500 
sing may alter in all cases the different shades 
of grey or colour and become a real source of dif 
ficulty . 
4 GEOMORPHOLOGY AND WETLAND LANDSCAPES 
American authors recognize five major landscapes 
for Florida mangroves : overwash, basin, fringe, 
riverine, dwarf based on stand morphology, topography 
and inundation conditions. This system can be deve 
loped adding floristic and soil information, espe 
cially salinity. Five samples of airphotos are com 
mented along these lines. The largest wetlands occur 
around Grand Cui de Sac (G.C.S.). The most striking 
geomorphological features are : 
- A weak development of hydrography on the eastern 
side of G.C.S. and the existence of man-built canals. 
Because of moderate rainfall and karst relief of 
Grande Terre, silting is low and shore lines are 
static. 
- On the western side of G.C.S. the large river 
Grande Rivière à Goyaves (G.R.G.) brings some silt 
and builds a fluctuating (small) delta. Erosion 
by currents is visible on the northern side of 
Lamentin Bay whereas silt is deflected on the northern 
coast of the G.R.G. complex facing the open sea. 
This complex is composed of four units : two clay 
tables slightly above sea level bearing Avicennia, 
a lower Pterocarpus unit and an Acrostichum unit 
clearly seen on photos. The mouth of G.R.G. is mainly 
Rhizophora. 
- Impeded drainage north of Ravine Gachet because 
of a low sand dune behind which a basin mangrove 
has developed (East of G.C.S.). Southwards down 
to Rivière Salée seawater has free access to a fringe 
mangrove. Coral reefs underlined by islands (Fajou, 
Macou) emphasize the opposition between these two 
shorelines and the load of the sea-currents (sand 
or mud). 
- A more or less buried karstic relief quite visible 
on photos is covered with deciduous or semi evergreen 
vegetation and suggests that the eastern coast of 
G.C.S. is sinking ; further evidence is brought 
by soil studies. 
- Wind does not generate dune movement (cf. Mexico, 
Venezuela) and cyclones are periodically destructive 
(1966, 1979). 
Pocket mangroves, mainly fringe and riverine 
are located along the southern coast of Grande Terre, 
SW and NW coasts of Basse Terre. The eastern coast 
of Grande Terre (one exception at Le Moule) and 
western coast of Basse Terre are practically without 
mangroves. 
5 NEED FOR EXTRA FIELD OBSERVATIONS 
What has been explained under 3 and 4 is only a 
framework. Field checks must correct the interpre 
tation and ease the extrapolation for mapping. Extra 
ecological observations will provide explanations 
for the present spatial distribution of vegetation 
and its evolution in time. 
The interest of transects lies in the continuous 
correlation established between the tones of the 
photos the corresponding vegetation and environmental 
factors. Several transects are self commented by 
the legend of figures 2-3-4-5 _ 7. 
An ecological interpretation needs at least a 
mud auger and a pocket salinometer (additional field 
measurements and laboratory analyses if it can be 
afforded). 
Salinity is the most significant factor to determine 
the ecological range of the species. Beyond 8,5% 
salt in soil solution any vegetation will die leaving 
a saltflat ("étang bois sec"), resulting from the 
evaporation of trapped seawater after cyclones during 
severe dry seasons. 
Figure 1. Grand Cui de Sac Marin (G.C.S.) 
Besidei the 4 areas shown, two others are studied: 
the mouth of Grande Rivière à Goyaves and Morne 
Rouge on its western side. 
Tides are \yeak in the Caribbean area and inundation 
classes are not useful ; most significant is the 
conjunction of the highest tides (0.5 m) and climax 
of the rainy season (Imbert, 1985). The accumulation 
of organic matter and intensive evaporation in 
a well marked dry season generate dwarf Rhizophora 
mangrove on saline peats (5,0 to 5,5 % salinity). 
Drilling the soil 1 to 2 m deep shows that below 
Rhizophora peat Cyperacea peat occur, hence the 
evidence of a vegetation chronosequence that can 
be refined with C14 and pollen analysis over the 
2000 or even 4000 past years. 
6 DYNAMICS OF WETLANDS 
We are concerned here with recent and present modi 
fications by comparing air-photos over the last 
20 to 35 years. In this period no drastic changes 
happened. Local progression of forest are not uncom 
mon. Nevertheless the general tendency is a slow 
insidious regression of forested areas. It is rather 
difficult to imagine what was the pre-colonization 
situation of Pterocarpus and marshlands. Nowadays 
the most important factor in the regression is 
urbanization and road construction, well seen in 
the vicinity of Pointe à Pitre, the main city, 
also quite visible in any town near the sea. Next 
in importance is agriculture : reclamation through 
drainage was active in the past (Abymes, Morne- 
à-1'Eau). To day the pressure is constant on the 
outer margins of Pterocarpus for dasheen (Colocasia) 
crops under the trees without felling. If trees 
are cleared and cultivation abandoned later cyperaceae 
come first maintained by hunter-fires. If fires 
stop Laguncularia or Pterocarpus recolonize. Fire 
sweeps are obvious on photos. Cyclones play an 
important role : local chablis in Pterocarpus and 
Laguncularia, killed Rhizophora induce thickets