Broadleaved forests

The eastern rainforest accounts for over half the country's closed forests, extending mostly unbroken from north to south and rising from the coast to the central highlands and mountains. It tends to be a heterogeneous forest between 25 and 30 m in height, made up of over 150 species mixed together, with no dominating species. The large trees rarely grow straight; they have many branches and are covered with epiphytes, mosses and lichens. There are no well-defined layers but rather a very dense, closely-mixed complex. The intermediate species grow much straighter and have a better shape than the dominant species. The understorey is very thick and often contains many lianas and bamboo-lianas. Generally speaking, the forest is wetter and richer toward the north and toward the coast. Its vigour and quality decline further south and especially further west, largely as a result of rainfall and temperature. Rainfall can reach 3 000 mm or even more in the north, but is considerably less than 2 000 mm in the south, and there is a similar difference moving from east to west on the eastern slope up to an altitude of 1 000 m. Four main types of eastern forest can be distinguished, depending on altitude:

  • Coastal forest occupies a fairly narrow strip from a few hundred metres to several kilometres wide, rarely over 10 m in altitude, almost completely on sand, mostly flat or slightly undulating, with swamps and rivers. Many species typical of the eastern region in general are found here, but also Afzelia bijuga, Calophyllum inophyllum, Trachylobium verrucosum and Diospyros spp. as well as the Chrysalidocarpus lutescens palm. Only a few dozen hectares of this type of forest are now left.
  • Hill and cliff forest stretches from the low valleys to an average altitude of 800 m. In the lower areas ­ up to 300 to 400 m ­ it is receding rapidly except for some areas in the north-east. The clay soil and the gentle, fairly unbroken undulation of the wide valleys and plains have allowed intensive cropping (coffee, banana, etc.). Species found in the few hundred thousand hectares of intact or only slightly degraded forest are very much the same as those on the coast, although Afzelia bijuga, Trachylobium verruscosum, Calophyllum spp. and Uapaca spp. are somewhat rarer, and Canarium spp. and Dalbergia spp. are more frequent. Higher altitude species found on cliffs between 400 and 800 m become increasingly frequent; given its relief ­ V-shaped valleys with many rivers, rapids and waterfalls. The higher part is still basically untouched and represents the most unexploited forest of the eastern strip. Ocotea spp., Revensara spp., Gambeya spp., Canarium madagascariensis, Syzygium spp., Symphonia spp., Sloanea spp., Dalbergia spp., Uapaca spp., Sarcolaena codomoclamys, Leptolaena bernieri and Schizolaena viscosa are the most frequent species, along with the traveller's tree (Ravanala madagascariensis) and the Ochlandra capitata bamboo. null
    • Highland forest (between 800 and 1 300 m) survives only in a few patches, most often in mountain depressions or along water courses. It differs especially from the hill and cliff forest in the presence of a single upper storey that forms a high forest about 20 to 25 m tall. The most frequent genera are Tambourissa, Weinmannia, Symphonia, Dombeya, Dilobeia, Dalbergia, Canarium, Vernonia, Diospyros, Eugenia, Protorhus, Grewia and Brachylaena. The undergrowth is also thicker and more impenetrable, with a well-developed moss and lichen layer, interspersed with low shrubs, large lianas and monocarpic bamboos. This forest has suffered extensive exploitation and clearing.
    • Lichen woodland, found at altitudes that are usually cloudy between about 1 300 and 2 000 m, and mainly with an eastern exposure, is made up of a high forest of fairly low (10 to 12 m) sclerophyllous trees with many branches forming a single storey above a shrubby undergrowth, often blending into it. The only surviving examples are now scattered as a result of frequent fires. The most common species here are Dicorypha viticoid, Tina isoneura, Alberta minor and Rhus taratana. The tree storey also contains Ilex mitis, bamboos such as Arundinaria spp. and Ochlandra spp., and conifers (Podocarpus). The moss and lichen storey is very thick, often several dozen centimetres. Trees and shrubs are draped in epiphytes.

    The low sclerophyllous forest on the western slopes of the eastern mountain chain has almost completely disappeared as a result of periodic fires. The rare and shrinking examples of this evergreen forest have a low upper storey (10 to 12 m), composed mainly of a large number of arborescent species such as Uapaca bojeri, Leptolaena pauciflora, Sarcolaena oblongifolia, Asteropeia densiflora, Agauria salicifolia, Dodonaea madagascariensis, Faurea forficuliflora, Dicoma incana, Rhus taratana, Protorhus buxifolia and Cussonia bojeri. The shrubs in the undergrowth are mainly Philippia spp., Vaccinium spp., Helichrysum spp., etc. Lianas are fairly numerous, but tend to lack vigour, epiphytes are rare, and there are no bamboos. There is no mossy layer, and only scattered low perennial plants.

    The western tropophilous forest comprises several large stands (Bara, Manasamody, Bongolava, Ankarafantsika, between Analalava and Ambato-Boeni and between Antsalova and the Mangoky, as well as along this river) and many small stands surrounded by expanding savannah. Bush fires and uncontrolled and often excessive logging are steadily eating away at this forest, which is rapidly disappearing everywhere. Rainfall is about 1 500 mm in the north-east, steadily decreasing to 600 mm in the south-west, but the special feature of this low-altitude "dry" zone is a long dry season lasting between five and seven months. The leaves fall during this period, unlike those of the closed forests of the eastern zone. One of the most common species, especially on calcareous soil, is Hildegardia erythrosiphon, a tall tree, easily recognisable by its habit, with its outspread, almost horizontal branches. As in the eastern forest, the high forest is generally thick, heterogeneous and rich in species, though to a lesser degree. The dominant trees do not exceed 20 to 25 m in the north and 15 to 20 m further south, although they can be quite broad. Nevertheless, their numbers and volume per hectare are lower than in the north-eastern forests. The undergrowth is very thick, but the herbaceous vegetation tends to be poor. Epiphytes are rare. The western forests have been divided into four categories, based on the wide variety in terrain:

  • On gneiss or basalt lateritic clay, where humus is thicker than in the east or centre, the native forest is a fairly open high forest reaching 12 to 15 m, with large trees scattered here and there. Dalbergia, Stereospermum, Givotia madagascariensis, Xylia hildebrandtii and Cordyla madagascariensis are found here. There are many lianas, but no mosses or epiphytes. These stands are mainly confined to the north-east.
  • Forests on sandy soils are fairly similar to those on crystalline ground, varying according to soil moisture. Tamarindus indica is frequent species on relatively moist soils and can cover large areas, for example on the Cretaceous sand of Ankarafantsika. On the usually dry soils of the southern zone, leafless arborescent species of Euphorbia that can reach 15 to 20 m (E. enterophora) are mixed with high-forest deciduous species (Chlorophora greveana, Securinega seyrigii, Hernandia voyroni, Protorhus deflexa and Flacourtia ramontchii), notably in the central Fiherenana valley.
  • Forests on the calcareous highlands contain many species exclusive to them. The high forest, reaching 12 to 15 m and dominated by some large trees of the Adansonia, Diospyros and Acacia genera, is made up particularly of Protorhus perrieri, P. humberti, Erythrophysa spp., Albizia polyphylla, A. greveana, Sideroxylon collinum and Poinciana regia. There are no palms, ferns or epiphytes. The undergrowth is made up of shrubs and the lianas are often vigorous.

Forests on alluvial soil and alongside watercourses have been almost totally destroyed, initially by clearing for crops, and then, after invasion by savannah grasses, by repeated fires during the dry season. The rare remnants have a high forest of 25 to 30 m containing both deciduous (Canarum multiflorum and Khaya madagascariensis) and evergreen (Eugenia sakalavanum) species. Terminalia mantaly, T. tricristata, Ficus sakalavanum, Albizia bernieri and A. boinensis are also found here. Two large palms, Medemia nobilis and Borassus madagascariensis, and Treculia perrieri are part of these formations. Undergrowth is sparse or absent.

On saline alluvial soils directly exposed to the tides, mangroves are found in the far north near Diégo-Suarez and then continue to just south of Morombe, almost exclusively on the western coast, with the following species: Rhizophora mucronata, Bruguiera gymnorhiza, Ceriops boiviniana, Avicennia officinalis and Sonneratio alba. These species are often mixed with Heritiera littoralis, Terminalia catappa, Thespesia populnea, Derris uliginosa and, on the edge of these stands, Casuarina equisetifolia, as well as a large fern, Acrostichum aureum. The largest stand is found along the Betsiboka estuary. Mangroves are of considerable economic value and are thus extensively exploited (tannin bark from the Rhizophora, Ceriops and Bruguiera genera, and firewood), easily regenerating under normal conditions.

Some swampy areas in the west often contain relatively pure stands, such as raffias on clay-based depressions, where the Raphia ruffia palm occurs in almost pure stands with two ferns, Nephrodium unitum and N. cucullatum. On crystalline soil or where swamps are temporary, Ficus sakalavanum is found together with Phragmites. On the other hand, Typha angustifolia and the fern Acrostichum aureum proliferate on calcareous ground.

Relics of gallery forests very similar to those along western rivers are found along water courses in the semi-arid southern zone. The main species found here include Colvillea racemosa, Eugenia sakalavanum, Protorhus grandidieri, Ficus spp. and Tamarindus indica, most of them evergreen.

The Malagasy term savoka refers to secondary formations varying widely in appearance and composition and following directly on closed forest destroyed by shifting cultivation (felling, followed by burning of what has been felled). There are few species capable of occupying the land immediately after the temporary cultivation has ceased, and they form almost impenetrable and generally nearly pure stands. In the east, they are mainly bamboos (Ochlandra capitata and Arundo madagascariensis), Afromomum angustifolium, Daniellia ensifolia, Psiadia altissima, Philippia spp., Solanum auriculatum and Harungana madagascariensis. The last is a small tree forming secondary stands that cover large areas and resembles an almost pure forest with an undergrowth of Pteridium aquilinum and Lycopodium clavatum, mixed with a small number of indigenous species such as Tristemma virusanum or naturalised species such as Psidium gujava and various species of Citrus, etc. Further toward the centre, medium-altitude (800 to 1 300 m) savokas contain Solanum auriculatum, Harungana madagascariensis, Ravenala madagascariensis, Trema orientalis, Dombeya spp. and bamboos. Savokas would revert to forest if farmers did not destroy them when primary forest starts to become scarce and they want to establish new crops or increase the area of savannah as grazing land for cattle. These secondary formations are very widespread in the eastern part of the country.

last updated: Monday, January 12, 2004