Section 5: Manual Update
With the improvement of forest management, all cutting sites have been artificially updated. Manual update typically involves planting seedlings. This method offers several advantages, including saving seeds, a high survival rate, early closure of young forests, easier tending and management, and the ability to form forests and materials effectively.
The success of Larix principis-rupprechtii plantation renewal is closely tied to site conditions. Larch is a shallow-rooted species with over 80% of its roots being horizontal. It requires high levels of nutrients, water, and light. In 30-year-old pure larch forests, high density and rapid early growth inhibit the regeneration of understory vegetation, especially in barren areas. After logging, using larch as the main species for artificial reforestation often leads to poor renewal due to land degradation. Adverse environmental conditions such as insufficient water or nutrients can result in small, old trees or even tree death, which significantly impacts future commercial forest development. However, in natural secondary forests with poplar and birch, or on fertile lands, artificial larch planting after harvest shows better growth. The reason is that the land is fertile, and there are more undergrowth plants, litter, and complex soil properties, preventing degradation. These sites are suitable for creating larch commercial forests, generally for two to three rotations. However, considering long-term forestry strategies, it's significant to create mixed coniferous and broad-leaved forests on larch cutting sites.
First, Advantages of Mixed Forests
(i) Prevention of Land Degradation
Due to the "Tianbao" project, the Mengzi Forestry Bureau mainly focuses on harvesting pure larch forests. After harvesting, tree species are still used for manual regeneration in the same year or the following year. On sandy loam (originally barren hills), the effect is poor, with low survival rates and slow growth. Pruning, binding, and interplanting seabuckthorn with larch help improve fertility and create mixed forests, showing superiority. Thus, overcoming land degradation and preventing soil deterioration by creating mixed forests is the best approach. Selecting deep-rooted species maximizes soil fertility and mitigates surface fertility issues.
(B) Mixed Forests Help Promote Ecological Balance
Maintaining biodiversity is essential for sustainable forestry. Continuous cultivation of single-species larch forests not only causes land degradation but also affects productivity. Research data show that plantations of Chinese fir and Pinus massoniana experience a 30-50% decrease in second-generation productivity. Artificial pure forests are not conducive to sustainable use of forest land. The basic components of a forest include trees, shrubs, herbs, wildlife, and microorganisms. After entering middle age, larch pure forests inhibit shrub and herb growth, leading to "Qingtang" stands, which negatively impact biodiversity. With fewer plant species, wildlife and microorganism diversity also declines. Statistics show that the Mengfu Forestry Bureau has faced over 181,000 hectares of disease and pest damage, mostly in pure coniferous forests. Mixed forests, however, show significantly lower incidence. Building mixed forests with appropriate ratios can address these issues.
Second, Mixed Forest Application Models
To build a mixed forest of Larix principis-rupprechtii, the mix proportion and model should be determined based on site conditions, including soil fertility, texture, elevation, aspect, slope, and selected tree species.
(a) Tree Species Selection
In suitable altitude and fertile areas, choose broad-leaved trees like birch alongside larch. In dry and infertile areas, select pine and birch. For severely degraded areas, choose sea buckthorn or Caragana korshinskii.
(b) Mixed Modes Based on Site Conditions
1. In good site conditions, large strip mixing is suitable. Use larch 1m × 1m × 5 lines + hardwood 1m × 2m × 5 lines or larch 1m × 2m × 10 lines + hardwood 1m × 2m × 10 lines, with a 5:5 ratio.
2. In less favorable sites, use pine and birch. Pine 1m × 2m × 3 rows + birch 1m × 2m × 3 or dumplings Pine 1m × 2m × 5 lines + birch 1m × 2m × 5 lines. This increases litter, changes soil properties, and prevents degradation.
3. In high-altitude, degraded areas, use larch or spruce with shrubs (Hippophae rhamnoides, Caragana korshinskii, or Lespedeza davidiana). Main species spacing 1.5 m×2m + associated species 1.5 m×2 m, reducing initial density and promoting growth.
Third, Artificially Updated Planting Density
Based on years of afforestation experience, the initial planting density is usually between 330 and 440 plants per mu. This allows the main species to benefit from the mass effect in the early stage, with density appropriately increased, followed by control of an insurance factor. However, in severely degraded areas, reduce density to promote water and fertilizer supply and ensure normal growth.
IV. Artificially Updating Seedlings and Young Forest Tending Techniques (refer to Chapter 4 Afforestation)
Chapter 7: Diseases, Insects, and Infestations of Larix principis-rupprechtii
Section 1: Major Diseases of Larix principis-rupprechtii
Forest diseases refer to pathological changes in trees caused by pathogenic organisms or adverse environmental conditions, leading to slow growth, deformity, or death, resulting in economic losses and ecological impacts.
There are many pathogenic factors, divided into biological and non-biological agents. Biological factors include fungi, bacteria, viruses, etc., while non-biological factors include temperature, humidity, and nutrient deficiencies. Symptoms of forest diseases include visible signs and conditions, with physiological diseases having no symptoms.
Forest disease diagnosis includes investigation, symptom observation, microscopic examination, and treatment inspection. These methods are fundamental to studying forest diseases.
The main diseases of Larix principis-rupprechtii are larch early defoliation and larch shoot disease.
First, Larch Early Defoliation
(I) Distribution and Hazards
This disease is mainly found in Northeast and North China. It was discovered in 1963 in Hebei Province and is a serious leaf disease of larch.
After infection, leaves fall about 40 days earlier, affecting growth rates and volume.
(b) Symptoms
Yellow spots appear on leaves, gradually turning reddish brown, with black spots indicating spores. Severe cases lead to entire canopy discoloration, with premature leaf fall.
(c) Pathogens
Caused by Mycosphaerella larici-leptolepis. Spores and ascospores are produced, with specific sizes and structures.
(d) Incidence Law
Disease occurs once a year, with ascospores spreading via wind. High humidity and temperature increase infection risk.
(v) Control Methods
Promote mixed forests, manage young forests, and apply chemical treatments.
Second, Larch Shoot Disease
(I) Distribution and Hazards
Discovered in Japan in 1939, it became widespread in China in 1973. It affects new shoots, causing severe damage and up to 100% mortality.
(b) Symptoms
Shoots become bent, discolored, and lose needles. New shoots may replace old ones if infected consecutively.
(c) Pathogens
Caused by Botryia phaeria. Ascospores and conidia are involved, with specific sizes and structures.
(d) Incidence of Disease
Ascospores and conidia spread via wind and rain. High humidity and rainfall increase infection risk.
(v) Control Methods
Strengthen quarantine, clear infested areas, avoid pure larch forests, and apply chemical treatments.
III. Investigation and Forecast of Major Diseases
(I) Investigation of the Condition
Line investigations and standard surveys are conducted annually to determine disease extent and severity.
Larch larvae disease classification criteria and larch shoot disease grading standards are provided for accurate assessment.
Investigation formulas include infected strain rate and disease index calculations, with summaries leading to distribution maps and condition reports.
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