Shrubs

Dense high-mountain (over 2 000 m) thickets form communities of varying sizes found from the north to the south of the island, with certain common features which lend them a definite similarity in appearance and composition wherever they are found. This vegetation is made up, for the most part, of many species of heath (Ericaceae) ­ for example, briar (Philippia) ­ and Compositae (Psiadia, Senecio and Vernonia). Some species are common to several mountain areas, while some genera have different endemic species in almost every area, for example Heteromorpha spp. and Helichrysum spp. The genera Syncephalum, Vaccinium, Kosteletzkia, Dialypetalum, Nicodemia, Gentianothamnus, Radamaea, Terminalia, Aristea and Arthropodium are each represented by one or two endemic species. Here and there, some trees rise slightly above these thickets: Agauria salicifolia (Ericaceae), Ilex mitis, Cussonia bojeri, Alberta minor, Dodonaea madagascariensis, Tambourissa gracilis, Podocarpus rostratus, Vitex humbertii, Pittosporum chysophyllum, Faurea forficuliflora, Weinmannia spp., etc. There are almost no lianas and very few epiphytes. The moss and lichen layer is patchy and herbaceous plants fairly rare.

Frequent clearing and repeated fires have degraded the original forest into heath-like bushland of Helichrysum, Philippia, Agauria and Pteridium. On the other hand, degradation of the tropophilous forest results in "thicket woodland" with a broken dominant tree layer and a bushy layer, sometimes closed, sometimes less so.

The semi-arid southern zone, where annual rainfall is only 300 to 500 mm, is composed for the most part of plains and low plateaux of 200 to 400 m. It is covered by a xerophilous vegetation with a large number of species, although two main groups can be distinguished: one is the endemic family of Didiereaceae (Didierea madagascariensis, D. trollii, Alluaudia procea, Decaryia madagascariensis and Alluaudiopsis spp.), the other the Euphorbia genus (E. stenoclada and E. laroo). These are fairly small trees, not growing to more than 10 or 12 m, and do not form forests. Rather, together with some other more scattered species ­ Adansonia za, A. fony, Tetrapterocapon geayi, Dicoma incana, D. carbonaria, Gyrocarpus americanus, Maerua filiformis and Ficus marmorata ­ they tend to dominate thickets, which are fairly open on rocky soils, but more closed and impenetrable elsewhere. The woody species making up these thickets belong to many genera, including Acacia, Chadsia, Commiphora, Grewia, Solanum, Dichrostachys, Iphiona, Uncarina, Jatropha, Gardenia, Rhigozum, Cadaba, Megistostegium and Sclerocarya. Lianas are abundant, but not large. Trees, shrubs and lianas are partly leafless or have sparse evergreen or deciduous foliage. There are many thorn species, as well as species with thick, succulent leaves. Low plants are scattered over the ground, including grasses and various members of the Abutilon, small Aloe and Senecio genera. An unusual palm with tristichous leaves, Neodypsis decaryi, is confined to the eastern part of the southern zone, growing on the lower slopes of the first mountains along its edge.

The salt flats contain various genera typical of such ecological conditions, represented here by shrubs or grasses: Erblichia, Turnera, Flumbago, Salicornia, Salvadora angustifolia, Cryptostegia pluchea, etc. Scaevola koenigii, S. pluieri and Lumnitzera racemosa are common shrubs on dunes, helping to hold them in place.

last updated: Tuesday, January 13, 2004