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CONCEPTS

OF

AGROFORBSTRY

BY

K
...
S
...
O
...


Agroforestry is a system

of land management which seems to be suitable for these ecologically
brittle areas, It combines the protective characteristics of forestry
with tbe productive attributes of bath forestry end agriculture
...


It

It is suggested that if the concepts of

competition among plants are understood, and appplied in the practice
of the system of agroforestry, the system would achieve the objectives
that have been stated above
...


CONCEPTS

OF

AGROFORESTRY

K
...
S
...


The group

came up with the following definition:
"Agroforestry is
...

(See Bene et
...
, 1977)
...

You will note that by the addition of the phrase "on the same unit of land"
we sought to emphasize that zonal arrangements of agricultural crops and
forest crops were not considered to be agroforestry, and to imply that the
mixtures of the combined agricultural and forest crops should be intimate
...


The definitions are inadequate in another respect, in that they do not
distinguish the many types of systems which may possibly fall within their
ambit
...

Agroforestry should be considered to be a generic term which embraces the
following specific components:
Agri-silviculture - the conscious and deliberate use of land for the
concurrent production of agricultural crops (including tree crops) and forest
crops
...

Agro-sylvo-pastoral systems - in which land is managed for the concurrent
production of agricultural and forest crops and for the rearing of domesticated animals
...

Multi-purpose forest tree production systems - here forest tree species
are regenerated and managed for their ability to produce not only wood, but
leaves and/or fruit that are suitable for food and/or fodder
...

It is suggested, as a working hypothesis, that agroforestry might be considered to be practised whenever trees and agricultural crops are grown in
mixture, provided that the combined widths of the rows of agricultural crops
do not exceed the heights, at maturity or at the end of the selected rotation,
of the forest tree crops with which they are grown in mixture;

provided

further that the combined widths of the rows of the forest tree crops do not
exceed the height of the tree crop at maturity or at some selected rotation
...


It assumes

that agriculture crops that are grown in strips etc
...


- 3 premises of agroforestry
The premises on which the concept of agroforestry is based are partly biological and partly socio-economic
...
Biological premises
It is known that, generally, forests have a beneficent effect on the soil
...
This
litter is transformed into humus,

and later incorporated into the soil
...


For, a well managed forest is to a large extent a closed

system, and can be maintained that way
...


Trees are

generally deeper-rooting than other types of crops, and are often able to
trap and utilise nutrients that have been leached from the upper layers of
the soil
...


This nutrient pumping attribute implies, of course,

that the natural nutrient input side of the equation in a forest is greater
than that in an agricultural field
...


The crowns in the canopy, and those

in the intermediate strata of the forests, progressively reduce the potential
impact of rain on the soil below
...


The net effect is that the

compacting effects of falling rain on the soil are reduced, there is little
or no erosion on the forest floor, and another possible source of leakage of
nutrients from the system is at least partially plugged
...
- The most important properties of the earth's
surface which influence climate, and which human activity can influence, are

17

The following few paragraphs are based on King, K
...
S
...
Congress Rep
...
Oslo

Reflectivity, heat capacity and conductivity, availability of water and
dust, aerodynamic roughness, emissivity in the infra-red band, and heat
released to the ground (Wilson, 1970)
...


The reflectivity of the

forests is low because of the high radiant absorptive capacity of their green
leaves when converting radial energy to chemical energy
...
8°F (U
...
A
...


Recently, in an interesting experiment

two

integrations of a global general circulation model, differing only in the
prescribed surface albedo in the Sahara, showed that an increase in albedo
resulting from a decrease in plant cover causes a decrease in rainfall
...
al
...

Moreover, because large amounts of latent heat are fixed during the evapotranspiration process, the capacity of the forests to absorb heat is high
...

In addition, forests, by acting as windbreaks,
and assist in arresting dust particules
...


create aerodynamic roughness

Their emissivity of the infra-red band

It is evident, therefore, that the forests play roles which

affect all the important factors which influence climate
...


It is submitted,

however, that it is sufficiently long and wide-ranging to indicate that
trees grown in mixture with agricultural crops, or agroforestry systems, might
a priori, especially in brittle ecosystems, be a productive form of land-use
...


- 5 -

B
...

First, forests are being felled in all the developing continents of the
world by farmers who require the land to produce food for their very existence
...

The people who clear the forests to produce food are often not unaware of the
possibly deleterious effects of their practices upon the ecosystem:

in terms

of erosion hazards, the possibility of droughts and floods, and the possibility
of soil fertility decline
...

action
...


Secondly, the consequences of ill-advised land-use are often experienced not
only in the areas in which such practices are perpetrated, but also in others
that are either adjacent or far-removed from the originally damaged sites
...

Third, the failure to develop the marginal lands often leads to a retardation
of the rate of development of the general economy
...


The point is that the developmental

and technological options are fewer in marginal than in most other ecosystems
...


It is one of the arguments of this paper that when the biological influences
and services of forests are considered along with the specific socio-economic
problems of those who exist in marginal areas, together with the general
developmental problems of national economies, this technological package
should include agroforestry systems
...


Moreover, in a survey which was made a decade ago (King,

1968) most foresters who practised the taungya system gave as their opinion
that land-hunger and unemployment were prerequisites
...


By effectively

keeping farmers outside the forest reserves they have in fact acted as land
banks of natural high forest, retaining land capital for possible future
development outside forestry
...


On the other hand, this type

of reservation has often led to a local shortage of agricultural land, and
where the system of shifting cultivation is still practised to a reduction
of the fallow period with its attendent evils
...

The point that is being made is that the system of agri-silviculture has been
practised,in the past, mainly in the forest reserves, that the farmer had no
rights to the land within these reserves, that the land-hunger was in most
cases created by the Forest Departments, and that unless a person was destitute
(i
...
unemployed and landless) there was no incentive for him to practise agroforestry
...
Indeed, the
the system was geared to conditions of land-hunger and unemployment which had,
in the past, been created by the exploiters
...


Some Biological Considerations in Agroforestry
Agroforestry is a system of land management in which tree crops are grown
together with agricultural crops, one objective being to optimise and sustain
the joint yields of the combined crops
...
These, it has been submitted, would
positively contribute to the optimisation and sustention of the joint yields
of the combined crops, provided that the influence of the tree crops on the
agricultural crops and vice versa do not adversely counteract the positive
influences of the forest ecosystem
...

Clements et
...
(1929) have described competition as a purely physical
process
...


Competition arises from the reaction

of one plant upon the physical factors about it and the effect of the modified
factors upon its competitors
...

When the immediate supply of a single necessary factor falls below the
combined demands of the plants, competition begins"
...

Both Clements (1929) and Donald (1963) have stressed that competition for
space is exceptional, and that what are really important are water, nutrients,
light, oxygen and carbon dioxide
...


Temperature and humidity

which also affect growth are not commodities in finite supply and therefore
are not the subject of competition
...


However,

it is perhaps apposite at this stage, before referring specifically to the
agroforestry requirements, to emphasize the following:
1)

"Most of the factors for which there is competition are found as a
pool of material from which competitors draw their supplies
...
If all the plants
in the community are nearly equal in competitive ability

they will

tend to share equally in its supply until it is exhausted, and then,
simultaneously, to suffer the effect of depletion of the pool"
...

ii)

With respect to nutrients, "the capacity to draw from the pool is in
varying degree an expression of the differing ability of plants to
make use of the nutrient in different chemical and physical forms"
...
"There is no store of light energy
in the immediate environs of the plant
...


A dense canopy will intercept

all light, but the young crop characteristically covers only a small
proportion of the soil surface and most of the energy is absorbed or
reflected by the soil" (Donald, 1963)
...
As far as possible, the forest and agricultural species that are utilized
in the system should be compatible and should complement each other in growth
patterns over most stages of their lives
...

Elsewhere (King, 1979), I have indicated the characteristics of the tree
species that should be grown in agroforestry systems:
a
...


they should possess self-pruning properties;

c
...
e
...


they should have a low crown diameter to bole diameter ratio i
...

the width of their crowns should be small relative to bole diameter;

e
...


they should be tolerant of side-shade, if indeed not of full over
head shade in the early stages of growth;

g
...


their phenology, particularly with respect to leaf flushing and
leaf-fall, should be advantageous to the growth of the annual crop
in conjunction with which they are being raised;

1
...


their "above ground" changes over time in structure and morphology
should be such that they retain or improve those characteristics
which reduce competition for solar energy, nutrients and water;

k
...


they should be efficient nutrient pumps
...


In addition,

cognisance must be taken of the known responses of the tree species to various management practices (such as pruning, thinning, and coppicing, for
example) and to individual tree and stand manipulation
...

Put in another way, the plant architecture and morphology, the phenology of
woody perennials, and the root distribution, root growth and root activity
of the trees, must be examined
...

In addition, the influence of genotype and environment on dry matter distribution in herbaceous and woody plants; the effects of management on plant
growth, dry matter distribution and plant development;

and the factors

affecting the plant's nutrient needs and the distribution of nutrients within
plants should be examined
...


This is not the place to

review the prodigious volume of literature that is extant, but Iwaki's (1959)
work on interspecific competition in plant communities, Hall's (1974 and 1974a)
and de Wit's (1960 and 1963) work on the nature of interference between plants
of different species, the analysis of Trenbath and Angus (1975) on the relationship of leaf inclination and crop production, Grime's (1966) investigations
on shade avoidance and tolerance, and the studies of Puckridge and Donald (1967)
on competition among plants sown at a wide range of densitites, give but a
small proportion of the knowledge that is already available and that can be
used with advantage in the practice of agroforestry, in the formulation of
research policies and in the design of research projects in agroforestry
...


-11-

lt is also possible to construct predictive, models which would suggest
the probable responses of plants in various mixtures and combinations
agroforestry systems (Trenbath, 1974 and 1978)

in

REFERENCES "

Bene, J
...
, and Cote, A
...

Charney J
...
, and Quirk, W
...

Science, Vol
...
E
...
E
...
(1929) - Carnegie Inst
...

Publ
...
(1963) - Competition among crop and pasture plants
...
Agron
...

F
...
O
...
U
...
Conf
...

Grime, J
...
(1966) - Shade avoidance and shade tolerance in flowering
plants
...
Bainbridge, A
...
Evans and 0
...

Light as an Ecological Factor
...
Oxford
Hall, R
...
(1974) - Analysis of the nature of interference between
plants of different species
...
Aust
...
Agr
...
25
...
C
...
II Nutrient relations in a Nandi
Setaria and greenleaf Desmodium association with particular
reference to potassium
...
J
...
Res
...

Iwaki, H
...
I
...
Journ
...
17(1)
King, K
...
S
...
University of Ibadan, Ibadan
King, K
...
S
...
Congr
...
XVI
IUFRO World Congress
...
F
...
(1978) - Agroforestry
...
c
...
Agr
...
303, Dept
...
Agr
...
, R
...
I
...

King, K
...
S
...
Pap
...
Mat
...

King, K
...
S
...
T
...
ICRAF, Nairobi
Puckridge, -D
...
and Donald C M
...
Aust
...
Agric
...
18
...
R
...
Proc
...

Grassland Congr
...
R
...

In Plant Relations in Pastures,J
...
Wilson (Ed
...


Trenbath, B
...
and Angus, J
...
(1975) - Leaf Inclination and Crop Production, Field Crop A
Wilson, C
...
(Ed
...
I
...
Boston

de Wit, C
...
(1960) - On competition
...
Landbouwkd
...
66(8)
de Wit, C
...
(1965) - Competition between herbage plants
...
J
...
Sci
...

U
...
A
...
Washington, D
...




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