(v) Quantitative Thinning Based on Volume
In Finland, pine forests undergo thinning 2 to 4 times during the rotation period, using a method that controls thinning intensity based on volume. This technique is known as "rushing into thinning," where the thinning age is determined by a specific growth prediction equation. The advantages include high precision and controlled thinning amounts (see Table 5-8).
Table 5-8 Sparseness Scale with Age and Superiority
Age | High Advantage (m) | Logging Volume per Hectare (cubic meters) | Thinning Volume Percentage (%)
---|---|---|---
18 | 5 | 8 | 40
33 | 11 | 48 | 33
53 | 17 | 108 | 38
73 | 21.5 | 101 | 32
This high-intensity directed thinning involves an initial thinning of about 2200 trees per hectare. Subsequent thinnings mostly harvest rods, ultimately leading to the production of main building materials.
Based on tree species, site conditions, and forest management objectives (such as cultivation period or desired wood specifications), an ideal number of standing trees is designed, and a thinning density management table is developed. For example, Longtoushan Forest Farm has used the law of tree height change over recent years, taking the height of the upper forest stand as a parameter. It shows the rule that diameter and volume change with stand density—this includes the growth rules of tree height, stand density effects, maximum density curve, natural sparseness, and sparse density curves. These elements together form the stand growth model and are transformed into two practical tools: "site index curves" (Figure 5-2) and "density management maps" (Figure 5-3). By checking the site index using the actual height of the stand (measured from a 500-2000 m² sample plot, selecting the tallest tree per 100 O for the upper forest and calculating its average height), and then consulting the site index curve, the site index can be determined. Based on this index and the corresponding site-type retention sparseness, the number of trees and volume that should be retained is found on the density management map. This allows for determining the thinning intensity.
With these charts, it's also possible to design a directional cultivation process according to the predetermined cultivation period and wood species specifications, enabling forest cultivation to reach a level of prediction and orientation.
For instance, if a plantation larch has a diameter D=12 cm and a density N=2000 plants/ha, and the required sparse density after thinning is not less than 0.8, with yield M, density P, height H, and the number of thinning plants ΔN, the volume of logs ΔM, and the diameter after cutting D1, you would check Figure 5-3.
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Figure 5-2 Site Index Curve of Artificial Larch Forest
Figure 5-3 Density Control Map of Artificial Larch Forest
1. According to the D and N drawn, the volume of M = 174 m³/ha was read on the scale of the ordinate, at the intersection of the equidistant line marked with 12 cm and the line with the abscissa 2,000 lines per hectare (there are X marks).
2. Since the intersection point lies between the density line and saturation density line marked with 0.9, P = 0.94 can be read out in proportion to the increase in the upper layer height.
3. Therefore, the intersection point is marked between the two tree line heights of 14m and 16m. Therefore, H = 15m can be read in proportion to the increase in the upper floor height.
4. According to the measured retention density of 0.8, the upper layer height is 15m. When the isodensity line marked with 0.8 is intersected with the imagined 15m tree line (there is the point), the retention after the thinning is determined by the ordinate. Quantity M1 = 148 m²/ha. The reserved density N1 = 1,400 plants/ha was determined on the abscissa. The diameter D1 = 13.3 m after the thinning was determined on the scale of the adjacent straight line.
5. According to the volume and density after thinning, the number of thinning and the volume of the thinning were determined. The results were as follows:
ΔN = N - N1 = 2000 - 1400 = 600 plants/ha
ΔM = M - M1 = 174 - 148 = 26 m²/ha
In recent years, significant progress has been made in experimental research on quantitative thinning, with the use of mathematical analysis, statistical methods, and various variables of forest stands (e.g., number of trees per hectare, average height of the stand, average diameter at breast height per hectare, changes in canopy diameter, crown height ratio, forest height, site conditions, etc.). Computer-assisted regression and linear equations have been used to design stand growth models and even sustainable management models, addressing issues such as tree species growth forecasting and tending thinning. Researchers continue to explore long-term management and sustainable use strategies.
To summarize, in the process of forest cultivation, comprehensive consideration is given to the application of thinning techniques based on the direction of fast-growing and high-yield forests, site conditions, and growth factors of forest trees. This helps mediate the forest growth environment and achieve fast-growing and high-yield goals. In practical applications, the selection criteria for "harvesting wood" can be flexibly adapted based on the growth status of the stand.
Sixth, Survey Design
In the forest stand, a representative area is selected for the layout of standard plots and different tending methods (lower, upper, integrated, or mechanical). Referring to the principles of "forest classification" and "three cuts and three stays," the selection of cuttings will be carried out and marked. Then, the intensities of thinning, timber production, estimates of revenues and expenditures, etc., shall be calculated on a standard basis. This section does not describe in detail.
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