Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986 
499 
Photo-interpretation of wetland vegetation in the Lesser Antilles 
B.Rollet 
Office National des Forêts, Basse-Terre, Guadeloupe, France 
ABSTRACT: The wetlands of Guadeloupe are typified through photo interpretation on panchromatic 1:20000 flown in 
1984 and earlier. Examples of interpreted photos are given and discussed. 
Geomorphology is a useful approach. Field observations for checking and collecting additional data especially 
on soils are indispensable before producing an ecological map. 
RESUME: Les terres basses de Guadeloupe sont classées en types de végétation par interprétation de photos 
aériennes panchromatiques au 1:20000 prises en 1984 et antérieurement. On donne des exemples de photos inter 
prétées et commentées. La géomorphologie est une approche utile mais des observations de terrain sont indis 
pensables pour vérifier avant extrapolation et pour prendre d'autres données, en particulier sur les sols 
afin d'établir une carte écologique. 
1 INTRODUCTION 
Wetland vegetation is understood in a broad sense 
i.e. a vegetation under the influence of periodic 
inundation (fresh or seawater) or with poor drainage.; 
this includes mangroves, Pterocarpus and open swamps 
with 0 to 10 ? salinity submitted to tides or perma 
nent inundation during 6 to 8 months a year. Inun- 
dable pasture lands are discarded. 
2 WETLAND VEGETATION TYPES 
The following is distinguishable on 1:20000 panchro 
matic : 
- Mangrove as a whole and its subtypes 
- Pterocarpus swamp forest 
- Dry deciduous or semi evergreen forest on karst 
Chrysobalanus thicket, sedge and fern swamps 
- Mudflat with algal cover, saltflats. 
Minor types, essentially woodlands or thickets are 
not readily recognizable : Hibiscus tiliaceus, 
Thespesia populnea, Conocarpus erectus, Annona 
glabra, Symphonia globulifera ; Dalbergia monetaria, 
Montrichardia along rivers. 
3 PHOTO INTERPRETATION 
In Guadeloupe available airphotos are 1:20000 pan 
chromatic flown by IGN in 1962-63, 1968-69, 1982, 
1984, also 1:50000 in 1950; and on limited areas 
1:10000 colour taken by ORSTOM. The same applies 
to Martinique except that false colour 1:20000 was 
flown is 1975 (chanteur et al, 1980). 
The scale 1:50000 is indadequate to map distinct 
forest types within mangroves but mature monospe 
cific stands on large areas are recognizable (young 
stages much less so). Rules of generalization are 
necessary to map the innumerable mixtures of age- 
classes and species in a readable way. The identi 
fication of small areas e.g. 5 mm diameter of thickets 
woodlands and forests will not be possible generally 
for all the species enumerated above. 
Detailed field checks are always necessary. 
Cyperaceae (Cladium, Eleocharis, Rhynchospora) and 
fern swamps (Acrostichum, Nephrolepis) are well 
recognized as a whole but the species are difficult 
to separate even with the help of ecological consi 
derations. Unless there is a need for agriculture 
(disease detection, yield prediction), it is unli 
kely that special photography will be used for 
forestry only. 
Concerning the main vegetation types the situation 
is much brighter. Pterocarpus forests are easy 
to delimitate in general ; they show a dark velvety 
tone when crowns are fused ; emergents, irregularly 
open stands, transition zones, food crops beneath 
the forest introduce differences in the normal 
pattern. Large patches are quasi monospecific but 
quite often there is an assemblage with scattered 
rainforest species (Ficus, Symphonia, Cassipourea, 
Maytenus guianensis), and sometimes with Rhizophora 
(northern bank of the lower course of Grande Rivière 
à Goyaves or Laguncularia (west of Rivière Salée), 
in all cases undetectable. 
Mangroves can be subdivided fairly easily when 
stands are pure and mature : Rhizophora mangle 
is almost black, Avicennia germinans is salt and 
pepper (white with grey dots), Laguncularia racemosa 
is darker than Avicennia. Young stages of the three 
species are indistinct, pale grey, getting progres 
sively darker for Rhizophora when stands grow older. 
False colour is available in Martinique (not 
in Guadeloupe). Chanteur et al (1980) mention that 
Rhizophora and Laguncularia come out red, Avicennia 
blue, Conocarpus blue grey. Young stages are not 
distinguishable. These results confirm the findings 
in Mexico (Rollet, 1974) except that on 1:10000 
Conocarpus was rather purple grey. 
On colour photos 1:10000 Avicennia is pale green, 
more yellowish than the two other species, not 
very distinct. On mature stands Rhizophora is bottle 
green, Avicennia yellow green, Laguncularia grey 
green easily mistaken for Rhizophora in mixtures. 
Mudflats come out white or mauve. The use of colour 
is questionable because of the extra cost for a 
limited additional information. 
False colour is an obvious breakthrough for spot 
ting Avicennia pure or in mixtures. Another device 
is needed to separate Laguncularia from Rhizophora. 
Undergrowths are not seen in most cases so that 
succession escape interpretation. Ill or decaying 
trees turn blue in false colour, in particular 
Rhizophora (Rollet, 1974), a source of misinterpre 
tation. Other mistakes will be avoided with some 
care : water bodies may be black or white in pan 
chromatic according to sun reflection and should 
not be taken for saltflats or mudflats. Film proces