The following points highlight the three main methods of logging. The methods are:- 1. Felling 2. Mechanized Harvesting Systems 3. Reduced Impact Logging.
Forest management concepts have changed over years from production forestry to conservation forestry and sustainable forest management. Yet logging is a very important aspect in forestry and forest management. There is one school of thought that the only way to prevent forest depletion is to discard all forms of timber extracting practices. Other feels that if the timber production stops, the economic value of forests diminishes and forest land would be diverted for more profitable and productive options.
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In between these two are some who believe that forests could be sustainably utilized. Logging is a very important economic activity in the temperate regions and tropical regions. Timber is an important economic product that contributes to the State exchequer. Hence it is very essential to understand logging operations and how best they could be carried out without resulting in depletion and degradation of our forests and forest resources.
Logging generally refers to the process of felling and extracting timber from the forests. In forestry, the term logging is sometimes used in a narrow sense where it refers to the log making only and consists of trimming off the branches, debarking and cutting into sections. In some instances, logging is used to refer to the whole logistics of moving wood from the site of felling to somewhere outside the forest, usually a saw mill or a depot from where it is further disposed.
However, the term may be used to indicate a range of forestry or silviculture activities including the felling, on-site processing, extraction and transportation to saw mills or storage depots. Logging is distinct from timber harvesting in the sense that the latter includes all the stages of harvesting starting from pre-harvest planning to harvest, technical supervision and post-harvest assessment and even the impact of the operations on the non- timber forest resources and the state of forests.
Since logging is a very broad term, there is an array of methods which may be considered under the purview the term logging. The method adopted normally depends on the nature of forests, topography, accessibility, the local conditions, the technology available, etc. Logging is an age old practice. In the earlier part of the century, it was completely a hand process where trees were felled by axe and transported by sledges or carts or drawn by oxen, horses, mules or floated down river.
Conventional logging operations were done manually with saws or chain saw where are the trees are felled followed by delimbing and topping. Bucking into log lengths, skidding to a landing, sorting the logs for specific products or purposes and finally loading onto a truck or trailer or removed with the help of animal power are the other important operations in timber harvesting.
Several variations of this system are followed depending on site conditions and season. For example, the most popular method of transport of timber during the monsoon season in the mountainous regions is to float it on water where as in high altitudes and steep slopes a skyline may be much preferred.
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The conventional logging systems have as much potential for low site impact as any alternative system if operators are trained and careful measures are taken. In fact, conventional logging systems using smaller skidding machines cause less damage to remaining trees and have lesser impact on the soil.
The process from the ‘tree to mill’ can be broken down into 5 phases or five minor operations viz. the felling, processing, extraction, loading and transportation to saw mills or storage depots. Every phase has a set of operations that leads to the other and the whole series of operations starts from the standing tree.
Method # 1. Felling:
Felling refers to cutting trees at the stump level or severing the tree from the stump and bringing it to the ground. Trees are felled to recover the log or timber volume and value. Historically this was carried out with an axe or saw or both. Throughout the major part of the Indian forests, felling is done by axe but the use of axe and saw combined is also practiced widely. The felling axe is usually made locally, the weight of the head varying from 0.7 to 1.8 kilograms.
Felling is carried out by a team of two or more workers. Stumps are very often high up to 60 centimeters for ease of working. The most commonly used tools for felling and crosscutting are two-man manual crosscut saws with peg teeth. Later on came the chain saw which increased a person’s efficiency to fell the trees. The process became much faster while using chain saw and the wastage produced while using an axe was considerably reduced.
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The system of felling can also be categorized as monocyclic logging and polycyclic logging. In monocyclic logging, the entire growing stock is removed in a single operation (clear-felling or clear-cutting) and the interval between two felling operations is typically equal to the maturation period of the main species of trees felled, the so-called rotation period. This may be as long as 60-80 years in natural forests.
Monocyclic logging removes not only mature but also semi-mature trees and hence a relatively large proportion of the forest may be affected. The volume of timber removed during monocyclic operations is very high as 120 m3 per ha in certain forests where as in polycyclic the harvested volumes are around 60 m3 per ha. Such intense logging creates large gaps in the canopy and the potential for damage to both soil and remaining trees through monocyclic logging is relatively high.
Polycyclic logging is the selective removal of only the largest individuals of desirable species. The objective is to wait for a sufficient number of trees to reach maturity and then to remove them Compared with monocyclic logging, fewer trees and a lower volume of timber are harvested, but the intervals between harvests are shorter. Volumes of wood removed are typically 20-30 m3 per ha per coupe.
Disturbance to the forest flora and fauna occurs more frequently than under monocyclic cutting regimes and the amount of damage caused to the overall forest is, theoretically, considerably less for each operation due to the smaller amounts of timber being extracted. As smaller gaps are created, polycyclic logging alters the forests less and most forests in tropical regions are logged under some form of polycyclic system.
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This system is much similar to the selection felling where selected trees above a certain DBH are removed. In certain cases, only the dead and diseased trees are removed and are referred to as salvage felling where felling is restricted to the trees or the forest areas that have been damaged by wildfire, flood, severe wind, disease, insect infestation or other natural disturbance.
The three common timber harvesting methods are:
i. Tree-Length Logging:
Trees are felled and then delimbed and topped at the stump. The log is then transported to the landing, where it is bucked and loaded on a truck. This leaves the slash (and the nutrients it contains) in the cut area.
ii. Full-Tree Logging:
Trees and plants are felled and transported to the roadside with top and limbs intact. The trees are then delimbed, topped and bucked at the landing.
iii. Cut-to-Length Logging:
It is the process of felling, delimbing, bucking and sorting (pulpwood, sawlog, etc.) at the stump area, leaving limbs and tops in the forest.
Manual felling is performed by a person with a chainsaw. Professional chainsaws range from 3 to 9 hp and can be equipped with various bar lengths to allow cutting a tree of any diameter. The important tools that may also be carried are axe, wedges, saw fuel and oil, first- aid kit, fire extinguisher and tools for minor repairs. Special tools such as jacks and felling levers have been designed to aid manual fellers in directing a tree’s fall. Manual felling is the most dangerous task in timber harvesting and proper training and experiences are required to minimize the risk of injury.
To cut a tree, the person must first evaluate a number of factors including lean, desired direction of fall, distribution of the crown weight, presence of any defects in the stem and anything else that may affect the dynamics of the falling tree. In manual felling of trees, four important points are considered: direction of fall, undercut, back cut and holding wood or hinge wood.
i. Direction of Fall:
The feller has to decide which direction the tree has to fall. The tree’s height should be the major determining factor when deciding where you want it to fall. It should be made sure that clear spot is present with no obstacles in the way. Any branches which can disturb the direction of fall should be cut down. Branches that are not too large should be cut down. A rope to the top of the tree may be tied to help it fall in the preferred direction.
ii. Undercut:
After clearing around the tree and locating an escape path, the expert makes an undercut (face cut), and a back cut. The face cut/ undercut is a wedge-shaped cut that opens in the direction the tree is intended to fall. Undercut will be a V-shaped notch into the tree. After cutting, the notch should fall out. The undercut should be 1/3rd to 1/4th of the tree’s diameter.
The two cuts meet at the apex of the angle and neither cut bypasses the other. Along with controlling the direction of the fall, the undercut also allows the tree to slide rather than jump off the stump. Various forms of undercut have been developed for different types of felling applications.
iii. Back Cut:
With the undercut wedge removed, the feller is ready for the back cut. Back cuts are designed to release the wood that holds the tree from falling over the undercut. This is a horizontal cut usually 1 to 3 inches above the face cut that is on the opposite side of the tree. Saw or chainsaw blade should be held parallel to the ground and horizontally sawn into the trunk. Wedges are used to prevent the tree from sitting back on the saw blade.
iv. Hinge Wood:
The narrow strip of wood (holding wood) between the undercut and back cut is the hinge that controls the fall. While sawing, it should not be cut all the way through. Instead a hinge is left of about 1 inch (2.5 cm) or 10 per cent of the diameter of the tree. The hinge will stop the tree from immediately falling down, giving the feller a chance to get out of the way. The feller can “push” a tree to fall in direction other than way it is leaning using wedges or jacks.
In high-value timbers, it is important to minimize breakage during falling. Leaving low stumps, avoiding dropping trees across rocks or other obstacles and properly placing the cuts are necessary skills for timber fellers. Studies of manual felling productivity have found that the average time to fell a tree is affected by tree spacing, tree diameter and slope.
Method # 2. Mechanized Harvesting Systems:
Mechanized harvesting systems have taken over the conventional systems especially where the growing stock is uniform and even aged. The level of mechanization varies from low level to high level where felling and processing are done using highly specialized equipments and machines.
High efficiency is the often quoted advantage of using machines in logging. There are three basic types of mechanical felling machines. Single-function machines are only capable of directionally felling a tree, while dual-function machines (called feller-bunchers) are able to fell a tree and move the cut stem to a pile. There are also multifunction machines (called harvesters) that can fell, delimb, buck and place the processed pieces. Mechanized felling is faster and safer than manual felling.
For example, a shear feller-buncher can fell a tree in 3 to 6 seconds compared to 30 and 90 seconds for a person with a chainsaw. Feller-bunchers are capable of felling and bunching upto 200 trees per hour in favourable conditions. Manual felling cannot maintain steady levels of productivity comparable to mechanized felling. Mechanization has certain advantages and disadvantages.
Advantages of Mechanized Logging:
i. High Efficiency in harvesting trees especially smaller trees
ii. Wide applicability in commercial thinning
iii. Reduced residual stand damage due to controlled felling and proper placement of felled stems.
iv. Higher wood utilization due to lower stump height
v. Safely used in weather and lighting conditions that are unacceptable for manual cutters
vi. Improved safety
vii. Use of improved and modern techniques
Disadvantages of Mechanized Logging:
i. Very high initial and operational costs
ii. Soil disturbances
iii. Potential wood damage with shear-type cutters
iv. Stability limitations on steep slopes
v. Equipment utilization needs technical knowhow and skill upgradation of the persons
vi. Tree stem size and terrain could be major limitations
vii. Mechanization may not be feasible in all types of forests
Various mechanized harvesting systems and methods are practiced depending on the form in which the wood is delivered, the terrain, the size of the trees, etc. Harvesting systems refers to the whole set of tools, equipments and machines used to harvest an area where as the harvesting methods or logging methods refer to the form in which wood is delivered to the main access road and the amount of processing (e.g. delimbing, bucking, debarking, chipping) which occurs after felling. The different harvesting equipments are described under felling, extraction, processing and loading.
Logging Operations in Tropics:
Though timber is one of the major sources of revenue for the Government, unlike in temperate regions, timber operations are less mechanized and organized in tropics. This is partly due to the nature and type of vegetation and partly due to easy availability of human labour. Even aged uniform forests of single species is characteristic of the temperate regions, where as in the tropics the forests are mainly non-uniform and uneven aged with multi layers of vegetation and varied species.
In spite of the high biodiversity and high biomass in the tropical forests, the volume of merchantable timber per unit area is much lesser than temperate forests. The volume of timber harvested per hectare of tropical forest worldwide is less than 30m3 and involves usually 10 or less than 10 trees of different species where as a typical coniferous forests yields nearly 500 m3 of timber per ha from 200-300 trees of the same species.
Since the volume of merchantable timber per unit area is lesser, more area needs to be worked to meet the timber requirement resulting in construction of more number and additional length of roads. Extensive areas get disturbed and though the impact on unit area basis is much lesser than temperate forests in the tropics, logging results in greater total impact in the tropics.
In spite of the fact that the total biomass removed per unit area in tropical forests is much lesser when compared to the temperate forests, since it is spread over extensive areas and the damages to vegetation and soil are more in the tropics. Logging becomes an issue of major concern in the tropics.
Method # 3. Reduced Impact Logging:
At the United Nations Conference on the Environment and Development convened at Rio de Janeiro in 1992, concerns were raised about the mechanized logging and its impacts on the long term sustainability of forest resources. At about the same time, the term low impact logging was introduced by the Tropical Forest Foundation. But the term was contradicted by many experts since they claimed that logging can never be of low impacts.
In 1993, when the term Reduced Impact Logging (RIL) came into usage denoting the ‘environmentally sound timber practices’, it was widely accepted and has gained great attention. The term has even become interchangeable in the vernacular with timber harvesting. RIL is not an entirely novel idea. It is nothing but a systematic approach to planning, implementation, monitoring and evaluation of harvesting techniques.
Though most of the RIL technologies have been developed in the temperate regions due to the heavy mechanization there, it has substantial potential in the tropical regions also and code of practices for forest harvesting are prevalent in many of the counties in the temperate and Asia-Pacific regions.
Reduced impact logging can be defined as the intensively planned and carefully controlled implementation of timber harvesting operations to minimize the environmental impact on forest stands and soils (ITTO).
It generally requires the following practical measures:
i. A pre-harvest inventory and the mapping of individual crop trees
ii. The pre-harvest planning of roads, skid trails and landings to minimize soil disturbance and to protect streams and waterways with appropriate crossings
iii. Pre-harvest vine-cutting in areas where heavy vines bridge tree crowns
iv. The construction of roads, landings and skid trails following environmentally friendly design guidelines
v. The use of appropriate felling and bucking techniques including directional felling, cutting stumps low to the ground to avoid waste and the optimal crosscutting of tree stems into logs in a way that maximizes the recovery of useful wood
vi. The winching of logs to planned skid trails and ensuring that skidding machines remain on the trails at all times
vii. Where feasible, using yarding systems that protect soils and residual vegetation by suspending logs above the ground or by otherwise minimizing soil disturbance
viii. Conducting post-harvest assessment in order to provide feedback to the resource manager and logging crews and to evaluate the degree to which the RIL guidelines were successfully applied.