CACTUS database unites decades of vegetation records from the Dutch Caribbean

Six islands in the Caribbean belong to the Kingdom of the Netherlands, and together they hold a remarkable slice of one of the world’s great biodiversity hotspots. Aruba, Bonaire and Curaçao lie just off the Venezuelan coast, while Saba, Sint Eustatius and Sint Maarten sit further north in the Lesser Antilles. Now, a newly described database called CACTUS has brought together decades of vegetation records from these islands into a single, continuously updated resource that researchers hope will underpin conservation policy across the Dutch Caribbean.

CACTUS, an acronym for Caribbean CACTUS Vegetation Database, is registered in the Global Index of Vegetation-Plot Databases under the identifier SA-00-006. It currently contains more than 4,000 vegetation plots, or relevés, spanning records made between 1954 and 2023. The database was described in a recent paper in the journal Vegetation Classification and Survey by a team led by John Janssen of Wageningen University & Research in the Netherlands.

The islands themselves are strikingly different from one another. Aruba, Bonaire and Curaçao are low-lying, dry islands where cacti and thorny scrub dominate the landscape. Saba and Sint Eustatius are volcanic, with Saba’s Mount Scenery rising to 870 metres and supporting elfin woodland near its cloud-wrapped summit. Sint Maarten combines dry hillsides with coastal wetlands. This diversity of environments within such a small territory is one reason the archipelago supports hundreds of plant species, including many found nowhere else on Earth.

Building the database meant tracking down records scattered across decades of reports, theses and unpublished surveys. Some plots were recorded by researchers in the 1950s and 1960s, others during environmental impact assessments in the 1990s, and many more during recent fieldwork. The team digitised each plot, standardised plant names against current taxonomic references, and linked every record to precise coordinates, so that the full history of vegetation sampling across the islands can now be queried in one place.

One immediate payoff is a clearer picture of how vegetation has changed. By comparing older plots with new surveys from the same locations, researchers can quantify shifts in species composition over half a century. Early analyses suggest that introduced grasses and shrubs have spread across many dry sites, while some woodlands have recovered where grazing pressure has eased. Such comparisons are difficult or impossible without archived plot data, which is precisely what makes databases like CACTUS valuable.

The database also feeds directly into conservation planning. Plot records underpin the distribution maps used to assess the conservation status of plant species for Red List evaluations, and they help identify areas where rare vegetation types persist. On Sint Eustatius, for example, plot data informed the management plan for the Quill volcano’s cloud forest, one of the most threatened habitat types in the region. Similar analyses are now being extended across the other islands.

CACTUS is part of a broader effort to make vegetation data findable and reusable. It joins a network of national and regional vegetation databases coordinated through the Global Index of Vegetation-Plot Databases, which catalogues thousands of plot databases worldwide. The Dutch Caribbean archive is also connected to VegBank and to the European Vegetation Archive infrastructure, allowing its records to be combined with datasets from neighbouring regions such as the Guianas and the wider Caribbean.

The team emphasises that the database is a living resource rather than a finished product. New surveys are added as fieldwork continues, and the taxonomic backbone is updated as plant names change. The authors hope that CACTUS will encourage further ecological research in the Dutch Caribbean, from studies of drought resilience in dry forests to monitoring the spread of invasive species, and that it will serve as a model for other small island territories seeking to consolidate their botanical heritage.

For an archipelago whose terrestrial ecosystems face pressure from development, free-roaming livestock and climate change, a comprehensive record of what grows where, and how that has changed since the 1950s, is a powerful tool. CACTUS turns scattered field notes into a permanent, searchable archive of island nature, one plot at a time.

The ecological setting of the six Dutch Caribbean islands helps explain why their plant life is so distinctive. Aruba, Bonaire and Curaçao lie in the rain-shade of the mountain chain along the northern coast of South America, which leaves them with a dry, semi-arid tropical climate despite their tropical latitude. The three islands further north experience a genuinely subtropical climate with far higher rainfall, and they lie in a hurricane belt that shapes vegetation dynamics every autumn. Rainfall on all six islands varies strongly with altitude, and it is this gradient, from arid coastal scrub to montane cloud forest, that allows so many different plant communities to coexist within a remarkably small total land area.

The geological underpinnings of the islands add further variety to this climatic mosaic. Soils across the archipelago derive mainly from three origins: volcanic substrates, limestone formations, and, on Curaçao, the Knip formation of deep-water siliceous sediments. Alluvial soils and recent marine deposits occur as well. Each substrate supports its own characteristic flora, so a limestone terrace, a volcanic slope and an alluvial wash within a few hundred metres of one another can host strikingly different plant assemblages. Plot-based recording, in which all species in a defined area are inventoried together with site conditions, is the only method that captures this fine-scale variation in a standardised, comparable way.

The wider Caribbean context underscores the stakes. The region is recognised as one of the world’s biodiversity hotspots, harbouring roughly 11,000 native plant species, of which about 72 per cent are endemic, meaning they occur nowhere else. Yet terrestrial ecosystems across the Caribbean remain poorly documented compared with the region’s celebrated coral reefs, and much of the existing knowledge is buried in internal reports and student theses that are effectively invisible to science. Funding and institutional attention have historically flowed toward marine conservation, leaving large data gaps on land. CACTUS was conceived specifically to close one of those gaps, and it grew out of a partnership between Wageningen University & Research in the Netherlands and Carmabi, the long-standing marine and terrestrial research institute on Curaçao.

The historical depth of the archive deserves emphasis. The oldest records date from 1952, when the first extensive vegetation survey of the islands was carried out, with results published a few years later. Substantial bodies of plots from the 1980s and 1990s entered the database through student projects and island-wide inventories, many of which had only ever been summarised in synoptic tables rather than preserved as full plot records. Digitising these older sources rescued primary data that would otherwise have remained locked in printed tables or ageing reports, and it now allows modern ecologists to revisit sites sampled across seven decades.

Resurveying historical plots is among the most powerful applications of such an archive. When the same locations are recorded again with comparable methods, differences between the old and new inventories reveal how vegetation has responded to changes in grazing, development, climate and management. Such studies have already been carried out in Christoffel National Park on Curaçao, on the island of Saba and in parts of Aruba, with resurveys of Sint Eustatius and Bonaire scheduled for 2023 and 2024. Because vegetation change is often slow and gradual, only long-term baselines of this kind can distinguish genuine directional trends from short-term fluctuation, and only archived plot data make the comparisons possible.

The taxonomic backbone of the database is itself a significant contribution. Vascular plant names across the six islands have been harmonised using dedicated floras and species lists for the Leeward and Windward groups, complete with synonyms, so that records made under older nomenclature can be aggregated correctly. The species list also carries limited trait information, including growth form, geographical distribution and whether a species is native or introduced. Plans are under way to align all names with World Flora Online, which will make the database interoperable with global plant datasets. Several species in the list are endemic to one or a few of the Dutch islands, including the endemic palm Sabal antillensis, which grows on scree slopes on Curaçao and features among the vegetation types documented in the archive.

The range of vegetation captured extends well beyond the dry scrub that most visitors associate with these islands. Zonal communities in the database span tropical rainforest and cloud forest on the higher volcanic peaks, dry tropical forest and woodland, xeromorphic woodland and cactus scrub, secondary shrubland, grassland and pioneer communities. Azonal types include mangroves, salt marshes, dunes, alluvial forests, wetlands, rock slopes and even seagrass beds. This breadth means the database can support analyses across nearly the full spectrum of terrestrial and coastal habitats in the archipelago.

Beyond vegetation science, the plot records feed a parallel plant species distribution database holding more than 50,000 unique observations, compiled by combining relevé data with herbarium specimens, photographs, literature and other sources. These distribution maps, which are updated whenever new data arrive, provide the geographic evidence base for Red List assessments of individual species. The same analyses can flag priority areas for conservation or inform environmental impact assessments, as happened in the nature-inclusive development vision for Bonaire, where priority areas were selected directly from an analysis of CACTUS data.

The initiative also reflects a broader movement in conservation science: the principle that nature policy and management should rest on evidence and data rather than intuition alone. By registering the database in a global index, maintaining a transparent taxonomic standard, and making species distribution maps publicly available, the team behind CACTUS has positioned a small island archipelago’s botanical heritage within international research infrastructure, ensuring that records gathered since the 1950s remain usable for generations of scientists and policymakers to come.

Subject of Research: A vegetation plot database for the Dutch Caribbean islands

Article Title: CACTUS – Vegetation database of the Dutch Caribbean Islands

Article References: Janssen, J., Houtepen, E., van Proosdij, A., & Hennekens, S. (2023). CACTUS – Vegetation database of the Dutch Caribbean Islands. Vegetation Classification and Survey, 4, 69-74. https://doi.org/10.3897/vcs.101114

Image Credits: AI Generated

DOI: 10.3897/VCS.101114

Keywords: CACTUS database, Dutch Caribbean, vegetation plots, biodiversity, conservation, Caribbean islands, plant ecology, Aruba, Bonaire, Curaçao, Saba, Sint Eustatius