Broadleaved

In the eastern zone, after prolonged cropping, savoka is invaded by grasses that burn very easily, leading to a reduction in secondary woody vegetation. The resulting savannah is therefore man-made and not due to climate. It is covered by tall grasses, Hyparrhenia rufa being dominant on good soils, and Eleusine indica and Pennisetum spp. on degraded land. It can reach heights of 1.5 to 3 m. There are a few species that resist repeated fires. For instance, Ravenala madagascariensis is able to withstand fires and is thus found dotted about the countryside. Some species from the low sclerophyllous forest found on western slopes, such as Uapaca bojeri, have spread into the fairly recent secondary savannah, although they eventually disappear because of the repeated fires that destroy the young trees ­ especially Dicoma incana, Stereospermum euphorioides and Acidocarpus excelsus. However, older and more widespread exemplars of other species ­ for example Brachylaena ramiflora and a Nuxia and a Ficus species ­ have resisted the fires, thanks to their virtually incombustible bark and the absence of grasses under their leafy cover.

The savannah in the western zone is made up chiefly of grasses that are taller and generally thicker than those in the eastern or central zones (Hyparrhenia spp.). On fertile soil, where grasses grow more strongly and fires have thus been fiercer, there are no trees or shrubs. On dry, sandy or stony soils, where grasses are thinner, the savannah is dotted with trees or shrubs. Again, this is a man-made formation. Even so, the western forest does contain a number of fire-resistant woody species that are even capable of multiplying within grassy formations when the latter start to spread. Various species of palm are particularly fire-resistant, the most remarkable and the most common in most of the zone being Medemia nobilis. Another palm that proliferates especially on sandy soil is Hyphaena shatan, while Borassus madagascariensis is more restricted in range. Apart from these palms, the other trees most commonly found in the western savannahs are (in decreasing order) Sclerocarya caffra, Acridocarpus excelsus, Stereospermum euphorioides and Incoma incana, as well as some shrubs, although most of the latter are eliminated by the frequent fires: Strychnos spinosa, Gymnosperia linearis, Bridelia pervilleana, Terminalia seyrigii and Grewia triflora.

last updated: Wednesday, October 6, 2004