Guide to the Naturalized and Invasive Plants of the Caribbean

By Arne Witt

The Caribbean region is one of the world's greatest centres of biodiversity. It includes about 11,000 species of plants of which 72% are found nowhere else on earth. Endemic vertebrates include all of the 189 species of amphibians present in the Caribbean; 95% of the 520-reptile species; 26% of the 564-bird species; and 74% of the 69 species of mammals, mostly bats. Species endemic to this hotspot represent 2.6% of the world's plant species and 3.5% of the world's vertebrate species. This biodiversity, and the livelihoods of people that depend on it are threatened by, among others, the uncontrolled spread of invasive alien species (IAS). This Field Guide has been developed to help address one of the barriers to effective IAS management, which is the lack of information on the presence, impact and management of invasive alien plant species in the Caribbean. In general, we have only included those species that we consider to be threatening biodiversity and livestock production.

• Language: English
• Publisher: CAB International
• Release date: Mar 28, 2024
• ISBN: 9781800623453

Arne Witt

Arne Witt is currently the Regional (Africa and Asia) Coordinator for Invasive Species for CABI, based in Wilderness (George), South Africa. He has been an International Project Coordinator and/or Technical Advisor for a number of regional and national UNEP-GEF IAS Projects in Africa, Asia, Caribbean, and the Middle East. In these roles he has worked with countries in developing policies, building capacity, creating awareness, and developing and implementing best management practices, including biological control. He continues to develop and implement IAS projects in these regions. Arne has a PhD from the University of the Witwatersrand, South Africa. He has Master of Science degrees in Entomology (Stellenbosch University) and Conservation Biology (University of Cape Town). He has published a number of journal articles, and authored or co-authored book chapters and books on the identification and management of invasive alien species.

Book preview

GUIDE TO THE NATURALIZED AND INVASIVE PLANTS OF THE

CARIBBEAN

GUIDE TO THE NATURALIZED AND INVASIVE PLANTS OF THE

CARIBBEAN

Arne Witt, CABI

First published in 2023

The Global Environment Facility (GEF)-funded project Preventing the COSTS of Invasive Alien Species (IAS) in Barbados and the OECS, is implemented by the United Nations Environment Programme (UNEP) and executed by CABI, in partnership with the Governments of Antigua and Barbuda, Barbados, Grenada, Dominica, St. Kitts and Nevis, Saint Lucia and Saint Vincent and the Grenadines.

CABI is a trading name of CAB International

CABI

Nosworthy Way

Wallingford

Oxfordshire OX10 8DE

UK

T: [phone]

F: [phone]

E: [e-mail]

www.cabi.org

© CAB International 2023. The copyright holder of this work is CAB International (trading as CABI). It is made available under a Creative Commons Attribution-Noncommercial Licence (CC BY-NC).

Reproduction of this publication for educational or other non-commercial purposes is authorised without prior permission from the copyright holder provided the source is fully acknowledged. Reproduction for resale or other commercial purpose is prohibited. A catalogue record for this book is available from the British Library, London, UK.

ISBN-13: 9781800623446 (ePDF)

9781800623453 (ePub)

Design: Sarah Hilliar, CABI

Typesetting: TNQ Technologies

Printed and bound by Gutenberg Press Ltd., Tarxien, Malta

Contents

Foreword

Executive Summary

Introduction

Acknowledgements

One Hundred Naturalized and Invasive Plants in the Caribbean – Identification, Impacts and Control

Useful Websites

References

Appendix A: Summary table of plant species included in this Guide that are considered to be naturalized, potentially invasive or invasive in the Caribbean.

Appendix B: Biological control agents that have established in the Caribbean, or elsewhere, on some of the plant species recorded as naturalized and/or invasive in the region.

Appendix C: Herbicides registered or permissible with minor or emergency use permits in Australia against some of the plant species included in this Field Guide.

Appendix D: Registered and minor-use herbicides applied in South Africa for the control of some of the plant species included in this Field Guide.

Glossary

Index

Arne Witt is currently the Regional (Africa and Asia) Coordinator for Invasive Species for CABI, based in Wilderness (George), South Africa. He has been an International Project Coordinator and/or Technical Advisor for a number of regional and national UNEP-GEF IAS Projects in Africa, Asia, Caribbean, and the Middle East. In these roles he has worked with countries in developing policies, building capacity, creating awareness, and developing and implementing best management practices, including biological control. He continues to develop and implement IAS projects in these regions.

Arne has a PhD from the University of the Witwatersrand, South Africa. He has Master of Science degrees in Entomology (Stellenbosch University) and Conservation Biology (University of Cape Town). He has published a number of journal articles, and authored or co-authored book chapters and books on the identification and management of invasive alien species.

Foreword

The Caribbean region, encompassing more than 700 islands, islets, reefs, and cays spread over 229,540 km² of land and 2,754,000 km² of ocean is an aweinspiring tapestry of natural wonders. This unique region is a global biodiversity hotspot, harboring an array of habitats ranging from montane cloud forests to tropical rainforests and cactus shrublands, all displaying an incredibly high degree of regional endemism. Some 13,000 plant species have been identified of which 205 genera and 6,500 species are endemic. All 200 native amphibian species in the Caribbean are endemic, many to single islands, while more than 600 native reptile species occur in the Caribbean, of which 82% are found nowhere else on earth. The Caribbean region once supported 127 terrestrial mammal species, of which 23 are now considered extinct. Today, 25% of the 104 extant mammal species are globally threatened. Of the 565 species of birds recorded in the Caribbean hotspot, 55 are currently listed as globally threatened. The marine space is also globally unique with endemism levels of 25.6%, and includes the world’s second largest barrier reef.

Overexploitation, habitat destruction and fragmentation due to agricultural, urban, tourism, and commercial development pose significant risks to the Caribbean. However, perhaps one of the most insidious threats to the region’s biodiversity comes in the form of invasive alien species (IAS).

IAS refers to exotic, non-native, non-indigenous, or foreign plant or animal species that humans have introduced, intentionally or unintentionally, beyond their natural range and dispersal potential. Once established in their new environments, these invasive species proliferate, posing detrimental effects on biodiversity, livelihoods, and economic development. The detrimental effects of IAS are poised to intensify further with increased global trade, travel, transport, and the looming specter of climate change.

While the presence, distribution, and impacts of invasive alien vertebrate species have received some attention, our understanding of invasive alien plant species in the region remains limited. Though certain species like water hyacinth and casuarina are well-known and have gained notoriety for their negative impacts, the influence of many other exotic plant species in the Caribbean remains poorly understood. In contrast to crop pests, invasive plant species have wideranging ecosystem impacts. Despite these far-reaching consequences, very little has been done to manage invasive alien plant species at a national or regional level in the Caribbean. This inaction can be partially attributed to the limited knowledge regarding the presence, distribution, impacts, and potential management interventions for most invasive alien plant species.

To bridge this critical knowledge gap, CAB International has partnered with the Global Environment Facility (GEF) and the United Nations Environment Programme (UNEP) to produce this guide to the naturalized and invasive plants of the Caribbean. The Guide, which covers 100 species of naturalized and invasive plant species of the Caribbean, offers detailed species descriptions and accompanying color images to aid in identification. Furthermore, it provides valuable insights into impacts, distribution, and methods of control, enhancing our understanding of and ability to manage invasive alien plant species in the region. Importantly, this guide assists countries in taking action toward fulfilling their obligations under international agreements and treaties such as the Convention on Biological Diversity (CBD) and the International Plant Protection Convention (IPPC).

We hope this field guide is an invaluable resource that will contribute significantly to the management of invasive alien plants in the Caribbean. By equipping ourselves with knowledge and taking decisive action, we can advance the achievement of our Sustainable Development Goals while preserving the natural heritage of this biodiverse region for future generations.

Dr Susan Gardner, Director, Ecosystems Division, UNEP

Executive Summary

Invasive alien species (IAS) pose a serious threat to biodiversity, livelihoods and economic development in the Caribbean. Yet the management of invasive species, and of invasive alien plant species in particular, is constrained by a number of factors. Common constraints include weak policies or poor implementation of policies pertaining to IAS management; insufficient coordination at national and regional levels; lack of awareness and of access to critical information, particularly on the presence, distribution, impacts and management of IAS; inedaquate resouces available for effective prevention and control, and a general lack of capacity.

While this situation has improved over the past 10–20 years, with publications by Kairo et al. (2003), Van der Burg et al. (2012), Rojas-Sandoval and Acevedo-Rodríguez (2015), Rojas-Sandoval et al. (2016), and others, further progress has been hampered by the absence of tools to aid in the identification and management of IAS. Interested and affected parties throughout the Caribbean have repeatedly expressed the need for a comprehensive field guide, as a tool to assist in the identification of naturalized and invasive alien plant species, and in understanding their impacts, both existing and potential, while also providing pointers on what can be done to manage such species.

This information is seen as essential, not only in enabling countries to develop effective IAS management strategies, but also in helping them to meet their obligations under various international agreements and treaties, including Article 8 (h) of the Convention on Biological Diversity (CBD) which states that, 'Each contracting Party shall, as far as possible and as appropriate, prevent the introduction of, control or eradicate those alien species which threaten ecosystems, habitats or species.' Without information on the presence, distributon and impacts of alien species it is obviously not possible to prioritize species for control interventions. Without effective IAS management, many of the goals agreed to under these and other protocols, such as the 2030 Sustainable Development Goals (SDG), will remain elusive. In fact, many of the SDGs will not be achieved unless IAS are effectively managed because they also, among others, impact on food and water security, and human and animal health.

In providing such a database, this Guide is intended to give Caribbean nations the information they require, in order to be able to develop effective strategies for combating the existing and rapidly increasing menace posed by invasive alien plants. It is further hoped that this Guide will foster increased collaboration between nations in the Caribbean, and possibly also other countries in the region, especially in responding to the challenges of managing shared invasive plant species. As such it is hoped that the Guide will contribute to increased collaboration across all of the Caribbean, including mainland countries in South, Central and North America.

The Guide is based on the findings of roadside surveys undertaken in Antigua and Barbuda, Barbados, Dominica, Grenada, Saint Kitts and Nevis, Saint Lucia, and Saint Vincent and the Grenadines; casual surveys in Trinidad and Tobago and Jamaica, and on a review of the literature pertaining to naturalization and/or invasiveness among alien plants in the Caribbean. These surveys and literature reviews have revealed that the majority of invasive plants have been intentionally introduced, and have subsequently escaped from cultivation, establishing populations in the ‘wild’, to the detriment of natural resources.

Included in the Guide are descriptions of 100 exotic, non-native or alien plant species (some may have an uncertain origin or be considered native on some islands but introduced and naturalized and/or invasive on others) which are either naturalized or invasive already or which are deemed to have the potential to become invasive in the Caribbean. The profiled species include aquatic invasive plants or waterweeds (2 species); 14 invasive grass species; vines, creepers or climbers (16 species); terrestrial herbs (11); shrubs (15); succulents (10); and trees (32). This Guide only provides descriptions and other relevant information for a sub-set of plant species that have been recorded as naturalized or invasive in the Caribbean (see Appendix A). There is also no doubt that this list is incomplete since many islands, and areas on islands, with very few exceptions, have not yet been adequately surveyed, but we are confident that this Guide may provide users with the impetus to gather additional data on the presence and distribution of invasive alien plant species.

One of the main challenges in determing which species should be included, and which should rather be excluded, has been the determination of origin. The literature is often full of contradictory information, making this task considerably more difficult. Some species are considered to have been introduced to all Caribbean islands, while other species are considered to be native to some islands but alien and invasive on others. In some cases, species have even been listed in the published literature as native and alien on the same island. This confusion generally only applies to species which are also considered to be native to North, Central or South America. As such we cannot be 100% certain that all species included in the Guide are exotic to all islands in the Caribbean, and as such users of the Guide should undertake additional research to confirm the status of a plant species before initiating any control activities.

In reference to this I provide a little background. A review of the biogeography of Caribbean plants by Santiago-Valentin and Olmstead (2004) may provide some insights into the origin of some of these species, and if they should be considered to be native or introduced. Initial observations led to distinguish distributions in the Caribbean flora as being primarily Greater Antillean [Cuba, Hispaniola (Haiti and Dominican Republic), Puerto Rico, Jamaica and the Cayman Islands], or Lesser Antillean (Anguilla, Antigua and Barbuda, Barbados, Dominica, Grenada, Guadeloupe, Martinique, Montserrat, Saint Lucia, Saint Kitts and Nevis, Saint Vincent and the Grenadines, Virgin Islands; and the isolated island groups of Bahamas and Turks and Caicos, and those of the South American shelf, including Trinidad and Tobago, Aruba, Curaçao and Bonaire). In other words, the floras of islands in the Greater Antilles were considered to be more similar to each other than floras of islands in the Lesser Antilles, and as such they would intuitively have had different origins. The Greater Antillean flora was considered to be older and to have North, South, and especially Central American affinities (Alain, 1958, in Santiago-Valentin and Olmstead, 2004). Relationships between these islands and the mainland were largely explained by land bridges between Honduras (Central America) and the Greater Antilles (Asprey and Robbins, 1953, in Santiago-Valentin and Olmstead, 2004), and by Cuban land connections with Yucatan and Florida (Alain, 1958, in Santiago-Valentin and Olmstead, 2004). In contrast, dispersal, and not land bridges, were considered to be the origin of the vegetation of the Lesser Antilles. However, the existence of land bridges between the Greater Antilles and the American mainland were later rejected.

Howard (1973) later provided a summary of affinities based on the total number of genera sharing a similar range, and concluded that there were five main patterns or units, namely (1) Pan-American: all islands and surrounding continents; (2) Western Continental: Central America, northern South America and the Greater Antilles; (3) Southern Continental: Central America, northern South America and the Lesser Antilles; (4) Antillean: restricted to the West Indies but better developed in the Greater Antilles; and (5) Greater Antillean: endemic to one or more islands of the Greater Antilles. Acevedo-Rodriguez and Strong (2008) concluded that the West Indian flora, despite 72% of its taxa being endemic to the West Indies, is clearly related to the flora of the surrounding continents. For example, 26 genera are exclusively shared between the West Indies and North America, probably as a result of southward migration – 11 genera reached the Bahamas, 16 Cuba, eight Hispaniola, two Jamaica, two Puerto Rico, and zero the Lesser Antilles (Acevedo-Rodríguez and Strong, 2008). Of the eight genera shared exclusively between South America and the West Indies, all are in the Lesser Antilles, seven in Puerto Rico, six in Hispaniola, five in Cuba, four in Jamaica, and four in the Bahamas, suggesting dispersal from South America north. At the same time there are 111 genera present in South America, Central America and the Greater Antilles that are missing from the Lesser Antilles, despite their proximity to South America, suggesting that migration into the Greater Antilles occurred before the Lesser Antilles were formed (Acevedo-Rodríguez and Strong, 2008). Acevedo-Rodríguez and Strong (2008) conclude that the West Indian flora shows a mosaic of affinities to surrounding continents that are stronger with Central and South America as a whole than with either of them separately or with North America. To elucidate the origins of the West Indies flora it is suggested that phylogenetic studies be undertaken as the next necessary step (Acevedo-Rodríguez and Strong, 2008). Until such time it will be difficult to confirm if some plant species native to Central, South or North America are also native or introduced to some Caribbean Islands.

The distribution of invasive alien plants is largely determined by the prevalent climate on the Caribbean Islands aided by the massive destruction of natural habitats during European colonization, resulting in the loss of most of the forest cover, with only 25% remaining on average across all of the West Indies. The Caribbean climate is tropical humid but locally both temperature and rainfall vary with elevation, island size and ocean currents. For example, cool up-wellings keep Aruba, Bonaire and Curaçao semi-arid. Rainfall distribution, and as such the type of vegetation present on various areas on islands, is largely determined by the size, topography and position of the islands in relation to the trade winds with, for example, flat islands receiving slightly less rainfall. As such individual islands can consist of many habitat types across a small area. For example, due to the heterogenic landscape and climate, St Eustatius (at 21 km² one of the smallest islands of the Lesser Antilles) harbours diverse vegetation types, from xeric shrubland with cacti to seasonal deciduous and evergreen tropical forest (Roobol and Smith, 2004; Helmer et al., 2008; De Freitas et al., 2014). This diversity in habitat types, largely driven by climate, increases the probability of significantly more introduced species being able to establish and proliferate, even on very small islands. In other words, a diversity of habitat types across a small area, largely driven by climate variability, will provide more suitable niches for the establishment of introduced plants than would be the case if a whole island was arid, or covered in a tropical forest. As such it would not be unusual for a plant species such as a cactus, adapted to a semi-arid environment, and a tropical species such as the tulip tree (Spathodea campanulata P. Beauv.; Bignoniaceae) to be invasive on the same small Caribbean island.

Some of the most problematic invasive plant species in the Caribbean include wild tamarind [Leucaena leucocephala (Lam.) de Wit; Fabaceae]; coral creeper (Antigonon leptopus Hook. & Arn.; Polygonaceae); casuarina (Casuarina equisetifolia L.; Casuarinaceae); buffalo grass [Megathyrsus maximus (Jacq.) B.K. Simon & S.W.L. Jacobs; Poaceae]; castor-oil plant [Ricinus communis L.; Euphorbiaceae]; tulip tree, broad-leaved paperbark tree [Melaleuca quinquenervia (Cav.) S.T. Blake; Myrtaceae]; Indian almond (Terminalia catappa L; Combretaceae); and water hyacinth (Pontederia crassipes Mart.; Pontederiaceae). Other widespread and abundant species include lebbeck tree [Albizia lebbeck (L.) Benth; Fabaceae], jungle rice [Echinochloa colona (L.) Link; Poaceae], Indian goosegrass [Eleusine indica (L.) Gaertn.; Poaceae], air plant [Bryophllum pinnatum (Lam.) Oken; Crassulaceae], mother-in-law’s tongue [Sansevieria hyacinthoides (L.) Druce; Agavaceae]; para grass [Urochloa mutica (Forssk.) Nguyen; Poaceae]; white siris [Albizia procera (Roxb.) Benth.; Fabaceae]; giant sensitive plant (Mimosa pigra L.; Fabaceae); and creeping foxglove [Asystasia gangetica (L.) T. Anderson; Acanthaceae].

Many plant species are currently confined to one or a very few islands but have the potential, based on research undertaken elsewhere, to possibly become considerably more widespread and problematic throughout the Caribbean. Such species include hickory wattle (Acacia mangium Willd.; Fabaceae); black wattle (Acacia mearnsii De Wild.; Fabaceae); orchid tree (Bauhinia variegata L.; Fabaceae); prickly acacia [Vachellia nilotica (L.) Delile; Fabaceae]; Mexican sunflower [Tithonia diversifolia (Hemsl.) A. Gray; Asteraceae]; Bryophyllum species (Crassulaceae); yellow flamboyant [Peltophorum pterocarpum (DC.) K. Heyne; Fabaceae]; pink cassia (Cassia javanica L.; Fabaceae); sickle bush (Dichrostachys cinerea Wight et Arn.), water lettuce (Pistia stratiotes L.; Araceae); Asparagus species (Asparagaceae); Clerodendrum species (Lamiaceae); Hedychium spp. (Zingiberaceae), and a number of grass species, among others.

Many areas on Caribbean islands, and in some cases whole islands such as Aruba, Bonaire and Curaçao are considered to be arid or semi-arid. Introduced species such as various sisal species (Agave spp.; Agavaceae), Barbados aloe [Aloe vera (L.) Burm.f.; Asphodelaceae], mesquite [Prosopis juliflora (Sw.) DC.; Fabaceae], Bryophyllum spp. (Crassulaceae), calotropis [Calotropis procera (Aiton) Dryand.; Apocynaceae], mother-in-law’s tongue, rosy perwinkle [Catharanthus roseus (L.) G. Don; Apocynaceae], and others, are well adapted to deal with limited rainfall and high temperatures, and have established widely in these habitats.

Plants growing along the coast need to be very tolerant of strong winds and salt- and sand-loaded ocean spray. Many introduced plants are well adapted to these conditions and have proliferated along the coasts of many Caribbean islands. Coastal areas have been invaded by, among others, creeping foxglove, casuarina, Indian almond, beach cabbage [Scaevola taccada (Gaertn.) Roxb.; Goodeniaceae], bonduc nut [Caesalpinia bonduc (L.) Roxb.; Fabaceae], mother-in-law’s tongue, cork tree [Thespesia populnea (L.) Sol. ex Corrêa; Malvaceae], and Orange River lily [Crinum bulbispermum (Burm.f.) Milne-Readh. & Schweick.; Amaryllidaceae].

Disturbed forests, secondary forests and forest edges and gaps throughout the Caribbean have been invaded by a host of non-native species such as Singapore daisy [Sphagneticola trilobata (L.) Pruski; Asteraceae], hyacinth bean [Lablab purpureus (L.) Sweet; Fabaceae], tulip tree, flamboyant (Delonix regia (Hook.) Raf.; Fabaceae], arrowhead vine (Syngonium podophyllum Schott; Araceae), Ceylon creeper [Epipremnum aureum (Linden & André) G. S. Bunting; Araceae], bead vine (Abrus precatorius L.; Fabaceae), hickory wattle, ivy gourd [Coccinea grandis (L.) Voigt; Cucurbitaceae], jasmine (Jasminum fluminense Vell; Oleaceae), boat lily (Tradescantia spathacea Sw.; Commelinaceae), impatiens (Impatiens balsamina L.; Balsaminaceae), Bengal trumpet vine [Thunbergia grandiflora (Rottl.) Roxb.; Acanthaceae], golden bamboo (Bambusa vulgaris Schrad. Ex Wendl.; Poaceae), bleeding-heart (Clerodendrum spp.; Lamicaeae), and limeberry [Triphasia trifolia (Burm. f.) P. Wilson; Rutaceae].

Abandoned sugarcane fields, and other highly disturbed areas have been invaded by a large number of species including, among others, coral creeper, wild tamarind, a host of introduced grass and sedge species, spider plant (Cleome gynandra L.; Cleomaceae), wild mustard (Cleome viscosa L.; Cleomaceae), parthenium (Parthenium hysterophorus L.; Asteraceae), yellow bells [Tecoma stans (L.) Juss ex Kunth; Bignoniaceae], needle-leaved goosefoot [Chenopodiastrum murale (L.) S. Fuentes, Uotila & Borsch; Amaranthaceae], little ironweed [Cyanthillium cinereum (L.) H.Rob; Asteraceae], creeping foxglove, and wild hops [Flemingia strobilifera (L.) W. T. Aiton; Fabaceae).

Water bodies, including swamps and marshes, and/or riparian areas have been invaded by broad-leaved paperbark tree, giant sensitive plant, water lettuce, water hyacinth, wild ginger [Alpinia nigra (Gaertn.) Burtt; Zingiberaceae], white ginger (Hedychium coronarium J. Koenig; Zingiberaceae), wild taro [Colocasia esculenta (L.) Schott; Araceae], canna (Canna indica L.; Cannaceae), castor-oil plant, and ruellia (Ruellia simplex C. Wright; Acanthaceae).

Climate change is predicted to have a significant impact on the distribution of many of these species, and in many cases will exacerbate invasions. It is predicted that climate change will contribute to an increase in extreme weather events, something which is already being experienced in the Caribbean, which will contribute to increased land degradation/disturbance. These severe weather events will create conditions suitable for the establishment and subsequent spread of invasive species. Increased disturbance will reduce resistance in recipient communities and create enemy-free sites for the establishment of invasive plants. The spectacular success of Miconia calvescens DC. (Melastomataceae) in Tahiti is often attributed to the six hurricanes that hit the Society Islands between December 1982 and April 1983. Reports suggested that the cyclones explained the ‘demographic explosion of miconia’, and that ‘the speed of the invasion then became astonishing’ (Birnbaum, 1994, in Meyer, 1997). Similarly, invasive species in rainforests in Queensland, Australia capitalized to a greater extent than native species on the disturbance created by Cyclone Larry; and after the major tsunami in SE Asia in 2004, Sri Lanka witnessed a significant expansion of erect prickly pear [Opuntia stricta (Haw.) Haw.; Cactaceae], mesquite [Prosopis juliflora (Sw.) DC.; Fabaceae], lantana (Lantana camara L.; Verbenaceae) and chromolaena [Chromolaena odorata (L.) R.M. King & H. Rob; Asteraceae] in degraded coastal areas, as well as of water hyacinth (P. crassipes) and cattails (Typha angustifolia L.; Typhaceae) in lagoons and estuaries.

Increasing temperatures may also enable species to expand their current ranges. For example, studies have shown that the root biomass of the invasive tree P. juliflora increases significantly in areas with a higher mean annual temperature. Increased temperatures may also improve germination rates of a host of invasive plant species. Invasive species may be able to expand their range to higher altitudes, areas that are often the last refuges for endangered and threatened species because these areas have been less affected by human activities in the past.

Some invasive plant species will also benefit from higher carbon dioxide levels (Kriticos and Filmer, 2007). For example, the invasive shrub A. nilotica is likely to benefit from increases in water-use efficiency as a result of increased CO2 concentrations, allowing it to invade drier sites, while increased temperatures will allow it to complete its reproductive life cycle in areas which are currently too cool to sustain populations (Kriticos et al., 2003). In laboratory trials chromolaena, which is considered to be one of the worst weeds in the world, benefitted significantly from increased CO2. Under doubled atmospheric CO2 concentrations (700 μmol/mol) total biomass, height, stem diameter, branch number and total leaf area were increased by 92%, 41%, 60%, 325% and 148%, respectively (Weiling et al., 2014). Of interest, native congeners do not demonstrate the same changes in growth or reproductive output under elevated CO2 levels.

Climate change is also likely to affect rainfall patterns with an increase in the length of the dry season, and a decrease in the length of the rainy season predicted for the Caribbean. Extensive fires in West Africa in the 1980s during extremely dry years contributed to the proliferation of invasive species such as paper mulberry [Broussonetia papyrifera (L.) Vent.; Moraceae] which took advantage of an increase in the size of forest gaps and reduced competition from native species. Invasive grasses, of which there are many in the Caribbean, will alter fire regimes, especially during dry years. An analysis of 12 invasive grass species in the USA documented regional-scale alteration of fire regimes for eight species, which are already increasing fire occurrence by up to 230% and fire frequency by up to 150% (Fucso et al, 2019). These frequent and intense fires are likely to have a significant negative impact on native biodiversity.

Global climate change will thus exacerbate the already serious levels of habitat degradation resulting in further loss of ecosystem services and species. Degraded landscapes are more amenable to plant invasions, which means that climate change will facilitate the expansion of areas suitable for the spread and proliferation of non-native species.

Introduction

The main aim of this Field Guide is to enable people to identify some of the alien plant species that have been identified as naturalized and/or invasive in the Caribbean (see Figure 1), and to enable them to learn more about the impacts of these species and about possible options for managing such plants.

Figure 1 The Caribbean includes thirteen countries classified as sovereign states by the United Nations, and nearly 24 non-sovereign territories.

The status of introduced plant species profiled in this Guide was determined through roadside surveys, including surveys of towns, villages and gardens, of some Caribbean Islands (Antigua and Barbuda, Barbados, Dominica, Grenada, Saint Kitts and Nevis, Saint Lucia, and Saint Vincent and the Grenadines; casual surveys in Trinidad and Tobago and Jamaica), and through a review of the existing literature, both published and unpublished.

Covering only 100 species, this is by no means a comprehensive guide. Indeed, it is a very conservative selection of the naturalized and invasive alien plant species that have been recorded in the Caribbean (see Appendix A). It should also be noted that many islands and localities were not surveyed, and that some species, even on islands that were surveyed, may have been overlooked. Other species may have escaped attention simply because they are not recorded in the literature as being naturalized or invasive in the Caribbean.

This Guide includes only species deemed to be having a negative impact, or as having the potential to impact negatively, on biodiversity or rangeland production (including through toxicity to livestock), even though many of the species may also have impacts on crop production and on other productive sectors. In other words, introduced plant species that, in our view, impact only on crop production have largely been excluded. This is not because such plants are considered to be less important, only that we have chosen to focus on species that are contributing, or which may contribute, to biodiversity loss and reduced pasture production in the region, now and in the future.

In our view, all the species profiled in this Guide are either naturalized and/or invasive, in the Caribbean. While it is obvious that some species, including coral creeper (Antigonon leptopus Hook. & Arn.; Polygonaceae), wild tamarind [Leucaena leucocephala (Lam.) de Wit; Fabaceae], creeping foxglove [Asystasia gangetica (L.) T. Anderson subsp. gangetica; Acanthaceae], wild mustard (Cleome viscosa L.; Cleomaceae), ivy gourd [Coccinea grandis (L.) Voigt; Cucurbitaeae], clammy cherry [Cordia obliqua Willd.; Boraginaceae), flamboyant [Delonix regia (Hook.) Raf.; Fabaceae], and water hyacinth [Pontederia crassipes Mart.; Pontederiaceae] are invasive, we cannot be entirely certain that other species we have 'labelled' as naturalized, will necessarily become problematic. In some instances, we cannot even be100% sure if they are introduced or native to particular islands.

The decision to include naturalized species is based on observations in the field and on the ecology and the biology of species and/or of closely related congeners which, elsewhere in the world, or even on other islands in the Caribbean, are known to have become problematic, threatening biodiversity and livelihoods. So, while some of the listed species may never become problematic on all islands in the Caribbean, it is better to be ‘safe than sorry’, and so avoid growing or disseminating exotic plant species that could damage our environment and/or economy in the future. This is what is known as the Precautionary Principle. As the sayings go, ‘a stitch in time saves nine’, and ‘forewarned is fore-armed’.

This Guide is sub-divided into five major sections: Aquatics; Grasses; Climbers (including vines and creepers); Herbs (including spreading or flat-growing plants); Shrubs; and Trees. Some species may be regarded as both shrubs and small trees, or as both small and large trees, or as both shrubs and climbers, but have been included in only one of the sections or categories in order to avoid duplication. The species appear in alphabetical order within each section, based on their scientific names.

The text gives the scientific name for each species, along with its English common name, or names. There is a brief description of each species, complete with colour photographs, as well as information on its origin, the reasons for its introduction, the habitats it invades and its impacts.

The information on impacts has been obtained from multiple sources, often from studies undertaken outside of the Caribbean. This can be instructive in that impacts, for most invasive species, tend to be generic, i.e. similar, irrespective of where a particular invasive species is adventive. In some cases, the impacts of introduced plant species within the Caribbean are not well documented in the literature. It is hoped that the case studies cited in this Guide will lead to a more thorough assessment of impacts within the region.

Any species found to be widespread and abundant, or even localized but abundant in the countries surveyed, was recorded as being invasive. The assumption is made that all the invasive species present in the Organization of Eastern Caribbean States (OECS) have been recorded, although some naturalized and (as of now) range-limited species may have been missed. The information on best management practices and on herbicide applications has been adapted mainly from sources in Australia and South Africa.

What is an alien plant?

An alien plant is an exotic, non-native, non-indigenous or foreign plant species that has been introduced by people, either intentionally or unintentionally, outside of its natural range and outside of its natural dispersal potential. Plants that have been introduced into an area without the help of people from an area in which they are already exotic are also regarded as alien. In other words, a species which does not belong to the native flora is alien. This includes most of our crops (wheat, maize, rice, potatoes, etc.), ornamental plants and agroforestry species.

What is an invasive alien plant?

An invasive alien plant is a species of plant that is both alien, as described above, and destructive to the environment in which it grows. As such, invasive plants can have negative impacts on biodiversity and/or livelihoods. It should be noted that most alien species are useful and do not become invasive. In the context of this Guide, destructive alien species that were found to be widespread and abundant, or even localized but nevertheless abundant, were recorded as being invasive within a particular locality. The same criteria were used in recording the status of native species that we consider to be invasive.

What is a naturalized plant?

In the context of this Guide, a naturalized plant is an alien plant that has established self-perpetuating populations without any human assistance, but which is not yet considered to be invasive, in terms of being either widespread and/or abundant or destructive in the areas where it is found. Most plants that are considered to be naturalized go on to become invasive, but in many cases they do not. The same applies to those exotic species profiled in this Guide that are not naturalized or invasive at present, but which have all of the characteristics or attributes of invasive species; some of these species may never become problematic, but we need to be conscious of their presence in the region and monitor their popuations.

What is a casual alien?

The term is not