D.P. Dykstra and R. Heinrich
Dennis P. Dykstra is Professor of Forest Engineering at Northern Arizona University, Arizona, USA.
Rudolf Heinrich is Chief of the FAO Forest Harvesting and Transport Branch. This article is based on a monograph currently in preparation for publication as an FAO Forestry Paper.
If tropical forests are to be retained as forests, then for the most part their resources must be utilized. Otherwise, they risk being perceived by local people and government decision-makers as having less value than other land-use options. With proper incentives, knowledge of appropriate harvesting practices, technically competent supervision and adequate controls, the process of harvesting industrial wood from tropical forests can be accomplished as part of an overall forest management plan in a way that is environmentally sound, economically profitable and that simultaneously promotes the sustainability of both the timber and non-timber values of the forest.
Many tropical forestry experts agree that it will be impossible to sustain tropical forests over the long term without the establishment and enforcement of appropriate government policies. For instance, authorities such as the Brundtland Commission (WCED, 1987), FAO (1989b), Poore (1989) and FAO (1989c) suggest that policies must be developed to ensure comprehensive land-use planning; improve timber concession agreements; provide incentives for sustainable practices through taxation and other fiscal controls; encourage the increased use of agroforestry and forest plantations; ensure the participation of local peoples in the benefits of timber harvesting; and protect the permanent forest estate once it has been established. After such policies have been developed, governments must also have the political will to enforce them; only then will there be a chance for tropical forests to be sustained.
There is little question that economic, social and political considerations will play dominant roles in determining whether substantial areas of tropical forest exist a century from now. However, even if problems associated with these factors can be overcome, improper harvesting practices can so degrade the forest that future timber and non-timber values may be substantially reduced. Therefore, it seems essential that efforts to sustain tropical forests must proceed simultaneously along two fronts: the socio-political front which endeavours to develop economic, social and political conditions that will permit tropical forests to be sustained; and the technological front which seeks to ensure the use of harvesting practices that are environmentally sound and economically acceptable and that simultaneously promote the sustainability of both the timber and non-timber values of the forest.
This article focuses on the second of these two essential lines of action. Without denying the critical importance of efforts to improve socio-political conditions in tropical countries, the premise is that improvements in logging practices are needed with equal urgency if tropical forests are to be sustained.
Although almost everyone agrees that the sustainability of tropical forests is a necessary objective, there is much confusion over the precise meaning of "sustainability". We prefer to think of sustainability in the context of human use and the aspirations of people in developing countries to thrust off the yoke of poverty. In this context, FAO defines sustainable development as "the management and conservation of the natural resource base and the orientation of technological and institutional change so as to enable the attainment and continued satisfaction of human needs for present and future generations" (FAO, 1991). Similarly, the Brundtland Commission (WCED, 1987) says that "sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs".
To contribute to sustainable development, then, a critical aspect of the utilization of tropical forests is that the activities associated with this utilization must not irreversibly compromise the potential of the forest to regenerate and continue to provide the industrial wood and non-wood forest products, environmental services, social benefits and global values (such as the maintenance of biodiversity) that are essential for the well-being of both current and future generations. In fact, the goal should be to maximize the aggregate potential of the forest to provide these goods and services over the long term. This implies that where industrial wood is to be removed from tropical forests, harvesting operations must be carried out in such a way as to leave the forest in a condition that favours a rapid recovery to its pre-harvest state or to some other state that is silviculturally, ecologically and sociologically desirable.
Since the 1950s, a series of research papers have quantified the nature and extent of damage associated with logging operations in tropical forests. Perhaps the most influential of these have resulted from studies in Africa by Dawkins ( 1958) and Redhead (1960), and from a series of studies in Southeast Asia (Nicholson, 1958 and 1979; Wyatt-Smith and Foenander, 1962; Fox, 1968; Marn and Jonkers, 1982.
More recently, similar studies have been published for the Latin America and Caribbean region by Jonkers (1987), Hendrison (1989), Schmitt (1989) and Costa Filho (1991). From these studies, it seems clear that the extent of damage commonly associated with logging operations in tropical forests is inconsistent with the preservation of many non-timber forest values. Thus, although current logging practices may permit the sustained yield of wood, they are likely to interfere with the sustainability of other services and functions provided by tropical forests.
Furthermore, there is evidence that the degree of damage is increasing as logging operations extend over more rugged terrain and become increasingly mechanized, relying to a greater extent on "horsepower" rather than on technical competence (Fox, 1968; Nicholson, 1979; Marn and Jonkers, 1982). This is an alarming trend because it suggests that the sustainability of both timber production and non-timber services is increasingly at risk in tropical forests.
This paper makes a distinction between "harvesting" and "logging". As used here, logging refers simply to the process of felling and extracting wood from forests whereas harvesting includes pre-harvest planning, technical supervision and post-harvest assessments that reflect concern about non-timber resource values and the future state of the forest. "Harvesting technology" is a collective term that refers to the use of scientific and engineering principles in combination with education and training to improve the application of labour, equipment and operating methods in the harvesting of industrial timber.
We believe that sufficient information now exists to permit sustainable harvesting operations in virtually any area of tropical forest worldwide. Furthermore, the motivation for doing so is not just to promote sustainability; at least three recent studies (Mare and Jonkers, 1982; Hendrison, 1989; and Schmitt, 1989) have demonstrated clearly that harvesting operations designed to satisfy requirements for sustainability can simultaneously reduce harvesting costs by a substantial margin through improved planning and technical control.
The key to promoting sustainability of tropical forests during wood harvesting operations is to utilize the best knowledge available regarding five critical elements: harvest planning; forest roads; felling; skidding and yarding; and post-harvest assessments. The following sections address these elements individually.
Harvest planning
Comprehensive planning of harvesting operations is essential in order to set the stage for sustainable harvesting practices and also to reconcile greater technical control during harvesting with the need to reduce costs. However, there is considerable evidence that harvesting operations in tropical forests are rarely preceded by thorough planning of the kind that is commonplace in temperate forests(Schmidt, 1987; Hendrison, 1989; FAO, 1989b). Furthermore, observations made by Nicholson (1958, 1979) over more than two decades suggest that, if anything, harvest planning for tropical forests is less common now than it was during the colonial era.
As in temperate forests, harvest planning in tropical forests should include the collection of detailed timber inventories and topographical data, plus other information essential for laying out a transportation system. A transportation plan should ensure that the logging crews have efficient access to the trees to be harvested; it should therefore circumvent problem areas, avoid streams and minimize the total area disturbed by roads, landings, skidtrails and cableways. Suggested procedures for collecting the necessary data to permit this kind of planning are provided by Marn and Jonkers (1982) and Hendrison (1989).
A harvesting plan should also specify the equipment to be used and the timing of operations, and should include contingency plans for severe storms and other extreme events. It should consider the possibility of complementary harvesting of non-timber forest products (for example, the cutting of rattan or tapping of resins prior to the timber harvest, or fuelwood gathering after the harvest). Local communities should be consulted about potential scheduling problems or opportunities (for instance, to take advantage of labour availability during slack agricultural periods). The normal onset of the rainy season should be considered, as should the time of seedfall in areas where seed is not produced year-round; in deciduous or semi-evergreen forests, for example. In some cases, harvesting operations may need to be scheduled to avoid conflicts with the reproductive cycles of animals or plants of value to local people.
Although harvest planning implies an increase in initial expenditure, it can help avoid many problems and can substantially decrease overall costs by reducing wastage and improving efficiency of operations. A study by Marn and Jonkers (1982) found that operations preceded by comprehensive planning were characterized by better organization and supervision, fewer accidents, fewer merchantable trees left unfelled and fewer logs lost after felling. In addition, operations utilizing comprehensive harvest planning were found to cost 20 to 45 percent less overall than comparable operations carried out under virtually identical conditions but for which only minimal harvest planning was done (Mare and Jonkers, 1982; Hendrison, 1989). Perhaps more importantly, total soil disturbance and damage to residual trees was significantly less in the case of pre planned operations than in operations undertaken with a minimum of planning.
Roads
Roads are unquestionably the most problematic feature of timber harvesting operations. An estimated 90 percent or more of the soil erosion resulting from timber harvesting in the tropics is directly attributable to roads (FAO, 1977). Nevertheless, except in cases where large waterways can be used, roads are essential for industrial timber extraction and providing access for management and control purposes. Building roads involves removing vegetation and rearranging the soil to permit an easier passage for vehicles. Such actions are almost always accompanied by increased rates of erosion. To minimize erosion and reduce its destructive effects, road locations must be planned in advance and according to proper layout and construction procedures.
Competent technical supervision of road layout and construction is essential. By restricting the area cleared for haul roads to the minimum width possible while still allowing for efficiency and safety, soil erosion can be reduced and the area retained in forest increased. For example, guidelines developed for rain forests in northern Australia specify that the maximum clearing width should be less than 7.5 m for major haul roads and less than 5 m for secondary haul roads (Ward and Kanowski, 1985). This contrasts sharply with the average road clearing width of 18.4 m, reported in a recent study in Papua New Guinea (FAO, 1989a).
Felling operations
By itself, selective felling practically mimics natural tree falls and is generally considered to be relatively benign from an environmental perspective (Hamilton, 1988). Indeed, the forest gaps created by trees felled properly under any of the selective harvesting systems common to the tropics are often indistinguishable from gaps caused by natural tree falls (Jonkers, 1987). Nevertheless, improper felling can cause considerable damage to advanced regeneration and can also reduce efficiency in skidding operations.
Of particular importance is the common situation of tree crowns interconnected by woody climbers. Under such conditions the tree being felled can pull neighbouring trees with it, thereby breaking or uprooting them. In fact, shifting cultivators reportedly take advantage of this, pulling down large blocks of forest by felling a single, climber-infested tree. Pre-harvest cutting of climbers is essential in such areas, and can substantially reduce damage to residual trees. For instance, one study (Fox, 1968) found that the cutting of climbers several months in advance of felling reduced the number of trees knocked over or broken by as much as 50 percent. Because many of the residual trees damaged or destroyed during felling are in the pole-sized classes that will form the commercial timber crop for a subsequent harvesting entry, sustainability of timber production depends upon saving as many of these trees as possible. In addition, much of the floral biodiversity in tropical forests resides in trees that do not attain large sizes and are not currently utilized for timber (K.D. Singh, FAO Forestry Department, personal communication, 1991). Therefore, ensuring minimum damage to young trees and regrowth is also important from the point of view of biodiversity conservation [Ed. note: see also article by Kemp in this issue of Unasylva].
Improper felling techniques are another common problem in tropical forests. According to DeBonis (1986), felling crews are often untrained and, in some cases, do not understand the need to make an undercut to direct the fall of a tree. Once the trees have been felled, proper cross-cutting is essential in order to maximize the value of the tree and to reduce wastage. A recent global assessment of the tropics suggests that the percentage of felled timber left unutilized in the forest is more than twice as high in the tropics as in the temperate regions (Dykstra, 1991). Utilization of these residues through improved felling and crosscutting techniques could substantially reduce the area of tropical forest that has to be logged each year to provide the current volume of tropical industrial roundwood.
Skidding and yarding operations
Most logging in tropical forests is done with ground skidding equipment. Cable yarding has the potential of substantially reducing road requirements and soil disturbance in steep or swampy areas (Aulerich, Aulerich and Piedrahita, 1990) but its proper application requires a highly skilled crew and even so it will probably be more costly and may result in more extensive damage to residual trees (Nicholson, 1979).
Conventional ground skidding systems cause two forms of damage in tropical forest operations. The skidders tend to wander through the forest searching for felled trees, thus causing a proliferation of skid trails and resulting in excessive damage to residual trees and advance regeneration. The skidders also cause soil disturbance and soil compaction, thus increasing the potential for erosion and retarding both regeneration and the growth of residual trees. Both of these problems can be substantially reduced by comprehensive pre-harvest planning as discussed earlier. Comparative studies have shown that skidding costs can be reduced by one-third or more through comprehensive planning coupled with competent technical supervision (Mare and Jonkers, 1982; Hendrison, 1989). In addition, when preplanning of skid trail locations is combined with directional felling of trees toward the skid trails, the number of merchantable logs left in the forest can be reduced substantially (Mare and Jonkers, 1982).
Where appropriate, low-pressure ground skidders can be used to reduce soil disturbance and soil compaction, particularly on steeper slopes or permanently damp soils (Buenaflor and Heinrich, 1980). Animal skidding is also a feasible alternative in many areas and the use of draught animals, such as elephants or oxen, has been shown to significantly reduce soil disturbance, soil compaction and damage to residual trees (Sundquist, 1985; Cordero, 1988).
Post-harvest assessments
As stressed at the beginning of this article, harvesting is one part of overall forest management. Therefore, regular feedback regarding the success or failure of harvesting operations with respect to long-term sustainability of the forest is essential. Part of this feedback can be provided through post-harvest assessments. Such an assessment should report on operation costs and revenues; an evaluation of the degree to which both silvicultural and non-timber objectives are met; the extent of damage to residual trees; the area disturbed by roads and trails, the quality and quantity of regeneration; etc. Requirements for post-harvest operations such as the revegetation of skid trails and landings should be noted. Finally, it is essential that the results of the post-harvest assessment be communicated to the harvesting crew. Financial incentives for good work and penalties for substandard work will reinforce a company's commitment to sustainable harvesting practices.
Although many logging practices commonly used in tropical forests today are incompatible with the long-term sustainability of non-timber values, there are signs that significant improvements are under way. Perhaps the most comprehensive effort is the one being carried out in Suriname, as analysed by Jonkers (1987), Hendrison (1989) and others from the Agricultural University of Wageningen in the Netherlands. This undertaking involved the development of compatible silvicultural and harvesting systems for minimizing environmental impacts associated with selective harvesting operations in tropical high forest. The cornerstones of the system include comprehensive pre-harvest planning; thorough training of logging crews; technically competent supervision; and extensive post-harvest assessments as part of the feedback on the overall management plan. An important aspect is that the procedures were developed and tested in collaboration with private timber companies. These companies have benefited both by ensuring the sustainability of the tropical forest resource and by reducing the direct cost of their logging operations by 30 percent or more in comparison with conventional logging.
A somewhat different approach, also with the objective of improving sustainability of both timber and non-timber forest values, is being tested in the Peruvian Amazon. Using the ecological principles of gap dynamics, the harvesting system is based on small clear-cut areas in long, narrow strips along the contour to take advantage of the regeneration characteristics of local timber species and so to improve logging economics [Ed note: see articles on strip clear-felling, by Ocaña-Vidal, and pilot natural forest management in Latin America, by Kiernan et al., in this issue of Unasylva].
Improved harvesting systems are also under development for other parts of the tropics, including Malaysia (Mare and Jonkers, 1982) [Ed. note: see article on the sustainability of forest management in Malaysia, by Mok, in this issue of Unasylva]; French Guiana (Schmitt, 1989); Colombia (Aulerich, Aulerich and Piedrahita, 1990); Papua New Guinea (Buenaflor, 1990); Brazil (Costa Filho, 1991); and Indonesia (Hasan, 1991). Research on sustainable harvesting technologies in the Zaire basin is also being carried out by the Centre technique forestier tropical of France in collaboration with local African organizations. Although most improved harvesting systems that have been tested to date are experimental, assistance from international organizations to test pilot applications and develop the requisite skills needed by planning teams and logging crews could provide the impetus necessary to make these systems operationally feasible on a larger scale.
Aulerich, D.E., Aulerich, S.P. & Piedrahita, M. 1990. Applying steep terrain harvesting technology to the forests of Latin America. Proc. XIX Cong. IUFRO, 511 August 1990, Montreal, Canada Montreal, IUFRO.
Buenaflor, V.D. 1990. Forest management research and development, Papua New Guinea: report on improved forest harvesting. Project FO: DPPNG/86/009. Rome, FAO.
Buenaflor, V. & Heinrich, R. 1980. FMC tracked skidder logging study in Indonesia. Project FO:INS/78/054. Working Paper No. 7. Rome, FAO.
Cordero, W. 1988. Utilización del sulky en la extracción de madera con bueyes. Serie informativa tecnológica apropiada No 18. Cartago, Costa Rica, Instituto Tecnológico de Costa Rica.
Costa Filho, P.P. 1991. Mechanized logging and the damages caused to tropical forests: case of the Brazilian Amazon. Paper presented at the 10th World Forestry Congress, 17-26 September 1991, Paris, France. (unpubl.)
Dawkins, H.C. 1958. The management of tropical high forest, with special reference to Uganda. Oxford, Imperial Forestry Institute.
DeBonis, J.N. 1986. Harvesting tropical forests in Ecuador. J. Forest., 84(4): 43-46.
Dykstra, D.P. 1991. Wood residues from timber harvesting and primary processing: a global assessment for tropical forests. Report to the Forest Harvesting and Transport Branch, FAO. (unpubl.)
FAO. 1977. Guidelines for watershed management. Conservation Guide 1. Rome, FAO.
FAO. 1989a. Forest management research and development, Papua New Guinea: project findings and recommendations. Project FO:DP/PNG/84/003, terminal report. Rome, FAO.
FAO. 1989b. Review of forest management systems of tropical Asia. In A.J. Leslie, ed. Synthesized from contributions by C.T.S. Nair, M. Chundamannil, Thang Hooi Chiew, A. Bin Mat Amin and the Bureau of Forest Development of the Philippines. Forestry Paper No. 89. Rome, FAO.
FAO. 1989c. Management of tropical moist forests in Africa. R.L. Willan, ed. Synthesized from contributions by M.S. Philip, P.K. Karani, P.R.O. Kio, S.A. Ekwebelam, A.B. Oguntala, D.O. Ladipo, F.O.C. Nwonwu and R. Catinot. Forestry Paper No. 88. Rome, FAO.
FAO. 1991. Statement on sustainable development from the FAO/Netherlands Conference on Agriculture and the Environment's-Hertogenbosch, the Netherlands, 15-19 April 1991. (unpubl.)
Fox, J.E D. 1968. Logging damage and the influence of climber cutting prior to logging in the lowland dipterocarp forest of Sabah. Malays. For., 31(4): 326-347.
Hamilton, L.S. 1988. Minimizing the adverse impacts of harvesting in humid tropical forests. In A.E. Lugo, J.R. Clark & R.D. Child, eds. Ecological development in the humid tropics. Morrilton, Arkansas, USA, Winrock International Institute for Agricultural Development.
Hartschorn, G.S. 1989. Gap-phase dynamics and tropical tree species richness. In L.B. Holm-Nielsen, I.C. Nielsen & H. Balslev, eds. Tropical forests: botanical dynamics, speciation and diversity. London, Academic Press.
Hasan, M. 1991. Sustainable forest management and utilization of timber for domestic timber industry. Proc. 10th World Forest. Cong., Paris, France, 17-26 September 1991, Vol. 6, p. 333-339.
Hendrison, J. 1989. Damage-controlled logging in managed tropical rain forests in Suriname. Series on the ecology and management of tropical rain forests in Suriname. Wageningen, the Netherlands, Agricultural University of Wageningen.
Jonkers, W.B.J. 1987. Vegetation structure, logging damage and silviculture in a tropical rain forest in Suriname. No. 3, Ecology and management of tropical rain forest in Suriname (series). Wageningen, the Netherlands, Agricultural University of Wageningen.
Marn, H.M. & Jonkers, W. 1982. Logging damage in tropical high forest. In P.B.L. Srivastava et al., eds. Tropical forests - source of energy through optimisation and diversification. Proc. of an int. conf., 11-15 November 1980, Penerbit University, Malaysia.
Nicholson, D.I. 1958. An analysis of logging damage in tropical rain forests, North Borneo. Malays. For., 21(4): 235-245.
Nicholson, D.I. 1979. The effects of logging and treatment on the mixed dipterocarp forests of Southeast Asia. Report FO:MISC/ 79/8. Rome, FAO.
Poore, D. 1989. No timber without trees. London, Earthscan.
Redhead, J.R. 1960. An analysis of logging damage in lowland rain forest in Western Nigeria. Nigerian Forest. Inf. Bull. (new series), 10: 5-16.
Schmidt, R. 1987. Tropical rain forest management. Unasylva, 39(156): 2-17.
Schmitt, L. 1989. Etude des peuplements naturels en forêt dense guyanaise: compte rendu de mise en application des traitements sylvicoles sur le dispositif de paracou. Nogent-sur-Mame, France, Centre technique forestier tropical, Départment du CIRAD.
Sundquist, G., ed. 1985. A handbook on basic logging and transport methods adapted to typical conditions in India. Spanga, Sweden, Forskningsstiftelsen Skogsarbeten (Forest Operations Institute).
Ward, J.P. & Kanowski, P.J. 1985. Implementing control of harvesting operations in north Queensland rain forests. In K.R. Shepherd & H.V. Richter, eds. Managing the tropical forest. Proc. from a workshop, Gympie, Australia, 11 July - 12 August 1983. Canberra, Australia, The Australian Nat. Univ.
WCED. 1987. Our common future. Oxford, Oxford Univ. Press.
Wyatt-Smith, J. & Foenander, E.C. 1962. Damage to regeneration as a result of logging. Malays. For., 25(1): 40-44.
