Madagascar ericoid thickets

Forests (main)

Published: June 17, 2015, 4:30 pm

Topics:

Ecoregions (main) Conservation Biology (main) Biodiversity (main) Ecology (main) Forests (main)

Parc National de Marojezy, Madagascar. Source: Steve M. Goodman

WWF Terrestrial Ecoregions Collection

The fragile montane habitats of the Madagascar ericoid thickets of Madagascar are naturally isolated zones which are threatened mostly by man-made fires to expand cattle pasture. Located on the upper slopes of Madagascar's four major mountain massifs, the ericoid thickets have only recently been explored biologically. There is presently much to be discovered about the biodiversity of this region and how it relates to Madagascar's original forest cover. However, it is established that similar to other ecoregions on Madagascar there are a number of narrowly distributed endemic species and recent biological inventories of the ericoid thicket has identified further endemic species. The Madagascar ericoid thickets is within the Montane grasslands and shrublands biome in the Afrotropics Realm.

Location and general description

Source: World Wildlife Fund

This disjunctive ecoregion includes the ericoid thicket habitats found above approximately 1800 metres on the upper slopes of Madagascar's four major massifs (listed from north to south): Tsaratanana (2876 m), Marojejy (2133 m), Ankaratra (2643 m), and Andringitra (2658 m). Tsaratanana is the most northern massif, at 14^o latitude and Andringitra the most southern, at 22^o latitude. The transition from montane sclerophyllous forest to ericoid thicket may occur at different elevations. On Tsaratanana montane sclerophyllous forest exists up to about 2500 m, and then transitions to ericoid thicket; moreover, on these other three massifs the ericoid thicket commences immediately below 2000 m. The Anjanaharibe-Sud Special Reserve in the north and Andohahela National Park in the extreme southeast contain small areas of ericoid thicket above 1950 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^oC. Further daily temperature extremes in the summital zone range over 30^oC. Rainfall is probably more than 2500 millimetres per annum 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 effect may be short-lived. The fundamental geology of the massifs is metamorphic and igneous Precambrian basement rock, overlain by thin, nutrient poor soils.

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.

Biodiversity features

Central Plateau, Madagascar. Source: Boerge Petterson

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. This ecoregion manifests a modest number of vertebrate taxa, with only 107 species present.The ecoregion has notable flora with a number of endemic species.

Flora

There are over 150 vascular plant endemics on the Andringitra massif, including 25 species of orchids. While endemism on these [[mountain]s] 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. There are other elements in the flora that link it with other high montane areas in Africa and Europe. For example, the Andohariana Plateau on Andringitra harbors Gunnera perpensa, which is also found in the Ethiopian highlands, as well as species recently 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.

Marojejy, Andringitra, Anjanaharibe-Sud, Tsaratanana and Andohahela are significant sites in that they are areas where there is an intactThe condition of an ecological habitat being an undisturbed or natural environment elevational cline from lowland forest through to ericoid thicket.

Fauna

Until the 1990s, 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, of Anjanaharibe-Sud in 1994, of Andohahela in 1995 and of Marojejy in 1996. An extensive survey of the herpetofauna of Tsaratanana was begun in 2001. 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 have not been systematically surveyed for small mammals, and thus this area holds the possibility of yielding some great 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 ten 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. 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 anuranAn amphibian that has limbs but no tail (includes all frogs and toads) taxa, were discovered in the upper reaches of the Tsaratanana Massif.

Example frog species found in this ecoregion are: the ecoregion endemic Ankafana Madagascar frog (Mantidactylus curtus); ecoregion endemic Dotted Madagascar frog (Guibemantis punctatus); the Endangered Andringitra Madagascar frog (Mantidactylus madecassus); and the Near Threatened Betsileo bright-eyed frog (Boophis rhodoscelis).

Several endemic bird species such as Crossley's ground-roller (Atelornis crossleyi), Cryptic warbler (Cryptosylvicola randrianasoloi) and Yellow-bellied sunbird-asity (Neodrepanis hypoxantha) occur in the upper portions of these mountains.

Ecological status

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.

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.

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.

Ecological 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 montane bioclimate boundaries. It includes the summits of Marojejy, Tsaratanana, and Andringitra massifs above the 1800 metre contour. The Madagascar ericoid thickets are accorded the ecocode AT1011 by the World Wildlife Fund.

Neighbouring ecoregions

The Madagascar ericoid thickets have tangency with only a single other ecoregion; in fact the six disjunctive elements of the Madagascar ericoid thickets are completely surrounded by the Madagascar subhumid forests.

References

• Cornet, A. 1974. Essai cartographique bioclimatique à Madagascar, carte à 1/2'000'000 et notice explicative N 55. Paris: ORSTOM.
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• 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 la ORSTOM, Paris.
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• 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.
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• 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.

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Citation

World Wildlife Fund, C. Michael Hogan (2015). Madagascar Ericoid Thickets. Encyclopedia of Earth. National Council for Science and Environment. Washinton DC  . (2015). Madagascar ericoid thickets. Retrieved from http://editors.eol.org/eoearth/wiki/Madagascar_ericoid_thickets