Method for transforming degraded natural silver birch forest with low water conservation function

Abstract

The invention discloses a method for transforming a degraded natural silver birch forest with a low water conservation function, which comprises the following steps of: screening, determining and marking to-be-cut object trees according to the diameter at breast height, crown breadth and tree height of the object trees and adjacent trees in the silver birch forest; cutting is carried out; and then carrying out nursery stock complementary planting. The method disclosed by the invention is simple, convenient and easy to implement, and accurate in forest measuring result, and by scientifically introducing picea crassifolia, ingeniously regulating and controlling the degraded natural silver birch forest structure and improving the stand angle scale, the forest distribution is more uniform and random, and the ecological diversity and stability are remarkably enhanced. A systematic selective cutting and transplanting method is adopted, the mixing ratio of the white birch and the picea crassifolia is accurately regulated and controlled to be close to an ideal ratio, the stand structure is optimized, the stand density is controlled within the optimal range, and effective guarantee is provided for stand health. The ecological function recovery and the stability enhancement of the degraded silver birch forest are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of forestry, in particular to a method for transforming degraded natural white birch forest with low water conservation function. BACKGROUND

[0002] Natural white birch forest is an important ecosystem type in China, widely distributed in cold temperate and alpine regions, with important water conservation, soil conservation and ecological barrier functions. However, due to the influence of climate change and human activities, some natural white birch forests have shown signs of degradation, with slow tree growth, soil water loss, and nutrient-poor problems, seriously affecting their ecological functions. Existing white birch forest transformation methods focus on the restoration of single tree species, ignoring the improvement of water conservation function, resulting in limited ecological restoration effect. Therefore, there is an urgent need for a white birch forest transformation method that considers the water conservation function to achieve sustainable restoration of the ecosystem.

[0003] However, the stand structure regulation technology of theoretical research method usually involves complex structure index calculation (such as angle scale and diameter size ratio number), these spatial structure index parameters cannot be directly measured, need to measure the position distribution, diameter size and other stand spatial structure of each tree in the field first, then use arcGIS software to calculate the size ratio number and angle scale of each tree to determine the corresponding selection cutting single tree, and when the forest land needs to be cut several times, each round needs to be calculated again. When calculating, each tree in the stand adjustment area needs to be taken as the object wood and the surrounding adjacent wood to compare the size of the diameter to calculate the diameter size ratio number; each tree in the stand adjustment area needs to be taken as the object wood and the surrounding each adjacent wood to measure the angle and compare the size to calculate the angle scale, the calculation is extremely complicated, time-consuming and laborious, and requires certain professional accomplishment. Therefore, stand structure adjustment is only in the research of some experts and scholars, it is difficult for grass-roots forestry technical personnel to understand and implement in practical application, or it is difficult for grass-roots forestry technical personnel to understand the drawings provided by scientific researchers, resulting in large error of the results after implementation, the stand structure of the transformed forest land still has defects, and a large amount of manpower and material resources are consumed.

[0004] The present application finds out the rule of the relationship between the tree characteristics of the object wood and its adjacent wood based on the statistical analysis method, establishes a set of forest thinning method based on the basic indexes such as forest height, diameter at breast height and crown width, compares the diameter at breast height, crown width or / and height of the object wood and its adjacent wood in the artificial timber forest to be controlled, selects, determines and marks the object wood to be thinned, and thins the marked forest, so that the spatial distribution of the reserved forest tends to be random or near nature. When the forest is thinned, the mixed tree species meeting the positive succession of the stand are selected, the planting hole is determined according to the forest replanting principle and forest replanting table provided by the present application after the diameter at breast height, crown width or / and height of the adjacent wood is visually observed (the replanting in the original thinning hole must be avoided), and the mixed seedling replanting of different ages is carried out.

[0005] The present application aims to provide a method for reconstructing degraded natural white birch forest based on water conservation function improvement, which realizes the ecological function recovery and stability enhancement of degraded white birch forest by optimizing stand structure, improving soil conditions and enhancing water conservation capacity. SUMMARY

[0006] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0007] A method for reconstructing degraded natural white birch forest with low water conservation function, comprising the following steps:

[0008] Step one) determining the degraded natural white birch forest that needs to be reconstructed according to the water conservation function of the natural white birch forest;

[0009] Step two) investigating the degraded natural white birch forest that needs to be reconstructed, and measuring the spatial position information, diameter at breast height, height and crown width of each tree one by one;

[0010] Step three) importing the basic coordinate information of the reconstructed stand sample plot into ArcGIS software to generate a forest position distribution map; using the near neighbor analysis tool to generate a Thiessen polygon map, and performing near neighbor analysis on all trees in the sample plot;

[0011] Step four) determining the competing trees of each object tree based on the Thiessen polygon map, and determining the white birch trees that need to be removed according to the diameter at breast height, height and crown width of the competing trees of the object trees;

[0012] Step five) felling the white birch trees selected in step four) that need to be removed; then transplanting Picea crassifolia; the transplanting position of each Picea crassifolia is spaced ≥1.5m from the reserved white birch, the forest gap area with a light transmittance ≥40% is selected, and the plant spacing is controlled within the range of 3-5m.

[0013] Optionally, the step one) determines the degraded natural white birch forest in need of reconstruction according to the water conservation function of the natural white birch forest, comprising: measuring the saturated water holding capacity of the tree layer, litter layer and soil layer of the natural white birch forest, and confirming whether the natural white birch forest is a degraded natural white birch forest in need of reconstruction according to the sum of the saturated water holding capacity of the tree layer, litter layer and soil layer of the natural white birch forest.

[0014] Optionally, the saturated water holding capacity of the tree layer, litter layer and soil layer is measured by standard branch soaking method, litter soaking method and ring knife method in the step one).

[0015] Optionally, the basic coordinate information of the reconstructed forest sample plot is introduced into ArcGIS software to generate a forest position distribution map, and a Thiessen polygon map is generated by using a nearest neighbor analysis tool, and the nearest neighbor analysis of all trees in the sample plot is performed, which specifically comprises: introducing the basic coordinate information of the reconstructed forest sample plot into ArcGIS 10.2 software to generate a forest position distribution map, generating a Thiessen polygon map by using the nearest neighbor analysis tool in the ArcMap toolbox, and performing nearest neighbor analysis of all trees in the sample plot; a 2m wide buffer zone is set around the degraded natural white birch forest in need of reconstruction, and the trees in the buffer zone are only used as competition trees and are not used as reconstruction object trees for reconstruction.

[0016] Optionally, in the step four, if a certain object tree meets any of the following selection index table conditions, it is selected as a white birch tree to be removed;

[0017]

[0018]

[0019]

[0020] Optionally, in the step four), the white birch trees to be removed are determined in two batches, and the white birch trees to be removed in each batch are less than 30% of all object trees.

[0021] Optionally, the determination method of the transplanting point of the transplanted Qinghai spruce comprises:

[0022] 1) randomly generating a candidate transplanting point;

[0023] 2) using Thiessen polygon analysis to analyze the spatial distribution pattern;

[0024] 3) through iterative optimization, the overall angular scale tends to 0.5;

[0025] 4) ensuring that the transplanting point meets: the distance between the transplanting point and the retained white birch is greater than or equal to 1.5m, the light transmittance is greater than or equal to 40%, and the plant spacing is controlled within the range of 3-5m.

[0026] Optionally, after transplanting Qinghai spruce, the stand density should be controlled at 1133-1739 trees / hm². 2 Between them, a mixed ratio of birch and Qinghai spruce of 7:3 was formed.

[0027] The present invention has the following beneficial effects:

[0028] (1) Innovative ecological restoration strategy: This invention introduces Qinghai spruce scientifically, cleverly regulates the structure of degraded natural birch forests, increases the stand angle scale, makes the distribution of trees more uniform and random, and significantly enhances ecological diversity and stability.

[0029] (2) Precise tree species configuration scheme: adopt systematic selective felling and transplanting methods to precisely adjust the mixed ratio of birch and Qinghai spruce to a near-ideal ratio, optimize the forest stand structure, control the forest stand density within the optimal range, and provide effective protection for forest stand health.

[0030] (3) Significant ecological benefits: Transplanting Qinghai spruce increases the mixed forest stand density, greatly enhances the resistance to pests and diseases, preserves the dominant birch, improves ecological stability, and lays the foundation for the sustainable development of the forest stand. Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 This provides basic spatial location information for the sample plots.

[0033] Figure 2 The trees to be selectively felled in the first round.

[0034] Figure 3 This is the second round of selective logging plan.

[0035] Figure 4 A transplanting plan for Qinghai spruce. Detailed Implementation

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0037] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0039] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0040] This invention proposes a method for transforming degraded natural birch forests with low water conservation function, comprising the following steps:

[0041] (1) Survey of basic information of sample plots

[0042] By visually observing the basic conditions of the sample plots, the uniformity of the stands, the integrity of trees, shrubs, and grasses, and the number of dead and leaning trees were assessed to preliminarily determine that the birch forests were of poor growth and had low water conservation capacity. Based on this, 20m × 20m rectangular sample plots for standard tree surveys were established. Diameter at breast height (DBH) was measured using a diameter-at-breast-meter (DBH) ruler, tree height was measured using an altimeter, and the canopy closure was estimated using the sampling method. Simultaneously, the species composition and quantity of trees within the sample plots were statistically analyzed, stand density was calculated, and the average DBH and average tree height of the sample plots were measured. Based on the average DBH and average tree height, trees with DBH and tree height closest to the stand average were selected as standard trees. From these standard trees, healthy, disease-free, and naturally shaped branches from the upper and middle parts of the crown were selected and collected using pruning shears for subsequent determination of the maximum water holding capacity of the tree layer.

[0043] (2) Identification of birch forests with low water conservation function

[0044] Within the sample plot (a rectangular plot of 20m × 20m), the saturated water holding capacity of the tree layer, litter layer, and soil layer was determined by the standard branch soaking method, litter soaking method, and ring cutter method.

[0045] Formula for calculating the maximum water holding capacity of the tree layer:

[0046] W 乔木层 =W 标准枝 ×1 / P×N×C (Equation 1)

[0047] W 乔木层: The maximum water holding capacity of the tree layer.

[0048] W 标准枝 : The maximum water holding capacity of the standard branch being measured.

[0049] P: The ratio of standard branch volume to the total canopy volume, i.e., the proportion of standard branch volume to the total canopy volume.

[0050] N: Stand density - Number of trees per unit area.

[0051] C: Canopy closure of birch stands. The standard branch-to-crown ratio of natural birch forests is between 0.001 and 0.003, meaning that the volume of a standard branch accounts for approximately 0.1% to 0.3% of the total canopy volume. Here, we take 0.002 as the standard branch-to-crown ratio for natural birch forests. The formula for calculating the maximum water holding capacity of the litter layer is:

[0052] W 枯落物 =(W 24h湿重 -W 干重 ) / W 干重 (Equation 2)

[0053] Five 25cm×25cm quadrats were set up in the litter sampling area. After collection, the litter was brought back to the laboratory, soaked, weighed, and the weight was calculated.

[0054] The formula for converting the maximum water holding capacity of the soil layer is:

[0055] W 土壤 =(W 24h湿 -W 干 ) / W 干 (Equation 3)

[0056] Within the standard pit (50cm×30cm×60cm), the sample was divided into three layers: 0-20cm, 20-40cm, and 40-60cm. Samples were taken from each layer using a ring sampler and brought back to the laboratory for analysis.

[0057] Subsequently, based on the calculation results of the maximum water holding capacity of the tree layer, litter layer, and soil layer, the overall water conservation function of the sample plot was evaluated to determine whether it belonged to a birch forest stand with low water conservation function. The overall maximum water holding capacity of the sample plot can be calculated using the following formula:

[0058] W 总 =W 乔木层 +W 枯落物 +W 土壤

[0059] in:

[0060] W 乔木层 The maximum water holding capacity of the tree layer is calculated by measuring standard branches.

[0061] W枯落物 : The maximum water holding capacity of the litter layer, calculated using the five-point sampling method.

[0062] W 土壤 Weighted calculation of maximum water holding capacity at different soil depths (e.g., using a layer ratio).

[0063] If the calculated result is lower than the regional normal water conservation function standard (the threshold can be determined based on long-term regional monitoring data or relevant literature), then the birch forest stand is judged to be degraded and artificial transformation and upgrading work is required.

[0064] (3) Investigate forest stand spatial structure information

[0065] A comprehensive survey was conducted on the stands requiring modification, and the spatial location information of trees within each plot was measured. Specific procedures included: using the first tree in the southwest corner of the plot as the origin (0,0), an S-shaped movement was employed to record the spatial coordinates (x,y) of all trees, providing data for subsequent calculations of stand spatial structure indicators such as angular scale, size ratio, and mixing degree. The angular scale, size ratio, and mixing degree were calculated using the formulas from the following literature:

[0066] Hui Gangying. Angular scale—a structural parameter describing the distribution pattern of individual trees [J]. Forestry Science, 1999, (01): 39-44.

[0067] Hui Gangying et al. A new stand spatial structure parameter—size ratio [J]. Forestry Science Research, 1999, (01): 4-9.

[0068] Hui Gangying, Hu Yanbo. Study on the expression of spatial isolation degree of tree species in mixed forests [J]. Forestry Science Research, 2001, (01): 23-27.

[0069] (3) Determine the optimal birch forest stand structure for water conservation function.

[0070] With the goal of fully enhancing water conservation function, the optimal forest stand structure for maximizing this function was determined to be a mixed forest of birch and Qinghai spruce, with a mixing ratio of 7:3; the optimal stand density was 1133-1739 trees / hm². 2 .

[0071] (4) Generate a location distribution map of the birch forest.

[0072] The basic coordinate information of the modified forest stand plots was imported into ArcGIS 10.2 software to generate a tree location distribution map. Using the nearest neighbor analysis tool in the ArcMap toolbox, a Thiessen polygon map was generated, and nearest neighbor analysis was performed on all trees within the plots. The modification area was a standard 20m × 20m plot, with a 2m wide buffer zone around it. Trees within the buffer zone were considered only as competing trees and not as trees to be modified. Trees within the modification area could participate in the nearest neighbor analysis as either competing or modifying trees.

[0073] (5) Determine the birch forest stand transformation plan

[0074] Based on the Thiessen polygon diagram, competing trees for each target tree were identified, and its stand spatial structure indices (angular scale, size ratio, and mixing degree) were calculated. The general principle of selective felling was to prioritize the removal of trees with poor growth, small diameter at breast height (DBH), and low height. Specifically, target trees with larger angular scales and larger size ratios were selected for priority felling. A larger angular scale reflects a more clustered distribution of trees, indicating higher competition intensity; a larger size ratio indicates that competing trees have larger DBHs, and the target tree is under competitive pressure and thus has poor growth. By removing these poorly growing and clustered trees, competition within the stand can be effectively reduced, stand structure optimized, and the water conservation function of the stand fully utilized.

[0075] Based on the selective felling criteria determined in this invention, all target trees are screened. When a neighboring tree simultaneously meets all four selective felling criteria in the table, it is determined to be a harvested tree and is specially marked. Trees located within the buffer zone are not considered target trees, but only neighboring trees. The screening results are as follows: Figure 2 :

[0076]

[0077]

[0078]

[0079] During the transformation process, Qinghai spruce was transplanted into the forest land according to the principle of random distribution to create birch-Qinghai spruce mixed forests, thereby increasing the stand mixing degree. Higher mixing degree leads to more efficient water conservation. Through multiple selective felling and replanting, the stand density was controlled at 1133-1739 trees / hm². 2 Between these elements, an optimal mixing ratio of 7:3 between birch and Qinghai spruce is formed, further enhancing the water conservation function and ecological benefits of the birch forest.

[0080] Example 1

[0081] (1) Basic survey of sample plots

[0082] A high-density birch forest was selected as the target for remediation. Visual observation revealed that the forest stand suffered from problems such as low tree height, small diameter at breast height (DBH), and incomplete forest structure. Furthermore, due to poor light penetration, low understory species diversity, and weak overall water conservation capacity, remediation measures are urgently needed to improve its water conservation capabilities.

[0083] A 20m × 20m standard tree survey plot was established under a high-density birch forest. The diameter at breast height (DBH) of all trees in the plot was measured using a DBH measuring tape, and the tree height was measured using an altimeter. The average DBH and average tree height of the plot were calculated. Based on the calculation results, the tree with the DBH and tree height closest to the average values ​​was selected as the standard tree. Healthy, disease-free, and naturally shaped branches from the upper and middle parts of the crown of the standard tree were selected and collected using pruning shears for subsequent determination of the tree's maximum water holding capacity.

[0084] The investigation revealed that the average diameter at breast height (DBH) of the birch forest in this case study was 11.3 cm, and the average tree height was 15.3 m. The standard trees selected had a DBH of 10.6 cm and a height of 15.5 m. Within the standard plot, there were 93 birch trees, with a stand density of 1615 trees / hm². 2 The canopy closure of the plot was determined using the sampling method, and the canopy closure was found to be 0.75. Taking the first birch tree in the southwest corner of the plot as the starting point, numbered 1, and marked with coordinates (0,0), an S-shaped movement was used to number and record the coordinate information of all trees in the plot. The plot survey information is shown in Table 1.

[0085] A 20m × 20m standard tree survey plot was established under a high-density birch forest. Detailed measurements and records were made regarding the stand characteristics within the plot. The diameter at breast height (DBH) of all trees in the plot was measured using a DBH measuring rod, and their height was measured using an altimeter. The average DBH and average tree height of the plot were calculated. Based on the calculation results, trees with DBH and height closest to the average values ​​were selected as standard trees. From these standard trees, healthy, disease-free, and naturally shaped branches from the upper and middle parts of the crown were selected and collected using pruning shears for subsequent determination of the tree's maximum water holding capacity.

[0086] The survey showed that the average diameter at breast height (DBH) of the birch forest in this case study was 11.3 cm, and the average tree height was 15.3 m. Trees with a DBH of 10.6 cm and a height of 15.5 m were selected as standard trees. The standard plot contained 93 birch trees, with a stand density of 1615 trees / hm². 2 The canopy closure of the plot was determined by the sampling method, and the results showed that the canopy closure of the plot was 0.75.

[0087] To record the spatial distribution characteristics of trees within the sample plot, the first birch tree in the southwest corner of the plot was designated as the starting point, numbered 1, with coordinates (0,0). Subsequently, an S-shaped movement was used to number all trees within the sample plot and record their coordinates. A summary of detailed survey information for the sample plot is shown in Table 1.

[0088] Table 1: Basic Information Table of Sample Plots

[0089]

[0090]

[0091] (2) Water conservation function was determined by soaking standard branches, litter, and soil in the sample plots.

[0092] The maximum water holding capacity of trees, litter, and soil were measured separately as important indicators for assessing the water conservation capacity of the sample plot. The relevant calculations were performed according to Formulas 1, 2, and 3, and the results are as follows: The maximum water holding capacity of trees is 12.36 t / hm². 2 Slightly higher than the minimum water holding capacity threshold of a healthy birch forest canopy (10 t / hm). 2 This demonstrates a certain water-holding capacity of trees. The maximum water-holding capacity of litter is 4.64 t / hm². 2 Slightly below the minimum water holding capacity threshold for litter in healthy birch forests (5 t / hm). 2 The water conservation function of the litter layer is insufficient. The maximum water holding capacity of the 0–60 cm soil layer is 271.8 t / hm². 2 It is significantly lower than the minimum water holding capacity threshold of healthy birch forest soil (300 t / hm). 2 This indicates a significant deficiency in the soil's water conservation capacity. The total water holding capacity of the stand was 288.8 t / hm², far below the minimum threshold for healthy birch forests (315 t / hm²). 2 This indicates that the overall water conservation capacity of the forest stand is low. In summary, the high-density birch forest has a weak water conservation capacity, especially with low contributions from soil and litter, failing to meet the water conservation requirements of a healthy birch forest. Therefore, necessary forest stand improvement measures are urgently needed to enhance its ecological function of water conservation.

[0093] (3) Generate the Thiessen polygon map of the sample plot

[0094] The spatial location information of trees in the sample plot was imported into ArcGIS software, and Thiessen polygons were drawn using the nearest neighbor analysis method to identify the nearest competing trees for each tree. Further calculations were made of the spatial structure indices of the trees, including angular scale, size ratio, and mixing degree. A standard 20m × 20m test plot was set up, with a 2m wide buffer zone outside the plot. Trees within the buffer zone were used only as competing trees to calculate the spatial structure indices of target trees in the test plot, but were not considered for selective felling. Trees falling into the test plot were considered target trees, participating both as competing trees in the calculation of the spatial structure indices of other target trees and as targets for selective felling. The original spatial distribution of trees generated from this sample plot is shown in [link to original text]. Figure 1

[0095] (4) Determine the target timber species for selective felling

[0096] Nearest neighbor analysis of the target trees in the sample plot using Thiessen polygons yielded an average size ratio of 0.5 and an average angular scale of 0.28 (Code 1). The results indicate that the stand exhibits a clustered spatial distribution, low space utilization, and intense competition among trees. Therefore, appropriate modifications are needed to optimize the stand structure and improve the growing environment.

[0097] For a detailed list of the first round of selective felling, please refer to Table 2.

[0098] Table 2: Summary Table of Timber Targets for the First Round of Selective Logging

[0099] tree number adjacent trees size ratio angular scale 7 6,18,8 1 0.17 10 8,9,11,18 1 0.17 12 17,18,14,13 1 0.18 20 23,22,19,25 1 0.2 21 23,22,24,25 1 0.21 26 69,68,27,67,19,29,30,25 1 0.33 28 32,15,33,31,34 1 0.33 38 36,4,37,35,39 1 0.33 53 49,51,47,48 1 0.33 61 64,65,92,59,63,60,93,58 1 0.4 79 83,78,80,81 1 0.67 33 32,42,66,28,34,43,40,35 0.88 0.21 6 7,18,5,1,2,8,36 0.86 0.19 90 67,81,91,89,80,85,86 0.86 0.33 13 12,11,18,15,9,14 0.83 0.2 40 42,33,41,37,35,39 0.83 0.27 59 65,62,61,52,57,58 0.83 0.4 31 27,32,15,28,14 0.8 0.4 48 50,49,51,53,45 0.8 0.4 5 36,6,4,2 0.75 0.33 43 42,66,33,44,62,46,52 0.71 0.19 51 52,47,53,46,45,48 0.67 0.27 69 70,68,71,73,30,26 0.67 0.33

[0100] It is evident that the size ratios of the trees selected for this round of selective felling are all greater than 0.67, indicating that these trees have smaller diameters at breast height (DBH) compared to their neighbors and are weaker in growth; their angular scales are all less than 0.5, reflecting their relatively clustered distribution and intense competition. Therefore, these weaker and more competitive trees were prioritized for felling. For details of the trees selected for the first round of selective felling, see [link to first-round selective felling list]. Figure 2 .

[0101] (5) Determine the target timber for the second round of selective felling

[0102] Calculations show that after the first round of selective felling, the average size ratio of the plot decreased from 0.5 to 0.46, and the angular scale increased from 0.28 to 0.5, indicating that the spatial distribution of the forest stand tended to be more uniform, the trees were more evenly distributed, and the competitive pressure was reduced. However, after the first round of selective felling, some areas still showed excessive clustering, such as tree species 25, 29, and 30. Therefore, a second round of selective felling was carried out on the plots. The felling intensity still followed the principle that no more than 30% of the tree species in a single round of selective felling was removed. After the first round of selective felling, a total of 70 birch trees remained in the plot, so no more than 21 birch trees were felled in this second round of selective felling. A detailed list of trees to be felled in the second round is shown in Table 3.

[0103] Table 3: Summary Table of Selective Logging Targets in the Second Round

[0104]

[0105]

[0106] This round of selective felling followed the principles of the first round, and a total of 20 target trees were felled, with the felling intensity not exceeding 30%, which complies with the standards for healthy forest management. For details of the target trees for the second round of selective felling, please refer to [link to relevant documentation]. Figure 3

[0107] Trees should be harvested and transplanted instead of directly felled to ensure their healthy growth in the new environment. Before harvesting, trees should be pruned while preserving their shape to reduce transpiration during transport, maintain adequate tissue moisture, and no more than 30% of the total branches should be pruned. Cuts left after pruning should be treated promptly to accelerate healing and prevent excessive loss of water and nutrients. During harvesting, a root ball transplanting method should be adopted, with the root ball's width approximately 10 times the tree's diameter at breast height (DBH) and its height approximately 80% of its width, ensuring the root system is well protected by the root ball.

[0108] (6) Transplanting Qinghai spruce

[0109] After two rounds of selective felling, the number of birch trees in the sample plot decreased from 93 to 50, resulting in a significant reduction in stand density, an increase in forest gap area, and a marked improvement in light conditions. Spatial structure analysis showed that the birch size ratio decreased from 0.46 to 0.39, while the angular scale increased from 0.5 to 0.55, indicating a more uniform tree distribution, reduced competitive pressure, and improved resource utilization efficiency. Based on the target of a 7:3 birch-Qinghai spruce mixed planting, 20 Qinghai spruce trees need to be transplanted.

[0110] This study uses a Python-based simulated annealing algorithm combined with Thiessen polygon spatial analysis to determine the transplanting location. Figure 4 This method is implemented through the following steps:

[0111] 1) Randomly generate candidate transplanting sites;

[0112] 2) Analyze the spatial distribution pattern using Thiessen polygons;

[0113] 3) Through iterative optimization, the overall angular scale is made to approach the ideal value of 0.5;

[0114] 4) Ensure the transplanting sites meet the following requirements: distance from the remaining birch trees ≥ 1.5m, priority should be given to forest gap areas with light transmittance ≥ 40%, and the spacing between trees should be controlled within 3-5m. This method effectively simulates the natural regeneration process and achieves a scientific configuration of Qinghai spruce.

[0115] After transplanting, replanting should be carried out in early spring when the soil has thawed to a depth of 30-40 cm. Generally, two-year-old seedlings with well-developed root systems should be selected. When lifting the seedlings, thoroughly water the area around the roots, ensuring the roots are enclosed in a soil ball. The soil ball should be large enough that most of the fine roots are not exposed. Wrap the soil ball with fiber cloth and transport it to the desired replanting site, where it should be planted promptly. Before replanting, the seedling roots should be dipped in a water-retaining agent. Then, planting should be carried out according to the technical specifications of "three burials, two tampings, and one lifting." The planted trees should be watered promptly to ensure a high survival rate. For different functional forest stand types, different tree species should be replanted to meet the local ecological service needs, achieving a mixed stand ratio of 7:3 after replanting. The initial planting methods for pure natural forests are mostly uniform distribution in a horizontal and vertical pattern; the distribution of invasive tree species is mostly in a clumped pattern; when replanting in forest land after logging, avoid using equal rows and equal spacing, and instead use a random distribution method, and try to replant in open areas of the forest gaps.

[0116] (7) Evaluation of transplanting effect

[0117] After transplanting, the diameter at breast height (DBH) of Qinghai spruce trees was relatively small, making comparisons of size ratios less meaningful. This assessment primarily focused on two indicators: angle scale and mixing ratio, to reflect the distribution and species diversity of the stands. The angle scale of transplanted trees increased from 0.28 to 0.32, indicating a more even and random distribution, reducing competition among trees and thus improving resource utilization efficiency. Furthermore, the mixing ratio increased from 0 to 0.3, indicating a significant increase in stand species diversity and improved resistance to pests and diseases. After two rounds of selective felling, the remaining trees were mainly birch with larger DBH, whose growth was no longer restricted, further enhancing stand stability and health. After transplanting 20 Qinghai spruce trees, the birch-to-Qinghai spruce mixing ratio was 5:2, close to our target stand control ratio of 7:3. In a 24m × 24m plot, there were a total of 70 trees, with a stand density of 1215 trees / hm². 2 The results indicate that the birch forest density falls within the optimal range for birch stand density. These results fully demonstrate that the birch natural forest transformation technology based on enhanced water conservation function proposed in this invention can effectively improve stand quality and provide reliable technical support for cultivating healthy and stable mixed coniferous and broadleaf forests and enhancing the water conservation capacity of forest stands.

[0118] Table 3: Comparison of the effects of forest stand structure improvement

[0119] stand structure initial plot first thinning second thinning after transplanting ideal stand size ratio 0.5 0.46 0.38 — 0.4-0.6 angular scale 0.28 0.5 0.55 0.32 0.45-0.55 mixing degree 0 0 0 0.3 1 mixing ratio 0 0 0 5 to 2 7 to 3 stand density 1615 1215 868 1215 1133-1739 strains / hm 2 ]]>

[0120] The selective felling and transplanting technology proposed in this invention provides a scientific approach for constructing uneven-aged, multi-layered coniferous and broad-leaved mixed forests with efficient water conservation functions. Through systematic selective felling and directional transplantation of Qinghai spruce, a structurally sound mixed coniferous and broad-leaved forest stand can be formed after the spruce canopy closes. This stand has the following significant advantages: First, the retained dominant tree species, birch, as the dominant species ensures the structural stability of the stand; second, the introduction of Qinghai spruce significantly increases the mixedness of the stand (from 0 to 0.3), enhancing the ecosystem's resistance to disturbance; most importantly, this uneven-aged, multi-layered structure can maximize the forest's water conservation function while maintaining the stand's health. This invention not only achieves precise enhancement of the forest's water conservation function but also constructs an ideal forest community that combines ecological function and structural stability.

[0121] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method of rehabilitating a degraded natural white birch forest having a low water source conservation function, characterized by, The method comprises the following steps: step 1) determining the degraded natural birch forest needing to be reconstructed according to the water source conservation function of the natural birch forest; Step 2) investigating the degraded natural birch forest needing to be reconstructed, and measuring the spatial position information, diameter at breast height, tree height and crown width of the trees one by one; Step 3) importing the basic coordinate information of the reconstructed forest sample plot into ArcGIS software to generate a forest tree position distribution map; Using the nearest neighbor analysis tool, a Thiessen polygon map is generated, and nearest neighbor analysis is performed on all trees in the sample plot; Step 4) determining the competitor trees of each object tree based on the Thiessen polygon map, and determining the birch trees needing to be removed according to the diameter at breast height, tree height and crown width of the competitor trees of the object trees; Step 5) cutting the birch trees selected in step 4) needing to be removed; Then transplant Qinghai spruce; the transplanting position of each Qinghai spruce is spaced apart from the retained birch by 1.5 m or more, the forest gap region with a light transmittance of 40% or more is selected, and the plant spacing is controlled within the range of 3-5 m.

2. The method of claim 1, wherein the degraded natural white birch forest with low water source conservation function is reconstructed. The step 1) of determining the degraded natural birch forest needing to be reconstructed according to the water source conservation function of the natural birch forest comprises: measuring the saturated water holding capacity of the tree layer, litter layer and soil layer of the natural birch forest, and confirming whether the natural birch forest is the degraded natural birch forest needing to be reconstructed according to the sum of the saturated water holding capacities of the tree layer, litter layer and soil layer of the natural birch forest.

3. The method of claim 1, wherein the degraded natural white birch forest with low water source conservation function is reconstructed. The saturated water holding capacities of the tree layer, litter layer and soil layer in the step 1) are measured by a standard branch soaking method, a litter soaking method and a cutting ring method.

4. The method of claim 1, wherein the degraded natural white birch forest with low water source conservation function is reconstructed. The basic coordinate information of the reconstructed forest sample plot is imported into ArcGIS software to generate a forest tree position distribution map. The nearest neighbor analysis tool is used to generate a Thiessen polygon map, and nearest neighbor analysis is performed on all trees in the sample plot. The method for determining the birch trees needing to be removed according to the diameter at breast height, tree height and crown width of the competitor trees of the object trees in the step 4) is specifically as follows: if the condition of a certain object tree meets any one of the following selection index table conditions, the object tree is selected as the birch tree needing to be removed.

5. The method of claim 1, wherein the degraded natural white birch forest with low water source conservation function is reconstructed. The birch trees needing to be removed are determined in two batches in the step 4), and the birch trees needing to be removed determined in each batch are less than 30% of all object trees.

6. The method of claim 1, wherein the degraded natural white birch forest with low water source conservation function is reconstructed. The method for determining the transplanting points of the Qinghai spruce comprises:

7. The method of claim 1, wherein the degraded natural white birch forest with low water source conservation function is reconstructed. 1) randomly generating candidate transplanting points; 2) using the Thiessen polygon to analyze the spatial distribution pattern; 3) making the overall angular scale tend to 0.5 through iterative optimization; 4) ensuring that the transplanting points meet the following conditions: the distance from the transplanting points to the retained birch is 1.5 m or more, the light transmittance of the forest gap region is 40% or more, and the plant spacing is controlled within the range of 3-5 m. ​ 8. The method of claim 1, wherein the degraded natural white birch forest with low water source conservation function is reconstructed. Transplanting of Picea crassifolia to control stand density between 1133 and 1739 trees per hectare and to form a mixed stand of Betula platyphylla and Picea crassifolia in a ratio of 7:

3. 2 Transplanting of Picea crassifolia to control stand density between 1133 and 1739 trees per hectare and to form a mixed stand of Betula

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