Chapter 5 Tending Section I Forestation Foundations for Thinning Twisting and thinning is the practice of cutting part of forests regularly and repeatedly in immature forests to create good growth conditions for the remaining economically valuable forest trees, so that they can better meet the requirements of national economic and ecological environment construction. It is also possible to obtain a part of wood by tending thinning. In this sense, thinning is an effective means of obtaining timber in the early stage before the main cutting. Therefore, it is of double significance, and it can also be called middle use cutting or short thinning. In production practice, we must carefully handle the relationship between tending and utilization, and we must not emphasize the use of wood. Although it is impossible to produce timber during the young age, in order to cultivate fast-growing, high-yield, and high-quality forest stands, it is still necessary to maintain thinning in accordance with the growth and development of forest trees. First, the purpose of tending thinning Since forests have multiple roles in the development of the national economy, different types of forests have different tending purposes. In timber forests, the main purpose of the thinning should be to obtain a large number of economic materials with good quality; in shelter forests, the main task of thinning is to maximize the effectiveness of forest protection. In short, the following objectives should be achieved through systematic thinning of thinning. (I) Adjusting forest density and improving forest growth conditions With the increase of forest age and the growth of forest trees, the relative density of forest stands increases, and the nutrient space of individual forest trees shrinks. By tending thinning, the density of forest stands is adjusted in time to create a suitable growth space for wood retention. At the same time, it can accelerate the decomposition of litter under the forest and improve soil fertility, thus creating better growth conditions for forest trees. (B) To shorten the mature period of forest technology and increase the total amount of production per unit area By rearing thinning, the duration of tree cultivation can be greatly shortened, and the requirements for specifications products required by the society can be achieved as soon as possible, and the nutritional space for preserved wood can be expanded to improve the ability of underground roots to absorb nutrients and moisture. The canopy was stretched to produce a moderate crown and leaf area, which allowed the tree to grow better and increase the total production per unit area. (3) Clearing inferior forests and improving the quality of stand Through tending thinning, the poor quality forests are cleared, and artificial selection is carried out purposely to improve the quality of the stands, and at the same time increase the middle utilization rate of the stands. (4) Improve the health status of stand and enhance the stand resistance Tending thinning removes pressed wood, diseased rotted wood, windbreaks, windslides, and snow folds in forests, improving the health status of forests, and the illumination and ventilation conditions in forests. This not only reduces the occurrence and spread of pests and fires, but also improves the retention of wood. Resistance to natural disasters. (V) To achieve early utilization and increase the total utilization of wood As a result of the use of thinning, the use of the small trails of trees that have died due to natural sparseness and some of the defective upper layers allow the production unit to obtain a portion of the wood early, so that a small amount of funds can be accumulated for the purpose of expanding the reproduction and time. Cutting to increase the total utilization of timber in the stands. (6) Establish suitable forest stand structure and bring into play a variety of forest efficiency By tending thinning, the forest has appropriate structures, moderate density and canopy density, and reasonable levels, effectively improving various protective effects of the forest and other beneficial effects. The principal-subsidiary relationship of the above-mentioned purposes differs depending on the forest species and the age of the forest. In timber forests, the main purpose of thinning is to increase the total wood output per unit area, increase the specifications of materials and materials, and shorten the maturity and maturity of forest trees. Second, the theoretical foundation of tending (I) Growth and development of forests The entire growth and development process of forests, from the young to the mature, requires a long period of time due to climatic conditions, soil conditions, and man-made management measures. However, they have to go through several basic stages of growth and development. Usually based on the characteristics of changes in growth and development of forest stands, between forest trees and each other, and between forest trees and the environment, six growth and development stages are summarized: the forest formation period (age forest), the fast growth period (age forest), and In the long-term (middle age forest), near mature stage (near mature forest), mature stage (mature forest) and senescence stage (over mature forest), the basic characteristics of each growth and development period are described as follows: 1. The forest formation period refers to the period before forest closure. During this period, the target tree species have basically been isolated, and natural pruning has not yet occurred. In general, seedling weeds are flourishing on the forest land, and some non-purpose tree species grow. The main contradiction in this period is manifested in the adaptation of the target tree species to the environment and competition with non-purpose tree species and shrubs and weeds. The characteristics are that the saplings are rooting and the aboveground parts grow slowly, but they are gradually accelerating. Through the management of the forest land and the tending of the young trees, the saplings undergo a period of rooting and adapting to the environment. The growth speeds up and the crowns connect with each other. The entire forest stands That is, entering the fast-growing period. 2. The fast-growing period of the forest This period is characterized by the fact that the growth of forest trees, especially high-growth, has accelerated and reached its peak. The rapid growth of forests results in the canopy height being closed, the illumination in the forest becoming significantly weaker, the undergrowth vegetation being relatively scarce, the characteristics of the “forest environment†being more prominent, non-purpose tree species, shrubs and weeds being suppressed, and the competition between forest trees for nutrient space. The rise is the main contradiction, and the trees begin natural pruning and clearly differentiate. During this period, forest management measures should guarantee the conditions for high-speed growth of forest trees, continue to strengthen soil management, and reasonably conduct thinning, so as to maintain proper density of forest stands, promote the high growth of forest stands, and play an important role in fostering good stem formation. 3. After the fast growth period of the forest, the appearance and structure of the forest have been largely established, but the growth is still strong. At this time, the high growth gradually becomes slower, and the diameter growth gradually reaches the highest point, and the crown growth reaches its peak, with the largest In terms of leaf area, the trees need more sunlight. At this time, the amount of volume growth is also the most vigorous. Natural sparseness is still underway. However, it has eased slightly compared with the previous period. At this time, attention should be paid to the development of the forest and timely thinning of the forest stand. The forest will maintain sufficient light and growth space to promote the growth of forest trees and shorten the timber production period. 4. At the time of forest maturity, trees are naturally sparse. The diameter and volume growth of forest trees have been slow, showing a certain degree of stability. In order to promote the diameter growth of trees, thinning still needs to be done. 5. The mature period of the forest is characterized by a large number of forest trees, and the height, diameter, and volume of the timber grow very slowly. Forests have matured in terms of biology and technology. At this stage, natural sparseness basically stopped. Contradictions between forests and trees were eased, and forest canopies closed gradually. At this time, the forest should be used for the main cutting. 6. During the aging period of the forest, the trees have become old, the fertility and seed quality have declined, and some forests are dying due to physiological decline. Even the amount of dead damage exceeds the growth, the economic value and beneficial effects of the forest are declining. From the point of view of forest management, it is not appropriate to retain forests during this period. In short, it is very important to accurately control the growth and development of forests and adopt various measures according to local conditions. Therefore, fast-growing and high-yielding forests with high intensive management levels can be roughly divided into three phases according to the stand population and individual development process: First, the individual growth stage. This is the initial stage of interspecies competition between the target tree species and weeds, shrubs and non-purpose tree species after afforestation. In order to ease the competition between the target tree species and other plants, and to promote the individual growth of the target tree species, nurturing measures such as weeding and cutting should be carried out. Second, it began to close. As the growth rate is accelerated, the branches and leaves of the adjacent trees and forests converge, and sunlight, moisture, and nutrients compete with each other. In this stage, due to the fast growth of forest trees, natural pruning gradually occurs, and other plants under the forest gradually disappear and tend to disappear. This status indicates that the forest has been closed, and the first thinning should be carried out at this stage. Third, the natural sparsity stage. As the forest grows, the degree of canopy closure gradually increases and the competition among the individual species becomes increasingly fierce. There are obvious differences in size and pros and cons among the individuals. The suppressed inferior wood gradually withers, and thus produces a natural sparse process, which indicates that the forest stands The maximum density has been developed. According to the purpose of cultivation, multiple thinning operations are also conducted at this stage to adjust the stand to maintain the optimum density. This division method is relatively simple and has a clear purpose. It can serve as a basis for intensive management of fast-growing and high-yield forests and can meet the requirements of production practice. (b) Forest differentiation and natural sparseness 1. Reasons for Tree Differentiation There are differences in the form and viability between different individuals of the same age in the plantation forest created. This difference between trees in the forest is called tree differentiation. The main causes of differentiation of forest trees are: (1) The seeds are hereditary and therefore have significant differences in seedlings. (2) There was no significant difference between some individuals at the initial stage, but the differences became more and more obvious due to the competition among individuals and the environmental conditions. When the forest is closed, the conflict between forests and trees is becoming more and more serious, which makes the differentiation process more intense. As the forests continue to grow, the gap will increase. 2. Factors influencing the natural sparseness of forest trees Due to the differentiation of forest trees, natural sparseness of the forest is inevitable. Therefore, as the forest ages, the ever-decreasing phenomenon of trees and trees per unit area is called natural sparseness of the forest. Factors that affect the natural sparseness of trees: (1) Tree species characteristics: Larch is a positive tree species that grows rapidly and quickly, so its sparseness begins earlier and stronger. (2) Initial planting density: The greater the density, the earlier the survival competition between plant individuals occurs, so the natural sparseness starts early and the intensity is also large. (3) Age stage: Stands after forest closure impede the growth of forests due to the tree crowns joining together. As the age increases, the supply of light, moisture, and nutrients cannot meet the needs of all forests, and some forest development is affected. Causes poor growth or death. During the period of young forests, the phenomenon of tree differentiation and natural sparseness was observed; during the period of middle age forests, the growth of forest trees was strong, and the differentiation of forest trees and natural sparseness were more obvious. (4) Environmental conditions: Under good environmental conditions, the forest grows quickly when the young trees are young, and the trees are closed early. The natural sparseness at the early stage of the forest stands is earlier. On the contrary, under the harsh conditions, the forest grows slowly, the vegetation closes later, the forest trees The relationship between individuals is not yet intense, so nature is sparse. Therefore, according to the law of forest growth, especially for plantations with comparatively intensive management, the constant adjustment of the number of trees per unit area is very necessary to reduce the damage and promote the normal growth of trees. Practice has proved that the use of tending and thinning methods instead of natural sparseness by artificial selection can greatly shorten the period of forest cultivation and improve the quality of forest trees, and can make full use of tending products, and the amount can reach 50% of harvested volume. (3) Classification of trees Forest trees are the main body for cultivating forests, and tree differentiation is a common natural phenomenon. In forestry production, trees are often graded according to the degree of differentiation of forest trees to provide a basis for forest management. There are many grading methods. This section only introduces the commonly used five-level classification method of plantation. 1. Advantage wood (or Class I wood) The upper part of the canopy extends beyond the forest canopy, and the canopy expands to the fullest, and the trunk has the highest and the diameter is the thickest. Straight trunks of these trees can be cultivated, but so-called "Overlord Wood" and other trees with other defects, such as poor dry shape, large canopy, and harmful to neighboring preserved trees, should be removed. 2. Sub-dominant wood (or class II wood) Tree height and diameter are second only to dominant wood, and they are the main components of the canopy. They can obtain sufficient overhead illumination, and the sides are often covered by neighboring trees. Most of these fine trees can be cultivated wood, and they will play a good pruning role in the woods adjacent to each other. In subdominant wood, there is often a tree with a slender tree trunk and a narrow canopy. It is blown by the wind, swings back and forth, and jeopardizes the adjacent cultivated wood. It is said that this kind of forest is “whiplash†and should be subject to cutting. . 3. Medium wood (or Class III wood) The tree height, diameter, and canopy size are all medium in the stands. Because they are lower than the subdominant wood, only a small amount of direct light can be obtained at the top, but the side cannot be obtained. This type of forest can play a good role in pruning adjacent wood, can be used as a wood, when it is under pressure, it should be gradually cut. 4. Pressed wood (or IV grade wood) Slender trunks with narrow canopies are usually covered by the canopy. These forest trees have very few development prospects and should be removed before death. 5. Dead wood or dead wood (or V grade wood) In the lower canopy of the canopy, it is completely compressed and cannot obtain direct light. The growth is extremely backward, and it is about to die or have died. It should be removed. This method is most suitable for middle-aged forests of the same-age pure forest. In the undisturbed and disturbed stands, the distribution of the fifth-class wood is normal; that is, the number of woods in the second and third grades is the highest, I, IV, The number of V-level wood is relatively small. When the thinning is carried out, the forest level can be comprehensively assessed to determine the felling and retention of wood. (4) Regularity of diameter distribution of tree species Within the stand, the individual size distribution of the trees can reflect the growth status of the stand and the competition relationship between the trees, which is an important indicator of the structural characteristics of the stand. Generally, in the moderate-density and normal-growth age stages, the number of tree species in diameter distribution is normal or similar to the normal distribution curve. The order of the number of trees according to diameter distribution has nothing to do with the tree species or the status level, but it has a certain relationship with the age of the stand. The stands grow in the juvenile period along with the growth and development of forest stands. The competition is getting more and more intense, and the tree differentiation is becoming more and more obvious. When the small individuals occupy the majority of forest trees, the distribution of the number of plants in diameter becomes the shape of the leftward curve of the peak, which reflects that the growth and development of forest stands are severely inhibited. If it is less time-consuming and natural development is allowed, the number of standing trees will continue to increase. At this time, if the lower-level thinning is carried out with a higher intensity, and the pressured wood and the dead trees are cut off, they will tend to peak towards the right. Curves; if thinning is not carried out, let it sparse naturally until the sparsely mature stage of natural spawning. Therefore, in practice, the type of skewness of the distribution curve of the number of trees is often used to understand the degree of competition in the nutrition space and the dynamics of changes in the structure of the forest within the same-aged forest, to test the density of the stand at the present stage. The changes in forests at all levels and at all levels are used as the basis for formulating measures for tending and thinning. The thinning is another powerful means of adjusting this distribution curve. (5) The relationship between density and stand growth Density is an important basis for the stand characteristics. It refers to the number of trees per unit area. It affects the canopy closure, the extent of forest land use, and environmental conditions. In turn, these factors, in turn, affect the speed and duration of the forest's growth and development, as well as the quality, yield, and specifications of the wood obtained through the interaction between trees. 1. Density and leaf volume With the increase of density, the leaf area per unit area also increased, but after reaching a certain amount, the leaf volume remained almost unchanged. According to the study, in the closed forest without thinning, if the stand density is kept constant, the leaf volume of the stand almost does not change and the leaf volume of the individual plant does not change much even though the forest age is increased. Because there is not much difference in the assimilation ability of the leaves, the annual material productivity of the forest stand has not changed much. However, with the growth of forest stands, the height and diameter of forest trees are increasing. If the material productivity does not increase, the annual ring width will gradually narrow. Therefore, if you want to increase the growth of a single plant, you must increase the amount of leaves per plant. It can be seen that it is necessary to carry out thinning and reduce the number of standing trees. After the thinning, the amount of leaves suddenly decreases, but after the restoration of canopy closure, even if the thinning intensity is different, the leaf area per unit area is roughly the same. However, the amount of leaves per plant has been greatly changed due to the difference in the retention density, and the vertical distribution of the amount of crown leaves is also different. Therefore, in practice, we must not only maintain the maximum amount of leaves per unit area, but also adjust the stand densities through tending to maintain a certain amount of leaves per tree in order to obtain the maximum yield. This is a problem that needs to be solved for tending and thinning. . 2. The relationship between the density and the ratio of stems and leaves: Generally, the greater the stand density, the lower the proportion of shoots in the total production of branches, stems, and leaves, and the greater the proportion of shoots. Therefore, in order to increase the proportion of tree trunk volume, it is better to cultivate as dense as possible; but if the density is too large, the trunk diameter is small, which requires full consideration of the specification of the species to be obtained when the process is mature. 3. Density and shape of tree trunk are also important issues in production. Trunk roundness is one of the important indicators of trunk quality. Conformity differs significantly due to different densities. The smaller the general stand density, the greater the sharpness of the dry wood; the greater the stand density, the greater the success of the dry branches; the lower the density, the lower the height of the branches; the higher the density, the higher the natural pruning height, the stand density The bigger, the smaller the tree section, the faster it will be in the trunk. 4. Effect of Density on Forest Output The average single plant volume increases with the decrease of the density. (1) The relationship between the density and the average individual plant volume: the same level and age, low-density forest trees have strong mutual competitiveness, and the average tree volume is not affected by the density. In high-density forest stands, the nutrient space is narrow and the competition is fierce, so the average volume per plant becomes smaller. (2) The relationship between density and volume per unit area: In stands and conditions of the same age, the volume per unit area increases in proportion to the density before the stand closes. When the forest stands close to full closure, the yield per unit area does not appear to be significantly different due to the increase in density; at the mature stage of the forest, the yields of different densities are very close. Third, the economic premise of tending and cutting The technical measures for thinning are composed of a series of technical elements, such as the initial cutting density, the time of the beginning cutting, the method of selecting the thinning, the intensity, the repetition period, and the choice of cutting wood. These elements are also based on economic conditions, business purposes, and expected output. Stem quality, etc., as a prerequisite. Whether or not the thinning can be implemented depends on the economic conditions of the business units, which are mainly traffic, labor and product sales conditions. Only when the transportation is convenient, the source of labor is abundant, and thinning materials are sold, thinning is possible. Tending thinning should be adapted to business objectives. For example, in the production of large-diameter timber, on the basis of dense planting, the first thinning is carried out in a timely manner and thinning is repeated several times. If a large number of small-diameter timbers are produced for business purposes, the short-term form of thinning or weak thinning is adopted. However, if the small-diameter material that has been thinned is not fully utilized, or the cost of low-level thinning is high and the operating conditions are extensive, the time for the first thinning may be delayed, the number of thinning may be reduced, and a concentrated thinning may be performed to provide a large intensity. Larger diameter thinned timber and reduced thinning costs. The thinning is also related to the expected growth. For example, when the planting density is high, the thinning begins early, the thinning is often repeated, the production per unit area is large at the time of the final cutting, and the wood quality is good; however, the average diameter and the average volume of the forest are Small, moderate-density thinning, the number of plantings is less than the former, and it is often in a small density after thinning. Therefore, the total output and the final cutting production are smaller than the former, but the average diameter of the stand is small. And the volume per plant is much larger, forming sharp cuts. Therefore, in order to cultivate fast-growing, high-yielding, and high-quality forest stands, it is generally only appropriate to plant dense plants and tending thinning in due course. It is possible to use thinned timber, and to promote the growth of forest trees and improve the quality of forest trees. Section 2 The Kinds and Methods of Thinning In different stands (mainly the stand growth and development stages), the purposes and tasks of tending are not the same. The types of thinning of fast-growing and high-yielding forests cultivated by larch are generally divided into four types: transparent cutting, thinning, growth cutting, and health cutting. First, transparent light cutting: Transparency cuts are generally carried out in young forests. In order to solve the contradiction between the growth of forest trees, artificial larch forests that are originated from cutting sites in secondary forests are mainly cut off non-purpose tree species and shrubs that suppress the growth of larch, creating a good growth space for the target tree species. For pure forests, it is mainly interspersed and sparser, leaving excellent and inferior. However, in the places where the main tree species are short of plants, some minor tree species should be properly preserved to ensure the number of plants per unit area and suppress the growth of weed shrubs. (A) Transparency target 1. The density of young L. olgensis young plants is too large, the canopies overlap and overlap, the trunk is slender, and the growth is backward. 2. In mixed forests dominated by larch, secondary trees, shrubs, vines, and tall herbaceous plants that inhibit the growth of major tree species are suppressed. 3. The secondary forests artificially renewed the clustered plots of the plots, selecting the best and remaining, and cutting off other redundant moths. 4. In the natural regeneration or artificial promotion of natural regeneration has been a successful afforestation or under the forest canopy, the new young forest has grown into, you need to cut off the old or over mature wood, in order to liberate the next generation of the target tree species. When deciding on objects to be felled, it is necessary not only to consider the competing relationships between tree species, but also to consider the mutual adaptation between tree species. Although some tree species or plants do not have long-term cultivation prospects, they are temporarily retained to cover the soil and reduce forest land. There are certain benefits to weed breeding, climate regulation, and the growth of the main tree species. Therefore, some wood must be kept. (B) Method of Translucent Care There are three ways to implement light penetration: total tending, slug tending, and banding tending. 1. Comprehensive tending In all forest lands, secondary tree species that inhibit the growth of major tree species are generally removed at a certain intensity. This method is suitable for convenient transportation, sufficient labor, and availability of fuel and carbon materials, and where the dominant tree species are dominant and evenly distributed. 2. The saplings of the major tree species tending to be unevenly distributed on forest lands, and this method is used when the number is not enough. In sub-clusters of major tree species, minor tree species that inhibit the growth of young trees of the main tree species are eliminated. Where there are no major tree species, care is not taken. This saves labor and costs. 3. Banding tends to divide the forest land into several zones, carry out tending in the band, keep the main tree species, remove the minor tree species, and leave gaps in the middle to avoid tending. After the belts are tended, the appearance of the forests forms an alternate arrangement of translucent corridors and spaces. Within 5 to 10 years after tending in the zone, if the trees on the gap prevent the growth of the forest, the trees on the affected zone should be cut off. When carrying out banding, terrain and weather conditions should be taken into account to determine the direction of the belt. Generally gentle slopes, preferably north-south, provide young trees with more light; in bad weather conditions, dry soils are suitable for east-west direction; areas with frequent windy winds should be perpendicular to the direction of the main wind, wind fall, wind deflection and trunk deflection, The hazard of bending; in the steep slope of the mountain, the belt should be parallel to the contour, which will help maintain the soil and water. In order to cultivate fast-growing, high-quality Larix principis-rupprechtii forest stands, comprehensive tending is generally used. (3) Time, frequency and intensity of tending In most cases, light transmission tends to cut off non-purpose tree species that have a fast growth rate and a strong sprouting ability. Therefore, it is of great significance to select the cutting season, preferably in the late spring and early summer (five to June), when the spring dry wind has stopped, the temperature is warming, and environmental changes have little effect on the liberated trees. To make weak, slender trunks more solid in summer. At the same time, the sap has begun to flow and the branches are soft, and it is not easy to trip and fall when harvesting. In the fall, the winter is the worst, because the winter young shoots are relatively brittle. In the production and operation, it is very easy for bruises to break. Especially the newly released saplings suddenly encounter the dry wind in the early spring and often cause a large number of plant deaths. Light transmission tends to be used to calculate the harvesting intensity using the stock volume or the number of plants. Because in the young stage, the forest is mostly composed of dense forest trees. Although the number of plants per unit area is large, and the volume is small, it is sometimes possible to cut down the individual large superstructures that are mixed in the forest. The number of plants is small, but the individual plant volume is high. Therefore, if the harvesting strength is calculated according to stock volume or number of trees, the variation range is often very large, and there is no practical significance in production. Therefore, the harvesting strength is often uncertain, and the number of plants that have liberated or retained some major tree species per unit area can be used. As a reference indicator of strength. First, thinning: After the young trees have been bred by the light, they enter the stage of the young-age forest. The forest has basically formed the appearance of its composition, and thereafter the growth and cultivation is called thinning. Its task is to use the forest for a long period of time from the age of maturity to the maturity of the previous level. In order to solve the contradiction between the individual species of the target tree, the forest density is constantly adjusted so that the preserved wood grows well and the quality of the wood is improved. Shorten the material period and achieve the goal of fast growth, high yield and high quality. Thinning is the most important type of tending and cutting in plantation forests. It has the effect of further adjusting the composition of tree species in the mixed forest after the light cutting. According to the way larch manages its cutting and retention of forests, it is divided into the lower tending method (applicable to pure forest) and comprehensive tending method (adapting to the mixed forest dominated by larch). (I) Lower Education It is characterized by basically following the process of natural sparseness and the thinning of the trees to be eliminated naturally. First, weeding out dead trees and dead trees that are underdeveloped and smaller in diameter in the lower canopy of the forest canopy. Therefore, after the tending, the impact on the canopy structure is not significant, and good canopy closure can still be maintained. Only the vertical growth of the canopy Shortened to form a single canopy. Secondly, due to the timely removal of the pressed wood, the nutrient space of the reserved wood was expanded, thereby promoting their growth. This method is based on Kraft's growth grading method. The cutting intensity varies according to the requirements and is determined by the level of logging. The strength of the lower layer tends to be divided into three types. Weakness of thinning - cutting off grade V wood; moderate thinning - cutting off grade V wood and grade IV wood; strength thinning - cutting off all grade V wood, grade IV wood and a small amount of grade III wood. The advantage of the lower tending method is that it is simple and easy to use, and the use of forest tree classification can not only control reasonable harvesting strength, but also facilitate the selection of felled timber. After tending, the forested land will be preserved in the process of changing the forest, and the lower layer will be pressed to increase the space for the reserved wood. Therefore, a large gap will be formed under the forest canopy, which will not cause wind fall, snow pressure, etc. Bad consequences and ventilation inside the forest. As a result of the removal of standing trees, dead trees, and backward-growing forest trees, the sanitation status of forest stands has been improved, the pests and diseases have been reduced, and the stability of forest stands has been improved. However, this method also has its shortcomings. Basically, it is "taking small people to stay large." If weak thinning is used, there is little effect on sparse forest canopy and improvement of forest sanitation conditions. The wood obtained during the harvesting process is mostly wood with small diameters. In order to overcome the shortcomings of the lower tending method, at the time of lower-level thinning at home and abroad, it is also appropriate to cut off some of the dominant or sub-dominant woods with large or poorly-dried crowns. This is not only economic but also biologically effective. Studies have shown that after a certain period of time, the diameter distribution of forest trees tends to a normal distribution when the number of trees destroyed by felling is reduced according to the regularity of diameter distribution. This is due to the fact that when some large-diameter trees are felled, they will cause the trees in the small-diameter class to overshoot. This will be able to better exert the once-repressed growth potential of the small-diameter trees and help accelerate the development of low-diameter forests. Grow. (b) Comprehensive tending (applicable to mixed forests dominated by larch) The comprehensive tending method integrates the characteristics of the lower tending method and the upper tending method, and the cutting objects are distributed in various parts of the forest canopy. This method is based on the fact that, after the tending, due to changes in environmental conditions (especially light conditions), the growth of trees that fall behind can restore and accelerate growth. The comprehensive tending method is to cut forest trees at all heights and diameters of trees. The harvesting intensity has great flexibility and depends on the nature, composition, forest phase, and business purpose of the forest. After harvesting, the remaining large, medium and small forest trees can be directly exposed to sufficient sunlight to form multi-level canopy closure. This method is more flexible. It is more appropriate to use the four-level method when selecting the wood. Cut the harmful wood, retain the beneficial wood, cultivate the good wood, and temporarily keep the reserve wood. The four-point criteria: Good wood - the most advantageous tree, is the object of cultivation. Beneficial wood - trees that are more advantageous, because of changes in the environment after tending, it is possible to develop and change to dominant wood, which is the object of reservation. Harmful wood - which hinders the growth of adjacent main trees, should be cut. Reserve wood - trees that can not determine its role, temporarily retained, in order to observe aftereffects. The advantage of this method is that good wood and stunted trees can receive light together, but they also have certain shade. The depth of the forest canopy is not reduced due to felling, and it always maintains multiple layers of canopy closure. The canopy is ladder-like, allowing the light and CO2 airflow to be cleared in the forest, increasing the growth of forests at all levels, and class V wood and poor quality of the IV. The wood was cut down, and at the same time, Class I and Class II wood with poorly dried and densely grown upper layers were cut off. As a result, not only was a good economic effect achieved, but also the growth of the preserved wood was more effectively promoted. Third, the growth of cutting The growth cutting is mainly a kind of tending to accelerate the growth of the diameter of forest trees. To eliminate forest trees that have no future for cultivation and determine the reasonable density of the forest stands, so as to maintain the maximum amount of leaves per unit area as much as possible, expand the nutrient area of ​​each tree, promote its growth, and shorten the process maturity. . Fourth, health cutting Health cutting, also known as health care cutting, is a breeding and logging operation to maintain and improve the health status of the entire forest. In general, it is combined with other types of tending. Only when the forest is suddenly damaged by natural disasters such as diseases, insects, wind, snow, fog, rain, etc., and a large number of forest trees are damaged, it will be carried out separately. The occurrence of forest pests and diseases in the northern part of North China is more serious. The small larvae cause larch flake deaths. The larch caterpillars, larch tussock moths, and larch larvae are all harmful to larch, sometimes occurring in large areas, causing serious damage. The occurrence of diseases is also serious in some stands, such as early defoliation, stem rot, etc., which cause the growth of trees to decline and even cause death. Health clearance is carried out, and forest trees infected with pests and diseases are removed from forest stands in a timely manner. This is extremely important to prevent the spread of pests and diseases and improve the growth potential of preserved wood. The harvesting of trees damaged by these pests and diseases does not necessarily result in some direct benefits, sometimes even at a loss, but it is necessary in the long-term interest. The harvesting intensity should be determined based on the number of damaged trees, current status of forest stand, and economic conditions. In general, the affected trees should be completely cut off, but in order to maintain a certain degree of canopy density (usually not less than 0.5 degrees of canopy) and to protect the forest environment, the victims should be kept as much as possible. Therefore, before harvesting these trees, they must consider their role in the entire ecosystem. Section III The Technical Elements of Felling and Cutting First, the beginning of thinning Timely tending has a close relationship with increasing the growth of forest trees and the quality of forest stands. The growth of forest trees with high diameters and diameters enters the fast-growing period. It creates a good growing environment for the cultivated wood and promotes the growth and development of forest trees. It is a management measure to cultivate high-yield forests. Through the implementation of real fast-growing and high-yield targets. The determination of the start time of tending is related to the conditions of site conditions, stand density, forest growth status, cultivation objectives, “quantity maturationâ€, “process maturity†and other factors. How to determine the start period of tending should be comprehensively considered from the following aspects: determine. (I) Determined by the appearance characteristics of the stand According to the size of the forest canopy. After the canopy closure, the trees begin natural pruning, the stronger natural pruning, and the smaller the canopy, the more intense the competition between trees. The canopy size can be expressed by the percentage of the height of the tree crown as a percentage of the height of the whole tree. The "crown height ratio" is called. The canopy height ratio can be used as a tree to provide an indicator of the whole plant nutrient capacity. In general, a tree with a crown-to-height ratio higher than 1/3 can grow well; when it is 1/3 or lower, it grows and declines; when the height ratio is too low, thinning restores slowly and can even die. Therefore, when the ratio of crown-to-grain ratio of dominant wood in forest stand is close to 1/3 or so, thinning should begin. (b) Determined by year-on-year growth A significant decline in annual growth (diameter, diameter, area or volume) indicates that growth has been inhibited, ie, thinning should begin. Together with the Longtoushan Forest Farm, the Academy of Forestry in Hebei Province, jointly studied the density and volume of the chest height of the larch plantations. The amount of determination, found that the growth rate of chest height area of ​​forest under various densities decreased with the growth of young age, but there are also obvious growth rates from a certain year. For example, the growth rates of 3300 to 4400 plants/ha were significantly decreased after 13 years, 6600 plants were significantly decreased after 12 years, and 8800 plants were significantly decreased after 10 years. Therefore, it is proposed that the age for the thinning between 2,500 and 3,000 plants should be 14 years, 3000 to 4,800 for 13 years, 4,800 to 6,600 for 12 years, and 6,600 to 8,400 for 11 years. (iii) Determined by successive year growth and average growth Before the annual growth of breast diameter and the average growth curve intersect, the first thinning should be carried out. In some dense forest stands or in forests with large initial planting densities or even in bar plantations, there is a case where the growth of annual volume growth and the average growth curve of the timber volume intersect, which indicates that the loss of time should be handled in time.ç§æž—分，但第一次强度ä¸èƒ½è¿‡å¤§ã€‚ ㈣ æŒ‰èƒ¸å¾„å’Œæ ªæ•°ç¡®å®š åˆ©ç”¨æ ªæ•°ä¸Žèƒ¸å¾„å…³ç³»åæ€çš„分布以确定åˆä¼æ—¶é—´ã€‚如龙头山林场调查å‘现林分ä¸æœ‰30%以上的林木胸径å°äºŽæž—分平å‡ç›´å¾„时，å³åº”进行第一次ç–ä¼ã€‚ ㈤ 按分级法确定 æ ¹æ®æž—木分级：Ⅳã€Vçº§æœ¨åœ¨æž—å†…æ¯”ä¾‹åŠ å¤§ï¼Œç‰¹åˆ«æ˜¯åœ¨è‡ªç„¶ç¨€ç–ä¸ï¼Œæž¯æ»æœ¨æ¯”ä¾‹åŠ å¤§ï¼Œå³åº”进行ç–ä¼ã€‚
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