The Natural History of Madagascar - Essay Example

MADAGASCAR A forest is one of Madagascar's most remarkable features. There are rainforests in the east, deciduous forests in the north and west, spiny desert conditions in the south, and high mountain forests in the island's interior. This diversity is largely a function of Madagascar's unique climate, which in turn is a consequence of its geographic position and topography. Madagascar is 587,040 km2 in total area. It is the world's fourth largest island after Greenland, New Guinea, and Borneo. From north to south, the island extends over 13 degrees of latitude, from 12 S to about 25.5 S, and measures 1600 km, making it slightly larger than the state of California (Goodman and Benstead, 21). The geology of Madagascar consists of a backbone of Precambrian rock running from north to south down the length of the island, forming the central highlands (Figure 1, see Appendix). To the east of the plateau, there is an abrupt escarpment, while in the west the highlands slope more gently down to the Mozambique Channel. There is a wide variety of soil types, as well as considerable variation in elevation; several large massifs reach more than 2000 m. The trade winds, which come from the southeast across the Indian Ocean, produce moderate to high levels of orographic precipitation as they encounter this topographic relief. As a result, the majority of rain falls on the eastern side of the island. The western region is under the rain shadow of the central mountains, and conditions gradually become hotter and drier towards the Mozambique Channel. During the austral summer the western region is subject to a monsoon regime that originates in the north and dwindles to the south (Goodman and Benstead, 29). Consequently, there is a double rainfall gradient over the island, declining from east to west on the one hand, and north to south on the other. The northeast of Madagascar is the wettest part of the island and the southwest is the driest. The combined effect of Madagascar's rainfall regimes and varied relief is an abundance of localized climatic conditions, which result in the variety of habitat types found on the island. Habitat heterogeneity varies considerably, as do the species represented within the remnant natural habitats. Even within relatively short distances, there is notable turnover in species and flora composition. In 1921, the French botanist Henri Perrier de la Bathie proposed a two-tiered hierarchical classification of the vegetation of Madagascar, which has served as the basis for most subsequent biogeographic work on the island (Fig. 2, see Appendix). The major contribution of this study was the division of Madagascar into two major floristic zones corresponding to different climatic conditions and structurally distinct vegetation types. The flore au vent (windward flora) was defined as the area that comes under the direct influence of the moist southeast trade winds. The windward flora was later equated with the Eastern region of Madagascar, which includes the non-deciduous vegetation of both the coastal lowland region and central highlands (Goodman and Benstead, 239). The flore sous le vent (leeward flora) was defined as the area influenced by the drying effects of the trade winds as they descend after having crossed over the central highlands. This zone includes the deciduous vegetation of the west. The leeward flora was later equated with the Western region of Madagascar (Goodman and Benstead, 240). The fundamental biogeographic distinction between the "wet" non-deciduous forests of the east and "dry" deciduous forests of western Madagascar has been supported by numerous studies of plant, invertebrate, and vertebrate distribution patterns. Simultaneously, WWF ecoregion model divides the Eastern floristic zone into three primary regions that correspond to broad altitudinal ranges: humid ("lowland") forest (0-800 m), subhumid ("moist montane") forest (800-1800 m), and ericoid thicket (roughly above 1800 m). The major ecoregions of the Western floristic zone are dry deciduous forest, succulent woodland, and spiny thicket (Figure 3, see Appendix). The final ecoregion, mangrove, exists in a wide range of climatic conditions along the low coastal western zone. The moist forests located along a portion of the eastern escarpment and coastal plain of Madagascar have long been recognized as a particularly important center of life and diversity for small mammals. The humid forests consist a narrow strip of lowland forests along the east coast of Madagascar, including the littoral forests of the narrow coastal plain and up to the crest of the eastern escarpment. The eastern escarpment traps humid air from the sea, forming a continuous cloud layer at 900 - 1200 m (Burgess et al., 108). This moisture supports a band of forest from just north of Marojejy in the north to the Tolagnaro region in the southeast corner of the island. At the northern edge of ecoregion around Vohemar, the moist forests transition to the dry deciduous forest ecoregion. To the east, at approximately 800 m elevation, the lowland forests merge gradually with the subhumid forests. At the ecoregion's southern limit, in the rain shadow of the Anosyennes Mountains, the humid forest changes over a short distance from a dry transitional forest to spiny forest (Burgess et al., 112). The primary natural vegetation is lowland rainforest. Dense evergreen trees characterize the canopy vegetation at a height of 30 m, with taller emergent species in some areas (Goodman, 12). With increasing elevation, the forests have decreasing stature, less stratification, and a better-developed and more diverse herb layer (WWF, 2001a). In contrast to the west coast, the eastern coastal region of Madagascar has few mangroves (WWF, 2001b). The forests of eastern Madagascar are the most diverse habitats on the island. Many species of vertebrates, especially lemurs, and plants are strictly connected to the humid forest ecoregion. Although animal and plant species change significantly with elevation, the transition is often gradual across eastern Madagascar (Goodman, 6). It is estimated that only a third of the original lowland forest remains intact. Seven percent of the lowland forests that remain are protected in national parks and reserves. Key protected areas include the Reserve Speciale d'Analamazaotra and Anjanaharibe-Sud, Mananara Biosphere Reserve (including the Pare National de Verezanantsora), Parcel 1 of Pare National d'Andohahela, and the Pare National d'Andringitra, Marojejy, Mantadia, Masoala, and Ranomafana. WORKS CITED Burgess N.D., D'Amico Hales J., Underwood E.C., Dinerstein E., Olson D., and others. Terrestrial Ecoregions in Africa and Madagascar: A Conservation Assessment. Washington, DC: Island Press, 2004 Goodman S.M. and Benstead, J.P. eds. The Natural History of Madagascar. Chicago: The University of Chicago Press, 2003 Goodman S.M. A Floral and Faunal Inventory of the Reserve Naturelle Integrale d'Andohahela, Madagascar with reference to elevation variation. Fieldiana: Zoology, 94:1-297, 1999 World Wildlife Fund (2001a). Madagascar lowland forests. Available at < http://www.nationalgeographic.com/wildworld/profiles/terrestrial/at/at0117.html> Retrieved Sep 27, 2010 World Wildlife Fund (2001b). Madagascar mangroves. Available at < http://www.nationalgeographic.com/wildworld/profiles/terrestrial/at/at1404.html> Retrieved Sep 17, 2010 APPENDIX Figure 1. Topographic map of Madagascar with elevation color-coded. Map is from Sep 28, 2010 Figure 2. Map of Perrier de la Bathie's vegetation classification (Goodman and Benstead, 2003) Figure 3. Terrestrial ecoregions of Madagascar. Black - mangrove; dark grey - dry deciduous forest; light grey - succulent woodland; white - subhumid forest; horizontal stripes - spiny ticket, vertical stripes - lowland forest (Goodman and Benstead, 2003). Read More