R.E. Pulkki
Reino E. Pulkki is Chair, Forest Management Department, Faculty of Forestry, Lakehead University, Thunder Bay, Ontario, Canada.
Note: This article is based on two background papers prepared for the FAO Global Fibre Supply Study (Pulkki in FAO, 1997a; 1997b).
Reduced-impact logging can do much to ensure sustainable forest management while helping to meet future demand for veneer and sawlogs, and the techniques involved - increasing use of lesser-known species, establishing diameter felling limits and reducing in-forest losses, etc. often lead to added economic benefits as well.
Econometric models generally show a continuously increasing global consumption of raw forest products. Although many authors conclude that there will be no overall global wood fibre shortage in the near future (notwithstanding some possible regional shortages), such a global consideration may be misleading. If the price of raw wood is sufficiently high, fast-growing plantations can be established fairly quickly to deal with increases in "low-quality fibre" demand (FAO, 1989a; ITTO, 1993; Byron and Perez, 1996). However, the demand for large-diameter and high-value non-coniferous tropical logs cannot be met in this manner, and there are indications that if current harvesting practices continue future supply may be inadequate.
This article considers the impact of current harvesting practices on future supply of non-coniferous tropical veneer logs and sawlogs and the potential impact that the adoption of environmentally sound harvesting practices and sustainable forest management in general may have on future supplies. Two modelling scenarios were run: the first assumes that conventional unsustainable logging practices will continue; the second assumes environmentally sound harvesting within a context of overall sustainable forest management. Under current practices, the first model foresees widespread shortages of tropical timbers, although this could be avoided with the implementation of environmentally sound harvesting practices.
According to Johns (1992), the most effective management of most tropical forests entails the protection and encouragement of advanced growth in optimally sized canopy gaps created during logging, with planting in gaps where no advanced growth exists. Critical for the sustained management of these forests is the implementation of environmentally sound harvesting techniques - often referred to as reduced-impact logging (ISTF, 1995; Marsh et al., 1996; Weidelt, 1996). Palmer and Synnott (1992) state that "while the merits of various forest management systems are being debated, tropical silviculturists are of one voice in advocating the use of reduced-impact logging techniques".
Environmentally sound harvesting entails appropriate planning and implementation to ensure that future tree crops and other vegetation are left undisturbed, wildlife and other non-timber forest values are preserved, waterways and soils are protected, scenic beauty and recreational opportunities are enhanced and that the forest itself is perpetuated.
If environmentally sound harvesting techniques are fully used on an operational scale, the increased income gained through more efficient operations (when compared with conventional logging practices) will generally offset any additional costs in planning, layout and control, and thus make it at least cost neutral (Hendrison, 1989; Pinard et al., 1995; Bruenig, 1996). However, the implementation of reduced-impact logging has been sporadic in practice and sustainable management of tropical forests is rare (FAO, 1989b; Jonsson and Lindgren, 1990). Where environmentally sound harvesting techniques are not implemented, the volumes extracted in second and third cuts will be much reduced compared with those of the first cut. This is reflected in the logging intensities both from forests undisturbed by humans and forests disturbed by humans, as contained in FAO's Global Fibre Supply Study (GFSS) database (Pulkki in FAO, 1997a).
Throughout all of the literature there is consensus that the vast majority of logging in non-coniferous tropical forests continues to be inefficient, wasteful and excessively destructive to both residual trees and the site itself. Logging as currently practiced in non-coniferous tropical forests is not sustainable and this is reflected in the GFSS scenarios with considerable reductions in veneer log and sawlog harvesting intensity in the second cutting cycle. It is expected that, if current logging practices continue, the third cut will be still lower or even nonexistent. On the other hand, with the implementation of reduced-impact logging techniques and silvicultural systems, a major benefit is that stable future yields and sustainable forest management operations should result in future income which otherwise would be lost.
Actual logging intensities vary considerably between regions and countries and even within countries (Pulkki in FAO, 1997b). The cutting cycle also varies considerably, hut many reports suggest 40 years is sustainable when reduced-impact logging is implemented. This allows for the ingrowth of trees into the next higher diameter class; for example, from the 40 to 60 cm into the 60 to 80 cm dbh class (average diameter growth of 0.5 cm/year).
Based on the literature, and with the implementation of reduced-impact logging and appropriate silvicultural treatments, it is felt that an average logging intensity of 20 m3/ha on a 40-year cycle is possible in closed non-coniferous tropical forests in Africa and Latin America and the Caribbean (Thang, 1986; FAO, 1989a; FAO, 1989b; Buenaflor in FAO, 1989c; Hendrison, 1989; Lamprecht, 1993; d'Oliveira and Braz, 1995; Bruenig, 1996). Sundberg (in FAO, 1978) gives a logging intensity of 20 m3/ha as the economic threshold, below which the relative logging cost increases exponentially. This economic threshold becomes very important with the extraction of more lower-value logs and species and with the implementation of reduced-impact logging. In the dipterocarp forests of Asia and Oceania an average logging intensity of 40 m3/ha on a 40-year cycle should be easily achievable. It must be remembered, though, that these are conservative and general averages, and the actual logging intensity and cutting cycle will depend on the condition of the forest itself and the species involved. In addition to the full implementation of reduced-impact logging, a wider range of species must be commercialized and the utilization of felled trees improved.
Increasing use of lesser-known species
In many areas, species initially viewed as weeds have become valuable sources of raw material. Increased use of previously disregarded species is seen by many as a way to make the management of forests more viable economically, since increasing the volume removed generates more revenue per hectare (Sarre, 1995). Of the 19 country summaries given in ITTO (1997), 11 make reference to initiatives to improve utilization of currently underutilized or lesser-known species for veneer logs and sawlogs.
Where logging intensities are low, underutilized species may be a good source of additional log volume (Yeom, 1984). However, increased logging intensity can lead to greater disturbance (Wagner and Cobbinah, 1993), and thus lead to reduced yields in subsequent cutting cycles and unsustainable forest management (FAO, 1989a). Re-entry prior to the full rotation in order to harvest a species which becomes commercially attractive in the meantime must be prohibited (Jonsson and Lindgren, 1990).
Establishment of minimum-diameter felling limits
There is a trend to reduce felling limits to increase logging intensity. This, however, can seriously affect the regeneration potential of non-coniferous tropical forests managed under polycyclic silvicultural systems (Thang, 1986; d'Oliveira and Braz, 1995). Maintaining sufficient canopy cover is also necessary to reduce erosion caused by high-intensity tropical rainfall, to maintain the forest as a fire-resistant ecosystem and to control invasion of the site by climbers and lower-value pioneer species. The minimum felling limit needs to be matched to the silvics of each species and, where information is not available, to justify its being lowered it should be maintained at current levels (e.g. minimum diameter of 50 to 60 cm). Bruenig (1996) argues that the minimum felling size should not be lower than 60 cm in dipterocarp forests.
Reduction of in-forest losses
The extent of logging waste reported in the literature generally ranges from 30 percent (Silitonga in FAO, 1987b; Gerwing, Johns and Vidal, 1996; Scharpenberg in FAO, 1997c) to 50 percent (Dykstra, 1992; Noack, 1995) of the extracted log volume. Variations in felling recovery rates reported in the literature are due to operational efficiency and skill of workers, available markets for lower grade logs and differences in the definition of merchantable wood.
An important source of logging waste is felled and bucked trees that are not found during the skidding operation. For example, Mattsson-Marn and Jonkers (in FAO, 1981) found that 11 m3/ha (20 percent of extracted volume) of logs could not be found by the skidder in current operations. Through the adoption of environmentally sound harvesting techniques and the mapping of felled trees and felling directions, the loss of logs can be significantly reduced. In a well-planned harvesting block the volume lost was reduced from 11 m3/ha to 5.5 m3/ha (Mattsson-Marn and Jonkers in FAO, 1981).
Logging wastes also result from poor work methods and felling and bucking techniques which result in the splitting and breaking of felled trees (Hendrison, 1989). The estimated volume of waste resulting from felling and bucking losses is about 6.5 to 8.5 percent of the utilizable stem volume (FAO, 1989b; Winkler in FAO, 1997d). In addition to volume losses caused by poor felling and bucking techniques, there can be significant value losses. Logger training is a key factor in reducing logging waste and value loss. Uhl et al. (1997) found that trained loggers were able to achieve a 300 percent reduction in waste associated with telling and bucking, while Winkler (in FAO, 1997d) found a 120 percent reduction. DeBonis (1986) also found that a 15 to 30 percent increase in wood volume at the mill could be realized through proper felling and bucking techniques.
Out-of-forest losses
Wood volume losses or waste also occur at roadside landings, export ports, mill yards and in manufacturing itself. For example, Kilkki (in FAO, 1992) found in a study in Papua New Guinea that 10-35 percent of the export volume was left at the harbour as not fulfilling export grade rules.
Mill process yields have been reported to be as low as 33 percent of delivered log volume (Gerwing, Johns and Vidal, 1996; Uhl et al., 1997). Noack (1995) reported sawmill timber recovery factors ranging from 36 to 57 percent. When sawing large-diameter tropical hardwood logs, the recovery factor should be at least 50 percent (Uhf et al., 1997) and yields of 56 to 68 percent should generally be expected (Niedermaier, 1984).
Less wasteful processing is also essential. In the photo: a training facility in Zimbabwe
Logging damage to the residual stand
Minimizing the damage to the residual trees and advance regeneration during logging is essential for the success of all polycyclic silvicultural systems. In practice, however, very little consideration is given to this, and levels of damage typical of conventional logging operations (in actual harvesting and in skidding) are unacceptably high. The percentage of residual trees damaged ranges from 33 to 70 percent in areas with a higher logging intensity (e.g. >30 m3/ha) (Uhf and Viera, 1989, Pinard et al., 1995; Dykstra et al., 1996). In areas with a lower logging intensity (e.g. in African countries with the removal of one to two trees/ha), residual stand damage generally ranges from 10 to 20 percent (White, 1994; Scharpenberg, in FAO 1997c). However, tree damage does not increase in direct proportion to felling intensity (Verissimo et al., 1992).
Implementation of reduced-impact logging can permit an increase of logging intensity with a significant reduction of residual tree damage. For example. Buenaflor (in FAO, 1989c) found 67 percent of residuals damaged in uncontrolled logging with 23 m3/ha removed while, in a controlled logging area, 22 percent of residuals were damaged with 32 m3/ha removed.
Some damage to the residual stand will always occur with the felling of trees and, therefore, there is a maximum logging intensity threshold beyond which the maintenance of stand integrity is difficult in selection cutting. Watanabe (1992) gives this threshold as 30 percent of stand basal area.
Logging damage to the site
As with residual stand damage, site impacts in conventional logging of non-coniferous tropical forests are excessive. Typically, under conditions of high logging intensity (e.g. >30 m3/ha), 10 to 25 percent of the area is impacted by roads, skid trails and landings (FAO, 1989a; Hendrison, 1989; Uhl and Viera, 1989, Verissimo et al., 1992, Winkler in FAO, 1997d). In lower logging intensity areas (e.g. <20m3/ha), the soil disturbance is from 6 to 13 percent of the area (Uhf et al., 1991; White, 1994; Scharpenberg in FAO, 1997c). Bruenig (1996) states that, with excessive reading and skidding and, thus, excessive compaction and erosion, felling cycles of 25 to 50 years are not sustainable and that a cycle of 60 to 100 years is more realistic.
The implementation of reduced-impact logging techniques results in significantly fewer site impacts. Winkler (in FAO, 1997d) found that, under conventional logging practices, 14.4 percent of the area was covered by roads, skid trails and landings, while in reduced-impact logging areas only 4.5 percent of the area was impacted. Marsh et al. (1996) found similar results, with areas subjected to reduced-impact logging having only 3.8 percent of the area used for skid trails, compared with 12 percent in adjacent conventionally logged areas. Malvas (in FAO, 1987a) determined that with optimally spaced and located roads, skid trails and landings a minimum of approximately 5 percent of the area would be impacted. It is significant to note that properly planned skid trails generally develop good regeneration and crown cover (ISTF, 1995).
Two modelling scenarios were devised to estimate the future availability of tropical non-coniferous veneer logs and sawlogs from forests undisturbed by humans and forests disturbed by humans (not including plantations). The first scenario utilizes information in FAO's GFSS database regarding logging intensities and cycles. It assumes that logging practices will continue more or less as at present and that future logging intensities will be progressively and significantly reduced owing to a creaming of the forest and logging damage to residual trees and the site.
The second scenario assumes that environmentally sound harvesting practices have been implemented and calculates a conservative average logging intensity of 20 m3/ha on a cycle of 40 years for closed moist tropical forests in Africa and Latin America and the Caribbean. In the moist dipterocarp forests of Asia, a conservative average logging intensity of 40 m3/ha on a 40-year cycle was assumed.
Model description
To yield a commercial volume that is theoretically available over the long term, the available forest area for each class is multiplied by the logging intensity. The ratio of non-coniferous sawlogs and veneer logs coming from each forest class is calculated by dividing the commercial volume available in the class by the sum of commercial volume available (i.e. 63196000 m3) from all forest classes. The average annual (1990-1995) veneer log and sawlog production for a country is then multiplied by the ratios to estimate a volume of wood coming from each forest class. The share of production coming from each forest class is then divided by the logging intensity to calculate the area with harvesting operations for the year. However, to maintain long-term sustainability, the maximum area harvested in any forest disturbed by humans cannot exceed the area available divided by the cutting cycle. For example, the closed non-coniferous forest disturbed by humans has an available area of 133333 ha and this is equal in Cameroon to the area of forest to be harvested. If this condition is not met in the initial volume assignment, the model iteratively reduces the volume harvested in each forest disturbed by humans being over-harvested until the constraint is met.
After the areas logged within a particular year are determined, the areas of forest undisturbed by humans and forest disturbed by humans are revised to form the basis for the next year's calculation (i.e. the area of forest undisturbed by humans that is harvested is deducted from area of forest undisturbed by humans and added to the area of forest disturbed by humans). Table 1 presents a sample calculation of the first year for Cameroon.
TABLE 1. Calculation of non-coniferous forest area harvested in Cameroon (example)
|
|
Forest undisturbed by humans 1 |
Forest disturbed by humans 1 |
Forest undisturbed by humans 1 |
Forest disturbed by humans 1 |
Total |
|
Available forest (ha) |
6894000 |
4000000 |
0 |
1876000 |
12770000 |
|
Logging intensity (m3/ha) |
7.0 |
3.5 |
2.0 |
0.5 |
- |
|
Logging cycle (years) |
- |
30 |
|
50 |
- |
|
Commercial volume available (m3) |
48258000 |
14000000 |
0 |
938000 |
63196000 |
|
Area available (ha) |
- |
133333 |
- |
37520 |
- |
|
Share of production |
0.7882 |
0.2036 |
0.0000 |
0.0082 |
1.000 |
|
Volume from forest type (m3) |
1806907 |
466666 |
0 |
18760 |
2292333 |
|
Area of forest harvested (ha) |
258130 |
133333 |
0 |
37520 |
428983 |
|
Revised forest area (ha) |
6635870 |
4258130 |
0 |
1876000 |
12770000 |
1
Refers to non-coniferous forest area.
Note: In 1995 total sawlog and veneer production from non-coniferous forest was 2.3 million m3.
As is evident, the critical values are the average sawlog and veneer log production from the FAOSTAT database, together with GFSS database estimates of areas available for wood production, and logging intensities and logging cycles by forest classes. All other values are calculated.
The model continues harvesting until no forest area undisturbed by humans exists or the run has gone for 500 years. The volume harvested once the available production forest is all disturbed by humans represents the sustainable long-term yield, assuming successive logging cycles yield the same volume as the second cycle. This, however, cannot be assured with the conventional uncontrolled and unplanned logging operations that are typical in tropical broad-leaved forests, possible illegal logging and deforestation.
Limitations of the model
The calculation of harvest area per year is based on the area of tropical broad-leaved forest commercially available for non-coniferous veneer log and sawlog production as well as the logging intensities and cycles for each forest class contained within the GFSS database. It is assumed that the current production forest area will remain as production forest, except where official areas for forest conversion have already been established, for example Malaysia and Indonesia. Furthermore, no account is made for possible deforestation or forest degradation, since it is not known which forest classes are actually being affected. Forest depletion caused by conventional logging practices is taken into account through reduced logging intensities for forests disturbed by humans.
Veneer log and sawlog production is held constant, at the average production for 1990-1995 contained in the FAOSTAT database. There is no account made for possible illegal or otherwise undocumented logging operations. As a result, the model results can be held as optimistic in nature.
At the national level, the model indicates a wide variation. In some countries, current official veneer log and sawlog removals are well below the estimated long-term sustained yield (i.e. countries for which the allowable harvest level once all forest is disturbed by humans is still greater than 200 percent of current harvest levels). In others, especially in countries of Africa and Asia, the current harvest level is already significantly above long-term sustainable yield levels. On a regional basis, assuming current logging and forest management practices (Table 2), it appears there will be a major supply shortage of non-coniferous tropical veneer logs and sawlogs in Asia and Oceania. In Asia and Oceania the estimated long-term sustainable yield generated by the model is only 59 percent of current harvest levels, even when deforestation and illegal logging are not considered. Africa, mainly because of the large forest area available in the Democratic Republic of the Congo, seems to have some room for expansion (i.e. long-term sustained yield of 30 million m3 versus a current harvest level of about 17 million m3). In Latin America and the Caribbean the long-term sustained yield and current harvest levels are more in balance, with some surplus in long-term sustained yield expected to be "eaten up" by deforestation and illegal logging. On a global scale it appears there will be a non-coniferous tropical veneer log and sawlog shortage since the long-term sustained yield is only 91 percent of the current official harvest level.
TABLE 2. Initial regional areas available for wood production and long-term sustained yield once the available area consists of forest disturbed by humans 1
|
|
Available forest undisturbed by humans |
Available forest disturbed by humans |
Total available non coniferous forest area |
Average production, 1990-95 |
Long-term sustainable yield |
Percentage of production, 1990-95 |
|
|
(ha) |
(ha) |
(ha) |
(m3) |
(m3) |
(percentage) |
|
Africa |
59569000 |
112938000 |
172507000 |
17133116 |
29767301 |
174 |
|
Asia and Pacific |
53000000 |
91911000 |
144911000 |
97605368 |
57223831 |
59 |
|
Latin America and Caribbean |
42150000 |
122500000 |
164650000 |
33822618 |
47632039 |
141 |
|
Total |
154719000 |
327349000 |
482068000 |
148561102 |
134623171 |
91 |
1
Assuming GFSS logging intensities and cycles.
Sustainable logging intensities and cycles with reduced-impact logging
With the implementation of reduced-impact logging and the sustained removal of 20 m3/ha on a 40-year cycle in tropical closed broad-leaved forests in Africa and Latin America and the Caribbean and 40 m3/ha on a 40-year cutting cycle in Asian dipterocarp forests, the model results show higher long-term sustained yield harvest levels for almost all countries, with the exception of Côte d'Ivoire, Costa Rica, Panama, Malaysia and Viet Nam. With the implementation of reduced-impact logging, and assuming a parallel increase in removals of currently underutilized species, most countries could have increases in long-term sustained yield harvest levels when compared with current official log production values.
On a regional basis (Table 3) the implementation of reduced-impact logging and "proper" selection cutting results in regional non-coniferous tropical veneer log and sawlog surpluses when compared with current official production levels. However, the small surplus (16 percent) in Asia and Oceania is more likely to be a deficit in reality, even with the implementation of reduced-impact logging, owing to the effect of deforestation and logged volumes not reported in the official statistics.
TABLE 3. Initial regional forest areas available for wood production and long-term sustained yield once the available area consists of forest disturbed by humans 1
|
|
Available forest undisturbed by humans |
Available forest disturbed by humans |
Total available non-coniferous forest area |
Average production, 1990-95 |
Long-term sustainable yield |
Percentage of production, 1990-95 |
|
|
(ha) |
(ha) |
(ha) |
(m3) |
(m3) |
(percentage) |
|
Africa |
59569000 |
113238000 |
172807000 |
17133116 |
51512929 |
301 |
|
Asia and Pacific |
53000000 |
91911000 |
144911000 |
97605368 |
113614500 |
116 |
|
Latin America and Caribbean |
42150000 |
122500000 |
164650000 |
33822618 |
80625107 |
238 |
|
Total |
154719000 |
327649000 |
482368000 |
148561102 |
245752536 |
165 |
1
Assuming reduced-impact logging, a 40-year logging cycle and logging intensities of 20 m3/ha in tropical closed broad-leaved forests of Africa and Latin America and the Caribbean and 40 m3/ha in moist dipterocarp forests of Asia.
Based on the modelling exercise, it is quite clear that the implementation of reduced-impact logging and sustainable forest management could have a major impact on future non-coniferous veneer log and sawlog availability. As pointed out earlier, improved utilization of felled trees and increased use of lesser-known and utilized species could also have a significant impact in terms of fibre supply. However, even with the implementation of reduced-impact logging there are a number of countries which will still face major log shortages in the near future. Continuing current logging practices, with excessive damage to residuals and the site, would result in imminent log shortages in most countries and a general worldwide shortage of non-coniferous veneer logs and sawlogs within the very near future.
This article has attempted to demonstrate that the adoption of environmentally sound harvesting practices can go a long way towards ensuring sustainable forest management - and towards meeting future projected demand for veneer and sawlogs. The elements of such improved harvesting include increasing use of lesser-known species, establishing or re-establishing diameter felling limits and reducing in-forest losses. These techniques lead not only to more environmentally sound harvesting but are often of long-term economic benefit as well. However, in the long term, widespread use and implementation of improved harvesting depend on a strong policy commitment, accompanied by an articulated programme of education, training, monitoring and evaluation.
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