Western Madagascan Vegetation

Plant Formations in the Western Madagascan BioProvince

Peter Martin Rhind

Western Madagascan Dry Deciduous Forests of Lateritic Clay These soils support the most luxuriant forests of east Madagascar and are usually characterized by endemic species such as Cordyla madagascariensis and Givotia madagascariensis, and a variety of endemic species of the genera Dalbergia and Ravensara. Other important trees include Stereospermum euphorioides and Xylia hildebrandtii. Most of the lianas belong to the Asclepiadaceae or genera such as Combretum, Dichapetalum, Landolphia and Tetracena, while most of the under story is characterized by species of the Euphorbiaceae, Fabaceae and Rubiaceae. A feature unique to these forests is the presence of a species Dracaena and a bamboo that have deciduous leaves.

Western Madagascan Dry Deciduous Forests of Sandy Soils The soils of these forests are derived from Jurassic and Cretaceous sandstones, but where they are very dry the forests are reduced to thicket. In the more fully developed forests the arborescent species usually display a three-layered structure. The upper layer or canopy consists of trees taller than 12 m, but comparatively few species are capable of reaching these heights. They normally include mainly endemic species such as Adansonia grandidieri, A. rubrostipa, A. za, (Malvaceae), Capurodendron greveanum (Sapotaceae), Cedrelopsis grevei (Rutaceae), Commiphora arafy, C. mafaidoha (Burseraceae), Cordyla madagascariensis (Fabaceae), Dalbergia purpuresens (Fabaceae), Delonix boiviniana (Fabaceae) and Hazomalania voyroni (Hernandiaceae). The middle layer grows to between 6-21 m high and frequently includes a number of evergreen species. Among the common taxa are endemic species such as Cedrelopsis gracilos, C. microfoliolata (Rutaceae), Fernandoa madagascariensis (Bignoniaceae), Operculicarya gummifera (Anacardiaceae) and Tetrapterocarpon geayi (Fabaceae). Below this layer is often dense undergrowth extending up to a height of 5 m. The common components here include genera such as Bauhinia, Byttneria, Chionanthus, Grewia, Rothmannia, Scurinega, Strychnos, together with the endemic Baudouinia (Fabaceae) and Cedrelopsis (Rutaceae). Drought resistance amongst these species takes various forms. Adansonia, Delonix and Givotia store water in their trunks (pachycauly), Gyrocarpus and Neobeguea do so in root bulbs or tubers, and most species have small, xeromorphic leaves. In the south of the BioProvince, the dryness is exemplified by the fact that most of the deciduous forests support large numbers of cactoid Euphorbia species, with Euphorbia enterophora reaching heights of 20 m. Other associated species here include Broussonetia (Chlorophora) graveana, Flacourtia indica, Hernandia voyroni, Protorhus deflexa and the endemic Adansonia grandidierii (Malvaceae). Moister soils are often characterized by Tamarindus indicus, but possibly more characteristic of wet sandy soils are species such as Berchemia discolor, Colubrina decipiens, Ficus trichopoda, Rhus perrieri, Stereospermum arcuatum, Terminalia species, Triculea africana, together with endemics like Astrotrichilia astrotricha (Meliaceae), Quivisianthe papinae (Meliaceae) and Rhopalocarpus lucidus (Sphaerosepalaceae).

Western Madagascan Dry Deciduous Forests of Calcareous Soils These forests generally have a lower stature than other east Madagascan dry forests. They also have fewer lianas and fewer evergreen species, while trees and shrubs with swollen stems such as Adansonia, Bathiaea and Harpagophytum are more abundant. Protorhus humbertii, P. perrieri, Sideroxylon collinum and species of Albizia and Erythrophysa are some of the more important canopy taxa. The endemic but widely Copyright © 2010 Peter Martin Rhind cultivated Delonix regia (Fabaceae) is also part of this community but is now very rare in the wild. A few larger trees occur as emergents such as the endemic Adansonia rubrostipa and A. za (Malvaceae) and the endemic Diospyros perrieri (Ebenaceae) but these tend to grow in deep fissures.

Further information required.

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