Over the last two decades, international concern about the rate of tropical deforestation has increased considerably: policy-makers, the forestry sector and general public have become more aware of the major role tropical forests play and the important consequences they have in social, ecological, and economic domains. Out of these it is the economic domain that until now has attracted the greatest interest at a local as well as an international level. Tropical forests regulate the climate and contribute to the balance of natural elements such as air and water, both on a regional and world-wide scale. They encircle a natural habitat for many species of flora and fauna; they have a social value by providing a natural sphere for human life and employment; they are often of religious value to the indigenous population and, last but not least, they contribute to national incomes by not only providing a source of wood, but also non-wood products and services.
In spite of an awareness campaign aimed at the general public, the annual deforestation rate is still high. The tropical forest cover has shrunk from 1 910 million ha in 1980 to 1 756 million ha in 1990 which makes up for an annual loss of 0.8 percent [4]1. Although the most recent FAO statistics [5] indicate that the average annual deforestation rate of natural forest in developing countries apparently decreased from 15.5 million ha for the period 1980-90 to 13.7 million ha for the period 1990-95, the actual deforestation of forested area is still alarming.
In most tropical forest regions, the main economic sectors are forestry and agriculture. These two sectors do not contribute equally to the annual deforestation. According to all scientists [1, 3, 10], the direct impact of forestry activities accounts for less than 20 percent, whereas the agricultural sector (especially small-scale farming and shifting cultivation, including the collection of fuelwood) is designated as the main cause of deforestation. The table below shows that fuelwood counts for 80 percent of the total wood production of developing countries.
Developed Countries (million m3) |
Developing Countries (million m3) |
World (million m3) | ||||
Industrial wood |
1 051 |
84% |
417 |
20% |
1 468 |
44% |
Fuelwood |
190 |
16% |
1 700 |
80% |
1 890 |
56% |
Total |
1 241 |
100% |
2 117 |
100% |
3 358 |
100% |
World wood production 1994 (Source: FAO 1997, [5])
Needless to say, it is difficult to make a clear distinction between the effects of both sectors. In many forest regions, the forestry industry is the first economic activity to be undertaken in previously untouched forests. When these unspoiled forests begin to be the object of any kind of economic activity, about 70 percent of them are initially touched by the forestry sector. Moreover, it has been observed that forestry activities have subsequently led to the conversion of forests to agricultural use because areas of previously dense forest have been opened up to small-scale farmers. With easier access they are able to market their products more easily and thus increase their agricultural incomes. According to FAO [16] "the deforestation rate due to conversion to agricultural land is eight times higher in forests which have undergone forest activities than in untouched forests."
It therefore appears that forest roads have economic advantages, but endanger the environment. On the one hand, it is evident that they are necessary for forest access and the transport of wood and non-wood products towards national and international markets. From this point of view they contribute to national incomes and to the development of tropical countries in general. On the other hand, they appear to facilitate agriculture and hunting by opening up the forests hence leading indirectly to deforestation and the destruction of wildlife. The forest road networks are both good and evil at the same time! What should we do about it?
Since this question is one of the fundamental problems in the debate surrounding the sustainable management of tropical rain forests and consequently the survival of these forests, ATIBT has initiated this present project in order to assemble all the opinions, ideas and proposals from representatives of all concerned parties: political decision-makers, scientists, professionals, ecologists. Their opinions are exposed in this special issue. The aim of this publication is to provide information on:
· the role of forest roads and the importance they play in the economic development of tropical forest countries;
· the danger which they can present for the environmental management of forest ecosystems.
Our common aim is to achieve a sustainable development without jeopardizing the right of future generations to benefit from the multitude of forest functions.
This summary presents the conclusions which have been developed in the contributions received. It deals with the following aspects:
· the principal direct causes of deforestation,
· the contribution of forestry activities to a social and economical development,
· the negative ecological effects - real or potential - of forest infrastructures.
The conclusion will outline the search for a feasible balance between development and environment according to their advantages and disadvantages, with an emphasis on specific, clear and economically practicable measures.
As already mentioned in the introduction, the forest sector is responsible for only a small proportion of annual deforestation. The main reason being that as a general rule industrial wood harvesting is very selective: only a small number of trees are extracted [1,6,8]. For instance, for one hectare of natural forest containing approximately 280 m3 of usable wood, no more than 8 m3 to 33 m3 is extracted [4,14]. Indeed, Grut [7] describes, that the interventions of selective logging are hardly more destructive than nature itself.
Photo 1: Road network in mountainous area in the Asian forest | ||
These observations have been confirmed by several other contributors: Mengin-Lecreulx [m] explains that the foresters, with low intensity harvesting, actually leave behind them a forest which is fully able to regenerate itself if given sufficient time; Mabala [l] describes that the gaps in the forest cover, caused by modern harvesting, even allow several commercially valuable species (such as Okoumé) to regenerate faster than under closed cover. As Gnomba [h] states, even with high intensity harvesting (70 m3/ha), the forest growth dynamics are not hindered for longer than 5 years: growth is induced without upsetting too much botanical variety.
In contrast, the contributors describe the damage caused by agricultural activities. Agriculture often needs to clear forest cover and as a consequence the environmental impact is usually greater than the direct effects of forestry. Two types of agricultural activities can be singled out: small-scale farming and larger, intensive activities. The latter are often permanent plantation settlements (palm oil trees, rubber trees, and bananas). These so-called industrial plantations have often been the economic basis of tropical countries, in many cases allowing the financial backing for a political strategy on better forest management and even the conservation of surrounding forests. Not all of these plantations have prospered as expected; some having been established on unsuitable soil [c].
Nevertheless, agricultural work is done for the greater part by small-scale farmers. A study carried out in Ghana comes to the conclusion: "the wood industry, as a factor in the destruction of valuable forest, is in no sense as dangerous as the traditional system of shifting cultivation" [q].
In general, shifting cultivation can be sustainable if the cultivation period is short enough (to prevent soil impoverishment) and the fallow period is long enough (to allow soil recovery). Unfortunately, many developments (mainly increasing population pressure) can render this traditional farming technique unsustainable. Such consequences are described by several contributors [c, p, q].
Photo 2: On the contrary, the transformation to plantation (here oil palms) makes total deforestation necessary | ||
Where planned deforestation is concerned, many governments have drawn up land use plans that allocate the forest region to different uses such as permanent forests (including conservation areas and sustainable wood production areas) and forests areas designated for conversion to agricultural use. Effectively, most of the countries described in the contributed articles (the Congo, Ecuador, Gabon, Ghana, French Guiana, Liberia, Malaysia) have established land use plans.
However, deforestation can also be stimulated by governments without any explicit policy in the form of land use plans. This has been the main subject of a publication by Repetto and Gillis [13], and is confirmed by several contributors [c, m, q]. For example, governments induce deforestation by:
· making land rights dependent on previous forest clearing,
· constructing roads to facilitate access to land resources and in consequence to facilitate the marketing of food and cash crops, and
· stimulating cash crop production (such as coffee and cocoa) by guaranteeing minimum prices (stabilization funds).
Often referred to as one of the leading economic activities in tropical countries, the forestry sector has made a valuable contribution. The forest industry and the economic activities which stem from it have made a significant impact on the gross national product, as well as on exports and on employment figures in developing countries. According to FAO [5], the contribution of the forest industry to GNP is 6 percent in Africa, 3 percent in Latin America and 2 percent in Asia. Of course, the forest industry has some way to go before overtaking the oil industry [d] but it is a renewable resource compared to fossil fuels. Forest incomes in foreign currency also play an important role in the balance of foreign trade. Moreover, taxes generated by the forest industry should permit the State to ensure a real management of forest or agricultural resources.
Photo 3: Industrial plant | ||
The forest sector is often the leading economic activity in large forest regions. The majority of ATIBT members have been settled in countries for a number of years and take great care to exploit the forest through sustainable management. They thus secure not only their own long-term survival but also contribute to regional development [e]. In terms of direct employment [d], several hundred jobs are often created per company. This figure can be doubled when looking at indirect employment provided by the services sector, for example, equipment maintenance, transport and transit industries, and local food markets. Each worker directly "maintains" a dozen people on average. Specific in-company training for workers in forestry, industrial or mechanical professions, the setting up of schools and dispensaries [p] as well as the infrastructure created by companies encourage a general social development [a]. At the same time, this leads to a settling process of the local population and reduces the rural exodus. If these forest industries did not exist, many people would find themselves with no resources, forced to look for work in the large towns and cities. The commitment of companies towards socio-economic development is welcomed by governments, local politicians and the population [e, p].
Agriculture in tropical forest regions is also an important factor in economic development [1, 2, 11]. Mengin-Lecreulx underlines this when he affirms that Côte d'Ivoire has become the major world producer of cocoa thanks to forest conversion [m].
It could also be said that the forest road networks improve the socio-economic situation of the population: regional incomes increase because the roads permit the transport of agricultural surplus towards national, even international, markets. They facilitate the marketing of non-wood products and improve mobility (which means that the population can take advantage of employment opportunities outside the forest sector). Moreover, the roads provide better access to education, medical services, etc. [a, d, e, j, i, n, o, p]. An example has been witnessed in the Amazon where oil companies who have set up road infrastructures for the exploration and transport of oil have launched an economic development in isolated and inaccessible regions [d].
Photo 4: Connection of a forested area by construction of a permanent bridge (foundation and cemented with metal span) | ||
However, it has to be mentioned that certain disadvantages can result from an increased contribution to the national and international economy, in particular, the loss of religious and cultural values. But this is a more general problem of development which is beyond the forestry sphere, even the tropical one.
Although forestry activities are not the main direct cause of deforestation as it has just been seen, they still affect the forest ecosystem both directly and indirectly.
Although the direct consequences of forest activities are limited (see chapter 1), wood extraction does cause damage to the forest ecosystem. However, when the forest is granted sufficient time to recover, most changes are temporary rather than permanent. Notwithstanding the extraction itself, felling knocks down adjacent trees; skidding tracks and selection areas create forest gaps. When tree crowns are left abandoned, the natural regeneration is smothered and there is a high risk of forest fires. The forest gaps, harvesting, and noises from engines and felling also disturb the wildlife, which make studies necessary to try and minimize the damage.
Photo 5: Temporary log stocking bay - loading of trucks by frontloader | ||
Road construction represents the most harmful aspect of forestry activities. The forest has to be cleared for them and they are thus a direct cause of deforestation. Yet there are also other undesirable ecological consequences:
· excessive stream sedimentation,
· water flow obstruction,
· soil erosion with loss of forest production alongside roads,
· danger of land slides (especially in steep areas),
· disturbance of breeding areas or migration routes of animal species, and
· compression of soil structures [f, g, m, k, o].
Likewise, open spaces are overrun by a certain type of grass (Cromolaena odorata) which hinders forest regeneration and exposes them to forest fires [m].
During the post-war period the big companies practised traditional forestry methods which helped to safeguard the environment but unfortunately they are now applied less and less. The severe decline of these methods has resulted from a dispersion of competent foresters, economic difficulties, the reduced size of forest structures and the greed of certain so-called "foresters". The too-short natural regeneration cycles have also considerably intensified the direct impact of forestry activities.
The ATIBT is well aware of these disruptions and therefore joined up with other investigations into reducing forest damage. It has acquired a new role in those areas which require the direct responsibility as well as the competence and know-how of foresters. It is also believed that financial means should be provided to carry out concrete and effective studies whose results can be put to use by the forestry profession. The ATIBT is ready to assume this new pedagogical role if it can obtain the necessary financial means.
Photo 6: Forest road being levelled | ||
In practice, forestry activities are often observed to be the first step in the process of deforestation: the forestry industry induces changes in land use mainly due to the fact that the perspective of new agricultural land in tropical forests is an attraction to peasant households for two reasons. Firstly, the presence of a road network facilitates access to the forests as well as the marketing of agricultural surplus, thus increasing agricultural incomes [1, 2, 8, 11, 15]. Secondly, encroachment on already selectively harvested forests is attractive since the clearing costs are much lower due to the removal of the larger trees and abandoned tree crowns which facilitate burning [11]. This is especially true in regions where shorter distances to markets permit the exploitation of a number of important species. This corresponds in particular to areas with a significant population pressure.
Indeed, this view on the indirect impact of forestry activities is shared by many of the contributors. Kaimowitz [i] states that econometric models based on empirical data from Belize, Brazil, Cameroon, Costa Rica, Honduras, Mexico, Philippines, Thailand, and the Democratic Republic of the Congo all show that areas near roads are more likely to be deforested. This observation continues to hold even after controlling for variables such as soil quality and distance to markets; this statement is supported by Lorbach [k].
However, there is easier access to game and easier transport of bushmeat [e, f, k, l, m, o, p]. Given the fact that large mammals are attracted to the open areas on roadsides, game is more likely to be seen and is thus more vulnerable [e, f]. Traditional hunting has been replaced by almost "industrial" hunting where bows and arrows have been substituted by semi-automatic rifles. Of course, roads also induce illegal tree felling [k, l, m] whether it is for village consumption or an illegal market.
Not all roads are likely to induce substantial immigration on an equal basis. Roads that link towns through forests attract more peasant households because of marketing facilities; "dead end" forestry roads are somewhat less attractive [q]. The population density of the region is also important: if the density is low in the areas surrounding the forests, the likelihood of substantial immigration is limited [h].
There seems to be a consensus that these indirect consequences of logging are more damaging to the environment than the forestry activities themselves [m, o].
Other industrial activities such as hydroelectric dams and the oil sector also require road infrastructures. In general these activities have a permanent and often more destructive impact on the forests [d] but for some reason this is overlooked by the media. Sustainable forest management only seems to involve wood!
As already mentioned, infrastructures are essential for economic development but environmentally dangerous. However, it is possible to attenuate the ecological risks: economy and ecology are not necessarily incompatible. It is preferable to find a balance and this can be done through simple proposals which must involve all stakeholders.
There is now sufficient knowledge on how to considerably reduce the direct environmental damage resulting from road construction [c, k, o]. One of the main measures consists in carefully planning the itinerary of forest routes:
· avoid steep slopes (i.e. more than 20 percent) in order to prevent excessive soil erosion,
· avoid passing too close to ecological sites or even going through them,
· a density of permanent roads should not exceed 40 m/ha, etc. [j, m, o],
· likewise, in order not to obstruct water flows, roads should be built as perpendicular as possible to streams with adequate drainpipes [g, m, q].
Moreover, the way in which roads are constructed could also help to restrict their environmental impact.
The width of the area to be cleared for construction can also be reduced. Large areas are usually cleared away on both sides of the road surface in order to ensure sufficient sunlight for drying and to allow rain water to drain away. The width can be reduced in several ways, for example, the roads are usually built just before the start of operations: this should be done at least six months earlier in order to ensure adequate exposure to weather conditions and to allow soil stabilisation [o]. East-west roads can be built with smaller shoulders since they have plenty of sunlight exposure, the width can be reduced by using soil compactors to seal the soil surface [m, o, p]. In this way the width on both sides can often be reduced from 20 m, which is generally the case, to 8-10 m [o]. An arched profile of the road, adding if possible a covering of laterite, can also facilitate water drainage and reduce the need for prolonged sunlight exposure. It is also preferable to dig lateral water drains every 50 m using a bulldozer shovel, which will prevent torrents from forming during the rains and making gullies in the road. The damage caused by tree felling during construction can also be limited by felling all trees measuring more than 15 cm in diameter into the road axis rather than towards the forest [q]. According to Blate and Zweed [b], the requirements that the forest roads have to meet (and as a consequence the amount of damage inflicted) depend on the purpose for which the roads are built: for instance, whether they are built for access only, for dry conditions or all season use, for light or heavy traffic, for intermittent or continuous use, etc. The foresters are well aware of the difference between "main roads" and "tracks" and the care needed in building them with regard to the different types of traffic.
Photo 7: Construction of a principal road with dry embankments | ||
Finally, a particular mention should be given to experiments carried out in French Guiana with the aim of reducing wildlife disturbance: Gaucher and Mengin-Lecreulx [g, m] describe how wildlife migration routes can be preserved by building special forest "corridors" to allow animals to cross roads more easily, and how "tree bridges" have been left in the forest cover for primates.
For various reasons only a small number of tropical forest roads have been built according to appropriate specifications, or with mitigation measures.
Firstly, companies have usually built them to fulfil short-term transport requirements without considering the possible long-term risks of damage caused by their construction. This is generally the case of foresters for whom the objective of road construction depends on the duration of the logging permit. This short-term objective, or merely a way of cutting costs, means that they are inclined to overlook investments necessary to avoid environmental damage. The general lack of planning and zoning by governments has allowed roads to be built without considering how they will be used, or whether it would feasible to enforce that use [b, c].
Decision-makers in various fields, whether they are civil servants or private operators, should be encouraged to limit the impact of road construction. The experience in Ghana shows that the above-mentioned measures can indeed substantially reduce direct inflicted damage: thanks to government policies which manage the location and construction of roads, damage is 1.5 to 5 times less serious than observed elsewhere [q]. Of course, private companies cannot be expected to financially substitute the road construction task of the State. If companies are forced to construct roads themselves at high costs they should at least benefit from tax rebates.
Photo 8: Secondary road under construction | ||
Photo 9: Traditional construction of a bridge by using the crib system | ||
There is a consensus among the contributors that the indirect impact (burning, hunting) of road construction is much harder to control than its direct impact because this enters within the sphere of individual freedom and ancestral rights. It seems reasonable, however, that the occasional harvesting which is permitted under a right of personal provisions of fauna and flora should not be tolerated without a limit or control for commercial or industrial use. The main focus of these articles is on how to determine which measures can avoid unauthorized conversion of forests for agriculture and illegal hunting due to the opening up of the forests to the rural population.
One proposed approach to counteract this danger is perhaps rather harsh: several contributors have suggested denying forest access to all activities which are incompatible with sustainable wood production as, for example, encroachment by local villagers, or even national or international settlers looking for land, which often comes as a consequence of opening up the forest. Secondary harvesting roads which do not belong to the national infrastructure (i.e. through-roads) should be strictly controlled [l, m, n, o]. The clearly manifested interest of the local population in opening up communication roads is not necessarily aimed at illegal exploitation: connecting roads provide access to hospitals, education, exchange of goods and news with neighbouring villages and towns. Yet governments are not always capable of effectively controlling access to the forests: forestry administrations are often understaffed and under-equipped, especially with respect to transport [i, k], and can therefore be easily tempted by bribery. As a consequence, some contributors suggest simply blocking off the roads once logging has ended [l, m, o]. Demolishing bridges is easy and effective but the decision to demolish these roads can only be made by the legal authorities. The same rule applies to commercial hunting - only the State can prohibit it and not the forester.
Photo 10: Floating bridge on Ayous logs (300 m3) | ||
There are also indirect ways to prevent the population from encroaching on the forest. For example, by rearing and providing meat at reasonable prices to workers. Many large wood companies even forbid their personnel to transport game meat to urban centres on their logging trucks or those of their contractors [o].
It would be even more efficient to increase the population's interest in safeguarding the forest in order to (i) slow down deforestation, and (ii) prevent encroachment by newcomers [a, d, i, q]. This approach has been adopted by many development projects financed by international donors. Enhancing the forest's value whether in socio-economic, ecological or religious terms, is an important requisite to induce the local population to protect their forest and territory.
Local populations can also be responsibly involved in management contracts through the intermediary of village chiefs or organized groups such as co-operatives. The contract partners would be the government and the local population, controlled by the national administration. This often requires a certain adaptation of legislation and institutions as well as a comprehensible distribution of revenues between the government, population and forest management funds.
Furthermore, agricultural encroachment can be limited by offering alternative employment opportunities [n], such as in local industry or the craft industry. Moreover, the conversion of economically valuable forests may be restricted by stimulating the switch from crop cultivation to the harvesting of non-wood forest products. However, Mabala [l] draws attention to the fact that the harvesting of non-wood forest products is not necessarily sustainable especially if the harvest is intensified by trade.
All alternative employment opportunities should at any rate be an integral part of regional or master development plans (see chapter 5).
Photo 11: Embankment: the road network supplies motorbarges | ||
The local forestry sector can also be persuaded to try to limit agricultural encroachment upon their concession areas. In many countries national foresters have no incentive to prevent conversion because the concession periods are too short to ensure a second logging cycle. Kaimowitz [i] suggests establishing incentive systems that companies will forfeit if farmers encroach upon their forest concession lands. This latter suggestion does however seem risky since the role and control of the government is transferred to the forester.
Given the developing countries' need for development, the contributors to this issue generally assess that forest roads are in some ways a "necessary evil": forestry activities should not be stopped, but everything should be done to minimize the direct, and especially the indirect, environmental risks. Of course, it is the foresters who are being called upon in the first place to take the necessary care in the construction of road infrastructures. But this is by no means enough. A general environment has to be created which is favourable and protective for regional development and especially for forest management. Governments should therefore attentively design their land use plans, by working closely with the representatives of the different stakeholders involved. They should base these land use plans on correctly conducted environmental impact studies (EIE), economic evaluations and socio-economic studies. Foresters and farmers must be presented with an appropriate set of incentives (legal and economic) to encourage them to respect the land use plans. This means that the various stakeholders should reach an agreement before drawing up and implementing the final plans.
Photo 12: Well-constructed forest road integrated into the environment | ||
The government could induce the local population to be more environmentally aware through positive and concrete measures. Based on positive results of a regular assessment hospitals, schools and other institutions could be built for the benefit of the local communities. In any case, a participative strategy of nature protection is only feasible if the local population has a clear understanding of the benefits. Lorbach's conclusion [k] is probably the most eloquent: ". . .it depends on the users whether the roads are leading to development or destruction. It is like a medicine the doctor is prescribing to his patient, if properly taken, the patient will recover soon, if taken in too large a dose it is toxic and harmful to him and he might die."
New budgets inflated by CO2 funds and pollution taxes provide great optimism in developing awareness and concern for a better safeguard of the forest heritage.
This collection of contributions is an initiative of the ATIBT Secretariat, which has also elaborated the present summary:
· Jean-Jacques Landrot, Secretary General
· Daan van Soest, Technical Assistant
· Jörg Maxin, Technical Assistant
[1] Amelung, T. and M. Diehl (1992), Deforestation of Tropical Rain Forests: Economic Causes and Impact on Development, J.C.B. Mohr, Tübingen
[2] Barbier, E.B., J.C. Burgess, J.T. Bishop and B. Aylward (1994), The Econ-omics of the Tropical Timber Trade, Earthscan Publications, London
[3] Bruenig, E.F. (1989), Die Erhaltung, nachhaltige Vielfach-nutzung und langfrist-ige Entwic-klung der tropischen im-mergrünen Feucht-wälder, Bundes-fors-chungsanstalt für Forst- und Holzwirt-schaft, Ham-burg
[4] FAO (1993), "Forest Resources Assessment 1990: Tropical Countries", FAO Forestry Paper no. 112, Food and Agricul-ture Organization of the United Nations, Rome
[5] FAO (1997), State of the World's Forests, Food and Agriculture Organization of the United Nations, Rome
[6] Grainger, A. (1993), Controlling Tropical Deforestation, Earthscan Publica-tions, London
[7] Grut, M. (1990), "Revenue and Concession Policy for the Timber Forests of West Africa", Paper presented at the Seminar of the International Timber Trade Organization in Denpasar, Bali, Indonesia on May 19
[8] Lamprecht, H. (1992), "Umfang, geographische Verteilung und Ursachen der Zerstörung der Tro-penwälder", Schweizerische Zeitschrift für das Forstwesen, 143(3), pp. 207-218
[9] Lanly, J.P. (1982), "Tropical Forest Resources", FAO Forestry Paper no. 30, Food and Agriculture Organization/United Nations Environment Programme, Rome
[10] Myers, N. (1991), "Tropical Forests: Present Status and Future Outlook", Climatic Change, 19(3),- pp. 3-32
[11] Panayotou, Th. and P.S. Ashton (1992), Not by Timber Alone: Economics and Ecology for Sustain-ing Tropical Forests, Island Press, Washington D.C.
[12] Panayotou, Th. and S. Sungsuwan (1994), "An Econometric Analysis of the Causes of Tropical Deforestation: The Case of Northeast Thailand", Chapter 13 in K. Brown and D.W. Pearce (eds.), The Causes of Tropical Deforestation: The Economic and Statistical Analysis of Factors giving Rise to the Loss of the Tropical Forests, UCL Press, London
[13] Repetto, R. and M. Gillis (eds., 1988), Public Policies and the Misuse of Forest Resources, World Resources Institute/Cambridge University Press, Cambridge
[14] Rietbergen, S. (1989), "Africa", Chapter 3 in D. Poore, P.F. Burgess, J. Palmer, S. Rietbergen and T. Synnott (eds.), No Timber without Trees: Sustainability in the Tropical Forest, Earthscan Publications, London
[15] Southgate, D., R. Sierra and L. Brown (1991), "The Causes of Tropical Deforestation in Ecuador: A Statistical Analysis", World Develop-ment, 19(9), pp. 1145-1151
[16] Sun, C. (1995), Tropical Deforestation and the Economics of Timber Concession Design, Doctoral Dissertation Proposal, Depart-ment of Agricultural Economics, University of Illinois at Urbana-Champaign, Urbana
[17] Terborgh, J. (1992), Diversity and the Tropical- Rain Forest, Scientific Ameri-can Library, New York
1 Note of the authors: To facilitate reading, the sources of our scientific references have been numbered from [1] to [17] and the authors of the contributions have been referenced from [a] to [q].
