First, the impact of thinning on the growth of stands.
(I) Impact of high growth
In practical forestry, it has been observed that the effect of tending on the average height growth of artificial larch forests is not very significant (references 5–9). Tree height growth depends on site conditions and the age of the stand. Generally, under better site conditions, height growth is faster. In young forests, the growth rate of height is higher compared to middle-aged or near-mature forests. However, when converting mixed forests into fast-growing and high-yield ones, removing some broad-leaved dominant trees can promote the height growth of larch. For example, in the Liujiaying Forest Park of Taoshan Forest Farm, two small classes, 6/19–1 and 6/19–2, were reforested on 75-year-old broad-leaved cutting land. These areas underwent an intense light cut, reducing the number of broadleaf trees from 40% to 20%. The 6/19-2 class did not receive any intervention at that time. By 1999, the larch in the 6/19-1 class became dominant with an average height of 11.3 meters, while the 6/19-2 class remained suppressed, with an average tree height of only 9.7 meters.
Table 5-9: Effect of thinning on the height and diameter growth of larch forest
Location of investigation: Shirenliang Forest Park, Taoshan Forest Farm
(b) Impact on diameter growth
Thinning has a clear effect on the diameter at breast height (DBH) of trees. Through tending, the number of reserved trees per unit area is reduced, expanding the nutrient space for each tree, which promotes individual tree growth and increases the overall average DBH of the stand. The impact of thinning on DBH growth varies depending on the initial density of the stand. Generally, stands with higher pre-cutting density show weaker effects on DBH growth, whereas those with lower density show more noticeable improvements. According to Table 5-10, within a certain range, the influence of thinning on the stand’s diameter is proportional to the cutting intensity—higher cutting intensity leads to greater impact on DBH growth. However, once the number of trees per unit area reaches a certain level, the growth of DBH remains relatively stable.
Effect of different tending intensities on the diameter growth of larch stands
Schedule 5-10
Location: Shirenliang Forest Park, Taoshan Forest Farm
Small class: 50/22
Forest age: 30 years
Cutting strength: 35.7%
Number of acres: 49
Before cutting: 33 cm
After cutting: 33 cm
Average diameter growth: 16.7 cm
Four years later: 17.1 cm
Observation period: 19.2 cm
Growth rate: 2.1 cm
Percentage increase: 191%
Control group: 49
Before cutting: 16.7 cm
After cutting: 17.8 cm
Growth rate: 1.1 cm
Percentage increase: 100%
Second, the impact of thinning on forest quality
Tending improves tree quality as the preserved trees are mostly high-quality main species, naturally pruned, straight, and free from defects.
1. Impact on wood species
Table 5-11 shows that tending increases the proportion of commercial materials and improves the economic output of the stand. The percentage of standard materials increased by nearly 182.2%, indicating that tending enhances the economic value of the forest.
2. Impact on annual rings
According to Ando et al., densely planted and poorly managed stands have smaller annual ring widths, while medium-density stands show larger and more consistent widths. Tending also increases the proportion of latewood, enhancing wood hardness and structural strength.
3. Influence on trunk shape
Higher stand density reduces trunk sharpness, while lower density increases it. Excessive thinning can negatively affect trunk shape, lowering forest quality. Table 5-12 demonstrates that as tending intensity increases, the number of trunks decreases, and trunk sharpness increases.
4. Effect on knots
Stand density influences knot size and number. Denser stands lead to stronger natural pruning, resulting in fewer and smaller knots, producing higher-quality wood.
Third, increasing economic benefits through thinning
Timely and moderate tending in North China's larch plantations shortens the cultivation cycle and advances the main harvesting age. It also improves tree quality and the ratio of commercial materials, contributing to long-term economic gains. From Table 5-13, in 1987, a 20-year-old larch plantation generated 36.2 yuan per mu in revenue, with total expenses of 16.05 yuan, yielding a profit of 20.15 yuan per mu. By 1991, after a second tending, the revenue per mu rose to 175.5 yuan, with expenses of 39.7 yuan, resulting in a profit of 135.8 yuan per mu.
The Mengzi Forestry Bureau emphasizes tending practices for Chinese larch. Although income varies based on economic conditions, stand status, and tending intensity, these practices generally provide economic benefits. Additionally, they support local industries such as timber processing and transportation, create employment opportunities, and help address fuel shortages in forest areas. Therefore, tending and cutting offer both social and economic advantages.
Marine Gre Plastic Pipe,Hot Fusion Plastic Pipe,Large Diamater Gre Pipe,Fiberglass Reinforced Pipe,GRE plastic pipe
Jingjiang Haihong Plastic & Rubeer Science -Technology Co.,Ltd , https://www.marineplasticpipe.com