Freitas, J.A. de

The cosmopolitan Barn Owl Tyto alba (Scopoli) lives on many Caribbean islands, where a number of morphologically distinct forms have evolved. Some of these forms have been considered separate species, like the taxa glaucops, nigrescens, and insularis on Hispaniola and the Lesser Antilles (Peters, 1940; Bruce in Del Hoyo et al., 1999; Ko¨nig et al., 1999). In the Netherlands Antilles (southern Caribbean) only Curac¸ao is known to have a breeding Barn Owl population. This endemic form, known as bargei, differs markedly from the taxa of the nearby mainland by its small size and relatively well-feathered feet

Het Terrassenlandschap Midden Bonaire (TLMB) is een groot gebied (ca. 3350 ha) in het midden van het noordelijke deel van Bonaire en bestaat voornamelijk uit kalksteenterrassen en –heuvels (zie Fig. 1). Het gebied is geologisch gezien vrij complex en bestaat uit: een vrij goot gebied dat in het Eoceen is ontstaan (omgeving Porta Spaño), en verder ook uit de Seroe Domi Formatie, eolianieten en zowel erosie- als depositieterrassen (de Buisonjé 1974). Van deze laatste twee formaties zijn in het gebied het Laag, Midden en Hoger Terras te vinden. Het gebied begint in het oosten bij Seru Largu en loopt door tot aan het Gotomeer in het westen. In het noorden loopt het kalksteengebied door tot aan het noordkustgebied dat ligt tussen Boca Onima in het westen en Leeuwaarden in de omgeving van het landsailing circuit in het oosten.

De hogere delen van het gebied vallen onder het sub-landschapstype TH1 dat circa 3⁄4 deel van het TLMB uitmaakt (De Freitas et al. 2005) (zie Fig. 2). In dit gebied valt ook de sub- landschapstype TH2 te onderscheiden welke alleen in Roi Sangu te vinden is. Beide gebieden zijn voor het natuurbehoud op Bonaire belangrijk omdat ze enkele van de minst verstoorde vegetatietypen van het eiland bevatten. Verder komen in het gebied de volgende landschapseenheden voor: B1, TL6, TL8, TL9, TL1 TM6, TM5, TM4, E1, E2, TM8, TM9, TM7, en D3. De Freitas et al. (2005) geven aan dat TH1, TH2, TM4, TM6, E1 en D3 bijzondere conserveringswaarde hebben op grond van de erin voorkomende relatief onverstoorde en goed ontwikkelde vegetatietypen. Met uitzondering van D3 komen deze landschapstypen en de daarbij behorende vegetatietypen niet voor in het wettelijk beschermde Nationaal Park Washington-Slagbaai. Het B1 landschap is ook van belang gezien de relatief weinig verstoorde conditie waarin het verkeert. In het Natuurbeleidsplan Eilandgebied Bonaire (1999) is voorgesteld om het TLMB gebied (inclusief de Laag Terrassen) tot Eilandelijk Natuurgebied te bestemmen. In genoemd natuurbeleidsplan staat het volgende over de ecologische betekenis van het gebied:

‘De gebieden in de bergen ten zuiden en oosten van het dorp Rincon zijn ruig en slecht toegankelijk en daarom veel minder in cultuur gebracht dan de valeigronden. Het terrassenlandschap bestaat uit de deelgebieden Rooi Sangu, Tolo en Colombia. Deze natuurgebieden (mondi) zijn van grote betekenis voor de natuur op Bonaire. Men treft er veel van de op Bonaire voorkomende plantensoorten aan. De gebieden zijn leef- en voedselgebied voor tal van inheemse vogelsoorten, waaronder de Lora, Prikichi, Chuchubi spaño, kolibries, duiven en zeldzame roofvogels als de Warawara en de Falki, en voor (de endemische) hagedissen en de Yuana.’

In het Ruimtelijk Ontwikkelingsplan Bonaire (R.O.B.; Eilandgebied Bonaire 2010) heeft het overgrote deel van het TLMB de bestemming ‘Natuur’ gekregen. In het R.O.B. heeft het noordelijke Laag Terras landschap de bestemming ‘Open Land’ gekregen en het B1 landschap de bestemming Recreatie. In een andere publicatie is het noordelijke deel van het TLMB als ‘Important Bird Area’ (IBA) aangegeven (Wells & Debrot 2008). Figuur 3 geeft een illustratie van alle IBA’s op Bonaire. Het westelijk deel van het gebied AN011 valt binnen het TLMB gebied. 

Abstract:

A semi-detailed landscape-based vegetation map (scale: 1: 37,500) based on field data from 1999 has been available as an update of Stoffers’ 1956 map of the Lesser Antillean island of St. Eustatius, Netherlands Caribbean, but up to now was never finalized or published. In this report we complete the documentation of that map to provide new insights into vegetation change over a period of more than 40 years, and a quantitative reference point for future studies on landscape-level vegetation development for the island.

The principal lower sections of the 21 km2 island of St. Eustatius possess a tropical savannah climate according to the Köppen (1931) classification system, and the documented flora of the island amounts to 505 species. Color aerial photographs (1: 8,000) taken in 1991 and field data from 1999 were used to produce the map. A total of 84 vegetation sample plots were analysed using a stratified random sampling design and TWINSPAN cluster analysis.

Four main and 16 sub-landscape types were distinguished based on geology, geomorphology and different mixes and expressions of the component vegetation types. The five principal landscape types are in descending order of importance: H1, H2, M4, M9 and C, and covered some 67 % of the seminatural habitat of the island. H1 and H2 are the Pisonia-Justicia hills and Pisonia-Bothriochloa hills and are limited to The Mountains area. Analysis of the sampling data resulted in the distinction of 13 (semi)natural vegetation types. The three principal vegetation types were, the Pisonia-Justicia type, Pisonia-Ayenia type and Bothriochloa-Bouteloua type which together accounted for 38 % of total (semi)natural vegetation cover. The following well-developed vegetation types of St. Eustatius represent primary climax communities: Types 1, 2, 3, 5 and 7, all found in and around the Quill in the southwestern part of the island. A comparison of the vegetation types in the present study with those of Stoffers (1956) showed that only one vegetation type closely resembles one in Stoffers’ study. Major changes have taken place in certain types of the natural vegetation of the island in the intervening five decades.

The majority of the central sections of the island around Oranjestad the so-named “Cultuurvlakte”, amounting to approximately 25 % of the surface of the island, have suffered intensive disturbance due to past agriculture, livestock husbandry and invasive species and were not mapped. Only a small remnant portion of the semi-natural lowlands vegetation (L1 and L2) was left in the coastal reaches of Billy’s Gut. Nevertheless, this area is heavily affected by grazing and the invasive vine Antigonon leptopus.

A comparison with the 1950s vegetation map by Stoffers shows that the rarest and most valuable elfin woodland vegetation of the rim of the Quill crater had been largely lost and that the areas he described as “Montane thickets” (Type 2) had declined and been degraded. We speculate that these losses may be most directly attributable to the impact of recent hurricanes and/or grazing by introduced livestock. On the lower slopes of the Quill, several areas mapped by Stoffers as farmland had been abandoned and have evidently regenerated into mixed deciduous and evergreen thorny woodlands.

The vegetation of the Mountains area showed some recovery since the 1950s. There were more evergreen bushes, and less Acacia and Leucaena than Stoffers described. The vegetation Stoffers described for the lowlands had more Acacia than we found but the invasive Antigonon has since dramatically increased as a ubiquitous and often dominant species. The former importance of Opuntia prickly pear cacti in disturbed vegetations has dramatically declined since the 1950s. We ascribe this to the likely effect of the invasive parasitic insect Cactoblastis cactorum. In the 1980s and 1990s many Opuntia cacti were seen affected by this insect (G. Lopes, pers. comm.).

Our field data show that all wilderness areas of St. Eustatius remained heavily affected by grazers. This reduces the resilience of natural vegetations and interferes with natural succession by imparting heavy losses to hardwood seedlings and saplings (see e.g. Melendez-Ackerman et al. 2008), by reducing plant biomass (which increases exposure to wind and sun), and by favoring hardy invasive plant species. In Curaçao, large scale reduction in densities of feral grazers in the Christoffelpark since 1993 has led to rapid recovery of several rare plant species and vegetation types. The problem of feral livestock remains severe. Therefore the number one priority for terrestrial conservation in St. Eustatius will be to reduce feral grazer densities and impacts in key wilderness areas.

Management Recommendations:

Parts of the natural areas of both The Mountains and the Quill are protected by law, but goats and other roaming livestock are omnipresent in all habitats and continue to have evident impacts on the vegetation. Aside from generally reducing the resilience of the vegetation to major disturbance, intensive impact in the herbaceous layers likely affects regeneration of rare hardwood species directly through selective predation and indirectly by overall desiccation and increased exposure to the elements. Goats have a broad diet in the region and species eaten include canopy, mid-canopy and understory species (Melendez-Ackerman et al. 2008). Vegetation degradation further also affects the competitive balance towards (unpalatable) invasive species such as Antigonon leptopus, Pedilanthus tithymaloides, and Leucaena leucocephala, which have expanded massively into natural habitat in the last 50 years. Not only is general vegetation degradation suggested as a problem to endangered breeding seabirds, but goats likely also directly trample nesting burrows of seabirds (Collier & Brown 2009).

Consequently, priorities for nature conservation are to:

• Reduce grazer densities in all areas,
• Protect the most sensitive vegetations using total grazer exclusion, and
• Experiment with methods to spur vegetation recovery, including erosion control, propagation of rare and endangered species and reforestation with indigenous species
• Establish permanent plots in areas with the most sensitive vegetations in order to better understand causal factors of short- and longer term changes. 

This report is part of the Wageningen University BO research program (BO-11-011.05-004) and has been financed by the Ministry of Economic Affairs, Agriculture and Innovation (EL&I) under project number 4308202004.

Abstract:

The aim of the present project–commissioned by the management of the Washington-Slagbaai Park (WSP)- was to set-up a more strategic management of the natural elements of this protected area.

The results are presented in three sections: I. Rare plant species; II. Exclosures and III. Monitoring. The survey of the rare plants resulted in the discovery of three plant species not previously known for Bonaire: Capparis linearis (a tree), Adiantum capillus-veneris (a fern) and a yet undetermined Thelypteris sp.( (a fern). Occurrences were also documented for rare species already known to occur in the WSP. The survey also led to the rediscovery of Capparis tenuisiliqua for the WSPand Bonaire. Brassavola nodosa is reported for the first time for the WSP.

The search for rare plants took place on a number of the higher hills in the WSP. The ‘Matadó di Pasku’ was the hill with the most rare plant species (15). Most of the higher hills in the WSP have a number of denuded areas or areas with scanty vegetation. This is the result of vegetation and soil degradation caused mainly by goat grazing. The negative impact of these animals is also reflected in the almost complete absence of seedlings or other stages of rejuvenation of the rare plants and the exclusive occurrence of the orchid Brassavola nodosa on rock boulders at inaccessible heights for goats.

Isolation of vegetation results in reduction of its dispersal capabilities. As a way to counteract this it is recommended to fence off small areas around the rare tree species identified during the survey. A number of indigenous plant species have been identified that should receive priority in a monitoring and recovery plan: Capparis tenuisiliqua, C. linearis, Schoepfia schreberi, Maytenus tetragona, Eugenia procera, Myrcia curassavica, Psidium sartorianum and Celtis iguanaea. A monitoring protocol is presented to aid in the collection of the data. It has also been recommended to start a propagation program for the orchid species B. nodosa and Schomburgkia humboldtii. The latter was reported in a botanical study in 1994 and must occur in small numbers but could not be relocated. While Sideroxylon obovatum, Guapira fragans and G. pacurero were considered rare in a botanical study done in the WSP in 1994 we did not consider these species rare because they occur quite frequently on the hills visited and are also found in other areas of the island. The results of the present study indicate that it would be valuable to have a botanical survey done of the higher hills of the WSP that could not be visited in the present study.

Three exclosures (9 x 9 m) and three adjacent control plots of the same size (accessible to goats, donkeys and pigs) have been established in the dominant Casearia-Prosopis vegetation type of the D3 landscape type of the WSP. Data collection took place in nine sub-plots of 3 x 3 for both the exclosures and adjacent control sites. The control site was the area of which the vegetation most resembled the vegetation inside the exclosure.

TL7 was the second landscape type in which exclosures and control sites were established. TL7 was chosen above the second most frequent landscape type (D2) of the WSP because its exclosures will provide insight into the development of limestone vegetations and effects of introduced animals (mammals) on them. Limestone vegetations are characterized by dominance of (semi-)evergreen plant species. The sample plots surveyed are characterized by a low number of plant species and high incidence of goat dung pellets.

It is recommended to repeat the data sampling of the exclosures and control sites in two years order to gain insight in the short-term changes in the different vegetation types. Longer-term changes will be seen over a number of years.

To gain a broader insight in natural vegetation development (which will also help to understand development in animal communities) it is necessary to establish several 50 x 50 m permanent plots in (at least) the two most dominant vegegation types in the WSP: Casearia-Prosopis type (D3) and Croton-Haematoxylon type (D2). Because the Slagbaai area will be the first part of the WSP where the goats will be removed, these plots should be placed in this part of the WSP. A data sheet to aid in the data collection (developed by ITC) is presented. A total understanding of the natural development of the vegetation of the whole WSP will be possible through the making of a detailed vegetation map (scale 1:10,000-1:25,000) and repeating it after 20 -30 yrs.

Only one bat species (Glossophaga elongata) is found in the two caves and a well in the WSP. A monthly monitoring program of especially the cave on Seru Grandi is needed in order to determine its significance for G. elongata and possibly other bat species occurring on Bonaire. The easily accessible small cave at Slagbaai should be fenced off to prevent unnecessary disturbance of the bats roosting there by visitors of the WSP.

The monitoring top priorities for bird species are: Buteo albicaudatus, Amazona barbadensis, Sterna hirundo, S. antillarum and Phoenicopterus ruber. Monitoring methods are presented for these species.

No data is available on the impact of exotic plant species in the WSP, but it must be low because invasives were not recorded in any of the sample plots from the park used for the production of the vegetation map of the island and Cryptostegia grandiflora was only seen on the Juwa. In order to be able to control the impact of these species (Cryptostegia grandiflora, Leucaena leucocephala, Azadirachta indica and Jasminum fluminense) they should be monitored. Deleterious exotic animals causing damage in the park at present include goats, donkeys, pigs, cats and dogs. These should be controlled and monitored also. It is therefore recommended to make it a duty of the WSP rangers to report on plant or animal exotic species seen during their patrols and fieldwork. A design for a simple monitoring protocol to record and monitor exotic species is presented. A quick assessment by a biologist of the level of presence of exotic plant species in the WSP will help form the basis of such a program for the exotic plant species and determine the necessary level of interventions by park management. At present there is a trapping program for goats in place using a number of fenced off areas in Slagbaai.

Among the group of remaining animal species three species have been indicated as indicator species for monitoring: Poecilia vandepolii (euryhaline fish), Gecarcinus ruricola (land crab) and Phoebis agarithe (butterfly).

Six habitat types have been distinguished in the WSP: Cave systems, salina habitat, freshwater habitat, vegetation types of Washikemba formation, vegetation types of limestone formations and beach landscape. Their characteristics, occurrences in the WSP, importance for the survival of native fauna and flora species and management and monitoring options are given for these habitat types. 

Abstract:

A preliminary inventory is given of key terrestrial nature values of Bonaire in order to determine their occurrence in relation to areas designated as “nature” and “open landscape”, according to the Spatial development plan of Bonaire. This was based on a literature study and supplemented by expert advice.

In 2010 a spatial development plan was written in order to determine the spatial policy and regulation for the future development of Bonaire. The island was partitioned into areas for different uses such as agriculture and recreation. Two specific designations are “nature” and “open landscape”. The occurrence of nature values within these areas remained unclear. This makes implementation of protective measures based on international treaties and island legislation problematic. An inventory of the occurrence of these values should help facilitate more effective implementation of these protective measures. In the present study key nature values are determined, both in terms of protected species and essential habitat (e.g. caves). 

From the literature study it became apparent that data on the occurrence of most of the priority species of flora and fauna, is limited and scattered, especially with respect to “open landscape” and “nature” outside parks. Therefore, only a preliminary inventory is provided showing the general distribution of nature values across the entire island, as linked to various habitat types. An exact distribution of the different nature values was not possible at this time, but extrapolation from areas of known occurrence into other areas of similar habitat type was used to show the occurrence of overlapping distributions of nature values within the designated areas of “nature” and “open landscape”. The number of overlapping distributions of nature values may contribute to setting conservation priorities.

From the results it can be concluded that the areas of “open landscape” and “nature” (outside the national parks) seem to harbour unique and critical nature values. These areas are not actively managed or protected as national parks. The “open landscape” of Bolivia possibly harbours a few rare plant species (unique), an important population of critical key columnar cacti and at least two columnar cactus-pollinating bat species. The “open landscape” of Washikemba/Bakuna harbours key mangrove species that only have another main location at Lac Bay (national park). The “nature” area of Terrace Landscape Middle Bonaire seems to harbour a concentration of unique (e.g. Tillandsia balbisiana) and rare plant species (e.g. Krugiodendron ferreum etc.) and four bat species. The same is the case for Lima (e.g. Sabal palm, Maytenus versluysii and three bat species) while in Southern Bonaire key mangrove species also still occur. Table 1 shows which nature values are found or expected to occur within each “open landscape” and “nature” (outside national parks) area.

It can be concluded that outside the current parks, the main regions that harbour a concentration of key nature values are Terrace Landscape Middle Bonaire/Sta. Barbara, Bolivia, Washikemba/Bakuna and Lima. Terrace Landscape Middle Bonaire is designated as “nature” area, while Washikemba/Bakuna and Bolivia are in part designated as “open landscape”. Lima has both “nature” and “open landscape” designations. Sta. Barbara is designated for other uses, but the present review shows that the occurrence of several significant nature values is likely within this area.

Additionally, based on the preliminary inventory, the combination of apparent concentrations of rare plants, occurrence of critical bat species and the high probability of corridor values show that the areas of Terrace Landscape Middle Bonaire/Sta. Barbara and Lima are important areas concerning conservation and further research. The areas of Bolivia and Washikemba/Bakuna follow closely.

To be able to implement the necessary protective measures within these areas, it is recommended that more extensive research through fieldwork is done, in order to obtain a complete inventory of the different nature values found on Bonaire, not only in the areas of “nature” and “open landscape” but also in areas with other designations. Additionally, it is recommended to assess the list of vulnerable and endangered species (‘Informatieblad beschermde dier- en plantensoorten Bonaire’) as certain species that may be of importance to Bonaire are not included.

When executing a complete and extensive inventory of Bonaire it would be of value to also determine the ecological conditions needed for the different species to survive. Based on the ecological conditions necessary for their life functions, it may be possible to pinpoint those areas of main ecological importance per species. A complete inventory of the nature values on the island can contribute to better management of nature values (e.g. determining the distribution of caves and the distribution, health status and diversity of keystone cacti species for better management of bat populations). It is also recommended to determine areas with high potential for the occurrence of rare or relict species and which areas harbour high corridor values.

Management Recommendations:

For future research it is recommended to execute a complete and extensive inventory of Bonaire, through fieldwork, in order to implement the necessary protective measures to ensure the conservation of these nature values. The present study shows that the areas of WNSP/Brasil, Terrace Landscape Middle Bonaire, Lima and Bolivia may be of priority as these areas seem to harbour a concentration of unique and critical plants.

Present studies shows that key nature values may occur in areas with a different designation than “nature” or “open landscape”. For future research it is recommended not to limit inventory research to the areas of “nature” and “open landscape”, but to include other areas with different designations.

In the present study the nature values chosen were based on the list of vulnerable and endangered species (Informatieblad beschermde dier- en plantensoorten Bonaire). During the study several species were added based on expert knowledge. The list used therefore seems to be limited. For future research it is recommended to assess if there are other nature values that are important to Bonaire that should be included on the list (e.g. Clusia sp, Ammodramus savannarum).

A complete inventory of the nature values on the island can contribute to the better management of nature values. A good example is the management of Bonaire’s bat population. In order to define the priority areas to maintain for the management of the different bats on Bonaire it is essential to obtain a detailed inventory of the different caves that these species use as habitat.

Additionally for the nectar-feeding bats it is crucial to map the occurrence of the different candle cacti on which they feed. The nectar-feeding bats are the critical pollinators of the three candle cacti (Petit, 2001). As already mentioned these cacti are key species on the island as they provide food for several species of animals during the dry season, when many other plant species are non-productive (Petit, 2001). Research on the distribution, health status and diversity of candle cacti on Bonaire is recommended in order to pinpoint priority areas for nectar- feeding bats. The cactus populations are threatened severely by feral livestock (goats, donkeys) which remove the bark of the mature trees, thereby threatening the food supply for frugivores and nectarivores. From our analysis open land areas of Bolivia would seem to possess large cactus populations of vital interest to conservation of endangered bird species on an island-wide scale.

When executing a complete and extensive inventory of Bonaire it would be of value to determine the ecological conditions and various habitats needed for the different species to survive. Based on the ecological conditions necessary for their life functions it may be possible to pinpoint those areas of principal ecological importance per species.

It is necessary to identify those areas with a high potential for the concentration of nature values rare species or relict vegetation species in order to secure the survival of these species and to be able to implement the necessary protective measurements. Such areas for instance are the open land and nature sections of Lima, Terrace Landscape Middle Bonaire (nature) and Bolivia (open). For future research it is recommended to determine those areas with high corridor values for the implementation of ecological corridors and buffer zones on Bonaire. 

A semi-detailed landscape-based vegetation map (scale 1:50,000) is presented for the southern Caribbean arid island of Bonaire (mean annual precipitation is 463mm). Color aerial photographs (1:8,000) taken in 1995 and 1996 were used to produce the map. A total of 302 vegetation sample plots were analyzed using a stratified random sampling design and twinspan cluster analysis.

A total of 18 vegetation types, and 32 (sub-)landscape types were distinguished. The three principal vegetation types, Casearia tremula-Prosopis juliflora type (Type 17), Croton flavens-Haematoxylon brasiletto type (Type 14) and Prosopis juliflora- Opuntia wentiana type (Type 16), account for 40% of total vegetation cover. The four principal landscape types also cover 40% of the island and are: D3 (Prosopis- Casearia Landscape), TH1(Haematoxylon-Croton Higher Terrace), D2 (Haematoxylon- Casearia Landscape) and TM7 (Acacia-Croton Middle Terrace). The vegetation on the volcanic Washikemba Formation is more uniform than that on the limestone forma- tions. Most of the vegetation types can be categorized as secondary. This is consid- ered mainly to be the result of the impact of introduced grazing mammals (principally goats and donkeys) and woodcutting in the past. Six vegetation types are considered of relatively high natural value. Three of these (Types 1, 9, and 10) are comparable to Stoffers’ less degraded communities. The other three have been selected based on cri- teria such as structural complexity, diversity and number and rarity of rare species.

A comparison with a vegetation map from the 1950’s shows that three types of areas can be distinguished: areas in which the vegetation has remained more or less the same, areas in which the vegetation shows improvement and areas that show broadscale de- terioration of the vegetation. The largest area that shows deterioration is the southern part of Bonaire. The northern part of the Washington-Slagbaai National Park is the largest area with improvement. The findings are discussed in relation to the Nature Management Plan for Bonaire and conservation recommendations are made. 

Abstract:

The Netherlands are signatories of the international Convention on Biological Diversity (CBD). This implies that the nation will protect biodiversity on its territory. This includes the protection of natural fauna and vegetation from negative impact caused by invasive alien species (see 2.1. for a definition). By 10-10-2010 the BES islands (Bonaire, St Eustatius and Saba) became ‘special municipalities’ of the Netherlands. They together form “Caribisch Nederland” (Caribbean Netherlands, Hulanda Karibe). Due to this stronger link to the Netherlands many responsibilities have moved from the Antillean government to the Netherlands. This includes important responsibilities with respect to the protection of nature.

The present study was financed by the Dutch Ministry of Economic Affairs, Agriculture and Innovation and included a literature study, a field trip and writing of the present document with main observations, conclusions and recommendations. A major part of the report consists of an alphabetical list of (known) invasives with their current status (4.1.1.). Apart from the three islands belonging to Caribisch Nederland, for completeness, some attention is given to Aruba, Curacao and St. Maarten as well (esp. in 4.1.1. and Appendix II).

Stages of invasion
In order to define the problem of invasive alien (non-native) species of plants more accurately it is relevant to recognise the following categories:

Exotic: Species that are not part of the natural indigenous vegetation are called exotics. Examples are introductions as ornamental or agricultural species. If contained within the confines of gardens and farms, these species are not considered problematic.

Established: Species that occur ‘in the wild’, i.e. outside the control of cultivation or husbandry and are able to reproduce themselves resulting in new individuals, we call established (present). Species can stay in this phase, the ‘lag phase’ (see 2.1), for quite some time. It is the stage in which the species adapts to its new environment using its genetic flexibility. At this stage complete eradication is still an option, because the number of individuals and locations is limited. This means that the costs can be relatively low, compared to eradication at a later stage.

Naturalised: If given enough time, species may start to adapt genetically to the new environment, by optimising its physiology and/or growth habit. As a result the species will start spreading more rapidly and effectively and becoming part of the natural flora. In most cases this is not considered a major problem; the plants will get their own function within the ecology of the island and will not replace indigenous species entirely. Moreover, the costs of complete eradication have become prohibitive at this stage, so only containment is an option.

Invasive: It is generally believed that about one in one thousand exotics becomes really problematic, e.g. with respect to environmental, ecological or economical impact (Williamson 1995). They start to grow out of control, massively invade natural habitats and reduce or eliminate native species. They have broken down the dispersal barrier and have become invasive. At this stage one can only try to achieve a stage of equilibrium, of mitigation, by intensive control measures. These are usually limited by financial resources, and can normally only be successful with commitment of the local society, e.g. shown by the enthusiastic support and hand labour of many volunteers.

Invasives of the Caribbean Netherlands
In this report 65 species of invasives are enumerated (4.1.1.) with their history and properties, based on a literature survey and completed with experience and findings of the authors. Four of the main problematic species are treated more extensively in 4.1.2. These are the Coral vine (Antigonon leptopus) which poses a great threat to nature, especially in St. Eustatius; the Rubber vine (Cryptostegia grandiflora) which is able to overgrow and smother shrubs and trees and is especially spreading on the Leeward Islands; the neem tree (Azadirachta indica) which is planted for shade and medicinal purposes, but is escaping on Bonaire; and ‘Donna grass’ (Bothriochloa pertusa) which is a very problematic species replacing the more palatable local grasses on the Windward Islands, most notably on St. Eustatius.

In a complementary list a further 80 species that need more investigation are mentioned (4.1.3.). This list is not complete but it enumerates species that are present on at least one of the islands. They need special attention because it is best to prevent them from entering at all or to eliminate the few plants or populations that have established themselves. Some species in this list are already present at some scale, like some of the arable weeds, but need careful monitoring to prevent them from entering nature.

A general problem are the free-roaming animals, cows, donkeys and especially goats (all non- native species) that are destroying nature in an uncontrolled way. Their presence has a detrimental effect on biodiversity, eating young seedlings and trees, and thereby preventing the natural regeneration and succession. Moreover, the bare soils that result are susceptible to water and wind erosion; material that is deposited in the surrounding seas.

Management recommendations:

Before an exotic has been introduced prevention is the most important action, i.e. keep the chance that exotic species may be introduced as low as possible. As soon as a first introduction has been realised and the exotic still occurs at low densities at few sites, eradication after first observation will be the most important action. Finally, if an exotic has already spread over different sites or even different habitats and has increased in densities, eradication might not be an achievable option anymore. Then containment and population management will be the most relevant actions to minimise the negative impact (mitigation). In general, prevention will generate the most cost-effective options to avoid problems due to invasive exotic plants (Davis 2009). The main observations are:

Prevention: Prevention plans need to be developed with regulations restricting the import of exotic species. This includes the development of ‘Black lists’ for the Leeward and Windward Islands respectively. Public awareness (customs and other officials, general public, landscapers, new inhabitants) must be raised and alternatives for imported exotics must be offered. Agricultural departments and customs offices on all islands are understaffed and not able to control the many routes through which exotics enter.

Eradication after first observation: Rapid first observation of an exotic plant after introduction into the wild is essential for the success of an eradication action. Therefore a ‘Watch list’ or ‘Grey List’ needs to be developed. Since the difference in climates, these watch lists will partly differ between islands and differ even more between the Leeward and Windward islands. Also knowledge about the natural flora and invasives must be increased through education, at schools as well as for professionals (rangers, customs personnel, agricultural department, etc.). Floras for the Windward Islands are outdated and not accessible.

Containment/population management: Management plans need to be developed for the control Antigonon, Cryptostegia and neem to be able to stop further spreading and to mitigate the impact on nature. Research on the life cycle of invasives and experiments for their control have to be carried out. The problem of roaming animals must be tackled. Small island communities are not able to do this without outside assistance. If chemical control is considered, special Dutch Caribbean regulations apply based on restricted import permissions for crop protection agents.