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.
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.
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.
COEFOR/CI, 1993. Répertoire et Carte de Distribution : Domaine Forestier de Madgascar. Direction des Eaux et Forets, Service des Ressources Forestières, Projet COEFOR (Contribution a l’étude des forêts classés), et Conservation International, 20p + 1 map.
Cornet, A. 1974. Essai cartographique bioclimatique à Madagascar, carte à 1/2'000'000 et notice explicative N° 55. ORSTROM, Paris.
Dransfield, J. and H. Beentje. 1995. The palms of Madagascar. Royal Botanic Gardens, Kew London, UK. xii+475p.
Du Puy, D.J. and J. Moat. 1996. A refined classification of the primary vegetation of Madagascar based on the underlying geology: using GIS to map its distribution and to assess its conservation status. In W.R. Lourenço (editor).Biogéographie de Madagascar, pp. 205--218, + 3 maps. Editions de l’ORSTOM, Paris.
Goodman S. M., editor. 1996. A Floral and Faunal Inventory of the Eastern Slopes of the Réserve Naturelle Intégrale d’Andringitra, Madagascar: with reference to elevational variation. Fieldiana: Zoology, new series, 85: 1-319.
Goodman S. M., editor. 1999. A Floral and Faunal Inventory of the of the Réserve Naturelle Intégrale d’Andohahela, Madagascar: with reference to elevational variation. Fieldiana: Zoology, new series, 94: 1-297.
Goodman S. M., editor. 2000. A Floral and Faunal Inventory of the Parc National de Marojejy, Madagascar: with reference to elevational variation. Fieldiana: Zoology, new series, 97: 1-286.
Harcourt, C., editor. 1990. Lemurs of Madagascar and the Comores. IUCN Red Data Book, IUCN, Gland.
Hilton-Taylor, C. 2000. 2000 IUCN Red List of Threatened Species. IUCN, Gland, Switzerland and Cambridge, United Kingdom.
Humbert, H. 1955. Les territoires phytogéographiques de Madagascar. In. Colloques internationaux du C.N.R.S., 59: Les divisions écologique du Monde. Moyen d’expression, nomenclature, cartographie. Paris, juin-juillet 1954. Année biologique, 3e sér. 31: 439-448.
Humbert, H. 1959. Origines présumées et affinités de la flore de Madagascar. Mém. Inst. Sci. Mad. Sér. B (Bio. Vég.), 9: 149-187.
Jolly, A., P. Oberlé, and R. Albignac. 1984. Key Environments: Madagascar. Pergamon Press, Oxford.
Kremen, C. in press. The Masoala Peninsula in S. M. Goodman and J. P. Benstead, editors. The Natural History of Madagascar. The University of Chicago Press, Chicago.
Langrand, O. 1990. Guide to the Birds of Madagascar. Yale University Press, New Haven.
Lewis, B.A., P.B. Phillipson, M. Andrianarisata, G. Rahajasoa, P.J. Rakotomalaza, M. Randriambolona, and J.F. McDonagh. 1996. A study of the Botanical Structure, Composition, and Diversity of the Eastern Slopes of the Réserve Naturelle Intégrale d’Andringitra, Madagascar in S. M. Goodman (ed). A floral and Faunal Inventory of the Eastern Slopes of the Réserve Naturelle Intégrale d’Andringitra, Madagascar: with reference to elevational variation. Fieldiana: Zoology, new series, 85: 24-75.
Lourenço, W.R., editor. 1996. Biogéographie de Madagascar. Paris, ORSTOM.
Lourenço, W.R. and S.M. Goodman, editors. 2000. Diversité et Endémisme à Madagascar. Mémoires de la Société de Biogéographie, Paris.
Lowry, P.P. II, G.E. Schatz, and P.B. Phillipson. 1997. The classification of natural and anthropogenic vegetation in Madagascar. Pages 93-123 in S.M. Goodman and B. D. Patterson, editors. Natural change and human impact in Madagascar. Smithsonian Institution Press, Washington, D.C.
Mittermeier, R.A., N. Myers, P.R. Gil, and C.G. Mittermeier. 1999. Hotspots: earth's biologically richest and most endangered terrestrial ecoregions. CEMEX, Conservation International and Agrupacion Sierra Madre, Monterrey, Mexico.
Mittermeier, R.A., I. Tattersall, W.R. Konstant, D.M. Meyers, and R.B. Mast. 1994. Lemurs of Madagascar. Conservation International, Washington, D.C.
Nelson, R. and N. Horning. 1993. AVHRR-LAC estimates of forest area in Madagascar, 1990. International Journal of Remote Sensing 14 (8): 1463-1475.
Nicoll, M.E. and O. Langrand. 1989. Madagascar: Revue de la conservation et des Aires protégées. World Wide Fund for Nature, Gland, Switzerland.
Olson, D.M. and E. Dinerstein. 1998. The global 200: A representation approach to conserving the earth's most biologically valuable ecoregions. Conservation Biology 12 (3): 502-515.
Perrier de la Bathie, H. 1936. Biogéographie des plantes de Madagascar. Société d'éditions géographiques, maritimes et coloniales, Paris, France.
White F. 1983. The vegetation of Africa, a descriptive memoir to accompany UNESCO/AETFAT Vegetation map of Africa. UNESCO, Paris.
Prepared by: Helen Crowley
Reviewed by: In progress