vegetation

Dutch below

Two researchers from Wageningen University and Research surveyed the steep inner slopes of the Quill Volcano. The field work is part of a long running study of the flora and vegetation of the Dutch Caribbean islands. The steepness of these slopes and presence of loose rocks makes the inner slopes argely inaccessible. Consequently, little is known on the species that live there. By using remote techniques, the researchers tried to identify the plant species growing on the slopes and describe the vegetation.  John Janssen and André van Proosdij worked in close cooperation with STENAPA during this and previous visits to Statia.

Studying the flora and vegetation

Vegetation on the South-facing, sunny slope showing yellow blossom (Tecoma stans), monkey tail (Anthurium cordatum), eyelash orchid (Epidendrum ciliare), columnar cactus (Pilosocereus royenii), and tillandsia’s.

The team was able to identify most species found on the slopes. Not surprisingly, the slope vegetation clearly differs from any other vegetation type on the island. The sun-facing slopes harbor a sparse vegetation with yellow blossom (Tecoma stans), Monkey tail (Anthurium cordatum), Eyelash orchid (Epidendrum ciliare), Columnar cactus (Pilosocereus royenii), White cedar (Tabebuia heterophylla), Pudding white (Cissus verticillata), and Tillandsia’s. The North-facing slopes are more densely covered, due to the shade and lower drought-stress and show large clumps of Monkey tail (Anthurium cordatum), Clapper (Pitcairnia angustifolia), Wild balsam tree (Clusia major), Strangler figs (Ficuscitrifolia), and several species of ferns. Particularly the large numbers of orchids and ferns are important, as on rocks accessible to goats these are eaten.

Spectacular discovery

West Indian Tree Fern Cyathea arborea rediscovered after 138 years on the steep inner slope of the Quill.

By far the most spectacular discovery were five individuals of West Indian Tree Fern (Cyathea arborea). Tree ferns originate from the Carboniferous era, a geological period dating back 360-300 million years ago. This species was first recorded for Statia in 1885 but was never seen again. There were found growing on the lower part of steep, north-facing slopes, where the microclimate is cool and moist.  For 138 years, this ancient plant species survived, in places truly inaccessible for humans and not visible from the main viewpoints. The presence of these rare tree ferns illustrates the high biodiversity in the Quill National Park and the importance of safeguarding the natural vegetation.

More to be discovered

Janssen and Van Proosdij state, “This discovery points out that on these most inaccessible steep slopes and the crater rim, more rare and critically endangered species are yet to be discovered.” STENAPA and the WUR researchers intend to continue the exploration of these areas.

Twee onderzoekers van Wageningen University and Research hebben de steile binnenwanden van de Quill vulkaan op Sint Eustatius onderzocht. Het veldwerk is onderdeel van een langlopend onderzoek naar de flora en vegetatie van de Nederlands Caribische eilanden. De steilheid van de hellingen en de losliggende rotsblokken maken deze hellingen ontoegankelijk voor mensen. Als gevolg daarvan is er weinig bekend over de soorten die op deze hellingen leven. Door gebruik te maken van remote technieken probeerden de onderzoekers de planten te identificeren die op de hellingen groeien en de vegetatie te beschrijven. John Janssen en André van Proosdij werkten nauw samen met STENAPA tijdens dit en eerder veldonderzoek op Statia.

Het team kon de meeste van de aangetroffen plantensoorten identificeren. Zoals verwacht, is de vegetatie duidelijk anders dan elke andere vegetatie op het eiland. De op de zon gerichte hellingen herbergen een ijle vegetatie met o.a. Tecoma stans, Anthurium cordatum, de orchidee Epidendrum ciliare, de zuilcactus Pilosocereus royenii, Tabebuia heterophylla, Cissus verticillate en Tillandsia’s. De naar het noorden gerichte hellingen zijn dichter begroeid, als gevolg van de schaduw en lagere droogte-stress. Hier groeien grote groepen Anthurium cordatum, Pitcairnia angustifolia, Clusia major, de vijg Ficus citrifolia en meerdere soorten varens. Met name de grote aantallen orchideeën en varens zijn belangrijk, aangezien deze op andere rotsachtige plaatsen die wel voor geiten toegankelijk zijn, worden opgegeten.

West-Indische Boomvaren Cyathea arborea na 138 jaar herontdekt op de steile binnenhelling van de Quill. Credit: John Janssen.

De meest opzienbarende vondst is die van vijf exemplaren van de West-Indische boomvaren (Cyathea arborea). Boomvarens ontstonden in het Carboon, een geologisch tijdperk 360-300 miljoen jaar geleden. De aanwezigheid van deze soort is voor het eerst op Statia gedocumenteerd in 1885, maar is sindsdien nooit meer waargenomen. De vijf aangetroffen exemplaren groeien op het lagere deel van de noord-georiënteerde helling, waar het microklimaat koel en vochtig is. Gedurende 138 jaar kon deze soort voortbestaan op plekken die niet voor mensen toegankelijk zijn en die niet zichtbaar zijn vanaf de uitzichtpunten op de wandelpaden. De aanwezigheid van deze zeldzame boomvarens illustreert de hoge biodiversiteit van het Quill nationaal park en onderstreept het belang van bescherming van de natuurlijke vegetatie.

Janssen en Van Proosdij spreken zich uit: “De vondst van deze boomvarens wijst erop dat op deze uiterst steile hellingen en op de kraterrand nog meer zeldzame en ernstig bedreigde soorten voorkomen die nog niet ontdekt zijn.” STENAPA en de WUR zetten het onderzoek naar deze gebieden graag voort.

Published in BioNews 71

Abstract
Mangroves are important intertidal forests that exist in tropical and subtropical areas around
the world. They are important coastal protectors, providing coastal stabilization and wave
mitigation. Besides their protective ability, they fulfill a number of ecosystem services like
nursery grounds for juvenile fish, carbon sequestration and pollutant filtering. However,
mangroves have been under heavy threat in many countries due to anthropogenic pressure,
causing major degradation rates. In Lac bay, Bonaire, a big lagoon consisting of mangroves
and seagrass for example, high sedimentation due to erosion has caused channels to close,
creating hypersaline conditions in ponds together with high temperatures. The forest around
Lac bay therefore experienced high mortality rates and a strong decline in the systems’
health. Another bay, Lagun, showed similar degradation in the back pond, but due to lack of
documentation the actual cause is still uncertain. It is important to find out whether siltation,
hypersalinity and high temperatures are also an issue at Lagun in order to create a
successful restoration plan.

Vegetation, soil composition, conductivity and temperature were analyzed for several plots at
different location types around Lagun, including the degraded part in the pond. Results
showed that the silt layer in the pond was significantly higher than the other location types,
which indicates root burial caused by high sedimentation rates. Conductivity (as a measure
for salinity) and temperature were, contrary to the hypothesis, not higher in the pond
compared to other locations, and showed no significant relationship to mangrove abundance.
This could be explained by fresh water input due to heavy rainfall during the rainy season
that had just ended. For now, restoration measures should focus on mitigating external
pressures through habitat regeneration. Sediment trapping in and around watersheds and
runoff areas connected to Lagun could decrease the sedimentation rate and prevent burial
and floor elevation. Channel connection to Lagun could increase water circulation and might
help to prevent a larger part of the pond from drying out during the dry season. Active
planting can be combined with habitat restoration measures to increase survivability of
mangrove seedlings. Besides restoration efforts, more research needs to be done on the
existing pressures at Lagun, including Sargassum and trash inflow from the ocean, erosion
rates, pond water and soil quality and the effect of the nearby landfill on mangroves.
Documentation and monitoring of Lagun should be continued in order to obtain more
information about the processes at hand. With sea levels rising due to climate change, it is
crucial for Bonaire to have stable coastlines that can mitigate effects of storm surges, in
which mangrove forests play an important role.

Abstract The vegetation database CACTUS (registered in GIVD under SA-00-004) aims to bring together all plot-based relevés from the Dutch Caribbean Islands that are available from literature, unpublished resources, and recent field surveys. The database currently contains 2,701 vegetation descriptions. The database is used for vegetation classification, to investigate vegetation change over time, to assist in the planning of vegetation surveys, as a source for plant species distribution maps, and to inform nature conservation and policy.

https://www.fs.usda.gov/rds/archive/catalog/RDS-2022-0047

Abstract:

This data publication contains six raster datasets detailing the land cover and forest structure of several Caribbean islands. These include the islands of St. Kitts, Nevis, St. Eustatius, Grenada and Barbados. Each dataset represents land-cover and woody vegetation formations and is provided as an ERDAS IMAGINE georeferenced raster file and as a GeoTIFF raster file. Spatial land cover datasets for Barbados were created using Landsat ETM+ imagery from 2001 and 2002. Grenada datasets were created using Landsat ETM+ imagery from 2000 and 2001 and Landsat 5 TM imagery from 1986. Lastly, spatial land cover datasets for St. Kitts, Nevis, and St. Eustatius were created using Landsat ETM+ imagery dated between 1999 and 2003.

 

Keywords:

land cover; land use; forest formation; forest type; forest conservation; biota; environment; imageryBaseMapsEarthCover; planningCadastre; Ecology, Ecosystems, & Environment; Landscape ecology; Forest Products; Bioenergy and biomass; Inventory, Monitoring, & Analysis; Resource inventory; Natural Resource Management & Use; Landscape management; Timber; Wilderness; St. Kitts; Nevis; St. Eustatius; Grenada; Ronde Island; Barbados; Caribbean; Lesser Antilles; Netherland Antilles

The distribution is presented in 1 km-grids, based on vegetation relevés and digitized data from herbarium specimen, photos, literature and field surveys. Releves date back to 1880.

Commissioned by Sint Maarten’s Ministry of Public Housing, Spatial Planning, Environment and Infrastructure (VROMI), a color vegetation map produced by CARMABI and Wageningen University & Research shows a 25% decrease in overall vegetation cover of the Dutch side of the island since 1956.  Results show that this loss can be attributed to massive urbanization and touristic development, overgrazing by introduced mammals (goats), the impact of hurricanes and the negative effect of invasive plant species. By investigating and mapping the vegetation of the island, spatial planning strategies can work to protect and connect the remaining sensitive landscape ecological units, to prevent further loss of biodiversity and vital natural resources.

Usefulness of vegetation maps

Credit: Marjolijn Lopes Cardozo: SHAPE/DCNA

Vegetation maps are a useful tool in understanding the status of the biodiversity and species make-up of a particular area (e.g. of an island). These maps are used by a wide variety of actors, -from scientists to policy makers- and are key to spatial planning and designing nature management and conservation strategies. This gains extra relevance based on the fact that St. Maarten is a biodiversity hotspot in the Caribbean area: the island is inhabited by over 100 species which can only be found within the Lesser Antilles region and 12 species which can only be found on St. Maarten.  Furthermore, the vegetation types that are associated with the hilly landscape (the dominant landscape of St. Maarten) belong to the most threatened ecosystems in Latin America and worldwide.

A well-developed natural vegetation plays a critical role in securing balanced and healthy ecosystems. Areas with such a vegetation influence soil properties, prevent erosion, aid in water retention and provide important buffers between land and sea (preventing damage to coral reefs by sedimentation).  Not to mention the importance they play in providing food and shelter for a wide variety of the island’s native animal populations.

Changes in the islands’ natural vegetation since 1956

Credit: Christian König: SHAPE/DCNA

The results of an island-wide field study done at the end of 1999 shows that in comparison to a vegetation map published in 1956, a 25% decline in vegetation cover has taken place. In addition, five different vegetation types -found in coastal areas- have disappeared beyond recognition over those 40 plus years.  The interconnectedness of ecosystems on islands make them vulnerable to the impact of habitat loss and fragmentation as well as the negative impact of grazing by introduced mammal grazers and invasive plant species. Of course, we must not forget the detrimental effects of hurricanes and global warming.

Over time, habitat loss and fragmentation on St. Maarten have been caused by agriculture, grazing by introduced mammals and since the 1960s by an explosive growth in tourism. Particularly since 1980 tourism has skyrocketed on the island. Some vegetation units described in 1956 have also disappeared due to actual vegetation regeneration and succession to a more diverse state following the decline in agriculture and livestock grazing.

Although there has been some regeneration, the overall process witnessed for St. Maarten is that of loss of natural and semi-natural vegetated areas in all parts of the island. The largest disappearance took place in the western parts of the island that in 1956 were characterized by the presence of two evergreen vegetation types. In the Low Lands area, a climax evergreen vegetation type covering a large part of the area in 1956 has disappeared almost totally except for a very small area still present but seriously threatened. Large areas of a vegetation type with a deciduous character to the west of the eastern hill range have been lost. One could observe that the general trend shows that the hills are regenerating while the low and coastal areas are degrading at a faster rate, resulting in a net vegetation loss. This trend demonstrates the economic shift from mainly agricultural practices towards an economy heavily reliant on tourism.

Towards a more sustainable future for St. Maarten

Vegetation maps similar to the one produced in the present report have been completed by Carmabi for other Dutch Caribbean islands as well.  This includes maps of Curaçao (1997), Bonaire (2005), St. Eustatius (2014) and Saba (2016).  Since the 1980’s land-use planning has become a hot topic, and understanding the current status of each island’s terrestrial areas is critical in both sustainable land development as well as implementing conservation and restoration strategies moving forward. The report ends with five recommendations to works towards a more effective terrestrial nature management on the island: establish a protected areas network, control of roaming livestock, protection of endangered plant species, an invasive species action plan and long-term vegetation monitoring. Findings of this report point to the importance of protecting and connecting rare and individual landscape units, such as those found in the Low Lands and at the remaining naturally vegetated beaches. It is also clear that the landscape ecological units that are characteristic of the high hills have a high conservation value that call for protection.

For more information, you can read the full report here

https://www.dcbd.nl/sites/default/files/documents/landscape_ecological_v...

Article published in BioNews 46

An update to a 40-year-old Sabal palm survey for the islands of Bonaire and Curaçao highlighted the striking differences between the two islands. Through active park management, Curaçao has seen over more than a three-fold increase in adult Sabal palms, whereas an unmanaged palm population on Bonaire has seen a decrease of nearly 20% of adult palms. Actively protecting these valued endemic palms may be the only way to ensure their future.

The Sabal palm, or Kabana as it’s known locally, is the only native species of palm tree found on the islands of Bonaire and Curaçao. In fact, the true identity of this palm has been heavily debated, with its classification changing throughout the years until it was finally recognized in two scientific publications as two endemic species Sabal antillensis on Curaçao, in 2017, and on Bonaire Sabal lougheediana, in 2019.

On both islands the Sabal palm population is found in very limited distribution areas. On Curaçao, its range is limited to the highest hills in the southwestern part of the Christoffelpark and its direct surroundings there. On Bonaire, this palm is only found within the Lima area, the very low limestone terrace located west of Lac Bay and north of the salt pans.

Photo credit: © John de Freitas

In 1979, researcher J.E. Winkelman first surveyed  the number of palms on both islands, which she found to be 1,062 specimens in total. Of these, only 354 were mature palms, and only 31 of these could be found on Bonaire. In this initial study, Winkelman also noted that the largest threat to these remaining palms was most likely free roaming animals, such as goats and donkeys, who could eat and trample seedlings. Since this initial assessment, no follow-up surveys have been conducted, creating a significant knowledge gap concerning the current status of these iconic palms.

Luckily, a new study worked to close this gap. Researchers documented current populations on both islands and compared these results to the initial 1979 survey. The goal was to not only provide an updated count, but also note if any change to their range have occurred, providing important insight into factors that will contribute to designing an effective conservation strategy.

The Study

In 2018, surveys were conducted by counting the number of palms on each island. Given the small geographical areas and uniqueness of the terrain, it was generally easy to find and spot these palms. By using similar techniques and survey sites, a direct comparison between the 1979 and 2018 studies could be completed to help evaluate the local populations as decreasing, stable or increasing.

Interestingly, populations on these two islands have had very different developments over time. There has been  a 318% increase of adult palms on Curaçao, whereas Bonaire has seen a decrease of approx. 20%. In addition to population changes, there was also fairly significant shifts in their range as well. On Curaçao, the overall geographic range of these palms increased, from less than 5 km2  in 1979 to 8 km2  in 2018. Again, Bonaire saw a very different trend, with the geographic range shrinking from 5 km2 to less than 1 km2.

Other results

For both islands, there were a relatively large number of seedlings seen through their geographical range. On Curaçao, this could have been the result of the increase in  adults. On Bonaire, it is more likely attributed to the time of year the surveys were conducted. The 2018 survey was conducted right after the wet season, which could account for the increase in the number of seedlings due to the fact that fresh seeds germinate quite easily.

Changes in overall numbers of palms can be attributed to a wide range of factors. Christoffelpark has actively managed their goat and donkey populations since the mid-1980s. This decrease in free roaming grazers may have given these palms a higher probability of survival. These grazers have been known to feed on and trample seedlings, along with reducing vegetation and soil cover, further threatening the ability of seedlings to successfully grow. The increase in Curaçao’s range could have been due to the successful dispersal of seeds by local animal populations, as there are various species of birds, deer, rodents, and iguanas inhabiting this area and are known to feed on these seeds.

Recommendations

The findings of this study have led the researchers to provide four key recommendations for designing a successful conservation strategy for these palms. First, they recommend actively managing feral herbivores within the palm’s habitat. On Bonaire, this could be the construction of a 3.5 km long fence which runs along the perimeter of the Lima area in order to enclose the whole Sabal palm population in the Lima area.

Second, they recommend implementing a more rigorous monitoring plan to help track the health and recruitment of these palms to provide key indicators of change in future populations. Third, it has been recommended that Bonaire actively cultivates these palms in other areas of Bonaire, to improve overall population numbers. Lastly, the successful management program of the Christoffelpark should be continued, as this study shows the dramatic impact significantly reducing the number of feral grazers can have.

Future of the iconic Sabal palm

The free roaming animals of Bonaire are often part of the iconic charm of the island. A successful future of the island’s endemic species, both plant and animal, must include a balance to allow each a chance to thrive based on nature’s ecological capability. This study demonstrates how actively managing these feral animals can drastically improve the flora populations of the island. Understanding the impact each species has on the ecosystem will help nature management organizations design and implement environmental management plans to ensure a healthy future for the island.

For more information

Freitas, J. de et al. (2019). Sabalpalm (Sabal antillensis) Recovery Over 40 Years: Lessons for Successful Palm Conservation. PALMS Vol. 63(2): 57-68.

Article published in BioNews 41

Island ecosystems are vulnerable to the influence of goats which are invasive to most islands and are considered the most damaging for island vegetation. High grazing pressure has also been a challenge for the island of Curaçao which decided to remove goats from the Christoffelpark between the late 1980s and early 1990s. After almost 30 years of grazer absence and with no vegetation mapping campaigns in the park, vegetation maps created prior to the exclusion of goats were not representative anymore. Therefore, the vegetation was re-mapped in 2018/19 to analyse changes in vegetation. Results showed evidence of vegetation regrowth in the Christoffelpark. However, the rate of vegetation regrowth and when it first occurred in time was still unknown. This thesis aimed to gain understanding in the 30 years without vegetation data from the field and to compare effects on vegetation trends in areas where grazers are still present (Shete Boka National Park) and where grazers have been removed (Christoffelpark’s coast). Vegetation succession was found in the Christoffelpark’s coast with a decrease in coverage of grasses and herbs and an increase in coverage of trees and large shrubs. Contrary results were found in the Shete Boka park where grazing pressure is still high. Landsat satellite imagery were used time series analysis between 2000 and 2020 to get insight in vegetation trends. Based on a pixel-wise Mann-Kendall trend test, no perfect monotonous trends were found and only 10 vegetation communities showed a significant trend with 7 located in the Christoffelpark’s coast. Change detection analysis was performed to detect shifts in vegetation trends. The LandTrendr algorithm and the bfast01 algorithm showed contrary results. Considering the TWINSPAN vegetation communities, the LandTrendr algorithm detected an average of 18 breakpoints in the Christoffelpark’s coast and 13 breakpoints in the Shete Boka National Park whereas the bfast01 algorithm detected two breakpoints in the Shete Boka park and none in the Christoffelpark’s coast. The contrary results make it difficult to explain the drivers behind the detected breakpoints, especially as the period shortly after the exclusion of goats has not been part of the analysis. Further research is recommended to assess vegetation dynamics prior to 2000 as shifts in vegetation growth may have occurred more closely to the exclusion of goats in the Christoffelpark.

[MSc thesis report]

This vegetation survey is the outcome of an investigation of the islands of the Netherlands Antilles carried out under the auspices of the Foundation for Scientific Research in Surinam and the Netherlands Antilles. The data on which the present study is based were obtained during a trip which lasted from September 1952 until October 1953. During this trip the following islands were visited: Curaςao, Bonaire, Aruba, St. Martin, Saba, and St. Eustatius. A short visit was also paid to the island of St. Kitts (B.W.I.).

Botanisch onderzoek van een gebied heeft als regel in drie fasen plaats:

1. floristisch onderzoek, teneinde een overzicht te krijgen van de plantensoorten, variëteiten en andere systematische eenheden die in het betreffende gebied gevonden worden;
2. vegetatie-onderzoek, om een overzicht te krijgen van de samenstelling van het plantendek;
3. oecologisch onderzoek, om tot een causale verklaring van die vegetatie te komen.

Deze drie fasen zijn in de Nederlandse Antillen ook te onderscheiden en zullen daarom achtereenvolgens besproken worden

Uitgewerkte lezing gehouden op 27 november 1965, ter gelegenheid van het 20-jarig bestaan van de 'Natuurwetenschappelijke Studiekring voor Suriname en de Nederlandse Antillen.