Introduction

Why are more tropical trees needed?

Because so many have been lost, and too few have replaced them (C 1 in Manual 3). In many sites, natural regeneration of the trees (D 2 in Manual 4) contains relatively few of the local tree species, while in degraded land it can be insufficient to cover the ground.

Does it matter much?

Yes it does! Trees are crucially important for most people in the tropics, because they:

1. protect and enrich the soil in which their crops and forage plants grow;
2. produce many different items that they need on a day-to-day basis, or can sell.

How do trees do that?

1. By sheltering the soil from bright sunlight, heavy rain-drops and strong winds, and so checking erosion and providing favourable conditions for growth of plants (D 22–23);
2. Through providing the organic matter on which all the animals and micro-organisms in the ecosystem depend (D 10 in Manual 4);
3. By forming close associations with useful micro-organisms (C 30–32 in Manual 3), which assists in the very efficient recycling of nutrients (D 13); and
4. Through consisting of a diverse mixture of different species (D 30), many of them useful (D 30–42).

The presence of trees is vital in most tropical landscapes, forming the basis for sustained yield management (D 5).

I thought that development involved clearing away the natural vegetation.

Humans have always made openings in forest and savanna for houses, paths, crops and so on. More recently in our history, much larger clearings have been made for towns and cities, roads and airports, mining and factories, plantations and pastureland.

However, the idea that development means that most or all the natural vegetation should be cleared may turn out to be one of the most dangerous fallacies of the 20th century.

Surely that's an exaggeration!

No, I don't think so; for many people's livelihoods and even their chances of survival do actually depend on trees.

Is that really so?

Yes it is, for without them more and more tropical land is becoming degraded (D 22); and yet
With appropriate numbers of suitable trees, many kinds of land-use can become sustainable.

But it is no use trying to turn the clock back, is it?

No; although people can learn quite a lot from the ways their ancestors devised for managing the land.
To-day a dynamic shift is needed in ideas and policies, because of the combinations of:

1. decreasing soil fertility together with increasing human populations; and
2. availability of machines and vehicles that can clear trees away rapidly, along with local and international pressures to do so on a large scale.

What would need to alter for there to be more trees?

Well, a lot of things are already changing, including:

1. the underlying assumptions, which are turning away from the exploitation of natural resources towards their conservation and sustainable use;
2. taking account of the ecological framework as well as of economic considerations;
3. valuing the many different contributions that trees can make, and their unique capacity for restoring degraded land back to productivity (D 20–25);
4. recognising the advantages of various kinds of agroforestry (D 3);
5. appreciating the roles of trees on slopes, along boundaries, water-courses and roads, and in built-up areas; and so
6. seeing that retaining and replanting trees are extremely important for each of us.

Can tree planting really help local communities that lack resources?

That is the 64,000 dollar question, isn't it?
I believe it can make all the difference, even for people with little or no money to spare.

What would be needed for that to happen?

1. Goverments, local authorities and non-governmental agencies promoting tree-planting as an integral part of primary education through to adult training courses;
2. The felling of trees being done on a sustainable basis, and with minimal damage;
3. Land tenure and tree ownership problems not being allowed to undermine the work;
4. Local experience being exchanged, and blended with information from international scientific and technical studies;
5. Information and appropriate seeds becoming available locally; and
6. Key people (D 5) seeing the need to encourage individuals, communities, departments, private companies and co-operatives to take on the job.

Wouldn't it all cost too much, though?

People and small communities can plant trees effectively without having to spend much money, provided that they are enthusiastic and supported. Larger agencies do need to allocate finance to tree-planting programmes, but these could prove a great deal cheaper than:

1. losing the productive capacity of the land;
2. requiring to import more and more food and materials; and
3. having to spend more on replacing the trees at a later date.

Is a lot of information needed to plant trees successfully?

Most of the ideas and techniques are straightforward, but information is usually required, as:

1. there are many different species and genetic origins to choose between, with big differences between them (B 20; C 5 in Manual 3);
2. most trees used to come up by themselves, so there is often a lack of knowledge about growing indigenous species; and
3. a single mistake at an early stage might undermine the whole enterprise.

Are ideas like those behind this series of manuals?

Yes, and of the videos planned to accompany them, as with Manual 1 and Video 1.
Translations of these are available in Spanish and Bahasa Malaysia, while other languages are planned. Some users have already been stimulated to write about individual species and local conditions.

Examples of further sources of information are given in sheets B 51–52.

Are there some other general guide-lines?

1. Planting is generally needed, even in sites where some trees come up by themselves.
2. Mixtures of species are usually better than monocultures, using indigenous as well as introduced trees and shrubs (D 30–31 in Manual 4).
3. Gaining the large improvements that can come from ‘domestication’ will depend in most species upon conserving some of the diversity of genetic potential they contain, and in some cases on saving them from extinction (B 20).
4. Good nursery-grown trees, with suitable root systems, are generally crucial to successful planting (Manual 3).
5. Trying trees out on a small scale first within existing situations is preferable to planting large numbers in new conditions.

How does raising trees from seeds differ from vegetative propagation?

Both techniques have the same general aim: growing good trees for planting; but
propagation by seeds uses the natural organs of dispersal (B 12), and produces planting stock that is generally quite variable; whereas
vegetative propagation utilises the ability of parts of plants to regenerate missing organs, and can give young trees that are much more uniform (A 3, A 11 in Manual 1).

Which method is best?

This depends a great deal upon the species. Since ‘domestication’ of most kinds of trees is at an early stage, or has not started (B 20; C 5 in Manual 3), it is usually sensible to:

1. start with the propagation method that has given success before; but also
2. try out the other way later on, as both might have advantages.

What are the advantages of seeds?

For instance, they can often be:

1. collected from the wild, transported and handled easily (B 31–32);
2. stored in a number of species (B 33) until the best time for sowing;
3. germinated and grown by standard techniques (B 40–48); and
4. able to provide automatic conserving of plenty of genetic variability.

How about rooted cuttings?

Amongst their advantages are:

1. nursery plants can be raised at any time, whether or not seeds are available then;
2. genetic improvement may be achieved more rapidly;
3. small but valuable seed-lots, including hybirds between different species (B 23), can be multiplied before testing them; and
4. research can be more precise, especially when standard clones are used (A 11 in Manual 1; C 7 in Manual 3).

And what about other methods of vegetative propagation?

Various types of grafting (A 3 in Manual 1) have been widely used for propagating fruit trees such as mango. Recently, a simple approach graft method has been developed in south India for tamarind, the multipurpose species (D 40 in Manual 4). Potted plants of the rootstock are brought close to a selected clonal stockplant, and shoots of similar size grafted together. After 45 days the clonal scion has become attached to the rootstock, and can be separated from the stockplant.

Grafting selected parent trees is also used when making seed orchards (B 23).

What disadvantages are there with seeds?

In some tree species, the seeds may be:

1. produced rarely (B 10–11), and not necessarily on the desired parent trees (B 22);
2. derived from related parents, and therefore liable to inbreeding depression;
3. difficult to collect, because they are so high up, are blown away or eaten (B 31);
4. prone to have low levels of viability (B 13);
5. naturally short-lived, and so difficult or impossible to keep for more than a few days (B 13); or
6. regularly attacked by pests or diseases (B 47).

Aren't there also some disadvantages with rooted cuttings?

Yes, shoots for leafy cuttings are:

1. more easily lost than seeds through drying up or overheating during collection and transport; and
2. not able to be stored for more than a day or so (A 42 in Manual 1).

If poor techniques are used, rooted cuttings may also:

1. be lost during during propagation, weaning or hardening, if they are subject to climatic or mechanical stresses (C 41 in Manual 3);
2. fail to produce a vertical leading shoot, if the wrong type of shoot is used (A 6)
3. develop poor root systems, if the propagation conditions are unsuitable (A 61); or
4. succumb to the same problem if only one or a very few clones are used.

NOTE: use the recommended 10–30 clones for large plantings (A 11).

What are the main points about good seed germination environments?

1. Learning how to maintain the water balance (C 13 in Manual 3) in the young trees during this key stage of development (C 3);
2. Using a germination medium that is freely-drained and allows air to reach the seeds, but also retains enough water to keep them moist (B 40, B 42);
3. Providing shade, but allow sufficient light to reach the germinating seedlings (B 41);
4. Checking the germination conditions regularly (B 47), including signs of pests or rotting of seeds; and
5. Avoiding unnecessary stress when potting up or transplanting young seedlings, or moving them into a different environment.

What should I do about a species I haven't grown before?

For the commonly grown species, you could ask for advice from other growers, look for local sources of information about seed collection, handling and nursery techniques, or consult publications from other countries (B 51–52).

For indigenous trees, however, there may well be no information available. If you obtain some fruits or seeds, the first thing to do is to decide whether to try and store some seed.

How should I make that decision?

If the fruits are fleshy and the seeds are moist (B 33), then it is usually best to sow them all, because they may not retain viability (B 13) if stored. You could for instance divide them into similar batches, and do a small trial (B 48) comparing different germination media or environments, perhaps in trays and seed beds, including methods successful with other species. Use this approach also if the seed-lot is small.

If the seeds are dry when collected, you could try germinating some, and storing the rest in conditions that are favourable for other dry seeds. This gives you more flexibility, as you can:

1. wait and see whether any of the seeds germinate;
2. consider carrying out simple germination tests (B 48);
3. take account of the possibility that the seeds are dormant (B 13); and perhaps
4. be able to make sowings later, so that the young trees would then reach the desired size at the right time for planting (C 34, C 47 in Manual 3).

What if I only get a very few plants?

You might grow most of them on (in large pots or in the nursery soil) as stockplants (A 23– 24), taking cuttings from them to multiply the numbers.

Are there any other ways of growing trees that I could try?

Yes, there are several, including:

1. encouraging natural regeneration of trees (D 2 in Manual 4);
2. collecting wildings or seeds that are already germinating (B 44);
3. direct sowing in the place where the trees are to grow (B 4);
4. planting leafless cuttings (A 4 in Manual 1); and
5. micropropagation (A 5), for which techniques are being developed in some species.

Are there a lot of difficulties when propagating from seeds?

Various problems can certainly occur (B 50), but usually few of them are troublesome provided that the seed sources, nursery handling and germination conditions are good.

What sort of problems might come up?

1. Difficulties in obtaining seed of the desired tree species (D 30–42 in Manual 4) and genetic origins (B 20–24);
2. Poor germination because of low initial seed viability, dormancy (B 13), handling methods (B 30–32) or storage conditions (B 33); or
3. Loss of germinating seeds and seedlings, for instance because of unfavourable germination environments (B2, B 40–48), stress, diseases or pests (B 47).

See sheets C 3 and C 60 in Manual 3 for:

4. nursery problems during the later stages in growing good young trees for planting;
5. accidental hazards; such as fire, unexpected storms or floods; and
6. organisational difficulties; like lack of experienced staff, training opportunities, suitable workers, adequate supervision, regular finance, relevant tools, materials and information.

But I thought that germinating seeds was easy!

Well, that's what it can often be. These are just the main areas to be aware of, in case they should apply in your case.
It is important to take them into account, since any one of them might hinder or stop production of sufficient, good planting stock, even when you had dealt with all the others.

Are some of these problems insuperable?

A combination of organisational problems can sometimes stand in the way of success, but the risks of accidents can be greatly reduced and solutions found to most biological and nursery problems.

Aren't there some kinds of trees that are hard to raise from seed?

Yes, a number of species can be difficult, but you could try:

1. collecting wildings or germinating seeds under fruiting mother trees (B 44), for instance with Lovoa and many dipterocarps;
2. rooting juvenile leafy cuttings (Manual 1), which is likely to be possible with most tree species;
3. looking for information or advice that may have been published recently (B 51–52);
4. applying treatments that might stimulate flowering (B 14) or pollination (B 11); or
5. carrying out a series of seed experiments (B 48).

What sorts of problems might occur with seed supply?

1. Pollen and seed production delayed and irregular, because of:
   1. a non-flowering juvenile period that can last for decades (B 10);
   2. great variation between individual trees in their inherent tendency for reproduction, and in the local environments they experience (B 11);
   3. differences in flowering times and sex ratios; and
   4. the uncertainties of pollination and fruit set (B 11–12);
2. Seed collection problems (B 31), such as:
   1. flowering being concentrated in the upper crown of often tall trees;
   2. fruits being eaten by larger and smaller animals; or
   3. seeds being shed and dispersed before collection.

How about difficulties concerning suitable genetic origins?

Linked with the problems listed in (A) and (B) above, are:

3. Consequences of trees being perennials with multiple benefits and yields, so that one:
   1. does not know which characteristics will be most important in the future;
   2. is unable to judge in young trees the features that will not be seen until they are older;
4. Uncertainty of desired characters of a selected seed tree being passed on to its seedlings, for reasons including:
   1. what one sees in a selected tree is the result of inherent traits expressed in a particular environment;
   2. not all of its inherited traits are passed on; and
   3. the pollen parent is usually unknown, as controlled pollinations (B 23) are generally difficult to achieve.

Doesn't all this make genetic improvement impossible?

No; although domestication only by seed is certainly slower and more difficult than in short-lived plants. Combining it with vegetative propagation is quicker and easier.

Is it possible to be unintentionally going backwards?

Yes, indeed! For instance, if seed is collected from:

1. provenances that are quite unsuitable for the planting site (B 21);
2. trees that show a lot of poor characteristics, negative selection might result (B 22); or
3. a small group of trees, or from an isolated tree, inbreeding depression could occur.

In such cases, inferior, stunted trees are more likely than improved, thriving stands.

Which kinds of stress can damage germinating tree seedlings?

The commonest kinds (C 40–41 in Manual 3) are to do with water, light levels, temperature, nutrients and mechanical breakage.

Too little and too much watering, or high transpiration rate.

When would young seedlings suffer water stress?

1. If they are growing in a germination medium with:
   1. too little soil moisture; or
   2. too much soil moisture, preventing air from reaching the roots freely;
2. If the air around them is very drying, because it gets too warm, sunny, dry or windy, causing shoots to lose a lot of water; or
3. If their root systems are not yet extensive enough to replace the water lost from their shoots.

How about light levels?

Stress can happen through young seedlings being grown:

1. without sufficient shade (B 41);
2. with sudden removal of shade, exposing them to bright sunlight (even for a short time); or
3. in very dim light for several weeks.

Can the temperature be too hot or too cold?

Yes; the best germination temperatures are generally between 20 C and 30 C.

What about nutrients?

Stress could be caused if the germination medium had:

1. a severe shortage of a main nutrients or micronutrients (C 14 in Manual 3);
2. too much of one or more nutrients; or
3. a pH that was highly acid or alkaline (C 23).

Certain trees, including tropical pines, may suffer nutrient stress if the germination medium contains no inoculum of a suitable fungus to form mycorrhizas (C 30–31), as these are essential for the trees' nutrition.

And how about mechanical breakage?

This can be caused by such things as wind, heavy raindrops, falling twigs, large leaves, flowers or fruits, or by animals of various kinds.

Are there some general guide-lines about avoiding problems?

1. Think about potential problems that could arise in your tree nursery (C 50), and take simple steps to avoid or detect them early.
2. Plan the nursery carefully (C 20–26 in Manual 3), as this can reduce stress and damage.
3. Remember that germination is one of the key stages in the life of a young tree when it is particularly easily damaged, and so start with plenty of protection and check frequently.
4. For the same reason, handle the seedlings especially carefully when they are first potted up or moved to a nursery bed.
5. Change the conditions gradually, so that the seedlings can become prepared step-by-step for ordinary nursery environments, and then to be hardened for planting out.
6. Water carefully and regularly (B 46), and do not allow container seedlings to root freely through into the ground, because then they lose their main roots when they are moved (C 6 in Manual 3).

But shouldn't trees be treated ‘rough’ if they are to survive?

No! - this is a misunderstanding that often leads to unnecessary problems.
Young nursery trees need to be given favourable environments and then gradually accustomed to less sheltered growing conditions.

What does direct sowing of seeds mean?

That the seeds (or sometimes the fruits containing them) are sown directly in the place where they are to grow, instead of being raised in a tree nursery and then transplanted.

Isn't that much simpler than having a nursery?

Yes it is; but direct sowing is usually only successful with relatively few kinds of tree.

Why is that?

For most species, tree nurseries are needed because:

1. sowing in seed trays or nursery seed beds with a suitable germination medium (B 42) generally gives a higher germination percentage and better seedling root establishment than in ordinary soil;
2. nursery plants need not compete with other vegetation; and
3. they can be given protection from drying up, heavy raindrops, bright sunshine, wind, diseases, pests and herbivores (D 10 in Manual 4), so that far more seedlings survive.

But every sort of tree regenerates itself naturally, doesn't it!

Yes it does - under natural conditions or when human disturbance has been slight. However, of all the many seeds a tree produces during its reproductive phase, only a handful ever grow into mature trees.
Although replacing one tree by another is enough to perpetuate both the species and the ecosystem (D 10), it is achieved through the failure of enormous numbers of seeds.

So even a million seeds sown directly might still not produce a good stand of trees!

Exactly! Losses are so high because there are such a lot of:

1. animals and micro-organisms likely to eat or damage the seeds; and
2. possibilities for unfavourable environments harming those that do germinate, including competition between seedlings of the same species.

What kinds of tree can be sown directly with reasonable success?

Those which are colonisers (D 14), rapidly establishing themselves in gaps and small clearings. These species usually produce large quantities of seeds, starting from an early age and continuing regularly (B 10–11).

Direct sowing has been suggested for the following multipurpose species (D 40): Albizia lebbek, Anacardium occidentale, Artocarpus heterophyllus, Azadirachta indica, Cassia siamea, Dalbergia sissoo, Derris indica, Erythrina poeppigiana, Gliricidia maculata, Moringa oleifera, Pithecellobium dulce, Prosopis juliflora, Samanea saman, Sesbania grandiflora, Syzygium cumini and Tamarindus indicus (Anonymous, 1997 in B 52).

Are there some well-tested examples?

1. Swietenia macrophylla, is sown directly at 2 m × 2 m spacing in gaps in logged forest in south-east Mexico, to supplement natural regeneration of valuable species (see Richards, 1991, in B 52); and
2. Leucaena, a prolifically seeding soil-improver (D 32), is regularly grown by direct sowing.

But doesn't Leucaena have ‘hard’ seeds?

Yes it does. For best results a suitable pre-sowing treatment (B 13, B 34) should be applied, although some of them may well germinate without it.

Are there any kinds of tree that might get out of hand?

Very occasionally, an introduced species can turn into a troublesome ‘weed’, as for example Melaleuca quiquenervia in southern Florida.
However, in most cases extra useful trees are welcome, and any unwanted plants can be cut back.

The edge of a small gap in the forest

How should I choose just where to sow directly?

1. Growing system: in order not to waste seeds, the best systems are to sow in groups or lines (D 50–54 in Manual 4). So look for suitable patches or alignments within the area where you want to establish the trees.
2. Light:
   for shade-bearing species, if possible arrange to sow under moderate (not heavy) shade cast by existing trees, but a few metres away from larger trunks. If the land is largely bare, you might consider mulching or temporary shading (Manual 5);
   for colonisers and other light-demanding species, plan to sow in the open or in gaps within existing stands.
3. Soil:
   generally sow in places where it is not too steep or stony, nor liable to flooding; and where there is a reasonable depth and texture of soil; but
   occasionally sow on steep slopes, among rocks, or in boggy or shallow soil, if previous trials or experience have indicated that the species can grow in such adverse conditions.

How should the ground be prepared for direct sowing?

Ground cover: remove any vegetation (especially troublesome weeds) covering the ground surface, except:

1. soil-improving woody species, which could be pruned back as needed; and
2. small plants that will not compete.

Soil cultivation (D 64): you could choose between:

1. disturbing the soil surface only enough to cover the seeds;
2. digging out clumps of grass and the roots of weeds; or
3. completely cultivating the topsoil.

Try to avoid unnecessary soil cultivation, as it increases the loss of soil by erosion (D 23).
This is especially the case when the soil is cultivated with machinery.

When should I do direct sowing?

In the same season as the sowing of farm crops, when the soil is already moist from early rains.

And how should it be done?

1. Clearly mark the area to be sown with some poles and a label showing the seed-lot and date (C 54 in Manual 3);
2. Put the seed in an open container with a strap that can be carried over the shoulder;
3. Scatter the seeds thinly and evenly as you walk over the patch to be sown; and
4. Use a stick, rake or fork to cover most of them.

What problems might I have?

Very light or winged seeds. To stop these blowing away, choose a windless day, sow close to the ground surface, cover at once and then tread lightly over the area.
Larger seeds. It may be easier to make individual small holes with a stick or hand trowel.
Palatable seeds. Seeds that are attractive to birds may need to be quickly covered with extra soil, sand or mulch. If insect pests are a problem, you could consider pre-treating the seeds with a copper salt.
Seeds with a tendency to rot. Avoid sowing during very wet weather, and if necessary dust the seeds with a suitable fungicide (C 45 in Manual 3).

How about looking after the seedlings?

If possible, visit the planting sites from time to time, and check whether watering (if feasible), weeding or other work is needed.
Later on, the trees might need thinning if some are growing too close to each other.