Eastern Madagascar

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Madagascar, the fourth largest island in the world, has been isolated for 150 to 180 million years from other land masses. This prolonged isolation is the major factor that led to extremely high levels of endemism of plant and animal species. Endemism within the island is approximately 80 to 90 percent for all groups, and endemic families and genera are commonplace. It is estimated that 85 percent of the island’s 12,000 species of flowering plants are found nowhere else in the world. This unique biodiversity has led to the recognition of Madagascar, which is roughly twice the size of Arizona, as a "living laboratory" and the "seventh continent" (Jolly et al. 1984, Lourenço 1996, Olson and Dinerstein 1998, Mittermeier et al. 1999, Lourenço and Goodman 2000). Since humans arrived in Madagascar about 2000 years ago over 90 percent of the original forest cover has disappeared, and forest destruction continues at a rapid pace. This means that virtually all the unique habitats and endemic animals of Madagascar face significant threats. It now has the greatest number of critically endangered primates of any country in the world (Hilton-Taylor 2000).

The moist forests located along the eastern escarpment and coastal plain of the island have long been recognized as a particularly important center of endemism and diversity (e.g. Humbert 1959). Hundreds of species of vertebrate animals and perhaps thousands of species of plants are strictly endemic to this ecoregion. These include a high diversity of mammals, especially lemurs. These forests are also home to the recently rediscovered Madagascar serpent eagle (Eutriochis astur), the hairy-eared dwarf lemur (Allocebus trichotis) and the recently described golden bamboo lemur (Hapalemur aureus), indicating that information on the biota of this ecoregion is far from being complete. These forests are also among the most threatened habitats in the world due to rapid clearance by the shifting cultivation practiced by local people. 

  • Scientific Code
  • Ecoregion Category
  • Size
    43,500 square miles
  • Status
  • Habitats

 Location and General Description
The lowland forests of Madagascar include a narrow strip of humid forests along the east coast, low elevation forests (from sea level up to 800 m). The forests extend from Marojejy in the north to the extreme southeastern corner of the island. At the northern edge of the ecoregion, around Vohémar, the moist forest changes to a transitional dry forest. This area has localized climatic conditions that lead to different vegetation, one of many such patches across Madagascar (Lowry et al. 1997). At the ecoregion’s southern limit, in the rain shadow of the Anosyennes Mountains, the moist forest changes in a very short distance from a dry transitional forest to spiny forest. At the ecoregion’s western edge, the forest grades into subhumid forests around the 800 m contour on the central highlands.

Rainfall is generally over 2,000 mm per year throughout the ecoregion. In some areas, such as the Masoala Peninsula, it can be as high as 6,000 mm per year (Kremen in press). There is a slightly cooler and drier period between May and September. Cyclones occur in some years between November and March, and they can cause considerable habitat destruction. The mean annual temperature in the forest is 26oC.

Most of this ecoregion is underlain by metamorphic and igneous basement rock. There are patches of marble and quartz north of the Antongil Bay. There is also an eastern lowland belt of lava and a narrow coastal plain of unconsolidated sands (Du Puy and Moat 1996). In general, the geology along the eastern length of the island is relatively homogeneous, and vegetational composition and structure vary more with elevation than with latitude (Du Puy and Moat 1996).

The ecoregion includes moist forests across an elevational range from sea level to around 800 m. There is ongoing research and discussion on the divisions of forest types throughout these eastern forests (Lowry et al. 1997). Generally, vegetation of this eastern region has been divided into three primary categories corresponding to broad elevational bands: "lowland rain forest" (0 to 800 m), "moist montane forest" (800 to 1,300 m), and "sclerophyllous montane forest" (1,300 to roughly 2,300 m) (White 1983). The first of these categories is placed in the lowland forest ecoregion and the latter two in the subhumid forest ecoregion. Local conditions can result in deviation from these generalizations (see Lewis et al. 1996). In fact, in many areas, the transition from lowland to montane forest may be closer to the 600 m contour. While it is clear that animal and plant species change significantly with elevation, the transition between low elevation and mid-elevation forest is relatively gradual across the complete latitudinal range of eastern Madagascar (Goodman 1996, 1999, 2000).

There are some general trends in forest characteristics with increasing elevation: decreasing stature, fewer straight unbranched and boled trees, less stratification, more epiphytes, more bryophytes and lichens, a better developed and more diverse herb layer, and floristic changes (Lewis et al. 1996). Dense evergreen trees characterize the lowland forest up to 800 m, with a canopy exceeding 30 m, and taller emergents such Canarium (Burseraceae), Albizia (Fabaceae), and Brochoneura acuminata (Myristaceae). The lowland forest is typified by plants from the following genera and families: Diospyros (Ebenaceae), Ocotea (Lauraceae), Symphonia (Guttiferae), Tambourissa (Monimiaceae), and Dalbergia (Leguminosae).

The mid-altitude moist forest is as rich in species as the lowland forest, but tends to have a shorter canopy of 20 to 25 m. Some of the canopy species are common to the lower-elevation forest and some are unique to mid-elevation forest such as the Weinmannia (Cunoniaceae) and Schefflera (Araliaceae). The shrub and herb layers of the mid-elevation forests include Compositae, Rubiaceae and Myrsinaceae. One distinctive feature of this forest is the diversity of Pandanus species (Pandanaceae), bamboos (Graminaceae) and epiphytic plants (Lowry et al. 1997, Nicoll and Langrand 1989).

The distribution patterns of some faunal groups differ from those of the flora within the eastern forests in that they vary with elevation and show less latitudinal homogeneity. This is illustrated by the distribution of the five subspecies of the lemur Eulemur fulvus and three subspecies of another lemur Propithecus diadema within the eastern moist forest (Harcourt 1990, Mittermeier et al. 1994). The important delineators for the distributions of these subspecies are the major rivers flowing from the central highlands to the east, such as the Mangoro and Mananara.


 Biodiversity Features
The moist forests of eastern Madagascar are the most diverse forests in the country, and contain exceptionally high levels of endemism. As with many other areas of Madagascar, there is little detailed information on many species within the eastern forests. The number and distribution of species is also continually changing as new research is completed.

The diversity of the forest mammalian fauna includes all five families of Malagasy primates, seven endemic genera of Rodentia, six endemic genera of Carnivora, as well as several species of Chiroptera. All five families of lemurs are represented in the eastern forests, with 15 endemic and near-endemic species. These species include the aye-aye (Daubentonia madagascariensis), recently rediscovered hairy-eared dwarf lemur (Allocebus trichotis), two subspecies of ruffed lemurs (Varecia veriegata variegata, V. v. rubra), indri (Indri indri), Eastern woolly lemur (Avahi laniger), diademed sifaka (Propithecus diadema diadema), Milne-Edwards’ sifaka (P. d. edwardsi), silky sifaka (P. d. candidus), golden bamboo lemur (Hapalemur aureus), greater bamboo lemur (H. simus), white-collared lemur (Eulemur fulvus albocollaris), collared lemur (E. f. collaris), and red-bellied rubriventer (E. rubriventer). The mammalian fauna is also highly threatened: out of 25 endemic and near-endemic species, 22 are threatened: 8 as critical, 9 as endangered, and 5 as vulnerable (Hilton-Taylor 2000).

The region harbors the greatest diversity of birds in Madagascar. Of the 165 breeding species recorded in the eastern forests, 42 are found nowhere else (Langrand 1990). Many of the species belong to the endemic families or subfamilies Mesitornithidae, Brachypteraciidae, Philepittinae, Vangidae, Bernieridae, and Couinae. In addition, 13 genera are represented only in this region (Langrand 1990), which comprise some of the rarest birds in the world. Two examples of Malagasy endemics include the Madagascar serpent eagle (Eutriorchis astur) and the Madagascar red owl (Tyto soumagnei), which have recently been rediscovered in several areas across this zone, including the Masoala Peninsula and sites further south.

Lowland rainforest is home to numerous amphibians and reptiles species. As an illustration, the following chameleon and dwarf chameleon forms are restricted to this ecoregion: Calumma gallus, C. cucullata, C. furcifer balteatus, Furcifer bifidus, Brookesia superciliaris, and B. therezieni. The ecoregion holds an assortment of locally endemic geckos: Paroedura masobe, Ebenavia inunguis, Matoatoa sparinnghi, Phelsuma antanosy, P. serraticauda, P. masohoala, P. flavigularis, Microscalabotes bivittis, Uroplatus lineatus, U. malama, and Homopholis antongilensis. A large number of skinks are only found in the ecoregion, such as Amphiglosssus astrolabi and A. frontoprarietalis. Moreover, an assortment of snakes occurs in this ecoregion that are unknown from elsewhere on the island: Pseudoxyrhopus sokosoko, P. tritaneatus, P. microps. P. heterurus, Micropisthodon ochraceus, Ithycyphus goudoti, I. pereneti, I. oursi and Brygoophis coulagesi. For amphibians, there are several species, specialists of lowland forest: Heterixalus alboguttatus, Mantella aurantianca, M. pulchra, M. laevigata, Mantidactylus argenteus, M. flavobruneus, M. klemmeri, M. microtympanum. M. microtis, and M. redimitus, etc.

In summary, about 50 species of reptiles, 29 species of amphibians (Achille pers. comm.), and probably more than 100 endemic species of freshwater fish, many of which are severely threatened (P. Loiselle, 2000 pers. comm.), that are strictly endemic to the lowland forest ecoregion.

The plant diversity and endemism in the eastern forests is suspected to be extremely high, with 82 percent specific endemism (Perrier de la Bathie 1936). For example, 97 percent of the 171 species of Malagasy palms (e.g. Dypsis, Neophloga) are endemic to the island, with a majority found in the eastern forests (Dransfield and Beentje 1995). Orchids (Orchidaceae) are also abundant, with many confined to these eastern forests. One of the most famous is the Angraeceum sesquipedale with a 35-cm spur that has evolved in tandem with its pollinator, a species of sphinx moth with a 30-cm-long tongue (Jolly et al. 1984).

There are many examples of rare animal species with restricted ranges in this ecoregion, such as the red-tailed newtonia (Newtonia fanovanae) or the brown-tailed mongoose (Salanoia concolor). Other notable species such as the Malagasy tomato frog (Dyscophus antongili) and the ruffed lemur (Varecia variegata rubra) are restricted to the area around the Masoala Peninsula. The golden bamboo lemur and the greater bamboo lemur are endangered primates that are restricted to relatively small patches of habitat that include primary moist forests with bamboo stands (Mittermeier et al. 1994).

The snail-eating coua (Coua delalandei), a lowland forest species from the endemic subfamily Couinae, was last recorded in 1834 and is almost certainly extinct. All specimens of this species with precise locality information come from the nearby off shore island of Isle Sainte Marie.

 Current Status
The forested habitats of this ecoregion have been very heavily degraded and fragmented and much has already disappeared. The process of deforestation has been going on for centuries and now, with increasing population and decreasing forest cover, there is intense pressure on the remaining forests. Recent estimates of the remaining forest cover vary (COEFOR/CI 1993, Nelson and Horning 1993, Du Puy and Moat 1996). This is due, in part, to the difference in classification used by different scientists. Du Puy and Moat (1996) estimated that 33,000 km2 of lowland forest and 32,500 km2 of mid-elevation forest remains.

A significant proportion of the forest cover has been totally removed in the lowlands of the southern and eastern parts of the ecoregion, and several remaining stands of this forest type are isolated from each other. In only a few locations (e.g., Masoala Peninsula), do the forests extend continuously through significant elevational gradients starting at sea-level. There are also only a few large blocks of lowland habitat remaining in the ecoregion, for example in the northeast on the Masoala Peninsula and northeast of Toamasina around the Mananara Biosphere Reserve. Many of the remaining large blocks are found in protected areas, such as Masoala National Park, Mananara Biosphere Reserve (including Verezanantsoro National Park), Ambatovaky Special Reserve, and Zahamena Integral Nature Reserve and National Park. However, significant areas of lowland forest occurs outside of protected areas and include such zones as the forests near Rantabe in the northeast and the eastern slopes of the northern Vohimena Mountains in the southeast.

Du Puy and Moat (1996) suggest that 7 percent of the remaining forests (see above for area) are "well protected" in some form of reserve, while 27 percent of the remaining forests are poorly protected in forest concessions and forest reserves. Integral nature reserves, national parks and special reserves may not be succeeding at some sites in protecting forests due to lack of logistic and financial resources, poorly marked and managed boundaries, and inadequately trained staff and increasing pressure from farming communities around the reserves. The forest reserves and concessions exist primarily for forest exploitation, and few have management plans.

 Types and Severity of Threats
The major threat to the Madagascar lowland forests is still, as it has been historically, the shifting cultivation practice of "tavy," or slash and burn agriculture. The forest is cut and burned to grow crops such as manioc and hill rice. After 2-3 years, the land is abandoned and regenerates into bushland and thicket. Ideally, after more than 10 years the land can be used again for agricultural crops. Due to increasing population pressure, fallow periods have become shorter. In some areas, the land has become degraded to the point where crops cannot be planted, and it becomes secondary grassland or is simply invaded by weeds, such as bracken (Pteridium). A reduction of the farming fallow period has led to lower crop yields and further pressure on the forests, as they are the only source of new farmlands.

Secondary threats to the forest include unintentional burning from wildfires as well as legal and illegal commercial logging. In some areas, over-exploitation of selected forest species for decorative purposes, such as palms and Cyathea tree ferns, can critically undermine the forest’s integrity (Lowry et al. 1997). Given the established agricultural practices and increasing human population, damage to the natural resources of the remaining eastern forests will continue. The extinction of numerous narrowly endemic species over the next few decades cannot be discounted in this ecoregion.


 Justification of Ecoregion Delineation
This ecoregion is based on Cornet’s humid bioclimatic division (Cornet 1974), which also corresponds to Humbert’s Eastern domain (Humbert 1955). It runs along the length of Madagascar’s east coast, with the inland boundary delineated roughly at the 800 m contour. This includes a narrow strip (1-5 km wide) of littoral forest that runs along portions of the coast, and contains a high number of endemic species. 


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Prepared by: Helen Crowley
Reviewed by: In progress


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