Target tree grading and tending and soil management method for promoting large-diameter timber formation of pinus yunnanensis

Abstract

The application discloses a target tree grading tending and soil management method for promoting large-diameter timber formation of Pinus yunnanensis, and relates to the technical field of forest cultivation.The specific steps of the method are as follows: a two-dimensional corresponding system of large-diameter timber cultivation priority and phenology rhythm of Pinus yunnanensis is constructed, and the tending and soil management rules of target trees at different levels corresponding to the phenophase are determined; according to different phenophases in spring, summer and autumn, differentiated tending and root zone management are implemented on the three-level target trees according to the system; the whole-process operation is integrated, a linkage closed loop is constructed, and annual circulation is executed to realize directional and accurate cultivation; the two-dimensional system of cultivation priority and phenology rhythm is constructed, accurate grading and differentiated tending of the trees are realized, the stem form quality is improved, and the overall cultivation efficiency is improved; accurate management of the root zone soil is implemented to meet the nutrient requirement and improve the stress resistance; a whole-process linkage closed loop and a dynamic adjustment mechanism are established to realize real-time optimization of the management strategy, shorten the large-diameter timber cultivation period, and improve the yield and quality of the timber.

Description

Technical Field

[0001] This invention relates to the field of forest cultivation technology, specifically to a method for graded tending and soil management of target trees that promotes the formation of large-diameter Yunnan pine. Background Technology

[0002] Yunnan pine, a native coniferous species endemic to Southwest my country, is a core species for plantation construction and commercial timber production. Its large-diameter timber is of excellent quality, has a wide range of uses, and its economic value far exceeds that of small and medium-diameter timber. It is a key cultivation target for improving the quality and efficiency of Yunnan pine plantations and promoting high-quality development of the forestry industry. Currently, Yunnan pine plantations mainly focus on cultivating small and medium-diameter timber, resulting in a significant shortage of large-diameter timber. Traditional cultivation methods employ extensive tending and management, lacking targeted target tree selection and grading mechanisms. This leads to a disconnect between soil nutrient supply and tree growth rhythms, resulting in insufficient trunk straightness, slow diameter growth, long cultivation cycles for large-diameter timber, and low timber yield, making it difficult to meet market and industry development needs.

[0003] Existing Yunnan pine tending and soil management techniques have many shortcomings: A quantitative grading system has not been established based on tree growth characteristics; there are no differentiated cultivation strategies for core dominant trees, auxiliary trees, and general trees; tending resources are allocated blindly; and the growth space and nutrient supply for core target trees are insufficient. Tending operations are not coupled with the phenological rhythms of rapid growth in spring, diameter increase in summer, and lignification in autumn; the timing and intensity of pruning and thinning are unreasonable, easily reducing photosynthetic efficiency or causing ineffective nutrient consumption. Soil management only uses conventional compound fertilizers, without the differentiated application of rhizosphere growth-promoting bacteria and organic fertilizers; root zone soil fertility regulation is lacking. There is no annual closed-loop cycle and dynamic adjustment mechanism; target tree grading is fixed; tending and soil management cannot be optimized with tree growth, ultimately leading to low efficiency in large-diameter timber formation and substandard trunk shape and diameter growth.

[0004] To address the shortcomings of existing technologies, such as extensive grading, insufficient phenological coupling, simplistic soil management, and lack of dynamic regulation, the industry urgently needs precise, differentiated, and time-sequential methods for cultivating large-diameter Yunnan pine. This invention constructs a dual-dimensional grading system based on cultivation priorities and phenological rhythms, implementing graded and phenologically differentiated target tree tending and soil management. This forms an annual linkage closed-loop and dynamic adjustment mechanism, overcoming the limitations of traditional technologies, improving the diameter growth rate and trunk quality of Yunnan pine, shortening the cultivation cycle of large-diameter timber, and providing core technical support for the efficient cultivation of large-diameter Yunnan pine in plantations. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for graded tending and soil management of target trees to promote the formation of large-diameter Yunnan pine. This method constructs a dual-dimensional system of cultivation priority and phenological rhythm, divides the target trees into three levels and clarifies the corresponding management rules; implements differentiated tending, root zone nutrient supply and growth promotion regulation, and other operations on the three levels of target trees at different phenological stages; integrates the entire process to construct a closed-loop linkage, and provides a supporting dynamic monitoring and adjustment mechanism to optimize management based on the growth status of the trees, thereby achieving targeted and precise cultivation of large-diameter Yunnan pine.

[0006] To solve the above-mentioned technical problems, this invention provides the following technical solution: a method for graded tending and soil management of target trees to promote the formation of large-diameter timber in Yunnan pine, the specific steps of which are as follows:

[0007] S100, Construction of a dual-dimensional grading system: Based on the priority of cultivating large-diameter Yunnan pine, three levels of target trees are divided into core retention trees, auxiliary retention trees, and general retention trees. The three levels of target trees are then linked to the Yunnan pine’s spring rapid growth period, summer diameter increase period, and autumn lignification period in full time sequence. A dual-dimensional correspondence system of cultivation priority and phenological rhythm is established, and the tending and soil management rules for the corresponding phenological periods of each level of target trees are clarified.

[0008] S200, Spring Rapid Growth Period Grading: After entering the spring rapid growth period of Yunnan pine, differentiated tending treatment is implemented for the three target trees according to the two-dimensional correspondence system, and the initial nutrient supply and growth promotion regulation of the root zone corresponding to the tending level are carried out simultaneously.

[0009] S300, Summer Diameter Increase Period Follow-up: After entering the summer diameter increase period of Yunnan pine, according to the dual-dimensional correspondence system, the canopy pruning and tending of the three-level target trees are carried out in accordance with the phenological period, and root zone fertilizer and rhizosphere growth-promoting bacteria agents corresponding to the tending level and cultivation priority are applied simultaneously.

[0010] S400, End of Autumn Lignification Period: After entering the autumn lignification period of Yunnan pine, according to the two-dimensional corresponding system, crown control or thinning and tending treatment is carried out on the three-level target trees, and root zone soil energy storage fertilization management corresponding to the tending level is carried out simultaneously.

[0011] S500, Linked Closed-Loop Cyclic Execution: Integrating the entire process of grading, tending, and soil management operations from S100 to S400, a linked closed loop covering all aspects of the target tree is constructed, and the targeted and precise cultivation of large-diameter Yunnan pine is completed through annual cyclical execution.

[0012] Furthermore, the three-tiered target trees are quantitatively classified according to the individual tree growth characteristics and suitability for large-diameter timber cultivation: each tree in the target forest stand is measured to obtain five indicators: diameter at breast height (DBH), tree height, trunk straightness, crown integrity, and health status. Dominant trees with DBH in the top 15% of the stand's cumulative total, trunk straightness ≥0.9, no pests or mechanical damage, intact crowns, and evenly distributed lateral branches are designated as core trees with the highest cultivation priority, with 80-100 trees retained per hectare. Associated trees with DBH in the 15%-40% range of the stand's cumulative total, trunk straightness ≥0.7, no serious pests or diseases, and stable crown shape are designated as auxiliary trees with medium cultivation priority, with 120-150 trees retained per hectare. The remaining trees with DBH below the 40% range of the stand's cumulative total, with poor trunk shape, or exhibiting signs of disease or weakness are designated as general trees with low cultivation priority.

[0013] Furthermore, the differentiated tending treatment corresponds to the phenological characteristics of the rapid growth period in spring, specifically as follows: for core trees, remove all competing trees in the upper and lateral canopy layers to control the canopy spacing to ≥1.5m; for auxiliary trees, remove overly dense and overlapping lateral branches and diseased or weak branches, retain healthy main branches, and control the canopy width to prevent it from extending into the growth space of the core trees; for general trees, remove dead, diseased, and broken branches from the stand, and do not carry out additional thinning or pruning operations to maintain the basic structure of the stand.

[0014] Furthermore, the root zone nutrient supply and growth-promoting regulation operations correspond one-to-one with the sturdiness treatment levels. Specifically, for core retention trees, a circular trench is dug 20cm outside the canopy projection, and 200g / tree of fast-acting nitrogen fertilizer and 50g / tree of nitrogen-fixing growth-promoting bacteria are applied, followed by covering with soil and watering. For auxiliary retention trees, point-like holes are dug at the canopy projection, and 150g / tree of conventional nitrogen, phosphorus, and potassium compound fertilizer is applied, followed by covering with soil. For general retention trees, no fertilization or growth-promoting bacteria application is carried out, and the natural fertility of the soil is relied upon.

[0015] Furthermore, the canopy pruning and tending operations correspond to the phenological characteristics of the summer diameter increase period and follow the S200 spring tending operations. Specifically, for core retention trees, remove vigorous shoots, crossing branches, and ineffective branches that block light in the inner canopy, with the pruning intensity controlled within 10% of the total canopy branches; for auxiliary retention trees, remove weak branches, drooping branches, and overly dense lateral branches in the lower canopy, with the pruning intensity controlled within 20%-25% of the total canopy branches, and the canopy height ratio controlled at 0.6-0.7; for general retention trees, no pruning or thinning operations are carried out to maintain the forest stand transition structure.

[0016] Furthermore, the application of root zone fertilizer and rhizosphere growth-promoting bacteria corresponds one-to-one with the level of tending operations and cultivation priority. Specifically, for core retention trees, radial fertilization holes are dug along the outer edge of the canopy projection, and 250g / tree of high phosphorus and potassium slow-release fertilizer with a nitrogen-phosphorus-potassium ratio of 5:15:20 and 60g / tree of phosphorus- and potassium-solubilizing rhizosphere growth-promoting bacteria are applied. After application, the trees are covered with soil and watered. For auxiliary retention trees, dotted holes are dug at the canopy projection, and 180g / tree of balanced compound fertilizer with a nitrogen-phosphorus-potassium ratio of 10:10:10 is applied. After application, the trees are covered with soil. For general retention trees, no fertilization or bacteria application is carried out.

[0017] Furthermore, the aforementioned tending treatment and soil energy storage fertilization management, matched with the phenological characteristics of autumn wood lignification and nutrient reflux storage of Yunnan pine, form an annual growth closed loop following the summer operations of S300:

[0018] In the tending and maintenance phase: For core trees, prune vigorous autumn shoots and water sprouts at the top of the canopy to control excessive growth and promote the accumulation of photosynthetic products in the trunk to facilitate lignification and distribution to the root system to store nutrients; for auxiliary trees, carry out light canopy control pruning and remove outward-extending competing lateral branches to avoid competing with core trees for light resources before winter; for general trees, carry out thinning at a rate of 15%-20% of the total number of trees in the stand, prioritizing the removal of diseased and weak trees and trees that crowd out the space of core trees, so as to release more nutrient space and light resources for core and auxiliary trees and achieve the orderly withdrawal of low-priority trees;

[0019] Soil energy storage and fertilization management: For core retention trees, dig a circular trench along the outer edge of the canopy projection, apply 3 kg of fully decomposed organic fertilizer per tree, and cover with soil after application to store sufficient nutrients for root overwintering and sprouting in the following spring, while improving the physical and chemical properties of the root zone soil; for auxiliary retention trees, dig spot holes at the canopy projection, apply 1 kg of fully decomposed organic fertilizer per tree, and cover with soil after application to meet the nutrient storage needs before overwintering; for general retention trees, no fertilization operations are carried out to maintain the natural fertility of the soil.

[0020] Furthermore, the pruning intensity of the core trees at different phenological stages is determined by a phenological rhythm coupled cultivation priority control algorithm to ensure that the pruning intensity is fully matched with the photosynthetic growth requirements of the target trees. The specific calculation and implementation steps are as follows:

[0021] The first step is to measure the effective photosynthetic area S of the canopy, the daily average effective photosynthetic radiation flux density PAR of the canopy of the target core tree during the corresponding phenological period, and the annual growth of the diameter at breast height G of a single tree at the initial stage of the corresponding phenological period for the target core tree.

[0022] The second step involves calculating the pruning intensity P of the core trees to be retained during the phenological period using a phenological rhythm coupling and priority control algorithm.

[0023]

[0024] in, The pruning intensity of the core trees retained during the target phenological period is a dimensionless number with a value between 0 and 1. The annual diameter at breast height (DBH) growth target for cultivating large-diameter timber of core retention trees, expressed in cm / year; The dry wood growth distribution coefficients for Yunnan pine corresponding to phenological periods are 0.3 for the rapid growth period in spring, 0.6 for the diameter increase period in summer, and 0.1 for the lignification period in autumn. The effective photosynthetic area of ​​the canopy layer is preserved in the core area, in m². The average daily photosynthetically active radiation flux density of the canopy layer during the corresponding phenological period is retained for the target core, in μmol·m⁻²·s⁻¹; The photosynthetic conversion coefficient of Yunnan pine needles is the mass of dry matter that can be converted per unit of photosynthetically active radiation, expressed in g·μmol⁻¹. The biomass conversion factor, in physical terms, represents the accumulation of trunk biomass corresponding to every 1 cm increase in diameter at breast height (DBH), expressed in g / cm.

[0025] The third step is to carry out pruning operations on the core trees to be retained according to the pruning intensity P calculated by the formula, so as to ensure that the pruning intensity is precisely matched with the growth needs and cultivation priorities of the phenological period, and to avoid excessive pruning leading to insufficient photosynthetic products, or insufficient pruning leading to ineffective consumption of nutrients.

[0026] Furthermore, the total amount of fertilizer applied to the core trees at different phenological stages is determined by a cultivation priority coupled with a phenological rhythm nutrient matching algorithm, ensuring that the amount of fertilizer is completely matched with the growth needs and tending intensity of the target trees. The specific calculation and implementation steps are as follows:

[0027] The first step is to measure the diameter at breast height (DBH) of a single tree (D), the crown projection area (A), and the pruning intensity (P) of the target core tree at the initial stage of the corresponding phenological period for the target core tree.

[0028] The second step involves calculating the total fertilization amount Q for the core trees retained during the phenological period using a priority-coupled phenological rhythm-based nutrient matching algorithm.

[0029]

[0030] in, The total amount of fertilizer applied to the core trees retained during the target phenological period is expressed in g per tree. The diameter at breast height (DBH) of the core tree is measured in cm. The projected area of ​​the crown of the core tree to be preserved, in m²; The nutrient requirement coefficients for Yunnan pine corresponding to the phenological stages are 1.2 for the rapid growth period in spring, 1.5 for the diameter increase period in summer, and 0.8 for the lignification period in autumn. The pruning intensity for the core trees retained during the target phenological period; The target coefficient for cultivating large-diameter Yunnan pine is set at 1.2 for core retention trees, 0.8 for auxiliary retention trees, and 0 for general retention trees; δ is the unit conversion coefficient, which physically represents the amount of basic fertilizer applied per unit of diameter at breast height (DBH) multiplied by the crown projection area.

[0031] The third step is to calculate the total fertilizer amount Q according to the formula, and combine it with the nutrient requirements of the corresponding phenological stage to determine the ratio and application amount of nitrogen, phosphorus and potassium fertilizers. Then, carry out fertilization operations in the root zone of the core trees to be retained in the corresponding phenological stage, so as to achieve a full-dimensional linkage and matching of fertilization timing, fertilization amount, cultivation priority, phenological rhythm and tending intensity.

[0032] Furthermore, the annual cycle is complemented by a dynamic monitoring and adjustment mechanism: after the lignification period ends each autumn, a tree-by-tree measurement is conducted on all target trees in the stand to obtain data on diameter at breast height (DBH), trunk straightness, and canopy structure changes for core, auxiliary, and general retention trees, while simultaneously measuring root zone soil fertility indicators; based on the measurement data, the classification of the three levels of target trees is dynamically adjusted, downgrading trees that are declining in growth or do not meet the standards for core retention trees, and upgrading trees with excellent growth traits that meet high-priority standards, while simultaneously updating the tending and soil management rules in the corresponding dual-dimensional grading system; according to the adjusted grading system, the full-process tending and soil management operations for the following year are carried out, continuously optimizing the efficiency of the linked closed-loop resource allocation and ensuring the continuous and stable advancement of Yunnan pine large-diameter timber cultivation.

[0033] Compared with existing technologies, this method for graded tending and soil management of target trees that promotes the formation of large-diameter Yunnan pine has the following beneficial effects:

[0034] I. This invention constructs a dual-dimensional correspondence system between cultivation priority and phenological rhythm to implement precise grading and differentiated tending management of forest trees. It classifies target trees into different cultivation levels based on their growth characteristics; combines the growth rhythms of rapid growth in spring, diameter increase in summer, and lignification in autumn to carry out adaptive tending operations; rationally regulates the spatial structure of the forest stand and canopy light conditions; ensures that high-priority target trees receive sufficient growth space and light resources; reduces ineffective nutrient consumption; and guides the efficient accumulation of photosynthetic products into timber; effectively improves the quality of tree trunk shape; changes the traditional situation of uneven distribution of tending resources and extensive management; enhances the overall cultivation efficiency of the forest stand; and promotes the steady development of Yunnan pine plantations towards the targeted cultivation of large-diameter timber.

[0035] II. This invention implements precise root zone soil management by matching target trees of different levels with their phenological needs. It combines tending grade with nutrient supply and rhizosphere regulation measures to optimize the soil fertility supply structure in stages, meeting the nutrient needs of trees at different growth stages, promoting root development and nutrient absorption and utilization, assisting in the lignification of dry wood and nutrient reserves, and enhancing the trees' stress resistance and growth stability. At the same time, it establishes a closed-loop linkage mechanism and an annual dynamic adjustment mechanism to optimize the target tree classification and management strategy in real time based on the trees' growth status, improve resource allocation efficiency, effectively shorten the cultivation cycle of large-diameter timber, increase the yield and quality of large-diameter timber, and significantly enhance the economic value and industrial benefits of Yunnan pine plantations.

[0036] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0038] Figure 1 This is a flowchart illustrating the steps of the present invention.

[0039] Figure 2 This is a flowchart of the three-level target tree quantization and classification process of the present invention;

[0040] Figure 3 This is a flowchart illustrating the integrated process of graded tending and soil management throughout the entire phenological period of this invention. Detailed Implementation

[0041] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0042] Example 1:

[0043] A pure stands of Yunnan pine in its middle to young age were selected as the cultivation target. These stands are at a critical stage of transition from vegetative to reproductive growth, exhibiting ample growth potential. By constructing a dual-dimensional system corresponding to cultivation priorities and phenological rhythms, forest growth resources can be precisely allocated, prioritizing the cultivation of high-value trees and establishing a scientific cultivation framework for large-diameter timber formation. Firstly, quantitative classification was conducted based on the compatibility of individual tree growth characteristics with large-diameter timber cultivation. A comprehensive tree-by-tree measurement was performed on the target stands, obtaining five core indicators: diameter at breast height (DBH), tree height, trunk straightness, crown integrity, and health status. Through comprehensive analysis of these five indicators, the growth advantages and cultivation value of trees were accurately distinguished, avoiding the allocation of cultivation resources to trees with poor growth characteristics and maximizing resource utilization efficiency. Dominant trees with a cumulative diameter at breast height (DBH) in the top 15% of the stand, a trunk straightness of at least 0.9, freedom from pests, diseases, and mechanical damage, and intact crowns with evenly distributed lateral branches are designated as core retention trees, with 90 trees retained per hectare. These trees possess the best trunk shape and growth vigor, and their retention will allow for concentrated sunlight and nutrient resources to promote rapid DBH growth, making them the core force in large-diameter timber cultivation. Associated trees with a DBH between 15% and 40% of the stand, a trunk straightness of at least 0.7, freedom from serious pests and diseases, and stable crown shapes are designated as auxiliary retention trees, with 130 trees retained per hectare. These trees will help maintain the stability of the stand structure, while gradually optimizing trunk shape and growth vigor, forming a high-quality timber tier and enriching the stand's large-diameter timber reserves. The remaining trees with a DBH below 40% of the cumulative DBH, poor trunk shape, or signs of disease or weakness are designated as general retention trees. These trees only play a role in maintaining the stand's ecological foundation, do not occupy additional cultivation resources, and ensure the overall ecological and growth balance of the stand. After completing the three-level target tree classification, the three-level target trees are associated with the rapid growth period in spring, the diameter increase period in summer, and the lignification period in autumn of Yunnan pine in a full time sequence. A two-dimensional correspondence system of cultivation priority and phenological rhythm is established to clarify the tending and soil management rules for the corresponding phenological periods of each level of target trees. This ensures that every cultivation operation conforms to the natural growth rhythm of the trees, maximizes the activation of the trees' growth potential, and provides clear execution standards for subsequent graded tending and soil management.

[0044] After entering the rapid spring growth period of Yunnan pine, the trees experience a peak growth period characterized by rapid bud break and root expansion. At this time, differentiated tending treatment is implemented according to a two-dimensional corresponding system. Simultaneously, initial nutrient supply and growth-promoting regulation in the root zone are carried out according to the corresponding tending level, precisely adapting to the growth needs of rapid spring growth and laying a solid nutritional foundation for subsequent trunk diameter thickening. For core trees, all competing trees in the upper and lateral canopies are removed, controlling the canopy spacing to no less than 1.5m. This completely eliminates competition for space and light from surrounding trees, allowing core trees to fully receive natural sunlight, rapidly expanding the canopy photosynthetic area, significantly improving the efficiency of photosynthetic product accumulation, and providing sufficient energy for rapid growth. For auxiliary trees, overly dense and overlapping lateral branches and weak or diseased branches are removed, retaining healthy main branches. The canopy width is controlled to prevent it from extending into the growth space of the core trees, optimizing the canopy structure of auxiliary trees, reducing nutrient consumption by ineffective branches and leaves, and avoiding interference with the growth space of the core trees. This ensures that the growth of primary and secondary trees does not conflict with each other and progresses synergistically. For general retention trees, dead, diseased, and broken branches are removed from the stand without additional thinning or pruning to maintain the basic structure of the stand and reduce the breeding and spread of pests and diseases from the source, ensuring the overall healthy growth of the stand. Simultaneously, initial nutrient supply and growth-promoting regulation in the root zone are implemented to precisely match the spring nutrient needs of different tree grades, quickly filling the nutrient gap during the rapid growth period. For core retention trees, a circular trench is dug 20cm outside the canopy projection, and fast-acting nitrogen fertilizer and nitrogen-fixing growth-promoting bacteria are applied. After application, the soil is covered and watered. The fast-acting nitrogen quickly meets the nutrient needs of rapid branch and leaf growth, while the nitrogen-fixing bacteria strengthen the nitrogen-fixing capacity of the roots and improve soil nutrient absorption efficiency, allowing core retention trees to quickly form a robust canopy and developed root system in spring. For auxiliary trees, dig pits at the canopy projection point, apply conventional NPK compound fertilizer, and cover with soil after application. This provides a balanced supply of nutrients needed during the rapid growth phase of the auxiliary trees, maintaining their stable growth without excessive fertilization that would waste resources. For general trees, no fertilization or growth-promoting agent application is performed; reliance is placed solely on natural soil fertility, aligning with their low cultivation priority and ensuring reasonable control of cultivation costs and resource allocation. The pruning intensity for core trees is determined using a phenological rhythm coupled with a cultivation priority control algorithm, the formula being: ,in, The pruning intensity for the core trees retained during the target phenological period; The annual target for cultivating large-diameter timber for core retention trees is the diameter at breast height (DBH) growth. The dry wood growth distribution coefficient of Yunnan pine corresponding to the phenological period; To preserve the effective photosynthetic area of ​​the canopy layer at the core; To preserve the average daily photosynthetically active radiation flux density of the canopy layer during the corresponding phenological period for the target core; The photosynthetic conversion coefficient of Yunnan pine needles; It is the biomass conversion coefficient; to ensure that the pruning intensity is fully matched with the spring photosynthetic growth needs of the core trees, to avoid excessive pruning that reduces the photosynthetic area, and to prevent insufficient pruning that leads to ineffective nutrient consumption, so that the pruning operation can precisely serve the rapid growth needs of the core trees.

[0045] After entering the summer trunk growth period of Yunnan pine, the trees enter the core stage of rapid trunk thickening, and photosynthetic products begin to be transported and accumulated in large quantities to the main trunk. At this time, canopy pruning and tending are carried out according to the dual-dimensional corresponding system and adapted to the phenological stage. Root zone fertilizers and rhizosphere growth-promoting bacteria agents corresponding to the tending level and cultivation priority are applied simultaneously. Following the spring tending operations, the canopy structure is continuously optimized, focusing on nutrient transport to the trunk and accelerating the growth of tree trunk diameter. For the core trees to be retained, vigorous branches, crossing branches, and ineffective branches that block light in the inner canopy are removed. The pruning intensity is controlled within 10% of the total number of branches in the canopy, streamlining ineffective branches and leaves in the canopy, reducing unnecessary nutrient consumption, allowing more photosynthetic nutrients to be concentrated on trunk thickening, improving canopy ventilation and light penetration, reducing the probability of pests and diseases in the high temperature and humidity environment of summer, and ensuring healthy trunk growth of the core trees to be retained. For auxiliary retention trees, remove weak, drooping, and overly dense lateral branches from the lower canopy. Pruning intensity should be controlled at 20%-25% of the total canopy branches, with a canopy height ratio of 0.6-0.7. This optimizes the canopy morphology of auxiliary retention trees, guides nutrient transport to the main trunk, gradually improves trunk straightness, and prevents excessive canopy shading of the core retention trees, ensuring priority growth for the core trees. For general retention trees, no pruning or thinning is performed to maintain the stand's transitional structure, ensure overall stand stability and ecological function, and avoid additional interference with their growth. Simultaneously applied root zone fertilizer and rhizosphere growth-promoting microbial agents precisely match the nutrient requirements during the summer diameter increase period, strengthening nutrient support for trunk growth. For core trees, radial fertilization holes are dug along the outer edge of the canopy projection. High-phosphorus and potassium slow-release fertilizer and phosphorus- and potassium-solubilizing rhizosphere growth-promoting bacteria are applied, followed by covering with soil and watering. The high-phosphorus and potassium nutrients directly promote trunk lignification and diameter increase, while the slow-release fertilizer provides a continuous supply of nutrients suitable for the long summer growing season. The phosphorus- and potassium-solubilizing rhizosphere growth-promoting bacteria improve soil nutrient utilization, allowing core trees to efficiently absorb nutrients and accelerate trunk diameter increase. For auxiliary trees, point-like holes are dug at the canopy projection, and balanced compound fertilizer is applied, followed by covering with soil. This evenly replenishes nutrients during the diameter increase period, maintaining stable diameter growth and matching the growth needs of trees with medium cultivation priority. No fertilization or bacteria application is performed on general trees; they rely on natural soil fertility for growth and do not occupy core cultivation resources. The total amount of fertilizer applied to core trees is determined based on a cultivation priority coupled with a phenological rhythm-based nutrient matching algorithm, using the following formula: ,in, The total amount of fertilizer applied to the core trees retained during the target phenological period; The diameter at breast height (DBH) of the core tree is preserved; The projected area of ​​the crown of the core tree to be preserved; The nutrient requirement coefficient for Yunnan pine during its corresponding phenological period; The pruning intensity for the core trees retained during the target phenological period; The target coefficient for cultivating large-diameter Yunnan pine is δ, which is the unit conversion coefficient. This ensures that the amount of fertilizer applied is fully matched with the summer growth needs and tending intensity of the core trees, and that the nutrient supply is precise and sufficient, avoiding insufficient fertilization from affecting diameter growth or excessive fertilization from causing soil pollution.

[0046] After entering the autumn lignification period of Yunnan pine, the trees enter a critical stage of trunk lignification and nutrient recirculation and storage. Photosynthetic products gradually transfer and accumulate in the trunk and root system. At this time, crown control or thinning and tending treatments are implemented according to a two-dimensional corresponding system, and root zone soil energy storage fertilization management is carried out simultaneously according to the tending level. This forms an annual growth closed loop following the summer operations, guiding the trees to complete the lignification process and improving their overwintering resistance. For core trees, vigorous autumn shoots and water sprouts at the top of the canopy are pruned to control tall and vigorous growth, forcing photosynthetic products to accumulate in the trunk and accelerating the lignification process. At the same time, nutrients are guided to be distributed and stored in the root system, strengthening the overwintering resistance of core trees and storing sufficient energy for rapid germination in the following spring, ensuring stable diameter increase year after year. For auxiliary trees, light crown control pruning is carried out to remove competing lateral branches extending outwards, avoiding competition with core trees for light resources before overwintering. This ensures that core trees have priority in obtaining light to complete nutrient storage, while optimizing the canopy structure of auxiliary trees to improve their lignification quality and overwintering stability. Thinning will be carried out on general reserve trees at a rate of 15%-20% of the total number of trees in the stand. Priority will be given to removing diseased and weak trees, and trees that crowd out the space of core reserve trees. Low-priority trees will be phased out in an orderly manner to free up more nutrient space and light resources for core and auxiliary reserve trees, optimizing the stand's spatial structure and improving the overall nutrient and light utilization efficiency. Simultaneously, root zone soil energy storage fertilization management will be implemented to store soil nutrients for wintering and the following year's growth, continuously improving the root zone soil environment. For core reserve trees, a circular trench will be dug along the outer edge of the canopy projection, and fully decomposed organic fertilizer will be applied and covered with soil. The organic fertilizer will continuously improve the physical and chemical properties of the root zone soil, enhance its water and fertilizer retention capacity, and store long-term nutrients for root overwintering and spring germination, ensuring the core reserve trees' stable growth year after year. For auxiliary reserve trees, point-like pits will be dug at the canopy projection, and fully decomposed organic fertilizer will be applied and covered with soil to meet the nutrient storage needs of auxiliary reserve trees before winter, improving their overwintering survival rate and the following year's growth vigor. No fertilization is applied to trees that are generally preserved, so as to maintain the natural fertility of the soil and conform to the resource allocation principle of low cultivation priority.

[0047] This system integrates a two-dimensional grading system, grading and tending during the rapid growth period in spring, continuous tending during the diameter increase period in summer, and final tending during the lignification period in autumn. It encompasses the entire process of grading, tending, and soil management, creating a closed-loop system covering all stages of the target tree cultivation. This ensures that each stage of cultivation is interconnected and mutually supportive, forming a systematic and standardized cultivation model. Through annual cyclical execution, it achieves targeted and precise cultivation of large-diameter Yunnan pine. Simultaneously, a dynamic monitoring and adjustment mechanism is established. After the lignification period ends each autumn, a tree-by-tree measurement is conducted on all target trees in the stand to comprehensively obtain data on diameter at breast height (DBH), trunk straightness, and canopy structure changes in core, auxiliary, and general trees. At the same time, root zone soil fertility indicators are precisely measured to monitor tree growth and soil nutrient supply in real time. Based on retesting data, the classification of the three-tiered target trees is dynamically adjusted. Trees with declining growth or that do not meet the core retention tree standards are downgraded, while trees with excellent growth traits and that meet high-priority standards are upgraded. Simultaneously, the tending and soil management rules in the corresponding dual-dimensional grading system are updated to ensure the cultivation system always aligns with the actual growth status of the trees and continuously optimizes the efficiency of resource allocation in a closed-loop system. Following the adjusted grading system, the full-process tending and soil management operations for the following year are implemented, continuously iterating the cultivation plan to ensure the sustained and stable progress of Yunnan pine large-diameter timber cultivation. This allows young and middle-aged Yunnan pine pure stands to gradually cultivate a large number of straight, robust, and high-quality large-diameter timber, significantly improving the economic value and cultivation benefits of the stands, and achieving efficient utilization and sustainable cultivation of forest resources. Figure 1 As shown.

[0048] Example 2:

[0049] A mixed forest of Yunnan pine at near-mature age was selected as the cultivation target. The trees in this stand already possess a certain foundation in trunk shape, and the mixed structure makes the stand's ecology more stable. By constructing a two-dimensional correspondence system based on cultivation priorities and phenological rhythms, high-quality trees for cultivation can be accurately selected, the spatial structure of the mixed forest can be optimized, and the focus can be on improving the quality and diameter of core trees, further enhancing the quality of large-diameter timber cultivation. Firstly, a quantitative classification was conducted based on the individual tree growth characteristics and the suitability for large-diameter timber cultivation. A full-coverage tree-by-tree measurement was carried out on the target stand to accurately obtain five indicators: diameter at breast height (DBH), tree height, trunk straightness, crown integrity, and health status. These five indicators were used to comprehensively evaluate the trees' potential for large-diameter timber cultivation, distinguishing between core cultivation, auxiliary cultivation, and basic cultivation trees. This ensures that cultivation resources are precisely allocated to high-value trees, avoiding resource competition within the mixed forest that could restrict the growth of high-quality trees. Dominant trees with a cumulative diameter at breast height (DBH) in the top 15% of the stands, a trunk straightness of at least 0.9, freedom from pests, diseases, and mechanical damage, and intact crowns with evenly distributed lateral branches are designated as core retention trees, with 100 trees retained per hectare. These trees represent the highest potential for quality improvement within the mixed forest. Their retention will allow for concentrated resource allocation to promote rapid DBH growth and continuous trunk shape optimization, making them the core producers of large-diameter timber. Associated trees with a cumulative DBH between 15% and 40%, a trunk straightness of at least 0.7, freedom from serious pests and diseases, and stable crown shapes are designated as auxiliary retention trees, with 150 trees retained per hectare. These trees are well-suited to the mixed forest environment, gradually improving their growth quality and forming a supplementary cultivation echelon for the core trees, enriching the reserve of high-quality large-diameter timber in the mixed forest. Trees with a remaining diameter at breast height (DBH) below 40%, poor trunk shape, or signs of disease or weakness are designated as general reserve trees. These trees are only used to maintain the basic ecological structure of mixed forests, do not occupy special cultivation resources, and ensure the ecological balance and growth stability of mixed forests. Figure 2 As shown, after completing the three-level target tree division, the three-level target trees are associated with the rapid growth period in spring, the diameter increase period in summer, and the lignification period in autumn of Yunnan pine in full time sequence. A two-dimensional correspondence system of cultivation priority and phenological rhythm is established to clarify the tending and soil management rules for the corresponding phenological periods of each level of target trees. This ensures that the cultivation operation conforms to the growth characteristics and phenological patterns of mixed forest trees, and maximizes the activation of the diameter increase and quality improvement potential of near-mature trees.

[0050] After entering the rapid spring growth period of Yunnan pine, trees in mixed forests enter a rapid growth phase, with accelerated bud break and root expansion. At this time, differentiated tending treatment is implemented according to a two-dimensional system, simultaneously providing initial nutrient supply and growth-promoting regulation to the root zone, corresponding to each tending level. This adapts to the growth needs of the rapid spring growth period, alleviates competitive pressure among trees in the mixed forest, and clears obstacles for the rapid growth of core trees. All competing trees in the upper and lateral canopies of the core trees are removed, controlling the canopy spacing to be no less than 1.5m. This completely eliminates light and space competition from other tree species and inferior trees in the mixed forest, allowing the core trees to exclusively enjoy high-quality growth space, fully receive sunlight to improve photosynthetic efficiency, and rapidly expand canopy size to accumulate growth energy. For auxiliary trees, excessively dense and overlapping lateral branches and diseased or weak branches are removed, while healthy main branches are retained. The canopy width is controlled to prevent it from extending into the growth space of the core trees, optimizing the canopy structure of auxiliary trees, reducing ineffective nutrient consumption, and preventing them from encroaching on the growth space of core trees within the mixed forest. This ensures tiered growth and coordinated quality improvement of primary and secondary trees. For general trees, dead, diseased, and broken branches are removed from the stand. No additional thinning or pruning is carried out to maintain the basic structure of the mixed forest, reduce the spread of pests and diseases, and ensure the overall healthy growth of the mixed forest. Simultaneously, initial root zone nutrient supply and growth-promoting regulation are implemented to precisely match the spring nutrient needs of different tree grades, quickly replenishing nutrients during the rapid growth period. For core trees, a circular trench is dug 20cm outside the canopy projection, and fast-acting nitrogen fertilizer and nitrogen-fixing growth-promoting bacteria are applied. After application, the soil is covered and watered. The fast-acting nitrogen quickly meets the needs of rapid branch and leaf growth, while the nitrogen-fixing growth-promoting bacteria enhance the root system's nutrient absorption capacity, allowing the core trees to quickly develop a growth advantage in the mixed forest environment. For auxiliary trees, spot-shaped pits are dug at the canopy projection, and conventional NPK compound fertilizer is applied. After application, the soil is covered to evenly supplement the fast-growing nutrients of the auxiliary trees, maintaining their stable growth and adapting to the medium cultivation needs of the mixed forest. For general trees, no fertilization or growth-promoting bacteria application is carried out; they rely solely on the natural fertility of the soil, rationally controlling the input of cultivation resources in the mixed forest. The pruning intensity of core trees is determined based on a phenological rhythm coupled cultivation priority control algorithm to ensure that the pruning intensity is completely matched with the spring photosynthetic growth needs of the core trees. This precisely optimizes the canopy of core trees in the complex canopy structure of the mixed forest, ensuring the efficient accumulation of photosynthetic products.

[0051] After entering the summer trunk diameter growth period of Yunnan pine, nearly mature trees enter a critical stage of trunk diameter increase and material improvement. A large amount of photosynthetic products are transported to the main trunk. At this time, canopy pruning and tending should be carried out according to a two-dimensional corresponding system, adapted to the phenological stage. Simultaneously, root zone fertilizers and rhizosphere growth-promoting bacteria agents corresponding to the tending level and cultivation priority should be applied. This follows spring tending to optimize the canopy structure of the mixed forest, guiding nutrients to concentrate on supplying the core trees for trunk diameter increase and quality improvement. For the core trees, remove vigorous shoots, crossing branches, and ineffective branches that block light from the inner canopy. The pruning intensity should be controlled within 10% of the total canopy branches. This streamlines the ineffective branches and leaves of the core trees in the mixed forest, reducing nutrient consumption and allowing photosynthetic products to be fully supplied to the main trunk for thickening. At the same time, it improves canopy ventilation and reduces the risk of pests and diseases caused by high temperature and humidity in the mixed forest. For auxiliary trees to be retained, remove weak, drooping, and overly dense lateral branches from the lower canopy. Pruning intensity should be controlled at 20%-25% of the total canopy branches, with a canopy height ratio of 0.6-0.7. This optimizes the canopy morphology of auxiliary trees, guides nutrient transport to the main trunk, improves trunk quality, and avoids shading core trees in mixed forests. No pruning or thinning is performed on general trees to maintain the transitional structure of the mixed forest and ensure its ecological stability. Simultaneously applied root zone fertilizer and rhizosphere growth-promoting microbial agents precisely match the nutrient requirements during the summer trunk diameter increase period, strengthening the nutrient support for improving the quality and diameter of core trees. For core trees, radial fertilization pits are dug along the outer edge of the canopy projection. High-phosphorus and potassium slow-release fertilizer and phosphorus- and potassium-solubilizing rhizosphere growth-promoting bacteria are applied, followed by covering with soil and watering. The high-phosphorus and potassium nutrients promote trunk thickening and wood quality optimization, while the slow-release fertilizer provides long-term nutrients suitable for the summer growth cycle. The phosphorus- and potassium-solubilizing rhizosphere growth-promoting bacteria enhance the utilization rate of soil nutrients in the mixed forest, allowing core trees to efficiently absorb nutrients. For auxiliary trees, point-like pits are dug at the canopy projection, and balanced compound fertilizer is applied, followed by covering with soil. This evenly replenishes the auxiliary trees with nutrients for trunk diameter growth and maintains their growth status. General trees are not fertilized or treated with bacteria; they rely on the natural fertility of the soil for growth. The total amount of fertilizer applied to core trees is determined based on a cultivation priority coupled with a phenological rhythm nutrient matching algorithm, ensuring that the amount of fertilizer is perfectly matched with the summer growth and tending intensity of the core trees, accurately supplying nutrients in the mixed forest soil environment, and avoiding nutrient waste or deficiency.

[0052] After entering the autumn lignification period of Yunnan pine, the trees enter the final stage of dry wood lignification and nutrient return and storage. At this time, crown control or thinning and tending treatments are implemented according to a two-dimensional corresponding system, and root zone soil energy storage fertilization management is carried out simultaneously according to the tending level. This forms an annual growth closed loop following the summer operations, improving the lignification degree and overwintering ability of mixed forest trees, and laying the foundation for quality improvement cultivation in the following year. For core trees, vigorous autumn shoots and water sprouts at the top of the canopy are pruned to control tall and vigorous growth, forcing photosynthetic products to accumulate in the dry wood to enhance the lignification degree, while guiding nutrients to the root system for storage, improving the overwintering ability of core trees, and ensuring continued diameter increase and quality improvement in the following year. For auxiliary trees, light crown control pruning is carried out to remove outward-extending competing lateral branches, avoiding competition with core trees for pre-winter light in mixed forests, ensuring that core trees complete nutrient storage first, and optimizing the lignification quality of auxiliary trees. Thinning will be carried out on general reserve trees at a rate of 15%-20% of the total number of trees in the stand. Priority will be given to removing diseased and weak trees, and trees that crowd out the space of core reserve trees. Low-priority trees will be phased out in an orderly manner to free up more nutrient and light space for core and auxiliary reserve trees in the mixed forest, thus optimizing the spatial structure of the mixed forest. Simultaneously, root zone soil energy storage fertilization management will be implemented to store nutrients for wintering and the following year's growth, improving the root zone soil of the mixed forest. For core reserve trees, a circular trench will be dug along the outer edge of the canopy projection, and fully decomposed organic fertilizer will be applied and covered with soil. The organic fertilizer will improve the physical and chemical properties of the mixed forest soil, enhance its water and fertilizer retention capacity, and store long-term nutrients for the core trees to overwinter and sprout the following year. For auxiliary reserve trees, point-like pits will be dug at the canopy projection, and fully decomposed organic fertilizer will be applied and covered with soil to meet the nutrient needs of the auxiliary trees for wintering and improve their wintering stability. No fertilization will be carried out on general reserve trees to maintain the natural fertility of the soil. Figure 3 As shown.

[0053] A closed-loop system integrating grading, tending, and soil management operations is established to precisely cultivate large-diameter timber in near-mature Yunnan pine mixed forests through annual cyclical implementation, coupled with a dynamic monitoring and adjustment mechanism. Each autumn, after the lignification period, every target tree in the stand is remeasured to obtain data on diameter at breast height (DBH), trunk straightness, and canopy structure changes, as well as root zone soil fertility indicators, providing a comprehensive understanding of tree growth and soil conditions in the mixed forest. Based on the remeasurement data, the three-tiered target tree classification is dynamically adjusted, downgrading declining trees and upgrading high-quality trees. Simultaneously, the tending and soil management rules of the corresponding two-dimensional system are updated to continuously optimize the efficiency of mixed forest cultivation resource allocation. The adjusted system is followed for the next year's cultivation operations, continuously adapting to changes in mixed forest growth, ensuring the continuous advancement of large-diameter timber cultivation in near-mature Yunnan pine mixed forests. This allows for continuous growth in the trunk diameter and optimization of the trunk shape of core trees in the mixed forest, cultivating high-specification, high-quality large-diameter timber, enhancing the economic and ecological benefits of the mixed forest, and achieving efficient quality improvement and sustainable utilization of near-mature mixed forest timber resources.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for graded tending and soil management of target trees to promote the formation of large-diameter timber in Yunnan pine, characterized in that, The specific steps of this method are as follows: S100, Construction of a dual-dimensional grading system: Based on the priority of cultivating large-diameter Yunnan pine, three levels of target trees are divided into core retention trees, auxiliary retention trees, and general retention trees. The three levels of target trees are then linked to the Yunnan pine’s spring rapid growth period, summer diameter increase period, and autumn lignification period in full time sequence. A dual-dimensional correspondence system of cultivation priority and phenological rhythm is established, and the tending and soil management rules for the corresponding phenological periods of each level of target trees are clarified. S200, Spring Rapid Growth Period Grading: After entering the spring rapid growth period of Yunnan pine, differentiated tending treatment is implemented for the three target trees according to the two-dimensional correspondence system, and the initial nutrient supply and growth promotion regulation of the root zone corresponding to the tending level are carried out simultaneously. S300, Summer Diameter Increase Period Follow-up: After entering the summer diameter increase period of Yunnan pine, according to the dual-dimensional correspondence system, the canopy pruning and tending of the three-level target trees are carried out in accordance with the phenological period, and root zone fertilizer and rhizosphere growth-promoting bacteria agents corresponding to the tending level and cultivation priority are applied simultaneously. S400, End of Autumn Lignification Period: After entering the autumn lignification period of Yunnan pine, according to the two-dimensional corresponding system, crown control or thinning and tending treatment is carried out on the three-level target trees, and root zone soil energy storage fertilization management corresponding to the tending level is carried out simultaneously. S500, Linked Closed-Loop Cyclic Execution: Integrating the entire process of grading, tending, and soil management operations from S100 to S400, a linked closed loop covering all aspects of the target tree is constructed, and the targeted and precise cultivation of large-diameter Yunnan pine is completed through annual cyclical execution.

2. The method for graded tending and soil management of target trees to promote the formation of large-diameter Yunnan pine according to claim 1, characterized in that, In step S100, the three-level target trees are quantitatively classified according to the growth characteristics of individual trees in the stand and their suitability for large-diameter timber cultivation: each tree in the target stand is measured to obtain five indicators: diameter at breast height (DBH), tree height, trunk straightness, crown integrity, and health status; dominant trees in the stand with a DBH in the top 15% of the stand's cumulative total, trunk straightness ≥0.9, no diseases, pests, or mechanical damage, and intact crowns with evenly distributed lateral branches are designated as core trees with the highest cultivation priority, with 80-100 trees retained per hectare; companion trees in the stand with a DBH in the 15%-40% range of the stand's cumulative total, trunk straightness ≥0.7, no serious diseases or pests, and stable crown shape are designated as auxiliary trees with the medium cultivation priority, with 120-150 trees retained per hectare; the remaining trees in the stand with a DBH below the 40% range of the stand's cumulative total, with poor trunk shape, or exhibiting disease or weakness are designated as general trees with the low cultivation priority.

3. The method for graded tending and soil management of target trees to promote the formation of large-diameter timber in Yunnan pine according to claim 1, characterized in that, In step S200, the differentiated tending treatment corresponds to the phenological characteristics of the rapid growth period in spring, specifically: for the core retention tree, remove all competing trees in the upper and lateral layers of the canopy and control the canopy spacing to ≥1.5m; for the auxiliary retention tree, remove overly dense and overlapping lateral branches and diseased and weak branches, retain healthy main branches, and control the canopy to not extend into the growth space of the core retention tree. For general trees to be preserved, dead, diseased, insect-infested, and broken branches should be removed from the stand, and no additional thinning or pruning operations should be carried out to maintain the basic structure of the stand.

4. The method for graded tending and soil management of target trees to promote the formation of large-diameter Yunnan pine according to claim 1, characterized in that, In step S200, the root zone nutrient supply and growth promotion regulation operation corresponds one-to-one with the tending treatment level. Specifically, for the core preserved trees, a circular trench is dug 20cm outside the canopy projection, and 200g / tree of fast-acting nitrogen fertilizer and 50g / tree of nitrogen-fixing growth-promoting bacteria are applied. After application, the soil is covered and water is applied. For trees that are retained as an auxiliary measure, dig pits at the canopy projection, apply 150g of conventional NPK compound fertilizer per tree, and cover with soil after application; For trees that are generally preserved, no fertilization or growth-promoting bacteria are applied; the trees rely solely on the natural fertility of the soil.

5. The method for graded tending and soil management of target trees to promote the formation of large-diameter Yunnan pine according to claim 1, characterized in that, In step S300, the canopy pruning and tending operation corresponds to the phenological characteristics of the summer diameter increase period and follows the spring tending operation in S200. Specifically, for core retention trees, remove vigorous shoots, crossing branches, and ineffective branches that block light in the inner canopy, and control the pruning intensity within 10% of the total canopy branches; for auxiliary retention trees, remove weak branches, drooping branches, and overly dense lateral branches in the lower canopy, and control the pruning intensity within 20%-25% of the total canopy branches, with the canopy height ratio controlled at 0.6-0.7; for general retention trees, no pruning or thinning operations are carried out to maintain the forest stand transition structure.

6. The method for graded tending and soil management of target trees to promote the formation of large-diameter Yunnan pine according to claim 1, characterized in that, In step S300, the application of root zone fertilizer and rhizosphere growth-promoting bacteria corresponds one-to-one with the level of tending operation and cultivation priority. Specifically, for core retention trees, radial fertilization holes are dug along the outer edge of the tree canopy projection, and 250g / tree of high phosphorus and potassium slow-release fertilizer with a nitrogen-phosphorus-potassium ratio of 5:15:20 and 60g / tree of phosphorus- and potassium-solubilizing rhizosphere growth-promoting bacteria are applied. After application, the soil is covered and water is applied. For auxiliary retention trees, dotted holes are dug at the tree canopy projection, and 180g / tree of balanced compound fertilizer with a nitrogen-phosphorus-potassium ratio of 10:10:10 is applied. After application, the soil is covered. For trees that are generally preserved, no fertilization or microbial inoculant application will be carried out.

7. The method for graded tending and soil management of target trees to promote the formation of large-diameter Yunnan pine according to claim 1, characterized in that, In step S400, the tending treatment and soil energy storage fertilization management are matched with the phenological characteristics of autumn wood lignification and nutrient reflux storage of Yunnan pine, forming an annual growth closed loop following the summer operation in S300: Tending and management: For core trees, prune vigorous autumn shoots and water sprouts at the top of the canopy to control tall and vigorous growth; for auxiliary trees, carry out light canopy control pruning and remove competing lateral branches extending outward; for general trees, carry out thinning at a rate of 15%-20% of the total number of trees in the stand, and prioritize the removal of diseased and weak trees and trees that crowd out the space of core trees. Soil energy storage and fertilization management: For the core trees to be preserved, dig a ring trench along the outer edge of the tree canopy projection, apply 3 kg of fully decomposed organic fertilizer per tree, and cover with soil after application; For trees that are to be retained as an auxiliary measure, dig small holes at the canopy projection, apply 1 kg of fully decomposed organic fertilizer per tree, and cover with soil after application. For trees that are generally preserved, no fertilization is carried out to maintain the natural fertility of the soil.

8. The method for graded tending and soil management of target trees to promote the formation of large-diameter Yunnan pine according to claim 1, characterized in that, In steps S200, S300, and S400, the pruning intensity of the core retention tree at different phenological stages is determined by a phenological rhythm coupled cultivation priority control algorithm to ensure that the pruning intensity is fully matched with the photosynthetic growth requirements of the target tree. The specific calculation and implementation steps are as follows: The first step is to measure the effective photosynthetic area S of the canopy, the daily average effective photosynthetic radiation flux density PAR of the canopy of the target core tree during the corresponding phenological period, and the annual growth of the diameter at breast height G of a single tree at the initial stage of the corresponding phenological period for the target core tree. The second step involves calculating the pruning intensity P of the core trees to be retained during the phenological period using a phenological rhythm coupling and priority control algorithm. in, The pruning intensity for the core trees retained during the target phenological period; The annual target for cultivating large-diameter timber for core retention trees is the diameter at breast height (DBH) growth. The dry wood growth distribution coefficient of Yunnan pine corresponding to the phenological period; To preserve the effective photosynthetic area of ​​the canopy layer at the core; To preserve the average daily photosynthetically active radiation flux density of the canopy layer during the corresponding phenological period for the target core; The photosynthetic conversion coefficient of Yunnan pine needles; Biomass conversion coefficient; The third step is to carry out pruning operations on the core trees to be retained according to the pruning intensity P calculated by the formula.

9. The method for graded tending and soil management of target trees to promote the formation of large-diameter Yunnan pine according to claim 1, characterized in that, In steps S200, S300, and S400, the total amount of fertilizer applied to the core trees at different phenological stages is determined by a cultivation priority coupled with a phenological rhythm nutrient matching algorithm to ensure that the amount of fertilizer is completely matched with the growth needs and tending intensity of the target trees. The specific calculation and implementation steps are as follows: The first step is to measure the diameter at breast height (DBH) of a single tree (D), the crown projection area (A), and the pruning intensity (P) of the target core tree at the initial stage of the corresponding phenological period for the target core tree. The second step involves calculating the total fertilization amount Q for the core trees retained during the phenological period using a priority-coupled phenological rhythm-based nutrient matching algorithm. in, The total amount of fertilizer applied to the core trees retained during the target phenological period; The diameter at breast height (DBH) of the core tree is preserved; The projected area of ​​the crown of the core tree to be preserved; The nutrient requirement coefficient for Yunnan pine during its corresponding phenological period; The pruning intensity for the core trees retained during the target phenological period; The target coefficient for cultivating large-diameter Yunnan pine is δ; δ is the unit conversion factor. The third step is to calculate the total fertilizer application amount Q according to the formula, and combine it with the nutrient requirements of the corresponding phenological stage to determine the ratio and application amount of nitrogen, phosphorus and potassium fertilizers, and carry out fertilization operations in the core root zone of the tree to be retained for the corresponding phenological stage.

10. The method for graded tending and soil management of target trees to promote the formation of large-diameter timber in Yunnan pine according to claim 1, characterized in that, In step S500, the annual cycle is implemented with a dynamic monitoring and adjustment mechanism: after the lignification period ends each autumn, a tree-by-tree measurement is conducted on all target trees in the stand to obtain data on diameter at breast height (DBH), trunk straightness, and canopy structure changes for core, auxiliary, and general trees, while simultaneously measuring root zone soil fertility indicators; based on the measurement data, the classification of the three levels of target trees is dynamically adjusted, downgrading trees that are declining in growth or do not meet the standards for core trees, and upgrading trees with excellent growth traits that meet high-priority standards, while simultaneously updating the tending and soil management rules in the corresponding dual-dimensional grading system; according to the adjusted grading system, the full-process tending and soil management operations for the following year are executed to continuously optimize the resource allocation efficiency of the closed-loop linkage.

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