2.1. Phytogeography of the country
2.2. Utilization patterns of forest species
2.3. Threats
According to FAO/UNEP (1981), wood and shrub-lands occur on the largest part of the Guinea, Sudan and Sahel zones of Nigeria. Tree vegetation is generally rare in the Sudan and Sahel zones while it is more common in the Guinea and the derived savanna zones. The vegetation of these two latter zones is cursively presented as follows: “In the Guinea zone, Acacia spp are relatively rare, and trees which are completely bare in the dry season are rare. Large areas in the northern and median Guinea zones are dominated by Isoberlinia doka, and one distinction between the northern and the median guinea zones is the association of Uapaca togoensis and Bridelia ferruginea in the latter but not in the former. In the southern Guinea zones Isoberlinia doka is much rarer, and Daniellia oliveri is a very abundant tree (though it occurs in the others zones). The tree vegetation of the derived savanna zone is broadly similar to that of the southern Guinea zone, though the grass composition differs”.
The broadleaved woodland is mainly composed of Annona senegalensis, Vitellaria paradoxa, Cussonia barteri, Daniellia oliveri, Isoberlinia doka, Lannea acida, Monotes kerstingii, Prosopis africana, Terminalia avicennioides, Uapaca togoensis.
The Sahel zone is characterized by small, widely dispersed, small-leaved trees, particularly Acacia species such as Acacia tortilis subsp raddiana, Acacia seyal, Acacia nilotica and in the northern parts Acacia Senegal. A fairly high proportion of the trees are deciduous in the dry season. Some characteristic species (through not confined to this zone) are Anogeissus leiocarpus, Sclerocarya birrea, Combretum micranthum and Guiera senegalensis.
Interpretation of radar imagery distinguishes the following (predominantly) shrub vegetation types:
Within the Northern dry region of Nigeria dietary habits are similar with slight variations influenced by cultural backgrounds. All the trees selectively protected in the parklands provide one or combinations of the following tangible and intangible services: food items (edible fruits, nuts, leaves, flowers, livestock fodder, fuel wood, medicine, aesthetics, shade, agricultural tools and cooking utensils, avenues, and other services such as ropes, fibres, tannin, manure, latex gums and oils). Patterns of utilization are quite similar for the entire region and fall within various headings mentioned above. However more trees are protected for their medicinal values and food.. Fuel wood (fuel energy and heating) are equally of importance. With the exception of Adansonia digitata and Calotropis procera, all species are utilized as fuel wood obtained from prunings, complete felling or pollarding. All the component parts of the tree featured daily and regularly in the food security and dietary habits of the people with some quantity for market as income. Many of the cattle farmers still rely substantially on these trees for lopped fodder, while the fruits, shells are also fed to the livestock. Shade provision is unique with Parkia biglobosa, Adansonia digitata and Tamarindus indica along side with Mangifera indica due to their broad canopies. Currently, income from the sales of fruits of Parkia biglobosa, Vitellaria paradoxa, Adansonia digitata, Tamarindus indica and Balanites aegyptiaca and Acacia seyal account for 30 - 45% of the farmers income. Commonly known exotics including Mangifera indica, Anacardium occidentale and Azadirachta indica are on a par with most the indigenous trees and are equally protected. Soil fertility sustenance is secondary role from some of these trees through litter falls.
Table 1: Different uses of forest species
|
Ecological zone |
Item |
Percentage representation (%) |
|
Zone A (Zaria) southern. Guinea savanna zone
|
Medicine |
50 |
|
Food |
35 |
|
|
Fuelwood |
20 |
|
|
Industrial |
<5 |
|
|
Soil conservation |
1-3 |
|
|
Zone B (Kano-Jigawa) central. Northern Sudan zone
|
Medicine |
45-50 |
|
Food |
35-40 |
|
|
Fuelwood |
10-15 |
|
|
Industrial |
<5 |
|
|
Soil conservation |
1-2 |
|
|
Zone C (Sokoto-Bornu) Northern. Semi arid region.
|
Medicine |
45-50 |
|
Food |
25-40 |
|
|
Fuelwood |
10-15 |
|
|
Industrial |
5-8 |
|
|
Soil conservation |
1-3 |
Inadequate fuel wood supply, low precipitation, and desertification encroachments from the Sahel the conservation of forest genetic resources in the Northern semi-arid region of Nigeria. Demographic pressures and rapid urbanization are not perceived as major culprits. The increasing rate of uncontrolled over-exploitation of many of the woody trees species in the region particularly for fuel wood energy is becoming an area of major concern. The demand for poles and small timber and shifting cultivation are minor sources of threats. The presence of Azadirachta indica, Anogeissus leiocarpus and Piliostigma thonningii in most of the parklands is significant in meeting fuel wood supply along with the exotics. Low income levels of most inhabitants predispose them from having access to alternative sources of energy (kerosene and domestic gas). Generally, the parklands are ageing and are less dense compared to what they were two decades ago. In some cases certain size classes for these woody tree species are difficult to assess due to poor regeneration. Other recognizable threats to forest genetic resources within the region include over-grazing, which encourages sand dunes, and wind erosion. In many areas within the region, the absence of enrichment planting is visible for most indigenous woody trees species.
