Method for transforming pinus massoniana low-quality and low-efficiency water source forest into coniferous and broad-leaved mixed forest

Abstract

The invention belongs to the technical field of forestry ecological restoration, and discloses a method for transforming a pinus massoniana low-quality and low-efficiency water source forest into a coniferous and broad-leaved mixed forest, which comprises the following steps: (1) forest stand diagnosis and planning; (2) three-dimensional complementary planting; and (3) innovation of a mixed mode. The biological characteristics of different fireproof tree species are utilized, upper, middle and lower mixed spaces are matched, shade-tolerant and sun-loving tree species are matched, and the mutual promotion effect is achieved. The characteristics of various tree species are effectively utilized, matching of deep and shallow root system tree species is fully considered, the improvement of the water and soil conservation function of forest land soil is effectively ensured, and the water and soil conservation function of a water source forest region is particularly promoted.

Description

Technical Field

[0001] This invention belongs to the field of forestry ecological restoration technology, specifically involving a method for improving the fire resistance and ecological restoration of low-quality and inefficient Masson pine water source forests. Through artificial intervention, fire-resistant broad-leaved trees are introduced to promote the formation of mixed coniferous and broad-leaved forests, thereby improving the fire resistance of water source forests, increasing economic benefits, and enhancing the stability of the ecosystem. Background Technology

[0002] Masson pine, an important native tree species in my country, is characterized by its rapid growth, straight trunk, and tolerance to drought and poor soil conditions. It is a key timber, resin, and ecological species in southern China. According to data from the Ninth National Forest Resources Inventory, my country's planted Masson pine forests cover over 2.5 million hectares, accounting for 4.41% of the total forest area, with a total stock of 187.6 million cubic meters, representing 5.54% of the national total planted arbor forest stock. It plays a vital role in timber supply, rosin industrialization, integrated forestry and paper production, and forest ecosystem services.

[0003] However, a large number of pure stands of natural or secondary aerial-seeded Masson pine exist in the protected forest areas of southern water source regions. These stands originated from aerial seeding restoration in areas with large-scale vegetation destruction and severe soil erosion. Their soil and other site conditions are significantly inferior to those of broad-leaved forests, Chinese fir forests, and natural Masson pine forests. The trees grow poorly, have low water conservation capacity, and are highly susceptible to fire due to multiple factors, resulting in low-quality and low-efficiency forests caused by fire. The specific reasons are as follows:

[0004] (1) Flammable characteristics of tree species: The resin content of Masson pine branches and leaves is as high as 3-5%, and the calorific value of litter is 18-20 MJ / kg, which is more than 30% higher than that of broad-leaved tree species; Most aerial seeding stands have low density and canopy closure of only 0.4-0.6, with sufficient sunlight under the forest, which promotes the growth and withering of flammable herbs such as Miscanthus sinensis, increasing the risk of fire.

[0005] (2) Impact of climate change: In the past decade, the drought index in southern my country has increased by 15%, the average annual rainfall has decreased by 200-300 mm, and the frequency of forest fires has increased by 40%. Such forest stands are mainly distributed in hilly areas of 300-800 m. The fragmented terrain leads to a fire spread speed of 3-5 m / min, which is 1.5-2 times that of flat land.

[0006] (3) Human interference is aggravated: 65% of fires in afforestation sites were caused by agricultural fires, and pure forests accounted for more than 80%; the density of firebreaks in some areas was less than 0.5 km / 100 ha, and there were also problems with the selection and planting of fire-resistant tree species.

[0007] The burning of low-quality and inefficient water source forests by Masson pine trees has triggered a series of serious ecological problems:

[0008] (1) Soil degradation: After burning, the organic matter in the topsoil decreased from 35 g / kg to 15 g / kg, a decrease of 50-60%, and the pH value increased by 0.8-1.2;

[0009] (2) Imbalance in soil and water conservation: The surface runoff coefficient increased from 0.25 to 0.55, and the soil erosion modulus reached 5000 t / (km²). 2 •a);

[0010] (3) Decreased carbon sequestration capacity: Within 3 years after the fire, the carbon storage only recovers to 30-40% of the original forest stand;

[0011] (4) Inefficient forest stand cycle: Natural restoration forms "small old tree" stands, with 20-year-old Masson pine trees having a stock volume of less than 60m³. 3 / ha, only half the size of a healthy stand;

[0012] (5) High risk of fire recurrence: The fire risk level of the forest stand remains at Level IV (high risk) for 8-10 years during the recovery period;

[0013] (6) Difficulty in vegetation restoration: Fire caused a 90% mortality rate of seeds in the 0-5cm soil layer, and natural regeneration takes more than 10 years.

[0014] The aforementioned low-quality and inefficient state stems from the combined effects of "flammable tree species + fragile habitat + human disturbance," urgently requiring structural transformation to break the vicious cycle of the ecosystem. However, existing technologies have significant defects and shortcomings:

[0015] (1) Natural regeneration easily forms monoculture forests, which leads to persistent problems such as low biodiversity, high fire risk, and soil degradation;

[0016] (2) The mixed broad-leaved tree species used did not have fire prevention as the core objective, and their fire resistance was poor;

[0017] (3) The method of replanting eucalyptus and other single tree species after comprehensive forest clearing is often adopted. This not only results in a single ecological function and weak water and soil conservation capacity, but also eucalyptus is not a suitable water and soil conservation tree species for water source forests.

[0018] (4) The economic benefits are low, the timber output of low-quality forest stands is low, and there is a lack of high-value broad-leaved tree species.

[0019] The specific manifestations of the poor fire resistance of existing low-quality and low-efficiency Masson pine water source forests are as follows:

[0020] (1) Unreasonable forest stand structure. The forest stand structure determines the ease and speed of fire spread in the forest, manifested in: A. Low canopy closure, many gaps in the forest, and low-efficiency forests are usually characterized by sparse trees and low canopy closure (the ratio of tree canopy projection area to forest land area), which makes the forest sunny and windy, forming a "wind gap" environment. B. Pure forests with a single structure. A pure pine forest means that the same flammable material is used from the ground to the air, lacking a natural "fire barrier". Fire can spread unimpeded on the ground and in the canopy at the same time, forming a highly destructive "three-dimensional combustion". If it is a mixed pine and broad-leaved forest, broad-leaved trees (such as Schima superba, Quercus, etc.) usually have high water content and are not easily flammable, which can effectively block or slow down the spread of fire. C. It is easy to form a connection between "surface fire" and "crown fire". The bark of Masson pine is rough and rich in resin. In particular, the low branches (sparse forest stand leads to well-developed lateral branches and low branch height) are easily ignited by surface fire, thus leading the fire from the ground to the crown, forming a highly destructive crown fire that is extremely difficult to extinguish.

[0021] (2) The forest environment is dry, making it easy to achieve "fire hazard" meteorological conditions. A. Poor regulation capacity; the low-quality and low-efficiency forest ecosystem is fragile, and its ability to conserve water and maintain soil and water is inherently poor. The forest soil is barren and has poor water retention. B. A dry microclimate is formed: the sparse canopy cannot effectively block sunlight, the temperature inside the forest is high, the humidity is low, and the wind speed is high, which together create an abnormally dry microenvironment. The dead branches, fallen leaves, and weeds under the forest can quickly lose moisture and are in a flammable state for a long time.

[0022] (3) Low-quality and low-efficiency forests contain a large quantity of high-quality combustibles that are continuously distributed. Masson pine is an evergreen coniferous tree, and its needles contain a large amount of oil (pine resin) and wax, making them highly flammable. These needles are renewed and fall off every year, forming a thick, loose, and well-ventilated layer of litter on the forest floor. This layer of pine needles dries quickly and is easily ignited, making it a "ignition source" and the main "carrier" for forest fires. Because pine needles contain wax and resin that are not easily decomposed, coupled with the dryness of the forest and weak microbial activity, the decomposition rate of these litter materials is very slow, accumulating year after year and forming a huge combustible load. In low-quality and low-efficiency forests, due to the sparse canopy, sunlight can directly reach the forest floor, promoting the growth of a large number of light-loving, drought-resistant, and flammable grasses (such as bulrush and cogongrass) and shrubs. These herbaceous plants wither rapidly in autumn and winter, have extremely low water content, low ignition point, and spread fires very quickly, acting as "accelerants" during the fire season.

[0023] Currently, although my country has conducted mixed planting experiments with some tree species and Masson pine, these experiments have all adopted conventional mixed planting methods such as inter-row, strip, and block planting, and are mostly mixed plantings of the same age. This has led to mutual interference between tree species, failing to achieve the expected mixed planting effect and significantly inhibiting the growth of the main tree species. The results are poor mixed planting effects and high afforestation costs, failing to leverage the complementary effects of mixed tree species. At present, there is a lack of technical solutions for the transformation of pure Masson pine forests in water source forest areas, especially regarding the selection of fire-resistant tree species in important ecological security forest areas, resulting in unsatisfactory overall transformation effects.

[0024] The above background information is provided only to aid in understanding the inventive concept and technical solution of this invention. It does not necessarily belong to the prior art of this patent application. In the absence of clear evidence that the above information was disclosed on the filing date of this patent application, the above background information should not be used to evaluate the novelty and inventiveness of this application. Summary of the Invention

[0025] The purpose of this invention is to propose a method for transforming low-quality and low-efficiency Masson pine water source forests into mixed coniferous and broad-leaved forests, in order to solve the problems of poor fire resistance, ecological function degradation, and low economic benefits of low-quality and low-efficiency Masson pine water source forests, so as to build a resilient and sustainable mixed coniferous and broad-leaved forest ecosystem and ensure the ecological security of water source forest areas.

[0026] To achieve the above technical objectives, the technical solution adopted by this invention is as follows:

[0027] A method for transforming low-quality and inefficient Masson pine water source forests into mixed coniferous and broad-leaved forests includes the following:

[0028] (1) Forest stand diagnosis and planning;

[0029] (2) Three-dimensional replanting;

[0030] (3) Innovation of mixed breeding mode.

[0031] Furthermore, stand diagnosis and planning include the following:

[0032] Damage levels were determined in the first year after the fire: Classified into Level I, Level II, and Level III based on the canopy burn rate; Healthy Masson pine trees were preserved: Individuals with a DBH ≥ 25cm, a surviving canopy width > 40%, and good trunk shape were selected and maintained at a suitable density.

[0033] Furthermore, a canopy burn rate of ≤30% is classified as Class I, Class II as 30-60%, and Class III as >60%.

[0034] Furthermore, a suitable density of 20-25 plants per hectare should be maintained.

[0035] Furthermore, three-dimensional replanting includes the following:

[0036] 1) Spatial configuration: The upper layer of trees is replanted with fire-resistant broad-leaved trees, the middle layer is planted with precious trees or nitrogen-fixing trees, and the lower layer is planted with edible and medicinal shrubs.

[0037] 2) Timing and specifications: Replanting should be done during the rainy season, using container seedlings.

[0038] Furthermore, the upper layer tree species include one or more of *Michelia champaca*, *Phoebe zhennan*, and *Hemu*, the middle layer tree species include one or more of *Gnaphalium affine* and *Phoebe zhennan*, and the lower layer planting includes one or more of *Ficus microcarpa* and *Ficus spp.*.

[0039] Furthermore, the height of the container seedling is >50cm and the ground diameter is >0.5cm.

[0040] Furthermore, innovation in hybrid hybridization models includes the following:

[0041] 1) Strip mixed planting: Create replanting strips along contour lines, with fire-resistant broad-leaved trees spaced 4m apart and 3m apart; shade-tolerant precious tree species or nitrogen-fixing trees are interplanted between the fire-resistant tree rows at a ratio of 1:5; edible and medicinal shrubs are planted in the replanting strips, with a plant spacing of 0.5m and a row spacing of 0.5m.

[0042] 2) Proportion control: Maintain 20-25 Masson pine trees per mu, 45 fire-resistant broad-leaved trees, 9 shade-tolerant precious tree species or nitrogen-fixing trees, and 800 edible and medicinal shrubs; through natural thinning, a suitable vertical structure of tall and short trees and shrubs of appropriate proportion will eventually be formed.

[0043] Furthermore, the planting width is 1.5-2m, and the spacing between the strips is 3m.

[0044] Furthermore, the final result is a vertical structure of tall and short trees and shrubs, with Masson pine accounting for 20-25% and broad-leaved trees accounting for 75-80%.

[0045] Compared with conventional mixed afforestation of low-yield Masson pine forests, the outstanding advantages of this invention are as follows:

[0046] 1. Traditional mixed afforestation models do not fully consider the fire-resistant biological characteristics of species in mixed planting, and do not give full play to the fire-resistant effect of mixed tree species. This invention utilizes the biological characteristics of different fire-resistant tree species, mixes them in upper, middle and lower layers, and combines shade-tolerant and sun-loving tree species to achieve a mutually reinforcing effect.

[0047] 2. Traditional mixed afforestation models mostly use single timber species or broad-leaved trees for mixed planting. The harvesting time is uniform, and the resulting economic benefits are short-lived, especially since they cannot generate long-term ecological benefits. In contrast, this invention combines tree species with long, medium and short-term economic benefits, and the economic benefits can last for more than 50 years.

[0048] 3. Traditional mixed afforestation models mostly use single timber species or broad-leaved trees for mixed planting, without considering the utilization of low-lying spaces under the forest canopy, and the construction process also results in exposed soil in these low-lying spaces. In contrast, this invention plants edible and medicinal shrubs in the lower layer, which effectively utilizes forest space to increase income, promotes the restoration of understory vegetation, and enhances biodiversity.

[0049] 4. Traditional mixed afforestation models cannot fully utilize the different characteristics of the root systems of pine, fast-growing broad-leaved tree species, and precious broad-leaved tree species, nor can they make full use of soil fertility and space. This invention effectively utilizes the characteristics of the three species, fully considers the combination of tree species with deep and shallow root systems, effectively ensures the improvement of the soil and water conservation function of forest land, and particularly promotes the soil and water conservation function of water source forest areas.

[0050] 5. This invention is designed for water source forests of Masson pine or other pine trees in southern my country. It allows for the selection of suitable mixed tree species based on local climate conditions, making it widely applicable and practical.

[0051] 6. The seedlings used in this invention all meet the national first-class seedling standard. The seedlings are robust and have well-developed root systems. In addition, planting during the rainy season in March and April can significantly improve the survival rate of afforestation. Attached Figure Description

[0052] Figure 1 This is a diagram of the three-dimensional mixed tree species configuration of the present invention. Detailed Implementation

[0053] In an embodiment of the present invention, a method for transforming low-quality and inefficient Masson pine water source forests into mixed coniferous and broad-leaved forests includes the following:

[0054] (1) Forest stand diagnosis and planning

[0055] Damage levels are classified in the first year after the fire: Class I (≤30%), Class II (30-60%), and Class III (>60%) according to the canopy burn rate; Healthy Masson pine trees are preserved: Individuals with DBH (diameter at breast height) ≥25cm, surviving canopy width >40%, and good trunk shape are selected, and the retention density is 20-25 trees / hectare;

[0056] (2) Three-dimensional replanting system

[0057] 1) Spatial configuration: The upper layer of trees is planted with fire-resistant broad-leaved trees (such as *Milaopa*, *Firewood*, and *Hemu*), the middle layer of trees is planted with precious trees or nitrogen-fixing trees (such as *Hemu* and *Phoebe*), and the lower layer is planted with edible and medicinal shrubs (such as *Sarcandra glabra* and *Ficus stenoptera*).

[0058] 2) Timing and specifications: Replanting should be done during the rainy season using container seedlings (seedling height > 50cm, ground diameter > 0.5cm).

[0059] (3) Innovation of mixed breeding model

[0060] 1) Strip Mixed Planting: Planting strips are established along contour lines, with a strip width of 1.5-2m (to avoid excessive width leading to soil erosion) and a strip spacing of 3m (to ensure growing space). Fire-resistant broad-leaved trees (such as *Michelia champaca* and *Machilus thunbergii*) are planted at a spacing of 4m between plants and 3m between rows; shade-tolerant precious tree species or nitrogen-fixing trees (such as *Phoebe zhennan* and *Machilus nanmu*) are interplanted between the fire-resistant tree rows at a ratio of 1:5 (i.e., 1 *Phoebe zhennan* 5 *Michelia champaca*, 1 *Machilus nanmu* 5 *Machilus thunbergii*); edible and medicinal shrubs (such as *Ficus microcarpa* and *Ficus lyrata*) are planted in the planting strips at a spacing of 0.5m between plants and 0.5m between rows.

[0061] 2) Proportion Control: Maintain 20-25 Masson pine trees per acre, 45 fire-resistant broad-leaved trees (such as *Michelia champaca*, *Machilus thunbergii*, and *Helianthus altissima*), 9 shade-tolerant precious tree species or nitrogen-fixing trees (such as *Phoebe zhennan* and *Machilus nanmu*), and approximately 800 edible and medicinal shrubs (such as *Sarcandra glabra* and *Ficus hirta*). Through natural thinning, the final result will be a vertical structure of tall and short trees and shrubs with a proportion of 20-25% Masson pine and 75-80% broad-leaved trees (e.g.,...). Figure 1 (As shown).

[0062] Final Results: The project fully utilizes the existing land space, promoting the height growth of Masson pine. Based on the growth rate of natural forests in the southern Guangxi water source region, the 10-year height growth of the mixed-species trees is h + 5 meters (where h is the original height of the Masson pine at the time of replanting). The introduced fire-resistant broad-leaved trees, *Michelia macclurei* and *Machilus thunbergii*, are native fast-growing broad-leaved trees. After 10 years, the average tree height growth is 10 meters, with straight trunks. The 10-year-old understory litter reaches 6.5-10.5 tons / hectare, with a litter layer thickness of approximately 3-6 cm. This promotes the decomposition of pine needles and branches, serving as an important fire-resistant barrier layer and a crucial material basis for soil nutrient cycling and improved soil physical properties. It also promotes the germination of fallen seeds and seeds of introduced species, accelerates the regeneration of the understory shrub layer, and ensures biodiversity. Medicinal shrubs under the forest canopy increase economic income.

[0063] Technical principle of the invention:

[0064] The principles and technical points for improving the fire resistance of existing low-quality and low-efficiency Masson pine watershed forests: The fundamental approach to improving fire resistance is to address the three basic conditions for forest combustion (combustible material, oxygen, and ignition source), especially by managing and controlling combustible material, and by optimizing the forest stand structure to create an ecological environment unfavorable to the occurrence and spread of fire. The technical measures of this invention revolve around the following core principles:

[0065] (1) The principle of forest stand structure optimization and transformation is the most fundamental and long-lasting measure, which aims to solve the problem from the perspective of the ecosystem. The ultimate goal is to build a three-dimensional community structure that is "fire-resistant and fire-resistant", and to use technical means to carry out thinning and replanting of broad-leaved tree species (fire-resistant and fire-resistant tree species such as Schima superba, Phoebe zhennan, Castanopsis fargesii, Quercus glauca, etc.).

[0066] a. Thinning: Cutting down diseased, weak, and crushed trees while retaining healthy trees not only reduces flammable materials in the forest (especially future dead standing trees), but also creates growing space and light conditions for replanted broad-leaved trees.

[0067] b. Replanting fire-resistant broad-leaved trees (such as *Symplocos macrantha*, *Machilus chinensis*, *Castanopsis fargesii*, *Quercus glauca*, etc.): This forms a "wet carpet." These fire-resistant broad-leaved trees produce a large amount of fallen leaves, resulting in loose, high-moisture, and fast-decomposing litter that is not easily flammable. This effectively covers and suppresses the flammable pine needle layer below. It also constructs a "green barrier." The large canopies of broad-leaved trees and the high water content of their branches and leaves effectively prevent surface fires from spreading upwards into crown fires, forming a natural three-dimensional firebreak. Furthermore, it improves the forest environment. Increased canopy density reduces sunlight, lowers wind speed, and increases humidity, creating a humid microenvironment that makes it difficult for combustibles to reach their ignition point.

[0068] The ultimate goal is to create multi-layered mixed forests, breaking the single structure of pure forests that are easily flammable. By utilizing the fire-resistant properties of broad-leaved trees, the continuous combustible space can be divided, greatly reducing the speed of fire spread.

[0069] (2) Principles of forest understory combustible material management. The most important method is biological measures (planting fire-resistant plants), which involves planting some shade-tolerant, evergreen, high-moisture, and non-flammable low shrubs (such as coral grass, fig, ferns, etc.) under the forest canopy. Advantages: "Suppressing fire with greenery," by covering the ground with living plants, the growth of flammable weeds is competitively suppressed, while the plants themselves form a living firebreak. It has both economic and ecological benefits.

[0070] In summary, improving the fire resistance of low-efficiency Masson pine forests is a systematic project that cannot be solved by a single measure. It follows the principles of combining short-term symptomatic relief (clearing combustibles) with long-term fundamental solutions (improving forest stand structure) and combining biological measures (understory afforestation) with engineering measures (forest strip opening). The ultimate goal is to build a healthy, stable, and efficient forest ecosystem with strong self-regulation capabilities, low flammability, and easily controllable fire even when it occurs. This is not only necessary for fire prevention but also a core pathway to enhancing its water conservation function.

[0071] To make the present invention more fully disclosed, the present invention will be further explained below with reference to specific embodiments.

[0072] Experimental Demonstration Examples:

[0073] Example 1

[0074] The comparative experimental forest of different mixed ratios of Masson pine and Machilus laurentii in Pingtianshan Forest Farm, Guigang, Guangxi, was established in 1981. Treatments with mixed ratios of Masson pine and Machilus laurentii of 40%–60% (T1), 10%–30% (T2), and a pure Machilus laurentii forest (T3) were set up. A total of 12 fixed observation plots were established, each with an area of ​​400 m².2 (20m×20m), the 30-year growth data from the sample plot survey are as follows:

[0075]

[0076] It can be seen from the above table:

[0077] (1) The single-tree volume of T1 was the highest, 33.94% higher than that of T2 and 51.71% higher than that of the pure forest of T3, indicating that a certain mixed planting ratio can promote the growth of single-tree volume. Among the three treatments, T2 had the highest average single-tree volume of Masson pine at 0.6113 m3, which is 1.79 times that of the pure forest of Phoebe zhennan (0.3405 m3). The establishment of mixed forests of Masson pine and Phoebe zhennan can promote the growth of both diameter at breast height (DBH) and tree height of Masson pine and Phoebe zhennan, compared with pure forests. Among them, the mixed planting of Masson pine with the ratio of T1 can ensure the number of Masson pine trees per unit area and the growth of single trees, which plays an important role in promoting the utilization of resin from Masson pine and can also ensure the growth of single trees of Phoebe zhennan. Analysis of timber output value of various tree species in mixed and overmature forests showed that the economic output value of mixed forests was 33.66-49.89% higher than that of pure forests. Among them, T2 mixed forest reached 10,740 yuan / mu, which was 12.1% higher than T1. This was mainly because the timber output value of Phoebe zhennan accounted for a large proportion, reaching 83.7%.

[0078] (2) Based on soil sampling and understory biomass survey, the shrub communities of the mixed forest of Masson pine × Machilus and its pure stands were mainly composed of Machilus willow-leaved, Acer palmatum, Ficus scabra, and Camellia oleifera, while the herbaceous communities were mainly composed of Acer buergerianum, Rhamnus spp., Sargassum fusiforme, and Adiantum capillus-veneris. The overall understory plant diversity index was significantly higher in the mixed forest type with a 50% mixed ratio of Masson pine × Machilus than in other forest types. The soil physicochemical properties of the mixed forest of Masson pine × Machilus and its pure stands showed significant differences (p<0.05). Among them, capillary porosity, total porosity, total phosphorus, available phosphorus, total potassium, and available potassium were the highest in the 50% mixed ratio, significantly higher than those in the pure stands of Masson pine and Machilus. pH, organic matter, total nitrogen, and available nitrogen were the highest in the 75% mixed ratio, significantly higher than those in the pure stands of Masson pine. Therefore, in the process of forest management, more attention should be paid to the rational combination of mixed forests and the management of monoculture forests should be avoided in order to improve the overall ecological capacity of forests. Especially in the process of monoculture forest transformation in the main production areas of Masson pine in the south, the forest type with a 50% mixed ratio of Masson pine and Michelia champaca should be considered first. The optimal forest structure should be controlled by timely and reasonable dense planting, pruning, thinning and reasonable fertilizer application to improve the ecological stability and productivity of the forest.

[0079] Example 2

[0080] This study investigated the changes in litter yield in a *Pinus massoniana* plantation and its mixed pine and broadleaf forest, conducted at the applicant's experimental forest farm in Xixiangtang District, Nanning City, Guangxi Province. The forest stands were established in 1992 and comprised five main stand types: pure *Pinus massoniana* stands, pure *Machilus chinensis* stands, pure *Castanopsis fargesii* stands, mixed *Pinus massoniana* × *Castanopsis fargesii* forests, and mixed *Pinus massoniana* × *Machilus chinensis* forests, as well as two stands with different mixing ratios and retention densities. Fourteen fixed observation plots were established, each with an area of ​​900 m². 2 (30m×30m) During the experimental phase from July 2019 to January 2024, litter was collected quarterly (90 days). The litter was brought back to the laboratory, dried at 80°C to constant weight, weighed, and the yield changes of each forest stand type were analyzed. The experimental survey showed that the 30-year growth of each forest stand was as follows:

[0081]

[0082] It can be seen from the above table:

[0083] In this invention, the total amount of litter from Masson pine, Machilus laurentii, and their mixed forests, from largest to smallest, is: T2 Masson pine (41.284 t / hm²). 2 )>T1 Fire Nan (39.879t / hm 2 > T4 Masson Pine × Ficus microcarpa Mixed Forest (35.815 t / hm) 2 The total litter volume of Masson pine, white cone, and their mixed forests, from largest to smallest, is as follows: T2 Masson pine (41.284 t / hm). 2 > T7 Masson Pine × White Pine (34.660t / hm) 2 > T8 white cone (30.194t / hm) 2 The mixed planting of different tree species results in significant differences in litter volume between mixed and pure stands. This is because different tree species have different nutrient requirements and allocation strategies. Some species may prioritize above-ground growth, while others may focus more on root development and maintenance. This difference affects litter production. Actual experimental results show that pure Masson pine stands produce the most litter annually, with the thickest ground cover, averaging 3-5 cm. In contrast, mixed pine and broadleaf forests produce less litter due to their higher decomposition rate, resulting in a 11.13-15.27% reduction in total annual litter. Furthermore, the litter composition of mixed Masson pine and broadleaf forests is easily decomposed, increasing topsoil moisture content and generally contributing to forest fire prevention. However, the thicker pine needle litter layer in pure Masson pine stands exacerbates soil acidification, reduces natural regeneration of other understory species, lowers biodiversity, indirectly affects soil biological and microbial activity, and slows down soil fertility self-circulation.

[0084] Example 3

[0085] In the Guangxi State-owned Qipo Forest Farm in Wuwei Town, Jiangnan District, Nanning City, Guangxi, a demonstration forest of mixed forests of Masson pine, Castanopsis fargesii, and Machilus thunbergii was established to address low-yield, overmature Masson pine forests. The Masson pine trees were planted in 1966, and the broad-leaved trees (Machilus thunbergii and Castanopsis fargesii) were replanted in 2000. The mixed forests were planted in strips with large embankments, and basal fertilizer was applied. Topdressing and weeding were carried out for three consecutive years. Six fixed observation plots were established, each with an area of ​​900 m². 2 (30m×30m) According to the survey, the number of 57-year-old Masson pine trees is 21 per mu, with a total volume of 15.673m³. 3 / mu; the total number of broad-leaved trees is 35 per mu, including 28 red castor trees per mu and 7 firewood trees per mu; the best growing species is firewood, with an average annual diameter at breast height (DBH) of 17.54 cm and a tree height of 17.64 m, which is about the same as that of Masson pine, and the height at the base of the branches is also the same; the second best growing species is red castor, which is shorter than firewood at 13.16 m. The growth of each tree species is as follows:

[0086]

[0087] It can be seen from the above table:

[0088] The mixed forests grow well, with distinct layers of coniferous and broad-leaved trees, high space utilization, no pests or diseases, and abundant understory vegetation. Various broad-leaved trees and Masson pine seedlings are constantly being renewed, and litter (mainly branches and leaves of Phoebe bournei and Conophytum purpureus) decomposes quickly, which to some extent helps prevent the formation and spread of forest fires.

[0089] Example 4

[0090] In the Guangxi State-owned Qipo Forest Farm in Wuwei Town, Jiangnan District, Nanning City, Guangxi, a demonstration forest of mixed forests of Masson pine and various broadleaf trees was established, transforming low-yield, near-mature Masson pine forests. The Masson pine was planted in 2001, and after thinning in 2016, broadleaf trees (Castanopsis fargesii, Magnolia officinalis, Machilus thunbergii, and Michelia alba) were interplanted under the forest canopy in 2017. The mixed planting was done in strips with large embankments, and base fertilizer was applied. Topdressing and weeding were carried out for three consecutive years. A total of 12 fixed observation plots were established, each with an area of ​​900 m². 2 (30m×30m) According to the survey, the number of 22-year-old Masson pine trees is 24 per mu, with a total volume of 12.528m³. 3 / mu; the total number of broad-leaved trees is 50 per mu, including 23 red pine trees per mu, and 9 trees each of the other three species. The growth of each tree species is investigated as follows:

[0091]

[0092] As shown in the table above, the Red Castanopsis has the largest diameter at breast height and tree height, and the highest single-tree volume, followed by the Michelia champaca and Magnolia grandiflora, while the Firewood has the lowest.

[0093] Example 5

[0094] In the Guangxi State-owned Qinlian Forest Farm in Qinzhou City, Guangxi, a demonstration forest of mixed Masson pine and Red Castanopsis trees was established in the low-yield, overmature Masson pine watershed area. The Masson pine was initially sown by aerial seeding in 1977, and later replanted using a one-hoe-one-tree method organized by the forest farm. From 1995 to 2005, the forest farm contracted out resin tapping multiple times, resulting in a typical low-quality, low-efficiency forest stand. In March 2012, *Machilus chinensis* was planted under the forest canopy in a mixed row and row planting pattern with a spacing of 3m x 3m. Fertilization and tending were carried out continuously for four years after planting. The sample plot survey was completed in June 2023, establishing 12 fixed observation plots, each with an area of ​​400m². 2 (20m×20m). The survey results of various tree species in the forest stand in 2023 are as follows: ① The average diameter at breast height (DBH), tree height, and single-tree volume of Masson pine were 23.2cm, 11.9m, and 0.2621m³, respectively. 3 The number of plants preserved was 602 per hectare. 2 The volume is 155.8662 m³. 3 / hm 2 ②The average diameter at breast height (DBH), tree height, and single-tree volume of *Machilus thunbergii* are 9.4 cm, 8.5 m, and 0.0430 m², respectively. 3 The retention rate is 223 plants / hm² 2 The volume is 10.2877 m³. 3 / hm 2 ③ The average diameter at breast height (DBH), tree height, and single-tree volume of miscellaneous trees were 5.9 cm, 5.2 m, and 0.0112 m³, respectively. 3 The retention rate is 285 plants / hm² 2 The volume is 3.0746 m³. 3 / hm 2 The proportion of mixed forest understory trees (non-target tree species) reached 25.67%, indicating that mixing promoted understory vegetation regeneration, increased the number of other associated tree species, enhanced biodiversity, and contributed to the ecological stability of the water source forest area. In early 2024, a forest fire occurred in the area, burning 600 mu (approximately 40 hectares). The burned forest land was mainly pure Masson pine forest. Most of the mixed pine and broadleaf forest areas experienced small burned areas and slow spread, allowing for timely extinguishing. This fully demonstrates the positive role of establishing mixed pine and broadleaf forests in forest ecology and fire prevention.

[0095] Example 6

[0096] In the Guangxi State-owned Qinlian Forest Farm in Qinzhou City, Guangxi Province, a mixed forest demonstration area of ​​low-yield, overmature Masson pine and Miluopai was established in the water source forest area. The Masson pine was sown by aerial seeding in 1977, and the forest farm contracted out resin tapping multiple times between 1995 and 2005, resulting in a typical low-quality, low-efficiency forest stand. In 2016, Miluopai was planted under the forest canopy in a mixed row and row planting pattern, with a spacing of 3m x 3m. Fertilizer and tending were applied continuously for four years after planting. The sample plot survey was completed in June 2023, establishing 12 fixed observation plots, each with an area of ​​400m². 2(20m×20m). The survey results of various tree species in the forest stand in 2023 are as follows: ① The average diameter at breast height (DBH), tree height, and single-tree volume of Masson pine were 16.8cm, 8.8m, and 0.1125m³, respectively. 3 The number of plants preserved was 898 per hectare. 2 The volume is 99.5761 m³. 3 / hm 2 ②The average diameter at breast height (DBH), tree height, and single-tree volume of Milaopai are 7.7 cm, 8.4 m, and 0.0261 m², respectively. 3 The retention rate was 663 plants / hm². 2 The volume is 17.0662 m³. 3 / hm 2 ③ The average diameter at breast height (DBH), tree height, and single-tree volume of miscellaneous trees were 5.3 cm, 5.7 m, and 0.0113 m³, respectively. 3 The retention rate was 125 plants / hm². 2 The volume is 1.3150m. 3 / hm 2 Monitoring showed that when mixed with *Millettia laurentii* at a 1:1 ratio, the survival rate of *Millettia laurentii* reached 73.8%, and its average tree height was only 4.7% lower than that of *Pinus massoniana*, basically consistent with the height distribution of the *Pinus massoniana* population. This indicates that the mixed planting was effective, significantly promoting the improvement of the canopy structure of the tree species, and also promoting the competitive growth of *Pinus massoniana* trees and the increase in the height of branches. The litter under the forest floor consisted mainly of branches and leaves from *Millettia laurentii*, comprehensively slowing the spread of forest fires and reducing their intensity. The high density of *Millettia laurentii* resulted in a well-developed and interwoven root system in the forest surface, abundant and rapidly decomposing litter, which also promoted the improvement of soil physical structure and soil water conservation function.

Claims

1. A method for transforming low-quality and inefficient Masson pine water source forests into mixed coniferous and broad-leaved forests, characterized in that, Includes the following: (1) Forest stand diagnosis and planning; (2) Three-dimensional replanting; (3) Innovation of mixed breeding mode.

2. The method for transforming low-quality and low-efficiency Masson pine water source forests into mixed coniferous and broad-leaved forests according to claim 1, characterized in that, Forest stand diagnosis and planning include the following: Damage levels were determined in the first year after the fire: Classified into Level I, Level II, and Level III based on the canopy burn rate; Healthy Masson pine trees were preserved: Individuals with a DBH ≥ 25cm, a surviving canopy width > 40%, and good trunk shape were selected and maintained at a suitable density.

3. The method for transforming low-quality and low-efficiency Masson pine water source forests into mixed coniferous and broad-leaved forests according to claim 1, characterized in that, The canopy burn rate is ≤30% for Class I, 30-60% for Class II, and >60% for Class III.

4. The method for transforming low-quality and low-efficiency Masson pine water source forests into mixed coniferous and broad-leaved forests according to claim 1, characterized in that, The appropriate density is 20-25 plants per hectare.

5. The method for transforming low-quality and low-efficiency Masson pine water source forests into mixed coniferous and broad-leaved forests according to claim 1, characterized in that, Vertical replanting includes the following: 1) Spatial configuration: The upper layer of trees is replanted with fire-resistant broad-leaved trees, the middle layer is planted with precious trees or nitrogen-fixing trees, and the lower layer is planted with edible and medicinal shrubs. 2) Timing and specifications: Replanting should be done during the rainy season, using container seedlings.

6. The method for transforming low-quality and low-efficiency Masson pine water source forests into mixed coniferous and broad-leaved forests according to claim 1, characterized in that, The upper layer of tree species includes one or more of *Michelia champaca*, *Phoebe bournei*, and *Hematoxylin indica*; the middle layer of tree species includes one or more of *Phoebe zhennan* and *Phoebe bournei*; and the lower layer of tree species includes one or more of *Ficus microcarpa* and *Ficus spp.*.

7. The method for transforming low-quality and low-efficiency Masson pine water source forests into mixed coniferous and broad-leaved forests according to claim 1, characterized in that, The container seedlings are >50cm in height and >0.5cm in diameter at the ground.

8. The method for transforming low-quality and low-efficiency Masson pine water source forests into mixed coniferous and broad-leaved forests according to claim 1, characterized in that, Innovation in hybrid hybrid models includes the following: 1) Strip mixed planting: Create replanting strips along contour lines, with fire-resistant broad-leaved trees spaced 4m apart and 3m apart; shade-tolerant precious tree species or nitrogen-fixing trees are interplanted between the fire-resistant tree rows at a ratio of 1:5; edible and medicinal shrubs are planted in the replanting strips, with a plant spacing of 0.5m and a row spacing of 0.5m. 2) Proportion control: Maintain 20-25 Masson pine trees per mu, 45 fire-resistant broad-leaved trees, 9 shade-tolerant precious tree species or nitrogen-fixing trees, and 800 edible and medicinal shrubs. Through natural thinning, a vertical structure of tall and short trees and shrubs, with an appropriate proportion of Masson pine and broad-leaved trees, is eventually formed.

9. The method for transforming low-quality and low-efficiency Masson pine water source forests into mixed coniferous and broad-leaved forests according to claim 1, characterized in that, The planting strip width is 1.5-2m, and the strip spacing is 3m.

10. The method for transforming low-quality and low-efficiency Masson pine water source forests into mixed coniferous and broad-leaved forests according to claim 1, characterized in that, The final result is a vertical structure of tall and short trees and shrubs, with Masson pine accounting for 20-25% and broad-leaved trees accounting for 75-80%.

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