Biotropica

Phenological trajectories of Caribbean very dry tropical forests diverge under different geologic formations

Abstract
Tropical dry forests experience pronounced seasonal changes in precipitation mani- 
fested in varied plant phenologies. At landscape scales, geologic substrate—one of the 
least understood abiotic factors interacting with precipitation—may modulate phe- 
nological responses in these forests through a combination of mechanisms regulat- 
ing water and nutrient use. We leveraged a phenological dataset from the semiarid 
island of Curaçao to examine the extent to which plant phenology at multiple levels 
of biological organization diverge under different geologies. Monthly observations 
over a 30-month period of leaves, flowers, and fruits of 69 plant species of different 
life forms at three nearby sites differing in their underlaying geology were used to 
examine intra- and inter-annual plant responses at species, community, and system 
levels. The integration of leaf, flower, and fruit observations at intra-annual scales 
revealed diverse phenological strategies among species, broad associations with geo- 
logic substrate, and the extent of intra-specific variation as a function of geology. The 
community- and system-level analyses at inter-annual scales showed a reduction in 
mean leaf scores during the 30-month period, a weak and strong leafless period in 
1993 and 1994, respectively, and differences among geologic substrates. Finally, we 
observed significant and positive relationships between precipitation and the pheno- 
phase scores; the strength of the relationships varied with phenophase and geologic 
substrate. Results of this work emphasize the importance of geologic substrate, and 
more broadly speaking landscape heterogeneity, in modulating plant phenological re- 
sponses in tropical dry forests. Ultimately, this information will become important to 
understand and mitigate global climate change impacts.
Abstract in Spanish is available with online material.

Date
2022
Data type
Scientific article
Theme
Research and monitoring
Journal
Geographic location
Curacao

High spatial resolution mapping identifies habitat characteristics of the invasive vine Antigonon leptopus on St. Eustatius (Lesser Antilles)

On the Caribbean island of St. Eustatius, Coralita (Antigonon leptopus) is an aggressive invasive vine posing major biodiversity conservation concerns. The generation of distribution maps can address these conservation concerns by helping to elucidate the drivers of invasion. We test the use of support vector machines to map the distribution of Coralita on St. Eustatius at high spatial resolution and use this map to identify potential landscape and geomorphological factors associated with Coralita presence. This latter step was performed by comparing the actual distribution of Coralita patches to a random distribution of patches. To train the support vector machine algorithm, we used three vegetation indices and seven texture metrics derived from a 2014 WorldView-2 image. The resulting map shows that Coralita covered 3.18% of the island in 2014, corresponding to an area of 64 ha. The mapped distribution was highly accurate, with 93.2% overall accuracy (Coralita class producer's accuracy: 76.4%, user's accuracy: 86.2%). Using this classification map, we found that Coralita is not randomly distributed across the landscape, occurring significantly closer to roads and drainage channels, in areas with higher accumulated moisture, and on flatter slopes. Coralita was found more often than expected in grasslands, disturbed forest, and urban areas but was relatively rare in natural forest. These results highlight the ability of high spatial resolution data from sensors such as WorldView-2 to produce accurate invasive species, providing valuable information for predicting current and future spread risks and for early detection and removal plans.

 

Referenced in BioNews publication (BioNews Article). 

 

Related Resources:

1. Supplementary Infromation (Report)

2. Topographic Wetness Index raster layer for Statia developed for use in the Coralita mapping publication (Raster Layers). 

3. Raster layers: High spatial resolution mapping identifies habitat characteristics of the invasive vine Antigonon leptopus on St. Eustatius (Lesser Antilles) (Raster Layers).

Date
2021
Data type
Scientific article
Theme
Research and monitoring
Journal
Geographic location
St. Eustatius

High spatial resolution mapping identifies habitat characteristics of the invasive vine Antigonon leptopus on St. Eustatius (Lesser Antilles)

On the Caribbean island of St. Eustatius, Coralita (Antigonon leptopus) is an aggressive invasive vine posing major biodiversity conservation concerns. The generation of distribution maps can address these conservation concerns by helping to elucidate the drivers of invasion. We test the use of support vector machines to map the distribution of Coralita on St. Eustatius at high spatial resolution and use this map to identify potential landscape and geomorphological factors associated with Coralita presence. This latter step was performed by comparing the actual distribution of Coralita patches to a random distribution of patches. To train the support vector machine algorithm, we used three vegetation indices and seven texture metrics derived from a 2014 WorldView‐2 image. The resulting map shows that Coralita covered 3.18% of the island in 2014, corresponding to an area of 64 ha. The mapped distribution was highly accurate, with 93.2% overall accuracy (Coralita class producer's accuracy: 76.4%, user's accuracy: 86.2%). Using this classification map, we found that Coralita is not randomly distributed across the landscape, occurring significantly closer to roads and drainage channels, in areas with higher accumulated moisture, and on flatter slopes. Coralita was found more often than expected in grasslands, disturbed forest, and urban areas but was relatively rare in natural forest. These results highlight the ability of high spatial resolution data from sensors such as WorldView‐2 to produce accurate invasive species, providing valuable information for predicting current and future spread risks and for early detection and removal plans.

 

Date
2021
Data type
Scientific article
Theme
Research and monitoring
Document
Journal
Geographic location
St. Eustatius

The impact of hurricanes Irma and Maria on the forest ecosystems of Saba and St. Eustatius, northern Caribbean

In September 2017, Irma became the first recorded category 5 hurricane to hit the Caribbean Windward Islands. The second category 5, Maria, followed two weeks later. In November 2017, we assessed the structural impact of this disturbance on highly valued Caribbean forest ecosystems. We recorded the status of 935 tree stems on Saba and St. Eustatius in stands at different elevations. Tree damage was substantial on both islands, with 93 percent of stems being defoliated, 84 percent having lost primary and/or secondary branches and 36 percent having structural stem damage. Average tree mortality was 18 percent, with mortality being nearly twice as high on St. Eustatius than on Saba. Surprisingly, we found that neither individual stem size nor community size distributions mediated the forests’response to the hurricanes. Our results show that these hurricanes comprised a density-independent disturbance, which may become more common as the frequency of strong hurricanes is projected to increase.

Key words: defoliation; density-independent disturbance; forest community structure; island ecology; tree mortality; tree size distribution; tropical cyclones.

Date
2018
Data type
Scientific article
Theme
Research and monitoring
Document
Journal
Geographic location
Saba
St. Eustatius

A comparison of ungrazed and livestock-grazed rock vegetations in Curacao.

Five of the largest remaining patches of livestock-inaccessible rock vegetation of Curacao, Netherlands Antilles, were described and compared to rock vegetation which has experienced centuries of livestock grazing. Study rocks (maximum diameters: 20-47 m) were located at two sites differing in rock type and altitude. At the St. Christoffelberg site, study rocks were siliceous and at altitudes of 240-310 m while at the Tafelberg site the rocks were of limestone and at altitudes of 35-150 m. The main vascular species on livestock-inaccessible rocks at both sites was Tillandsia flexuosa. a bromeliad. At the St. Christoffelberg, Tillandsia was principally accompanied by the grass Paspalum secans, the orchid Brassavola nodosa and the herb Portulaca venezuelensis, while at the Tafelberg it was principally accompanied by the vine Serjania curassavica. On livestock-accessible rocks Tillandsia ground cover was reduced to insignificant levels and mature plants were virtually eliminated from the population. Grazed vegetations also showed reduced vascular cover and were principally dominated by the annual grass Aristida adscencionis (St. Christoffelberg site only), the prickly pear Opuntia wentiana and the shrubby tree Acacia tortuosa. None of these weedy species, all of which are widely distributed on the island, were of any significance in ungrazed rock vegetations. It is hypothesized that Tillandsia-dominated ground cover may have been a common feature of the rock vegetation of the island prior to the introduction of livestock.

Date
1993
Data type
Scientific article
Theme
Research and monitoring
Journal
Geographic location
Curacao

The pollinators of two species of columnar cacti on Curaco, Netherlands Antilles

Three species of columnar cacti (Stenocereus gri seus, Subpilocereus repandus, and Pilosocereus lan uginosus) are conspicuous elements of arid vegetation in northern Venezuela and several nearby islands induding Aruba, Bonaire, and Curacao. Stenocereus griseus and Subpilocereus repandus produce most of their flowers and fruits during the dry season (from January to September) on Curacao, Netherlands Antilles (Petit 1995). They provide food for several species of animals (especially bats and birds) during part of the dry season, when many other plant species are non-productive. The major pollinators of these self-incompatible cacti in Venezuela are the bats Leptonycteris curasoae and Glossophaga longirostris (Phyllostomidae) (Nassar 1991). An exhaustive census showed that bats of all species, induding L. curasoae and G. longirostris were threatened on Curagao (Petit 1995). Unidentified sphinx moths and two species of hummingbirds are other potential cactus pollinators on the island. In the Sonoran desert, all three groups are important pol linators of columnar cacti (T. Fleming, pers. comm.), and in most systems studied so far, bats are not exdusive pollinators of key plants. I determined the importance of moths, birds, and bats as pollinators of S. griseus and S. repandus pollination on Curacao because bats were expected to contribute significantly to cactus pollination, and evidence of their ecological importance was needed to prompt conservation action for bats and caves.

Date
1995
Data type
Scientific article
Theme
Research and monitoring
Tags
Journal
Geographic location
Curacao
Author

Nectar Production of Two Sympatric Species of Columnar Cacti

We examined the potential for exploitation competition by differential attractiveness in two sympatric species of columnar cacti on Curaçao, Netherlands Antilles. Stenocereus griseus and Subpiloccreus repandus have temporally overlapping flowering phenologies and share pollinators. We examined nectar volume, energy contents, and sugar ratios for the entire night and at two-hour intervals in both cactus species. Except for a burst in nectar volume and sugar concentration by Subpilocereus repandus during the first two hours of anthesis, nectar secretion patterns, energy contents, and sugar ratios (70% hexose) were similar for the two species. The standing crops of nectar in both species were kept very low by bat pollinators. We suggest that the potential for exploitation competition between Stenocereus griscus and Subpilocereus repandus is currently very low on Curapo.

Date
1997
Data type
Scientific article
Theme
Research and monitoring
Journal
Geographic location
Curacao