Flora of Dominica, Part 2 - Smithsonian Institution Libraries

Flora of Dominica,
Part 2: Dicotyledoneae
Dan H, Nicolson
As explained in “Acknowledgments,” I have summarized
information from Dr. Hodge’s preface to Part 1 of the Flora of
Dominica (1954). The summary covers environmental factors
(physiography, soils, climate), vegetation (seven plant communities,
including a key), and additions to his list of plant
collectors.
PHYSIOGRAPHY
Dominica, lying between the French islands of Guadeloupe
and Martinique, is about 28 miles (45 km) long and 15 (24 km)
miles wide (304 sq. miles or 1088 km?, centered at 15025’N,
61’20’W. It is very rugged with a central volcanic axis with
several subdivisions. In the north, standing alone, is an old
volcanic peak, Mome au Diable (2826 ft or 861 m), with loo0
ft (305 m) cliffs to the north. Farther south is the highest
mountain, Morne Diablotins (4700 ft or 1433 m) with
associated peaks. The peak was named for the diablotins,
Black-capped Petrels (Pterodroma hasitata), that used to nest
in cliffs near the summit (cf. Wingate, 1964), now only known
from Hispaniola. Morne Diablotins is relatively easy to climb
(from Syndicate Estate) but the associated mountains are
inaccessible. These taper to a central dissected plateau drained
to the west by the Layou and, to the east, by the Pegoua and
Castle Bruce rivers.
The central area is dominated by the steep Morne Trois
Pitons (4600 ft or 1402 m). To the south lies Morne Micouin
(or Macaque) with the associated lakes, Boeri and Freshwater.
A road goes from Roseau up the shoulder of Micotrin to
Freshwater Lake, becoming a trail that descends to Rosalie Bay
on the east coast. A trail leads from Laudat to the Valley of
Desolation with its famous Boiling Lake. Farther south is the
inaccessible Morne Watt (4075 ft or 1242 m), accessible Morne
Anglais (3683 ft or 1223 m, also called Couliaboune) and
Morne Plat Pays (2636 ft or 803 m). At the southern end are
high sea-cliffs.
Dan H . Nicolson, Department of Botany, National Museum of Natural
History, Smithsonian Institution, Washington, D.C. 20560.
Introduction
SOLS
A Red Earth clay soil covers much of the wet interior. It is
highly leached, acid, poorly aerated and water-logged (with
tree roots mainly confined to a dense surface mat). It is,
agriculturally, highly infertile.
The Yellow and Brown Earths are commonest and most
important for agriculture. The former is without stones and the
latter a stony clay, but both are young and fertile. They are
found on the slopes of Diablotins, the adjoining northem part of
the Layou Valley, and south of a line drawn from Rosalie to
Roseau.
The Shoal Soils of the dry west coast have poor agricultural
qualities.
In some areas, such as north of Trois Pitons, there is a light,
friable, stoneless clay underlaid by a cemented “hardpan” that
results in very poor drainage and poor agricultural characteristics.
CLIMATE
In general, Dominica has a drier season from midJanuary to
midJune and wetter season from midJune to mid-January. As
the northeast trade winds move over the central mountain axis,
rainfall increases, with the result that the eastern (Atlantic or
windward) side gets more rain than the western (Caribbean or
leeward) side, the latter being in the “rain shadow.”
The wetter season tends to have an autumnal “break”
(mid-September to mid-November), characterized by clear
days with heavy showers at night. This “break” tends to be a
windless, doldrum-type of weather.
Rains are nearly always heavy, often short with intermittent
sunshine. At times the rains are torrential and rivers rise to
amazing and destructive heights. Dominicans comment that
“the rivers have come down.”
Humcanes are “in season” from July to September; they
originate east of Dominica and usually miss the island or lack
full strength. Nonetheless, Hurricane David of 1979 was the
most destructive to ever hit Dominica. According to White
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