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Striving to understand and reduce the harvesting impacts in tropical forests of Congo (left) and Brazil (right).

Harvest Impacts

Substantial time and effort are expended worldwide considering and discussing the multiple effects of forest harvesting. Upon examination, one soon discovers that the knowledge of harvesting cause and effect relationships is severely limited in all forest types. And further, that the dissemination of reliable information is even more limited.

Progress in gathering knowledge is being made but the pace is slow for many reasons. First among those reasons is that forest ecosystems and forest operations are very complex and difficult to reliably measure. Issues are further complicated by the long time frame of most forest processes.

Several examples of recent forest harvesting studies and associated efforts are summarized on the following pages. We have studies from Africa, South America, North America, and Asia. Other news and information come from many sources around the world. If you have questions or comments about any of these items, please contact the original authors and let them know that you appreciate their efforts. Or give your thoughts to Rudolf Heinrich at FAO, Rome. (Additional information is also available with the internet version of this Bulletin, see page two for addresses).

Toward Sustainable Forest Management

In Malaysia the director of the Sabah Forestry Department, Haji Awang Tengah Awang Amin, says that the forestry policies and practices of Sabah are on track to attain ITTO's target of sustainable forest management by the year 2000. Sabah is the first state in Malaysia to use a skyline system to extract timber from its remote forests. The new skyline method minimises the effects of logging on the environment. The State Government is also able to increase its revenue collection through the sale of the timber in an open tender. This process yields a higher income as compared to royalties and premiums.

The Sabah Forestry Department restricts the felling of trees of less than 60 cm dbh, restrains the felling of certain tree species, and completely bans the felling of Belian trees. This year the Department will enforce reduced impact logging regulations to ensure systematic tree felling and transportation. A training syllabus on tree felling will be introduced at the School of Forestry Training which is undergoing expansion at Telupid near Keningau to produce a pool of skilled loggers. Malaysian Timber Bulletin

Congo, Natural Forest Harvesting

A case study on forest harvesting in natural forests of the Congo has been completed. The study report is part of a series of case studies published by FAO in the field of forest harvesting. It is the first one carried out in collaboration with a private industrial enterprise. The objective of the study was the establishment of reliable data on a ground harvesting system in the tropics, using power saws, crawler tractors and wheeled skidders. The study was carried out in cooperation with a large private contractor operating a concession in the Republic of Congo. The concession consists of approximately 145000 ha of closed-canopy, broad-leaved forest located in the Chaillu Massif. The annually harvested area is approximately 15000 ha. Annual rainfall in the region averages approximately 1800 mm.

The case study consists of a study inventory, a harvesting recovery analysis, and a harvesting impact assessment. The size of the study area is 150 ha, subdivided into three harvesting compartments of 50 ha each. The terrain is hilly, with water courses and seasonal swampy areas between hills. The average harvesting intensity is only 5-6 m3 net log volume or approximately one tree per ha. The main commercial species is Okoumé (Aucoumea klaineana), which is a medium density timber and is used for the production of peeled veneer, mainly for plywood.

The study inventory of all trees revealed an average density of 455 trees per ha (>10 cm dbh) including 15 Okoumé trees/ha. The proportion of Okoumé was significantly greater in larger diameter classes. During harvesting operations, all Okoumé trees above 80 cm dbh with adequate stem quality were felled and removed. The average net log volume was 5.8 m3. The extracted log volume was 70% of the standing stem volume (from ground to first branch).

Three well defined stands, 59.5 ha total, were selected for the harvesting impact assessment. Crawler tractors were used for short hauls and for bunching and wheeled skidders were used for the long haul to the landing.

Harvest Impact Assessment  
1. Harvest intensity  
a) Volume removed (m3/ha) 5.8
b) Average skidding distance (m) 403
2. Damaged trees (dbh>10 cm)  
a) Felling  
1 Damaged trees/ha 17.3
b) Skidding  
1 Damaged trees/km of skidtrail 212
2 Damaged trees/ha 11.5
c) Total damaged trees  
1 All species (%) 6.3
2 Okoumé (%) 7.2
3 Okoumé 40-80 cm (%) 9.0
3. Disturbed area  
a) Total disturbed (%) 8.4
b) Felling sites (%) 3.8
c) Skidtrails (%) 2.7
d) Secondary roads & landings (%) 1.2
e) Primary roads (%) 0.7

Under the prevailing conditions, the observed forest operation can be called "low impact" by definition due to the low removal rate of approximately one tree per ha. However, as with any harvest operation, gains are possible toward the objective of sustainable forest practice by placing high priority on harvest planning and assessment.

For more information and to order the study report, contact Rudolf Heinrich, FAO. See addresses on this page.

Effects of Logging on Forest Soil Physical Properties in Eastern Amazonia

In 1992 a cooperative project between the Jari Celulose S.A., Pará, Brazil and the Institute for Forest Utilization and Forest Work Science, University Freiburg, Germany was developed with the participation of the UNESP (Universidade Estadual Paulista) and the UFPR (Universidade Federal do Paraná). The study was carried out in a natural evergreen rainforest with a canopy of 30-40 m height. The site is situated on a plateau about 150 m above sea level. Average annual precipitation is about 2100 mm with the dry season from September to November. The average annual temperature is 26.4_ C.

(Photo - P. Fenner)

The aim of this project was to develop and improve a low impact logging system for the native non-flooded forest (terra firme) in the Amazonas basin, Brazil. Three felling intensities were used. They were 20, 40, and 60 percent of all trees over 40 cm dbh. Felling and bucking operations were done with a crew of two workers using a chainsaw.

Timber extraction was done by a crew of three workers using a blade and winch equipped Cat 528 skidder. Skid trails were built with the skidder. The skid trail spacing was from 80 to 120 m. Soil effects were examined in both dry and rainy seasons. Dry season soil moisture ranged from 39-43% by volume, the rainy season soil moisture was near saturation. Bulk density, saturated hydraulic conductivity,and intrinsic permeability were measured after 0, 1, 3, (Photo - P. Fenner) and 9 skidding passes at different soil moisture contents. Soil parameters were measured at soil depths ranging from 0 to 60 cm.

Some observations:

· The total area of compacted soils can be reduced by concentrating vehicle movement on skid trails.

· The use of smaller diameter winch line allows an increase in the distance between skid trails by reducing the manual effort required to pull the winch cable.

· Poorly positioned logs and the communication problems between the chokersetter and skidder operator were the principal causes of damage to the residual forest and excessive skidding time. Hand held radios would help

· The felling direction or the position of logs after felling is directly correlated with the degree of damage caused by extraction and to operational productivity.

· Increased traffic caused an increase in mechanical and shear strength down to a soil depth of 20 cm and a decrease in water conductivity and air permeability. Water conductivity and intrinsic air permeability were reduced drastically after the first pass.

· Signs of compaction were found 12 years after the skidding occurred.

· Less soil damage due to skidding should always be the aim so as to maintain the ecological systems favoring the presently growing species in the area.

· Studies on the implications of soil compaction on the growth of trees, especially commercially valuable species, must be undertaken.

For more information contact: Rolf Grammel, Institute for Forest Utilization and Forest Work Science, University of Freiburg, Werderring 6, 79085 Freiburg, Germany, Fax: (0761) 203 3763 or Paulo Fenner, Department of Forest Sciences, São Paula State University, Cx. P. 237, 18603-970 Botucatu-SP, Brasil Fax: (014) 821 3438

Residual Stand Damage with Mule Logging

A soon to be published technical report by Robert L. Ficklin, Graduate Research Assistant, John P. Dwyer, Associate Professor, Bruce E. Cutter, Associate Professor, and Tom Draper, Assistant District Forester, examines residual stand damage. The case study compares logging damage between two extraction systems (1) a rubber-tired skidder and (2) a mule.

COFO, Committee on Forestry, Thirteenth Session, 10-13 March 1997, Rome, Italy. Contact R. Heinrich for results.

The study examines the use of animals (mules) for reducing both the extent and severity of residual tree damage compared to a rubber-tired skidder operation. The short-term objective of this study is to determine if animal skidding offers an alternative to rubber-tired skidders for reducing residual stand damage. The long-term objectives are: 1) determine if relationships exist between tree damage during timber harvest and growth and productivity of the post-harvest forest, and 2) determine if a relationship exists between the species of trees damaged during timber harvest and the future developments of tree rot and disease.

Two upland oak-pine harvest sites under uneven-aged management regimes were selected in the Missouri Ozark Mountains. Pre-and post- harvest stand conditions were measured on both sites so inferences can be made about the relative levels of stand damage for both the animal and the mechanized skidder. Six plots (40 m x 80 m) were established systematically from a random starting point on both study sites, and a minimum buffer area of 20 m was maintained between all the plots. The total harvest area was 9.7 ha on the animal skidded site and 7.7 ha on the conventionally skidded site. A full inventory was made of all trees _12 cm dbh for all of the study plots. Site indices and slope measurements were made for each plot.

Following the harvest operations, each plot was fully inventoried again, and a total of 861 remaining trees were tagged. Each residual tree was measured and classified by species, by type of damage, and by severity of damage. There are four categories of damage: none, skidding, felling and destroyed. Skidding damage to roots or the bole was measured as the area of cambium exposed (cm2). Felling damage which exposed the cambium in the butt log (2.4 m) was measured in the same manner as skidding damage. Crown damage resulting from felling was estimated as a fraction (quarters) of the crown destroyed. Volumes were calculated for sawtimber and for total cubic volume, including sawtimber, pulpwood and residue. The cut trees, volume and basal area per ha were determined by the difference between the pre-harvest plot observations and the post-harvest measurements.

Mule vs Tractor Skidding

Summary results, mean values from six plots

Mule skidding

Tractor skidding

Residual Trees/ha



Cut Trees/ha



Residual Volume (m3/ha)



Cut Volume (m3/ha)



Tree damage


· Residual Trees Damaged (%)



· Area of Cambium Damage (cm2/plot)



Soil impact


· Area in skidtrails (% of total)



· Steepest slope, range (%)



There were three times as many trees destroyed with the tractor skidding system. Although this case study cannot conclusively state that animal skidding reduces stand damage under all conditions, the summary statistics do suggest that the mule skidding operation resulted in less damage to the residual stand. Timber cutting can be an important component of any wildlife or recreation management plan, and alternative logging systems could mitigate concerns over the impact of harvesting. The long-term effect of residual stand damage on site productivity is still unclear, but minimizing stand damage through effective supervision and appropriate harvest techniques is an achievable and worthy goal. For more information contact the authors at the University of Missouri, 1-31 Agriculture- UMC, Columbia, Missouri 65211. Read the entire paper at URL:

The STREK Project, Indonesia

STREK is the acronym for Silvicultural Techniques for the Regeneration of logged over forests in East Kalimantan, Indonesia project. The Ministry of Forestry of Indonesia and CIRAD-Forêt were the lead institutions. The Indonesian state-owned company INHUTANI I was the implementation agency in the field. The study area is located in the Indonesian province of East Kalimantan. The INHUTANI I concession was mainly covered by primary and logged lowland mixed dipterocarps forest. Two sites, 1000 ha each, were selected. On the first site (RKL 1), logged in 1978-1979, six plots, 4 ha each were set up. On the second site (RKL 4), covered by primary forest until 1991, 12 plots, 4 ha each were set up. In the plots, all trees with dbh _10 cm were measured, numbered, and mapped on a scale of 1:200. Other important physical features such as topography and soil were also assessed in each plot. Two different silvicultural treatments (chemical thinning) were tested in RKL 1. Reduced-impact logging techniques (RIL) were applied and compared to conventional ones in RKL 4. Four treatments were defined: two RIL, with two different diameter limits (>50 and >60 cm), one conventional and a control without harvesting. Reduced-impact logging techniques included planning of skid-trails before logging, directional felling, and climber cutting three months before logging.

On the nine harvested plots in RKL 4 the mean felled volume was 87 m3/ha with large differences between plots. Mean extracted commercial volume was 46.6 m3/ha, giving an average ratio between the felled volume and the commercial volume of 53 %.

Sample of

STREK Results

Primary Forest

RKL 1, 1978 Cut

RKL 4, 1991 Cut

Mean annual mortality (% trees _10cm dbh)




Mean annual diameter increment (mm/year)


· All stands




· Dipterocarps species




Net annual growth of Dipterocarps (m3/year)


· Without harvest



· Reduced impact cut



· Conventional harvest




· With thinning




On average, logging damage was suffered by 40% of the original tree population. Skidding was the primary cause of mortality (up-rooting). This study clearly showed that logging damage to residual stands can be reduced significantly from 40-50% to 25-30% if several recommended improvements to conventional logging methods are implemented. Reduced-impact logging must include effective planning of roads, log landing, directional felling, and optimization of skid-trail network based on topographic maps and tree location. Close supervision and the employment of well trained and responsible staff are also important conditions to success in low-impact harvesting. The database created by STREK includes more than 30000 trees with dbh _ 10 cm measured every two years. Three measurements carried out in RKL 1 and four measurements in RKL 4 have provided important basic information on forest dynamics.

This database is the largest one in Indonesia. The continuity in the monitoring of these 30000 trees will provide valuable information for forest management applications. The growth and yield data analysis will improve our knowledge of forest regeneration after logging. All the basic information, such as logging intensity, damage area, topography, soil characteristics, crown form and tree position coordinates, has been recorded for the plots. The availability of these data will allow analysis of interactions between physical and biological features.

During the last workshop of the STREK project, held in Jakarta, 25-27 June, 1996, the main results were presented to the national and international scientific community. The proceedings, which aim to be the synthesis of a six year forestry research project, will be published in 1997. For more information contact Plinio Sist, CIFOR, PO Box 6596 JKPWB Jakarta 10065 Indonesia, Fax: +62 251 326 433, Tel: 343 652, Email:, or Jean-Guy Bertault, CIRAD-Forêt, Programme forêt naturelle, BP 5035, 34032 Montpellier, France, Fax: +33 67 59 37 33, Tel: 67 59 37 61, Email:

Tropical Forest Damage Study, Indonesia

This study analyzed the productivity, costs, and environmental impact of conventional and reduced impact wood harvesting with the Indonesian Selective Cutting and Planting system (TPTI). The study was carried out in natural tropical in East Kalimantan, Indonesia. Both harvest methods used the same equipment and operators and were conducted in the same general forest area. Felling was conducted with chainsaws and skidding with a crawler tractor. Time studies were conducted for felling, skidding, bucking, loading, hauling, and unloading activities to assess timber harvesting performance, productivity, and costs under comparable conditions of conventional and reduced impact timber harvesting. Environmental impact assessments were done for the felling and skidding operations.

Some impact results

Method of Harvesting



Reduced Impact

Residual stand damage by stage of vegetation (%)

· Seedlings

· Saplings

· Poles and trees









Tree damage based on injury size (%)

· Light and medium injury

· Heavy injury





Opened areas (%)

· Caused by felling

· Caused by skidding





The comparison of production costs shows no significant difference in cost between conventional and reduced impact harvest methods.

Actions recommended as a result of this case study:

Skyline yarder, East Kalimantan, Indonesia

· Promote the implementation of reduced impact timber harvesting systems in the natural tropical forests.

· Develop local codes of practice based upon the FAO Model Code of Forest Harvesting Practice.

· Regularly conduct training for chainsaw operators, tractor operators, felling and skidding foremen, timber harvesting supervisors, and planners.

· Improve payment/salary systems, e.g. tariff system based on work quality, quantity, and site conditions.

· Further studies on reduced environmental impact harvesting in tropical natural forests, e.g. alternatives to extraction of logs by crawler tractors on steep slopes, namely on skyline cable systems and aerial systems.

This paper will be published as a FAO case study in 1997. For more detailed information contact Elias, Bogor Agricultural University, Indonesia.

A Strategy that Protects Tropical Forest by Making Use of Them

Precious Woods, a six year old mainly Swiss financed corporation, reports that it promotes the wise utilisation of forest resources in Latin America. By producing tropical forest products in accordance with sustainable forest management methods, the company simultaneously achieves three goals. 1) It generates profits for the benefit of the shareholders. 2) In recognition of the fact that the overall value of tropical forests is constantly increasing, the forests are managed to conserve a sound ecosystem, instead of being converted to more immediately profitable use for agriculture or buildings. 3) The company encourages the transfer of technology and know-how, creates earning opportunities in rural regions, and generally contributes to real sustainable growth in developing countries.

By integrating economic, social, and ecological criteria into a "symbiotic" process, Precious Woods hopes to achieve its objective of conserving tropical forests by making use of them. Central to the concept is the idea that forest management must prove its ability to create greater potential value than any competing use of the land occupied by primary forest. The value of the forest products harvested must therefore be great enough to prevail against any efforts to replace forests for economic reasons. Precious Woods hopes to demonstrate that sustainable forest management is economically feasible; indeed that tropical timber products have a strong appeal in world markets and can be profitable for all concerned.

In northwestern Costa Rica, Precious Woods reforested roughly 2000 ha of cleared, partially damaged, and abandoned land. By the year 2010 the company expects to have reforested a total of 12000 ha with various species of precious wood while avoiding industrial scale monocultures.

In Brazil, the inventory of each annual coupe of 2000 ha includes all relevant data such as species, diameter, geographic location, and silvicultural condition. Each measured tree is numbered and marked.

Timber Cutting for Cable Operations, Indonesia

An October 1996 article in Asian Timber by Ed Aulerich emphasizes the quality of timber cutting needed in cable operations. No logging system is more affected by the quality of the cutting than cable logging, especially in partial-cuts. Every effort should be made in the felling process to align the log in such a way as to facilitate the yarding activity.

There are many reasons for controlling the direction of the fall of a tree. With cable logging operations, the reason is to increase the production of the yarding operation and reduce damage to the residual stand. The basic guideline to follow is that before the timber is felled, the yarding system and the direction of yarding must be known so that the best cutting solution can be applied to the conditions at hand. This is especially important for partial-cut units. Cutting should never be conducted without considering the effect on the yarding.

With some species it is very difficult to practice "directional falling." In the tropical forests, some of the major problems are due to the vines that grow in the trees and tie throughout the forest canopy. These vines can change the direction of tree fall even though a major effort has been made to control the direction of fall. Another condition encountered in the tropical forests is the structure of the tree. Large trees often have large buttresses that fan out at the base. These in themselves are not the primary problem, but the fact that the central core of the tree becomes smaller closer to the ground reduces one of the most important factors for controlled falling, which is called "holding wood." Holding wood is the part of the trunk of the tree that breaks after the tree is started in its direction of fall. Holding wood helps control the direction of fall. In tropical hardwoods, such as Meranti, the holding wood can be very small thus losing the ability to help control the fall.

Cutting is an art form that requires experience by the cutters as to how the tree will react. However, even experienced cutters should be aided with tools that will enable them to do a better job. Operations in East Kalimantan have shown that improved control is possible by using simple wedges and hydraulic jacks to control direction of fall. Experienced cutters, using all available tools, will do a better job of falling, which will improve the yarding.

Some guidelines to improve felling and bucking activities:

· Impress upon the cutting crew that just dumping the tree may be adequate for tractor operations (really, it is not!) but it is unacceptable for cable operations.

· Train the cutters in directional falling techniques such as the use of wedges and jacks.

· Provide the necessary tools to do directional falling.

· Adjust the pay rate to reflect the additional effort required to do directional falling. The additional expense will be recovered many times over in reduced yarding costs.

· If the cutters cannot be convinced of the importance of good cutting to the yarding, transfer them to the yarding crew and make them yard what they cut.

In summation, cable logging requires close coordination of all activities for the operation to be successful and cutting is only one of them. There must be good planning and equipment selection. The roads must be located in the right place. The cutting must service the yarding by 1) putting the trees into the right spot and 2) bucking the trees into the correct lengths to be yarded. Contact: FEI, 620 SW 4th, Corvallis, OR 97333, USA, Fax: +1 541 754 7559, Email:, URL:

Workshop on Methods for Research in Reduced-Impact Logging

With assistance from FAO, USAID, and the USDA Forest Service, CIFOR (the Center for International Forestry Research, Bogor, Indonesia) held an international training workshop 14-27 July which was aimed at young scientists working in natural forest management research. The purpose of the workshop was to provide training in techniques for planning, designing, conducting, and analysing research on reduced-impact timber harvesting and other aspects of natural forest management.

Seventeen participants took part in the workshop. Although the focus of the workshop was on Southeast Asia, one scientist each from Africa (Ghana) and Latin America (Bolivia) was included in order to build expertise for future workshops in those regions. Asian participants were drawn from Indonesia, Malaysia, Myanmar, the Philippines, Taiwan, Thailand, and Vietnam. The participants are employed in the private sector, universities, national research institutes, and a government forest management agency.

Chief instructor for the course was Francis E. Putz, CIFOR senior associate and professor of tropical forestry and botany at the University of Florida. Other instructors were Rudolf Heinrich (FAO, Rome, Italy), Elias (Bogor Agricultural University, Indonesia), Leonard A. Newell (USDA Forest Service, Honolulu, Hawaii), and CIFOR scientists Plinio Sist, Andrew Gillison, Ravi Prabhu, and Dennis Dykstra.

Throughout the workshop, field exercises were integrated with classroom activities, first in the experimental forest plantation near CIFOR's new headquarters building and later at an industrial timber concession in East Kalimantan.

Each participant was required to plan and carry out a one-day field experiment on a subject of his or her choosing. Upon returning to Bogor, each student then analysed the data with statistical software, presented the results orally, and prepared a brief written report.

The written reports have been compiled into a workshop document published by CIFOR under the title Research Methods for Reduced-Impact Logging: Workshop Results. Obtain copies from D. P. Dykstra, DDG-Research, CIFOR, P.O. Box 6956 jkpwb, Jakarta 10065, Indonesia; fax +62 251 326433 or 622100, e-mail

Forest worker fatigue

Manual forestry work worldwide is a job requiring moderate to heavy physical workloads. The work is often carried out in harsh environments and in close proximity to potentially dangerous equipment and situations. Fatigue may not only reduce the amount and quality of work but may also affect the ability of workers to counter unexpected hazardous situations. By implementing a few easy changes to diet and work practices, a worker's physical performance, endurance, safety, and productivity can be improved. Some example recommendations:

· Have a good breakfast.

· Drink small amounts of water frequently throughout the day. The recommended intake rate for workers doing hard physical labor is one litre per hour. Endurance can be reduced by 50% by losing and not replacing three to four litres of fluid.

· Use a simple five minute warm-up session to reduce strains, sprains, and pulled muscles.

· Use at least two evenly spaced 30 minute rest breaks during the working day.

LIRO Report, Vol. 21, No. 3, 1996, Reducing the Impact of Fatigue on Forest Workers by Patrick Kirk,

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