At present, a large variety of logging systems can be found in the Amazon and elsewhere in the tropics. The “worst-case scenario” described in this section, which is commonly known as “conventional” or “traditional” logging, is unfortunately still very common in the Amazon region, although improved practices are gradually being adopted throughout the region.
In the conventional system, timber companies buy timber from private owners, typically small farmers or settlers. The price is usually fixed through a stand evaluation performed by a consultant hired by the timber company. Commonly the price is very low because the landowner perceives little value from the trees and is generally more interested in having the land cleared than in receiving significant income from the harvest.
Felling operations usually are performed by poorly equipped and unskilled workers, who in many cases are only hired for a single job. Their remuneration depends only on the volume felled, with no reward for careful work or for the application of special techniques such as directional felling. Little care is taken for the residual stand, as in many cases the landowner will burn the remaining trees after the harvesting operation has been completed in order to clear the land for agriculture or pasture.
After felling has been completed, a bulldozer typically opens a path to the centre of the area and also clears landings at roadside where logs can be accumulated for loading onto trucks. The Logging operation is usually carried out with little or no advance planning. The operator of the skidding machine often has canopy openings as his only guide when searching for felled logs. Each log is removed to the landing by the most convenient route, regardless of the amount of vegetation that might be destroyed or the soil that might be disturbed. This unplanned searching and skidding often results in a dense network of skidtrails. Winkler (1997) reported that about 19% of the overall area was occupied by skidtrails in Plot B/F09, where conventional logging was done. Other authors have reported even higher degrees of disturbance, with skidtrails occupying as much as 40% of the forest area in steeper terrain or where the density of harvested timber is higher (Moura-Costa 1997).
Typically, after conventional logging has been completed a high percentage of utilisable timber remains in the forest, even in areas where the landowner's intention is to clear the remaining stand for agriculture or pasture. This is because the harvestable trees are not mapped in advance, so the felling crew may miss trees that could be commercialised. In addition, because the operator of the skidding machine typically has little or no contact with the felling crew, logs that have been prepared for extraction by the felling crew may be missed by the skidder and left to rot in the forest.
The forest harvesting system used by PWA is based on the CELOS System described by de Graaf and Poels (1990). PWA's local implementation of this system has also been influenced by the selective cutting system formulated for the Amazon region by Higuchi et al. (1991). The basic principles of this system, as implemented by PWA, are as follows:
A complete inventory is made of all areas to be harvested, either now or at some future date, to provide basic information for planning the application of silviculture and harvesting activities.
Harvesting is undertaken in a manner designed to reduce environmental impacts to the minimum, and to maintain ecosystem integrity.
The harvesting system is polycyclic, with a cutting cycle of 20–30 years depending on site quality and the harvesting intensity (i.e., the relative volume of extracted wood per hectare as compared to the volume left standing).
Forest compartments are embedded in a permanent infrastructure of multi-purpose roads.
The basis for preserving forests for long-term sustainable production of forest products system is careful and comprehensive planning. With PWA, this is done through a general management plan and a tactical operating plan.
The General Management Plan covering the entire PWA ownership identifies non-production areas such as preservation zones, watershed protection sites, and areas of non-forest land use such as dominions of the settlers who live within the PWA area. The remaining production forest area has been divided into compartments that define annual operating areas. These have been delineated to meet the annual input requirements of the sawmill, between 60,000 and 80,000 m3 of logs. Geographic details of the general management plan are shown on a Forest Management Map drawn to a scale of 1:20,000. The map is based on aerial photographs and includes information such as existing and planned roads, elevation contour lines, forest cover, and compartment locations. The general management plan covers a harvesting cycle of 25 years and is updated every 5 years.
The Tactical Operating Plan for one compartment is associated with the annual operating area and provides operational details that are to be carried out during one year. Each compartment consists of about 2000 hectares of production forest and up to 800 additional hectares of non-production areas. The non-production areas include buffer zones around rivers and water springs, where harvesting is prohibited by Brazilian law up to a distance of 50 m, as well as steep land with slope gradients above 45% where harvesting and skidding is considered impractical. The compartments are subdivided into cutting units of 10 ha that form the smallest administrative units1. During the establishment of cutting units the locations of landings and skidtrails are planned as well.
Forest roads are built at least one year before the start of any harvesting operations, and a terrain reconnaissance and forest inventory are also carried out, together with detailed mapping of the cutting unit. In addition to harvesting boundaries, the map includes all features that might influence the harvesting plan such as water courses, swampy areas, and slopes. In addition the map shows the location, species, diameter, and stem quality of each individual tree of commercial species.
The information obtained during the development of the cutting unit map is analysed to determine which trees should be harvested in relation to their species, diameter, stem quality, and spatial distribution within the cutting unit and compartment. This decision process considers the sustainability of forest utilisation as well as market acceptance of each species. Species that are considered rare within an operating area are not harvested.
A Harvesting Map of the cutting unit is generated from data obtained through the inventory and mapping process, produced by geographic information system software. This map shows the location of each harvestable tree and its selection status (i.e., whether or not it is to be felled). Features such as slopes, springs and rivers, and infrastructure are also shown. In addition the map shows the spatial distribution of trees selected as Potential Crop Trees (PCTs), about 25 trees per hectare of commercial species with diameters from 20 to 50 cm that are expected to be harvested during the subsequent harvesting entry. PCTs are given special attention during harvesting to ensure that they are not damaged.
The harvesting map provides basic information used for the layout of skidtrails. Field checks by the responsible forest engineer are undertaken to verify the feasibility of the layout. The harvesting map is accompanied with a file of information on all harvestable trees.
In an effort to optimise regeneration and ensure sustainability, no more than 80% of the trees of commercial species with DBH ≥ 50 cm are harvested. Rare species (less than 1 tree with DBH ≥ 50 cm per 100 hectares) are preserved in order to maintain the natural diversity of tree species. Harvesting intensity is limited to a maximum of 40 m3/ha in order to prevent excessive opening of the canopy and to minimise damage to residual trees.
All felled trees are marked on the harvesting map and their logs are identified individually with plastic numbers recorded on data sheets. The log number enables the permanent identification of each log until it is processed in the sawmill. Information from the felling data sheets is also used to ensure that no log is left in the forest during skidding operations.
As required under Brazilian law, the environmental impact of the harvesting operations is monitored through a series of 1 ha permanent sample plots established throughout the production forest at the rate of one plot per 200 ha.
Both the harvesting map and the file of information on trees to be harvested are taken to the forest by the felling crew. Before a tree is felled, an investigative cut is made into the stem with the chainsaw in order to detect hidden defects such as internal decay. If the tree is rejected due to internal decay or because of some other problem, an alternative tree is chosen in an effort to maintain the desired felling volume per species and cutting unit. Problems that might preclude felling a particular tree include poor form, the opening of a felling gap that would be excessively large (possibly because other trees have been felled nearby), interference with the spatial pattern of PCTs, or skidding difficulties that might be caused if the tree were felled.
The fact that the harvesting map accompanies the felling crew (and later the extraction crew) helps ensure that the field operations are attuned to both the Tactical Operating Plan and the General Harvesting Plan, even if alterations are necessary.
Felling operations are carried out by company-trained, experienced workers using chainsaws and related tools. The felling crews are equipped with safety gear and a full complement of felling and maintenance tools. Safety is monitored through close supervision, regular training, and careful selection of crew leaders. Crews are trained in directional felling and are taught to use these skills to minimise damage to residual trees and to improve efficiency of the skidding operation. Crew leaders are given a high degree of responsibility, as they make the final decision about whether a tree is to be felled and if so, its felling direction. In taking these decisions, the spatial distribution of PCTs, opening of the canopy that would result, effect on skidding efficiency, and potential damage to nearby residual trees are considered.
Each felling crew includes three members: a crew leader who operates the chainsaw part of the time, a main chainsaw operator, and an assistant. Chainsaws used at PWA are Stihl AV 066 models. In addition to a regular complement of felling and maintenance tools, the crew is also provided with a radio for general communications and for quick rescue in case of an emergency.
The typical productivity of a PWA felling crew is 80 to 100 m3 of logs per day, equivalent to 1500–2000 m3 per month. Felling all of the designated trees in a cutting unit of 10 ha usually requires four or five days.
Formerly, PWA's policy was to cut climbing vines (lianas) two years in advance of harvesting. This was done to minimise damage to residual trees when vines connect the crown of the tree being felled with the crowns of adjacent trees. In areas where large vines are common, cutting the vines well in advance of felling so that they die and become brittle may prevent nearby trees from being pulled over or broken when the harvested tree falls. On PWA's operation, however, tests showed that cutting vines in advance of felling had little effect and the procedure has therefore been abandoned.
In order to avoid unnecessary risks of accidents or mutual disturbance, skidding commences only after felling has been completed in the cutting unit and the felling crew has moved to another cutting unit.
Before extraction begins, skidtrails are opened by a Caterpillar D4H crawler tractor assisted by a chainsaw operator. The skidtrails are established in relation to local terrain features and aligned in accordance with the Tactical Operating Plan at an average spacing of about 100 m, in order to keep the maximal skidding distance of a log from the felling site to the skidtrail at 50 m. The width of the skidtrail is about 4 m. Any tree within the skidtrail and having a diameter larger than 15 cm is cut by chainsaw before the crawler tractor passes. The maximum gradient permitted on skidtrails is 45%. The length of an individual skidtrail to the nearest landing normally does not exceed 1200 m. Only occasionally, skidtrail lengths reach 2000 m when the forest road density is unusually low.
After the skidtrails have been opened, the crawler tractor is used to “pre-skid” logs from the felling sites to the skidtrails. During this process the tractor remains on the skidtrail while the winch line is pulled out to the logs by an assistant. The logs are then winched to a concentration point on the skidtrail. During this process the chainsaw operator assists by crosscutting big logs that are too heavy to be moved, and cutting smaller trees that inhibit movement of logs along the cableway. Signals between the tractor operator, the assistant who attaches the winch line on the logs, and the chainsaw operator are exchanged by means of simple whistles, as radio sets have proven unsatisfactory due to the noise of the tractor and the chainsaw.
The pre-skidding crew includes a crew leader who also operates the chainsaw, an assistant, and a tractor operator. All are equipped with safety gear. The productivity of the pre-skidding crew averages 2500–3000 m2/month, including opening the skidtrails.
Transport of logs to the landing is done by wheeled skidders equipped with grapples. The skidders never move off the skidtrails because logs have already been concentrated along the skidtrails during the pre-skidding process.
The skidding crew consists of a machine operator and an assistant. Each crew is equipped with a chainsaw in addition to the standard complement of tools and safety gear. Skidders used are Caterpillar 518C wheeled skidders with grapples. The productivity of the skidding crew averages 2500–3000 m3/month.
The general principles for the location and layout of landings are described in the General Management Plan and depend on the distribution of forest roads. Landings are orientated along the roads with an average spacing of about 500 m. Each landing has an area of about 0.2 ha.
The landings have three general functions. Firstly, three assortments are made: softwoods, hardwoods, and logs to be used for masts or breakwaters (e.g., Acaricuara). Secondly, the landings are used to store a certain volume of logs as a buffer to ensure a continuous supply of timber to the sawmill independent of delays in the extraction process. Thirdly, sorted logs are loaded onto company-owned trucks by a Caterpillar 966F front-end loader.
Long-distance transport from the landings to the sawmill is done with company-owned trucks, each of which has a load capacity of about 25 t. On average about 30 m3 of logs are transported per load, so the gross weight of the loaded truck may reach 50 t.
For an annual production of 80,000 m3 of roundwood, the following number of crews is necessary:
The harvesting crews of PWA use the following equipment:
All of the heavy machines listed above have been used since harvesting operations at PWA began and are still in good condition thanks to excellent maintenance. Table 4 gives an overview of the heavy machinery used in harvesting.
Table 4. Machines used for skidding and long-distance transportation.
| Activity | Machine type | Power, kW | Weight, t | Width, m |
|---|---|---|---|---|
| Skidtrail opening and pre-skidding | Caterpillar D4H crawler tractor | 70 | 10.4 | 2.2 |
| Skidding | Caterpillar 518 C | 117 | 11.5 | 2.4 |
| Loading | Caterpillar 966 F | 175 | 14.2 | 2.8 |
| Long-distance transport | Volvo NL 12 | 301 | 50 (loaded) | 2.6 |
Based on five years of continuous use, an effective lifetime of 10 years can be presumed for the machines listed in Table 4. The average lifetime of chainsaws is estimated as 4 or 5 years, as some of the original ones are still in use whereas others have already been replaced.
The “Strada de Várzea,” a public, year-round road, cuts through the PWA forest in a north-south direction for a distance of 30 km. According to the General Management Plan, 400 km of private forest roads will have to be constructed by PWA during the first harvesting cycle of 25 years in order to provide access from this public road to the entire forest area.
Although most of PWA's forest roads are designed to be used throughout the year, at certain sites this objective cannot be realised at reasonable cost. In such areas, the tactical operating plan recognises that roads will be unusable during extended rainy periods. During such periods, operations are concentrated in areas with all-weather roads.
Road construction activities are limited to the dry season and are performed by local construction companies under contract to PWA. Machinery owned by PWA may be used by the construction companies when appropriate. Forest road construction costs range from 5000 to 15,000 US$/km, depending on local terrain features and the frequency of streams.
After clearing vegetation to a width of 10 m and building the road base, a 10–15 cm layer of gravel is added to the 5 m running surface of the road. The roads are designed to support long-term traffic of loaded trucks travelling at average speeds above 30 km/h.
In addition to the 400 km of forest roads needed to access PWA's production forest area, another 5000 km of permanent skidtrails provide the necessary access for the harvesting operations. As an average over the entire PWA production forest, 52 m2/ha are or will be dedicated to forest roads and 400 m2/ha to skidtrails. Thus, about 5% of the production forest area is dedicated to infrastructure and the average forest road density is 6–7 m/ha, giving an average of 16 km of road per compartment.
Average costs for the different phases of harvesting are shown in Table 5.
Table 5. Operating costs of harvesting activities.
| Activity | Cost, US$/m3 |
|---|---|
| Forest inventory | 2.50 |
| Tree felling | 5.00 |
| Pre-skidding | 7.00 |
| Skidding | 5.00 |
| Transport to sawmill | 1.50/10 km |
