Located 400 km from the east coast of Africa and covering a surface of more than 580 000 km2, the Republic of Madagascar is the fourth largest island in the world after Greenland, New Guinea and Borneo. Extending about 1600 km from north to south and extending for about 570 km at its widest point. A mountainous skeleton, with the highest peak of Maromokotro at 2,876 m, extends the entire length of the island, roughly defining the eastern escarpment, the steep coastal plains of the plateaus and plains of the island. West more gently sloping.The relief of Madagascar is very rugged with Highlands (more than 800 m of altitude) which occupy all the north-south axis with culminating points such as in the north, the Maromokotra (2 876 m), in the centre Ankaratra (2643 m) and south Andringitra (2658 m). The eastern slopes abruptly go down towards the Indian Ocean. The western side, on the other hand, has gentler slopes occupied by large plains that join the Mozambique Channel. In these plains flow the longest rivers that lead to the sea by important deltas such as Betsiboka, Tsiribihina, Mangoky.

The relief naturally divides the hydrographic network into five entities namely: 1 the Amber Mountain basins; 2 basins on the eastern side with fast and short rivers; 3 basins of the southern slope with intermittent flow; 4 the basins of the western slope with long, slow-flowing rivers; 5 the basins of Tsaratanana.

In this division, the Maevarano watershed straddles two entities; right tributaries are included in the Tsaratanana slope while left tributaries are included in the western slope. The right tributaries are indeed under the effects under of the orographic precipitations of Tsaratanana, but this watershed drains also a southern zone of the dried up region of the western slope. The largest watershed in terms of surface areas are Mangoky 55750 km2, Tsiribihina 49800 km2, Betsiboka 49000 km2, Onilahy 32000 Km2. The largest Eastern Watershed, Mangoro has an area of 17175 km2, less than a third of that of Mangoky. Rivers and streams are short there, almost perpendicular to the coast, with two exceptions: Mangoro and Southern Mananara. The rivers of the southern slope are south of the tropic of the Capricorn and cover about 48750 km2 of superficies. All these rivers are dry at least part of the year.

Madagascar is subject to a modal united tropical climate characterized by alternating rainy season (November-March) and dry season (April-October), whose lengths vary from one region to another. The altitude also accentuates the temperature variations. The dry season can thus be particularly cool in the Highlands where, sporadically, it can freeze (regions of Antsirabe and Ambatolampy). The East coast is well watered (more than 2000 mm of rain/year during eleven months), while the southern part of the island is subject to a long dry season, usually accompanied by a rainfall deficit (275 mm at Tulear). Madagascar undergoes annual damage in the middle of the rainy season (from January to March). cyclones from the Indian Ocean or the Mozambique Channel.

The Biomes

Biomes are large and homogenous natural community of flora and fauna. Madagascar’s ecological habitats are mainly divided into three main parts: the east, the west and the south.

The biomes of Madagascar are the savannah, the desert, the tropical forest, several types of mountain ecosystems and wetlands. The savanna is a dry meadow, while the desert is extremely dry and has little vegetation. The tropical forest is mainly located in the east of Madagascar. Mountainous ecosystems are at higher altitudes. The savannah is found along the west side of the island, where most of the rains fell on the east side. The desert is also on this side of Madagascar. Tropical forests are on the opposite side of the savannah and desert biomes because most of the rains have fallen there. And finally, the mountainous ecosystems are in the middle of Madagascar, where the elevation is higher.

The terrestrial habitats comprise three major divisions:

– Primary formation

– Secondary formations

– Various crops and plantations.

Primary Formations: these formations have existed since ancient times, before any human intervention. Two groups can be distinguished: primary forests and thickets.

Primary forests:

  • Eastern biome

Evergreen moist forests characterize the Eastern Biomes in general. Depending on the altitude, both types exist:

  • Low altitude moist evergreen forest
  • High altitude moist evergreen forest
  • Sclerophyllous forests grow at altitude. Two types exist:
  • The sclerophyllous mid-altitude forest
  • The mountain sclerophyllous forest

Thickets

  • The West Biome

Dry deciduous forests dominate in the west. In this region, the forests are in an altitude range of 0 to 800 m, but they present several varieties according to the different bioclimatic types. The physiognomy of the vegetation is characterized by a height of 25m with a closed canopy and well-defined undergrowth vegetation. The formation is a mixture of three types of vegetation: evergreen, sclerophyllous and dry (on rocky outcrops).

  • Southern Biome

The dry forests of the Southern Ecoregion cover an area of 57,721 square kilometers and are characterized by deciduous shrubs or thorny thickets that extend south from Morombe along the coast and cover most of the southern part of Madagascar from sea level up to 400 m. Rainfall in this region is low and erratic. These are the driest forests in Madagascar and the region is commonly known as the Spiny Desert. There remain approximately 19,131 square kilometers (33%) of intact original forest in the Southern Ecoregion

  • The Wetland areas

The wetlands of eastern Madagascar take the form of lakes, rivers and marshes. There are few large in the region but the largest lake in the country, Alaotra Lake, is there, as well as the system of acidic and barren coastal lagoons of Pangalanes. The most important wetlands in the east are marshes, usually constructed from small marshy vegetation areas at medium and high altitude, and often located in narrow valets or on the edges of lakes.

The western wetland is shallow and often slightly alkaline. Other types are the shores and the large rivers

Malagasy coastal habitats differ considerably between the east and west of the island. The east has mostly sandy beaches sparsely populated with birds. The west is richer and more diverse with extensive mangroves, salt marshes, coastal lagoons, estuaries, sandbars, sandy beaches and offshore islands.