Previous - Next
What it
is
Guiding
principles
Objectives
Potential consequences of improper cutting
operations
Recommended
practices
Cutting includes all activities undertaken to fell standing trees and prepare them for extraction. In some regions this set of activities is referred to as "felling." Cutting activities include felling the standing tree, measuring its length to determine the best log lengths, removing the limbs and crosscutting the stem (and sometimes also large limbs) into logs. Removal of bark from the stem, when done, is also considered part of the cutting operation.
Cutting is among the most hazardous of all industrial occupations. Trees are large, heavy objects, and fall with a tremendous force that can smash or uproot neighbouring trees. Their limbs may break off and fly in unpredictable directions. The felled tree may roll or slide downhill, and its stem may shatter into pieces that can bounce into the air and roll uncontrollably. In felling operations, therefore, much emphasis must be placed on safety and training.
Since cutting, when properly done, approximately mimics natural tree falls, it is often considered to be a relatively benign operation from an environmental perspective. In mixed broad-leaved forests, however, especially in the tropics where tree canopies tend to intertwine and are often tied together by climbers, damage to residual trees and seedlings caused by felling can be so extensive that it hampers the attainment of the silvicultural objectives associated with harvesting operations.
Cutting operations in developing countries are often performed by poorly equipped and unskilled workers who have had little or no training, are not closely supervised and are given little incentive if any to minimize damage through carefully controlled directional felling. In addition to causing excessive damage to advance regeneration and residual trees, uncontrolled felling can also substantially reduce efficiency in the subsequent extraction operation. In comparison, directional felling can reduce damage to both vegetation and soils, keep trees away from streams and increase the utilizable volume of the tree stem by reducing breakage. It can also help reduce the frequency and severity of accidents associated with felling operations. High priority, therefore, should be given to measures aimed at improving the skills of workers in felling crews and at providing incentives that will promote good practices.
Properly conducted cutting operations should:
- ensure the safety of cutting crews and other personnel working
in the vicinity of the cutting operation;
- minimize damage to residual trees and seedlings, especially
those that are expected to make up the population of future crop
trees;
- minimize damage to soils and streams;
- maximize the volume of wood that can be profitably utilized
from each felled tree;
- maximize the value of the logs prepared for extraction;
- facilitate extraction activities.
Potential consequences of improper cutting operations
Improper felling operations may result in:
- a poor safety record and high insurance or compensation costs;
- high cutting costs;
- low utilization rates;
- low profitability from improperly crosscut logs;
- inefficient and costly extraction due to the haphazard
placement of tree stems rather than their correct alignment with
respect to extraction routes;
- excessive damage to residual trees and seedlings;
- excessive damage to soils and streams;
- poor postharvest condition of the forest that does not meet
silvicultural objectives;
- infestation of the site by pioneer species or vines.
Crosscutting a felled tree into logs.
- In cutting operations, the first consideration must always be safety. This implies that all members of the crew must be in good health and that continuous training and close supervision are essential. Details of safety and health aspects of felling operations and other forest work are provided in publications such as Chainsaws in tropical forests (FAO and ILO, 1980) and Fitting the job to the forest worker (ILO, 1992).
- Cutting must only be done by competent personnel outfitted with appropriate safety gear and using properly maintained equipment. Most cutting worldwide is done with chainsaws. These are inherently dangerous tools that are easily mishandled by persons not thoroughly acquainted with their proper use. By far the largest number of logging accidents occurring annually are associated with chainsaws.
- In some areas, manual tools such as crosscut saws are still commonly used in cutting operations. Properly used and kept in good condition, these are perfectly good tools that can be far more cost-effective in many developing countries than chainsaws. Even such simple tools can be very dangerous, however, and their use requires proper training and supervision.
- There are very few situations in which axes or other chopping tools can be used efficiently for felling or crosscutting trees. Such use causes an enormous waste of wood. Axes are excellent tools for removing limbs and cutting underbrush, but they should not be used for felling or crosscutting. Any perceived savings from such use are purely illusory. Saws, which produce only a thin kerf of sawdust, are always preferable to chopping tools, which inevitably convert a large volume of usable wood into chips.
-Where selection harvesting is being used, trees to be harvested should be marked before cutting begins. The detailed harvesting map prepared during the planning stage should be taken into the field and used to help decide which trees are to be removed. This information should be noted on the map for use by the harvesting crews.
- The recent experience of several organizations working to develop low-impact harvesting systems for tropical forests suggests that damage to residual trees can be reduced by also marking those trees that are expected to form part of the future crop tree population. Doing so provides visual reinforcement for the felling and extraction crews concerning those trees that should be protected whenever possible.
- In forests where climbers tend to bridge across tree crowns, the climbers should be cut well in advance of the cutting operation so that they will die and become brittle. This reduces the chance of a felled tree pulling over neighbouring trees as it falls. Climber cutting can often be done at the same time as the trees are being marked for felling.
- The planned direction of fall should be indicated on the bole of each tree to be harvested. In general, trees should be felled either towards or away from skid trails or cableways, preferably at an oblique angle to the skidding direction (between 30° and 45° is often suggested as the "optimal" angle range unless trees can be felled directly on to the skid trail or cableway). Felling away from the skid trail or cableway will reduce problems for the extraction crew when tree crowns are large, but felling towards the skid trail or cableway can reduce the extraction distance substantially. The decision whether to direct trees towards or away from the skid trail or cableway will depend upon local experience, terrain conditions and the type of logging system being used as well as other factors.
- Where possible, trees should be felled in the direction of existing canopy gaps in order to reduce damage to nearby standing timber. Trees near a skid trail or cableway should be felled so that their crowns fall alongside the skid trail or cableway for easy extraction.
- It is often desirable to direct the tree being felled towards the crown of another tree that has been felled previously. This cushions the impact, reduces the area of forest damaged and helps bunch the logs to improve skidding efficiency.
-On steep slopes, trees should not be felled directly down the slope unless their downhill lean is so great that directional felling techniques are unable to pull the tree into another direction. Felling laterally across the slope or along the contour will reduce the tree's momentum and thus minimize breakage of the felled tree and damage to neighbouring trees. To prevent a tree from rolling downhill after it has been felled, it should be lodged against the uphill side of a nearby tree if possible. This is likely to damage the second tree, but the total damage should be substantially less than the destruction that could be caused by the felled tree's crown if it were to roll or slide down the steep hillside.
- Where social conditions and the size of trees permit, the use of felling or integrated harvesting machines can greatly increase felling productivity and, at the same time, substantially reduce the frequency and severity of accidents. Because of their high cost and the requirement for trees of nearly uniform size, in practice, the use of such machines is currently limited primarily to industrial plantations or to natural stands of smaller trees. They can be used effectively either for clear-cutting or for selection harvesting.
- Whenever possible, trees selected for felling within streamside buffer strips, where this is permitted, should be felled so that their crowns fall outside the buffer strip.
- In general, trees should not be felled across streams. In some countries, in fact, it is prohibited. There are instances where this may be the best option, however, because of terrain and safety considerations. When trees are felled across or into streams, extraction must be undertaken carefully in order to minimize damage to stream banks and streamside vegetation.
- To maximize the volume and value of wood recovered from each tree, cutting crews should be trained to follow proper crosscutting procedures. This requires that the entire bole be measured prior to crosscutting and that log lengths be determined according to mill requirements. The experience of training programmes to improve crosscutting skills suggests that improved utilization of 20 percent or more and increased log values of 10 to 50 percent can be attained by such training.
-Special safety precautions must be taken whenever there is a possibility that members of the public or other persons not directly involved in the felling operations might be endangered. When felling is to be done near roadways, for instance, it is essential that a flag bearer be posted on the road to halt traffic until the tree has been safely brought to the ground.
-A large proportion of tree nutrients, especially in tropical forests, reside in the bark and foliage. Removing the limbs and bark at the felling site will thus leave nutrients in the forest, contributing to improved growth in the new crop of trees. However, it is not always practical to remove the bark at the felling site; this will depend upon labour costs and the ease with which the bark can be separated from the wood. Also, for some species, the bark may be needed to help protect the log from abrasion or the wood from insect and fungal attack, or to prevent the log from splitting as a result of drying out while being stored prior to processing.
