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Grisollea thomassetii

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Taxonomy [top]

Kingdom Phylum Class Order Family
PLANTAE TRACHEOPHYTA MAGNOLIOPSIDA CELASTRALES ICACINACEAE

Scientific Name: Grisollea thomassetii
Species Authority: Hemsl.
Taxonomic Notes: A distinct species in a genus with only two species, one on Madagascar and the Comoros, and one endemic to the Seychelles.

Assessment Information [top]

Red List Category & Criteria: Critically Endangered B1ab(iii) ver 3.1
Year Published: 2011
Date Assessed: 2007-02-01
Assessor(s): Ismail, S., Huber, M.J. & Mougal, J.
Reviewer(s): Gibbs, D. & Lutz, M.L.
Justification:
Grisollea thomassetii is only known from Mahé and Silhouette, Seychelles. The estimated extent of occurrence (EOO) and area of occupancy (AOO) are both at most 26 km² and the population is thought to be declining. On Silhouette, the species is well distributed and seems to reproduce well, forming the only healthy subpopulation left (between 500 to 1,000 individuals). On Mahé, G. thomassettii is however close to extinction and at the present stage only four sites with a few individuals (<50 individuals) are known. Furthermore, while a few saplings have been found on Mahé no seedlings have been recorded and it is assumed that the individuals cannot support a viable population. The species is therefore regarded as severely fragmented. The forests at intermediate altitudes, where this species is found, are heavily invaded by alien species causing a decline in the quality of the habitat. Despite the healthy subpopulation on Silhouette, it is therefore adequate to list this species as Critically Endangered.
History:
1998 Vulnerable (Oldfield et al. 1998)
1998 Vulnerable
1997 Vulnerable (Walter and Gillett 1998)

Geographic Range [top]

Range Description: This species is endemic to the Seychelles and is found only on Mahé and Silhouette. The EOO on Mahé is 5.7 km² and the total area of Silhouette is only 20 km² (National Statistics Bureau 2005). The total EOO (as well as the AOO) is therefore at maximum 26 km².
Countries:
Native:
Seychelles (Seychelles (main island group))
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: There are probably fewer than 1,000 mature individuals left and the population is thought to be declining. On Silhouette, the species is well distributed and seems to reproduce well, forming the only healthy subpopulation left (between 500 to 1,000 individuals) (J. Gerlach pers. comm. 2006). On Mahé, G. thomassetti is close to extinction (<50 individuals) and at the present stage only four localities with a few individuals are known. It can be assumed that these individuals cannot support a viable subpopulation as hardly any regeneration has been observed (RDLP workshop 2006). The only record of five saplings was made by Küffer in 2006, however there is no evidence for any seedlings. The species is regarded as severely fragmented.

The species was collected numerous times on Mahé and Silhouette (Horne 1871 or 1874, Thomasset, Diels 1899, Gardinier 1905 or 1908, Dupont 1930-40, Vesey-Fitzgerald 1938-39, Jeffrey 1961-62, Procter 1970-72, Bernardi 1973, in Robertson 1989). These historical records don’t give any indication of the abundance or the range of G. thomassetti.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Tree up to 15 m tall. Probably originally a component of the understory of forests at intermediate altitude, 300 to 500 m.
Systems: Terrestrial

Threats [top]

Major Threat(s): The major threats to this species are the invasion of alien species affecting the quality of its habitat, its restricted range and poor regeneration (especially on Mahé). As a member of the former intermediate forests, this species has suffered much since these forests have been almost entirely cut down. The forests at intermediate altitude are heavily invaded by introduced species, such as Cinnamomum verum, leading to a decline in the quality of its habitat.

Conservation Actions [top]

Conservation Actions: The species is present in the Morne Seychellois National Park.

Citation: Ismail, S., Huber, M.J. & Mougal, J. 2011. Grisollea thomassetii. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 30 October 2014.
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