A.F.A. LAMB of the Department of Forestry at the Commonwealth Forestry Institute, Oxford, England, prepared this paper for the first session of the FAO Committee on Forestry Development in the Tropics, held at Rome 18-20 October 1967
The techniques of artificial regeneration within the humid lowland tropical forest that have been used on a commercial scale are: the taungya plantation system; clear felling and planting; line planting; and the afforestation of grasslands.
The forest manager's approach to these four systems is to calculate, for the local conditions, which will give the biggest return on the effort and money spent and supply the product most suited to the domestic or export needs of the future. There is no doubt that the taungya system should be given priority wherever it can be successfully practiced.
The circumstances under which this method of regeneration may be successful can be summarized as follows:
1. Farmers must fully understand what is expected of them and what is expected of the forest officer, and each must trust the other. They must agree that the bargain is fair to them and that the return they get from the site offered will recoup them for the labour of clearing the forest. Many forest authorities have drawn up agreements and required the farmers to sign them before being given a farm. This is a waste of time if the farmer understands and trusts the forest officer. All that is needed are two things: (a) a map showing the current coupe and the subdivision in it of each farm on which the farmer's name is written; and (b) a list of farmers with the record of their past efficiency as farmers. The latter may be called a reputation list. If a farmer does not cooperate one year, he gets a smaller farm or no farm the next; if he does well and wants a larger farm, he gets one.
2. The forester must adjust his planting techniques and selection of species so as to meet the farmer halfway. The attitude should be one of understanding and enquiry, to achieve the maximum degree of integration between farm and forest interests.
3. The system is more likely to be widely accepted where the farmer is unable to maintain soil fertility by any other system than bush fallow. This occurs where the soil is sandy and the rainfall high. The best example is the Benin Sand formation 'in 'Nigeria, but the taungya system has worked on waterlogged white sand sites in Trinidad where pine was being planted and on more fertile areas where teak is the timber tree being established. In the Philippines, on the other hand, this system could not be operated because the soil retained its fertility for a long time and the farmers that refused to move were supported in their refusal by politicians. Thus there must be both a demand for the kind of land offered, acceptance of the obligations by the farmer and sufficient discipline in the community to deal with recalcitrant farmers.
Where demand for land is weak but discipline good, it is possible to operate the system if a payment is made to the farmer for each section of land successfully established. This may well be worth while where other systems of regeneration would cost much more and give poorer results.
CHOICE OF SPECIES
The choice of species must be influenced by their characteristics, the site conditions and the potential markets. A very useful example is evolving in Nigeria, where there is an expanding market for transmission poles and a valuable export market for furniture timbers of the Meliaceae. In the taungya plantations a mixture of opepe (Nauclea diderrichii), lovoa (Lovoa trichilioides), mahogany (Khaya ivorensis) and the entandrophragmas (E. utile, E. cylindricum and E, angolense) is planted at 12 X 12 feet (3.65 X 3.65 metres) in the proportion of five opepe to one of the group of Meliaceae. Because of variations in seed or wilding supply, Lovoa is more commonly planted than the others and Entandophragma utile is least planted, although it is a most desirable tree. In this mixture the opepe act as nurse and filler species during the first 12 to 15 years. During this time they grow slightly faster than the Meliaceae, their spreading branches fill up the space, shading out weeds and separating and shading the stems of the Meliaceae, thus reducing the incidence of the Hypsipyla shoot borer. By the 12th to 15th year the opepe have reached pole size and are acceptable locally as pressure-treated poles because of their excellent form and ease of impregnation. An early return at this age greatly improves the economics of the plantation, the Meliaceae have passed the danger period when they can lose their vigour through repeated shoot borer attacks and are starting to grow faster than the opepe. When most of the opepe have been thinned out, the mixture remains at near final crop spacing and an average annual girth increment of 2 inches (5 centimetres) is maintained by the Meliaceae, giving trees 8 to 10 feet (2.5 to 3 metres) in girth above the buttresses in 60 to 70 years.
FIGURE 1. - A "candidate plus tree" of teak growing as an exotic in Tanzania, aged about 30 years.
There is little doubt that these valuable tropical species are being severely overcut throughout their range and that they will be in short supply in the future. Such a system concentrates them in their homeland at very low cost. Establishment costs in taungya farms in Benin are said to be under £8 (U.S. $22), 26 man-days per acre (65 man-days per hectare) planted. This overcomes the factor considered by Catinot to be limiting in such a system, i.e., insect damage, and produces a forest where creepers have been severely curtailed. Thus two major causes of failure in the tropical shelterwood system (lack of desirable parent trees and profusion of creeper growth) have been corrected and natural regeneration may be feasible in the second rotation. In 1966 the taungya system was being applied over 2500 acres (1000 hectares), per year in Benin, but it could be greatly expanded with a bold plan of well-organized forest villages, provided the people continue to value its benefits to them.
Another successful species less extensively planted is Cedrela odorata. This has reached 7 to 10 feet (2 to 3 metres) in girth over bark breast height (obbh) in the taungya plantation of 1929 at Sapoba, a mean annual increment of 3 inches (8 centimetres) girth per year. Even in pure crops the shoot borer has failed to check it, because cedar is so vigorous on the excessively drained Benin Sands if planted or sown immediately after the removal of the high forest. A mixture of three opepe to one Cedrela would give the ground cover that cedar alone does not give in the early years and leave 75 Cedrela per acre (185 per hectare) from which to select the final crop. This species can be successfully raised by sowing at stake in the taungya farm before the break of the rains, if ample seed is available. About 20 seeds are sown per stake and thinned out a few months later to leave the most vigorous.
OTHER TAUNGYA TECHNIQUES
A few variations in the taungya technique are worth mentioning. In the Democratic Republic of the Congo, Belgian forest officers evolved a successful technique for very wide spacing (12 x 4 metres) of Terminalia superba on sites where farmers grew bananas. Large areas have been cheaply established in this way because of the revenue from the bananas (Dawkins 1955). A similar system on certain West Indian islands combines Mahogany (Swietenia macrophylla) and bananas which receive fertilizers and this increases the growth of mahogany.
Another variation is known as cocoa taungya. A large-scale trial of this method is in progress in eastern Nigeria in the Cross River North Forest. In this case all saleable timber in the original forest has been exploited and the remainder has been thinned out to leave a high top shade of natural species above the cocoa trees planted at 10 X 10 feet (3 X 3 metres) and the timber-tree, plantain and tree cassava shade planted at 20 X 20 feet (6 X 6 metres). The soil is fertile volcanic loam and the annual rainfall is about 100 inches (2540 millimetres). A criticism of this technique is that, as the crop grows up, the combination of top and planted-timber shade will become too dense for the cocoa to give its maximum yield and thinning out of top shade will damage the cocoa and timber-tree shade beneath even if a poisoning technique is used.
Trinidad has evolved a system on private estates where the whole forest is felled without burning and the shade, composed of bananas, timber trees and Erythrina spp., is established before the cocoa is planted. The timber trees used are Cedrela odorata, Cordia alliodora and Swietenia macrophylla, all furniture woods of high value in Trinidad. This crop is grown on 30 to 40 year rotation and the revenue from the timber trees at the end of the rotation may go far toward covering the cost of reestablishment of the cocoa crop. They sell for at least 4s. 6d. a cubic foot standing (U.S. $22 per cubic metre). However, foresters should not put too much faith in cocoa taungya systems, as the trend is to have no shade over cocoa once it is established and to maintain fertility by the use of artificial manures.
Near centres of population where firewood and poles of teak are in strong demand, as at Ibadan, Nigeria, teak is extensively planted under the taungya system. It may improve the economics of teak taungya plantations to clear-fell each couple at 10 years old, sell the produce as poles and fuel and then thin out the coppice and leave the crop to grow to timber size; in this way the form of the timber trees is improved, an early money return is gained and the very rapid growth of the single coppice shoot retained after the 10-year-old clear-felling gives a higher increment, so that the clear-felling in the 10th year does not necessarily extend the length of the timber rotation by an equal amount.
If all efforts to operate the taungya system fail and conditions for natural regeneration are adverse, the two other possibilities left to enrich high forest sites are clear-felling and planting or some form of line planting. Which system is used will depend on the market. If maximum yield for pulp, chipboard or similar bulk product grown on a short rotation is required, or if a species like teak is so valuable both as thinnings and final crop that it can repay the cost and cannot be successfully grown in line planting, then there is no alternative to clear-felling.
COST OF ESTABLISHMENT
The initial work is usually done on contract after as complete sale of the mature timber as possible. The cost in Nigeria in recent years has ranged from £14 to £17 per acre (U.S. $97 to $118 per hectare) for clear-felling and burning of the debris. Plants cost between 1½ to 2½d. each, or £6.5s. to £10.8s. (U.S. $17.50 to $30) per thousand in west Africa, but in east Africa plants may cost as little as £3 (U.S. $8) per thousand according to species and nursery technique. The highest cost is for plants in polythene tubes, the lowest is for stump plants.
The spacing in such plantations varies from 6 X 6 feet (1.8 X 1.8 metres) in the teak plantations of Trinidad to 12 X 12 feet (3.65 X 3.65 metres) for the mixtures in the taungya farms of Benin, Nigeria, i.e., from an area where the species benefits in form from close spacing and there is a local market for poles to a region where thinnings are delayed until the opepe trees are of the right pole size and thereafter little will be saleable until the remaining trees reach timber size.
In the Nigerian teak plantations, establishment costs to the third year in high forests cleared and burned but not farmed, and planted at 8 X 8 feet (2.5 X 2.5 metres), are about £30 per acre (U.S. $207 per hectare), equivalent to 100 man-days per acre (247 man-days per hectare) excluding overheads, compared with £15 per acre (U.S. $103 per hectare) in taungya plantation. Similar figures are lower for Gmelina, a species now being extensively established with the same technique for matches, veneer logs and pulpwood, owing to the wider spacing frequently used (10 X 10 feet [3 X 3 metres] in Ondo Province, Nigeria) and the quicker closing of the canopy and early suppression of weeds. These two favourable aspects of growing Gmelina can reduce the cost by £5 per acre (U.S. $34 per hectare). Other exotic species in this category which should cost no more than Gmelina to establish are Eucalyptus deglupta and Anthocephalus cadamba (both evergreen species), Cordia alliodora, Melia composita and Acrocarpus fraxinifolius. All of these provide good weed suppression, have very rapid growth, produce easily worked timber, and are likely to be used for a variety of purposes, including pulpwood, veneers and utility sawn timber.
It is still too early to obtain reliable figures of their volume output, except for Gmelina, which will produce between 500 and 600 cubic feet per acre (35 and 42 cubic metres per hectare) per year on a short rotation on favourable sites, such as Malaya. Even higher increment figures are estimated, but not proved in practice, by the Bislig Bay Company, from planting of Anthocephalus cadamba on Mindanao Island in the Philippines (Pollard 1967). This company is installing integrated utilization plant to use the total content of some of the finest Dipterocarp forests in the world, growing on volcanic soil in a wet equatorial climate. The cut-over forest is being replaced immediately with plantations of cadamba planted at 8 X 8 feet (2.5 X 2.5 metres) which, it is estimated, will have a standing volume of 7860 cubic feet per acre (550 cubic metres per hectare) after 10 years without thinning and an increment of 786 cubic feet per acre (55 cubic metres per hectare) per year. The cost of plants, planting and clearing is estimated at £30 per acre (316 pesos1), but the total cost including interest and road construction is estimated to be 11.355 pesos per hectare. There is no mention of trials of Eucalyptus deglupta by the Bislig Bay Company. This is indigenous in Mindanao. In a slower growth category should be placed Triplochiton sclerxylon and Cedrela as timber and veneer, not pulp, producers. The rotation of timber production of such species will be 25 to 40 years and for pulpwood production less than 10 years.
1 3.818 Philippine pesos = U.S. $1.00.
INFLUENCE OF GROWTH RATE ON WOOD
The wood of all these species requires testing after being grown under the high forest conditions under consideration. Nigerian-grown Gmelina, for instance, has been examined by Esan (1966) and shown to produce wood of 30 pounds per cubic foot (480 kilogrammes per cubic metre) air dry without any significant variation in density between the pith and the bark. It has very low shrinkage when dried, does not distort and has given an excellent report as a pulpwood (Chittenden et al., 1964). The wood is a pale creamy-brown colour, making it suitable where light colours are an advantage. Anthocephalus cadamba has been shown to be suitable for veneers and pulpwood from very limited tests on a few 14-year old trees at the Forest Products Research Laboratory at Laguna, Philippines (TPI report, 1963). In Indonesia, where very fertile sites are available, it has produced a total volume of 5440 cubic feet per acre (380.5 cubic metres per hectare) on a 24-year rotation and has been extensively planted. This species seems to require these humid equatorial climates for maximum production. Its form is excellent, with a single straight stem and radiating branches. The Trinidad cordia is a well behaved timber when grown in Trinidad and it coppices, but is still too young in Sabah, Sierra Leone and Nigeria for timber tests. Melia composita has shown remarkable growth in Nigerian plots in Mamu forest, where it closed canopy in the first year; Acrocarpus fraxinifolius is not far behind in this respect. Nothing is known of the quality of timber they will produce when grown at this rate. The last two mentioned, Triplochiton and Cedrela, appear to produce wood which is much influenced by site conditions. Triplochiton grown in the natural forest in Ghana is reported by the timber trade to be woolly and much inferior to Triplochiton from Nigeria. As the growing and soil conditions in Ghana are generally more favourable than in Nigeria, it is possible that texture in this species is related to growth rate. There is little doubt that this is true of cedar timber from cocoa plantations in Trinidad, which is softer and less dense than cedar grown more slowly in the natural forest.
Thus the evidence is conflicting. Gmelina wood grown fast is as dense as slow grown Gmelina, but this may not apply to some other hardwoods and certainly does not apply to conifers such as pine.
There is quite a possibility that on favourable sites plantations of some of these species will be grown purely as a source of pulpwood. On the other hand a combination of pulpwood from heavy thinnings in the early years followed by sawn timber production from the remaining trees is a preferable system of management. This will necessitate attention to thinning regimes. Again, Gmelina may be taken as an example of the kind of schedules required. In Benin, when planted at 8 X 8 feet (2.5 X 2.5 metres) it requires a 50 percent thinning at 3 years old, another of similar severity 2 to 3 years later and a third by the 7th or 8th year. From all of these pulpwood and particle board could be produced. Something very similar was applied in Sierra Leone to obtain sawable logs by the 18th to 20th year, when widespread death was liable to occur under the Sierra Leone soil and climatic conditions. On existing evidence equally drastic schedules will be needed for Anthocephalus and Melia. As all these species are strong light demanders and intolerant of crowding, delay in thinning can cause stagnation.
MIXTURES OF SPECIES
It may prove useful to try mixtures of compatible species, for instance Anthocephalus, a well formed tree, with Gmelina, a species of very bad form if side shade inadequate, Cedrela and opepe (already mentioned in section on the taungya system).
MAINTENANCE OF SOIL FERTILITY
A final point about the species under discussion is that they probably all require very favourable sites to give the results of which they are known to be capable. It is useless to assume that all high forest sites will prove equally productive. Much of the Amazon, the greatest tropical forest in the world, is on infertile white and brown sands incapable of sustaining repeated crops of light demanders. Parasol ants (Atta sp.), a pest of South American tropics, in Trinidad completely eliminated Gmelina from Arena forest plantations by constantly removing every leaf produced. They may do the same in the Amazon unless eliminated. Moreover, on deep sands like those in Benin, fertility may fall under pure crops of light demanders grown on short rotation for pulpwood, especially pines and eucalyptus, which have light crowns.
An alternation of crops of shade bearers such as the Meliaceae, grown on a 60 to 70 year rotation, and light demanders such as Gmelina, may give the best results, with or without one year of farming between each rotation of trees.
PESTS AND DISEASES
Very little is known about the risk to exotics from pests and diseases. It would appear that the risk from root rot is greatest in the first five years of a plantation, in which the debris and stumps of the original forest provide food for the multiplication of root fungi such as Fomes lignosus. Both teak and Gmelina plantations have suffered about 2 percent of deaths in Nigeria. This usually occurs in small groups. In Trinidad, Pawsey (1966) suggests that the risk in pine plantations grown on felled hardwood forest sites is not serious and will probably decrease as they get older. It is important, however, to watch for pathogens and test out a number of species in case one is devastated by a pest or disease. The known pests of the Meliaceae can be rendered ineffective by good silviculture.
Much more work on this system of artificial regeneration has been done in west Africa, and it would appear from Catinot's (1965) analysis of results that he prefers close line planting to a system of clear-felling, burning debris and planting. His main reasons are that it retains the forest environment and can be applied where the taungya system cannot. It can certainly save from destruction pole-size trees of economic species which would be sacrificed under clear-felling and planting. He advocates a closer spacing than Dawkins envisages and so loses one of the advantages of the system, low unit costs.
CRITERIA FOB SUCCESS
There are a number of criteria which must be met if this system is to produce a satisfactory stand of timber trees. These criteria have been clearly enunciated by Dawkins:
"In the sense used here, line-planting is the establishment of a tree crop to be closed at rotation age, in lines spaced at intervals equal to or slightly greater than estimated final-crop crown diameter."
There are five necessary conditions for line-planting, in addition to the normal requirements of healthy plant establishment:
1. There must be little or no demand for thinnings in the area concerned. If thinnings are required, the method is unsuitable; if large timber and veneer logs are in demand, the system is suitable.
2. The species planted must be fast-growing (5 feet [1.5 metres] of height per year as a minimum), naturally straight and self-pruning, i.e. generally of the colonizing or gap-filling light-demanding type.
3. There must be no upper canopy; only clear-felled, clear-poisoned or low secondary forest is suitable.
4. The regrowth between the planted lines must be noninflammable.
5. Browsing animals must be absent, scarce or of negligible effect on planted trees."
Provided all five conditions are met, the method can cut the cost of a final crop to less than a third of what would be incurred by close-planting. The technique then requires the following:
6. Planting lines should be spaced equal to or slightly more - up to 20 percent more is reasonable - than the expected crown diameter of healthy final crop trees of the species concerned. The reason for this is to prevent any possibility of serious between-line crown competition before maturity, to save on establishment costs and to give more scope for possibly superior species which may arise naturally between the lines.
7. Plants should be spaced along the lines at approximately one fifth of the spacing between them, to allow a selection of about one-in-four for the final crop. If poisoned overwood is likely to be abundant, as in very lightly felled natural forest being planted, then up to 30 percent losses must be expected and spacing in the lines should be nearer 1/6 to 1/7 of spacing between lines. Only by this means can good form of the final crop be assured.
8. Planting lines must be well cleared, about 6 feet (1.8 metres) wide at first and made easy to move along, at least along one side of the planted trees, by removal of most if not all woody snags. Once planted the lines must be kept clean and no overhanging or threatening growth tolerated. Since this clearing work is confined to a very small fraction of the area, labour costs are low and several cleanings (sometimes up to 6 or 7 are necessary) can be afforded in the first 12 months.
9. Plants must get away to a quick start. For most species this means using potted stock; stumps or striplings are not likely to be suitable. Cedrela has shown itself capable of starting from direct seed, but this is quite exceptional.
10. Planting must follow immediately on clearing the planting lines; clearing in the early dry season and planting 3 to 5 months later in the early rains is thoroughly bad technique and will result in at least two more clearings than necessary. Poisoning of the upper canopy also should be timed to let in the light at time of planting, not before. It is recognized, however, that this is not a precise possibility.
11. Trees arising between the lines, unless superior in value to the planted species, must be cut or poisoned immediately they "threaten" the plants, i.e., before they overshadow them. The greatest threat is from Musanga, Trema and Macaranga. Similarly, climbers overarching from the bush regrowth beside the lines, must be vigorously cut back before they overshadow the plants, provide ladders for climbers or obstruct quick access along the lines.
12. Thinning along the lines is a matter of selecting the stems of superior form and height. (Unless the disparity in size is very great, form and height should both be regarded as more important than mere girth.) The first thinning will generally be at 3 to 4 years, by which time the trees should be well above the shrub and climber regrowth. It will probably require about 50 percent culling of crop.
The above five principles and seven technical guides must be taken very seriously. Line-planting has very often failed and has a bad reputation among English-speaking tropical foresters because one or other of the principles has been flouted. If all the above are followed for a species sensibly chosen, the technique has a very high chance of success in tropical forest conditions.
In the special case of west Africa, species subject to epidemic insect attacks, such as Chlorophora or Khaya, would not be "sensibly chosen."
FIGURE 2. - A young trial plot of Pinus caribaea, one of the tropical pines, growing in Malaysia.
In practice, in west Africa the Meliaceae have been extensively used in line planting with disappointing results because of slow growth and shoot borer attack. Cedrela (see paragraph 9 above) is able to succeed from direct sowing in taungya farms but is less likely to do so in line planting because of root competition. The species best suited for this system are Terminalia ivorensis and T. superba, the former in the wetter forest types and sedimentary soils, the latter on the basement complex and less humid sites. These have very wide crowns and do not require side shade to produce straight stems. They do not produce as high volumes per acre as narrow crowned species nor are they easily saleable as thinnings. Another species showing promise in Nigeria is Triplochiton scleroxylon and in Gabon Aucoumea klaineana is widely planted under this system, although west of Cameroon it has not shown such promise.
FIGURE 3. 3. - A 14-year-old plantation of Casuarina equisetifolia growing on the coast in Mysore State, India.
In Fiji Swietenia macrophylla has grown at a very rapid rate when line-planted on moist volcanic loams in a high rainfall. In these islands the Hypsipyla shoot borer is absent and the clayey volcanic soils are highly fertile, thus the conditions are ideal for Swietenia. It is being planted over 2000 acres (810 hectares) per year.
Line-planting is suitable for areas of degraded or inaccessible forest which will not fall within either the felling series of the natural regeneration taungya or clear-felling and planting systems. As local demand increases and maximum production per acre becomes more important, it may be less used.
The wood quality of Triplochiton and Cedrela has already been briefly mentioned. Of the Terminalias, T. superba has a very variable reputation. In Nigeria it is seldom planted because of insect holes surrounded by staining throughout the heartwood of many trees; in Congo (Brazzaville) and Gabon it is much more popular. Aucoumea is well known as one of the best peeling timbers in the tropics.
Because the pines have not proved capable of suppressing regrowth of hardwood trees, creepers and saprophytes on sites where the high forest has been cleared, they cost more to grow on such sites than the faster growing hardwoods, produce lightweight weak timber and are not recommended as replacements for humid lowland tropical forest. There are, however, extensive areas in several countries within this zone where fire subclimax vegetation has replaced closed hardwood forest, either through the degradation of the soil following hurricanes and fire or through destruction of the forest by man followed by the invasion of grasses which are maintained subsequently by fires. Examples of such humid savannas occur:
(a) on the Amazon Guyana and Surinam coastal alluvium, where they are being afforested with Pinus caribaea;
(b) in Central America, Cuba and the Bahamas, where the same species is indigenous;
(c) in the Philippines, where pine plantations have been less successful because of the poorly aerated volcanic clays;
(d) in northern Queensland, where extensive sandy coastal plains are being drained and converted from scrub Eucalypt and Melaleuca to plantations;
(e) in Malaysia, where tin-mining has removed the high forest;
(f) in Indonesia and Fiji, where better drained volcanic soils degraded to grass are proving highly productive under pine plantations.
Conditions vary greatly in these savannas but they have certain features in common which make them suitable for pine plantation schemes. They all have a high rainfall - the lowest is in Queensland, 50 to 60 inches (1270-1520 millimetres) per year; the soils are usually low in pH and nutrients, especially nitrogen, because of leaching of minerals from the sandy soil by the high rainfall and lack of replacement of nutrients by leaf-fall; consequently mycorrhiza fungi spread easily through them; they are free of coppicing stumps, creepers, saprophytes and regeneration of hardwoods with which the pine cannot compete and which are expensive to control; they are cheap to plant, easy of access and can be cheaply cultivated by machines.
Pines are capable of thriving where available nitrogen is scarce if mycorrhiza is present and they are resistant to grass fires, but the wood they produce is used for utility purposes and must be produced at low cost to compete as pulp and building timber with imports from natural coniferous forests in temperate and subtropical regions. The two features of the soils under consideration of greatest importance are their texture and depth. Occasionally, as in Sarawak, trace elements may be deficient but usually growth of the pines can be closely related to the depth of well-aerated soil above the water table. A recent report from Zululand, South Africa, demonstrated this very clearly (Haigh 1966). On such sites pines are likely to give a larger volume production more cheaply than any hardwood if soil nutrients are deficient.
COST OF ESTABLISHMENT
Costs of establishment on such sites are similar to the costs of high level grasslands. In the absence of scrub forest the cost, excluding overheads such as draining, fire protection and road construction, averages about £8 to £10 per acre (U.S. $55 to $69 per hectare) including the cost of plants where the spacing is 8 X 8 feet (2.5 X 2.5 metres).
Yields vary enormously in Pinus caribaea var. hondurensis plantations on such sites according to soil conditions. The Trinidad savanna plots at Piarco gave a low mean annual increment at 12 years old of 80 cubic feet per acre (5.4 cubic metres per hectare), the Zululand plantations at Langipan had a mean annual increment at 15 years old of 500 cubic feet per acre (35 cubic metres per hectare). Apart from climatic differences between these two sites, the sandy loams in Zululand were deep and well drained and the pine roots could reach a water table over 12 feet (3.6 metres) down even in the dry season which permitted continuous growth. In Trinidad an impervious layer 12 to 18 inches (30 to 45 centimetres) below the surface caused waterlogging in the rainy season and drought in the dry season. The grasses seldom reflect such differences and a soil depth and texture survey is therefore an essential part of the assessment of potential pine plantation sites.
P. caribaea and P. merkusii should be preferred for low level sites, P. oocarpa var. ochoterenai and P. khasya for sites above 2000 feet (600 metres) above sea level.
The Araucarias, especially Araucaria cunninghamii and A. hunsteinii (formerly A. klinkii) are favoured in plantation schemes in Queensland and New Guinea on land cleared of high forest. They have the advantages of excellent stem form, a white wood with long fibres very suitable for refiner pulp for newsprint, veneers and utility furniture and an increasing rate of growth with age. Their mean annual increment may still be increasing in the fortieth year. A. cunninghamii is more drought resistant than most of the pines. On the other hand, they do not produce seed until 25 to 30 years old, and A. hunsteinii seed is large, heavy and quickly loses its viability. They require 18 to 24 months in the nursery with overhead shade; they are slow growing for the first 4 years in the field and this adds greatly to cleaning and establishment costs especially on high forest sites; they are fire tender; they require high nitrogen availability and are there fore not able to establish themselves in infertile grass savannas without the aid of nitrogenous fertilizers. They will, however, succeed under a nurse crop of pine on grass savannas.
Countries with large areas of derived savanna land underlain by reasonably fertile soils, such as Fiji, Ghana, Indonesia and Jamaica, should plant a sufficient area of these species to form a source of seed at a later date and at the same time test the potentialities of these species. Provenance trials are advisable as there are considerable variations in volume production between provenances of A. cunninghamii.
FIGURE 4. - Planting out teak seeds in Indonesia.
NETHERLANDS INFORMATION BUREAU
Costs of establishment in Queensland up to the 5th year in subtropical rainforest are approximately £60 (A $130 per acre or U.S. $415 per hectare) of which approximately half is the cost of cleaning after planting and A $23 per acre (U.S. $72 per hectare) the cost of plants.
PRODUCTION OF PLANTS
Nurseries in the high forest zone may be temporary or permanent. Where the soils have good structure and the rainfall is not above 50 to 70 inches (1270-1780 millimetres) per year, permanent nurseries may be preferred if suitable, reasonably level sites can be found. On the other hand, sandy soils quickly lose their fertility in high rainfall regions and their humus content. Under such conditions the addition of fertilizers may not maintain growth or may have to be so heavy as to become uneconomic. On the Benin Sands of Nigeria a large block is allocated near forest headquarters to nurseries and within this block a bush fallow rotation is practiced on a long enough rotation to maintain soil fertility.
Teak, Gmelina and the Terminalias are usually grown as stump plants after ten months to a year in the nursery. Eucalypts, araucarias and pines are always raised in polythene tubes or pots and the Meliaceae are planted out in taungya plantations as 2-year-old striplings 3 to 5 feet (1 to 1.5 metres) high, many of which are gathered in the forest as wildings owing to the difficulty in collecting sufficient undamaged seed. Cedrela is an exception. It can be sown at stake in taungya farms and this has the advantage that it receives no check, such as occurs when nursery stock is planted in the field. However, it has been successfully established as plants in Benin and plants would be preferred in line-planting and plantations following clear-felling and burning of the forest.
The fleshy, fruited, small seeded species, such as Nauclea and Anthocephalus, are very liable to damp off in seed beds. The seed can be extracted by separation from pulped fruits in water or by pulverizing dried fruits. They require protection from heavy rain and a light sandy soil not heavily shaded. A relatively small, well-protected germination bed sown in March can yield an enormous number of plants, which should be transplanted as soon as they are large enough to handle. There is much to be said for using polypots for these species; small polypots to which the seedlings are transplanted in April in preparation for planting out in the field in June. In this way the plants will get the minimum check and may more easily overcome the shoot borer Orygomophora medio-foveata which damages Nauclea in Nigeria. Such a system would cut down the nursery period from 12 to 3 months.
Another development indicated by an experiment in Nigeria is to use small polypots for Terminalia ivorensis also. Survival of polypot seedlings was far superior to survival of stump plants in the experiment and again the nursery period was greatly reduced.
Research is continuing in Nigeria into the size of polypots needed in the humid high forest conditions and into potting soil mixtures. There is evidence that in humid climates 6 months old plants can be as big in 5 X 3 inch (12.5 X 7.5 centimetre) flat pots as in 10 X 4 inch (25 X 10 centimetre) flat pots, and a great saving in transport could thus be achieved.
Large polythene bags are now in use for transporting stump plants, small polypot plants and Swaziland bed pine plants from the nursery to the field. These greatly facilitate administration because they keep the plants in good condition longer, provided they are kept cool and shaded from the sun.
1. Tropical humid high forests are a source of valuable timbers which can be produced nowhere else in the world and which are already severely depleted, e.g., the Meliaceae. The Nigerian plantation technique can grow them in mixture with Nauclea.
2. Population pressures on these forests are increasing. This makes it essential to produce the maximum useful timber from every acre. However, line planting still has limited application in the remoter regions.
3. Natural regeneration can be used to bring the forest to maximum production only in specially favourable circumstances. Artificial regeneration usually gives quicker results and higher yields, and will have to be used in most countries to raise the concentration of the few valuable species suitable for modern industry.
4. The taungya system is the best and cheapest method of establishing plantations, but it depends on a delicate balance of interest and on trust between the farmer and the forester. Not enough has been done to extend this system to the maximum by good public relations and education, especially education of politicians.
5. There is a recent tendency for forestry plantation schemes to be sponsored by industrial interests, both government and private. This is all to the good, provided the forester is not coerced into large-scale planting of species not properly tested under the conditions.
6. On existing evidence, the most promising hardwood on high forest sites for general use and pulpwood production is Gmelina if grown on suitable sites; furthermore, it coppices. Several others are under trial but their wood quality when grown quickly in plantations requires further investigation.
7. Plantations of light demanders in humid tropical lowland forest on light sandy soils may fail to maintain the fertility of the site if grown on short rotations, unless an understorey is encouraged. Examples are teak, Gmelina and Eucalyptus deglupta.
8. Pines have a part to play in the afforestation of degraded high forest sites now under grass within the high forest climatic zone, provided adequate attention is paid to soil depth and texture. Araucarias need further trial, longer rotations and will be more costly to establish.
9. In nursery practice the use of small polypots is increasing for some species usually planted as stumps. The economics of this development are under study.
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