Location and General Description
This ecoregion includes the ericoid thicket habitats found above approximately 1,800 m on the upper slopes of Madagascar’s four major massifs (listed from north to south): Tsaratanana (2,876 m), Marojejy (2,133 m), Ankaratra (2,643 m), and Andringitra (2,658 m). Tsaratanana is the most northern massif, at 14o latitude and Andringitra the most southern, at 22o latitude. The transition from montane sclerophyllous forest to ericoid thicket may occur at different elevations. On Tsaratanana montane sclerophyllous forest exists up to about 2,500 m and then shifting to ericoid thicket, while in on these other three massifs the ericoid thicket commences just below 2,000 m. The Anjanaharibe-Sud Special Reserve in the north and Andohahela National Park in the extreme southeast contain small areas of ericoid thicket above 1,950 m.
There is considerable daily and seasonal fluctuation in the temperature of these montane areas. Snow has been recorded on the Andringitra Massif during the cold season, and the temperature can fall as low as -11°C (Saboureau 1962, Paulian et al. 1971). Further daily temperature extremes in the summital zone can range over 30°C (Langrand and Goodman 1997). Rainfall is probably more than 2,500 mm per year on the wetter eastward facing slopes of these massifs, but is considerably less in the rainshadow on the western slopes. The temperature range and intense sunlight can lead to arid conditions, although this may be short-lived. The basic geology of the massifs is metamorphic and igneous Precambrian basement rocks. Thin, nutrient poor soils overlay these rocks (Du Puy and Moat 1996).
The upper montane sclerophyllous forest is dominated by plant species from the families Podocarpaceae, Cunoniaceae, and Pandanaceae, and the trees are shrouded with mosses, lichens, and epiphytes. At higher altitudes, this forest gives way to the ericoid thicket, which is dominated by the Asteraceae (Psiadia, Helichrysum, Stoebe, Stenocline), Ericaceae (Erica, Agauria, Vaccinum), Podocarpaceae (Podocarpus), Rhamnaceae (Phylica) and Rubiaceae plant families. A wide diversity of lichens and bryophytes are represented. Small, damp peat-filled depressions harbor specialized, endemic plants, while rock outcrops host a drought-tolerant flora including Aloe, Kalanchoe and Helichrysum. Plants that grow on rock outcrops are less threatened than other ericoid thicket species because the rocky areas block the local passage of fire. One species of note is Sedum madagascariense (Crassulaceae), the only Malagasy representative of this predominately northern latitudinal genus.
On the major mountain massifs of Madagascar, species richness of numerous groups, such as birds, reptiles and amphibians decreases with altitude, while other taxa such as rodents and insectivores (Lipotyphla) show distinct mid-elevational bulges. However, at the elevations of the ericoid thicket there is a pronounced decrease in species richness for all of these groups (Goodman 1996, 1998, 1999, 2000).
The ecoregion has notable flora with a number of endemic species. There are over 150 vascular endemics on the Andringitra massif, including 25 species of orchids (Preston-Mafham 1991). While endemism on these mountains is very high at the species level, they often belong to widespread genera. For example, the true heathers in the genus Erica are also represented in the Mascarenes and East Africa, but have undergone amazing speciation in Madagascar (Guillaumet 1984, Dorr and Olivier 1999). There are other elements in the flora that link it with other high montane areas in Africa and Europe (Vuilleumier and Monasterio 1986). For example, the Andohariana Plateau on Andringitra harbors Gunnera perpensa, which is also found in the Ethiopian highlands, as well as species from temperate genera – Rubus, Ranunculus, Geranium, Alchemilla – which are also found in East Africa. Southern African species represented here include Kniphofia spp., and Stoebe spp. (Guillaumet 1984).
Until recently, very little was known about the composition of the vertebrate fauna within these montane habitats. A detailed survey of Andringitra Massif was carried out in 1993 (Goodman 1996), of Anjanaharibe-Sud in 1994 (Goodman 1998), of Andohahela in 1995 (Goodman 1999), and of Marojejy in 1996 (Goodman 2000). An extensive survey of the herpetofauna of Tsaratanana is planned to start in 2001 (C. Raxworthy, 2000 pers comm.). Two mammals are considered endemic to this ecoregion or the ecotone between it and the upper limit of the subhumid ecoregion, both of which have been described as new genera over the course of the past few years, Monticolomys koopmani, known from the massifs of Ankaratra, Andringitra and Andohahela, and Voalavo gymnocaudus, apparently endemic to the Marojejy-Anjanaharibe-Sud massifs. The upper reaches of Tsaratanana has never been surveyed for small mammals and holds the possibility of yielding some wonderful surprises. Other near endemic mammal species living at the middle to upper reaches of eastern mountains include the rice tenrec (Oryzorictes tetradactylus), found only in the south central highlands, highland streaked tenrec (Hemicentetes nigriceps)), several shrew-tenrecs (e.g. Microgale gracilis, M. gymnorhyncha, and M. monticola), and a species of tuft-tailed rat (Eliurus majori).
The ericoid thicket supports more than 10 species of endemic and near-endemic reptiles including the geckos, Millotisaurus mirabilis and Lygodactylus arnoulti. Andringitra also has a newly discovered endemic Gekkonidae, Lygodactylus montanus (Raxworthy and Nussbaum 1996). At least one amphibian (Boophis williamsi) is strictly endemic, and five other species are nearly endemic to the ecoregion. Two chameleon species are restricted to the high elevational zone of the Marojejy National Park (Calumma peyrierasi) and Andohahela National Park (C. capuroni). A new subspecies of day gecko (Phelsuma lineata) and a new species of plated lizard (Zonosaurus), as well as some frogs, were discovered in the upper reaches of the Tsaratanana Massif. Several endemic bird species such as Crossley’s ground-roller (Atelornis crossleyi), cryptic warbler (Cryptosylvicola randianasoloi) and yellow-bellied sunbird-asity (Neodrepanis hypoxantha) (EN) occur in the upper portion of these mountains.
Marojejy, Andringitra, Anjanaharibe-Sud, Tsaratanana and Andohahela are significant sites in that they are areas where there is an intact elevational cline from lowland forest through to ericoid thicket.
There has been notable degradation of the natural vegetation of this ecoregion over the past century. The major threat is conversion to highland cattle pasture, as has been done on the Plateau d’Andohariana on the Andringitra Massif. Associated with these pasturelands are regular burns to stimulate young grass growth. In Tsaratanana and Ankaratra, frequent burning has degraded significant areas of the montane habitat. However, to some extent, fires from lightning strikes may have always been part of the natural cycle in this region (C. Raxworthy, 2000 pers.comm.).
Three of the four most important montane areas represented in this ecoregion are included in protected areas: Tsaratanana, Andringitra and Marojejy, which comprise 171 km2. Further, as mentioned earlier, there are also small areas of montane habitat protected in the Anjanaharibe-Sud and Andohahela reserves. The Andringitra and Marojejy massifs have the best-preserved montane habitats. Ankaratra has only very small areas of native forest and no formal protection. The Manjakatompo Forest Station in the Ankaratra Massif includes 6.5 km2 of native forest, but this area has no management plan. A priority setting workshop held in 1995 identified the protection of high altitude ecosystems as essential to preserve unknown ecosystems and to protect water quality. The workshop also recognized the Ankaratra region as an area of high biodiversity importance (Ganzhorn et al. 1997).
The high elevation patches that make up this ecoregion are naturally fragmented due to the dispersed location of the mountain ranges throughout Madagascar. Recent studies of the vicariant distribution patterns of several montane amphibians and reptiles suggest that there was a period in Madagascar’s recent geological history during cool and dry glacial periods when there was a continuous belt of montane habitats between the Andringitra and Ankaratra massifs (e.g. Raxworthy and Nussbaum 1996).
Types and Severity of Threats
Fire is the biggest threat to the ericoid thicket habitats. Fires are lit to promote pasture for cattle grazing. This ecoregion is buffered, to some extent, by the surrounding forests of lower altitudes. However, these forests are experiencing increasing pressure from expansion of domestic animal rangelands. Further, these animals may disperse through their feces the seeds of introduced plants into ericoid thickets.
Justification of Ecoregion Delineation
The line work for this ecoregion follows Cornet’s (1974) montane bioclimate boundaries. It includes the summits of Marojejy, Tsaratanana, and Andringitra massifs above the 1,800 m contour.
Cornet, A. 1974. Essai cartographique bioclimatique à Madagascar, carte à 1/2'000'000 et notice explicative N° 55. Paris: ORSTOM.
Dorr, L. J., and E. G. H. Oliver. 1999. New taxa, names, and combinations in Erica (Ericaceae-Ericoideae) from Madagascar and the Comoro Islands. Adansonia, sér. 3, 21 (1): 75-91.
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.
Ganzhorn, J.U., Rakotosamimanana, B., Hannah, L., Hough, J., Iyer, L., Olivieri, S., Rajaobelina, S., Rodstrom, C., Tilkin, G. 1997. Priorities for Biodiversity Conservation in Madagascar. Primate Report 48-1, Germany.\
Goodman S. (ed.) 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. (ed.) 1998. A Floral and Faunal Inventory of the Réserve Spéciale d’Anjanaharibe-Sud, Madagascar: with reference to elevational variation. Fieldiana: Zoology, new series, 90: 1-246.
Goodman S. (ed.) 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. (ed.) 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.
Guillaumet, J.J. 1984. The vegetation: an extraordinary diversity. pp. 27 – 54 in A. Jolly, P. Oberlé, R. Albignac (eds.) Key environments: Madagascar. IUCN, Pergamon Press, New York.
Jolly, A., Oberlé, P. & Albignac, R. 1984. Key Environments: Madagascar. Pergamon Press, Oxford.
Langrand, O. 1990. Guide to the Birds of Madagascar Yale University Press, New Haven.
Langrand, O., and Goodman, S. M. 1997. Inventaire des oiseaux et des micro-mammifères des zones sommitales de la Réserve Naturelle Intégrale d'Andringitra. Akon'ny Ala 20: 39-54.
Nicoll, M.E. & Langrand, O. 1989. Madagascar: Revue de la conservation et des aires protégées. World Wide Fund for Nature, Gland, Switzerland.
Paulian, R., Betsch, J.M., Guillaumet, J.L., Blanc, C., and Griveaud, P. 1971. RCP 225. Etudes des écosystèmes montagnards dans la région malgache. I. Le massif de l'Andringitra. 1970-1971. Géomorphologie, climatologie et groupements végétaux. Bulletin de la Société d'Ecologie, II (2-3): 198-226.
Preston-Mafham, K. 1991. Madagascar: a natural history. Facts on File, Inc., New York, NY.
Raxworthy, C. J., & Nussbaum, R.A. 1996 Amphibians and reptiles of the Réserve Naturelle Intégrale d’Andringitra, Madagascar: a study of elevational distribution and local endemicity in Goodman S. M.(ed) 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, 85:158-170.
Saboureau, M. 1962. Note sur quelques températures relevées dans les réserves naturelles. Bulletin de l'Académie Malgache, nouvelle série, 40: 12-22.
Vuilleumier, F. & Monasterio, M. 1986. High Altitude Tropical Biogeography. New York: Oxford University Press.
Prepared by: Helen Crowley
Reviewed by: In progress