- why plant tropical trees?
Why is tree planting important in the tropics?
Because tropical trees, forests and savanna woodlands play vital roles in:
- protecting the land from becoming degraded;
- providing the conditions needed for farming; and
- producing many of the necessities of life.
So, where only a few trees are left, it is bad news for the people who live locally, and can also
cause serious problems for those further away.
But surely trees just come up by themselves!
Yes they may do:
- when humans have had only a small impact on the area (D 16); or
- if trees are being managed to encourage natural regeneration (D 2);
But they may not do so:
- when humans have opened up the woodland or forest substantially; or
- if the area has been largely cleared of trees.
Why do fewer trees come up on more open sites?
For one or more of the following reasons:
- there are not enough seed and pollen trees nearby (Manual 2);
- the flowers on trees left in the area have not been pollinated;
- too few fruits and seeds ripened, or they were mostly eaten;
- the site is no longer a suitable seed bed for germination, because:
Some of these micro-organisms are crucial in maintaining soil fertility, and can help
seedling trees to become established (D 13, D 32 and Manual 3);
- the soil has been degraded or washed away (D 22–23);
- the topsoil is too hot and or too dry (D 11–13);
- there are not enough suitable fungi or bacteria in the soil.
- the area is choked with weeds (D 14);
- all the seedlings have been eaten or repeatedly browsed by wild or domesticated
animals (D 15, D 34).
So how can planting trees help?
Many of these problems can be reduced or overcome by:
- propagating trees in a nursery (Manuals 1–3);
- planting them out (Manuals 4–5); and then
- looking after them (Manual 5).
Planting is also very useful when:
- there are not enough natural trees and saplings on the site; or
- you want to add different tree species (D 30, D 53), fresh varieties (Manual 2) or new
clones (Manual 1).
But won't the planted trees get damaged or killed too?
Yes they are liable to many of the same risks, but
- they can be started off with good root systems (Manual 3);
- they can be weeded and protected more easily (Manual 5);
- generally tree and shrub types can be used that are good at colonising open ground
(D 14), or improving degraded land (D 22, D 32);
- valuable species can be chosen that are worth special care.
See D 4, D 70–71 and Manual 5 for more information on overcoming problems of replanting.
Does this mean that the existing trees don't really matter?
Not at all! They are needed to:
- keep sufficient cover over the site to protect the soil (D 12–13, D 50–51, D 60);
- maintain enough biodiversity (D 14, D 30–31, D 53);
- allow beneficial animals to live and breed (D 15);
- provide additional useful materials (D 33–40).
Planting and making the best use of existing trees go along together (D 2).
Why should one need a Manual to plant trees?
- there are many points to think about beforehand;
- although most steps are straightforward, a problem at only one point can easily prevent
- not all the relevant information is readily available; and
- everyone in the tropics needs to get involved with tree planting (D 5).
Who might want to use this series of Manuals?
The Manuals are meant for anyone who wants to grow and plant tropical trees, such as:
- farmers, including smallholders;
- staff of forestry, agriculture and horticulture departments;
- managers of private farming, forestry and timber firms;
- those involved in managing natural resources and promoting rural development;
- staff of international funding agencies;
- people in organisations concerned with sustainable development;
- teachers and school children;
- lecturers and students, research workers and extension staff;
- individuals working in agroforestry and community tree planting projects;
- people needing to protect their land from erosion by water or wind, or wanting to
reclaim degraded land.
What sorts of trees are the Manuals for?
Any kind of tropical tree.
But there are hundreds!
Yes there are. But this series of Manuals deals with the general principles of choosing,
growing, planting and establishing them. These principles apply to most species, grown for
many different reasons, throughout the tropics.
Choosing which species to plant is covered in sheets D 30–42 and D 53.
Are the Manuals available only in English?
No, they are being translated into Bahasa Malaysia. It is hoped that arrangements may also be
made for French, Spanish and other languages, and that they may support and stimulate
specific, local publications and further translations.
A video series is available to accompany Manual 1 (D 71).
How do trees protect the land?
There are many different ways in which the foliage, fallen leaves and extensive root systems of
trees can maintain or improve soil fertility, while protecting the site from sun, heavy raindrops
and wind. These include:
- shading the ground surface and topsoil, and so reducing excessive heating and
evaporation (D 11);
- reducing the blowing away of litter and fine soil in the wind (D 11);
- maintaining and improving the soil structure (D 12, D 60);
- providing good conditions for root growth, and for earthworms and other living
organisms that re-cycle nutrients (D 13, D 22, D 50);
- forming important associations with micro-organisms that fix nitrogen from the
atmosphere, or release insoluble nitrogen or phosphorus, adding to the available nutrients
in the soil (D 13, D 32);
- checking the impact of heavy raindrops and rapid run-off that would otherwise
greatly increase erosion, particularly on slopes (D 23);
- regulating water flow from watersheds into reservoirs (D 23);
- protecting water courses, lakes and lower farmland from excessive silt and mud
deposits (D 23);
- discouraging the spread of rampant weeds (D 14, D 51);
- moderating the local environment, including the capture of dust and pollutants
- acting as a focus for cultural and religious life (D 42), and giving people a background
that is stable and pleasant (D 41);
- counteracting possible changes to regional rainfall patterns and global climate, including
the withdrawal of carbon dioxide from the atmosphere (D 11).
Is this how trees provide conditions needed for farming?
Yes, many of these points mean that trees help by:
- maintaining more favourable soil conditions for farming (D 3, D 12–13, D 21);
- still providing some shade and shelter when the canopy has been opened up (D 41,
D 50–51, D 60); and
- restoring land that has become degraded (D 22, D 32).
What kind of products do tropical trees provide?
As well as all these indirect benefits, many different items come directly from tropical trees,
- foods and medicines (D 21, D 33);
- fodder and browse for domesticated animals, even in the dry season (D 3, D 34);
- firewood and charcoal (D 35);
- sawn planks and plywood (D 36);
- raw materials for processing into paper, particle boards and chemicals (D 37);
- a great variety of local building materials (D 38–39);
- household and agricultural implements (D 39).
Most of these tree products are used directly by those who collect them, sold locally or exported
to another part of the same country. Relatively few of them enter international trade,
but they are very important indeed for most people in the tropics.
Can one tree give several products?
Yes, quite often. Multipurpose trees and shrubs (D 40) are notable for producing a variety of
different things, for example:
- poles, fruits and other items that can bring in cash to the grower; and
- fodder, firewood and mulch, etc to use oneself.
Some of them are also valuable soil-improvers (D 32) that can help increase future yields.
What's necessary for successful tree planting?
The various steps are not difficult, but it is important to:
- plan things carefully beforehand (D 4–5);
- have some understanding of how trees interact with their environment (D 10–16);
- think about the particular type of planting site you have (D 20–29);
- consider what you want the trees for, and choose which groups of tree species to concentrate
on (D 30–42);
- arrange to grow adequate numbers of good plants (Manual 3), preferably from superior
genetic sources (Manuals 1 and 2);
- decide on a suitable growing system (D 50–55);
- prepare the site for planting (D 60–67).
How many trees are needed in the tropics?
A lot. Around a million tropical trees are disappearing each day, while the number planted
currently falls far short of this.
Isn't it too late to do anything now?
No, although the position is made harder because:
- getting the immediate necessities of life for today occupies many people's efforts, even
though they might wish to look to the future;
- human populations are increasing rapidly in many tropical countries;
- agricultural yields are often declining; and
- land is also needed for other purposes.
However, it is not too late to:
- recognise the multiple value of tropical trees;
- tackle misunderstandings and lack of communication (D 5); and
- change policies to overcome problems (D 4) and reduce incentives to fell trees without
replacing them (D 5);
- encourage everyone to plant trees in their own interests, and to make sure that at least
10 (and preferably 100) are replaced for each large one cut down.
Won't it all cost too much?
The Manuals describe techniques that:
- do not require expensive equipment or materials;
- can bring multiple benefits, yields and cash returns relatively quickly; and therefore
- are appropriate for smallholders, communities and larger programmes, and for many
different types of planting site.
For each tropical country, replanting the large areas of former forest and savanna lands that
have already been degraded (D 22) may well cost a fair amount, but not as much as losing
the use of them altogether.
Why hasn't tree planting been taken seriously before?
Partly because of various mistaken assumptions, such as:
- “trees aren't an important resource”;
- “there will always be unlimited numbers of them”;
- “ecological science isn't relevant to practical problems”;
- “local experience can be safely ignored”;
- “temperate zone approaches will apply in the tropics”;
- “export items are more important than local supplies”;
- “the bigger the scale of an enterprise, the better”.
Does it make economic sense to exploit renewable natural resources for a single short-term
gain, when they could be managed sustainably to bring yields and benefits in perpetuity?
- natural and artificial regeneration
What does natural regeneration mean?
In forest or savanna that has been little affected by humans, most kinds of trees and shrubs
produce large numbers of seeds. Although only a few of these get a chance to germinate, and
only some seedlings survive to become saplings, enough usually do so for the various species to
maintain their place in the community (D 10, D 14).
The term ‘natural regeneration’ can mean either:
- this natural process; or
- helping natural seedlings to come up and survive, and saplings to thrive.
What is artificial regeneration?
Planting trees, and helping them to become established.
Does that mean replacing natural vegetation with plantations?
No, it doesn't! This is sometimes done, but it is usually more instructive to think of planting as:
- adding more trees wherever there are not enough; and
- supplementing the existing species with other kinds.
Extensive plantations of a single species are no longer seen as necessarily the main way of
growing tropical trees (D 50–55). In many circumstances, it may be more effective to incorporate
tree planting within existing ways of using the land.
Why is that?
Because large plantations involve:
- displacing all the people who lived there (D 5);
- losing all the products that used to be freely available from the site (D 33–40); and
- disrupting the natural regeneration of the trees completely.
Large pure blocks of one species can also sometimes lead to:
- serious loss of soil fertility (D 13, D 50–51, D 60);
- extra flooding and silt deposits on lower-lying land (D 23);
- local extinction of useful plants and animals (D 14–16, D 28);
- poor returns for all the effort, because of the risks of relying on a single product
But surely it's much easier to make large plantations!
It might sometimes be simpler to plan and then plant trees in a large, pure block (D 53–54),
but it can be far from easy to bring them successfully to maturity. Indeed some existing
plantations are now being converted into more diverse stands (D 20, D 50–54).
When do plantations make sense?
See sheets D 30–31 and D 53.
How can one make more use of natural regeneration?
There are several ways. For example, by:
- opening up the canopy of a forest or woodland to a moderate extent (D 51), or in small
groups (D 54), just before or soon after a lot of seeds are shed;
- encouraging germination and survival by cutting patches of underbrush, grass, weeds,
etc (D 63), or perhaps by slight soil disturbance (D 34, D 64);
- favouring existing saplings and good immature trees when felling selected mature trees
(‘liberation thinning’, see D 24, D 51);
- not cutting or poisoning all the overwood when a plantation has become established,
but adopting a multi-storey system (D 52);
- accepting natural trees of any useful species when making a farm, and when preparing
the ground for weeding or thinning planted tree crops (D 30, D 53, D 60, Manual 5);
- growing trees in more than one storey (D 52).
Is a lot known about these methods?
Because so much of the emphasis has been on large, pure, single-storey plantations, both in
forestry and for agricultural tree crops, less research has been done until recently on:
- studying older productive systems of modifying the natural tree vegetation, including
those that have supported human populations successfully in the past; and
- working out newer methods of mixing trees and crop plants, which retain some of the
useful existing trees on various different kinds of sites (D 20, D 70–72).
NOTE: These approaches may well hold the key to sustainable use, based on soil protection
by mixtures of different sizes and kinds of trees with other plants (D 10, D 30, D 50, D 53,
D 60), so avoiding both loss of soil (D 23) and degradation of the site (D 22).
But I can't rely on something that isn't worked out yet!
This is a difficult situation (D 1), but:
- there are ways of tackling many of the problems (D 4);
- these Manuals are primarily concerned with planting trees, about which more is known;
- local field trials (formal and informal) can add important information (D 6).
Are there other ways of combining natural and artificial methods?
(A) Through increasing natural regeneration, for instance by:
- freeing the crowns of potential pollen and seed trees, so that they might produce more
flowers (D 33, Manual 2);
- applying treatments to encourage heavy flowering, where these are known (Manual 2);
- collecting local seed and sowing it directly in appropriate places on the site, for species
where this has been shown to be successful;
- collecting wildings, growing them in a nursery and planting them back on the site later
(B) By planting within existing vegetation, for example:
- enriching logged or secondary forest (D 24, D 26), where the existing canopy is
partly opened (D 51) so that additional useful trees can be planted in strips, lines or
small groups underneath (D 52, D 54), while encouraging any natural seedlings and
- farming within opened forest or savanna woodland, rather than removing the
trees in order to farm, and by planting suitable trees in farms (D 21, D 25, D 33–35)
and in other agroforestry situations (D 3);
- adding new trees amongst natural vegetation in parks and reserves (D 28), to
conserve more species (D 30, D 53), and extra diversity of genetic resources (Manuals
1 and 2).
Are there some guidelines for these approaches?
Natural vegetation can act as a useful indicator of how planting might be most successful. For
- Natural savanna exists as intricate patchworks of grasses and trees. In a managed
savanna (D 25), it may be useful to maintain or re-introduce such patterns by concentrating
tree planting in parts presently, or formerly, under trees. Fire protection might
be needed (D 66), and fencing or hedges (D 39) to keep out grazing animals while the
natural and planted trees are small.
- Tropical forests also show local variation, particularly up and down the slope (D 12),
whether this is steep or not (D 23). In managed forests (D 24), it is likely that fewer
species will thrive on exposed ridges or in swampy or flooded land (D 12, D 26). The
potential for mixed stands (D 30, D 53) is much higher on plateaus, the main slopes,
and in well-drained valleys.
What is agroforestry?
The intentional growing of trees or shrubs combined with agriculture.
Why combine trees and farming?
Because agriculture without trees:
- lacks protection for the soil (D 1, D 12–13, D 60), and (except on fertile valley bottoms
and swamps - D 12) may often be unsustainable, leading to degrading of the site
- often requires sizeable inputs of fertilisers, pesticides, etc, which are costly; and
- fails to provide the many valuable items that trees produce (D 1, D 33–40).
But surely the shade of the trees will reduce yields!
Dense overhead shade is not needed during cropping! Agroforestry is often done in
conditions of opened forest or savanna woodland, obtained by:
- partial opening up of the existing vegetation, that leaves enough protection for the
soil (D 21, D 51, D 60); and/or
- planting at wide spacing (Manual 5).
In addition, some of the trees may be cut, lopped or browsed in order to:
- reduce shading and/or root competition;
- yield forage for domesticated animals (D 34);
- provide mulch (Manual 5).
Who might be interested in agroforestry?
Many people (D 5), including:
- farmers with a smallholding that they want to improve or diversify (D 21);
- families with home gardens or orchard gardens;
- shifting cultivators whose yields are declining (D 22);
- farmers whose flocks of animals need more to eat (D 34);
- foresters who would like to use taungya methods, by which sites are prepared and trees
planted and tended together with a farmer's crops;
- tree-planting projects that intend to involve the local community (D 5, D 27).
Are there different sorts of agroforestry?
Yes there are many kinds, but they can be grouped into 3 main categories:
- ways of combining trees with food crops (silvo-arable systems);
- combinations of trees with domesticated animals (silvo-pastoral systems);
- multiple systems that include trees, crops and animals.
What methods combine crop plants with trees?
A great range of systems in different regions. Some are traditional, some novel, and others are
a mixture of both. They generally involve:
- crops alternating with a fallow period under trees; and/or
- crops grown amongst trees.
Traditional shifting cultivation was often a combination of (1) and (2).
But isn't shifting cultivation outdated?
It has in fact been practised sustainably for centuries, but:
- the declining amount and fertility of land available, and
- the pressure of increasing human populations,
mean that nowadays it is often not sustainable. It may lead to site degradation if done:
- with a short fallow period (1–6 years instead of 15–20 years), particularly when the
land is frequently burnt (D 63) and/or cultivated (D 64); or
- by resettled or migrant people who may not know about local conditions and experience.
However, traditional shifting cultivation is still practised sustainably in some areas. The same
applies to tree fallows, which also have an important role in the reclaiming of degraded land
(D 22), with soil-improving species (D 32).
What about crops grown among trees?
Many agroforestry methods have evolved or been developed as alternatives to shifting cultivation.
Here are some examples:
- farm crops under tall, widely-spaced trees, such as Grevillea robusta;
- arable crops such as cereals grown between parallel lines of shrubs such as Dactyladenia
(Acioa) barteri or Leucaena (alley-cropping);
- perennial shade-bearing crop plants under shade trees as a two-storey stand (D 52).
Examples include cocoa, coffee, spice and medicinal plants under Erythrina, Terminalia,
- intimate mixtures (D 54) of several kinds of farm crops, palms, fruit trees, etc, (including
home gardens, and forest gardens);
- woody plants as live supports for climbing plants like yams and pepper.
How can animals and trees be successfully combined?
Four systems of forage (D 34) can allow both trees and domesticated animals to thrive:
- fodder: where shoots are cut and carried to provide additional food for grazing
animals, or all their food for animals in pens;
- pasture: where animals graze the grassy vegetation covering the ground, provided
they do little damage to the natural or planted trees that give them some shade and
shelter (D 41);
- browse: where the animals are allowed to feed directly from the lower branches of
the shade trees; and
- pannage: where animals dig out roots and other food in the soil under trees.
But isn't there a clash between the two uses of the land?
Yes, there easily can be. For example:
- too many animals for the site can damage pasture and trees through overgrazing
(D 34), and sometimes by compacting the soil (D 12);
- goats usually destroy young trees rapidly, and can damage the bark of older ones.
They need to be tethered, watched or kept back by fences (D 27);
- coppice shoots can provide continuing supplies of animal food, but may need protecting
from over-use. Sometimes pollarding the stem at about 3–5 metres from the
ground means that new shoots grow where many animals cannot reach them;
- the tree species must not be poisonous.
(Note: some foliage, such as Leucaena, is mildly toxic, and should only form part of an animal's
How about multiple systems?
Here the three uses are all present; for example a combination of tall trees, a perennial crop
It all sounds very confusing!
Not if you look at agroforestry as many variations on a single idea: combining trees with
agricultural crops and/or livestock on the same piece of ground. For more information, see
D 21, D 34, D 71 and any examples in your area.
Well, what are the advantages of agroforestry?
There can be several, concerning both production and protection.
How about production?
The overall production has the potential to be greater in agroforestry, because there can be
several different yields and other benefits:
- production can continue for a longer time, or indefinitely, so that land-use becomes
- overall yields could add up to more than with a single type of product. (Sometimes
the yields of one component might exceed what it would be if produced singly);
- the farmer has greater security through diversifying, in case one yield fails, or products
drop in price. This is especially the case when multipurpose trees are used (D 40).
What about protection?
The presence of trees and shrubs can maintain or improve the site in a number of important
ways (D 1, D 20, D 22, D 32, D 50), such as:
- protecting the topsoil from overheating and from rapid drying out in the full sun
- checking the loss of soil and nutrients carried away by heavy rainfall or wind
(D 12–13, D 23);
- providing better soil conditions for farming, by giving light shade, adding green
manure, recycling nutrients and controlling weeds;
- having extra nitrogen and/or phosphorus available, because particular trees or
shrubs have been chosen (D 13, D 32, Manual 3).
Similarly, the farming can help the trees because:
- the waste products from crops and animals will help the trees to grow (D 15), and so
will any mulch or fertilisers used for the crops;
- grazing animals can keep down weeds (D 14) and lessen fire risks (D 66).
Won't the trees compete with the crops for water?
Water is lost by evaporation from trees, crops and bare soil. So the protective functions of trees
do have to be balanced with their use of water.
NOTE: the extensive root systems of the trees (including mycorrhizas) may tap reserves of
water and nutrients that would not otherwise be available to the crop plants.
Aren't there some disadvantages of agroforestry?
Practical difficulties could include:
- avoiding unsuitable tree species, that might cast too heavy a shade, compete strongly
for water and nutrients, or themselves become weeds;
- keeping a reasonable balance between the trees and the crops and/or animals;
- finding that trees got in the way of farming operations.
Other problems might be important, such as:
- finding out what would suit your particular conditions;
- feeling that all the available ground is needed to produce food;
- changing over to agroforestry where local practice has been to keep plantations and
- believing, as a farmer who had put effort into preparing land as taungya, that you were
entitled to a share in the yields from the trees.
Can these be overcome?
Here are some hints:
- think about how your grandfather used to manage the land (D 42), and how that
relates to to-day's circumstances;
- get hold of any local advice sheets, or send away for information (D 71);
- go along to see any demonstration plots in your area (D 29);
- see if there are any appropriate training courses in your region, or field staff to talk to;
- try and foresee any problems that might arise (D 4), and discuss them with others
involved (D 5);
- test new things out on a small scale first (D 6, D 30);
- plan how contrasting parts of the site could be used in different ways, rather than going
in for only one kind of land use. For instance, a naturally fertile patch of soil might be
managed intensively, while a steep, rocky slope could be put under a regime with less
How would preparing the site be different from single use?
- In not cutting down so many trees, and trying to space them out to give fairly even
shade (D 21, D 51);
NOTE: crops often need about 25 – 75% of full daylight.
- In selecting which kinds of trees to keep or plant (D 30–40, D 53), in relation to:
- soil protection (D 60) and improvement (D 32);
- producing items for sale;
- compatibility with animals;
- whether the trees are evergreen, leaf-exchanging or deciduous, and so how much
shade they cast in different seasons (Manual 3);
- their coppicing ability.
- overcoming the problems of replanting trees
Isn't planting trees easy?
Putting them in the ground may be, but getting them growing successfully needs careful planning
to avoid problems.
Are there so many difficulties, then?
When thinking about diverse sites throughout the tropics, and hundreds of different species,
there are bound to be many things that could go wrong. However, when considering a specific
situation, only some of these potential problems may come up.
Can this Manual help?
Yes, the aim of this series of Manuals is to help anyone in the tropics to overcome difficulties
and to grow trees successfully.
However, they are not like a computer manual, prescribing exactly what you must do. Instead
- point out things to look for;
- give both general advice and specific examples;
- show the range of choices available;
- include many guidelines, some check-lists for problem solving (see A 50 and A 61 in
Manual 1) and sources of further information;
- are meant to stimulate users to write further sheets, for example about specific local
conditions or a particular tree species.
Is it really worth bothering to make a plan?
Yes it is, because:
- working things out for tree planting often needs longer-term planning than for an
- although the techniques themselves are mostly straightforward, problems can occur
with any one of many points;
- it is discouraging if a lot of work is put into planting, and then the trees are damaged,
fail to survive or prove unsuitable;
- replanting offers the chance to use mixtures of superior clones or varieties that can give
higher yields and benefits (Manuals 1 and 2).
What kinds of problems can come up?
- Biological and technical difficulties and decisions;
- Problems concerning organisation;
- Conflicts of viewpoint and assumptions;
What sort of biological or technical matters?
A lot of points, including:
- which tree species to plant (D 30–42);
- what method of propagation is appropriate (Manuals 1 and 2);
- what sources of cuttings or seeds might be best (Manuals 1 and 2);
- how to grow good planting stock (Manual 3);
- its underlying chances of survival (D 10–16);
- the type of planting site (D 20–29);
- what growing system will be best (D 50–55);
- how to prepare the ground (D 60–67);
- when and how to plant the trees (Manual 5);
- how to look after them (Manual 5).
Choices need to be made in each of these areas, in order to anticipate problems and maximise
the likelihood of success.
How might the organising run into problems?
Various difficulties can come up, concerning such matters as:
- the people to do the work;
- the plan of work; and
(See also sheets A 2 and A 60 in Manual 1.)
What kind of people will be needed?
This will depend on the scale of the tree planting that is planned (D 54). For instance:
- in a small-holding (D 21), all or most of the work may be done by the farming family;
- for a community tree planting scheme (D 27), many people's voluntary efforts need to be
co-ordinated (D 5);
- in a private company, staff may be employed, or work put out to contract;
- in a government department, permanent employees may have a regular planting programme,
and also policy and advisory responsibilities;
- with a larger project, research staff may be engaged to study various aspects of tree
planting (D 29, D 55), with extension staff to spread relevant knowledge.
In all cases, the people involved in the tree planting need to have grasped the basic points
about the job.
Is a ‘key person’ needed?
Yes, this is usually vital for successful planting and establishment of trees. The key person
- have realised the multiple importance of trees;
- understand the basic requirements for tree growth and survival;
- have sufficient experience of local conditions to be confident that planting can be done
- know how to organise a job of work;
- be capable of transferring enthusiasm to others;
- be able to train people in both background and techniques.
What kind of plan of work is needed?
It may not need to be complicated, but a plan can help a lot if it includes:
- making a simple sketch-map of the whole area;
- working out how many trees can be cut sustainably (D 24–27);
- allowing for plenty of trees to replace those that are cut;
- deciding where to do the planting;
- keeping a record of what was done when, so that its successfulness can be assessed
Won't it all cost too much?
Not nearly as much as having few or no trees left! Small-scale tree planting can be done by
anyone, even when they have no cash to spare, because the trees can:
- save money, for example using soil-improvers (D 32) can reduce the need to buy
expensive fertilisers; and
- bring in money later on, from the sale of tree products (D 33–40).
More substantial funding may be needed for preparing and planting large blocks of land, and
- convincing people and organisations of the need to plant trees;
- finding out which methods may suit local conditions;
- spreading knowledge about how to plant trees successfully;
- continuing research into different kinds of trees.
How about conflicts between people?
Lack of understanding of other people's viewpoint is a very common reason for:
- trees being undervalued;
- trees being cut but not planted; and
- tree planting not being carried through successfully.
What sort of thing can go wrong?
Matters tend to be seen quite differently by various groups, such as farmers, private estate
owners, governments, scientists or international organisations (D 5). Here are a few general
- Useful suggestions are more likely to be adopted if they are modifications to existing
practice, rather than involving a completely different process;
- If trees are not valued, damage to them from grazing animals is more likely;
- If the tenure of a piece of land is not accepted by a group of people, there may well be
‘illegal’ cutting, burning and farming;
- A person who owns land or who has clearly defined tenure is more likely to be interested
in building up future yields and benefits than someone who lacks this motivation;
- Buying a small plot on behalf of someone living locally might be a novel way of tackling
problems of international debt and land tenure.
How can progress be made on such problems?
Good communication between all those interested is very important (D 5), because it can help
- reconcile some of the conflicting viewpoints and interests;
- avoid losing the advantages of trees because of misunderstandings;
- help to pool knowledge and skills.
What kind of accidents can cause problems?
- Fire destroying the young trees or damaging older ones;
- Violent storms damaging trees and equipment;
- Sudden floods washing newly planted trees away.
But you can't do anything much about things like that!
The risk of accidents will always be there, but both their likelihood and their severity can
usually be reduced, for instance by:
- thinking beforehand about what could happen;
- planting wind- and fire-breaks (D 41, D 66);
- considering the need for drainage channels or terracing (D 65);
- avoiding large, unbroken stands of trees like teak, whose dead leaves assist fire;
- clearing away inflammable material (D 63), or using grazing by animals (D 3, D 34) to
reduce the fire risk;
- discouraging the lighting of fires nearby.
See Manual 5 for more information about protection.
- involving everyone with an interest
Who is going to be interested in planting trees?
In a sense it should be everyone, because it is so important.
But everybody can't be involved!
Why not? Trees are vital in protecting tropical soil (D 1), so that without them most supplies
of food, water and materials are at risk.
Surely that's an exaggeration!
Actually, it is not. It could even turn out to be an understatement. A serious situation has
developed in many parts of the tropics, in which:
- Traditional methods of food production that used to be sustainable now often involve
extensive loss of trees and soil degradation (D 3, D 12–13, D 21–23);
- Introduced large-scale plantation and grazing systems are sometimes having
similar effects (D 2, D 14–16, D 30, D 50); and
- Rising human populations mean extra mouths to feed each year.
What does sustainable use mean?
Being able to continue using a piece of land to grow food and produce materials in perpetuity.
Unsustainable use means that today's yields are undercutting tomorrow's capacity to produce.
But people must have food to eat!
Yes, but that mustn't threaten their grandchildren with starvation.
This is the key problem for many tropical societies - how to use the land in ways that keep a
balance between present and future needs.
However did such a serious situation occur?
For many reasons (D 1, D 4), including;
- forgetting centuries of local experience;
- ignoring the ecological basis of tropical land use (D 10–16);
- relying on unhelpful assumptions.
Is it too late to do anything about it now?
Certainly not. But in many tropical regions the disappearance of the trees needs tackling
The first step is to listen to the people in different groups that have an interest.
Who would be specially interested in tree planting?
Firstly those most closely involved, such as:
- farmers, including both small-holders and larger scale growers;
- foresters, working outside forest reserves as well as inside them;
- fishermen, operating in rivers, lakes and estuaries;
- traders, especially those selling local foods and materials.
How do trees help farmers?
Directly, by producing various foods (D 33) and materials (D 39); and
Indirectly, by protecting the soil, and so providing sustainable conditions for crops and farm
animals (D 1, D 3, D 21, D 32, D 34).
Can foresters help farmers?
Yes, foresters can have an important role because of their knowledge of trees, and their understanding
of sustained yields (D 24, D 26). However, this depends on whether:
- they can adapt their methods for different sites and aims;
- such a role is accepted by forestry departments; and
- there is good collaboration with agriculture departments and farmers' co-operatives.
What about logging companies and large estate owners?
Their future is affected too. When sustainable management is adopted (D 62) before the
best trees have been removed, annual yields will generally continue to cover the year's expenses
(including some diversification) and produce reasonable profits.
However, if management practices mean that the land becomes degraded (D 22), then
yields and profits will decline and soon stop, while the costs of restoration will increase sharply.
Why are trees important to fishermen?
Because the fish all depend for food on the green plants that start the food chain (D 10). For
streams and rivers, and in mangrove woodland (D 26), trees as well as microscopic algae are
‘the producers’. They also provide the conditions in which fish populations thrive, and help to
stabilise water quality.
So continuing supplies of fish depend on the trees, as well as on choosing net sizes that conserve
Why should traders worry about trees?
Because, as the areas under forest and woodland decline, it will become increasingly difficult
to obtain supplies, especially of the following:
- bush-meat, fish and fruits (D 33);
- firewood and charcoal (D 35);
- household implements and materials (D 39).
Who else could be involved in tree planting?
- City-dwellers, who depend on trees, directly and indirectly;
- Administrators in local and national governments, and in private companies and
- Teachers at schools, colleges and universities, and those running training courses;
- Research workers in universities, research stations and projects, locally and abroad.
How can people living in cities promote tree planting?
- By understanding that they depend on trees outside the city;
- By encouraging the planting of ornamental and shade trees and shrubs (D 28, D 41);
- By planting suitable species themselves.
What about local authorities?
They can do a great deal to encourage local initiatives, for instance by:
- testing different systems of agroforestry (D 3);
- promoting the planting of demonstration plots (D 29);
- making information available to heads of villages, farmers' co-operatives, women's
- encouraging school and community tree planting (D 27);
- providing planting stock of appropriate species (D 30–42) and genetic origins (Manuals
1 and 2).
How about state governments?
They could, for instance:
- make a thorough study to estimate the present environmental situation regarding trees;
- consider human population growth in relation to the capacity of the land;
- support basic and applied research on trees;
- remove the incentives to cut trees without replacing them;
- adopt policies that provide incentives for tree planting and the wise use of existing
- reform land tenure so that local communities and individuals have a firm stake in the
trees they plant, and in sustainable management of natural resources;
- hold National Tree-Planting Weeks and official tree planting ceremonies.
What about international agencies?
They also have an important part to play, for example by working with governments, research
institutes and local groups to:
- continue the rethinking about what constitutes real, appropriate development;
- recognise more fully the value of local knowledge and skills;
- integrate this with existing and new scientific understanding;
- promote small-scale approaches that have the potential for self-perpetuation, rather
than large schemes that often disrupt communities and ecosystems;
- emphasize self-sufficiency in basic foodstuffs and in the diversity of materials derived
from trees, rather than concentrating on single-species commodity crops and trees for
- fund research and development on the domestication, growth, yields and protective
functions of indigenous tropical trees in relation to local conditions;
- encourage longer-term thinking, such as keeping older varieties of crop plants and
trees, while trying out newer hybrid cultivars and clones, so as to combine security
with innovation (D 31).
How can teachers help?
By including subjects such as the functioning of ecosystems, the multiple roles of trees and the
importance of sustainable use of land, which have often been overlooked.
Teachers at every level have a vital part to play in presenting a fuller picture, especially as more
young people get the chance of education.
Tree planting can encourage both understanding and practical skills, in girls and boys alike,
and in students and adults as well.
What about people doing research?
Here are a few guidelines for research workers, wherever you are:
- Consider working on specific aspects of the domestication, use or conservation of local
trees, a field in which there is much to discover;
- Remember that ‘high-technology’ approaches are not necessarily to be equated with
- Use an experimental approach wherever possible, and keep the layout relatively simple
(D 6, D 29, D 55, D 67);
- Try to build links with other people and organisations, locally and abroad, to bring in
different approaches, knowledge and skills.
How can all these people possibly get together?
They cannot, but it is actually more useful to think in terms of promoting a network with
many links, which can help to:
- overcome or avoid various misunderstandings;
- exchange thinking about the important points, without some of them being overlooked
or ruled out of order;
- set up training courses, provide demonstrations (D 29) and supply relevant information
(D 70–72) that will show the range of practical options;
- help people choose priorities for action;
- keep the work going with enthusiasm, in spite of obstacles (D 4).
What can be done about unhelpful assumptions?
The main needs are for:
- matters to be thought out from first principles, rather than relying on inappropriate
- approaches to be based on a sound understanding of the biological processes that
control tree survival and growth (D 10–16 and Manual 3);
- decisions to be related to local conditions and experience;
- attitudes not to be patronising, but involving an exchange of views, with everyone who
has an interest free to take part.
Is it possible to get agreement in a community scheme?
It is not easy (D 27), but one could try to:
- explain why tree planting is important to the community (D 1);
- think about how your parents and grandparents saw the land (D 42), and go and see
any demonstration plots (D 29) of newer techniques;
- make a list of actual and potential problems (D 4), and involve everyone with an interest
in discussing them at an early stage;
- see that the children know about the tree planting (D 27);
- arrange that many people take part in the work of preparing the ground (D 60–66),
planting and care of the trees (Manual 5).
When there are multiple requirements that might clash, such as firewood and grazing, or
production of forage and fruits, it may be best to plant small, separate blocks for each requirement.
And will that mean more trees are planted than at present?
Only time will tell. But if people see that local tree planting brings extra yields and improved
soil fertility, it will be more likely to catch on and be incorporated into existing practices.
Wouldn't tree planting be more effective in large blocks?
A lot of small-scale plantings might be equally or more effective (D 54). Large-scale projects
can sometimes be valuable, but often may:
- not seem relevant to ordinary people;
- stop abruptly because their external funding has dried up;
- be unable to spread their results in a self-perpetuating way.
- the need for field trials
Why bother with field trials?
Because there is a great deal more to growing trees successfully than is known at present.
Aren't trials the job of research people?
Part of the work is best done by research scientists, who:
- have time to investigate the subject in detail;
- might have specific relevant knowledge and experience;
- have access to the results of other scientists' work all over the world;
- may have equipment and laboratories for detailed study;
- can lay out experiments on land set aside for the purpose.
But a lot also needs to be done locally as informal trials, linked where possible to a co-operative,
a research station or perhaps an international project.
Why is this?
- there are not nearly enough tropical tree scientists;
- work is urgently needed on hundreds of species of trees and shrubs;
- even the simplest information on them is often lacking;
- most of them have not yet been domesticated (Manuals 1 and 2);
- deciding on priorities depends on seeing how they perform;
- promising kinds of trees need trying out locally;
- a novel idea requires practical testing before being used on a larger scale;
- comparing alternative methods in an informal trial helps the exchange of suggestions
and experience between researchers and growers.
But wouldn't trials be too difficult for ordinary growers?
They certainly do take extra time, care and thought. But often an informal field trial on the
- find out what works locally;
- show where problems are occurring;
- suggest new ways of improving survival, growth and yields;
- decrease the risks of damage and loss, and save a lot of wasted effort.
Who could help with informal trials?
Here are some suggestions:
- those interested could decide (D 5, D 27) to set up self-help groups or co-operatives to
plan and run trials;
- advice and help might be obtained from:
- national or local government staff;
- non-governmental organisations concerned with the environment;
- local tree nurseries;
- relevant publications.
If possible, discuss the plans at an early stage with someone who has experience of laying out
What is an experimenter really trying to do?
To compare sets of trees that receive one or more treatments with similar ones in an un-treated
control, or sets which come from different origins, in order to see:
- whether the treated trees grow differently from the controls or not;
- what the differences are;
- how big they are;
- whether they are temporary or persist for a longer time;
- what else might be tested in a future experiment.
Note: although a researcher may expect (or sometimes want) a particular result, the experiment
is designed to avoid:
- bias, so that one is misled by appearances; and
- just collecting a whole lot of irrelevant data.
How is a field trial planned?
The aim is to try and make the conditions as similar as possible for all the trees in the trial,
except for the point you are testing.
So in a mulching trial, for example, it would be no use if the mulched plants were at the
bottom of a slope, and the controls at the top. Similarly, comparisons would not be valid if the
treated plants started off bigger and the controls smaller (unless this was the ‘treatment’ being
How should field trials be laid out?
See D 29 for choosing a suitable site; D 55 for the growing system and layout; and D 67 for
preparing the ground.
Can any experiments be done with plants in pots?
Yes, some can; for example:
- seeing whether a newly introduced species can survive (D 31);
- comparing growth in different soil types (D 12);
- checking effects of major or micro-nutrients (D 13);
- looking at the influence of mycorrhizal fungi or nodule-forming bacteria (D 32, Manual
- doing selection tests for branching habit on young trees (A 13 in Manual 1).
Are there some general hints on experiments?
- Keep your experiment fairly simple. Between one and three treatments, plus a control
set, is usually enough.
- Make treatments sufficiently different from each other, so that any effects could
show up amongst the variability that is always present;
- Consider using a 2 × 2 trial if you suspect that there may be interactions between two
kinds of treatment, with the effect of one factor influencing the response to the other
(D 55). 2 × 2 trials can either take the form:
- + 1, + 2, + neither, + both; or
- low/low, low/high, high/low, high/high.
- Choose a site that is as uniform as possible (D 29), unless the trial is to compare
- Have sufficient trees in each plot or treatment (a minimum of 20–30, if possible, and
more if they are available) so that there are enough replicates to make the trial valid
- Use trees that are as uniform as you can, or grade them into size classes and allot
them equally to treatment (s) and control (A 45 in Manual 1);
- Think hard about protecting your trial from wind, fire, pests, diseases, browsing animals,
weeds and vandals (D 66, Manual 5);
- Don't be put off because a treatment might cost too much if applied on a larger scale.
The primary aim of the trial may be to show how the trees respond, and you can decide
later on how to apply the results.
How will the results of the experiment be assessed?
This will be covered in detail in Manual 5. Using simple and rapid scoring methods is described
on sheet A 65 in Manual 1. Other general hints are:
- identify the position of the trial and any plots with marker posts, and make a simple
sketch-map so that you can find them easily;
- keep records of what you have done, and label the trees clearly when different kinds are
being compared (A 64 in Manual 1);
- look at your trial regularly, and note down (with the date) any differences between
treatments that you notice, damage to trees, etc.;
- remember that some effects of treatments, and differences between trees, may take
time to appear.
But will anyone pay attention to the results?
This will be more likely if:
- the experiments or informal trials were carefully done;
- similar results have been found in more than one trial;
- other people have been involved in the planning (D 5);
- demonstration plots are set up to show important results (D 29).
Are there other kinds of research on trees?
Experiments and informal trials are very important research tools because they generate information
that is firmly based on what actually happened in specific controlled tests. Some other
methods of research and development are:
- remote sensing, including mapping changes in vegetation;
- detailed description of a stand, involving identification, distribution and structure
of plants, measurement of climate, soil conditions, etc;
- laboratory tests and investigations, for example of microscopic structure or chemical
- theoretical calculations and modelling of parts of natural or managed ecosystems
or the growth of trees.