J. EvansJulian Evans Director, Forestry and Land Use Programme, International Institute for Environment and Development (IIED), London, UK This account is based on two papers: (1) EVANS, J. 1986. The productivity of second and third rotations of pine in the Usutu Forest, Swaziland. Commonwealth For. Rev., 65(3):205-214; and (2) EVANS, J. & WRIGHT, D. 1987. The Usutu Pulp Company development of an integrated forestry project Conf. on Sustainable Development, regent's College, London, April 1987. IIED. Copies of the second paper are available from IIED, 3 Endsleigh Street, London WC1H ODD, UK Price: £350.
The author is grateful to Mr W.H. Rodgers, Managing Director and Mr Spencer Brook, Former Forest Manager at Usutu for their comments and assistance in preparing this article.
THE USUTU FOREST clearfelling 18-year-old pine plantations
In 1967, Unasylva No. 84 carried an article describing the development of the Usutu forest and pulp mill in Swaziland ("Planning an integrated forest programme", by William F. Hastie and John Mackenzie). At that time the forestry operation was about 17 years old.Another two decades have passed since then, and almost half the plantation forests of Usutu are now in their third rotation, supplying the raw material requirements for the annual production of about 180000 tonnes of unbleached Kraft wood-pulp. The author of this article has been involved since 1968 in monitoring the long-term productivity of successive rotations of the Usutu pine plantations. In the article he reports on the results of these studies, and assesses the various environmental consequences of converting some 52000 ha of high veld grasslands into what is essentially a pine monoculture.
The Usutu forest is an area of 52000 ha of predominantly pine plantations in the high veld of Swaziland in southern Africa (see Fig. 1). These man-made plantations supply the raw material for the annual production of about 180000 tonnes (air-dry) of unbleached Kraft wood-pulp produced in a mill situated in the middle of the forest beside the Usutu river. The pulp is exported throughout the world and, after sugar, is Swaziland's most important export. Manufacture of pulp from this project has continued uninterrupted for 25 years and, as an economic activity, generally represents about 20 percent of the nation's exports and about 12 percent of GNP. The enterprise is owned jointly by the Commonwealth Development Corporation and Courtaulds Ltd with holdings by the Swazi government.
FIGURE 1. Location map of Swaziland and the Usutu forest
Brief history The Usutu forestry enterprise was initiated by the Colonial (now Commonwealth) Development Corporation (CDC) in 1948 as a result of a report commissioned by Sir Evelyn Baring, who was then High Commissioner for the territories of Bechuanaland, Basutoland and Swaziland. He requested Dr Ian J. Craib, a South African silviculturist and then Managing Director of Peak Timbers (a new forestry company in the north of Swaziland), to survey 55000 ha of grassland in the Great Usutu valley for possible forestry use.
Following a favourable report, CDC funded land purchase and the first plantings took place in February 1950 during the latter part of the wet season. In the period up to 1958, 42000 ha were afforested, with the main plantings taking place between 1951 and 1957, creating the largest area of man-made forest in one contiguous block in Africa. The predominant species were Pinus patula and P. elliottii with a small proportion of P. taeda. The crops grew well under Swazi conditions, typically achieving a height of 20 m in 12 years and productivities of 15-25 m3/ha/yr.
Initially, it was intended that Kraft paper (for use in brown paper bags, cardboard boxes, etc.) would be manufactured for the South African market. However, development in South Africa satisfied Kraft paper demand, so it was decided in 1959 to form a joint company with Courtaulds Ltd to utilize the pine plantations to produce unbleached Kraft pulp for overseas export. A pulp mill was constructed with a designed annual production capacity of 90000 t to match estimated yield from the forest. The mill began commercial production in 1962 using 11-13-year-old trees. At the time, it was probably the only instance in the world where the private investor had ventured into the field of tree plantations with the object of converting all trees to pulp and/or paper (Hastie and MacKenzie, 1967).
It soon became clear that mill consumption of wood, at a rate of about 5.5 t of freshly felled timber for every tonne of dried pulp produced, was underutilizing forest growth potential. This, along with the general desire to maximize output and achieve further economies of scale, led to steady expansion in capacity, achieving, at the present time, an annual production of about 180000 t, i.e. almost double that originally designed. In the mid-1970s and again in the early 1980s there was some expansion of the forest by further tree planting and small acquisitions of plantations, creating today a total forest area of 52000 ha. In 1986, sustainable forest productivity, more than 900000 t of freshly felled timber per year, matches closely the pulpmill's annual consumption requirement at the present level of production.
It is worth noting that in the case of Swaziland afforestation of bare land was the only means to obtain an industrial wood resource. Natural forest cover is below 5 percent and little of this is found in the high veld where it is entirely confined to steep, wholly inaccessible gullies. One result is that the wildlife value of the high veld grasslands is low, and virtually anything that moves, owing to the lack of natural cover, is at risk from hunting.
Acquisition of land An important feature of the project is that afforestation took place on high veld land which was purchased directly from European settlers and, more recently, absentee South African farmers - both groups having been using the land mainly for sheep grazing. Virtually no Swazi villagers were displaced. Areas of land have also been leased from the Swazi nation which, in return, holds shares in the Usutu Pulp Co. Land quality varies, but the rough terrain and frequently boulder-strewn ground make much of the area unsuitable for arable farming while the quality of grazing on the sour veld grasses is not high. The soils are, for the most part, deeply rootable, but are also infertile and impoverished, with low levels of exchangeable bases. Acquisition of some 48000 ha of land, of which 42000 ha were afforested (the remainder being unplantable ground, fire-breaks, roads and land for villages) had cost, up to the time the Usutu Pulp Company was incorporated in 1959, 920000 South African rends. This was equivalent to about UK£10/ha.
Silvicultural work Creating the forest raising seedlings, planting, maintenance and protection and ancillary work amounted to an investment, up to 1959, of just over £2 million. One or two tree nurseries were established in each of the five main blocks and, in the early to mid-1950s, together sustained an annual planting programme requiring 4-7 million seedlings each year. The annual plantings of pine from 1950/51 to 1958/59 were, in hectares, 2022, 4253, 6242, 6296, 5960, 5126, 4144, 3307 and 1733, respectively.
Structures and improvements Before construction of the pulpmill and development of Bhunya village, two main forestry-related developments had to be paid for:
· accommodation: land being afforested was remote from Swaziland's capital of Mbabane (the nearest sizeable town) and it was necessary to establish a company village, located at Mhlambanyati, for supervisory staff, mainly expatriate; and forest villages for the industrial labour force close to the planting sites in each section. These villages, with a number of smaller communities for forest employees, include shops, medical and social facilities, and schools, although some of the latter have now been taken over by the government.· access: very few roads existed in the area, and only two suitable for motor traffic. Upgrading and development of a substantial road network has been, and continues to be a major investment. To date there are some 4000 km of roads, 1500 km of which are gravelled all-weather roads, and 64 km tarred at company expense.
Up to 1959, these infrastructure investments amounted to about £700000.
Forest expansion and current operational costs. As mentioned, a further 10000 ha has been added to the plantations under a variety of financial and leasing arrangements; these are not quantified here. The total area of land held by the company is about 67000 ha of which 55000 ha are productive forest.
Present running costs of the forest - i.e. those required to maintain a continually productive resource, including harvesting, reestablishment and other silvicultural operations and the all-important protection of the estate - are not published by the company. However, the delivered cost of pulpwood to the mill is among the lowest in the world.
Climate A large area of man-made forest has been created on land much of which has never, or certainly not in historic times, supported woodland. It forms part of an even larger area of "new" forest, amounting to perhaps one-third of a million ha, in a 100 x 300 km zone running along the Drakensburg escarpment of southeast Africa, where adequate rainfall allows productive forest.
Whether such establishment of forest has influenced regional climatic patterns, such as increasing rainfall or mistiness, is extremely difficult to prove. That forests bring such benefit, and deforestation the converse, is a popular hope largely lacking experimental evidence - such a macro-benefit can neither be claimed nor denied for Usutu.
Soil fertility The Usutu forest is productive, with the pine plantations achieving high rates of growth. Silvicultural practice is intense, with short rotations, no thinning or increasing applications of fertilizer and immediate replanting after crop harvesting. Despite the traditional view of forests' soil-improving value, such management, labelled tree-farming by some, could harm the soils in three main ways:
· drain of nutrients through removal of large quantities of biomass (about 350 t of wood and bark every 16-18 years);· alteration of soil characteristics, such as lowering of pH owing to uniform litter and humus - the layer of dead and decaying twigs, branches and needles covering the surface;
· directly damaging effects of extracting logs causing localized compaction and erosion.
There is some evidence of each of these three effects on some sites. Recent research (Morris, 1983) suggests that phosphate reserves have been critically depleted on about 15 percent of the forest, where the soils are derived from gabbro rock formations. But it is also on such soils that good responses to phosphate fertilizing have been observed, thus rendering amelioration possible.
A comparison based on nine plots compared nine years apart indicated a small drop in topsoil pH (3.96 to 3.87), but no detectable changes in the subsoil. Average litter depth (needles and twigs) doubled in this period from 5 to 11 cm.
In a few compartments, where logs had been extracted with heavy tractors in wet conditions, compaction and subsequently reduced growth of the replanted crops has been observed. Greater control over harvesting and a decrease in mechanization in recent years, with more use of mule teams, have largely overcome this problem. Indeed, expansion in the number of mule teams has been a feature of the last ten years, allowing easier harvesting of trees on steep slopes, less dependence on large machinery and, of course, more employment, quite apart from the benefit of less damage to the soil.
In assessing the effect of the plantations and silvicultural practices on soil fertility, me ultimate criterion is to examine yields of successive crops to discover whether one crop and its associated management are making conditions more or less favourable for its successor. The company has maintained a careful study of this which is reported later.
More generally, the forest cover has reduced risks of erosion within its boundary and brought into productive use land which, in the past, yielded very little.
Water yield Almost the whole of the Usutu forest is within the catchment of the Great Usutu river. And although only representing a tiny fraction of the total area, it does, within Swaziland, occupy a substantial proportion as the river passes through the high veldt If water use by productive plantation is greater than the former grass veld, the reduced water yield from me afforested parts of the catchment could be seen as an undesirable impact, or a price to pay for such productive forest, since some of the middle and low veld crops cultivated depend on irrigation.
No data exist for the Usutu forest's possible effects, although weir GS9, about 8 km south of the mill site, monitors flow rate. Seasonal How closely matches rainfall (see Fig. 2), but total effects are difficult to disentangle from annual rainfall patterns, which have been below average in recent years as in most of Africa, and the fact that winter How rates have been affected by the construction of storage dams, afforestation and urban water needs across the border in South Africa.
Nevertheless, this possibility of reduced water yield from afforested catchments led the South African government in 1968 to set up an interdepartmental committee to investigate the hydrological consequences. The investigation concentrated mainly on the effects to water supply of plantations of pines and eucalypts established on grassland. Among the conclusions and recommendations (Malherbe, 1968) were the following: "...dense phreatic vegetation, i.e. plants with roots constantly in contact with the ground water, promotes high vapour losses to the atmosphere through transpiration, irrespective of whether this vegetation is indigenous, or exotic, broad-leaved or coniferous, and mat the replacement of such vegetation by less dense, shallow-rooted ground cover will promote base-flow and increase the water yield from streams in the dry season."
Wildlife Stress has been laid on the substantial transformation of the high veld land that has taken place, from poor quality open grassland to dense pine forest, albeit dissected by fire-breaks, roads and ridges providing much edge habitat. Two main effects for wildlife result:
· a large area of "new" habitat, structurally much more diverse than grass veld;· exclusion of man over much of the forest for much of the time. In a word, the large area of forest is now excellent wildlife cover.
Systematic monitoring of wildlife has not been conducted, but the author has been able to observe over 19 years since 1968 that the numbers and varieties of animals have increased as the forest has become older and today greatly exceed those of the pre-existing grassland. Though the forest is monoculture, all of the following are now seen - seven species of antelope and buck, monkeys, baboons, porcupines, antbears, bushbabies, warthogs, guinea fowl, lynx, spring hares, rock rabbit, two species of mongoose, honey badger, cape fox, civet and cerval. These animals are uncommon or absent in the adjacent high veld, which remains typical of the land prior to afforestation. This does not seem to be because the plantation habitat itself provides much extra food or breeding sites, but because the large plantations provide shelter and refuge from man. In the Usutu forest, hunting is forbidden, man finds the monoculture relatively unattractive for recreation, and the distance of sight, hearing, and smell are all reduced; thus animals are safer and more protected. And, as populations of a species increase, its predators also increase, me food chain is strengthened and wildlife is enriched. In densely populated parts of the tropics, the relative exclusion of man from plantation forests can make them an important refuge for many birds and animals. There is much high veld in southern Africa; localized afforestation, even with monoculture of exotic species, appears to have encouraged wildlife though, of course, without a detailed pre-planting survey being available it is impossible to claim that it is wholly a net gain.
This increase in certain large wildlife species with afforestation has been recorded elsewhere, including the return of the leopard to the Nyika and Viphya plateaux in Malawi, and the jaguar in Venezuela. In both cases, this is a direct result of pine planting in grassland or poor savannah.
LOGGING WITH MULES animals minimize damage to soils
Plantation monoculture The Usutu forest in Swaziland continues to be one of the most intensive forms of plantation forestry in the world - short rotations, no thinning, high productivity and large areas of pine monoculture. The most accurate comparison of growth between rotations has failed to show any evidence of widespread or substantial decline in productivity with the one exception noted below. This result, when viewed in the light of the recent run of dry years, augurs well for the continuing success of plantation forestry in the tropics and subtropics.
Research into the maintenance of long-term productivity during successive rotations of pine in the Usutu Forest, Swaziland - the so-called "second rotation decline problem" - began in 1968. This was at a time when about one-third of the then 42000 ha forest was under second rotation. This research, and subsequent reassessments in 1973, 1977 and 1986 showed that the second rotation of Pinus patula initially grew significantly better than the previous crop but mat by the end of the rotation was not very different in its overall productivity. These results, along with a discussion of the effects of changing patterns of rainfall, were reported in the Commonwealth Forestry Review (Evans, 1975; 1978).
Owing to the age-class distribution and lack of young growth of the first rotation all previous comparisons of performance between the rotations were based on carefully matched pairs of plots and stem analysis of selected trees. This circuitous approach, with its many assumptions, required a large number of matched plots to achieve reasonable precision. The approach was not ideal but almost the only alternative available at the time. Methodologies for obtaining comparative data for long-term productivity studies have been reviewed in detail by Evans (1984).
The research reported here represents a substantial improvement in precision. Owing to the short pulpwood rotation at Usutu (15-18 years) most original long-term productivity plots have been felled and regenerated. Many have now been re-established and, for the first time, crop productivity has been assessed on exactly the same site in each rotation, at the same age, and using the same mensurational procedures and conventions (not to mention the same researcher!). Thus Lewis' (1967) observation that the most desirable way of comparing two rotations is with measurements from exactly the same sites, is now possible.
Productivity comparisons carried out in 1986
Four comparisons of growth between rotations were possible:
· third rotation compared with second rotation Pinus patula at six years of age (25 plots);· productivity at six years of age where Pinus taeda has replaced P. patula for the third rotation (nine plots);
· second rotation compared with first rotation P. patula at 12 years of age first report of second rotation performance from plots relocated on the same sites as in the previous crop (24 plots);
· second rotation Pinus elliottii compared with the first (ten plots).
Experimental work Seventy long-term productivity plots were reestablished among the crop types indicated above (two plots were in other stands). Most plots were relocated exactly since their centres had been surveyed during the earlier research, but a few relocations were only approximate (within about 20 m) based on judged position from large-scale maps. Correct siting of many was confirmed by discovery of an old soil pit or short logs from previous stem analysis work.
The same plot size and assessment procedures were used as described by Evans (1975), i.e. careful selection and measurement of three representative trees based on the diameter distribution, except for P. elliottii plots in which only top height was measured. Statistical analysis was straightforward with productivity data compared between rotations using the paired plots "t" test.
Throughout the research since 1968 one part of the Usutu Forest, Block A, covering about one-fifth of the total area, exhibited consistently poorer second rotation performance than elsewhere. Indeed, in this block significant declines in yields of the order of 20 percent in volume were found compared with very little difference between rotations in the other four blocks. Since 1977, this "block effect" as it was termed has been subject to further research and appears to be a result of poorer soil nutrient status related to the underlying geology, rather than an artefact of the author's data. This is why the data in Tables 1, 3 and 4 are subdivided by geological formation.
Table 1. Productivity of third rotation Pinus patula at six years
|
Rotation |
Block A |
Block D |
|||||||
|
Usushwana complex (9) 1 |
Granites (6) 2 |
(10) |
|||||||
|
SPH (stems per ha) |
Mean height (m) |
Volume per ha (m3) |
SPH |
Mean height (m) |
Volume per ha (m3) |
SPH |
Mean height (m) |
Volume per ha (m3) |
|
|
First 3 |
|
8.02 |
|
6.31 |
|
6.65 |
|
|
|
|
Second |
1273 |
8.33 |
49.52 |
1216 |
6.56 |
27.77 |
1309 |
7.93 |
50.34 |
|
Third |
1023 |
7.59 |
34.66 |
1237 |
7.23 |
33.73 |
1287 |
8.31 |
52.37 |
|
% change |
|
- 8.9 |
- 30.0 |
|
+ 10.2 |
+ 21.5 |
|
+ 4.8 |
+ 4.0 |
|
"t" value |
|
- 1.90 |
-2.86 |
|
1.65 |
3.09 |
|
1.98 |
0.68 |
|
Significance |
|
(*) |
* |
|
n.s. |
* |
|
(*) |
n.s. |
NOTES: 1 Indicates number of plots assessed. 2 Block A granite plots measured at 5 years of age only. 3 First rotation data from previous matched plot work. (*) significant at 90% level, significant at 95% level.
Table 2. Productivity at six years of age of Pinus taeda as the third rotation following second rotation Pinus patula (based on nine plots)
|
Rotation |
Species |
SPH (stems per ha) |
Mean height (m) |
Volume per ha (m3) |
|
First |
Pinus patula |
|
6.48 |
|
|
Second |
Pinus patula |
1287 |
7.55 |
43.70 |
|
Third |
Pinus taeda |
1200 |
7.61 |
44.64 |
|
% change |
|
|
+0.08 |
+2.15 |
|
"t" value |
|
|
0.15 |
0.18 |
|
Significance |
|
|
n.s. |
n.s. |
Table 3. Productivity of second rotation Pinus patula at 12 years of age
|
|
Usushwana complex (6 plots) |
Granites (18 plots) |
||||
|
SPH (stems per ha) |
Mean height (m) |
Volume per ha (m3) |
SPH (stems per ha) |
Mean height (m) |
Volume per ha (m3) |
|
|
First |
1300 |
17.69 |
261.27 |
1211 |
16.89 |
251.25 |
|
Second |
1291 |
16.70 |
240.15 |
1389 |
16.75 |
241.26 |
|
% change |
|
- 5.6 |
- 8.1 |
|
- 0.08 |
- 4.0 |
|
"t" value |
|
-1.44 |
-1.22 |
|
-0.32 |
-0.75 |
|
Significance |
|
n.s. |
n.s. |
|
n.s. |
n.s. |
Table 4. "Available" phosphate (ppm) in granite and Usushwana complex soils
|
Soil depth (cm) |
Site assessment (46) |
Granite soils |
Usushwana complex soils |
|||
|
Grass veld (1) |
Pine (1) |
Site assessment (9) |
Grass veld (1) |
Pine (1) |
||
|
5-15 |
2.61 |
6.80 |
8.60 |
1.20 |
2.55 |
2.90 |
|
40-50 |
0.72 |
3.95 |
4.80 |
0.32 |
2.00 |
2.00 |
|
About 90 |
0.61 |
2.80 |
2.90 |
0.31 |
0.70 |
1.80 |
NOTES: Figures in parentheses indicate number of plots used for means. Site assessment estimate of phosphate from pooled data from author's 1968/9 survey wing Bray's No. 1 extractant (ascorbic acid as producing agent). Grass veld and pine dab from comparison by A. Morris wing Bray's No. 2 extractant (Usutu Forest Research Report No. 53, 1983 [Unpublished]).
Third rotation of Pinus patula The 25 plots were re-established in (planting year) third rotation stands on former second rotation plot sites in five compartments. Four of these were in forest Block A where second rotation decline had been evident The comparison of growth between second and third rotations is shown in Table 1 with data subdivided as mentioned earlier.
With the exception of plots on the Usushwana complex soils, third rotation growth is at least as good as the previous crop and suggestive of being significantly better. On Usushwana complex soils a substantial and statistically significant decline in growth has occurred.
Third rotation of Pinus taeda In two compartments, in different blocks of the forest where some of the oldest second rotation P. patula was growing, the decision was taken to replant with P. taeda for the third rotation. As well as increasing species diversity and being suited to higher elevation sites above about 1400 m, it was hoped that the species' less persistent branching would preclude the need to low prune, an expensive but necessary practice for access and fire protection purposes in P. patula stands. Although this species change has reduced the number of plots with which to study the effects of successive rotations of one species (P. patula) it is interesting to report the benefit, or otherwise, of the decision on crop growth (see Table 2).
Pinus taeda, at least at six years of age, appears to be growing no better nor worse than the previous crop of P. patula. However, branching is unfortunately proving unacceptably dense and the trees are more heavily forked; the somewhat increased use of P. taeda may not be continued.
Second rotation Pinus patula Previous studies of the second rotation (Evans, 1975; 1978) reported the performance of the older age-classes, notably, all of which except the last were based on matched plots. During the present research, long-term productivity plots were re-established in stands, now 12 years old, on the former first rotation plot sites. Not only does this provide more accurate comparative growth data but 1974 was the first year after the practice of burning logging debris was abandoned. Leaving debris scattered was considered to be of some mulching value, but the main benefit of stopping burning was reduced mortality from Rhizina infection. Table 3 presents the results.
There is no significant difference in productivity between the two rotations although the slightly poorer average of the second rotation is interestingly very close to the result at the end of 13 or 14 years found in the older second rotation age classes (Evans, 1978). There is also some suggestion that on Usushwana complex soils the second rotation is doing rather less well, but the differences are not quite statistically significant.
Second rotation Pinus elliottii Second rotation productivity of species other than P. patula has not been reported previously because they constitute only a small proportion of the forest. However, P. elliottii is being increasingly planted, especially on new ground, and the opportunity was taken to gather what few data were available from successive rotations. These came from a limited site assessment survey of the first rotation in 1968, similar to that reported for P. patula (Evans, 1974), in which top height had been measured on 38 sites. Ten of these were relocated approximately, in 9-13-year-old second rotation stands, and top heights again measured using the same conventions.
Measurements were adjusted to a common age of 12 years and the two rotations compared. The average top heights were 15.57 m and 15.21 m for first and second rotations respectively. The 2.4 percent poorer height growth of the second rotation was not a statistically significant decline ("t" 0.67).
Silvicultural factors Many factors can change between rotations but one of importance introduced since 1979 is the use of superior seed of Pinus patula Prior to this, seed was bulk purchased from the eastern Transvaal, probably of mixed quality with some possibly coming from collections made from late thinnings in saw timber stands. The generally good performance of the third rotation of P. patula may be due to this seed improvement expressing itself, despite the unfavourable rainfall pattern of recent years.
Selection of P. patula specifically for pulpwood crops is at an early stage and further gains can be expected. Similarly, the careful evaluation of two closely related but locally little known taxa suited to many P. patula sites, P. oocarpa and P. patula, ssp. tecunumanii, which is just beginning, could prove valuable. Both show variation in growth rate and wood density with provenance (Wright, Gibson and Barnes, 1986).
With regard to rainfall, Pinus patula in Swaziland is near the lower limit of required rainfall for good growth and even one or two dry years can significantly depress the growth. In Figure 2 it can be seen that the last eight years have been very dry. With more normal annual rainfall during those years there is no doubt that performance would have been better than recorded at present.
Finally, it is worth noting the factor of weed competition. The first rotation was established in dense grass swards, the second rotation in a nearly weed-free site - a difference which probably explained the initial improvement in second rotation growth. No such contrast exists between the second and third rotations, both having similar establishment conditions. This absence of any relative advantage, apart from any benefit from spreading rather than burning logging debris further underlines the good performance so far of the bulk of the third rotation.
The above conclusions must not cause complacency: worldwide there are still very few data and, as this account shows, monitoring performance of successive rotations should be a priority. Significant yield decline has occurred at Usutu on some texturally good but deficient soils. Nevertheless, for the time being at least, the conclusion remains (Evans, 1978) that "second rotation decline" is the exception rather than the rule.
Pests and diseases One of the most serious dangers to a plantation is the possibility of destruction from a massive build-up of a pest or disease. It has been a subject of much dispute - whether monoculture itself is more susceptible to devastation from these causes - particularly when almost everywhere, successful agriculture is characterized by decreased diversity (Way, 1977), i.e. cultivating one crop extensively. Man-made forests in the tropics are often cited as being much more affected by disease and pest epidemics than those in temperate regions. However, it is becoming increasingly evident that the risks have often been overstated, especially in the light of the general success of plantation forestry wherever it has been tried. Nevertheless, Gibson and Jones (1977), in their comprehensive review of the subject, which makes particular reference to tropical tree plantations, conclude that the adoption of monoculture systems has led directly to an increase in the number and severity of pests and diseases of forest crops. They point out, though, that much of this has arisen from conditions in plantations rather than from the fact that only one tree species is present.
At Usutu, there have been localized outbreaks of defoliating insects, e.g. Nudaurelia cytherea and Euproctis spp., and both woolly aphis and the fungus Rhizina have arrived for the first time in Swaziland in pine plantations. So far, after nearly 40 years and three rotations of pine, no pest or disease threatens the enterprise as a whole, though prudent forestry practice will be to maintain observations, research and good forest hygiene to keep risks to a minimum.
Replicability Subtropical pine plantations are an important industrial forest resource in the southeast and central highlands of Africa.
By and large, these crops are growing successfully and one project, developed on the Viphya plateau of Malawi in the 1960s and 1970s, was partly modelled on Usutu's experience. Similar afforestation programmes with pine are found in Zimbabwe, the United Republic of Tanzania, Madagascar and Kenya. Growing pine plantations on tropical and subtropical grasslands is a wholly practicable, successful and sustainable form of industrial forestry development
MECHANICAL LOGGING COMPACTS SOILS effects show in depressed growth of second crop
TWO CROPS HAVE BEEN HARVESTED ALREADY a third one is growing
Correct choice of species There is no doubt that the original advice on species choice, drawing on experience in South Africa, laid the foundation for establishment of a successful forest. The species used were well-adapted to Swazi conditions. Refinements have been made since, but the choice of concentrating on Pinus patula and P. elliottii has not been called seriously into question.
Silviculture The single-minded objective, from the inception of the project, of growing solely pulpwood has avoided the dissipation of effort and funds in unnecessary silvicultural operations such as high pruning and thinning.
Research The long-term commitment, since the mid-1960s, to silvicultural research has provided one of the best long-term records of tree growth that exist anywhere. There is also an advance understanding of sustaining the soil fertility in and productivity of fast-growing plantations. By appraising appropriate machinery (e.g. for harvesting steep terrain) and developing techniques (e.g. nursery systems) the company has been able to contain wood production cost increases. This belief in the value of research and development is increasingly contributing to the sustainable nature of the operation.
Resource concentration Forestry is necessarily an extensive land use. Two advantages at Usutu leading to its success are containment of the entire plantation resource within 50 km of the mill and adoption of practices (e.g. carefully chosen spacing between-trees and clear felling at harvest time) which maximize yield per ha and hence minimize the costs per tonne of growing and extracting the wood.
Programmes of genetic improvement, fertilizer application on the small areas exhibiting phosphate deficiency, and keeping a careful check on pests and diseases will ensure the forest can continue to supply in excess of the required 1000000 t of wood per year. In the mill, the new wood-yard, along with other recent capital improvements, should keep Usutu's pulp price competitive. The devaluation of the lilangeni with the rend should also, on balance, have helped in this respect.
However, the costs of transport to buyers in the Far East and western Europe, together with Swaziland's landlocked position in an area of some political instability, must both be matters of concern. Furthermore, the declining market for UBK pulp could put Usutu in a vulnerable position between the desire to upgrade production, and the need to maintain environmental standards.
Nevertheless, nothing inherent in the project at present raises critical questions of continuing viability - environmentally, industrially or socially - to beyond the year 2000. It must be hoped that Usutu continues as one of Swaziland's major assets and genuine success stories.
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