Part I
REGIONAL SYNTHESIS (continued)

Chapter III
FOREST RESOURCES OF TROPICAL AFRICA (continued)

1. PRESENT SITUATION (continued)

TABLE 5c - Areas of established plantations estimated at end 1980
All plantations
(in thousand ha)

Some plantations areas had been underestimated for some countries; this is particularly the case of Sudan. This shows that it is very difficult in some instances to precisely assess the areas actually covered by plantations at the end of 1980 and also to distribute these areas between the various classes of industrial and non-industrial plantations.

East Africa and Madagascar contain two thirds of the total area established in tropical Africa and 94% of the softwood ones. Concerning industrial plantations, west Africa possesses 56% of plantations with species other than fast-growing ones (PHL1), of which one third has been established during the last five years. Concerning fast-growing hardwood species, Nigeria and Angola contain more than two thirds of the established plantations, with Tanzania Congo and Zimbabwe being the only three other countries with an area close or higher than 10 000 ha. 96% of industrial softwood plantations are located in east Africa. Kenya (150 000 ha) and Madagascar (112 000 ha) contain about half of the established plantations. As for non-industrial plantations Madagascar (154 000 ha), Sudan (129 700 ha), Ethiopia (97 000 ha) and Angola (89 200 ha) account for 60% of the established areas.

The total area of plantations in tropical Africa is very low: 1.18 million ha planted for a total population of 343.5 million people i.e. 0.003 ha per capita. Establishment of non-industrial plantations, more particularly of those for fuelwood and building poles (about 500 000 ha), is clearly insufficient when compared to current needs. Assuming an average productivity of 10 steres per ha and per year, 5 million steres of fuelwood are thus available i.e. 0.04 stere/inhabitant/year. Availability of fuelwood from existing forest plantations are insignificant in the vast majority of countries. Madagascar, Kenya, Sudan and Angola are the only ones which contain areas of significant importance compared to the needs of the population.

1.2.3 Plantation characteristics

General indications on plantation techniques

Distinction must be made between plantations in closed forest areas and those in woodlands and savannas when discussing plantation establishment techniques. The former ones require either a complete clearing of the forest cover or a poisoning of the natural forest which is thus likely to be destroyed more or less rapidly. Foresters, constrained by the lack of powerful clearing equipment for completely eliminating the forest vegetation, profited from agricultural clearings to establish plantations together with the crops according to a method developed in tropical Asia called “taungya”. The first plantations of teak, Gmelina and various local species were established in western Africa by this method. Limba was planted in Zaire and Congo on a 6 × 7 or 12 × 14 m spacing after destruction of the forests by clearing of the undergrowth, felling of the small trees, girdling of the large ones and burning of the remaining ones at the end of the dry season. The regrowth method (“recrû”) developed in French-speaking Africa, is somewhat similar to begin with but the regrowth, instead of being systematically cleared, is controlled to protect the ground and envelop the boles of planted trees. In Gabon okoumé plantations were carried out using tractors to fell trees less than 30 cm DBH, while big trees were girdled and poisoned. Windrows were formed in parallel strips and plantations established with a spacing of 5 × 4 m. Preference was given to planting in forests gradually cleared because of the high cost of mechanized clearing and the fragile nature of some species. After some trials of closed plantations under a forest gradually destroyed by girdling (“Martineau” method in Ivory Coast), line planting (“en layons”) was developed with variable spacing (10 to 25 m) with tree distance between 3 to 6 m along the lines. Lack of follow-up of these plantations where the original cover was kept too long and sometimes never cleared, lead to many failures. However, the modern forms of this type of plantations - undergrowth method (“sous-bois”) - were used successfully with Entandophragma, Khaya ivorensis and Tarrietia utilis. This technique is difficult and requires special attention for each stem and therefore demands high technical skill from the foresters and a large number of interventions. This is why when species can tolerate complete exposure from their early years, preference is now given to planting after total forest clearing with bulldozers and windrowing. Plantations established in this way may be tended mechanically later on. This technique has been applied with the following species: Khaya ivorensis, Tarrietia utilis, Terminalia superba, T. ivorensis, Cedrela odorata, Gmelina arborea, Tectona grandis. Fast-growing pulpwood plantations with pines, eucalypts, Cordia, Gmelina are also established according to this method but soil preparation is carefully carried out (soil ripping and ploughing) in order to have plants in optimal growing conditions. In some instances fertilizers are used (east Africa and Madagascar). This type of mechanized planting is extremely expensive; except in the case of pulpwood plantations, it is difficult to justify them in comparison with methods of improvement (or simply conservation methods) of natural forests. The question may be posed whether it is indeed worthwhile to destroy 150 to 250 m³ of gross bole volume per hectare to plant trees which will require 40 to 60 years to produce the same volume of wood.

In the savanna and woodland areas, soil preparation must be more intensive than in more humid zones since trees must be in a position to support drought periods. It is therefore necessary to destroy all competing herbaceous and tree vegetation, to arrange for a maximum water retention by soil and a widespread rooting of planted trees, thus allowing for easy tending and elimination of fire hazard. This preparation can be carried out manually. Work can be done by strips or plots and animal traction can be used for ploughing and harrowing. The “taungya” method is used in the derived savanna of west Africa, particularly in Ghana and Nigeria. The “citemene” technique developed in Zambia for the planting of eucalypts, consists of the piling and drying of cleared vegetation in long strips or windrows, to burn this debris and arrange seeds or plants on the burnt area. The so-called “tied ridging” (“bourrelets liés”) used in Tanzania to plant Cassia siamea consists of building banks at 3 metre intervals after soil preparation. Main ridges follow contour levels and secondary ones join them perpendicularly, forming small squares which retain water and prevent erosion. The “steppic” method consists of the planting of ridges of 70 cm in height at about 5 m intervals. In more broken terrain planting is carried out on terraces or in gulleys, or in ridges which are arranged before planting. Thanks to modern equipment large-scale planting and soil preparation can be carried out more efficiently nowadays (ripping and deep ploughing, harrowing, disc ploughing and elimination of original vegetation). These methods are used on a large scale in east Africa and Congo. Finally, when annual rainfall is very low (less than 600 mm) plantations can be irrigated. Tehcniques developed in Sudan are now used in Niger and Senegal, but all problems are not yet solved, in particular those deriving from underground water circulation following irrigation.

Characteristics of main species planted in tropical Africa ¹

1. Species planted in lowland humid tropical areas (mean annual rainfall higher than 1 500 mm)

Aucoumea klaineana (okoumé - African species): light-demanding species sown and 3–4 months in plastic bags. The crown of this species is very sensitive to any competition and shows signs of physiological imbalance when it is planted outside its original area. Its mean diameter growth is of the order of 1.2 to 1.4 cm/year, resulting in 100 trees of 60–75 cm DBH at 50 years, that is 300 m³/ha or a mean annual increment of 6 m³/ha/year;

Entandrophragma utile (sipo), Entandrophragma cylindricum (sapelli), Entandrophragma angolense (tiama) (African species): these species are fragile in their early years, tolerating a lateral cover but with a crown very sensitive to competition. The root system of young plants is very fragile, calling for direct sowing in polythene bags. The best type of plants have a high stem of 1 to 1.5 m. The phenomenon of necrosis of terminal buds has been noted in various countries. Growth is slow (0.6 to 0.7 cm/year of diameter increment) leading to a long rotation of 85 to 100 years for a DBH of 60 cm. Forty trees per ha could then produce 210 m³, that is a mean annual increment of 2.1 to 2.5 m³/ha/year;

Eucalyptus urophylla, E. deglupta, E. 12 ABL, E. grandis, E. cloeziana: these eucalypts have given best results in lowland humid climates. Increments vary much according to provenances. Selection of clones and their vegetative reproduction are developing (in particular in Congo). The best clones produce 35 to 40 m³/ha/year with a production of 200 m³ of pulpwood at 5–6 years. Non-select clones produce an average volume of 20 to 25 m³/ha/year with a production of 175 to 200 m³ at 7–10 years;

Gmelina arborea (Asian species): this most climatically tolerant species grows fast only with high rainfall. It cannot live very long, its lack of self pruning and its heavy branching require a very precise silviculture. This light-demanding species is generally planted in stumps. Diameter increment ranges between 1.7 to 2 cm/year according to soils and climate. Indicated growth ranges from 5 to 10 m³/ha/year of timber harvested at 30–40 years and from 7 to 20 m³/ha/year of pulpwood harvested at 10–15 years;

Khaya ivorensis (acajou - African species): this species which demands light at an early age is generally planted in the form of long striplings with bare roots. It is attacked by the caterpillar of the Hypsila butterfly (“shoot-borer”) which kills the terminal bud slowing down growth and creating forks. Mean diameter increment ranges between 1 to 1.3 cm/year corresponding to a diameter of 60 cm between 45 and 60 years. At this time a plantation of 70 trees/ha can yield 210 m³, that is a mean annual increment of 3.5 to 4.7 m³/ha/year;

Pinus caribaea var. hondurensis and P. oocarpa var. ochoterenai (American species): these two species can withstand a rainfall lower than 1 500 mm but their results are then less attractive. They can tolerate low fertility but demand a relatively high level of phosphorus. The success of plantations is often dependent on mycorrhization. Seeds are sown in sterilized seed boxes or beds and the young seedlings are replanted in polythene bags established at six months. These species are very sensitive to competition (in particular from broadleaved vegetation) during the first years of plantation and require regular tending. Growth and shape very much depend on provenances and their adaptability to the site. Many national and international trials have been established during the last 10 years in order to carry out comparative studies of provenances. Pine cutting techniques have been also investigated. Observed growth ranges from 20 to 25 m³/ha/year, corresponding to a harvest of about 240 m³ of pulpwood between 8 and 12 years;

Tarrietia utilis (niangon - African species): although fairly tolerant to light during its youth, it is most sensitive to edaphic conditions. It is planted in stumps 1.50 to 1.75 m high. Its shape is often poor and depends apparently on soil. There are no important parasitic attacks worth mentioning. Mean diameter growth is about 1 cm yearly. 70 trees with a mean DBH of 60 cm and a total production of 240 m³ can be obtained at 60 years, i.e. 4 m³/ha/year;

Tectona grandis: this Asian species has been planted in most diverse sites (annual rainfall from 1 100 to 2 500 mm) with very different results. The most favourable conditions are characterized by an annual rainfall from 1 500 to 2 500 mm with a well marked dry season of 2 to 5 months duration. It requires deep and well drained soils with a high base content. It is planted in stumps at high density (1 500 to 2 500 plants/ha), but heavy thinnings are needed already at an early stage. Annual diameter growth ranges from 0.8 to 1.2 cm and decreases significantly from 60 years onwards. It is possible to obtain trees of 60–70 cm mean DBH at 60–80 years with a timber log production of 250–300 m³/ha with 85 to 100 trees. Shape and growth are most variable according to provenances;

Terminalia ivorensis (framiré - African species): this species stands complete exposure to light from the early years. It is planted either in small bags at 3–4 months, or in stumps or by direct sowing. Dieback is sometimes noted but is most localized both in time and space. A commonly recorded mean diameter increment ranges from 1.7 to 2 cm/year. This allows for the production at 30–35 years of 65–70 trees with a 60 cm DBH, with 215–230 m³/ha or a mean annual increment from 6.1 to 7.7 m³/ha/year;

Terminalia superba (limba or fraké - African species): this species stands complete exposure to light from the early years. It is planted generally in 0.8 to 1.5 in high stumps. It is subject to attacks by wood borers resulting in black stains. Growth is excellent (1.5 to 2 cm/year on diameter) providing trees of 60 cm DBH at 30–40 years. 70 to 80 trees per ha correspond to an exploitable volume of 225 to 250 m³/ha, or a mean annual increment from 5.6 to 8.3 m³/ha/year. In Zaire and Congo this figure can reach 10 m³/ha/year in some outstanding plantations;

Triplochiton scleroxylon (samba, or ayous, or obeche - African species): this hardy species can stand relatively dry sites (1 200 mm/year). It is light-demanding from the early years. It can be planted in small bags or stumps of 1 year; small plants collected in forest can also be used. No serious disease is known except the stem borers. Growth in plantations is average (1.3–1.5 cm/year on diameter). This can result in 70–75 trees of 60 cm DBH per ha at 40–45 years with a production of 225–240 m³/ha/year, or 5–6 m³/ha/year.

2. Species planted at high elevations (above 1 000 m with an annual rainfall more than 1 000 mm);

Cupressus lusitanica (Mexican species): this species of mountains with medium rainfall (1 200 to 1 800 mm) does not support dry conditions. Its superficial rooting makes it sensitive to windfalls. It tends to exhaust soils and destroy their structure. It provides a white wood of low durability for interior joinery and can be used as pulpwood. It is harvested at 23–35 years (250 trees per ha), and yields 10 to 15 m³/ha/year;

Pinus elliottii: this species grows in Florida on swampy terrain and is therefore demanding concerning soil humidity. It can stand temperatures below 0°C and requires 1 200–1 500 mm annual rainfall. It is planted in bags at 10–12 months age with roots 15–25 cm length. It can be easily transplantable. Mean annual increment is around 15 m³/ha/year resulting in an harvest of 300 m³ at 20 years. Rotation is 50–70 years for the production of 250 m³ of sawlogs and veneer logs for internal joinery, cabinet furniture and boat building;

Pinus kesiya (or P. khasya) (Asian species): this species is most commonly planted in Zambia at 1 000–1 300 m elevation with a 1 000–1 800 mm annual rainfall. Growth is of the order of 15 m³/ha/year;

Pinus merkusii (Asian species): its natural habitat covers a considerable range of elevations, rainfalls and soils. Difficulties in collecting seeds are hindering its use. Growth is generally lower than that of Pinus khasya (about 12 m³/ha/year);

Pinus patula (American species): its natural area is limited. It can be planted at elevations between 1 000 and 2 700 m provided there are frequent mists. It grows fast only above 1 500 mm of annual rainfall and on non-acidic soils with little sand. It is planted in bags at 12–15 months and must be protected against fires. It is attached by many insects and fungi and this calls for various phytosanitary treatments. Growth is very fast until 20 years and then decreases. 300 to 375 m³ can be obtained at 15 years, i.e. 20–25 m³/ha/year of pulpwood. Sawnwood is of rather poor quality (boxes);

Pinus radiata: this species originating from the southern part of California (USA) is light-demanding. It does not stand frost. It has been planted in Kenya, Uganda and Malawi, with many failures due to premature dieback. It is practically abandoned nowadays in tropical Africa, but is used most successfully in South Africa where very high mean annual increments are obtained (more than 25 m³/ha/year).

3. Species planted in semi-humid tropical areas (annual rainfall between 1 000 and 1 500 mm and 4 to 6 dry months)

In addition to teak already mentioned for humid tropical areas and to less important species such as Acrocarpus fraxinifolius and Araucaria cunninghamii, the following species may be quoted:

Bambusa vulgaris (a bamboo native of Asia planted worldwide): its high ecological tolerance allows for its planting in very humid as well as dry zones below 1 000 m elevation. It has been planted in Gambia, Sierra Leone, Ghana, Ivory Coast, Congo, Uganda, Tanzania and Sudan. 50% of the yield can be harvested at 6–7 years and extraction can follow every second to fourth year. Yield ranges from 10 to 20 tons of dry matter per ha and per year;

Callitris calcarata, C. glauca, C. intratropica, C. robusta (Australian species): the diversity of original sites allows for a possible adaptation of the various provenances to different African conditions. These species require well drained sandy or loamy soils. They resist well to termites and are well shaped, hence their use as poles. In Zimbabwe and Malawi Callitris calcarata reaches 11 m in height and 12 cm in diameter at 15 years. Early growth of Callitris glauca in Nigeria and Zimbabwe appears to be slightly higher. Callitris intratropica (Zambia, Nigeria, Uganda) is less self-pruning and grows less fast. Callitris robusta is the least attractive as far as growth is concerned;

Cassia siamea (Asian species): it was widely used in Africa formerly (Ghana, Nigeria, Ivory Coast, Uganda, Zambia, Tanzania) but has been abandoned and replaced by eucalypts. This most hardy species is planted in stumps or bags. It requires rich and healthy soils. 10 to 15 steres of fuelwood can be obtained per ha and per year, corresponding to 80–100 steres at 7–8 years;

Casuarina equisetifolia and C. cunninghami (species of southeast Asia): they are widely used for the afforestation of poor sandy soils, notably coastal dunes. They are planted in bags at 5–8 months. They are harvested at 8–15 years and yield annually 15–20 steres of fuelwood. They do not coppice well;

Eucalyptus camaldulensis, E. citriodora, E. pilularis: these eucalyptus are particularly adapted to semi-humid zones and are used to produce fuelwood. Growth varies according to provenances and sites. An average production of about 12–20 m³/ha/year can be obtained, corresponding to a total of 150–200 steres of fuelwood at 5–6 years. Eucalyptus citriodora can also yield timber;

Oxytenanthera abyssinica (African bamboo species): it adapts to a wide range of soils except those heavily clayed or saline ones. It can grow up to 2 000 m. It has been planted in Sudan along the irrigated banks of the Blue Nile. Cuttings are planted on ploughed soil. 25% of the sprouts can be harvested every fourth year. Yields range from 5 to 10 tons of dry matter per ha and per year.

4. Species planted in dry tropical areas (annual rainfall between 400 and 1 000 mm and 6–8 months dry season).

In addition to Callitris spp., Cassia siamea and some provenances of Eucalyptus camaldulensis and E. citriodora, species which have already been mentioned for semi-humid tropical areas, the following ones may be quoted:

Anacardium occidentale (cashewnut tree - American species): this species has been used for soil protection, shelterbelts and production of nuts. It develops well on sandy soils and can stand an advanced stage of lateritization of the soils. Fresch nuts are sown directly at a wide spacing (6 to 10 m) for fruit production, at a narrower spacing (3 m) for soil protection. Wood can be used as fuel but its resin provokes sparkling. Trees produce fruits between 5 and 30–40 years: one hectare can yield 300 to 600 kg of nuts;

Azadirachta indica (neem - Asian species): this evergreen species can tolerate a wide variety of soils with a pH more than 6.5. One year old stumps are generally planted. Mean annual increment varies from 5 to 15 m³/ha/year depending on soil properties, corresponding to a possible production of 100–150 steres at 7–10 years;

Dalbergia sisso (Asian species): this species requires loamy soils with an underground flow of fresh water. It can be sown directly in pits or established as stumps of 12–15 months. Shape is generally defective. Fuel produced is excellent. 200 steres can be obtained per ha at 15 years;

Eucalyptus microtheca: this species reacts well to dry conditions if it can make use of an underground or irrigation water. Its rather poor shape and its average growth limit its use to the production of fuelwood and posts. It is termite resistant. It yields 15 steres of fuelwood per ha and per year, i.e. 200 steres at 15 years;

Eucalyptus tereticornis: some provenances adapt well to dry zones. It has a preference for fairly rich alluvial soils and sandy loams. It suffers badly from termites. In dry zones fuelwood production amounts to 25 steres/ha/year, corresponding to 250 steres at 10 years;

Prosopis juliflora (species of austral America): this species does not require more than well drained sandy soils. It is planted by direct sowing or in 2-year stumps and produces on a 15-year rotation an excellent wood for fuel and poles;

5. Species planted in very dry areas (annual rainfall between 200 and 400 mm and 8 to 11 dry months).

Acacia albida (panafrican species, from Senegal to Somalia and southern Africa): it is the only species which has its foliage during the dry season. It provides a shelter to cattle which fertilizes the soil by its dung. It is planted in plastic bags 4 months after sowing. It produces fuelwood, posts and poles and even timber, as well as excellent seeds for forage. It coppices easily and vigorously;

Acacia cyanophylla, A. decurrens, A. mearnsii (ex A. decurrens var. mollissima), A. melanoxylon: they are all native from Australia and are used for shelterbelts, for sanddune fixation and for wood production;

Acacia nilotica (native of India, Arabic peninsula and northern Africa): this species resists well to drought provided it receives annually the equivalent of at least 400 mm of water by rain, flooding or irrigation. Its hard wood is used in construction, for canoe building and as sleepers. Fuelwood is excellent. It is planted by direct sowing but weeding is necessary during the early years. Its shape is defective. This Acacia does not coppice well;

Acacia senegal (native from northwestern India to Senegal and over the whole northern Africa): this bush or shrub may reach 5 metres in height and adapts to very small rainfalls (100 mm). This hardy species propagates well by coppice and through root-suckers. It is planted by sowing in association with crops. Weeding and clearing of competing vegetation stimulates its growth. Wood is hard and heavy and is used for making implements and also as fuelwood. However the most important product is gum arabic. Average production is 150 g/tree/year. It is cut at 12–13 years;

Conocarpus lancifolius (native from Somalia): it succeeds very well in sub-desertic areas if the water table is close to the surface which explains the good results of irrigated plantations. Wood is used for boat building; it provides good sawn lumber. It is evergreen and its leaves are good as forage. One year old leafless plants are used but the species can be raised also in bags. Careful weeding and regular watering are needed during the first years. Mean annual increment would be 2 m³/ha/year.

¹ Growing stocks and increments indicated in these sections are in bole volume over bark except when stated otherwise.