The Madagascar dry deciduous forests represent a tropical dry forestecoregion situated in the western and northern part of Madagascar. The area has high numbers of endemic plant and animal species but has suffered large-scale clearance for agriculture. They are among the world's richest and most distinctive dry forests and included in the Global 200 ecoregions by the World Wide Fund. The area is also home to distinctive limestone karst formations known as tsingy, including the World Heritage Site of Bemaraha.
Geography
There are two separate areas within the ecoregion: the western side of Madagascar from the Ampasindava peninsula in the north to Belo-sur-Tsiribihina and Maromandia in the south (this is most of Mahajanga Province); and the northern tip of the island (apart from the high areas of Amber Mountain). Geological substrate is varied and includes the tsingy limestone massifs.[2]
These dry deciduous forests span the coastal plain with its limestoneplateaus emanating virtually at sea level to higher altitudes to roughly 600 metres (2,000 ft). The area includes wetlands and grasslands (mostly created by forest clearance for agriculture) as well as dry forests characterized by a deciduouscanopy extending to a height of 10 to 15 metres (33 to 49 ft).[2]
Climate is tropical, with summer daytime temperatures commonly exceeding 30 °C (86 °F), and a wet season between October and April. Rainfall, ranging from 1,000 to 1,500 mm, is more abundant than in the spiny thickets and succulent woodlands, but lower than in the eastern lowland rainforests.[2]
Flora
While the absolute number of plant species is lower than in the eastern rainforests of the island, the dry deciduous forests of Madagascar have a higher ratio of endemic species. Trees have adapted to the dry climate by shedding leaves in the dry winter season to limit evapotranspiration. Moreover, some species like baobabs and Moringa have adapted by evolving the ability to store copious water in their large bulbous trunks. Four species of baobabs, including three endemics (Adansonia grandidieri, A. madagascariensis and A. suarezensis) occur in this ecoregion. Other notable tree species include flamboyant tree (Delonix regia), Pachypodium species, and several Fabaceae and Rubiaceae. Forest understory plants include Lissochilus orchids [2] such as Oeceoclades calcarata, a large, cool growing, showy, terrestrial orchid which grows at medium elevation (1000 to 2000 meters) in western Madagascar. Its habitat is semi-arid and it is found growing in sandy or rocky soils in dry moss and lichen forests.[3]
Most dry forests have already been destroyed by human action, especially near the Central Highlands. The remaining forest is severely fragmented. Burning, grazing, and logging are the major threats, and siltation, overfishing and invasive species impact the wetlands. Some species such as lemurs suffer from hunting.[2]
The Ankarana Massif consists of a limestone shelf which imposes a picturesque land-form on the few adventurers who find this remote forest. As the limestone has weathered over geologic time, this karst formation often exhibits spiry pinnacles, called "tsingy" locally.[4] The name derives from the Malagasy word which means "walk on tiptoe", used by the earliest settlers from around 1500 years ago to describe the sharpness of the rugged limestone shelves. There are an abundance of limestone caves and virgin forests that shelter the diverse wildlife of the Ankarana region. In places the cave roofs have collapsed to form isolated forests and the vegetation of the gorges is also protected by the topography. Subterranean rivers provide a natural perennial irrigation system.
The Ankarana Special Reserve is one of the northernmost reaches of the Madagascar dry deciduous forests, and is very hot from December through March with this equatorial proximity. Access to wildlife viewing is through strenuous hiking, given the elevation differences, complex terrain and heat, but four-wheel drive vehicles can reach most of the actual campsites. Below the massif, and to the west, is a grassy savannah-with-palms that leads to the Indian Ocean. Within the massif, Lac Vert is found among tsingy formations.
Anjajavy Forest on Tsingy rocks juts into the Indian Ocean.
Anjajavy Forest is an example of a purely lowland dry deciduous forest in northwest Madagascar. It is punctuated with numerous tsingy outcroppings and limestone karst caves, and in many locations abuts the Indian Ocean, especially where the dramatic tsingy formations jut out into the ocean. The canopy height is typically 15 to 25 meters high, and is at its lowest at the coastal verge, where growth may be impeded by saline rocky soils. The forest resides on a small peninsula of land poking into the Indian Ocean, that is bounded on the north and part of its eastern extent by the Bay of Narinda and on the south by the Bay of Majajamba. Access to this forest is difficult since there are no roads connecting this peninsula to the Madagascar highway system; however, arrival by sea and by air are accomplished with some effort.[9]
In many places at the ocean edge as well as forest interior, several tree species are capable of taking root directly in the tsingy rocks. Several species of baobab and tamarind are among the tallest species forming the canopy. Considering the lower precipitation rates on the west coast (about 1,300 mm per annum at Anjajavy Forest), the vegetation is surprisingly verdant in the beginning of the dry season, but eventually will become mostly leafless by late winter. The forest understory is moderately dense but not impenetrable. Nor is the understory heavily thorned in most locations.[citation needed]
The dry forest is invaded by fingers of mangrove swamp in the form of riparian zones at several small coastal estuaries at the western verge of the Anjajavy Forest, where small tidal streams flow into the Indian Ocean. The species of the mangrove swamps are, of course, totally different from the dry forest, and the transition zone supports an interesting ecotone, providing unusual niches for several species of animals.[citation needed]
^Wilson, Jane (2013). Lemurs of the Lost World: exploring the forests and Crocodile Caves of Madagascar. Impact, London. p. 216. ISBN978-1-874687-48-1.
^Nick Garbutt, Mammals of Madagascar, Pica Press (1999)
^Wilson, J.M.; et al. (1989). "Ecology and Conservation of the Crowned Lemur at Ankarana, N. Madagascar with notes on Sanford's Lemur, Other Sympatrics and Subfossil Lemurs". Folia Primatologica. 52 (1–2): 1–26. doi:10.1159/000156379. PMID2807091.
