"The Technology of Fast-growing and High-yielding Forest of North China Larch"

(vi) Determined by initial planting density

Before the emergence of the highest peak of general timber volume growth, the annual growth of the diameter of the DBH has begun to decline. The initial planting density of Larch plantation is between 6600 and 8800 plants/ha. This is the first time that the thinning is carried out between 9 and 15 years. .

(7) Determined according to the purpose of cultivating stands

The utilization rate of wood obtained from the first thinning is very low and should be considered in combination with economic benefits. In areas where small-diameter timber and fuel wood can be fully utilized, the initial period should be as early as possible, otherwise it may be appropriately postponed so that the economic benefits of thinning can offset construction costs. However, it must be noted that the growth of young forest stands is in a period of vigorous growth, and the thinning is too late. The dense forest stands have a great impact on the subsequent volume growth. Therefore, when determining the initial period of thinning, it is necessary to consider current interests, and long-term interests must also be considered.

(viii) Determined by other conditions of stand

In other conditions, thinning should be carried out early in areas prone to pests, wind and snow. To accelerate the growth of diameter and root development, enhance resistance. For the purpose of fostering the construction of rods, poles and other direct-drying materials, in order to prevent the forest from being multi-sectioned and sharp, the thinning can be postponed.

Second, the interval between the thinning (or repeat)

The interval between tending and thinning refers to the number of years between two successive thinnings. The length of the interval is mainly determined by the speed at which canopy density increases. After the thinning of the forest, after a certain number of years, the canopy density of the forest is increased again, and when the growth of the forest tree begins to decline again, it should be thinned again.

The stand growth speed has a great influence on the standoff period. Stands for hi light and fast-growing species are shorter than those for shade-tolerant and slow-growing species; stand-off conditions are better than stand-off conditions. Short; Stands of young trees are shorter than the older ones. For example, the interval between the thinning in Denmark is 10 divided by the age of the forest, the interval for the 20-year-old stands is 2 years, the forest for the 30-year-old is divided into 3 years, and so on. It is also useful to determine the interval between tree height growth rates. A thinning is performed when the tree height is 2-3 meters long. After many years of production practice, the Mengzi Forestry Bureau concluded that the clear cutting period is set to 4 to 6 years; the thinning interval is set to 5 to 7 years; the growth cutting interval is set to 10 to 12 years. With the growth of forest age, the number of forest trees will decrease accordingly, and the growth rate will slow down, and the interval will gradually increase.

The interval is closely related to the thinning intensity. The intensity interval is long; the intensity is low and the interval is short. According to data from Japan, the thinning of larch (cutting all pressed wood) has a thinning interval of 2 years; moderate (cutting all pressed wood and some medium wood) has a thinning period of 5 years; strength (cutting To all the pressed wood, some medium wood and a small amount of dominant wood) The thinning interval is 8 years.

Therefore, the interval can be determined by the following formula.

V (logging and accumulation)

N (interval years) = ————————

Z (mass growth year after year)

A table of reference numbers is available in the Thinning Strength section for reference in determining the number of years between intervals.

Intervals are also related to economic conditions. Generally speaking, in areas where traffic is convenient, wood and wood fires are lacking, the principle of low intensity and short interval is applied. In regions where traffic is inconvenient, labor is lacking and products cannot be fully utilized after thinning, strength may be used. Long term practice. However, it should be noted that although "the quantity is less" is less than "the quantity is less", the benefits of less work and more profit can be obtained. However, it will result in a reduction in the total volume of the forest (the number of trees will be drastically reduced, and the growth space will not be fully utilized). Particularly in the forests that have not been thinned, the trees will grow thin and have a slightly higher intensity due to the high density. Snow pressure, pest damage, etc. In the tuyote area, this hazard is even more serious. Therefore, from the standpoint of cultivating forest trees and the overall economic benefits, it is advisable that the thinning should be early, with low intensity and short interval.

Third, the end of the thinning

The end of the thinning is generally carried out at a level of age prior to harvesting. For example, when larch plantation is harvested for 51 years, the final time for thinning can only be determined in about 40 years. The purpose of this thinning was to increase the total amount of diameter growth. In intensive management, fertilization can also be combined to achieve better returns.

Fourth, the choice of logging

Tree classification is the basis for selecting logging. Qualitative thinning is based on this foundation. Even if it is a quantitative thinning, it is important to select lumbering on the principle of “several cuts and few stays”.

Determine logging in the thinning is an important technical link. In the production practice, according to the 40-year experience, the Mengzi Forestry Bureau determined that the harvested wood uses “staying and leaving” and “several cuts and not-cuts”. Practice. For example: “three cuts and three stays” (ie, cut back and stay fine, chop down and stay thin, and cut small to stay large) and “four look” (ie, look at the crown to ensure that the degree of canopy closure is appropriate; look at the trunk to ensure that the park is preserved. Full, straight; look around, to ensure a reasonable spacing; look at tree species, keep the target tree species) and other methods of operation and forestry slang, to determine the reasonable density and canopy closure and the choice of thinning, a visualized summary.

The timber selection method according to the forest classification and the selection of wood for the septum in the thinning method are the selected methods for logging. The general requirements must comply with “three cuts and three stays”. The main principle is to “retain inferior".

Rare and dense distribution, although planted in a certain plant spacing in the plantation forest, but the current level of technology can not guarantee 100% survival, so there is also the phenomenon of uneven density. In order to make full use of the nutrient space in forest lands and to prevent the emergence of open spaces in forests, they should be cut as little or as little as possible in sparsely populated areas. In dense places, even if it is the target tree species or grows well and is well-dried, it should be followed by the appropriate cut.

The choice of logging is appropriate, it determines the direction and growth rate of the forest stand. In thinning it also determines the thinning intensity, which has a decisive influence on the quality and effectiveness of the entire tending. Only the correct selection of logging can guarantee the purpose of tending and thinning. Here, we must emphasize that we must prevent the idea of ​​simply drawing material, consider the amount of material out of one-sidedly, chop up large and small, and cut down the quality of retention and inferiority, so that the proportion of forests that grow backward in the stand after tending will increase, not only postponing the maturity of the entire stand. , And it will make the fast-growing high-yielding forest stand into a low-quality forest, resulting in a counter-productive effect of tending.

At present, at home and abroad, due to differences in starting points and focus points, there are two different views on the choice of logging within the forest stand: one is the emphasis on the growth of individual plants that retain wood, ie, each tree in the thinning plant has been To be oriented, or in the dense planting, to have previously and uneducatedly select the last-harvested “cultivation wood”, that is, the final logging (starting with paint signs or other obvious signs) until the final cutting. During each thinning, care was taken to create a good growth space for the crowns of these wood-cultivation trees, and the remaining wood was only taken care of generally. Another approach is to focus on the growth of the entire forest, that is, to create space for the retained wood generally at each thinning, and to select only the last-harvested cultivars before the replacement in the rotation period (final logging ). Which method is adopted depends on the purpose of the operation. The advantage of the former method is that each thinning forest will hinder the growth of the final logging. This will save labor and strengthen the training of the final logging. Such as pruning, fertilization, etc., can shorten the cultivation period; the latter method, each thinning should be fully considered, need to be mastered by skilled personnel, and thus get more output, more suitable for close planting, differentiation of the stand.

In the dense plantation, before the thinning, the logging should be registered and selected. It is advisable to fully inspect the forestry factors. Pay attention to the following six factors: the stand structure (tree height, diameter); the relationship between the canopy and the diameter; Inter-competitive relationship; the natural sparse development process and individual development prospects; upright decadence and hidden decay and health status; in the forest tree classification level; using external morphology combined to determine the individual's viability and development stage (on mixed forests Extraordinary important).

The choice of logging is related to the type, method and intensity of thinning. Or belong to the type and method of thinning. In the quantitative thinning, the diameter can be used as the established standard for selecting the wood. Even so, it can be flexibly controlled according to the situation.

Fifth, tending thinning intensity

Tending cutting intensity refers to how many trees are cut down and how many forest trees are kept, that is, how sparse the forest is by harvesting. It has a direct impact on tending and thinning and is a key issue in tending and thinning. It is also the most discussed issue in tending and cutting techniques.

There are three goals for controlling the thinning strength:

(1) Denote the harvesting strength (Pn) by the number of thinning plants per unit area (n) as a percentage of the total number of trees (N) before cutting:

Pn=n/N×100%

For example, “Technical Specification for Forest Management in Hebei Province (Trial)” stipulates that the intensity of light-cutting plants should be 15 to 50%, the number of reserved plants per hectare should be 2400 to 3600, the canopy density should be no less than 0.6 to 0.7, and the number of thinning plants should be 15 to 50. %, the number of preserved plants per hectare is not less than 750, the canopy density is not less than 0.6; the number of growing plants is 15% to 35%, and the number of preserved plants per hectare is not less than 750.

(2) It is represented by the percentage of the thinning or area (V) of the thinning or area (V) before cutting.

Pu(g) = u(g)/V(g) × 100%

The intensity obtained by using Pv and Pg as indicators is very similar and can be used as a method of expression. Using Pn as an indicator can indicate the change in nutrient area, but it cannot represent or control the size of the selected tree, so an indicator is added, ie, The ratio of the average diameter (d2) of harvested wood to the average diameter (d1) of the pre-cut stand stands, and the percentage of cut area (g) obtained by using the following three indexes is more significant in terms of production.

The relationship between the three indicators is as follows:

Pg=d2・Pn(d=d2/d1)

If d = 0.6 and the thinning intensities calculated from the number of plants is 15%, then the intensity calculated from the sectional area is:

Pg=0.62×15%=5.4%

(3) Indicators of canopy closure or control intensity:

When the light is cut through, the canopy density after the first thinning is preferably not less than 0.7; the canopy density after the second thinning is not less than 0.6. In a thinning, the canopy density does not decrease by more than 0.2.

The currently used strength calculation indexes are (1) and (2), and in the secondary forest area, the (2)th calculation method is preferable. A reasonable calculation of the thinning intensity should meet the following requirements: maintain a healthy and stable growth of stands, do not suffer from breeding of weeds and damage due to wind damage due to sparse forest stands, and can create the most suitable for straightened trunks and fine wood. The growing conditions; each time the harvest is relatively large, but in the end it does not reduce the total amount of wood. Therefore, in order to maintain the maximum yield of the forest, the amount of thinning should not exceed the total forest production during the logging interval.

If: Determine the average annual growth of a forest stand per hectare (a quotient of the total volume per hectare divided by the age of the forest) is 8 cubic meters and the interval is set at 5 years, the maximum amount of thinning should not exceed 40 cubic meters. In actual production, the amount of thinning should also be lower than the growth as appropriate. Table 5-1 shows that the amount of thinning is determined by 70% of the annual average growth.

(I) Determination of thinning intensity

Twisting intensity is expressed in terms of volume and is usually divided into the following four types:

Weakness - less than 15% of the original stock volume;

Moderate - 16 to 25% of the original stock volume;

Intensity - 26 to 35% of the original stock volume;

Extreme strength - more than 35% of the original stock volume.

The determination of thinning intensity should take into account various factors such as tree species characteristics, site conditions, stand characteristics, stand density, growth and development stages, previous thinning intensity and interval, and comprehensive consideration should be given to management objectives, product sales, Economic factors such as economic value, transportation, and labor sources. The ideal approach should be: according to a certain business purpose, through the experimental study of different thinning intensities, formulate the optimal number of trees that should be kept in unit area at each stage of forest age under certain site conditions. At present, there are many methods for determining the thinning intensity, which are divided into two categories: qualitative thinning and quantitative thinning.

Table 5-1 Thinning of average annual growth of 70%

※: The average annual growth is large, and the interval between thinning operations should be short; on the contrary, the average annual growth is small and the interval should be long. Available thinning is between the two thick lines.

Quantitative thinning is based on the standard average growth, and Table 5-1 is a table of operational management used by the United Kingdom to control the amount and interval of thinning.

For example, for a forest with an average annual growth of 8m3/ha, the annual thinning amount can only be 70% of its average growth, ie 5.6m3/ha. If the thinning interval is set at 5 years, the thinning amount from Table 5-1 is 28 m3/ha.

In Table 5-1, there is a reasonable amount of thinning between the two thick lines. Outside the thick line at the top, the thinning volume is too small and is economically reasonable. Outside the thick line at the lower right corner, it is the thinning volume that may aggravate wind fall.

Qualitative thinning methods are based on the classification of forest trees. The thinning and retention woods are divided according to the thinning amount (lower layer, upper layer, etc.), and the thinning intensity is determined accordingly. For example, in the above thinning, according to the different levels of logging, the selection is divided into weak thinning, medium thinning, and thinning. This type of approach requires that people who specifically select logging have skilled technology and extensive experience. Otherwise, the wood selection error is very large and the thinning intensity is also difficult to control. In addition, this type of method is basically based on the status of the forest to select the logging, so as to determine the thinning intensity. It lacks the analysis and prediction of the historical conditions and the development direction of the forest, which is difficult to meet the requirements of the directional cultivation. The thinning intensity is subordinate to the tree classification.

Quantitative thinning, this method is based on the number of growth and development in each age stage, determine the thinning intensity at each stage. When carrying out operations, first determine the appropriate density (or the number of thinning plants) according to the chart (such as density management map, thinning sheet, etc.), determine the appropriate thinning intensity, and then refer to the tree classification, in line with the "three cuts The principle of "three stays" was to select logging and the number of felling was limited by the predetermined intensity. In recent years, there have been many such methods, which can be summarized as follows:

(ii) Quantitative thinning according to tree height

As the tree height increases with age, and the impact of thinning is not significant, it can be used as a good standard indicator for the stand development stage. Therefore, it is not necessary for the stand to have an average height of the dominant wood (or the average height of the upper wood, and more than five sample plots can be evenly set throughout the forest. The area of ​​each plot can be determined according to the stand area, and the maximum DBH forest can be selected for each plot. 2 to 3 trees, tree height, total average, which means that the average value of the average high, and consider the business purpose, determine the optimum number of trees for harvesting, the following describes a convenient method for reference.

Calculate the suitable nutrient area (ie the canopy area) of a tree using the average high-yield square of the dominant tree to obtain the number of trees that should be kept per hectare. According to the study of the ages of most tree species, the use of the advantage of the average height of 1/5 square as a suitable tree crown area is more appropriate, that is, a tree nutrient area should be (n/5) 2, then a hectare should be retained The number of forest trees (N) is: N=1000/(n/5)=250000/(n*n)

Regardless of the stand age, as long as the average superiority is determined, the number of thinning trees and the number of reserved trees can be obtained. If thinning is performed every 2 m of the tree height (ie, the interval is limited by tree growth), the stand advantage can be obtained. The average height of the wood to develop the thinning process table such as 5 to 2, in the thinning operation, the actual density of the measured forest and the advantage of the average height of the dominant wood, check the table can be obtained between the number of intercropping and thinning intensity. Different tree heights.

Table 5-2 Table of Intermediate Cuttings

Advantage wood average high

(Meter)

Thinning retention number

(hectares)

Thinning

Number of plants (ha)

%

10

2500

-

-

12

1736

764

30.5

14

1276

460

26.5

16

977

299

23.4

18

722

205

21.0

20

625

147

19.0

twenty two

517

108

17.3

twenty four

434

83

16.1

26

370

64

14.7

28

317

51

13.8

30

278

41

12.9

According to the growth of tree species in different regions, it has been proposed that negative tree species (such as spruce and fir) should have a tree height of 1/6, and positive tree species (such as Pinus sylvestris and larch) should have a 1/4 height. For specific application, it is necessary to apply appropriate tree height scores after investigating and researching according to local specific site conditions and tree species characteristics. Take the standing index of 1.0 in Table 5.3 as the standard. The figures above or below the index are high or low standing indicators; and the strength of the corresponding index is A, B, C, D, E. Five thinning levels (less than 1.0 for intensity thinning; greater than 1.0 for weak thinning). According to Table 5.3, the number of trees per hectare that should be retained under the different high and different standing trees indexes can be found.

Table 5-3 Table of the number of trees with different advantages and different standing indicators per hectare

Standing indicator

Different tree heights per hectare

10 m

15 meters

20 meters

25 meters

30 meters

Corresponding thinning

0.5

1250

556

312

200

139

E

0.75

1875

833

468

300

208

D

1.0 standard

2500

1111

625

400

278

C/D

1.5

3750

1666

938

600

417

C

2.5

6250

2778

1562

1,000

695

B

4.0

10000

4444

2500

1600

1112

A

(b) According to the quantitative thinning of chest height diameter

1, according to the average diameter of stand diameter determined to retain the number of trees because the stand diameter is relatively easy to determine the average diameter, so the use of more. The following is the method adopted by Hebei Academy of Forestry.

By investigating the larch plantation, it is believed that there is a close relationship between the DBH growth and the canopy, and the relationship between the DBH growth and the size of the canopy area can be used as the basis for determining the suitable nutrient area for growing the standing tree. The increase in the diameter of the DBH and the increase in the area of ​​the tree crown will inevitably lead to a decrease in the number of standing trees per unit area in the stand. It is considered that the correlation between the growth of breast diameter, the size of canopy area, and the density of standing trees is not affected by differences in site type and forest stand. The correlation between DBH and the canopy area and standing tree density in the study is the common law in the growth and development process of Larch plantation, which has universal significance for application and production. Determine the theoretical value of the crown area at different stages of growth in diameter (Table 5-4).

According to the theory of the relationship between breast diameter growth and crown area, the larger the DBH, the smaller the area of ​​the crown, the higher the surface area occupied by individual individuals in the forest, which will inevitably increase the relative density per unit area in the forest. The number of standing trees in the forest stands in excess, affecting growth. Therefore, the regularity of the number of standing trees in forest stands gradually decreases with the increase of DBH, which is the natural sparse law during forest growth. This is the basis of forest tending.

By analyzing the relationship between DBH growth and nutrient area and standing trees of Larch plantation, the relationship between the number of standing trees per unit area and the average DBH of the stand in Larch Plantation was obtained at the maximum density, on the double logarithmic axis. In a straight line. Therefore, the maximum density empirical formula per unit area of ​​larch plantations is:

23036.67

N=100.97 + . Relevant score r=0.99

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