Introduction

Swietenia macrophylla (mahogany) is native to North America and now it covers a wide range of terrestrial areas in the world including tropical countries. The suitability of mahogany as a plantation crop has led to established 200, 000 ha of plantations worldwide, with extensive areas in Fiji and Philippines (Platino, 1997). In Sri Lanka private sector also started to establish mahogany monocultures especially in the intermediate zone and low country wet zone. However mahogany plantations in the country have not been able to most productive to attract further financial out comes. Nevertheless, information on growth of mahogany is not readily available in Sri Lanka. Since as a solution for this, need to establish appropriate management guidelines for mahogany monoculture plantations. Prior to introduce such management strategies, necessities are identifying growth rates and growth differences of plantation crop of mahogany. Hence this study concerning with distribution of breast height diameter (dbh) of mahogany trees growing in different site types with their age is vital requirement for the plantation sector.

Mahogany ( Swietenia macrophylla) is an exotic tree, which is heavily adapted to the climatic conditions of wet and intermediate zones of Sri Lanka. Although the state sector manages mahogany with longer rotations, private sector expects to achieve the maximum timber yield within a shorter period. Due to the land scarcity, many of these mahogany plantations have been established in barren and rubber uprooted lands which were heavily degraded. Therefore the soil conditions and site factors directly affect the growth of the mahogany within short rotations.

Seed Propagation

I. METHODS OF PROPAGATION

Planting materials may be propagated either from seeds or vegetative parts of plants.

A. SEEDS OR SEXUAL PROPAGATION

A seedling is a nursery-grown planting material developed from a seed. While most of the nursery-grown seedlings are healthy, some may have defects/ imperfections. These defects may or may not be visible to the eye.

Healthy seedlings come from superior seeds. Superior seeds come from selected mother trees. From such source, healthy seedlings ensure higher survival rate and will grow to be vigorous and productive trees. A mother tree has the following characteristics:

Height: the tree is the tallest in the stand of trees Diameter: the diameter of the bole is as big as possible for the

species Bole: the bole or trunk of the tree is straight from the base to the

top Crown: has well-balanced crown Branches: they are equally distributed and relatively perpendicular

to the bole Health: the tree is free from pests, diseases and defects

It is free from injuries such as torn leaves, broken/bent stems, and a nick or a cut on the stem.

It is free from diseases such as abnormal development and discoloration of plant parts.

It is free from insect infestation such as the presence of ants, grasshoppers, butterfly larvae that usually eat their leaves/stem.

It has a relatively thick or woody stem. It has a well-balanced shoot and root ratio. This means that the

shoot should be proportionate to the root system to balance the intake and loss of water.

For a bareroot seedling, it has a firm and fresh rootsystem with many rootlets.

Ensure healthy seedlings thru proper procedures/ technologies

Healthy seedlings can be produced through proper procedures and technologies.

Seed Collection

There are three ways to collect fruits/seeds from selected mother trees:

Collection from the ground

This practice is common for trees with fruits that fall to the ground after maturity, such as Kamagong (Diospyros philippinensis), Santol (Sandoricum koetjape), Mahogany (Swietenia macrophylla), and Katmon (Dillenia philippinensis).

Gather fruits and seeds right after they have fallen to avoid the risk of collecting immature, decayed and/or germinated seeds. Collect fruits that fall during the peak of the fruiting season to ensure higher viability of the seeds. Seeds from fruits collected during the initial, and towards the end, of the fruiting season are usually inferior.

Collection from standing trees

Gather fruits/seeds from standing trees by climbing trees either with a safety belt or with the aid of a rope tied on the bare feet.

Ladders can also be used to pick the fruits/seeds. Tree climbing is necessary for tall trees with small seeds such as Molave (Vitex parviflora), Bagras (Eucalyptus deglupta), Agoho (Casuarina equisetifolia), or Banaba (Lagerstroemia specbsa).

Collection by shaking branches

Another way of collection is by shaking the branches of the tree either manually or with the aid of a rope tied at the tip of the branches.

Other factors to consider:

Collect seeds from the local source whenever possible and/or in areas with the same climatic condition as the planting site.

Collect seeds from fruits or pods that have fallen to the ground before they begin to open and/or germinate.

Collect the seeds during the tree’s regular fruiting season. (Refer to Seed Collection Calendar in Annex A)

Seed Processing

Process the seeds properly to avoid damage and attain high percentage germination.

Extract the seeds from the collected fruits and immediately dry them for easier storage and transport. Sun or air dry the seeds to save them from fungal and micro-organism infection and insect attack.

In addition, separate the seeds from impurities through any of the following methods:

Floatation Submerge the seeds in water. Seeds that

float are empty and therefore will not germinate.

Winnowing or Blowing Expose the seeds to the wind. Those

seeds that are carried by air will not

germinate, thus are useless.

Screening or Sieving Sieve the seeds by shaking or rubbing

through a screen until all impurities are removed.

Sorting Sorting separates the defective from the

good seeds. This is applicable mostly to bigger-sized seeds.

Seed Testing

Seed testing is done to determine the quality and the capability of seeds to germinate into healthy seedlings. This can be done through the following:

Viability test. This is done by germinating randomly sampled seeds using appropriate pre-germination treatment to determine how many will germinate.

Seed health test. This is done through visual or laboratory examination of the seeds to identify disease-causing organisms, such as fungi, bacteria, viruses, as well as animal pest, such as worms and insects.

Seed Storage and Handling

Seed storage is a technique where seeds are kept under favorable environmental conditions to maintain seed viability. This is to keep excess viable seeds for future use when seeds are no longer available for collection.

Determine the moisture content (MC) of the seeds if they need further drying or are ready for storage without losing their viability. In general, orthodox seeds (long-lived or with more than a year of viability) require an MC that ranges from 6% to 12%, while recalcitrant seeds (short-lived or with less than one year viability) need an MC that is greater than 12%, depending onthe species. (Refer to Annex B for moisture content determination)

Some other requirements in storing and handling seeds:

For seeds stored under room temperature: spread or place them in cloth sacks. For seeds stored in cold storage: keep the temperature at about 10DC for orthodox and

about 15°C for recalcitrant. For seeds stored in sealed container: dry the seeds to their desired moisture content to avoid

deterioration. When transporting, place seeds in sealed containers or securely wrap them in wax paper.

Seed Germination

When the seed starts to sprout, germination is taking place. Generally, germination occurs from 3 days to 2 weeks after sowing. However, some seeds germinate longer, depending on species.

Treatment before germinationSeeds with hard coats require some treatments for faster and uniform germination. These include any of the following:

o breaking of hard seed coatso cold water soako hot water soako alternate hot and cold water soako dry heat treatmento acid and other chemical treatments, such as soaking in sulfuric acid

Methods of sowing a. Sowing in seedboxes

Benguet pine (Pinus kesiya), Bagras (Eucalyptus deglupta), Agoho (Casuarina equisetifolia), Kaatoan bangkal (Anthosephalus chinensis), and other species with very small or fine seeds (less than 1 cm in diameter) are sown only in seedboxes. Cover the seeds with fine sand, just enough to ensure surface cover.

b. Direct sowing or sowing in seedbedsLarge seeds (more than 1 cm in diameter) are either sown in seedbeds or directly in plastic bags and other containers. Examples of these are Ipil (Intsia bijuga), Narra (Pterocarpus indicus), Ma-hogany (Swietenia macrophyiia), Talisay (Terminalia catappa), Teak (Tectona grandis), Lumbang (Aleuhtes moluccana), among other species. Simply press the seeds into the soil until they are half covered.

The preferred sowing materials or germination soil mix consist of 50% sieved washed river sand and 50% top garden soil.

Water the sown seeds using a sprinkler with fine holes close to the soil to avoid dislodging of seeds. Continue watering every day - early in the morning or late in the afternoon — until the seedlings are ready for potting. For very fine seeds, water them very carefully so that the seeds are not eroded.

Preparation of potting materials

Sterilize the soil before using it as potting material to avoid problems with soil-borne diseases, such as damping-off and root rot. This is done using any of the following methods:

o heat the soil over a fire for about 15 minuteso apply chemical disinfectant (fungicide)o pour boiling watero spread the soil under direct sunlight in a clean area for one or two days.

Transplanting

a. Seedlings from seedboxes or seedbedsTransfer the seedlings from the seed boxes or seedbeds to plastic bags or other containers. This will provide them with adequate space to grow and develop. In transplanting the seedlings, consider the following:

1. Transfer the seedlings from the seedboxes or seedbeds when the second pair of leaves has fully developed.

2. Lift the seedlings with a trowel only 3. Plant the seedlings in plastic bags or

when they are already firm and the soil is moist.

other containers.

4. Water the seedlings immediately after transplanting.

5. Keep seedlings shaded for sometime until they have established themselves.

6. Set aside poorly developed seedlings for treatment to improve their quality, but discard infected ones.

b. WildlingsWildings are seedlings that grow naturally in the forest. These can be used when nursery-grown planting stocks or seeds are lacking or not available.The following are the steps on how to gather and transplant wildlings:

1. Collect wildlings when the soil is moist to minimize damage of roots.

2. Gather the wildlings by simply lifting them with the aid of a bolo or shovel.

3. Leave a ball of earth attached firmly around the roots.

4. Wrap the ball of earth with a banana sheath or a plastic bag with holes.

5. Transfer the balled wildings to a shaded portion of the nursery.

6. Let them develop before planting in the field.

c. Wildlings of Narra (Pterocarpus indicus), Mahogany (Swietenia macrophylla) or Ipil-ipil (Leucaena leucocephala) are lifted with the aid of a bolo or sharpened stick, leaving balls of earth attached firmly around their roots. For dipterocarp species, such as White Lauan (Shorea contorta), Red Lauan (Shorea negrosensis), and Bagtikan (Parashorea plicata), select wildlings with more than 7 mm diameter and height of 15-50 cm.

VEGETATIVE OR ASEXUAL PROPAGATION

Instead of seeds, this method of propagating trees uses plant parts, such as stems, leaves, roots, twigs, single cells, and tissues as initial material. This is done especially in plants that do not fruit regularly (seed-off) or when earlier fruiting is desired.

Some of the common techniques are propagation by cuttings, grafting, marcotting, and budding.

Propagation by cutting is commonly used in most forest tree species such as Narra (Pterocarpus indicus), Mahogany (Swietenia macrophylla), Yemane (Gmelina arborea), dipterocarp and bamboo species (Refer to Annex D on how to raise bamboo cuttings). Grafting, marcotting and budding are used for most fruit trees such as Pomelo (Citrus grandis), Santol (Sandoricum koetjape), and Mango (Mangifera indica).

Cuttings

A cutting may be a portion of a stem, root or leaf of a donor plant. This is placed under favorable condition to induce the development of roots and shoots. There are several effective propagation systems in which the rooting of stem cuttings are successful.

Rooting Stem Cuttings Using Non-Mist System

This technique is cheaper and a more practical way of propagating planting materials through rooting stem cuttings. The basic components of this technique are non-mist propagation chamber, rooting media, root containers and hand-mist sprays.

The non-mist propagation chamber is a structure enclosed with large transparent polyethylene bags with a dimension of 62 inches x 25 inches supported by a frame of bent wire. This chamber controls environmental conditions inside the rooting area and keeps it favourable for rooting.

The rooting media is a mixture of sterilized river sand and coconut coir dust with 1:1 ratio. For root containers, plastic hiko tray or plastic bags filled with rooting media can be used. Hand-mist sprayer is used to water the cuttings during the rooting period.

Foremost, collect cuttings from mother trees, seed production areas (SPAs), plantations, natural forests or established hedge gardens. Hedge garden is an orchard of plants that produce cuttings or other tissues for vegetative propagation.

The following are the steps in rooting stem cuttings:

1. Collect young shoots or cuttings for rooting and trim off their leaves into half.

2. Place them in a pail with water.

3. Cut them into two-nodal cuttings. 4. Sterilize them by soaking in fungicide solution from 30 to 60 minutes. To prepare solution, follow the direction indicated in the label.

5. Scrape the basal portion of the cutting. 6. Treat them immediately with rooting hormones, such as Indole Butyric Acid(IBA), Naphthalene Acetic Acid (NAA), and Indole Acetic Acid (IAA) using the recommended concentration.

7. Plant the treated cuttings in hiko tray or plastic bags.

8. Place them inside the non-mist propagation chamber. Keep them air-tight from 2 to 5 months.

9. Once rooted, lift the cuttings and dip in water to gently remove the soil from the roots.

10. Plant each in a plastic pot of mixed garden soil and river sand.

11. Return them to the enclosed chamber for a week of recovery. Gradually open the chamber during the succeeding 3 weeks. This will enable them to adjust to the outside conditions.

12. Transfer the potted cuttings in the hardening area. After 4 to 8 months, they are ready for outplanting.

GraftingConnecting two pieces of living tissues together so that they unite and eventually grow and develop as one plant is called grafting. This propagation method is used when cutting is not applicable. It is also used to:

Hasten reproductive maturity of seedlings Establish clonal seed orchards, clonal tests and clonal banks Obtain benefits of rootstocks.

There are several types of grafting, such as cleft, saddle, splice, and whip or tongue, among other methods with respective procedures.

The following steps are generally used in grafting:

1. Remove the leaves but retain the buds or nodes in the scion.

2. Split-cut the top end of the selected stock.

3. Sharpen the base of the scion. 4. Insert the scion between the split-cut of the stock.

5. Apply wax over the cut portion to prevent loss of water.

6. Tightly wrap the grafted part with a plastic sheet. Do not cover the nodes.

7. Cover the grafted portion loosely with a plastic bag.

8. Remove the plastic bag when young leaves appear but leave the plastic sheet.

9. Remove the plastic wrapping after 5 months.

10. Cut the grafted portion and plant the graft.

Marcotting

This is a propagation method which includes the development of roots on a stem while it is still attached to the parent plant.

The procedures for this method are:

1. Select a branch that is 0.5 to 3 cm in diameter.

2. Remove 3 cm of bark around the branch. The exposed part must be 15 to 30 cm from the tip of the branch.

3. Clean thoroughly the exposed portion with a knife.

4. Cover the exposed portion with moistened rooting medium, such as sphagnum moss or coconut husk with small amount of rich, loose soil.

5. Cover the rooting medium with plastic. Tie both ends with string to prevent seeping of too much water.

6. Cut the marcotted branch below the wrapped portion when the roots are fully developed.

7. Remove the plastic and plant the marcot. Keep the soil moist.

BuddingBudding is done when the scion is reduced in size to contain only one bud and a small portion of the bark, with or without wood. This process is applied or used in small plants.

A scion is a detached living portion of a plant, such as a bud, to be attached to a rootstock in the budding or grafting methods.

There are two types of budding:

Shield Budding. This is widely used on citrus.Procedure:

1. Make a horizontal cut in the rootstock, 2 to 3 cm long, as deep as the bark.

2. Make a vertical cut below the horizontal cut forming a T.

3. Slice a shield of bud from the bud stick about 2.5 cm under the bud to 2 cm above.

4. Open the bark of the T-shaped cut in the rootstock.

5. Insert the shield by pushing it downwards under the two flaps of bark.

6. Tie securely with a plastic tape but leave the bud exposed. Don’t press the tape too firmly against the inserted bud. This will destroy the growing bud.

Patch Budding. This is widely used on fruit trees with thick bark.Procedure:

1. Remove a rectangular piece of bark from the rootstock.

3. Insert the patch with the bud in the cut on the rootstock. The inserted patch should fit the cut tightly.

4. Wrap the part with the inserted bud with plastic, tape, or waxed cloth leaving the bud exposed.

5. Trim off the upper portion of the rootstock, just above the patched bud.

6. Cover the stem portion of the grafted bud with a clear plastic bag to reduce transpiration.

7. Water the root stock daily. 8. Remove the plastic cover once the grafted buds sprout.

SITE PREPARATION AND PLANTING

The planting lines should be deep ripped to at least 50 cm to prepare a favourable bed for the planting material and for ease of root penetration. This area should be sprayed with herbicide prior to planting and kept weed-free for at least the first two years of growth. Planting should occur as soon as the soil is moist enough to allow survival until the regular rains commence. Proper spacing of trees is very important as it affects the patterns of growth, weed suppression, water requirements and the economics of planting and tending of the plantation. Seed from superior trees with a good straight trunk can be spaced further apart than say seed collected from inferior poorly formed trees. A common spacing for superior seedlings on cleared and prepared sites is 5 metres between rows and 5 metres along the row (400 stems/ha).

Initial planting density may be around 1000 seedlings/ha (3 m spacings). This gives better early tree growth (younger trees protect one another and height growth is much better) as well as providing more trees from which to select from. Most of these trees are culled or thinned to leave the best 100-200 specimens to grow on into sawlogs.

FERTILISER

A complete fertiliser with trace elements should be applied at the time of planting at a rate of 200 g/tree. This can be done in two applications if necessary, one application after planting and the other halfway before the end of the wet. Earlier fertiliser trials carried out in the Top End with Khaya senegalensis showed applications of nitrogen, phosphorus and trace elements were very important for the successful establishment of this species. The fertiliser should be placed in pockets on either side of the tree and not spread on the surface of the ground, as this encourages weed growth.

THINNING

The growth of the trees should be monitored regularly and thinning started before the stand is suppressed. In a thinned plantation, the crop should look distinctly open, and individual crowns should have clear space all round. Normally, trees with the best crowns and stem-form are retained and are left evenly spaced within the stand, even if that means the sacrifice of some of the good formed trees. Because Khaya senegalensis has a tendency to form branches low on the stem, form pruning may be necessary on some trees. However all trees with poorly developed crowns and stems should be removed, provided this will not result in large canopy gaps.

Pruning

Clear wood pruning maintains high wood quality in the target log by controlling branch size and reducing knot defects. Thus a joint thinning and pruning regime will greatly reduce rotation length while maintaining high quality logs. Form pruning can also be beneficial with trees that tend to have poor form and heavy branching. The removal of double-leaders and tight branches cangreatly improve the chances of achieving a final stand of straight stems without knotty centres.

THE TIMBER

The heartwood is pale pink-brown when freshly cut, darkening with exposure to a deep redbrown with a purple tinge. The sapwood is not very distinct from the heartwood, being only slightly more pale and brown. The stripe or roe, characteristic of timber with interlocking grain, is often very marked. In texture and general appearance it more closely resembles Cuban mahogany than any other African species. It is moderately hard and heavy; density is between 680–750 kg/m3. It is the hardest and heaviest of all the mahoganies found in Africa (Alwyn Jay 1972).

Aim for large logs

For sawlog production, aim for larger diameter logs (>45 cm), as they have the advantages of higher milling recovery rates, they are cheaper to harvest than skinny logs (less logs per cubic metre of timber) and mills generally find larger logs (and the sawn timber from them) easier tohandle. Depending on the species, the age of the log can effect the quality of the wood. Juvenile wood and sapwood can have lower wood densities as well as being inferior in quality tomature heartwood. The time it will take to grow a 50 cm diameter sawlog will depend on the site quality and the thinning and pruning regime of the stand. Hint - a sawlog 50 cm in diameter and6 m in length will contain about 1 m3 of wood. A productive site in the Otways with an ideal management regime may produce trees 50 cm in diameter within 15 years! Bambra Agroforestry Demonstration Farm has already achieved this! More commonly however, the aim is to produce sawlogs over a 25-40 year period.

FUNCTIONAL USES

The most important uses of mahogany are for furniture and interior decoration, both in the solid wood form and as a veneer. It is also used for good quality joinery and ship cabins, plywood, turnery, carving inlay work, picture frames, linings and mouldings (ICRAF online). In the past this timber has been used for furniture and bench tops in the Top End. Previously, no proper drying schedule had been followed or determined, resulting in excessive shrinkage of the product. Schedules have now been developed and kiln drying should be practised in the future. The seeds have an oil content of 67% and are rich in oleic acid (66%). The oil is used in West Africa for cooking. Khaya senegalensis is an important medicinal plant in Africa, and the very bitter bark has a considerable reputation as a fever remedy. The young leaves contain fairly large amounts of digestible protein and are used in Africa as a fodder for cattle and camels,