Remote sensing for resources development and environmental management: Remote sensing for resources development and environmental management

Damen, M. C. J.

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Multivolume work

Persistent identifier:: 856342815

Title:: Remote sensing for resources development and environmental management

Sub title:: proceedings of the 7th international Symposium, Enschede, 25 - 29 August 1986

Year of publication:: 1986

Place of publication:: Rotterdam; Boston

Publisher of the original:: A. A. Balkema

Identifier (digital):: 856342815

Language:: English

Additional Notes:: Volume 1-3 erschienen von 1986-1988

Editor:: Damen, M. C. J.

Document type:: Multivolume work

Volume

Persistent identifier:: 856343064

Title:: Remote sensing for resources development and environmental management

Sub title:: proceedings of the 7th international Symposium, Enschede, 25 - 29 August 1986

Scope:: XV, 547 Seiten

Year of publication:: 1986

Place of publication:: Rotterdam; Boston

Publisher of the original:: A. A. Balkema

Identifier (digital):: 856343064

Illustration:: Illustrationen, Diagramme

Signature of the source:: ZS 312(26,7,1)

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: Damen, M. C. J.

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Volume

Collection:: Earth sciences

Chapter

Title:: 4 Renewable resources in rural areas: Vegetation, forestry, agriculture, soil survey, land and water use. Chairman: J. Besenicar, Liaisons: M. Molenaar, Th. A. de Boer

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: Photo-interpretation of wetland vegetation in the Lesser Antilles. B. Rollet

Document type:: Multivolume work

Structure type:: Chapter

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

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