|
|
|
|
Madagascar dry deciduous forests
|
| |
|
| |
The Madagascar dry deciduous forests represent a tropical dry forest ecoregion generally situated in the western part of Madagascar.
Discussion
Ask a question about 'Madagascar dry deciduous forests' Start a new discussion about 'Madagascar dry deciduous forests' Answer questions from other users |
Encyclopedia
The Madagascar dry deciduous forests represent a tropical dry forest ecoregion generally situated in the western part of Madagascar. The WWF has designated these forests as a Global 200 ecoregion, one of the world’s most crucial regions for conservation. These western dry forests are characterized by upper stories of deciduous canopy extending to a height of 14 to 30 meters, and lower stories with dense shrubs and saplings, which may also contain some evergreen species. 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. Trees have adapted to the drier climate by shedding leaves in the dry winter season (May to September) to limit winter evapotranspiration. Moreover, some species like baobabs have adapted by evolving the ability to store copious water in their large bulbous trunks.
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. The elevation of dry deciduous forests here spans the coastal plain with its limestone plateaus emanating virtually at sea level to higher altitudes to 800 meters. Considerable anthropogenic destruction has occurred, decimating whole regions of the forest, almost all of which has been driven by subsistence farming. After clearcutting and burning, a residual sparse, sometimes sterile grassland savanna is relict. Because trees grow slowly in the rocky soils, regeneration time may be measured in centuries, but the toll of extinct species is permanent. Several distinct subregions are found within the western dry forest zone, several of which will be discussed separately here.
Summer daytime temperatures commonly exceed 30 degrees Celsius in all the Madagascar dry deciduous forests. One characteristic in common with other tropical and subtropical dry broadleaf forests is the presence of relatively high densities of mammalian biomass. Like these other dry forests, the Madagascar dry deciduous forests are sensitive to overgrazing and deforestation. An interesting feature of these dry forests is the presence of Pachypodium habitats, often associated with tsingy outcrops. There are numerous distinct forests within the biome, Madagascar dry deciduous forests; the following text treats three of these, selected for representativeness as to location and size.
Ankarana Special Reserve
The Ankarana Massif consists of a limestone shelf which imposes a picturesque landform 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" by the natives. 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 many cases the cave roofs collapse and form forested gorges through which rivers may flow.
The Ankarana Special Reserve is one of the northernmost reaches of the Madagascar dry deciduous forests, and correspondingly very hot 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 is a grassy plain that leads to the Indian Ocean. In the higher elevations Lac Vert is perched 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 are the Crowned Lemur, Northern Sportive Lemur, Gray Mouse Lemur and Sanford's Brown Lemur. Numerous geckos inhabit the Reserve including 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 centimeters 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.
Anjajavy Forest
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 the Jajavy tree, which is endemic only to the forest itself. and, in fact, only is found within a five kilometer radius of Anjajavy village. Abundant diurnal lemurs that are found here include the Coquerel's Sifaka and the Common Brown Lemur. One nocturnal species of mouse lemur is seen, but its precise species is yet to be documented. A variety of birds are present including the endangered species Madagascar Fish Eagle, which has four (of the approximately 99 known) breeding pairs resident in Anjajavy Forest. Other birdlife present are the Crested Coua, kingfishers, Madagascar Wagtail and 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.
Kirindy Forest
Not a part of the official Madagascar National Park System, Kirindy Forest at is a private park situated in the southwestern part of Madagascar, 40km northeast of the town of Morondava. The forest was earlier operated as an experimental sustainable timber harvesting scheme, which activity 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.
Kirindy Forest, approximately 100 square kilometres in area, may be best known as the only location where the endangered species 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, Leaf-tailed gecko, Big-headed gecko, Madagascar Ground Boa, Giant hog-nosed snake, Spear-nosed snake and Kapidolo.
Future outlook
Madagascar's dry deciduous forests have been preserved generally better than the eastern rainforests or the high central plateau, presumably due to historically less population density and scarcity of water; moreover, the present day lack of road access further limits human access. There has been some slash-and-burn activity in the western dry forests, reducing certain 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, or without intervening fallow periods, the nutrient deficient soils may be exhausted or eroded to an unproductive state. Further protection of western forests would assist in preservation of these diverse ecosystems, which have a very high ratio of endemic organisms to total species.
Madagascar has many lemurs and 99.9% of the species is endangered due to habitat destruction.
See also
External links
|
| |
|
|
