Part I
REGIONAL SYNTHESIS (continued)

Chapter III
FOREST RESOURCES OF TROPICAL AFRICA (continued)

1. PRESENT SITUATION (continued)

TABLE 4a - Growing stock (VOB) estimated at end 1980 ¹
Broadleaved forests
(totals in million m³)

¹ Weighted means are indicated between brackets

TABLE 4b - Growing stock (VOB) estimated at end 1980
Coniferous forests (NS)
(totals in million m3)

TABLE 4c - Total growing stock (VOB) estimated at end 1980
Closed forests (broadleaved and coniferous)
(in million m3)

These tables are therefore more a reflection of the high quantitative diversity of closed forests than of differences between countries. The overall interval appears to be from 60 to 350 m³/ha. Mean values range from 60 to 120 m³/ha for dry and “semi-dry” closed forests, from 150 to 180 m³/ha for humid closed forests of the peripheral zones (Guinea, Sierra Leone, Liberia, Angola), for humid closed forests of the eastern coast (Kenya and Tanzania) and for montane humid closed forests (Uganda, Kenya, Ethiopia dna Madagascar), from 200 to 270 m³/ha for the whole of the evergreen forests and from 280 to 350 m³/ha for the whole of the semi-deciduous forests. Semi-deciduous forests are those which contain the highest volumes. These latter have been recorded in northern Congo, southeastern Central African Rep. and in the “Biafran” forests of the Edea region in Cameroon (VOB more than 400 m³/ha).

Figures indicated for VOB of logged-over closed broadleaved forests (NHCfiuc) are generally lower than those of undisturbed forests by 10 to 60 m³/ha. This difference corresponds to the average removals by logging in these forests (volume of extracted logs plus logging losses). If an average recovery factor of 60% is used, this matches with the average estimate of commercial volume extracted in the recent past in African forests which ranges between 5 and 35 m³/ha (high figures often relate to areas repeatedly logged).

Total volume of productive closed broadleaved forests (NHCf1) of tropical Africa is estimated at about 39 billion m^{3 1} of which around 30 billion are in undisturbed forests, more than 8 billion in unmanaged logged-over forests and about 240 million only in managed forests. If the wood volume of the crowns is estimated at 40% of that of the gross bole volume (VOB), the estimated of woody material above ground are about 54 billion m³ for the productive broadleaved closed forests and about 9 billion in unproductive broadleaved closed forests (NHCf2). The largest share of these resources is found in central Africa (88%) with 52% of the total volume for Zaire alone.

The total volume of coniferous wood is extremely low (about 134 million m³ of coniferous VOB, i.e. 0.3% of total VOB of African closed tropical forests). More than half of this volume is contained in the unproductive forests (NSf2 i.e. those inaccessible or located within parks and equivalent reserves.

b) Mixed tree forest-grassland formations (NHc/NHO)

VOB in the productive open formations (NHc/NHO1) ranges between 15 and 60 m³/ha, the most common values being 20 and 30 m³/ha. Total VOB volume is estimated at 4.2 billion m³ or about 10 times less the volume of the closed forests. East and southern Africa (and southern Zaire) account for 63% of these resources, the rest being contained in the belt of mixed tree forest-grassland formations south of the Sahara (from Senegal to Sudan).

The tables do not provide figures for unproductive mixed tree formations (NHc/NHO2i) of which tree cover can be estimated at less than 40%. Their VOB can be estimated between 5 and 15 m³/ha, depending on the crown cover percentage.

¹ 1 billion = 1 000 millions

Increments

There are few studies on the growth of closed forests of tropical Africa. Investigations concerning okoumé in Gabon (see corresponding country brief) have shown that this species has a current annual increment between 0.7 and 1.1 cm/year on diameter. Growth is fairly low during the early years (0.7 to 0.8 cm/year from 0 to 10 years) but increases rapidly until the age of 30 years. Growth then reaches a maximum between 35 and 50 years (1.0 to 1.1 cm/year), after which it decreases very slowly and irregularly until old age. Mean diameter growth curve shows that a diameter of 80 cm is reached at 85 years, that is a mean annual increment of 9.4 mm. If these figures are converted into volumes they correspond to a production of 6.4 m³ of bole volume at 85 years or a mean annual increment of 0.075 m³/year/tree. Growth is obviously strongly dependent on the environment of each tree. The dominated ones have their growth slowed down to a large extent but seem to keep a high growth potential as soon as they are freed, since they grow again at rates often faster than average. This process seems to be quite general for species of humid closed forests. In Ivory Coast, studies carried out on sipo (Entandrophragma utile) through the analysis of seasonal increment cores, have proved the existence of trees more than 300 years old which have reached 100 to 130 cm diameter, that is a mean increment of 0.33 to 0.43 cm/year, while other individuals had a diameter more than 120 cm at 200 years already, that is a mean increment of 0.6 cm/year. At 100 years, diameters range between 30 and 90 cm or 0.3 to 0.9 cm/year with a large majority of trees between 40 and 60 cm or an increment between 0.4 and 0.6 cm/year.

In Central African Rep. studies of increment cores have been carried out on sapelli, obeche, limba, sipo, kosipo, dibétou, iroko, doussié, mukulungu, difou, acajou, bossé, padouk, tiama and dabema. Results are provided in the corresponding country brief in the second part of this report. The range is between 0.43 and 0.94 cm/year of mean diameter increment. Ayous and limba, which are currently used in afforestation (Cameroon, Ivory Coast, Ghana, Nigeria) are the indigenous commercial species with the fastest growth.

Several studies carried out by the former INEAC at Yangambi in Zaire, confirm these results, as well as those of studies on limba in Congo. Tree growth in tropical closed forests is thus relatively slow if seen in relation to the quantity of light and CO₂ available for photosynthesis. The relative infertility of tropical soils is partly responsible: some growth variability exists according to aspect and soil type.

Figures between 1 and 2 m³/ha/year are often quoted for growth in volume to indicate the productivity of humid broadleaved closed forests, but there is confusion between increment of gross bole volume over bark (VOB) and “commercial” increment. The actual growth of African closed forests is likely to be between 0.05 and 1 m³/ha/year only in terms of actually commercialized volume, that is of the volume theoretically available every year (“annual allowable cut” - AAC - in intensively managed forests); this leads to rotations of a minimum of 80 years, a duration mentioned in many theoretical management studies in Africa. Figures provided for Uganda and Kenya (0.4 m³/ha/year) are of this order of magnitude, whereas those provided for Ghana and Sudan (1.8 and 1.6 m³/ha/year) seem to be relatively high.

Even less is known concerning growth in mixed forest-grassland formations. The table provided in the section on fuelwood gives mean growth levels in terms of total wood material (extracted fuelwood), but as far as timber is concerned productivity is extremely low (of the order of 0.05 m³/ha/year).

1.2 Plantations

1.2.1 Introduction

Plantations before 1914

The first trees were planted in Africa probably very long ago in the savanna zone close to the dwellings of farmer-hunters. These must have been fruit trees and for a long time the only trees planted were for fruit or seeds or even more simply for shade. The first plantations aiming at wood production, were carried out during the last years of the 19th century and the beginning of the 20th century, essentially in the form of very small trial plantations with indigenous and mainly exotic species. Eucalyptus globulus was introduced in Ethiopia in 1895; introduction of mlanje cedar (Widdringtonia whytei), cypress and Callitris was carried out in Malawi, then part of the British Zambezia; Germans introduced in their east African colony (nowadays Tanzania) Tectona grandis, Cassia siamea, Swietenia spp., Cedrela spp., Cupressus lusitanica, C. sempervirens, Cryptomeria spp., Araucaria spp., and some eucalypts; the first Cupressus were tried in Kenya around 1902; around 1902–1904 in the savannas of Togoland (nowadays Togo and eastern part of Ghana) the Germans planted Erythrophleum spp., Khaya spp., Tectona grandis, Azadirachta indica, Gmelina arborea; limba (Terminalia superba) was planted in 1905 as a shade tree over cocoa plantations in lower Zaire and the British tried Tectona grandis, Cassia siamea, Casuarina equisetifolia, Delonix regia, Chlorophora excelsa, Afzelia africana, Nauclea diderrichii in southwestern Nigeria. This first phase followed by first plantations on small areas is characterized by the use of a large number of species “just for the sake of it”. Many successes and failures were known only by the local people (civil servants, missionaries, planters). Only teak in west Africa and montane softwoods in east Africa have survived.

Plantations during 1920–1940

After the first World War several plantation programmes were carried out, in particular through the “taungya system” developed in Asia. The following plantations date back to this period: teak plantations in Togo, Benin and Ivory Coast; limba (Terminalia superba) plantations in Zaire; Eucalyptus camaldulensis and E. saligna in Angola; Pinus spp., Cupressus spp., and Vitex keniensis in Kenya; Eucalyptus robusta in Madagascar; Acacia senegal in Sudan; Eucalyptus globulus in Ethiopia; Pinus patula and P. elliottii in Malawi; Casuarina equisetifolia in Mozambique and Eucalyptus maideni in Rwanda and Burundi. Nowadays there remain only a few tens or hundreds of ha of these plantations in each country, except for Kenya where stands of Juniperus, Pinus, Cupressus and Vitex more than 40 years old cover about 12 000 ha, for Madagascar where 10 000 ha of non-industrial plantations of Eucalyptus remain from that period and for Rwanda, Burundi and Angola which possess a few thousand ha of non-industrial eucalypt plantations of that period. Total area of plantations of more than 40 years old in tropical Africa have been estimated at about 15 000 ha only of industrial plantations and 30 000 ha of non-industrial plantations.

Plantations during 1940–1960

After the second World War some colonial forest services continued planting in less scattered and numerous sites with species selected in relation to their first satisfactory results. In the other countries (e.g. Madagascar, Rwanda, Burundi, Ghana, Angola and Ethiopia) plantation programme were initiated with the participation of private individuals and rural communities. Plantations dating from this period are those with Aucoumea klaineana (Gabon, Cameroon), with Tectona grandis (Ivory Coast, Ghana, Togo, Benin, Sudan), with Terminalia superba (Nigeria, Zaire, Congo), with Nauclea diderrichii and Azadirachta indica (Nigeria), with Casuarina equisetifolia (Mozambique, Senegal), with Gmelina arborea (Sierra Leone and Nigeria), with Acacia nilotica (Sudan), Eucalyptus maideni (Burundi, Rwanda), with Eucalyptus saligna (Angola), with Eucalyptus spp. (Madagascar), with Pinus patula (Malawi, Kenya, Madagascar), with Pinus radiata and Cupressus spp. (Kenya).

Many of these plantations suffered unfortunately from a lack of maintenance and monitoring and were either suppressed by natural regrowth or prematurely exploited by populations. From this time there remain around 182 000 ha of industrial plantations and 212 000 ha of non-industrial ones. They are half softwood and half hardwood plantations. Among these latter, fast-growing plantations (eucalypts) are less important (16 000 ha only). The countries with the largest area of old hardwood industrial plantations are Sudan with 20 000 ha (essentially Acacia nilotica and teak), followed by Nigeria with 9 000 ha (essentially Terminalia and Gmelina) and Gabon with 7 000 ha of okoumé. Countries with important ancient softwood plantations are Kenya (46 000 ha of Pinus radiata, P. patula and Cupressus lusitanica), Madagascar (12 000 ha), Malawi and Zimbabwe. Non-industrial plantations are essentially hardwood ones (98%) of which 173 000 ha are fast-growing species (Eucalyptus and Gmelina) and about 34 000 ha of hardwoods with low and medium growth. Angola with 67 500 ha (essentially of Eucalyptus saligna and other eucalypts) and Madagascar (45 000 ha of eucalypts) account for 65% of non-industrial plantations. Rwanda, Burundi and Ethiopia have between 13 and 17 000 ha planted. Areas in the other countries are very small (less than 3 000 ha). In particular, savanna countries south of the Sahara do not have any planted areas more than 20 years old.

Plantations during 1960–1980

Activities of most African forest services decreased for some years between 1958 and 1963, corresponding to the Independence period for most of the countries. Then an important reforestation effort was initiated, assisted in part by external financing. The following table shows the trends in terms of areas still existing nowadays. Even if account is taken of areas planted which have now disappeared (either because they have been logged-over, or destroyed or simply died out) a sharp acceleration of annually planted areas during the last 40 years is conspicuous (20 000 ha per year from 1940–1960; 58 000 ha per year from 1961–1975 and 93 000 ha per year from 1976–1980).

Existing plantations (1980)
(in thousand ha)

This table shows also that during the period 1961–1975 priority was given to industrial plantations (for production of sawlogs and veneer logs and of pulpwood to a lesser extent), while during the last years (1976–1980) areas of non-industrial plantations planted annually (mostly for fuelwood production) have been proportionally more important than during the 1961–1975 period.

Five countries account for three quarters of the area of industrial hardwood plantations established during the last 20 years (about 360 000 ha). They are: Ivory Coast where 36 000 ja of hardwood plantations have been successively carried out by the Forest Service, the Centre Technique Forestier Tropical, and then the SODEFOR, a State Corporation founded in 1969 in charge of forest plantations; Ghana (about 22 000 ha) and Nigeria (135 000 ha), mainly by the forest services in association with rural communities; Angola (about 43 500 ha of eucalypt plantations established essentially between 1966–1975 by a pulp and paper company and by other individuals) and Sudan (33 000 ha of various hardwoodsestablished mainly by individuals). Congo (eucalypts and limba), Gabon (okoumé), Malawi, Tanzania and Zambia are the only other countries having established more than 8 000 ha of industrial hardwood plantations during the last 20 years.

Industrial softwood plantations established between 1960–1980 cover a total area of about 438 000 ha. Six countries of east Africa - Kenya (95 000 ha), Tanzania (51 000 ha), Zambia (23 000 ha), Malawi (61 000 ha), Zimbabwe (20 000 ha) and Madagascar (100 000 ha) - account for 80% of these areas. Areas of industrial softwood plantations in west and central Africa are negligible.

As far as non-industrial plantations are concerned (almost all with hardwoods) those with species other than fast-growing ones, have been established essentially in the savanna zone of the northern hemisphere and in Madagascar and Zimbabwe. Sudan alone accounts for about 45% of areas with 117 700 ha of plantations, of which 98 700 ha comprise Acacia senegal. Ghana is the only other country with more than 10 000 ha (28 000 ha with miscellaneous hardwoods). Areas planted in Madagascar between 1960 and 1980 have been established with cashew nut trees. Fast-growing plantations with eucalypts as the most important species, are almost exclusively located in east Africa (with the exception of Angola). Six countries contain 88% of areas established during the last 20 years: Madagascar (66 000 ha), Ethiopia (80 500 ha), Angola (19 500 ha), Uganda (30 000 ha), Tanzania (27 000 ha), Kenya (20 000 ha) and Rwanda (11 000 ha).

There has been an important plantation effort during the last 5 years (1976–1980) in the following countries: Ivory Coast (13 800 ha of industrial plantations with hardwoods of low and medium growth), Nigeria (63 000 ha of industrial plantations, half with fastgrowing Gmelina and half with miscellaneous hardwoods of low and medium growth), Kenya and Madagascar (35 000 ha of industrial softwood plantations each), Malawi (27 000 ha of industrial softwood plantations), Sudan (50 000 ha of non-industrial plantations with Acacia senegal and various other species), Ethiopia (30 000 ha of eucalypt plantations for fuelwood). If Ghana, Tanzania and Zimbabwe - which have been very active in all types of plantations - are added, the cumulative percentage of areas established between 1976–80 amounts to 68%. In many countries the annual plantation rate has been less than 500 ha during the same period.

1.2.2 Areas of established plantations (tables 5)

Tables 5a, 5b and 5c show the present areas resulting from the historical background described in the preceding section. Total areas of industrial and non-industrial plantations are thus estimated at about 1 million ha and 780 000 ha respectively at the end of 1980. If the areas established between 1976–80 are deducted, the areas of industrial plantations in 1975 are as follows: 225 000 ha of hardwoods other than fast-growing ones, 111 000 ha of fast-growing hardwoods and 397 500 ha of softwoods corresponding to a total of 734 000 ha.

Estimated of areas of industrial plantations provided by FAO in 1979 (article by Lanly-Clement in issue no. 123 of Unasylva) were: 399 000 ha of hardwoods other than fast-growing ones, 109 000 ha of fast-growing hardwoods, 398 000 ha of softwoods corresponding to a total of 906 000 ha of industrial plantations.

While estimates of fast-growing hardwood plantations and softwood plantations are almost identical, the areas of plantations with hardwoods other than fast-growing ones are significantly higher in the 1979 study. On examining these figures by sub-regions the following is found: (i) a very small overestimation of 1975 areas for western Africa is made in the Unasylva article which can be explained by a transfer of some areas classified as nonindustrial in this study; (ii) area estimates in 1975 for central Africa are 75 000 ha and 49 000 ha in the quoted article and in this study respectively: as there is no difference in the figures for non-industrial plantations, the discrepancy can be explained by a better assessment of the actually existing plantations, in particular in Gabon and Zaire; (iii) area estimates are 188 000 ha and 67 300 ha in the 1979 document and in this study respectively for east Africa: this important difference is explained by the fact that the eucalypt plantations in Madagascar were considered as industrial plantations in the former study while they have now been classified as non-industrial; these areas were estimated at 149 000 ha in 1975.