Madagascar subhumid forests

The Madagascar subhumid forests are a tropical moist broadleaf forest ecoregion which originally covered most of the Central Highlands of the island of Madagascar.

Setting

The Madagascar subhumid forests historically covered most of Madagascar's Central Highlands, above approximately 800 meters elevation on the east and above 600 meters elevation on the west. The ecoregion has an area of approximately 199,500 square kilometers (77,000 sq mi). The highlands catch the wet northeast trade winds, while the areas to the south, west, and north lie in the drier rain shadow of the highlands. The subhumid forests are bounded by the humid Madagascar lowland forests along the coastal strip to the east, by the Madagascar dry deciduous forests to the north, northwest and west, and by the xeric Madagascar succulent forests and Madagascar spiny thickets to the southwest and south. In four areas above 1800–2000 meters elevation, the subhumid forests yield to the montane Madagascar ericoid thickets. Montagne d'Ambre near the northern tip of the island, contains a significant pocket of subhumid forest, (surrounded at lower elevations by dry deciduous forest), as do Ankaratra, upland near Tsaratanana, Andringitra Massif, Ambohitantely Reserve, and the Ambohijanahary area. The subhumid forests ecoregion also includes the disjunct Analavelona and Isalo massifs to the southwest, surrounded by succulent forests at lower elevations. the region includes wetlands such as Lake Alaotra. The Sambirano region in the northwest is a particular centre of endemism.

Flora

The original flora of ecoregion has been much altered by human use; extensive areas have been cleared for agriculture, grazing, and rice cultivation, and some exotic species have been introduced. Pockets of closed-canopy evergreen forest still exist, as do open-canopy woodlands. Large areas are now covered by grassland, but the extent to which the grasslands are the result of human intervention is still subject to debate. Significant areas have become desertified following extensive slash-and-burn activity primarily from 1970 onward, as population pressures led indigenous peoples to seek agricultural production in increasingly unsustainable methods.

The subhumid forests shelter several species with origins in the temperate southern hemisphere Antarctic flora, including several species of podocarps (Podocarpus and Afrocarpus), and Takhtajania perrieri, from the magnoliid family Winteraceae.

Fauna

Endemic species include a number of birds, reptiles and mammals including the Alaotra gentle lemur (Hapalemur alaotrensis) and a number of shrews, tenrecs, and rodents.

The subhumid forests were formerly home to the island's distinct megafauna. Madagascar's long isolation from other continents resulted in a very limited land mammal fauna, and the endemic mammal lineages, in particular the lemurs, adapted to fill certain niches. Giant lemurs, now extinct, were as large as adult gorillas. Several species of elephant birds (Aepyornis), giant flightless ratites related to the ostrich, also became extinct since the arrival of humans approximately 2000 years ago, including Aepyornis maximus, the largest bird species ever to exist.

History, conservation, and threats

Madagascar's high plateau forests have been altered more than the eastern rainforests or the western dry forests, presumably due to historically greater population density and proximity to the capital city of Antananarivo; moreover, there has been extensive slash-and-burn activity by native peoples in the central highlands, eliminating most forest habitat and applying pressure to some endangered species. Slash-and-burn is a method sometimes used by shifting cultivators to create short term yields from marginal soils. When practiced repeatedly over a large scale area, or without intervening fallow periods, the nutrient poor soils may be exhausted or eroded to an unproductive state. A newer threat is the rice farming now taking place in the wetland areas.

Protected areas include the forests of Ambohijanahary and Ambohitantely, the eastern slopes of Andringitra and the upper slopes of Ranomafana National Park.