(French West Indies)boj_1 - CNCFlora
(French West Indies)boj_1 - CNCFlora
(French West Indies)boj_1 - CNCFlora
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216 M. J. M. CHRISTENHUSZ<br />
Figure 1. Map of the Lesser Antilles, showing the position of the Guadeloupe archipelago.<br />
allowing Guadeloupe to harbour a great diversity of<br />
vegetation types. Figure 3 shows that the fern diversity<br />
in Guadeloupe is most diverse at the mid elevations<br />
between 300 and 600 m. This mid-elevation<br />
effect has been shown in many mountainous areas. It<br />
is obvious in the Lesser Antilles, because the higher<br />
elevations are wet, but cool and often more disturbed<br />
by strong winds, whereas the lower elevations are<br />
often too dry. The optimal area for plants is thus<br />
found at mid elevations, where the climate is warm<br />
and humid and the forests are well developed.<br />
Guadeloupe is positioned at the margin of the Caribbean<br />
tectonic plate on the subduction zone with the<br />
Atlantic plate. It lies at the point where two island<br />
arcs are merging. The older (Eocene) arc stretches<br />
from Marie Galante and Grand Terre, northwestward<br />
to St Barthélemy and Sombrero Island,<br />
where the underlying volcanic base rock is covered by<br />
uplifted Pleistocene limestone. The second (younger)<br />
arc started taking shape during the Miocene (c. 5<br />
million years ago) and is still volcanically active. In<br />
the southern arc, south of Dominica, these island arcs<br />
have merged and have subsequently gone through<br />
two phases of volcanic orogenesis (Bouysse, <strong>West</strong>ercamp<br />
& Andreieff, 1990).<br />
The island of Basse Terre consists of seven main<br />
eruptive fields, each with a volcanic centre. The<br />
Grande Découverte–La Soufrière volcanic complex is<br />
the only centre to have been active in the last 10 000<br />
years. The last magmatic eruption occurred c. 560<br />
years ago and culminated in the formation of the<br />
current dome of La Soufrière. All historical hydrothermal<br />
activity and the explosive eruptions of 1690,<br />
1797–1798, 1812, 1836–1837, 1956 and 1976 have<br />
taken place from fractures and vents on this dome<br />
(Komorowski et al., 2004).<br />
Marie Galante, Petite Terre and Grand Terre are all<br />
covered by Pleistocene limestone. La Désirade is<br />
formed of Mesozoic and Tertiary rocks and is consequently<br />
the oldest island of the archipelago.<br />
Lazare et al. (1991) provided an overview of the<br />
vegetation types of Guadeloupe and he listed the<br />
© 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 161, 213–277