(French West Indies)boj_1 - CNCFlora

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