Natural forest formations
Forest cover map
The archipelago of the Republic of Cape Verde covers 4 033 km2 in the Atlantic Ocean and is composed of ten main islands and eight smaller ones. The windward group (those exposed to the trade winds) lies to the northeast, while the leeward group lies further south and includes Santiago, the largest and most densely populated island, and Praia, the capital. The archipelago is essentially of volcanic origin (basaltic rocks) and has a very pronounced relief as a result of volcanic activity and erosion, culminating in the crater on Fogo Island at 2 829 m. From a physiographical point of view, the archipelago can be divided into two groups: islands with a marked relief (reaching an altitude of at least 1 000 m) and relatively flat islands (not exceeding 500 m). The soil is generally little evolved, shallow, stony and permeable. Poor in organic matter but rich in mineral elements, it is in general highly eroded.
Thus, relief and exposure to prevailing winds (the southeasterly monsoon and especially the northeasterly trade winds), rather than position in the archipelago, are the factors that determine the microclimate of each island, from the total aridity of the flat ones to the very wet slopes in the northeast of Santo Antão. A common feature is the extreme irregularity of rainfall, with very marked variations from year to year and place to place, so that there are sometimes several consecutive critically dry years. However, the archipelago can be divided into four broad ecological zones (arid, semi-arid, subhumid and humid), according to altitude and average annual rainfall, which ranges from 200 mm in arid coastal zones to over 1 000 mm in humid high zones.
The natural plant associations are in a state of advanced degradation, and forest and shrub cover is basically composed of man-made plantations, mainly of introduced species. The combined action of climate and human interference (firewood gathering, the extension of agricultural land, and overgrazing, especially by goats) has seriously affected all the natural vegetation.
The natural vegetation contains a predominance of Sahelian-type species and has been expanded by arrivals from the African continent. Some 650 species of phanerogam, about half of them indigenous, were recorded in the first half of the last century. The flora is thus relatively poor, although it includes several distinctive species (for example Sideroxylon marmulana, a woody species in moist ravines exposed to the trade winds).
However, it is hard to distinguish true plant associations (with a clear floristic composition) in the archipelago, for two reasons:
the destruction of the original flora, together with an extreme climate and very irregular rainfall, does not allow the permanent establishment of indigenous species;
human, and especially animal, interference is constantly changing the balance, causing a state of advanced degradation of natural groupings.
The above map is an extract from the Global Forest Cover map produced as part of FRA 2000. Please refer to FRA Working Paper 19 for a background to the production of the map.
Nevertheless, the few natural forest associations found in the archipelago are mostly very open formations. Apart from these, there are formations in arid and very arid zones (altitude up to 200 m, annual rainfall under 200 mm) on the flatter islands (Sal, Boa Vista and Maio). These are very poor from the point of view of species, and are basically grass steppes (Acanthospermum hispidum, Alternanthera caracasana, etc.) of varying thicknesses on which isolated trees and shrubs -in most cases introduced species ( Acacia albida, A. nilotica, Ziziphus mauritania, etc.)- appear from time to time.
Associations in semi-arid zones (altitude 200-500 m, annual rainfall 200-400 mm) include woody species originating in other ecological zones: Tamarindus indica, Pithecelobium dulce, Z iziphus mauritania, Acacia nilotica, Lantana camara, Ficus spp., etc. This natural tree vegetation is sparse and is composed mostly of naturalized species (i.e. species introduced many years ago that have adapted to the ecological conditions and reproduce spontaneously). The whole of this zone suffers from human interference, primarily overgrazing.
Associations in subhumid zones (altitude 400-900 m, annual rainfall 400-600 mm) are groupings whose composition varies, depending on edaphic conditions and micro-climates. They include many endemic herbaceous species ( Tornabenea tenuissima, Euphorbia tuckeyana, etc.), while the most common woody species are Dracaena draco, Sideroxylon marmulano var. edulis, Khaya senegalensis, Grevillea robusta, Periploca chevalieri and Echium stenosiphon. These zones are mainly agricultural, so that the forest cover has receded considerably, if not entirely disappeared. At present, tree and woody shrub species are scattered sparsely over the farmland.
Associations in humid zones (altitude over 1 000 m, annual rainfall over 900 mm) are found mainly on mountain slopes. Many endemic herbaceous species (e.g. Campanula jacobaea) and tall grasses are predominant. Some shrub species make it a multi-storeyed forest (with a dominant storey of about 2 m). Associations of Euphorbia tuckeyana, Nauplius smithii, Periploca chevalieri, etc., are also found. At higher altitudes, Euphorbia tuckeyana is a bushy species forming mountain steppes at between 800 and 1 800 m. Furcraea gigantea, an agave introduced by the Portuguese, is found in steep rocky areas. The largest number of endemic species is found in the humid zones (e.g. Euphorbia tuckeyana, Echium stenosiphon, Nauplius smithii). However, the various forest plantations established at these levels mean that in some places the natural vegetation has been giving way to the new introduced or naturalized species.
Forest associations in valley bottoms usually consist of tall naturalized forest species: Acacia albida, A. nilotica, A. farnesiana, Ficus gnaphalocarpa, Phoenix atlantica, Tamarix canariensis, etc. Oases contain the endemic palm Phoenix atlantica, as well as Acacia nilotica stands, introduced from Senegal at an earlier date. In the least degraded zones, Acacia albida is still found, often confined to ravines, and in a few places Tamarindus indica .
The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.
Map source: Global Forest Resources Assessment 2000, base map: ESRI