Forest Tending And Intermediate Cutting PDF

Learning objectives: Identify and discuss the theory of tending and intermediate cutting Apply the principle of tending and intermediate cutting on the field. TOPICS: I. Response of Individual Trees to Thinning and Pruning II. Management of Growth and Stand Yield by Thinning II...

Learning objectives: Identify and discuss the theory of tending and intermediate cutting Apply the principle of tending and intermediate cutting on the field. TOPICS: I. Response of Individual Trees to Thinning and Pruning II. Management of Growth and Stand Yield by Thinning III. Methods and Application of Thinning IV. Thinning Schedule V. Release Operations VI. Application of Release Operations 4.1. Response of Individual Trees to Thinning and Pruning Among the attributes of trees that can be regulated are the size, shape and structure of their stems as well as their branching characteristics. The Silviculturist tries to influence the size and shape of each tree to achieve the desired stand structure and value. The amount of growing space that will be available to tree will limit the amount of growth and genetic makeup of a tree will dictate how the growth is allocated to different parts.  Response of Trees to Increased Growing Space (Thinning) The amount of carbohydrates produced by tree depends mainly on the size of the crown or leaf surface or the ability of the roots to supply the foliage. When the tree is released by cutting competing tree, any prompt acceleration of the growth is largely from an increase in water and nutrients supplied by the roots. The amount of foliage does not increase until has time for the crown to enlarge. The roots extend widely and swiftly than crown. The root system of health trees are much widely than crown. Many species form intraspecific root graft so that it is possible for a tree to incorporate part of the root system of an adjacent tree. Pruning Cutting or removal of branches of trees Natural pruning Most of the pruning that takes place in the forest is caused by physical and biotic agencies of the environment is called as natural or self-pruning. In most situation the branched died from lack of light resulting from shading by higher branches. Wind can cause the breakage and death of trees. As the tree become taller, the crown edges hit adjoining crowns with increasing force during wind sway. This results to crown shyness, a phenomenon in which leaves spaces between the crown of adjacent trees.  In closed stands, natural pruning proceeds from the ground upward and starts with the killing of branches by the shade of those above. If the object is to keep branches small and soon shade, then it is desirable to maintain high stand density and even to refrain from thinning until some desired branch-free length had been developed.  Artificial pruning Activities carried to remove dry branches and also aimed to remove live branches on a selective basis. As a rule of thumb, at least 60% of the foliage must be retained in pruning. Removal of forks. Important treatment in trees which tends to fork such as narra and other species which tends to fork. In other species, fork must treated as early as possible. Branch forming small angle is weak therefore must be remove as soon as possible. tree fork - is a bifurcation in the trunk of a tree giving rise to two roughly equal diameter branches  Abnormal branch Forked trees  It is recommended that forked branches should be removed when diameter is less than 4 cm. for larger forks, the maximum diameter must be 8 cm, and bigger stem should not be removed anymore. In young plantation, pruning is recommended when plantation reaches 2 meters in height and repeated when it reaches 6 meters. Removal of abnormal strong branches. In big branches two or tree cut is recommended to avoid bark strip. The first cut must be 2 – 3 feet away from the main stem, and the final cut must be on the branch collar to stimulate fast healing process on the cut portion. The final cut must be clean and apply paint or solignum on the cut to avoid entrance of pathogen. Removal of poorly shaped trees. Injury by fire, grazing etc, often result to crooked stem. The best treatment is to cut the tree just above the ground to stimulate branching. Select the best strongest branch to be retained. The same procedure be conducted to leaning stem. 4.2. Management of Growth and Stand Yield by Thinning One the primary objective of thinning is to manage the production of wood by individual trees and the aggregated yield of the forest stand. Thinning is direct intervention in this reallocation process by eliminating some individuals and thereby adding to the competitive strength of other individuals. Removing weak competitors, small trees, will have little effect on the overall growth of the stand. Removing large trees will shift growing space to weak competitors that will not immediately be able to use the additional growth efficiently. 4.2.1. Forest Productivity Energy from the sun is captured by photosynthesis, which is the combination of water from the soil with carbon dioxide from the air to form glucose. This simple sugar contributes most of the basic building materials for all the compounds that provides trees with energy and structural material. Growth is simply the amount of glucose produced which exceeds the energy requirements of tree, or the amount of photosynthesis minus respiration.  Productivity is limited by the amount of photosynthesis that is limited by the amount of CO2 in the air, the amount of sunlight, the availability of water in the soil, and the temperature. The amount of foliage controls the amount of photosynthesis is limited by the amount of water and the availability of certain nutrients such as nitrogen, which are needed for chemical compounds in the leaves. Forests are among the most productive plant communities. Biological productivity of forest is great (occupying about 1/3 of land surface) accomplishes almost half of the world’s annual photosynthetic fixation of carbon. 4.2.2. Analysis of Increment Current annual increment (CAI) - is the amount (in any unit of measure) that is actually added in a given year. Periodic annual increment (PAI) - which is the increment of a short period (normally 5-10 years) divided by the number of years in that period, usually taken as nearly equivalent to CAI.  Mean annual increment (MAI) - which is the average of substance accumulated each year over lifetime of the stand. Usually, this figure is easily determined by dividing the total accumulated substances and dividing by the age. The MAI provides the best estimate of the maximum production rate that can be continuously sustained by a given combination of species and site quality, provided the stand not are not replaced before or after the age of maximum MAI. The peak MAI is a key value for determining how much can be harvested annually if a forest is managed to produce a sustained yield of timber and how long the rotations should be to maximize production.  Gross increment - includes material that formed earlier in the life of the stand or measurement period but was no longer present at the end. Net increment includes only that present at the end.  Parameters of stand density Stand density - is a measure of the amount of tree vegetation on a unit of land. It can be number of trees or the amount of basal area, wood volume, leaf cover, or any of the variety of less common parameters. Stocking - is the proportion that any such measure of the stand density bears to any of a wide variety of norms expressed in the same unit and chosen for differing purpose. The simplest parameter of all is number of trees per unit area. Basal area per unit of land is far the most commonly used parameters. It measures the cross-sectional area of the physiologically dead wood 4.2.3. Thinning and Its Objectives The yield of merchantable timber volume by stands cam be optimized by judicious, temporary reductions in stand density that enhance diameter growth. Artificial reductions in stand density cause temporary reductions in gross total production but enable the remaining trees to accelerate their occupancy of growing space and their diameter growth. Surplus trees are removed to concentrate the potential wood production of the stand on the limited number of selected trees. 4.3. Methods and Application of Thinning Methods of Thinning 1. Low thinning the oldest, sometimes called thinning from below, ordinary or German method. Trees are removed from the lower crown classes. This mimics at an accelerated rate the natural mortality. can be applied through a range of severity. The gradient is divided into four grade ranging from A for the very light to D for the heaviest. They are differentiated on the basis of the crown classes removed.  In A-grade low thinning, removals are confined to overtopped trees or merely those dead or nearly dead of suppression. This are little more than salvage operations and the canopy remains unbroken. In B-grade low thinning, the intermediate crown class is also eliminated. The main virtue of A and B grade thinning is that they are practically the only kind of thinning that can be done without any risk of reducing the gross production of wood by plants. The heavier C and D-grades of low thinning are more commonly applied since most of the thinning aimed to stimulate the growth of remaining trees. Both of the heavier grades involves deliberate creation of temporary canopy gaps to accelerate crown expansion of the remaining trees.  In C-grade some co-dominants are cut along with lower crown classes. In D-grade many but not all co-dominants are cut. The concept of low thinning is based on the premise that all trees smaller or shorter than a given standard are cut. The general result of low thinning is most applicable to stands which nearly all trees are merchantable. Theoretically, it is most appropriate than other methods for sites where moisture or other soil factors are seriously limiting. 2. Crown thinning Trees are removed from the middle and upper portion of the range of crown and diameter classes rather than lower end. This technique is also called French method, thinning from above, high thinning and thinning in the dominant. The trees are removed from the upper crown classes in order to open up canopy and favor the development of the most promising trees of the of the same age class. Most of the trees are cut from the co-dominant class, but many intermediate and dominant trees interfering with the development of potential crop trees are also removed.  Low thinning and crown thinning differ radically from selection thinning in which dominant trees are cut to favor the lesser crown classes. Theoretically, overtopped and intermediate trees that do not interfere with crop trees are not cut in crown thinning. The immediate cash return from crown thinning is greater than low thinning of equal severity because the material removed is larger and of greater severity. One advantage of crown thinning is the division of the residual stands into two categories of trees. 1. Favored dominants and co-dominants which are destined for removal either in reproduction cutting or later thinning. 2. Subordinate trees which are favored only by indirect action and are gradually removed as they grow up and interfere with trees of the first category.  One important advantage of crown thinning lies in the opportunity to stimulate the growth of selected drops without sacrificing quantity production. It is more flexible method than low thinning, and it demands greater skill on the part of the forester. Application of crown thinning Can be applied uniformly throughout the stand or concentrated very specifically on the release of a limited number of chosen crops. Work best or at least can be repeated most often in a mixed stand or in pure stand of tolerant species. 3. Selection thinning or Thinning of the Dominants Dominants trees are removed in order to stimulate the growth of trees of the lower crown class. The same kind of vigorous trees that are favored in crown and low thinning are the very ones that are likely to be cut. Also termed high grading, that is, harvesting material of high grade. Selection thinning involves the cutting of scattered trees from even-age stand or aggregations of trees without the intent of or results of regenerating new age classes. Different forms of selection thinning: 1. Poorly formed dominants are eliminated in favor of satisfactory crop trees chosen from the highest possible level in the lower crown classes. The removal of such trees takes advantage of the fact that co- dominant and intermediate trees as well as the smaller trees often have smoother, straighter boles and smaller branches than most vigorous dominants. 2. The second approach are continued until the point is reach when further removal from the main canopy will open wholes too large to be filled by expansion of the crown of the remaining trees. 3. The third approach is combined with simultaneous low thinning in order to enhance the development of remaining co-dominants. Problems with selection thinning: 1. Trees released are likely to be of less than optimum vigor and have rather weak slender stem 2. Selection thinning tends to aggravate problems with wind damage because it removes the trees that have the most well-developed butt-swells and the more tapered boles which are the strongest. 3. The choices is in favor of slow-growing trees would be undesirable is undesirable from the genetic standpoint., while the discrimination against poorly formed ones would be desirable. 4. Geometric Thinning The trees to be cut or retained are chosen on the basis of some predetermined spacing or other geometric pattern, with little or no regards of their position in the crown canopy. Geometric thinning can be advantageous in treating young stands that are densely crowded and previously unthinned. Geometric thinning is employed only in the first thinning of a stand. Two patterns of geometric thinning: 1. Spacing thinning. Trees at fixed distance are chosen for retention and all others are cut. The most commonly applied in overcrowded stands that have developed from dense natural regeneration or artificial broadcast sowing of seeds. 2. Row thinning. The trees are cut out in lines or narrow strips at fixed intervals throughout the stand.  The overriding concern for geometric thinning patterns best address leads to their frequent application in pre-commercial thinning. These are thinning made purely as investments in the future of stands so young that none of the felled trees extracted are utilized. Commercial thinning when all parts of the felled trees are extracted for useful products, regardless their value is great enough to defray the cost of operation. Potential problems: 1. Row and strip thinning can lead to lopsided crowns. 2. There is substantial variation of individuals. 3. the removal of too many of the dominant trees have the same undesirable results as selection thinning. 5. Free thinning Cuttings designed to release crops without regards for their position in the crown canopy. Unrestricted to any one of the other methods. The greatest need for combining several methods in the single thinning is encountered in stands that are somewhat irregular in age, density, or composition. 4.4. Thinning Schedule A schedule of thinning should be systematic plan for a whole rotation based on deliberate decision about the kind of vegetation, benefits, and products desired. Choosing methods of thinning: Three considerations in formulation of thinning programs: 1. One set of choices has to with timing, which includes rotation length, time of the first thinning, 2. Intervals between subsequent thinning 3. Method or methods of thinning employed at each stage Timing of the first thinning The first thinning can be made as soon as the crowns or the root system of individual trees grow together and start to interfere with one another. Competition commences early in the sapling stage. The best single criterion for determining when to apply the first thinning is the live crown ratio of the potential crop trees. 4.5. Release Operations Treatments of the young stands of desirable trees, not past the sapling stage, from the competition of undesirable species that threaten to suppress them. In the release of young stands, the operation is in effect, an uncovering of them through eliminations of overtopping trees. The basic objective is to give the trees that are released enough light and growing space to grow adequately and developed into trees of the main canopy. Release cuttings are most readily visualized in terms of freeing the crowns of existing desirable trees, but there are several additional considerations. 4.5.1. Two Kinds of Release Operation: 1. Cleaning A cutting made in a stand, not past the sapling stage, to free the best trees from undesirable individuals of the same age that overtopped them or are likely to do so. The principal purpose is to regulate the composition of mixed stands fro the advantage of better species. Weeding - is conventionally reserved for the more thorough removal of all plants competing with crop species, regardless of whether their crows are above, beside, or below those of the desirable trees. Types of vegetation removed: Plants that are going to suppress, endanger, or hamper the growth of trees needed to constitute a stand. Overtopping trees of undesirable species and poorly formed specimens of undesirable species that are likely to compete with potential crops. Climbing vines, overtopping shrubs and rank herbaceous growth must also be removed or controlled. 2. Liberation Cutting Release of young stands, not past the sapling age, from the competition of distinctly older, overtopping trees. Trees that are cut or killed are those left standing when the previous stand was harvested, or present before the natural or artificial establishment was done. 4.5.2. Methods of Liberation: a. Cutting Felling of large undesirable trees. b. Girdling Traditional method of killing tress without felling. This involves severing the bark, cambium and sometimes, the sapwood in a ring entirely around the trunk of a tree. The materials stored in the roots can still be carried up in the crown in the xylem unless. Cutting Girdling Double hacking - horizontal line of chips is removed by striking two downward by two downward blows, the second is made about 2 inches above the other so the chips may be pried entirely out of the cut with the twist of the ax handle. Notching - involves cutting notch ring around the tree through the bark and a half inch or more into the wood. It usually cause the quickest kill and the most basal sprouting because it is the method that nearly halts the upward movement of water and nutrients. Peeling - strips of bark at least 8 in wide are stripped off after continuous cut are made at the top and bottom of the strips. Notching Hacking Peeling 4.6. Application of Release Operations Cleaning - is usually associated with intensive silviculture, but the liberation of young stand from the remnants of the old ones is a practice most characteristics of the early stages of program of long- term silviculture. Liberation operations command high priority in the early stages of intensifying silvicultural programs.