THE FOREST IN RELATION TO AGRICULTURE
The intimate and very important connection between Agriculture and
Forestry is not at all widely recognized, so it is desirable to bring
out more fully exactly how the one reacts on the other: the value of
forests from the climatic point of view to agriculture, the economic
effects on it, as well as the population connected with it.
In all the older civilized countries, such as France, England and
Russia, and the United States and Canada of the newer ones, definite and
almost exactly fixed quantities of land are used for agricultural
purposes on the one hand and for Forestry on the other.
In the Gambia, Sierra Leone, the Gold Coast and Nigeria, however, with
the exception of about 1,500 square miles of forest reserves and certain
native land planted with rubber or cocoa, all the land (even when
covered with finest mahogany forests) is liable to be farmed for a time
and then abandoned for another piece of forest-land under the system of
shifting cultivation. In practice, this means that every year thousands
of square miles of forest are ruthlessly cut down, in order that the
land may be used for agricultural crops, for one, two, or at the most
three years’ crops. In the drier parts of the countries named, through
such forests as exist, grass-fires annually burn, and destroy many trees
in order to provide poor grazing for herds of the nomads’ cattle.
It might be argued that in the comparatively damp and hot climate which
attains in a great part of the Gambia, Sierra Leone, the Gold Coast and
Nigeria, which are also to some extent still covered with forest, it
would be most advantageous to clear as much land as possible. This,
however, is a delusion resting on false impressions, notably that the
countries named are so much covered with thick forest. In most places
this so-called “forest” is in reality an almost worthless secondary
growth, consisting chiefly of umbrella trees (_Musanga Smithii_), soft-
wooded Hannoa, creepers, grass, with isolated half-burnt or decayed
trees from the original forest. Again, too, this system of clearing new
land is quite haphazard, so that, after the first crop has been taken
off, the land may be found to be too poor to be planted again; the
natives then abandon it. In some places, chiefly in the Benin and Oban
districts, they even go so far as to put a “Ju-ju” on the land, which is
in effect a notice to say that the land is of no use for a farm.
However, this is usually forgotten in a generation, so that the same
thing may happen again, only that insufficient time has elapsed for a
proper forest to be grown, as the cutting of the original forest may
have so altered the climatic factors of the locality that not only
different species of trees but also grasses have come in, and choked
nearly all the self-sown forest-tree seedlings. The main beneficial
effects of the forest may be summarized as follows:
1. The rainfall of the locality is increased, according to the figures
of the Indian rainfall stations. This may amount to as much as 16 to 28
per cent. increase on the annual rainfall.
Afforestation on the Russian steppes has shown that more rain now falls
on the planted area than in former years.
In Western Canada it is generally said that its climate is altering, and
a general increase of rain has been noticeable since plantations have
been made on thousands of farms and what forests there were originally
have been rigorously protected from annual fires.
2. The rainfall both above and in the ground is more regularly
distributed.
First of all, nearly 23 per cent. of the rain which falls on the trees
in a forest is re-evaporated into the air and does not reach the ground
at all. This in itself increases the humidity of the atmosphere, tends
to form clouds, and thus induces further rainfall. The clouds tend to
protect the plants from excessive sun at what may be a critical period
in the growing season. The extra humidity of the atmosphere does not
necessitate the plants transpiring so much moisture as they would
otherwise have to do, to keep them in growing condition. Compared to
that in the open, only 22 per cent. of the amount of evaporation takes
place in the forest, added to the fact that it occurs under the canopy
of the trees, thus creating the more humid atmosphere which is so
suitable, for instance, for the growth of cocoa and other such crops. In
other words, we can take one hundred parts as the amount evaporated in
the open, of which not a quarter is evaporated in the forest. Again, as
we have seen, twice as much of the rainfall soaks into the ground in the
forest as in the open, and owing to the tree-roots and general covering
of the soil the water can only flow away gradually. On the other hand,
in the open, if the ground is at all sloping, more than half of the rain
which falls to the ground runs away immediately, or lies on the land,
flooding it and making planting impossible.
[Illustration: FIG. 106.—=Rest House Teak Plantation at Ndeh, showing
rows of trees 9 feet apart and 4 feet between.=]
[Illustration: FIG. 107.—=View between the lines of one-year-old Teak
Plantation at Ndeh, in which trees were planted 4 feet apart.=]
To face p. 486.
The trees then act as a rainfall distributer and also as a rainfall
regulator. The roots of the trees act like a sponge, absorbing a great
deal of the rainwater besides preventing it from running away. It has
been calculated that it takes nearly six months for the rainfall to come
out in the springs of a forest. This also to some extent accounts for
the saying that if the wells are full in October in the Temperate Zone,
or at the end of March in the Tropical Zone, there will be sufficient
water the whole year round. With a varied distribution of forests in the
country, the above two effects are naturally felt on neighbouring
agricultural land, and in many cases make possible the growing of
certain crops, such as cocoa, Cola and rubber, which otherwise could not
be attempted. An interesting example of this is seen in the way in which
the natives of Ilobe, in Nigeria, have planted Cola trees just inside
and on the edge of the Ilaro Forest Reserve boundary.
3. The forest protects the land against corrosion. In most countries,
wherever the ground is sloping and bare the annual fall of rain washes
away large masses of good soil as well as stones and other debris, in
many cases destroying pasturage or agricultural land, and in any case
silting up the rivers with sand-banks and bars, thus hindering
navigation. It has often been said that, for its size, the Cross River
carries in the rainy season much more material in suspension and rolled
along its bed than many other African rivers. The main reason apparently
for this fact is that several of its tributaries, such as the Mbu, the
Fi, the Mfu and the Bago, rise at what are now partially grass-covered
mountain slopes, but which no doubt were a short time ago covered with
fine evergreen forests.
The immediate effect of clearing such slopes is that the water, to the
extent of nearly 90 per cent., rushes unchecked down the mountain slope,
gaining momentum with every mile and taking grass, soil and even whole
mountain slopes (1,500 feet in height) along with it. On the other hand,
if such slopes are covered with forest trees 25 per cent. of the
rainfall is re-evaporated into the air before reaching the ground, 10
per cent. is evaporated from the ground into the air of the forest, and
fully 65 per cent. soaks into the ground.
An instance of this last effect can be seen in the Cross River Divide
from the Bambuto Mountains, on the Nigerian border. In a few places the
native farmers understand this effect and make the terraces on which
they plant parallel with the contour of the hill-side; however, this is
insufficient when the whole mountain slope has been cleared of forest.
Only a definite distribution of the land between forest and farm would
prevent the undue corroding of hill-sides. The unrestricted rush of the
rainwater off the hill-sides has yet a further effect on the lower
ground of the country, in that it causes the streams and rivers to flood
and overflow their banks. This, in turn, prevents huge acreages of land
from being cultivated for many months in the year, and other large areas
lower down from being cultivated at all.
Yet another effect is that a vast mass of water hurries down into the
sea where it is not required, and where there is already plenty of
evaporation; whereas the greater part of it might have been stored up in
the forest to form perennial, almost unaltering springs, streams and
rivers. Two interesting examples of this are seen in the slight, almost
negligible rise in the Okwo and the Igbagon streams of the Benin
province. Both of these rivers rise in thick forest, and thick forest is
also found on their banks.
In a similar way, instead of the water of the rivers being used for
irrigating land which is sandy and dry in the dry season, it rushes away
into the ocean for nothing. The flooding of much of the land near the
rivers also kills many large forest trees and causes a rank growth of
shrubs, creepers and grass, which form the breeding-places for tsetse
and other harmful flies. It is rare to find any infected tsetse flies
near a clear perennial stream in the forest.
4. The forest improves the soil of a locality, whether in the primeval
or the planted forest. The trees stand at least eighty years, and
sometimes for several hundred, on the same land, before being cut down.
During this period the tree roots with their root-hairs are penetrating
far and wide into the soil, subsoil, and even underlying rock, gradually
causing the two latter to weather into finer and better constituent
parts. For instance, nothing appears so solid as a mountain of granite;
nevertheless, at the base and to the lee-side of each boulder, more
especially if there is any tree-growth there, a beautiful little bed or
pocket of blackish soil will be found. Then, again, besides this
weathering of the subsoil and rock, the tree leaves, even from evergreen
trees, fall down, gradually decay, and form a thick layer of humus. This
in itself forms an almost ideal seed-bed. At the edge of forests this
humus is washed out on to the agricultural lands and thus enriches them;
furthermore, dry leaves are blown out of the edge of the forest on to
neighbouring agricultural land, become dug in, or drawn into the land by
insects, and so tend to enrich it. In many civilized countries a regular
business is done in taking litter and leaf-mould out of the forest to
neighbouring garden and farm lands.
It is a well-known fact that when a forest is cut down after some
hundreds of years many plants appear in the clearing which did not exist
in the forest before, or, in fact, were not known in that locality, the
seeds having lain dormant during the whole period of time. This clearly
shows that the forest soil is an ideal medium for preserving seeds, and
that it improves rather than deteriorates, which is the case with bare
land. An instance of this from the Tropics is seen in the way in which
the Corkwood or Umbrella Tree (_Musanga Smithii_) comes up after the
mahogany and evergreen forest has been cleared. No Musanga trees are
usually found in the primeval forest. A parallel example from Europe is
seen in the way in which _Atropa belladonna_ almost invariably appears
when a beech forest is cut down.
Planting trees and thus forming a forest, though expensive, is another
way of clearly proving the beneficial effect of the forest, or
ameliorating the condition and plant-food content of the soil. On the
comparatively worn-out and poor soil near Ibadan a firewood plantation
was started some years ago; now already, in the shade of the Ayin,
_Anogeissus leiocarpus_ and _Cassia Siamea_ trees, the fallen leaves
have decayed and formed a layer of humus, killing out the lalang grass
at the same time. Needless to say, it is a very expensive method to wait
until the forest has been destroyed, the soil impoverished, and trees
again planted, before an improvement in the soil conditions can be
expected.
5. Individual trees, and thus trees in the aggregate, viz. forests, take
less mineral matter out of the soil than agricultural crops covering a
similar area. It has been calculated that the trees on an acre of land
only take one-twelfth of the amount of mineral matter out of the ground
which is required by an agricultural crop on the same area. It follows
from this that trees, and in the same way forests, may be left standing
upon or be grown on land which is nearly or absolutely worthless from an
agricultural point of view. In the more civilized countries this is
seen, for instance, in the way in which the mountain ranges of Germany
have remained covered with forest and the sandy Landes district of
France has been planted with forests of pine. In Canada, the Spruce
Hills Reserve, near the Canadian Pacific Railway in Manitoba, is another
example of the setting aside of poor, almost worthless agricultural land
as a permanent forest area. In Nigeria, the Oban Forest Reserve and the
forest-covered hills of Olokemeji are further examples of the practice
of this principle.
Generally speaking, in fact, in most civilized countries there are
really three types of land, viz.:
(_a_) Absolute farm-land, which comprises the very richest and best land
of the country, in which forests should only be allowed to stand, as an
exception.
(_b_) Relative forest-land, comprising land which can be used
permanently for agriculture, but requiring a great deal to be spent on
improvements or manures to make it suitable for the purposes, but which
in its natural state carries a heavy stand of timber, could be used for
forests indefinitely.
(_c_) Absolute forest-land, comprising land which, owing either to its
elevation, aspect, soil or position, cannot be used for the permanent
cultivation, or in some cases even the temporary cultivation, of crops.
6. The forest protects agricultural land against storms and insect
pests. In many places, owing to very strong winds, certain crops cannot
be grown. For instance, it is said bananas cannot be grown at Zaria
owing to the prevalent strong winds. In the Chang district of the
Cameroons the natives only plant plantains near their houses or behind
the very high fences or hedges which mark off one man’s compound from
another. Apparently this is done in order to protect the plants from the
wind, which otherwise tears their large leaves into shreds and prevents
their proper growth.
Some years ago, in the Ibadan district, a fierce tornado cut a path
about 100 feet wide and nearly a mile long through a forest, but the
agricultural land beyond was untouched. It goes without saying that had
all the land been under crops in this locality most of them would have
been destroyed, whereas the forest took the brunt of the storm, and the
force of the wind outside was thus weakened and comparatively harmless.
7. The forest protects the soil and its physical properties. In the open
it is noticeable that the native rarely clears the land properly, many
stumps both of forest trees and shrubs being usually allowed to remain
standing. It is true some of the shoots from the stumps are left on
purpose to be used as supports for the yam tendrils or other crops which
may be grown. Nevertheless, it is a fact that the native always says
that the land must not be absolutely cleared of all stumps and roots or
it will be useless for the growing of crops. Then, again, the native
speaks of a piece of ground as being “spoilt,” and that he cannot stay
there any longer. As an example of this, in the Oban district, the
people of Ekong left the village site because they said the ground was
too stony and was no good, and they went right away into the forest. On
an examination of the land being made, it was found that where they had
cleared the forest and farmed for a few years all the humus, tilth and
other soil had been washed away, with the result that boulders as well
as the underlying rock had to some extent come to view. Needless to say
no attempt had been made at farming under a rotation of crops, nor had
any manure, green or otherwise, been applied to the soil. On the other
hand, in the forest the soil is not washed away, the aeration of it is
almost perfect, the mineral content is always high, and it usually has
considerable depth, even where there are rock outcrops, for these become
covered with dead leaves or humus, which in their turn help to weather
the rock and thus make more soil.
8. The forest tends to regulate the temperature, almost preventing
extremes of heat and cold. Accurate measurements taken over a period of
forty years have established the fact that in the warmest season the
temperature of the forest is 5° to 10° lower, according to species
(altitude taken to be the same), than the air in the open over
agricultural land. In a similar way, in the coldest season of the year
the temperature of the forest is 5° to 10° higher than in the open over
agricultural land. Most readers will have experienced the feeling of
freshness and coolness in passing through the forest zone near Olokemeji
on the Nigerian Railway, or, if on leave in England, in passing through
the New Forest on the Bournemouth road. This is only the effect which is
expressed in this difference of temperature: as with other effects, so
this one affects the neighbouring lands near the forest. Even a dry wind
on reaching a forest must take up some moisture, and thus be less dry
when it reaches agricultural land farther on. It can often be seen how
the grain in the drier parts of the country planted near the edge of a
forest sprouts up sooner than that right in the open. Again, certain
crops, such as cacao-yams, cocoa, and Cola trees thrive best amongst
trees. Without the forests the Cola plantations of the Ilesha district
would cease to exist, or at any rate bear very small crops.
9. The forest increases the humidity of the air. According to accurate
measurements taken over a period of forty years, it has been proved that
the forest increases the humidity of the air up to 10 per cent. No doubt
in many of the Southern parts of Nigeria and the Gold Coast, people
travelling in the forests have often thought that there was far too much
moisture, not only coming from above and below, but also in the air
around them. However, this should not blind us to the fact that further
up country this greater humidity of the air of the forest is spread over
the adjacent lands, and thus makes possible the growth of agricultural
crops, such as cocoa, Cola, yams, and cacao-yams, which would not
otherwise be possible. This greater humidity also tends to induce local
minor rainstorms, which in their turn benefit the adjacent agricultural
land. This greater humidity of the air also tends to prevent the
excessive drying in the dry season of the land situated very near, and
taken in conjunction with the other factors, such as the regulating of
the temperature and the rainfall, makes it possible to put in crops
earlier and almost ensures their growing successfully.
10. The forests prevent the spread of insect and fungoid pests. So often
we read that the crops in South Africa or the Argentine have been
destroyed by locusts, and on the Gold Coast we read that various pests
are destroying cocoa-trees in large numbers. Here, again, a forest or a
belt of forests with large numbers of different species of trees
interpose a living barrier of green leaf food or woody tissue which
these pests may attack, owing to the diversity of the species of trees.
Most pests only find a few trees on which they can thrive or reproduce
themselves; thus on reaching the forest the scourge tends to lessen, or
even die out. Even in the worst case of large hordes of locusts, it is
cheaper to allow them into a forest, perhaps sacrificing it, rather than
they should spread further and further over agricultural lands.
Having shown that it is necessary in a new and comparatively unsettled
country to preserve a certain proportion of the forests, it remains to
be considered what proportion is desirable and necessary to fulfil the
conditions outlined before and give free play to all the beneficial
effects of the forests.
Taking the proportion of permanent forest to other land in the more
civilized countries, we get the following ratios:—
Forest per cent.
Finland 80
Russia in Europe 42
Austria 33
Hungary 29
Germany 26
France 16
Sweden 42
Switzerland 19
Norway 25
U.S.A. 10
India 38
Special note should be made of the fact that in all these countries the
agricultural development has gone hand in hand with the preservation of
the forest, and especially with no detriment to the development of
agriculture in any direction in which it seemed desirable. Russia has,
for instance, enormous exports of timber and enormous exports of wheat.
Austria-Hungary had before the war considerable exports of hardwood
timber, such as oak, as well as grain, both wheat and other kinds.
Judging by the experience gained in Germany with its hundred and seventy
years of forestry practice, a proportion of 25 to 33 per cent. of the
land area of any country can reasonably be retained under forest, or
afforested if bare. Such a proportion allows sufficient timber trees to
be grown to cover the large quantities of wood used in industrial
development and also a considerable surplus for export to other
countries.
Turning specifically to the West African Colonies, it would mean, out of
a total land area of 4,500 square miles, that in the Gambia, for
instance, an area of between 1,100 and 1,500 square miles should be
permanently set aside as Forest Reserves or Forest Reserve Afforestation
Areas. In the latter case, when all were planted up they would gradually
become forests.
In Sierra Leone, with a total land area of 34,000 square miles, the area
would vary from 8,500 to 11,000 square miles.
In the Gold Coast, out of a total land area of 80,000 square miles, the
permanent forest area would vary between 20,000 and 26,000 square miles.
In the Southern Provinces of Nigeria, with a total area of 79,000 square
miles, the permanent forest area would reach between 19,000 and 26,000
square miles.
In the Northern Provinces of Nigeria, out of a total area of 250,000
square miles, the permanent forest area, including the afforestation
areas, would reach between 62,000 and 83,000 square miles.
Large though these forest or afforestation areas appear to be, it can,
however, be shown that most of them do not at all trench on existing
farm-land. First of all, in Nigeria, taking the protective forests,
comprising all those lands or forests situated in most inaccessible
places on mountain ranges and hill-sides and the sources of streams,
they cannot be said to be desirable localities for extending farming
operations. Typical instances of this kind of land are seen in the Boji
Hills (Ogoja province), and on the rocky hills near the Cross River in
the Afikpo district (Owerri province). In Sierra Leone the peninsular
mountain forests and the hills near Kennema are similar typical examples
of this type of land or forest.
At the other extreme we have the dry-zone or desert formation, with its
sandy soil or bare rock outcrops. In either region, in order to make
agriculture possible and permanently profitable, afforestation areas are
most necessary. Near the sea, especially in Nigeria and to some extent
in Sierra Leone, there are the mangrove forests standing on land which
is never used for agricultural purposes. In Nigeria alone these comprise
several thousand square miles of land. Again, in Nigeria there are the
freshwater swamp forests, either near rivers or in other localities.
Although such lands produce quite a profitable amount of timber from
many excellent species of trees, no farms have ever been made in such
areas.
In other parts of the country, often comparatively level, there are
variations in the strata and soil formation, such as that of the
laterite formation. Over wide areas most of these lateritic soils are
nearly useless for permanent agricultural crops, so at any rate it would
certainly pay better in the long run if it were permanently covered with
forest. In a similar manner all forests found growing on or near rock
outcrops or otherwise stony formations, such as old gravel beds formed
by rivers, would be treated in the same way. One or two agricultural
crops may be raised on such land, but all the soil is soon washed away
in the rainy season each year, so that little is left after a short time
except boulders and stones. Many typical instances of this kind of
formation are found in the Ibadan and Oyo districts of the Oyo province.
In other parts of the country, where practically all the land is covered
with some sort of forest (either high forest, secondary growth or
scrub), the same proportion as before, viz. 25 to 33 per cent., should
be set aside in convenient blocks, well distributed over the area, as
permanent forests (so-called Forest Reserves).
Strange as it may sound, there is comparatively little, at the most an
area estimated at 7,000 square miles, of real high forest left in the
Southern Provinces of Nigeria. As is well known, the natives have a
special name for this type of forest; amongst the Efiks it is called
Ekai, the Yorubas term it Igbo, and the Benin people Egbo. Considering
the size of these last remnants of the real high forest, agriculture
cannot justly claim the right to clear and farm even this area when so
much (estimated at 28,000 square miles), apart from the area already
mentioned, has been cleared during the last fourteen years. In the above
estimate, areas even of 500 square miles for roadways and railways,
1,000 square miles for town, village and factory sites, and 2,500 square
miles for inland waterways were allowed for when computing the whole
area of forest land.
At the present time in Nigeria, with the exception of certain specified
trees, and less so in the Gold Coast, Sierra Leone and the Gambia, there
is nothing to hinder a native from cutting down any forest he pleases
for making a temporary farm. In fact, the difference between farming as
practised in civilized countries and in these tropical West African
Colonies is that the former partakes of a permanent cultivation of the
same land every year, whereas the latter is shifting cultivation of a
different piece of land almost every year. At the most, the Yoruba
returns to the land in five or seven years, and the native of Benin
after ten or twelve years.
Another point which bears on this question is really the comparatively
small amount of land which a native actually farms every year. For
instance, an energetic Yoruba farmer will make 2,000 yam heaps a year,
which, allowing for the distance of 6 feet between each heap, amounts to
1·6 acres per year. This also includes the help which he may receive
from his family.
Out of a total population of 8,000,000, at the most 2,000,000 are
actually men who make farms. It follows, then, that some 2,560,000
acres, or 4,000 square miles, are cleared and planted each year. Now,
allowing sufficient land for the native to be able to return to the
original piece cleared after seven years, the total amount of land
necessary for the existing farming population would be 28,000 square
miles, or rather more than a third of the total area of the country.
Even after allowing 19,000 or 26,000 square miles of forest in the
country, there would still remain nearly a third, or 25,000 square
miles, for the future development of agriculture and the natural
increase of the population. It should be especially noted that it is
under a system of shifting cultivation that this 28,000 square miles is
required. No doubt under permanent cultivation less would be necessary.
Quite apart, however, from this consideration, owing to the greater
heat, moisture and humidity in the Tropics generally, and in the
Southern Provinces of Nigeria particularly, agricultural crops grow much
more rapidly and are much more prolific than in the more temperate
zones, even without manures. Yet in another way there is not such an
enormous demand on the amount of land required per unit of population,
in that over an area of fully 30,000 square miles it is possible to
raise two crops a year on the same land, and over roughly an area of
10,000 square miles of the country it is possible to raise three crops
per year (in each case under a rotation of crops). In this manner less
land is required per person than in a temperate climate in order to grow
food either for local consumption or for export.
So far we have dealt with shifting cultivation. However, in most
civilized countries, sooner or later a system of permanent cultivation
is started instead of shifting farms. In England this was begun at a
time in which the population was less dense to the square mile than it
is now in the Southern Provinces of Nigeria (average 101 persons per
square mile). In Germany the density of population is 323 persons per
square mile, yet they had (before the war) 25 per cent. of the land area
of their country covered with permanent forests. If it were possible to
start permanent cultivation with a rotation of crops in England when the
population was less dense than in the Southern Provinces of Nigeria, it
should be feasible in Nigeria now. Again, if it is found possible for
Germany to retain 25 per cent. of the land area under permanent forest
crops, with a density of population three times greater than that of
Nigeria, at the same time maintaining a prosperous system of permanent
agricultural cultivation, it should also be much easier to have a
similar proportion of permanent agricultural cultivation in the Southern
Provinces of Nigeria; at the same time, taking into consideration the
more favourable climatic factors, it should be possible not only to grow
sufficient foodstuffs for local use, but also to grow sufficient to
develop into a large export trade for ground nuts, maize and beans,
besides cocoa and rubber.