Secondary Forests in Equatorial Africa Côte d ’ Ivoire-Cameroon

adapted by the editorial team.


SECONDARY FORESTS IN EQUATORIAL AFRICA
"Secondary" forests are very different to "primary", "noble" forests with their tall trees.Their exuberant, inextricable vegetation, with more lianas and small shrubs than trees, grows on formerly forested lands cleared for agriculture.In inhabited regions, they generally surround villages and grow along roadsides, pushing the primary forest back to rocky hillsides and swamps.In Equatorial Africa, "secondary" forests account today for 50 to 75% of all forested areas.These forests form in three stages: (i) seedlings appear of fast-growing sun-loving species (Musanga sp., Vernonia sp., Anthocleista sp.), which are not the same as primary forest species and which disperse their seeds over long distances; (ii) formation of an understorey, made up of the same shrub species as in "primary" forests but mixed in this case with a second group of banal sun-loving species characteristic of "secondary" forests, which quickly grow as high as the first group and sometimes higher; (iii) gradual reconstitution of "primary" forest with abundant Sapotaceae, Guttiferae and hard-wooded legu-minous species that are capable of regenerating in the undergrowth and through which some very tall trees eventually grow through the canopy.Okoumé (Aucoumea klaineana), a valuable species typical of "secondary" forests, is common in the socalled "primary" forests of Gabon, which in fact are on formerly cleared forest land.Today, the high potential of these "secondary" forests must not be allowed to "go up in smoke".Quite the reverse: we must learn to guide their development to hasten the establishment of commercially valuable species.
All those living in equatorial forest regions in the colonies have become familiar with the term "secondary forests", which are visibly distinct from "primary forests", those noble forests that stir the imagination with their mysterious shadows, their cathedral-like architecture, the impressive size of their giant trees and their vast extent across the equatorial regions where Pygmies formerly roamed and are now the domain of loggers in search of african mahogany and other fine timber for cabinet-making.Instead of giant trees, these luxuriant secondary forests abound with lianas, foliage, woody vines and herbaceous stems, and trees are no more than 20 to 25 m in height: these are the forests that uniformly line the roads and tracks that criss-cross our forest colonies and mask the true rainforest, and more or less densely surround the villages depending on how long they have been established: in regions that have long been inhabited by a relatively dense and stable population, they have entirely replaced the old-growth forests, fragments of which sometimes remain on rocky outcrops or in swampy valleys.Vast tracts of old-growth forest nevertheless remain in uninhabited regions, but for how long?This is hard to say, given the absence of maps, but the frenzied clearing by native populations of ancient and magnificent stands along newly opened roads, sometimes on slopes so steep one can barely walk upright, suggests that their years are numbered, except where the forestry services are taking measures to conserve them.When attempts are made to estimate the proportion of secondary forests in a colony, the usual figure ranges from 50 to 75%.A recent estimation made in Cameroon by M. Grandclément, the head of the forestry service for that country, gives the following in the table I.
These secondary forests therefore cover very large areas.They are made up of small trees with soft timber, which are specific species not usually found in primary forests, whose trees, in contrast, mainly grow tall and produce hard or very hard timber.These two types of forest, with their two types of flora, are contiguous and sometimes inextricably meshed together, but they are different nevertheless.Until today, these lower-growing secondary forests have attracted little attention, being considered as forest waste, offering no usable timber; foresters scorned such plebeian vegetation, giving all their attention to the lords of the forest, those great trees producing giant logs, fine timber and large tonnages for export.Yet if we look beyond the conventional merchant's view of high quality wood produced by classic timber trees, we will see that some secondary forest species, which may be mediocre as trees but are fast-growing, could become outstanding sources of cellulose that can be easily felled and used for new colonial industries, fibres, paper pulp, and other purposes.Secondary forests could therefore be of considerable interest for the future.
What assessment can be made of their current and potential value?
For those who are unfamiliar with the equatorial regions, it is hard to imagine the aspect of these forests, their structure, their composition and how they evolve.This article has therefore been written for those who have never visited a tropical country, and who therefore cannot have an accurate picture of these banal forest formations.France also has secondary forests, formed by the untidy regrowth that quickly appears after felling, but because it is temporary and not extensive, nobody has thought to refer to it as "secondary forest".In equatorial countries, they are indeed forests, of low height but so dense that, when the regrowth is recent, the only means of access is by wielding a machete to slash a narrow passage through the impenetrable tangle of stems, lianas, spiny palms and giant monocotyledons.
As we know, this secondary growth appears wherever a clearing has been made in the uninterrupted blanket of forest, which, we remind our readers, every native farmer must do to expose his subsistence crops to the sunlight.Farmers cut down the trees and burn them during the dry season.This is a very rudimentary method of cultivation because, after cutting, burning and spreading the wood ash, the native farmer merely places cuttings and seeds directly into the ground without ploughing, in between fallen and partly burned tree trunks and large branches.
After one or two harvests, the farmer considers that the soil is exhausted, abandons the land and moves on to make another clearing in the forest.The abandoned plot is soon covered with an exuberant tangle of shoots, lianas, herbaceous plants and tree seedlings, which grow extremely quickly.As the plants for the sunlight, they become tangled together, suffocate, grow ever upwards until a layer of brush several metres in height completely covers the former clearing and the partly burned stumps and stems that slowly decompose and re-form a layer of humus.
Usually, after leaving the ground fallow for some time, often about ten years, the native farmer returns to the initial plot, where the layer of humus has reformed and where there will be enough ash after burning the regrowth to make it possible to harvest a new crop.
This, then, is the well-known origin of these expanses of secondary forest, which have become so extensive because forest-dwelling populations have been slashing and burning in this way since cultivation began.
Because they are so common but have so far been devoid of any commercially exploitable resources, few studies have been made on secondary forests.In order to provide some knowledge of their structure through descriptive drawings supplemented with information from botanical surveys, we used a method of sampling based on exhaustive inventories trees in the vicinity.Thus, in former clearings, umbrella tree saplings become established, first as polewood thickets and eventually forming the umbrella tree clumps that are so common in African forests.The stems are sometimes very close together.In the Téké primary forest along the Abidjan-Agboville railway, which was clear-felled to provide firewood for the engines, the rulebook required the felled areas to be replanted with Azobé (Lophira procera), an excellent source of firewood for railway engines.Across the entire felled area, the regenerating umbrella trees quickly became so dense that the Azobé saplings died off beneath them.
The sudden proliferation of umbrella trees in primary forests where none existed before is a surprising phenomenon.After again noting the abundance of umbrella tree growth along a recently opened forest road in the Mamba forest, we commissioned the Côte d'Ivoire Water and Forests Service to extract the surface soil (to 5 cm in depth) from a 2x2 metre square, marked off under intact forest about 25 metres from the road.Sorting out the parasol seeds was not easy because of their small size, but 498 of them were collected from the soil sample.This provided proof that their seemingly miraculous regeneration originated from numerous seeds that were already present in the soil, remaining dormant until the warmth of the sun penetrating into the clearing triggered their germination.The tiny seeds of the umbrella tree usually do not readily germinate as they are protected by a relatively thick shell, which, on the other hand, endows the dormant seeds with great longevity.
Other seeds also germinate on the newly bare soil, brought by the small animals, birds and insects that are often attracted to sunlit clearings.
A great many seedlings of lianas and herbaceous, bushy and woody species thus appear.A distinction must be made between them: some, like the umbrella tree, are sun-loving species, small trees that belong to the primary forest environment; others are lianas, also sun-loving, which immediately twine around any nearby stems; a third group, finally, is made up of primary forest species, especially woody undergrowth, but also large tree species.
Finally, in amongst these numerous seedlings, shoots will also appear from the stumps of small or average sized trees.Trees in primary forests do not usually shoot from the stump, but some young trees and some shrubby species are the exception to the rule.
The hierarchy between all these growing stems soon becomes apparent.Stump shoots, lianas and sun-loving secondary forest species quickly begin to shade out the seedlings of species normally found in primary forests, which grow much more slowly.From the outside, secondary forests seem fairly uniform, as only the dominant species that emerge from the rest are visible, in other words, the small number of species characteristic of secondary forest.However, a whole complex community of slower-growing shade-tolerant species develops beneath them.
Within about 10 years, the sun-loving species typical of secondary forests rapidly grow to their maximum height of 15 to 20 metres, and sometimes more: this may be considered as the final stage in the first phase.
of narrow strips of forest, with which profiles can be easily established.The method can be quickly and simply applied elsewhere to compare the results in different types of forest where it would be materially difficult to undertake repeated counts over large areas.The method involves marking off a narrow strip 50 m in length and 45 m in width, divided into squares of 4 x 4 metres or 5 x 5 metres.In each square, the position, height and diameter of each woody plant more than 1 m in height is noted, along with a sketch of any tree or bush with a particular conformation.Once they have been measured, each tree and bush is felled in such a way that the standing trees that remain are entirely visible in the area of forest that has been cleared.The secondary formations are thus measured and felled, plot by plot.The smaller-diameter trunks are then sawn and stacked, and the larger trunks simply assessed for cubic volume.With this information, it is a relatively simple matter to set down on paper the profile of the forest at the chosen spot, and to make an approximation of the standing timber volume from the results of several such operations.
Below are given the inventories and documentation from five such surveys made in Gabon, in secondary forests of varying age, from young 2 to 3 year-old formations to very old secondary forests that have grown to closely resemble a primary forest.The first three were undertaken in the listed forest of La Mondah, located about 30 km to the west of Libreville on the road to Cape Esterias.The fourth was conducted in a secondary forest two and a half years of age that appeared to contain a great many young umbrella trees, near the Foulenzen logging concession obtained by the French rail network consortium in the southern part of the Gabon estuary.
The fifth survey, in a very old secondary forest, was conducted on the edge of the Kango experimental rubber plantation, beyond the eastern extremity of the Gabon estuary on the road to Njolé.
In Côte d'Ivoire, four surveys were made in the listed forests of Mamba and Yapo, between Abidjan and Agboville.With these few examples, we believe we can provide a fairly accurate picture of these bewildering secondary forests.

Origin: First Phase
If we observe how forest vegetation becomes re-established or in soils where indigenous slashing and burning has taken place, with incineration of the vegetation, we notice first of all, that a great many seedlings become established.Many belong to species different to those of the initial stand and some are not even present in the immediate vicinity of the plot under observation.These species are truly characteristic of secondary forests.The most outstanding, by far, is the umbrella tree (Musanga cecropioides), which takes its name from the umbrella shape of its delicate of large fanshaped leaves.All colonials know that after simply exposing the ground in the middle of a forest to sunlight, for example when building a road or establishing a plantation, young umbrella trees will appear within a few months, often in dense clumps, even when there are no seed-bearing umbrella quite long and they are liable to be directly destroyed by fires propagating from nearby savannah.This phase is the beginning of the end for forest cover of this kind.

Composition
The results of the surveys we have mentioned in this note show that the composition of secondary forests is still very heterogeneous.In each of the small 400 to 500 square metres parcels, 19 to 39 different species were counted, or twenty-nine on average.It should be noted that, in theory, the counts included all woody vegetation more than 1 m in height.
The vegetation is as heterogeneous as any that might be surveyed in a primary forest.It must be remembered that these secondary formations include true secondary sunloving species on the one hand, and remnants of cleared primary forests on the other hand, growing as stump shoots, saplings or trees that have not been felled.We did not make any surveys in exhausted secondary forests where no oldgrowth species are found at all.When the normal habitat of all forest species is known, it is fairly easy to distinguish several groups.We observe, first of all, that a small number are significantly larger in size than all of the others.These are, on the one hand, the most fast-growing species that are characteristic of secondary forests, generally dominated by umbrella trees, and will determine their shape for many years; and on the other hand, a few trees from the cleared forest that have been conserved by native farmers will suddenly begin to grow rapidly once the sun reaches them: these will be found at a later stage among the high stands of the second phase, and perhaps also in the reconstituted primary forest.
Finally, the many species forming the understory include numerous shrubby trees from the cleared forest undergrowth and some young specimens of large tree species.The latter, after a period of slow growth, will eventually grow taller than the sun-loving species that currently shade them out to form the high stands of the second phase.
Thus, only a few years after the formation of secondary forest cover, the trees that will eventually form a new primary forest can already be found, provided they are given time to grow.In the lists below, all the species that may become high forest trees in the second phase are shown in bold.
This experience has enabled us to draw up lists of the secondary forest species that become established in the first and second phases, in Côte d'Ivoire, in Gabon and, in part, in the Brazzaville region (tables II).
Although incomplete, these lists are still rather long: indeed, secondary forests over a whole colony are much more complex than they appear in a single locality.But in general, these forests seem fairly uniform: the same species are found everywhere.There is an apparent anomaly here that needs an explanation.The main species in the second phase are undeniably banal and widespread over large areas; they are found for example in Côte d'Ivoire, Gabon, the Congo, Uganda and Angola.The range of distribution of

Second Phase
An understory made up of the same shrubby species as in primary forests has now formed.The tree species characterising the first phase have remained after reaching their maximum height.A second group of sun-loving species, often more slow-growing with soft or semi-hard wood, has caught up with the first group and is tending to grow taller, with dominant crowns: these are large trees that will go to 30 or 40 metres in height or more.They are also secondary forest species characterised by their frequency in these environments and, conversely, their increasing rarity in primary forest, and by their sun-loving temperament and rapid growth.

Reconstitution of primary forest
In this, the third phase, the character of the forest again begins to change.The secondary species from the first phase have long disappeared; those from the second phase have reached maturity and are now large trees.In the understory, other species are patiently growing, slowly but steadily.Amongst these are many sapotaceae, guttiferae and leguminous species with hard or very hard wood.Once they manage to grow through the canopy above them, they revert to their natural place at the top of the stand's hierarchy.These are often very tall trees typical of primary forests, which are in harmony with the environment as a whole.They probably live longer than those that previously made up the upper story; they are capable of regenerating in the understory, which sun-loving species cannot do.As time is on their side, they will inevitably keep their place in the sun, where they will remain forever as long as humans do not intervene, because, as their seeds are often heavy, they regenerate in situ, unlike many sun-loving species whose winged seeds disperse far away from the parent trees and can therefore only multiply from the parent if they fall by chance in a sufficiently sunlit spot.
Their development thus comes full circle, but this does not always happen.Most often, it is interrupted before the final phase.These secondary forests are forest fallows that people return to cultivate within variable period, usually 10 to 15 years, and sometimes only a few years in regions with a relatively large population.The survivors from the old-growth forest then tend to disappear, remaining only as isolated trees in crop fields, because their wood is too hard, because they are too large or because their high crowns are light enough not to shade out the crops below, or as thickets on soils that are hard to cultivate.Eventually, secondary forests will thus lose the latent components that could reconstitute a primary forest; because they are periodically cultivated and the rotations are too short, these species can no longer develop.This is why entire regions are now uniformly covered in this dull vegetation.Many different degrees of retrograding plant cover can be observed: from vegetation that still seems luxuriant to low, stunted growth invaded by herbaceous plants, on the edges of equatorial forests, adjacent to savannah land, and in regions where the dry season is Chance alone will therefore favour the establishment of Umbrella trees, Anthocleista, Vernonia and other communities in a forest clearing, given of course that it is located within the overall range distribution of the species, and depending on circumstances: pre-existing seeds, seedbearing trees that remain in the immediate vicinity of the clearing, etc.The role of chance is such that it is impossible to forecast, with any certainty, the composition of the bush that will replace a cleared forest, and still less its composition in the second phase.We know that there will be a mixture of secondary species characteristic of the region, but with no certainty as to the frequency of each one.
In tropical forestry, there is an element of uncertainty that does not exist, or much less so, in temperate forests.Plant cover in a cleared forest evolves differently from one station to the next and can only be predicted in general terms, based on qualitative rather than quantitative observations made in the natural environment.If a secondary forest is then cleared in turn, it will not necessarily be replaced by the same species composition, unless all of the stumps produce shoots, which is by no means certain.Foresters have been surprised to observe that it is very difficult to regenerate a stand made up purely of Musanga, even though this species spontaneously and vigorously invades any clearing made in a primary forest.Every attempt up to now has partly or entirely failed: despite clearing the ground and preserving seed-bearing trees, there has been no significant regeneration, while coppicing attempts have not produced any satisfactory results: some of the stumps produce shoots, which are often fragile, while other stumps simply rot.The Musanga is a small tree growing from aerial roots; its shoots grow from dormant buds that form at the base of the trunk above the aerial roots 1, 2 or 3 metres above the soil and cannot form individuals with their own roots: they either reform the parent tree from its stump or disappear.Very little is known at present on the evolution of secondary forests or on the conditions their species need to regenerate: sylvicultural knowledge on these forests does not yet exist.

Origin of characteristic secondary forest species
Where do all these species come from, which are unknown in primary forests, yet have become so common and are steadily spreading further to the point that they

Gaertnera paniculata Benth.
Allyphyllus africanus P. Beauv.It is a pioneer species in secondary forests, but unlike the umbrella tree and others, it is tall and long-lived.We have shown elsewhere that this species probably originated in the compacted, dried-out alluvial soils of Gabon's coastal lake and delta region, and became established in the country's humid forests thanks to man-made clearings.

Macaranga barteri
The giant Kapok tree (Ceiba pentandra), a common species from the tropical Americas to Malaysia, probably did not originate in Africa but emigrated fairly recently, from the Americas according to some, or from Indo-Malaysia according to others.We do not have enough material to give an opinion on this subject, but it is certain that without forest clearing, the species would not be as widespread as it is today in Africa's forests.
Oil palm groves are very old secondary formations in which palm trees, first dispersed and now respected by native populations, became established.Some in Dahomey [Benin] and Togo are true plantations recently established by native farmers, mainly to harvest palm wine, but most are sub-spontaneous.Oil palms are not a primary forest species, although stunted specimens may be found that do not develop or reproduce.Their origin is certainly in Africa.The species undoubtedly grow spontaneously in swampy areas on dewatered soils where there is abundant light and water: this is probably its original habitat.

The economic value of secondary forests
All pioneer species are fast-growing with soft timber.They often reach a suitable felling diameter, usually 25 to 35 cm, within 10 to 15 years.They are therefore small trees that cannot be used for construction timber, which is why they have been ignored up to now, as loggers are only interested in large trees.When considered from the angle of cellulose production, however, they are clearly of particular interest for their yields in terms of annual woody growth and the relative ease of felling and processing.This is why, given the hopes held out for colonial forests by possibilities for establishing large-scale mechanical and chemical timber processing industries to manufacture cellulose pulp, fibre board, plastics, etc., the question of short-rotation felling of all secondary forests species has been raised.However, numerous objections immediately arise.
Young secondary forests produce fewer cubic metres of timber than might be thought on seeing their luxuriant vegetation.In fact, their lianas, foliage and vines form a mass of greenery that conceals their wood so that its quantities are over-estimated.The wood is also of highly variable quality, as our profiles show: these formations are very irregular, especially when they contain remnants of cleared forest, either in the undergrowth and particularly among high trees: some almost empty parcels contain large herbaceous monocotyledons 5 to 8 m in height (Aframomum in particular) and could one day replace the old-growth forest?Because, after all, before clearing began on such a large scale, at a time when Pygmies were perhaps the only human beings living in equatorial forests -and even before them -primary forests reigned supreme.The knowledge we have about the temperament of these secondary forest species, and the observations made in various undoubtedly primitive stations, since humans have not been able to modify them, indicate that they often originate in swampy areas and from riverbanks.Before humans arrived, they would only become established on recently dewatered alluvial soils, and along the edges of dense forest, where water and light were abundant.But if the soil dried out for any reason (changes in the relief, etc.), they would be suppressed by the primary forest species that could become established among them.This, in all likelihood, is where the origins of these characteristic secondary forest species may be found -those growing from aerial roots such as Musanga, Macaranga, Bridelia, Xylopia, Anthostema or Myrianthus, and all the other species growing on wet ground but without aerial roots, such as Cleistopholis or Trema, both much less widespread today: by clearing the forest, man himself opens up broad tracts of forest where they could not previously survive as normal plant communities.
The origins of other species are more hypothetical, because stations that are indisputably untouched by man and where they are certain to be found are very rare.Many species probably come from the undergrowth in high semi-dry stands, or from the high stands that previously marked the transition between humid equatorial forests and forests in regions with a long dry season.These are probably the sources of species such as Anthocleista, Fagara, Harungana, Trema, Phyllanthus, Vernonia, Albizia, Holarrhena, Allophyllus, Sterculia and Tragantha.Finally, many probably descend from xerophyllous scrublands, low-growing sunlit formations forming on rocky ridges, and steep mountain slopes where they are still found today.
All the species inhabiting stations in full sunlight, all those capable of rapid growth and of producing and disseminating large quantities of seeds that germinate easily have multiplied in the artificial clearings made by man.This is the origin of the "pioneer" species in secondary forests.However, for many other species, of which we know too little, we cannot say at present what their original environment might have been among many possible candidates.
The origins of the high trees peopling older secondary forests are generally different.Many are capable of regenerating in primary forests, but not well, as there is not enough sunlight.Saplings that vegetate for some time in the undergrowth will begin to grow as soon as a natural clearing appears when a large tree dies or is felled by a strong wind or struck by lightning.These species therefore existed in oldgrowth forests, but were not as frequent as in today's forests that have developed from clearings.This is likely to be the case for all the species producing the finest trees and the best timber in these forests: (Terminalia superba and T. ivorensis), mahogany (Khaya spp.), which also originate from riverbanks and swamps, Triphochiton scleroxylon, Pycnanthus), Iroko (Milicia), and so on.
We have treated three outstanding trees as a special case: the Gaboon mahogany, kapok tree and oil palm (Elaeis pure stands.If the problem of natural propagation by preserving individuals during felling, coppicing or artificial seeding were resolved -and unfortunately, as we have said, it is notour forest colonies would provide a source of cellulose of great interest. We will now list all these species, which current knowledge does not permit us to rank in order of value (table III).

Need for methodological studies
With a very few exceptions, we have virtually no knowledge, if any, on secondary forests and their timber in terms of mechanical, chemical and technological properties.These formations need to be systematically studied from all these angles in order to determine their value for the manufacture of paper pulp, fibre board, hydrolysed glucose, etc.
Sylviculture in these forests also needs to be systematically researched.We have seen that easy natural regeneration does not necessarily mean easy artificial regeneration.It would be essential to investigate possibilities for abundant propagation of the species, to determine the growth rates of trees and stands and to measure their productivity by means other than observations in the wild on spontaneous vegetation, of which we know virtually nothing as regards circumstances and conditions.Experimental plantations should therefore be established.About 10 ha per species would suffice: given that trials are needed on some fifty species, this would require planting about 500 ha in each major forest colony.There is by no means a vast undertaking, but it is essential nevertheless: until such plantings are established and methodically followed up, doubts, illusions and lack of forethought will continue to be the norm.
Concerning propagation trials for umbrella trees, a methodology testing programme was set up in Côte d'Ivoire in 1941-42.This was followed up methodically despite the World War context by successive foresters working in the country.The results were negative on the whole, but the trials should be taken up again and pursued with much more perseverance, taking the lessons from the first attempts into consideration.It is inconceivable that we should fail to identify the conditions for spontaneous germination of the umbrella tree: a careful and observant experimenter needs only a lucky chance, but that chance will only arise through a series of experiments.
Finally, exotic species should not be ignored.Some are very fast-growing and produce more cellulose than local species.The scope of the trials can be productively expanded with innumerable species that include Gmelina, Macaranga, Ochroma, Virgilia, Styrax and many more.

Secondary forests in the second phase
The characteristics of species in these forests are as follows: they are sun-loving, or at least require generous light during their growth, regeneration is impossible or mediocre an abundance of slender or knotty shrubs.Our production estimates vary from 55 to 750 stacked cubic metres per hectare.It is also difficult, and even impossible, when counting trees in these forests, to calculate average growth in volume with any certainty, because the age of the stands cannot be assessed.According to previous measurements made in Côte d'Ivoire in dense natural stands of umbrella trees, whose age was known within one two years, estimated volumes range from 200 to 250 m 3 per hectare on average, when logs more than 5 cm in diameter are stacked, or 165 to 200 m 3 when only logs more than 10 cm in diameter are considered usable.
These figures only concern pioneer species.If an older secondary forest is logged, they will obviously increase considerably.In young secondary forests, annual woody growth may be estimated at 14 to 17 stacked cubic metres of wood more than 10 cm in diameter, or 10 to 13 m 3 per year.These figures for natural forests are certainly much lower than those one would obtain for a cultivated forest or plantation.
The irregularity in the qualitative and quantitative distribution of woody material in secondary forests is a considerable handicap when attempting to forecast production.If we disregard the remnants of the previously cleared forest to consider only true secondary species, these forests are still very heterogeneous in their composition.
Not enough surveys have been made to make it possible to determine, to an acceptable degree of approximation, the average composition of secondary forests in a given region.By increasing the number of surveys or tree counts, over areas of 1 ha for example, there is a obviously a much greater probability of reaching a close estimation of the real average, but it must be admitted that we do not know a great deal about the subject since no major study has been conducted to date.
It is nevertheless unfortunate to have to rely purely on the qualitative stability of secondary forests, in other words, to have no certainty, when logging a forest today, of finding the same composition 10 to 20 years later when felling is next planned.We discussed this problematical issue of forest reconstitution at some length in the paragraphs above.It is possible, for example, that large stands of Musanga will disappear in secondary forests that have been cultivated for many centuries.We will not venture to express a formal opinion on this point, but it is not improbable; we must await more thorough knowledge on the biology of the species to form a definitive opinion on the subject.
In short, the question of exploiting wild secondary forests involves a great deal of uncertainty as to their current and future potential.
It should be remembered, nevertheless, that the option of cellulose production exists for these forests.If it were possible to multiply the trees through simple and inexpensive processes, the solution we are seeking may well emerge from this approach.What are the species concerned?We have provided an indicative list based on our impressions, although it is neither exhaustive nor definitive.This list is based on the spontaneous frequency of the species in secondary forests, broad dissemination of the species, their apparently rapid growth and the technological value of the tree (height, diameter and habit).
The umbrella tree indisputably leads the field.No other species has such rapid growth, frequency or aptitude to form When a sun-loving species is found in abundance in an apparently primary forest, this generally indicates that it originated in a secondary forest.This can be proved through studies of stand composition and latent regeneration.If a forest has an abundance of species like Mahogany, Limba, Iroko and Kapok trees, it is probably of secondary origin, which it is possible to confirm, with a few exceptions.This is particularly evident for Gaboon mahogany, a sun-loving species of the first order, which is a pioneer species in secondary forests but is also long-lived and persists in secondary forests that are so old that they take on the aspect of primary forests.We reported on the remarkable case of Gaboon mahogany in another research note and came to the conclusion that the very fortunate extension of this species into large tracts of Gabon's forests was certainly due to earlier clearing; the surprising fact is that these regions are now virtually uninhabited.This inescapably suggests that Gabon in shady undergrowth, and density is low or average in many cases.When they account for only a small proportion of trees in a stand and when trees with hard or very hard wood are dominant, then the environment is a primary or at least a virtually untouched forest.Conversely, when the former make up the majority of the stand and the latter are absent or in the minority, the environment is an old secondary forest.It is not unusual for primary forests to contain only a small number of species, but these are always shade-loving, usually have heavy seeds have become well established and reproduce on the spot in deep shade, thus preventing other species from developing amongst them.The most typical example is Macrolobium Dewevrei, a very abundant species in the Congo Basin where it is found in pure or almost pure stands.Other examples are the numerous species found in the middle and lower storeys and those found in humid and swampy ground.

Table III.
List all these species, which current knowledge does not permit us to rank in order of value.

Vernacular name Scientific name Particularities
The kapok tree Ceiba pentandra (L.) Gaertn.a very large fast-growing tree, easily propagated by seeding or cuttings, suitable for short rotations taller than all others, very fast-growing in full sunlight, possibilities for creating pure stands, possibilities for short-rotation felling for cellulose production if seed-bearing trees are preserved to ensure natural regeneration sun-loving species such as mahogany, iroko, African whitewood or limba that are most sought after, while we have no idea how to use the innumerable trees forming very hard timber that can be extracted from indisputably primary forests.But despite these happy outcomes of forest clearing, we should not unthinkingly cry "Long live the forester's axe!" nor yet entertain the fond hope that no regulatory obstacles should prevent clearing for crops.Because the anarchic freedom enjoyed by natives to cut down parcels of forest whenever they wish, notwithstanding the ultimate effect of encouraging the growth of certain useful species, also most certainly destroys existing stands in which useful trees, such as mahogany, are already in place, and subsequently, with a few blows of the axe or machete, destroys the trees that are already regenerating.It is not acceptable to allow old or young stands of valuable species to be massacred and vanish into a thin layer of ash and heavy clouds of smoke.
The lesson we should draw from these observations on the influence of human actions of the evolution of a forest is that it is possible to guide and hasten its evolution by applying sylvicultural techniques, to transform existing forests with few choice species into forests that are much richer.There is no lack of material with which to work: all these valuable trees and timber make up an economically and biologically varied resource with which foresters could create vast wealth for the future.
A. Aubréville, Inspector-General for Water and Forests in the Colonies.
The following pages contain the 12 "survey" pages annexed to Mr. Aubréville's study.
was formerly much more densely populated than it is today.This conclusion may seem astonishing, but on second thoughts, colonials who are familiar with the speed with which village populations disappear in Gabon's forests, even today, will not find it so surprising.
The same is true in Côte d'Ivoire and in Cameroon, and also elsewhere whenever a forest is dominated by secondphase species of secondary forests.Thus, vast tracts of uninhabited forest that appear to be untouched, with their gigantic trees, shadowy undergrowth, enormous lianas and almost bare soil, were in fact cleared a long time ago, if we go by the conclusions drawn from the composition of their plant communities.These forests were formerly inhabited, as were Gabon's mahogany forests.Human settlement therefore probably began earlier and across wider areas in equatorial forests than is generally thought.
To return to the case of the umbrella tree, its seemingly miraculous regeneration in apparently primary forests is due to pre-existing dormant seeds in the humus layer, but where did these seeds come from?Animals, and especially birds, certainly disperse them over large areas, but the density of seedlings in some areas suggests a different but plausible hypothesis, which is that a stand of umbrella trees existed previously in the location occupied today by the supposedly primary forest, but that it disappeared as part of the normal evolution of secondary forests, leaving an abundance of seeds in the shadows to await the chance event of fresh forest clearing to trigger their germination.
From the point of view of a forest's value, should these changes in its composition wrought by man in ages past be a cause for complaint?Clearly not, because in fact, it is the

Table I .
Recent estimation, of croplands versus forests, made in Cameroon by M. Grandclément, the head of the forestry service for that country, gives the following.

Oualélé Pycnanthus angolensis (Welw.) Warb. Bangbaye Albizia gummifera
This experience has enabled us to draw up lists of the secondary forest species that become established in the first and second phases, in Côte d'Ivoire, in Gabon and, in part, in the Brazzaville region.In the lists below, all the species that may become high forest trees in the second phase are shown in bold.umbrellatreethus coincides approximately with that of dense humid forests across Africa as a whole, while Harunga madagascariensis and Trema orientalis are found throughout Africa from Casamance to Madagascar.However, they are not evenly distributed across these vast areas; furthermore, many secondary forest species have a much smaller range of distribution, which means that these forests vary in type in different localities and different countries.It could be said that secondary forest species occur in communities -others might say associations -around Musanga, Trema,Carungana, Anthocleista, Rieinodendron, Albizia, Macaranga, Discoglypremna, etc.-in fact, most of the species listed above.

Plateau -Parcel 3 -0.02 ha) Secondary forest, young, species-poor, no distinct character
Volume: 8 stacked m³ + 3.34 m³ = about 13 stacked m³ i. e. 55 stacked m³ per hectareB O I S E T F O R Ê T S D E S T R O P I Q U E S , 2 0 1 , N ° 3 2 3 ( 1 ) SECONDARY FORESTS IN EQUATORIAL AFRICA