Madagascar dry deciduous forests
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The Madagascar dry deciduous forests represent a tropical dry forest ecoregion generally situated in the western part of Madagascar. The area has high numbers of endemic plant and animal species but has suffered large-scale clearance for agriculture. This clearance is ongoing and therefore the WWF has designated these forests as a Global 200 ecoregion, one of the world’s most crucial regions for conservation. The Manambolomaty Lake area in particular is home to many species of fish and birds. The area is also home to distinctive limestone karst formations known as tsingy including the World Heritage Site of Bemaraha.
There are two separate areas within the Eco-region: 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.
These dry deciduous forests span the coastal plain with its limestone plateaus emanating virtually at sea level to higher altitudes to 800 metres. The area includes wetlands and grasslands (mostly created by forest clearance for agriculture) as well as dry forests characterized by upper stories of deciduous canopy extending to a height of 14 to 30 metres, and lower storeys with dense shrubs and saplings, which may also contain some evergreen species. Several distinct sub-regions are found. 
Climate is tropical with summer daytime temperatures commonly exceeding 30 degrees Celsius throughout the region and a wet season between October and April. Rainfall is decidedly less than the eastern lowland rainforests of Madagascar, attaining levels as low as 50 centimeters per annum in the southwest to 200 centimeters per annum in the northwest.
These dry deciduous forests of Madagascar possess a very high ratio of species endemism, although the absolute number of total endemics is less than the wetter eastern rainforests of the island.Trees have adapted to the drier climate by shedding leaves in the dry winter season (May to September) to limit evapotranspiration. Moreover, some species like baobabs have adapted by evolving the ability to store copious water in their large bulbous trunks. Two species of baobab however are limited in range and are considered endangered, these are Adansonia grandidieri and Adansonia suarezensis. An interesting feature of these dry forests is the presence of Pachypodium habitats, often associated with the hot dry conditions of life in a landscape of canyons and tsingy (limestone karst outcrops). One well-known tsingy area is Ankarana (see below for detailed description).
One characteristic in common with other tropical and subtropical dry broadleaf forests is the presence of relatively high densities of mammalian biomass. Several of Madagascar's characteristic lemur species are found here including the fat-tailed dwarf lemur, five subspecies of Propithecus, three species of Lepilemur, and five species of Microcebus. Endemic mammals include three endangered species, golden-crowned sifaka (Propithecus tattersalli) and Perrier's sifaka (Propithecus diadema perrieri) and western forest rat (Nesomys lambertoni) as well as mongoose lemur (Eulemur mongoz), golden-brown mouse lemur (Microcebus ravelobensis), northern rufous mouse lemur (M. tavaratra), pygmy mouse lemur (M. myoxinus), Milne-Edwards' sportive lemur (Lepilemur edwardsi), and greater big-footed mouse (Macrotarsomys ingens). As well as lemurs the dry forests are home to the island’s largest predator, the fossa (Cryptoprocta ferox) and some smaller carnivores. Among reptiles the angonoka tortoise is also endangered.
The lakes and rivers of the dry forest region are homes to most of Madagascar's bird species.
Threats and future outlook
The dry forests have almost entirely been destroyed by overgrazing and deforestation and there has been slash-and-burn subsistence farming in much of the area, reducing 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. After clear-cutting and burning, a residual sparse, sometimes sterile grassland savanna remains. When practiced repeatedly, or without intervening fallow periods, the nutrient deficient soils may be exhausted or eroded to an unproductive state. Because trees grow slowly in the rocky soils, regeneration time may be measured in centuries, but the toll of extinct species is permanent. Further protection of western forests would assist in preservation of these diverse ecosystems, which have a very high proportion of endemic species.
Ankarana Special Reserve
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. 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.
Mammals found in this forest include the apex predator Fossa (Cryptoprocta ferox), the fanaloka (Fossa fossana), northern ring-tailed mongoose and numerous bat species. Lemurs occurring here include the crowned lemur, northern sportive lemur, gray mouse lemur, Sanford's brown lemur and the aye-aye. Numerous geckos inhabit the Reserve including the Henkel's Leaf-tailed Gecko, big-headed gecko and day gecko. Other local reptiles are the Madagascar ground boa, the white-lipped chameleon (Forcifer minor) and Oustalet's chameleon, the world's largest chameleon, which can attain 68 centimetres in length.
Some bird species commonly seen are the hook-billed vanga, Madagascar pygmy kingfisher, crested coua, white-breasted mesite and Madagascar ibis. Raptors sighted in the reserve include the Madagascar harrier-hawk and the Madagascar scops owl. Other avafauna occurring here include red-capped coua and Coquerel's coua, and the vangas Van Dam's vanga, rufous vanga and sickle-billed vanga. Vangas are significant in Madagascar, as 15 of the 16 vanga species are endemic to Madagascar. The greater vasa parrot and Madagascar green pigeon are also indigenous. An important endangered species, the Madagascar fish eagle, has a number of breeding pairs located in the Ankarana Reserve.
The 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.
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 130 centimeters 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 to the determined explorer. Nor is the understory heavily thorned in most locations.
The Anjajavy Forest is named for a kind of Salvadora tree, the jajavy tree, which might be endemic only to the forest itself. Abundant diurnal lemurs that are found here include the Coquerel's sifaka and the common brown lemur. Three nocturnal species of mouse lemur are seen, but their precise species are yet to be documented. A large variety of birds are present including the endangered Madagascar fish eagle, which has four (of the approximately 99 known) breeding pairs resident in Anjajavy Forest. Other birdlife present are the sacred ibis, crested coua, kingfishers and Madagascar wagtail. Butterflies include the magpie crow. Numerous lizards, chameleons and snakes populate the forest and are easily seen from the sparse trail network.
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.
Not a part of the official Madagascar National Park System, Kirindy Forest at Morondava. The forest was earlier operated as an experimental sustainable timber harvesting scheme, which has not left indelible scars on the region. Most of the canopy top is about 14 meters in height, but in wetter parts (e.g. in riparian zones) it may almost triple in vertical extent. There are three species of baobab trees present: Adansonia grandidieri, Adansonia rubrostipa and Adansonia za.is a private park situated in the southwestern part of Madagascar, 40km northeast of the town of
Kirindy Forest, approximately 100 square kilometres in area, may be best known as the only location where the endangered giant jumping rat (Hypogeomys antimena) occurs. This animal can hop like a miniature kangaroo, but is also seen walking on all four limbs. There are a number of species of nocturnal lemurs present: red-tailed sportive lemur, pygmy mouse lemur, gray mouse lemur, pale fork-marked lemur, Coquerel's giant mouse lemur and the fat-tailed dwarf lemur. Further mammalian species of fossa, narrow-striped mongoose, Verreaux's sifaka, common tenrec, greater hedgehog tenrec and red-fronted brown lemur are also found here.
Some of the local reptiles present are: Labord's chameleon, various plated lizards, Henkel's Leaf-tailed Gecko, big-headed gecko, Madagascar ground boa, giant hog-nosed snake, spear-nosed snake and kapidolo.
- Nick Garbutt, Hilary Bradt and Derek Schuurman, Madagascar Wildlife, Globe Pequot Press (2001)
- Nick Garbutt, Hilton Hastings, Wendy Pollecutt, C. Michael Hogan, Tahiana Andriaharimalala, Anjajavy, the village and the forest. May, 2006
- Wilson, Jane (2013). Lemurs of the Lost World: exploring the forests and Crocodile Caves of Madagascar. Impact, London. p. 216. ASIN B00DXKZX7O. ISBN 978-1-874687-48-1.
- 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: 1–26. doi:10.1159/000156379.
- Russell Mittermeier et al., Lemurs of Madagascar, Conservation International (1994)
- Gemma Pitcher and Patricia C. Wright, Madagascar and Comoros, ISBN 1-74104-100-7
- George E. Schatz, Generic Tree flora of Madagascar, Royal botanic Gardens, Kew, Crowmwell Press, United Kingdom (2001) ISBN 1-900347-82-2
- Sustainable forestry
- Tropical agriculture
- Tropical and subtropical dry broadleaf forests
- List of national parks of Madagascar