic plants in cultivation at the East African Agricultural Research Station, Amani. 1-511. Unpubl. MS. Groves, R.H. (1986) Plant invasions of Australia: an overview. In Groves, R.H. & Burdon, J.J. (Eds) Ecology of biological invasions: an Australian perspective, pp. 137-149. Australian Academy of Science, Canberra. Guppy, H.B. (1917) Plants, seeds and currents in the West Indies and the Azores. Williams & Norgate, London. Hamann, O. (1974) Contributions to the flora and vegetation of the Galpagos Islands. 3. Five new floristic records. Bot. Not. 127, 309-316. Harris, D.R. (1962) Invasion of oceanic islands by alien plants: an example from the Leeward Islands, West Indies. Inst. Brit. Geogr. Trans. 31, 67-82. Hauman, L. (1948) 9. Moraceae. In Flore du Congo Belge et du RuandaUrundi  Spermatophytes Vol. 1, pp. 52-98. INEAC, Bruxelles. Hawthorne, W.D. (1993) East African coastal forest botany. In Lovett, J.C. & Wasser, S.J. (Eds) Biogeography and ecology of the rain forests of eastern Africa, pp. 57-99. Cambridge University Press, Cambridge. Hobbs, R.J. (1991) Disturbance as a precursor to weed invasion in native vegetation. Pl. Prot. Quart. 6, 99-104. Hobbs, R.J. & Huenneke, L. (1992) Disturbance, diversity, and invasion: implications for conservation. Conserv. Biol. 6, 324-337. Hughes, C.E. (1994) Risks of species introductions in tropical forestry. Commonw. For. Rev. 73, 243-252. Hughes, C.E. & Styles, B.T. (1989) The benefits and risks of woody legume introductions. Monogr. Syst. Bot. Missouri Bot. Gard. 29, 505-531. Humphries, S.E., Groves, R.H. & Mitchell, D.S. (1991) Plant invasions of Australian ecosystems: a status review and management directions. Australian National Parks and Wildlife Service, Canberra. Hobbs, R.J. & Humphries, S.E. (1995) An integrated approach to the ecology and management of plant invasions. Conserv. Biol. 9, 761-770. Holm, L.G., Plucknett, D.L., Pancho, J.V. & Herberger, J.P. (1977) The world's worst weeds - distribution and biology. University of Hawaii, Honolulu. Irvine, F.R. (1961) Woody plants of Ghana. Oxford University Press, London. Iversen, S.T. (1991) The Usambara Mountains, NE Tanzania: history, vegetation and conservation. Uppsala Universitet Reprocentralen HSC, Uppsala. Jacobi, J.D. & Warshauer, F.R. (1992) Distribution of six alien plant species in upland habitats on the Island of Hawai'i. In Stone, C.P., Smith, C.W. & Tunison, J.T. (Eds) Alien plant invasions in native ecosystems of Hawai'i: management and research, pp. 155-188. University of Hawaii Press, Honolulu. Janzen, D.H. (1986) The eternal external threat. In Soul, M.E. (Ed.) Conservation biology, pp. 286-303. Sinauer, Sunderland. Joelson, F.S. (1928) Eastern Africa today. East Africa (London). JuhBeaulaton, D. (1994) Les jardins des forts europens de Ouidah: premiers jardins d'essai (xviiime sicle). Cah. du CRA 8, 83-105. Julien, M.H., Kerr, J.D. & Chan, R.R. (1984) Biological control of weeds: an evaluation. Prot. Ecol. 7, 3-25. Kendle, T. (1994) Island in intensive care. Landscape Design 223, 13-16. Kirkpatrick, J.B. (1977) Eucalypt invasion in southern California. Aust. Geogr. 13, 387-393. Kowarik, I. (1995) Time lags in biological invasions with regard to the success and failure of alien species. In Pysek, P., Prach, K., Rejmnek, M. & Wade, P.M. (Eds) Plant invasions  general apsects and special problems, pp. 15-38. SPB Academic Publishing, Amsterdam. Lawesson, J.E. (1990) Alien plants in the Galapagos, a summary. Monogr. Syst. Bot. Missouri Bot. Gard. 32, 15-20. Lonard, J. (1951) Note systmatique sur les parasoliers au Congo belge (Musanga et Cecropia - Moraces). Bull. agric. Congo Belge 42, 951-964. Little, E.L. & Skolmen R.G. (1989) Common forest trees of Hawaii (native and introduced). Agric. Handbook 679. US Forest Service, Washington. Lonsdale, W.M. & Miller, I.L. (1993) Fire as a management tool for a tropical woody weed: Mimosa pigra in northern Australia. J. environ. Mgmt 39, 77-88. Lonsdale, W.M., Miller, I.L. & Forno, I.W. (1989) The biology of Australian weeds. 20. Mimosa pigra L. Pl. Prot. Quart. 4, 119-131. Lust, N. & Speleers, L. (1990) The establishment of red oak and pedunculate oak seedlings in the experimental forest of Aelmoeseneie at Gontrode (Belgium). Sylva Gandavensis 55, 1-23. Macdonald, I.A.W. (1990) Strategies for limiting the invasion of protected areas by introduced organisms. Monogr. Syst. Bot. Missouri Bot. Gard. 32, 189-199. Macdonald, I.A.W. (1994) Invasive species specialist group. Species 21-22, 68-69. Macdonald, I.A.W., Thbaud, C., Strahm, W. & Strasberg, D. (1991) Effects of alien plant invasions on native vegetation remnants on La Runion (Mascarene Islands, Indian Ocean). Environ. Conserv. 18, 51-61. Mackey, A.P. (Ed.) (1996a) Prickly acacia (Acacia nilotica) in Queensland. Department of Natural Resources, Coorparoo. Mackey, A.P. (Ed.) (1996b) Rubber vine (Cryptostegia grandiflora) in Queensland. Department of Natural Resources, Coorparoo. Mackey, A.P., Miller, E.N. & Palmer, W.A. (1997) Sicklepod (Senna obtusifolia) in Queensland. Department of Natural Resources, Coorparoo. Mangenot, G. (1964) Espces introduites. IUCN Publ. NS 4, 253-260. Maydell, H.J. von (1989) Criteria for the selection of food producing trees and shrubs in semiarid regions. In Wickens, G.E., Haq, N. & Day, P. (Eds) New crops for food and industry, pp. 66-75. Chapman & Hall, London. McKey, D. (1988) Cecropia peltata, an introduced neotropical pioneer tree, is replacing Musanga cecropioides in southwestern Cameroon. Biotropica 20, 262-264. Miller, I.L. & Lonsdale, W.M. (1987) Early records of Mimosa pigra in the Northern Territory. Pl. Prot. Quart. 2, 140-142. Monnier, Y. (1992) L'empreinte des Amriques dans le paysage: de l'insolite au familier. Cah. OutreMer 45(179180), 441-460. Muniappan, R. & Viraktamath, C.A. (1993) Invasive alien weeds in the Western Ghats. Current Sci. 64, 555-557. NegrerosCastillo, P. & Hall, R.B. (1994) Four methods for partial overstory removal in tropical forests in Mexico. J. environ. Mgmt 41, 237-243. Patil, M.S. & Kumar, H.D.M. (1990) Seed dispersion in subabul - a case study. Ind. Forester 116, 598-599. Penfold, A.R. & Willis, J.L. (1961) The eucalypts. Hill, London. Phillips, O.L. & Gentry, A.H. (1994) Increasing turnover through time in tropical forests. Science 263, 954-957. Phillips, O.L., Hall, P., Gentry, A.H., Sawyer, S.A. & Vasquez, R. (1994) Dynamics and species richness of tropical rain forests. Proc. Natl. Acad. Sci. 91, 2805-2809. Pieterse, P.J. & Cairns, A.L.P. (1986) The effect of fire on an Acacia longifolia seed bank in the southwestern Cape. S. Afr. J. Bot. 52, 233-236. Pieterse, P.J. & Cairns, A.L.P. (1988) Factors affecting the reproductive success of Acacia longifolia (Andr.) Willd. in the Banhoek Valley, southwestern Cape, Republic of South Africa. S. Afr. J. Bot. 54, 461-464. Pieterse, P.J. & Cairns, A.L.P. (1988) The population dynamics of the weed Acacia longifolia Fabaceae in the absence and presence of fire. S. Afr. For. J. 45, 25-27. Putz, F.E. & Holbrook, N.M. (1988) Further observations on the dissolution of mutualism between Cecropia and its ants: the Malaysian case. Oikos 53, 121-125. Pysek, P. (1995) On the terminology used in plant invasion studies. In Pysek, P., Prach, K., Rejmnek, M. & Wade, P.M. (Eds) Plant invasions, pp. 71-81. SPB Academic Publishing, Amsterdam. Pysek, P., Prach, K., Rejmnek, M. & Wade, P.M. (Eds) (1995) Plant invasions, general aspects and special problems. SPB Academic Publishing, Amsterdam. Ramakrishnan, P.S. (Ed.) (1991) Ecology of biological invasion in the tropics. International Scientific Publications, New Delhi. Reichard, S.E. (1994) Assessing the potential of invasiveness in woody plants introduced to North America. Ph.D. Thesis, University of Washington. Reilley, A.E., Earhart, J.E. & Prance, G.T. (1990) Three subtropical secondary forests in the U.S. Virgin Islands: a comparative quantitative ecological inventory. Adv. Econ. Bot. 8, 189-198. Rejmnek, M. (1989) Invasibility of plant communities. In Drake, J.A., Mooney, H.A., di Castri, F., Groves, R.H., Kruger, F.J., Rejmnek, M. & Williamson, M. (Eds) Biological invasions, a global perspective, pp. 369-388. Wiley, Chichester. Rejmnek, M. (1995) What makes a species invasive? In Pysek, P., Prach, K., Rejmnek, M. & Wade, P.M. (Eds) Plant invasions, general aspects and special problems, pp. 3-13. SPB Academic Publishing, Amsterdam. Rejmnek, M. (1996) Species richness and resistance to invasions. In Orians, R.D., Dirzo, R. & Cushman, J.H. (Eds) Diversity and processes in tropical forest ecosystems, pp. 153-172. Springer, New York. Rejmnek, M. & Richardson, D.M. (1996) What attributes make some plant species invasive? Ecology 77, 1655-1661. Richardson, D.M. & Cowling, R.M. (1992) Why is mountain fynbos invasible and which species invade? In van Wilgen, B.W., Richardson, D.M., Kruger, F.J. & van Hensbergen, H.J. (Eds) Fire in South African mountain fynbos, pp. 161-181. Springer, Berlin. Ridley, H.N. (1930) The dispersal of plants throughout the world. Reeve, Ashford. Robyns, W. & Wilczek, R. (1950) Ocotea angustitepala (Krause) Robyns & Wilczek. Bull. Jard. Bot. Etat Brux. 20, 213-214. Rohwer, J.G. (1989) Ocotea angustitepala (Krause) Robyns & Wilczek (Lauraceae) from Cameroon is an introduced Neotropical Nectandra. Bull. Jard. Bot. Nat. Belg. 59, 468-470. Roussel, B. & JuhBeaulaton, D. (1992) Les plantes amricaines en Afrique tropicale. Cah. OutreMer 45(179180), 373-385. Sandlund, O.T., Schei, P.J. & Viken, A. (Eds) (1996) Proceedings of the Norway/UN conference on alien species. DN and NINA, Trondheim. Sauer, J.D. (1988) Plant migration (The dynamics of geographic patterning in seed plant species). University of California Press, Berkeley. Saxena, K.G. (1991) Biological invasions in the Indian subcontinent: review of invasion by plants. In Ramakrishnan, P.S. (Ed.) Ecology of biological invasion in the tropics, pp. 53-73. International Scientific Publications, New Delhi. Schofield, E.K. (1989) Effects of introduced plants and animals on island vegetation: Examples from the Galpagos Archipelago. Conserv. Biol. 3, 227-238. Scott, J.K. & Panetta, F.D. (1993) Predicting the Australian weed status of southern African plants. J. Biogeogr. 20, 87-93. Sheil, D. (1994) Invasive plants in tropical forests: warnings from the Amani Botanic Gardens, Tanzania. Bot. Gardens Conserv. News 2(3), 23-24. Sheil, D. (1994) Naturalized and invasive plants in the evergreen forests of the East Usambara Mountains, Tanzania. Afr. J. Ecol. 32, 66-71. Smith, C.S. & Miller, I.L. (1991) Mimosa or giant sensitive plant (Mimosa pigra). Agnote 466, 1-2. Spongberg, S.A. (1990) A reunion of trees. The discovery of exotic plants and their introduction into North American and European landscapes. Harvard University Press, Cambridge, Spooner, B., Upson, T. & Drucker, G. (1993) Sustainable environment and development strategy and action plan for St Helena. Vol. 2. Environmental profile. RBG, Kew and IIED, London. Starfinger, U. (1991) Population biology of an invading tree species - Prunus serotina. In Seitz, A. & Loeschke, V. (Eds) Species conservation: a populationbiological approach, pp. 171-185. Birkhauser, Basel. Stirton, C.H. (1979) Taxonomic problems associated with invasive alien trees and shrubs in South Africa. Proc. 9th Plenary Meeting AETFAT, pp. 218-219. Stone, C.P., Smith, C.W. & Tunison, J.T. (Eds) (1992) Alien plant invasions in native ecosystems of Hawai'i: management and research. University of Hawaii Press, Honolulu. Strahm, W. (1989) Plant red data book for Rodrigues. Koeltz Scientific Books, Konigstein. Strahm, W.A. (1993) The conservation of the flora of Mauritius and Rodrigues. Ph.D. University of Reading. Sussman, R.W. & Rakotozafy, A. (1994) Plant diversity and structural analysis of a tropical dry forest in southwestern Madagascar. Biotropica 26, 241-254. Swarbrick, J.T. (1986) History of lantanas in Australia and origins of the weedy biotypes. Pl. Prot. Quart. 1, 115-121. Swarbrick, J.T. & Skarrett, D.B. (1994) The Bushweed 2 database of environmental weeds in Australia. The University of Queensland Gatton College. Temple, S. (1990) The nasty necessity: Eradicating exotics. Conserv. Biol. 4, 113-115. Timler, F.K. & Zepernick, B. (1987) German colonial botany. Ber. dtsch. bot. Ges. 100, 143-168. Toops, C. (1979) Invaders of the Everglades. Am. For. 85(8), 3841, 50-54. Vietmeyer, N. (1986) Casuarina: weed or windfall? Am. For. 92(2), 22-24. Wagner, W.L., Herbst, D.R. & Sohmer, S.H. (1990) Manual of flowering plants of Hawai'i. Bishop Museum and University of Hawaii Press, Honolulu. Waterhouse, B. (1994) Discovery of Chromolaena odorata in northern Queensland, Australia. Chromolaena odorata Newsletter 9, 1-2. Wester, L.L. & Wood, H.B. (1977) Koster's curse (Clidemia hirta), a weed pest in Hawaiian forests. Environ. Conserv. 4, 35-41. Whitmore, T.C. (1991) Invasive woody plants in perhumid tropical climates. In Ramakrishnan, P.S. (Ed.) Ecology of biological invasion in the tropics, pp. 35-40. International Scientific Publications, New Delhi. Wild, H. (1968) Weeds and aliens of Africa: the American immigrant. University College of Rhodesia, Salisbury. Williamson, M. (1996) Biological invasions. Chapman & Hall, London. Willis, J.R. (1991) Review of Drake, J.A., Mooney, H.A., Castri, F. di, Groves, R.H., Kruger, F.J., Rejmanek, M. & Williamson, M. (Eds) biological invasions. Wiley, Chichester. J. Ecol. 79, 261-262.  PAGE 4 @.A....()()))()()b: phoenix JJHMgo2DFVX 2 C /5[2 U 1,D,W,k,,,3346G6::4P8P=PDPePkPmPrPtP{PPPPPPPQ Q'Q,Q.Q3Q8Q]`a chV]`a c U]`a U]`a c ]`a cU]`a c ]`a cP8Q=QiQpQrQxQ}QQQQQQRRjRqRvRRSSSSTTTT-T1TBTITYT`TnTzTTTTTTTTTTTTT UUU*U6UAUKURUbUiUwUUUUUUUUUUUUUUVV"V*V8V?VMVWV[[[[i`nRqNu?@U]`a c ]`a c ]`a cV]`a cYʜޜ 05CHY^ EAWY_ix);վ߾)27<06p&AI#(PU\jl|h}] V]`c ]`cuDC]`cG C]`cuDC]`c U]`cU]`a c ]`a cM@H#@OcmBJjv-;dnw|6JKa6BBJqvEN LQ "   U]`c ]`c V]`c^  / 4 i n hr-AES*/  !!""b"r"$$t%%&&))++,/,M,],,,,--+-B-R-k-}------..".;.S.1 22M2b2y222222222223)313@3M3]3r33333306163<@<B< U]`c ]`c V]`c^B<Q<>>J?P???DD$H)H\\______ `.`hhqq`q!r"ruuvvvv7w8wwwwwwwQxRxփ׃/0[\{|EF:;IJՠnɨ٨!%1H ]`a c U]`c ]`c V]`c[HX]oũݩ"@PWi,.>"$24KMY[puŮЯ +<EKt / '9,4<HIeg2B V]`c ]`c ]`cJ]`c`c U]`c ]`a c ]`c V]`cPBٿ/=v*Oa.]i(@#$7!.DT#$MU~F?GJR 8Xpk|3? (<V]] V]`c ]`c U]`c ]`a c V]`c ]`cU3 ? /  XXk^uP:aP: uDP:uD] V]`c ]`cIJKLM~6Qfg&4[no,0,0,,)12EFUVWX!"    . / 0 1 2 3 4 D E JKsZ,0,}~0 1 2 V W | } ''(())))))..../.1133333337799,0,999:::;1;6;V;u;;;;;</<N<m<<<<<='=F=e======:B;BDDDDPEQEEE#E#, `0@  !`',0(EE F3F\F]FFFFFG6G[GGGGGHDHkHHHHI.IUI|IIIIIJJKJtJuJJJJE#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E# ,`0@ ,`0, `0@  !`'&JKBKkKKKKLL:LiLLLLLOORRR.S/ScSSSST-TYTTTT U6UbUUUUVE#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E# E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#, `0@  !`',`0 ,`0@ &V8VMVbVcVdVXX[[L\M\\\>]]]]K^L^^^^P____`a``a[aaaQbbbGccc=d>dE#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#E#,`0@  ,`0)>d?dMeNeOePegeheyezeKhLhMhiiiZiiii?@Ҏ=sߏKѐ34iӑ,,5p 8 Xxp0P,`0(,G`0h8p 8 Xxp0Pӑ=rܒݒޒߒ%&,iYі I9u,p(,G`0h8p 8 Xxp0P,#D}~2n"^֛NƜǜȜɜʜߜ:W^}Ҡˡb(,G`0h8p 8 Xxp0P,p%b,- FG²(Niȳrs,(,G`0h8p 8 Xxp0P&snop#$gh45deVW'(wx;,-x !  oQd|"#  0 1 ?!#(((]*^***8+9+X+,fBy,J f y,'X+u++++,M,w,,,,,-B-k----.;.h...t0u001X1Y1~11112N2z222 ,p#,,J f y,fBy%22223*3B3^33334V4444 5a5b550616U6V69:j<k<>>>>,,50 @ P`p ,& 0 @ P`, ,p#>>HCEGNtPuPyTzTUVlWWYXXY[[[6\]}]]A^^G_v_w_/aaaTbb/e0ehhhhh?jSjjk[k,-[kkljllmkn oopqaqbqsstuuuuuuu'v^vvvvw6w\wwwwxPxxxxxx ,p#,p#,(x)yZyyyyz5zdzzzz{@{m{{{{{%|U|z|||}'}T}y}}}}~K~r~~~~"P 6_ ,p#,_ހAde߁K<pՃ .ZzƄDvͅ56a܆ ,p#,!UtćEeو"Qȉ)XJm&M͌4\yэ$Y ,p#,Yَ)Ktȏ +]ڐ 1gl"W9\ ,p#,'GhFmĖLk×Jz$;eϙ(U}Κ0Pr ,p#,›Û>|ĜŜ <=uҝHޞ/_An ,p#*֠נ fmn%]ũ@Wy-.?@01,,,p#((Cg}DWnٵAvҶ$-Eغ~>,J fy,,)2ٿ/vO](#89WX !/0ghde0,,J fy*01abstz{  KLJK,-)*,0,,^_[\YZWX/0-.JK`a<,-aFG  XYrs89/0,0<,+89}~Z[yzijij _`9:@A]^,,0,z{FG2378NO` a   T U       / 0   89<,-9BCPQ  XY4589 ~9h9`<,*=K"@"Normal3 ]a c"A@"Default Paragraph FontO Document 8O Document 4UVcO Document 6O! Document 5 O1 Document 2 ]a cOA Document 7OQ Bibliogrphy>Ob> Right Par 1P,3 0 ]a c@Or@ Right Par 2P,30 ]a c O Document 3 ]a cDOD Right Par 3pP,30p ]a cFOF Right Par 4"@ P,30p@  ]a cJOJ Right Par 5%,30p@  ]a cLOL Right Par 6(,30p@  ]a cPOP Right Par 7+P,3 0p@  ]a cROR Right Par 8.P,3 0p@  ]a c4O4 Document 1,30 ]a c O Tech Init ]a c6O6 Technical 5!,30 U]a c6O"6 Technical 6",30 U]a c"O1" Technical 2 ]a c"OA" Technical 3 ]a c4OR4 Technical 4 %,30 U]a c"Oa" Technical 1 ]a c6Or6 Technical 7',30 U]a c6O6 Technical 8(,30 U]a c2O2Pleading),30 ]a cODoc Init.@.TOC 1+0,(#$,@,TOC 2,0,(#$,@,TOC 3-p0,(#$,@,TOC 4.@ 0,(#$,@,TOC 5/0,(#$(@(TOC 600,(#$@TOC 7 10,(@(TOC 820,(#$(@(TOC 930,(#$. @.Index 14`,(#$. @.Index 250,(#$(.@( TOA Heading6,(#$"@Caption7O_Equation Caption @ Footer 9!)@ Page Number(B@( Body Text;, `a c$O$ Plain Text< ]a c)                                 ! " # $ % & ' ( )[$Z5AIXNep{yq^/v# h+l83M_nxL-$[K~ C_N :  F m 2OAHAQ,4+A !"#$%&'( 8Q B<HB^  9EJV>dnxJ\pӑbsxX+2>[kx_Y0a9 !"#$%&'()*+,-./0123456789 !Computing Manager\\LURCH\WWW\IWPT\WEB1-99.docComputing Manager\\LURCH\WWW\IWPT\WEB1-99.txtComputing Manager\\LURCH\WWW\IWPT\WEB1-99.txt@Acrobat PDFWriter 3.0LPT1:PDFWRITRAcrobat PDFWriter 3.0Acrobat PDFWriter 3.0 d 4d,,Acrobat PDFWriter 3.0 d 4d,,^Times New Roman Symbol &Arial1CourierCourier New5Courier New"9)z9{9x9Lx))")8_PIERRE BINGGELIp bComputing Manager  !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~      !"#$%&'()*+,-./0123456789:;<=>?@AHPRoot EntryE#E#E#E#E#E# E# F "  " GWordDocumentE#E#E#E#E#E#E#E#E#E#E#E#6E#CompObjjSummaryInformation(  FMicrosoft Word Document MSWordDocWord.Document.69qOh+'0 $ L X d p|_PIERRE BINGGELIdGp bGDNormalComputing ManagerG4GMicrosoft Word for Windows 95G@DocumentSummaryInformation8 ՜.+,0HPpx  University of Ulster _PIERRE BINGGELIG@ݝ! @c! @& " )Lx՜.+,0HPpx  University of Ulster _PIERRE BINGGELI