1 Background

1.1 The forest resource

The total area of Ghana is about 23.9 million ha. with a coastline of 567 km. It is divided into two main ecological zones: the High Forest Zone (HFZ) of southern Ghana covering 8.2 million ha (34%) and the northern Savannah Zone (SZ) covering 15.7 million ha (66%) (Table 1). The latter includes the Volta Lake, the largest artificial lake in Africa. These two zones merge into each other in the transition zone. There is also a very dry, Savannah zone in the South east corner.

The HFZ has a rich indigenous flora which satisfies the local population and contains species which are in great demand by the timber trade. In the SZ, most of the natural vegetation has been destroyed for agricultural purposes and there is a great shortage of wood for all purposes. Parts of the SZ are also heavily populated. The HFZ includes the wet and moist evergreen forest, moist and dry semi-deciduous forests (Hall and Swaine 1981, Hawthorne 1995, Swaine 1998).

Table 1. Vegetation zones and characteristics

Sources: FAO (1998) Agriculture in Ghana - Facts and Figures, MoA (1991)

NB: Sums may not tally due to rounding off.

Within The HFZ, the Moist Evergreen forest contains about 27% of the commercial/economic species, whilst the Moist Semi-Deciduous forest has up to 17% of such species. The Wet Evergreen is relatively poor in economic species (9%). The South-East outlier and the Southern Marginal contain no commercial timber.

1.1.1 Forest reserves

The forest reserves established by the Forestry Department (FD) total 266 in number. They cover about 20% of the HFZ (i.e. 1.63 million ha) and about 6% of the SZ (i.e. 0.88 million ha). The forest reserves have been classified into the following working circles (Table 2).

Table 2. Classification of forest reserves according to working circles

Source: MLF Master Plan (1996)

The permanent protection area consists of hill and swamp sanctuaries, areas of significant bio-diversity, those for security of seed provenance and fire protection areas. The convalescence areas are those with reduced stocking but which are considered capable of rehabilitation within one felling cycle. Conversion areas are in various stages of degradation, including grassland, and require planting for rehabilitation where there is inadequate regeneration. The FD considers these areas (c. 397,000 ha) to have potential for tree planting. They are mainly located in the Forest Transition Zone (FST). The condition of the reserved forests as assessed in 1995 is shown in Table 3.

Table 3. Area of forest reserves by condition and type

The above table illustrates a number of features of the patterns of disturbance. Almost exactly half of the reserved forest is in reasonable condition (1 - 3). However, only about 15% of the total forest reserve area has the lightest or no disturbance in recent history (1 - 2). There is a general increase in forest disturbance from wet to dry areas. This is a consequence of both greater fire damage and greater logging damage.

There are large areas of forest (condition 6) in the semi deciduous zones which have suffered excessively from fire and logging. A number of forest reserves in this condition class was not forested at the time of reservation but is rather savannah or open woodland reserves. Other condition 6 areas have been managed as plantations with no natural forest in them at the time of reservation.

1.1.2 Outside reserved forests

The extent of forestland outside the reserves is not accurately known. It has been estimated that there are few remaining areas of intact closed canopy forest outside forest reserves. The estimates vary from 374,000 ha (Nsenkyire 1992) to 270,000 ha (World Bank 1987) to 100,000 ha (IUCN 1992), while others (e.g. Hawthorne 1990, Norton 1991) estimate that closed canopy forest outside reserves may comprise as little as a fifth of the latter amount, much of it in small, scattered patches in swamps and sacred groves.

1.2 Climate

The HFZ has a two peak rainfall during April to July and September to November. The rainfall varies between 1,200 - 2,200 mm. There is a comparatively short dry season during January and February. The relative humidity is always high and is seldom below 85%.

The SZ has a one peak rainfall during August to September which is followed by a long dry season of four or five months when the humidity is low. The uni-modal rainfall (800-1200 mm) is erratic and frequently undependable. This coupled with the long dry harmattan winds makes tree planting and survival difficult.

1.3 Soils

Due to the high rainfall in the HFZ, the soils are highly leached and acidic in reaction (pH 4.0 - 5.5). They are low in cation exchange capacity, available phosphorus, nitrogen and organic matter. The degree of acidity and hydration with a consequent yellow appearance of the soil increases with rainfall. In the wettest zones, the soils are very infertile, strongly acid and often have high aluminium content. Inundation is common on lower catena sites especially of the lower profiles. The relatively short dry seasons coupled with the high humidity of the WE, ME and MS forest zones reduces the risk of fire in forest plantations. In the FST zone, where the soils are derived from basement complex rocks, they tend to be deeper, with high concentration of organic matter and nutrients and heavier textured. These are the best areas for tree growth.

The principal physiographic feature of HFZ is the gentle undulations - a dissected peneplain -remnants of which are frequently capped by ferrous crust of drift material which give rise to poor soils. Over these gently rolling hills occur a characteristic sequence of earth comprising sedentary soils on the summits and middle slopes with colluvial soils on the lower slopes and alluvial soils in the valley bottoms.

The HFZ supports two thirds of the population of 17 million. Most of the country's economic activities are concentrated in this zone. They include tree cash crops (cocoa, oil palm, para rubber, coconut), mining (e.g. gold, bauxite, manganese) as well as forest industries.

The Savannah Zone

The soils here are often light textured and relatively poor in fertility, although usually less acid than in the wetter zones. Except for the alluvial soils and the clays of the valley bottoms soils throughout the area are shallow with thin topsoils and unsuited for deep rooted crops. The soils rarely exceed 150 cm or 180 cm in depth. Most of the soils in this zone are subject to laterisation at about 30 to 60 cm below the soil surface which leads to seasonal flooding of the soil profile as well as soil erosion. The topography is often flat or gently undulating and hence it is difficult to delineate zones which are sensitive to flooding. Careful site appraisals are therefore required. The areas of soils derived from metamorphic rocks are mainly in demand as agricultural soils. The main economic activities are annual crop (cereals, root crops and cotton) and livestock production.

Soil fertility

Numerous studies have shown that in Ghana the bulk of the soil organic matter and nutrients are bound within the few centimetres of the topsoil below which there is drastic decrease in these. It is also known that the soils lose their fertility very fast when cultivated. Hence the application of especially nitrogen and phosphorus is necessary for the maintenance of the fertility of the soil (Asiamah 1988).

Soil conservation

The upland soils are fragile and susceptible to soil erosion hazards when large tracts are cleared. It is therefore important to adopt practices that will conserve the soils at all times such as strip cropping, cover cropping, as well as ploughing, ridging along the contours and agro-forestry.

Soil survey

It is important that soil investigations are carried out in detail to determine the soil limitations before embarking on any forest plantation project. This will facilitate the implementation of the necessary curative measures necessary to offset any soil condition that may adversely affect the growth of the trees. The fitting of the appropriate tree species to site would also be made much easier.

1.4 Land use

The land use in Ghana can be grouped into seven major categories (Table 4).

Table 4 Broad land use categories in Ghana

Source: MLF, Ghana.

*Includes human settlements, transportation infrastructure and utilities