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GIS and Conservation for Madagascar  - Vegetation mapping

 


MADAGASCAR: Vegetation Mapping and Biodiversity Conservation (using Geographical Information Systems)

Pie Chart (click for more information)Madagascar is singled out by the international scientific and conservation community as one of the richest countries in the world in terms of biodiversity, endemism and range of habitats. Its flora is diverse and unique. Of approximately 10,000 native higher plant species, about 8,000 species are thought to be endemic to the island. As a comparison, Madagascar is about 2.5 times as large as Britain, which has about 1,200 species of which only 10 to 20 are endemic. The value of the flora of Madagascar, both to the local peoples and in a global sense, is potentially immense. Despite its importance, this flora is under serious threat. Over 80% of the island has already been stripped of its native vegetation cover; the majority of this area is now very species-poor secondary grassland which is burnt annually and is subject to intense erosion. The heritage of biological diversity in Madagascar is probably under greater threat than in any other country. This unique diversity, combined with the threats to the remaining native vegetation, puts Madagascar amongst the highest conservation priority areas in the world.

In response to the Convention on Biological Diversity (resulting from the ‘Rio Summit’), a conservation strategy is being implemented as part of Madagascar's Environmental Action Plan: part of this Action Plan is to increase the number of protected areas. This project has aimed at providing assistance to the organisations involved in this new conservation impetus, through the prioritisation of key regions to include in the new network of reserves, and to provide a powerful conservation planning tool with all maps and data available and being used in Madagascar.

Our GIS studies in Madagascar are primarily aimed at analysing distribution patterns of vegetation types and plant biodiversity in Madagascar. Field work has shown that the structure and species composition of the vegetation often alters radically with changes in substrate. It is assumed, therefore, that different vegetation types, with different species compositions, occur on different rock types, and that a new, more informative map of vegetation types could be produced by subdividing the broad primary vegetation types on the basis of the rock type on which they occur.

The first stage was to digitise the geology map of Madagascar (BESAIRIE, 1964), and then to simplify it into broad categories of rock types which seem to have an important effect on the vegetation they support. The categories of sedimentary rocks include sandstones, loose (unconsolidated) sands, and two limestone categories of different ages (one of which produces the spectacular "tsingy" areas of jagged, highly eroded limestone pinnacles). A broad category of metamorphic rocks (including granites and migmatites), often covered by thick layers of laterites, covers large areas of the central and eastern areas of the island. Lavas and basalts, and several restricted rock types including quartzites, marbles and ultrabasics are also separated.

The remaining areas of good quality, primary vegetation were identified from the vegetation map of FARAMALALA (1988 &1995), which was derived from LANDSAT satellite imagery, and broadly maintained the vegetation zones defined by HUMBERT (1955). The primary vegetation was then classed into two major types, one evergreen (eastern and central) and the other deciduous (western and southern). The evergreen forests include the humid forests (at low, medium and high altitudes), along with the sclerophyllous woodland remnants (Uapaca dominated) of central Madagascar. The deciduous formations include the seasonally dry forests of the west and north, and the southern, dry forests and scrublands.
A map of the ‘Remaining Primary Vegetation, classified by the Underlying Geology’ was produced by overlaying the map of ‘Remaining Primary Vegetation’ (derived from satellite imagery) on a map of ‘Simplified Geology’. This map provides new insights into the patterns of distributions of plant species, and the various types of vegetation, especially in western and southern Madagascar where the geology varies substantially.

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Histograms of the area remaining of each vegetation type (in km2) could then be produced, and by overlaying a map of the protected areas (COEFOR/CI, 1993), the amount of protection for each type could be demonstrated. It is immediately obvious which vegetation types are poorly represented in the current system of protected areas. The maps can then be re-examined to show where large, intact areas suitable for conservation still exist. If Reserves were set up on each category, then the system of reserves would include as wide a range of vegetation types as possible, and therefore as high a species diversity as possible. When used in this way, as a mirror of plant diversity, this is obviously an important tool for conservation planning and management.

Click for more informationThe graphs and maps output have been used to succinctly convey complex arguments in an attractive, user-friendly format accessible to non-botanists, allowing politicians and decision makers to utilise the data. It also provides statistically based arguments for conservation priorities in an area which has previously been dominated by intuition, or based on the distributions of a few, well-known species. It is clearly evident, for example, that the deciduous, dry, southern forests and scrublands are insufficiently protected, especially given their recognised richness in endemic plant species, and the great variability in the underlying geology.

These maps and data have been compiled and distributed on CD-ROM, to the different organisations involved in conservation projects in Madagascar, including ANGAP (the National Association for the Management of Protected Areas), WWF and Conservation International. They are now being used in Madagascar, within the context of the Environmental Action Plan (a response to Madagascar signing the Convention on Biodiversity in March, 1996), to help identify areas of high priority for conservation of biodiversity, and to improve the network of Protected Areas.

Following the success of this initial work, it is envisaged that similar approaches will be used in other regions, and that the methodology could be standardised, perhaps using other sources of digitised map data (such as meteorological satellite data for climate or seasonality).

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References:

  • BESAIRIE, H. (1964). Carte Géologique de Madagascar, au 1:1,000,000e, trois feuilles en couleur. Service Géologique, Antananarivo.
  • COEFOR/CI (1993). Répertoire et Carte de Distribution : Domaine Forestier de Madagascar. Direction des Eaux et Forêts, Service des Ressources Forestières, Projet COEFOR (Contribution à l’étude des Forêts Classées), et Conservation International,

  •  20 pp. + 1 map
  • DU PUY, D.J. and MOAT, J.F. Vegetation Mapping and Classification in Madagascar (using GIS): Implications and Recommendations for the Conservation of Biodiversity. In: Cutler, D.F., Huxley, C.R. & Lock, J.M. (Eds.), The ecology, chorology and taxonomy of the African and Madagascan floras -  Proceedings of the Frank White Memorial Symposium. Kew Bulletin Additional Series. Royal Botanic Gardens, Kew.
  • DU PUY, D.J. and MOAT, J. (1996). A refined classification of the primary vegetation of Madagascar based on the underlying geology: using GIS to map its distribution and to assess its conservation status. In: W.R. Lourenço (editor). Proceedings of the International Symposium on the Biogeography of Madagascar, pp. 205--218, + 3 maps. Editions de l’ORSTOM, Paris.
  • FARAMALALA, M.H. (1988). Etude de la Végétation de Madagascar à l’aide des Données spatiales. Doctoral Thesis, Univ. Paul Sabatier de Toulouse, 167 p. + map at 1:1,000,000.
  • FARAMALALA, M.H. (1995). Formations Végétales et Domaine Forestier National de Madagascar. Conservation International (et al.), 1 map.
  • HUMBERT, H. (1955). Les Territoires Phytogéographiques de Madagascar. Leur Cartographie. Colloque sur les Régions Ecologiques du Globe, Paris 1954. Ann. Biol. 31: 195-204, + map.
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