Natural secondary forest succession stage quantitative division method

Abstract

The invention discloses a natural secondary forest succession stage quantitative division method, and relates to the technical field of forestry, and the method comprises a forest stand investigation step, a forest stand factor calculation and measurement step, and a stage determination factor calculation and succession stage determination step. The method is limited in determination such as tree species composition, forest tree size, under-forest renewal condition and the like. In addition to common forest tree size related factors, factors such as dominance degree of top-level tree species, mingling degree and soil total phosphorus which are difficult to directly and visually inspect are also included. Through the comprehensive factor consideration mode, the actual state and succession stage of the natural secondary forest can be reflected more accurately, and judgment errors caused by one-sidedness of a single factor or a part of factors are avoided.

Description

Technical Field

[0001] The invention relates to the technical field of forestry, and in particular to a method for quantitatively dividing succession stages of natural secondary forests. Background Art

[0002] Natural secondary forests are a type of degraded original forest ecosystem. Due to natural disasters or human destruction, their inherent forest structure, species composition, and basic functions will undergo quantitative or qualitative changes. The mountainous area in northern Hebei belongs to the remnant of Yanshan Mountain and is the main distribution area of ​​natural secondary forests in Hebei Province. Affected by a combination of factors such as high cold, strong winds, low rainfall, and poor soil, the natural secondary forests in this area generally have problems such as poor resistance, low productivity, and weak ecological service functions. Strengthening the restoration of degraded forests is one of the important contents of accurately improving forest quality.

[0003] Forest management requires targeted and appropriate management methods for different development stages of the forest, such as: mowing and weeding in the immature forest period; pruning and light-through felling in the young forest period; growth felling and competitive felling in the middle-aged forest and near-mature forest period; selective felling and gradual felling in the mature and over-mature forest period. However, compared with the age group division system (young forest, middle-aged forest, near-mature forest, mature forest and over-mature forest) in the artificial forest management technology system, natural secondary forests cannot be simply divided by age due to their unique heterogeneous structure, and it is difficult to find a clear dividing line between the two development stages in the actual forest stand. Therefore, a suitable basis for the division of management stages has never been found, which directly hinders the construction of the natural secondary forest management technology system. How to accurately divide the various management stages or development stages of natural secondary forests has become an urgent problem to be solved in promoting the construction of the natural secondary forest management technology system. Summary of the invention

[0004] In view of the shortcomings of the prior art, the technical solution adopted by the present invention to solve the technical problems is: a method for quantitatively dividing the succession stages of natural secondary forests, including a forest stand survey step, a forest stand factor calculation and measurement step, and a stage determination factor calculation and succession stage determination step. The forest stand survey step includes sample plot layout, tree-by-tree measurement, soil sampling and nutrient determination, wherein: the sample plot layout represents the overall characteristics of the forest stand according to the average state of the forest stand, the distance between the sample plot and the forest source and the distance between the sample plots are at least one time the average height of the forest stand, the average height of the forest stand is the average value of the height of all trees in the forest stand, and the sample plot area is 0.06hm 2 ;

[0005] The tree-by-tree ruler is used to measure and locate trees with a breast diameter greater than 5 cm in the plot. The measurement indicators include breast diameter, tree height, crown width and relative coordinates. The measuring tools are breast diameter ruler, ultrasonic altimeter, steel tape measure and laser rangefinder.

[0006] The soil sampling is carried out by collecting 100g of soil at 0-20cm from the surface at the four corners and the center of the sample plot as a nutrient determination sample by the 5-point method;

[0007] The stand factor calculation and measurement steps are used to calculate the dominance of top tree species, the average breast diameter of the stand, the average tree height of the stand, the degree of intermixing and the total phosphorus in the soil, wherein:

[0008] The dominance of top tree species was calculated by the proportion of basal area at breast height of the zonal top tree species in the forest stand;

[0009] The average breast diameter of a stand is the diameter corresponding to the average cross-sectional area of ​​the stand. The specific calculation formula is as follows:

[0010]

[0011] Where N is the total number of trees in the plot, di is the DBH of the i-th tree;

[0012] The average tree height of the forest stand was calculated based on the measurement data of each tree in the sample plot;

[0013] The intermixing degree is composed of the target tree and the four nearest adjacent trees as a spatial structural unit. The calculation formula is as follows: When the target tree i and the jth adjacent tree are of different species, v ji =1, otherwise, v ji =0;

[0014] The total phosphorus in soil was determined by acid fusion-molybdenum antimony colorimetry. The determination steps are as follows:

[0015] Step 1: Weigh 0.25g of air-dried soil sample that has passed through a 0.149mm aperture sieve, place it at the bottom of a nickel crucible, add 3-4 drops of anhydrous ethanol to wet the sample, spread 2.0g of sodium hydroxide on the sample, place the crucible in a high-temperature electric furnace, heat it up, and cut off the power supply when the temperature reaches 400°C, let it stand for 15 minutes, then continue to heat it up to 720°C, keep it for 15 minutes, and take it out to cool;

[0016] Step 2: Add 10 ml of 80°C water to the crucible, transfer to a 100 ml volumetric flask after the melt is dissolved, and wash the crucible with 10 ml of 3 mol / l sulfuric acid solution and water. Transfer the washing liquid to the volumetric flask, cool, fix the volume, dry filter with phosphorus-free filter paper or clarify by centrifugation, and do two blank tests at the same time;

[0017] Step 3: Pipette 5-10 ml of the sample solution to be tested into a 50 ml volumetric flask, dilute with water to about 30 ml, add 2-3 drops of dinitrophenol indicator, and adjust the solution to a light yellow color with 100 g / l sodium carbonate solution or 5% sulfuric acid solution, add 5.00 ml of molybdenum antimony anti-color developer, shake well, add water to make up to volume, and place at room temperature above 20°C for 30 minutes before testing;

[0018] Step 4: Pipette 0, 1.00, 2.00, 3.00, 4.00, 5.00, 6.00 ml of 5ug / ml phosphorus standard solution into a 50ml volumetric flask, add a blank test solution of the same volume as the sample solution used for colorimetric determination, dilute with water to about 30ml, adjust the acidity as with the sample determination, develop color, and adjust the volume. Dilute with water to about 30ml, add 5.00ml of molybdenum antimony anti-colorimetric agent, adjust the volume, and obtain a series of solutions with phosphorus contents of 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6ug / ml, respectively. After placing at a temperature above 20°C for 30 minutes, adjust the instrument zero point with the series of solutions with zero phosphorus content, perform colorimetric determination at a wavelength of 700nm on a spectrophotometer using a 1cm light path cuvette, and record the sample concentration value;

[0019] The calculation method of the stage determination factor is as follows:

[0020] DF=2.403*DD+0.035*DBHa+0.106*Ha+0.65*MI-1.101*P, where DF is the stage determination factor, DD is the dominance of top tree species, DBHa is the average breast diameter of the stand, Ha is the average tree height of the stand, MI is the degree of mixed vegetation, and P is the total phosphorus in the soil.

[0021] In the sample plot layout part of the forest stand survey step, the specific operations are as follows:

[0022] Step 1: After selecting the origin before measurement, set up the tripod and install the compass on the tripod, and use the legs to make a rough adjustment to the level of the instrument;

[0023] Step 2: Use the universal ball joint to fine-tune the level so that the two bubbles of the level on the compass box are centered;

[0024] Step 3: Tighten the ball socket connection screw to make the compass in a horizontal position; loosen the set screw at the bottom of the compass housing, turn the compass horizontally, and the wire puller pulls the wire (i.e., the tape measure) from the starting position. The observer adjusts the sight above the telescope tube and directs the wire puller to move forward according to the direction;

[0025] Step 4: When the wire puller reaches the specified distance, adjust the eyepiece so that the eyes can clearly see the crosshairs in the scope, and instruct the wire puller to stand in the center of the crosshairs and fix the position of the point;

[0026] Step 5: Loosen the magnetic needle fixing screw to allow it to rotate freely. When the magnetic needle is stationary, read the degree dial reading pointed by the north end of the magnetic needle.

[0027] Step 6: Move the tripod to this point, rotate 90° based on the azimuth of the starting point, use this as the azimuth of the next edge, repeat the previous steps to complete points 3 to 5.

[0028] In the section of measuring each tree in the forest stand survey, the specific operations are as follows:

[0029] The diameter at breast height is measured with a breast diameter ruler, which is accurate to 0.1 cm. The tree height is measured with an ultrasonic altimeter, with a height measurement error of 0.1 m. The crown width is measured with a steel tape measure and a laser rangefinder. The distance between the vertical projection of the farthest position of the crown in the horizontal direction in the four directions and the trunk is used as the standard. The long side of the sample plot is used as the X-axis and the short side as the Y-axis. The coordinates of each tree are recorded using a steel tape measure and a laser rangefinder.

[0030] The calculation formula for the top tree species dominance calculation part of the stand factor calculation and measurement step is:

[0031]

[0032] Where RD is the dominance of top tree species, BA is the basal area at breast height, i is the i-th top tree species, j is the j-th tree, n and m represent the number of top tree species and the number of all tree species, respectively.

[0033] In the stand factor calculation and measurement step, the stand average tree height calculation part is to average the tree heights of all trees based on the tree measurement data of the sample plot. The specific steps are as follows:

[0034] Step 1: Select and calibrate the measuring tool. The tree height measuring tool is an ultrasonic height meter. Before measuring, calibrate it according to the instrument manual.

[0035] Step 2: Tree-by-tree measurement and data recording. The height of each tree with a breast diameter greater than 5 cm in the sample plot is measured. When measuring, the operator aims the ultrasonic height meter at the top of the tree, obtains the tree height data according to the instrument operation method, and records it in meters. At the same time, the corresponding number and other identification information of each tree are recorded;

[0036] Step 3: Data collation: sort the measured tree height data of each tree according to the recorded identification information, check whether there are any missing or erroneous data records, and review and correct them in time if there are any problems;

[0037] Step 4: Sum calculation, add up all the sorted tree height data to get the total tree height, divide the total tree height by the total number of trees with a breast diameter greater than 5 cm in the sample plot to get the average tree height of the forest stand. The calculation formula is: Average tree height of the forest stand = total tree height ÷ total number of trees.

[0038] The beneficial effects of the present invention are as follows:

[0039] 1. The present invention breaks through the limitation of the existing technology that only relies on visually accessible stand factors, such as tree species composition, tree size, understory regeneration, etc., to determine the forest succession stage. In addition to the common tree size-related factors, factors that are difficult to directly observe visually, such as top tree species dominance, mixed degree, and total soil phosphorus, are also included. Through this comprehensive and integrated factor consideration method, the actual status and succession stage of natural secondary forests can be more accurately reflected, avoiding judgment errors caused by the one-sidedness of single or partial factors. A scientific technical system is constructed based on the Fisher discriminant analysis method to quantify each stand factor and use a clear calculation formula.

[0040] DF=2.403DD+0.035DBHa+0.106Ha+0.65MI-1.101*P to determine the succession stage. Compared with the qualitative description of the existing technology, this quantitative analysis method has higher accuracy and objectivity, and can provide a more reliable decision-making basis for the management of natural secondary forests.

[0041] Second, the existing technology mainly divides the succession stages of natural secondary forests based on qualitative descriptions, lacking a solid theoretical basis. The present invention has established a complete set of quantitative division technology systems for succession stages based on scientific principles and mathematical methods. From the screening and calculation of forest stand factors to the determination of stage determination factors and the determination of succession stages, each link has a clear theoretical basis and mathematical model support, providing a scientific theoretical framework for the field of natural secondary forest management. In addition, the DF value stage division principle constructed by the present invention takes into account that some real forest stands are in the transition period between two adjacent stages. This theoretical system can not only accurately divide the succession stages of natural secondary forests, but also provide effective guidance for subsequent forest management activities. For example, according to different succession stages, management measures such as mowing and weeding in the unforested period, pruning and light-transmitting felling in the young forest period, growth felling and competitive felling in the middle-aged forest and near-mature forest period, and selective felling and gradual felling in the mature and over-mature forest period can be formulated in a targeted manner, thereby improving the scientificity and effectiveness of forest management and promoting the healthy development of natural secondary forests.

[0042] 3. Positive impact on forestry projects. In the context of national policies emphasizing the strengthening of degraded forest restoration, the accurate succession stage division method provided by the present invention is of great significance for the rational planning and implementation of degraded forest restoration projects. By accurately understanding the succession stages of natural secondary forests, it is possible to formulate restoration strategies that are more in line with actual conditions, select suitable tree species for replanting, adjust the forest stand structure, improve the resistance and productivity of forests, and accelerate the recovery process of degraded forests. Managing natural secondary forests well is crucial to the implementation of forestry projects such as natural forest protection, national afforestation, and quality improvement in China. The present invention provides key technical support for these forestry projects, making the management of natural secondary forests more scientific and efficient, which helps to achieve the expected goals of forestry projects and ensure national ecological security construction.

[0043] Fourth, the present invention provides a clear and quantifiable standard for the division of succession stages for natural secondary forest management. Forestry operators no longer rely on subjective experience and vague qualitative judgments, but can quickly and accurately determine the succession stage of natural secondary forests based on the method of the present invention, thereby adjusting management strategies in a timely manner and improving the efficiency and scientific nature of management decisions. Since the method of the present invention is based on scientific principles and generally applicable mathematical models, it can be applied to natural secondary forests in different geographical regions and ecological environments after appropriate adjustment and application. This enables forestry operators to use the method of the present invention to carry out effective management and operation when faced with different natural secondary forest resources, thereby improving the versatility and practicality of the method. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of five-point sampling in the sample plot of the present invention;

[0045] Figure 2 It is a table based on the division of natural secondary forest succession stages of the present invention;

[0046] Figure 3 This is a table showing the differences in the division of natural secondary forest succession stages using different technologies of the present invention.

[0047] In the figure: I, II, III, IV and V represent the community establishment stage, competitive growth stage, quality formation stage, near-natural stage and permanent forest stage respectively. DETAILED DESCRIPTION

[0048] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments of the present invention are provided for the purpose of illustration and description, and are not intended to be exhaustive or to limit the present invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention, and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for specific uses.

[0049] Example:

[0050] See also Figure 1 - Figure 3 The present invention provides a technical solution: a method for quantitatively dividing the succession stages of natural secondary forests, including a forest stand survey step, a forest stand factor calculation and measurement step, and a stage determination factor calculation and succession stage determination step. The forest stand survey step includes sample plot layout, tree-by-tree measurement and soil sampling, wherein: the sample plot layout represents the overall characteristics of the forest stand according to the average state of the forest stand, the distance between the sample plot and the forest source and the distance between the sample plots are at least one times the average height of the forest stand, the average height of the forest stand is the average of the heights of all trees in the forest stand, and the sample plot area is 0.06hm 2 ;

[0051] Each tree ruler is used to measure and locate trees with a breast diameter greater than 5 cm in the sample plot. The measurement indicators include breast diameter, tree height, crown width and relative coordinates. The measurement tools are breast diameter ruler, ultrasonic height meter, steel tape measure and laser rangefinder.

[0052] Soil sampling was performed by the 5-point method, and 100 g of soil from the surface 0-20 cm was collected at the four corners and the center of the plot as nutrient determination samples;

[0053] The stand factor calculation and measurement steps are used to calculate the dominance of top tree species, the average DBH of the stand, the average tree height of the stand, the degree of intermixing and the total phosphorus in the soil, where:

[0054] The dominance of top tree species was calculated by the proportion of basal area at breast height of the zonal top tree species in the forest stand;

[0055] The average breast diameter of a stand is the diameter corresponding to the average cross-sectional area of ​​the stand. The specific calculation formula is as follows:

[0056]

[0057] Where N is the total number of trees in the plot, di is the DBH of the i-th tree;

[0058] The average tree height of the forest stand was calculated based on the measurement data of each tree in the sample plot;

[0059] The intermixing degree is composed of the target tree and the four nearest adjacent trees as a spatial structural unit. The calculation formula is as follows: When the target tree i and the jth adjacent tree are of different species, v ji =1, otherwise, v ji =0;

[0060] The total phosphorus in soil was determined by acid fusion-molybdenum antimony colorimetry. The determination steps are as follows:

[0061] Step 1: Weigh 0.25g of air-dried soil sample that has passed through a 0.149mm aperture sieve, place it at the bottom of a nickel crucible, add 3-4 drops of anhydrous ethanol to wet the sample, spread 2.0g of sodium hydroxide on the sample, place the crucible in a high-temperature electric furnace, heat it up, and cut off the power supply when the temperature reaches 400°C, let it stand for 15 minutes, then continue to heat it up to 720°C, keep it for 15 minutes, and take it out to cool;

[0062] Step 2: Add 10 ml of 80°C water to the crucible, transfer to a 100 ml volumetric flask after the melt is dissolved, and wash the crucible with 10 ml of 3 mol / l sulfuric acid solution and water. Transfer the washing liquid to the volumetric flask, cool, fix the volume, dry filter with phosphorus-free filter paper or clarify by centrifugation, and do two blank tests at the same time;

[0063] Step 3: Pipette 5-10 ml of the sample solution to be tested into a 50 ml volumetric flask, dilute with water to about 30 ml, add 2-3 drops of dinitrophenol indicator, and adjust the solution to a light yellow color with 100 g / l sodium carbonate solution or 5% sulfuric acid solution, add 5.00 ml of molybdenum antimony anti-color developer, shake well, add water to make up to volume, and place at room temperature above 20°C for 30 minutes before testing;

[0064] Step 4: Pipette 0, 1.00, 2.00, 3.00, 4.00, 5.00, 6.00 ml of 5ug / ml phosphorus standard solution into a 50ml volumetric flask, add a blank test solution of the same volume as the sample solution used for colorimetric determination, dilute with water to about 30ml, adjust the acidity as with the sample determination, develop color, and adjust the volume. Dilute with water to about 30ml, add 5.00ml of molybdenum antimony anti-colorimetric agent, adjust the volume, and obtain a series of solutions with phosphorus contents of 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6ug / ml, respectively. After placing at a temperature above 20°C for 30 minutes, adjust the instrument zero point with the series of solutions with zero phosphorus content, perform colorimetric determination at a wavelength of 700nm on a spectrophotometer using a 1cm light path cuvette, and record the sample concentration value;

[0065] The calculation method of the stage determination factor is as follows:

[0066] DF=2.403*DD+0.035*DBHa+0.106*Ha+0.65*MI-1.101*P, where DF is the stage determination factor, DD is the dominance of top tree species, DBHa is the average breast diameter of the stand, Ha is the average tree height of the stand, MI is the degree of mixed vegetation, and P is the total phosphorus in the soil. If the calculated DF value of a stand is in the overlapping range of DF values ​​of two succession stages, it means that the stand is in the transition period between two adjacent succession stages.

[0067] In the sample plot layout part of the forest stand survey step, the specific operations are as follows:

[0068] Step 1: After selecting the origin before measurement, set up the tripod and install the compass on the tripod, and use the legs to make a rough adjustment to the level of the instrument;

[0069] Step 2: Use the universal ball joint to fine-tune the level so that the two bubbles of the level on the compass box are centered;

[0070] Step 3: Tighten the ball socket connection screw to make the compass in a horizontal position; loosen the set screw at the bottom of the compass housing, turn the compass horizontally, and the wire puller pulls the wire (i.e., the tape measure) from the starting position. The observer adjusts the sight above the telescope tube and directs the wire puller to move forward according to the direction;

[0071] Step 4: When the wire puller reaches the specified distance, adjust the eyepiece so that the eyes can clearly see the crosshairs in the scope, and instruct the wire puller to stand in the center of the crosshairs and fix the position of the point;

[0072] Step 5: Loosen the magnetic needle fixing screw to allow it to rotate freely. When the magnetic needle is stationary, read the degree dial reading pointed by the north end of the magnetic needle.

[0073] Step 6: Move the tripod to this point, rotate 90° based on the azimuth of the starting point, use this as the azimuth of the next edge, repeat the previous steps to complete points 3 to 5.

[0074] In the section of measuring each tree in the forest stand survey, the specific operations are as follows:

[0075] The diameter at breast height is measured with a breast diameter ruler, which is accurate to 0.1 cm. The tree height is measured with an ultrasonic altimeter, with a height measurement error of 0.1 m. The crown width is measured with a steel tape measure and a laser rangefinder. The distance between the vertical projection of the farthest position of the crown in the horizontal direction in the four directions and the trunk is used as the standard. The long side of the sample plot is used as the X-axis and the short side as the Y-axis. The coordinates of each tree are recorded using a steel tape measure and a laser rangefinder.

[0076] The calculation formula for the top tree species dominance calculation part of the stand factor calculation and measurement step is:

[0077]

[0078] Where RD is the dominance of top tree species, BA is the basal area at breast height, i is the i-th top tree species, j is the j-th tree, n and m represent the number of top tree species and the number of all tree species, respectively.

[0079] In the stand factor calculation and measurement step, the stand average tree height calculation part is to average the tree heights of all trees based on the tree measurement data of the sample plot. The specific steps are as follows:

[0080] Step 1: Select and calibrate the measuring tool. The tree height measuring tool is an ultrasonic height meter. Before measuring, calibrate it according to the instrument manual.

[0081] Step 2: Tree-by-tree measurement and data recording. The height of each tree with a breast diameter greater than 5 cm in the sample plot is measured. When measuring, the operator aims the ultrasonic height meter at the top of the tree, obtains the tree height data according to the instrument operation method, and records it in meters. At the same time, the corresponding number and other identification information of each tree are recorded;

[0082] Step 3: Data collation: sort the measured tree height data of each tree according to the recorded identification information, check whether there are any missing or erroneous data records, and review and correct them in time if there are any problems;

[0083] Step 4: Sum the tree heights. Add up all the tree height data to get the total tree heights. Divide the total tree heights by the total number of trees with a breast diameter greater than 5 cm in the plot to get the average tree height of the stand. The calculation formula is: Average tree height of the stand = Total tree heights ÷ Total number of trees

[0084] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field and related fields without creative work should fall within the scope of protection of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention are implemented according to the conventional means in the field unless otherwise specified and limited.

Claims

1. A method for quantitatively dividing the succession stages of natural secondary forests, comprising a forest stand survey step, a forest stand factor calculation and measurement step, and a stage determination factor calculation and succession stage determination step, characterized in that: The forest stand survey steps include sample plot layout, tree measurement and soil sampling, among which: The sample plots are arranged according to the average state of the forest stand to represent the overall characteristics of the forest stand. The distance between the sample plot and the forest source and the distance between the sample plots are at least one time the average height of the forest stand. The average height of the forest stand is the average height of all trees in the forest stand. The sample plot area is 0.06hm 2 ; The tree-by-tree ruler is used to measure and locate trees with a breast diameter greater than 5 cm in the plot. The measurement indicators include breast diameter, tree height, crown width and relative coordinates. The measuring tools are breast diameter ruler, ultrasonic altimeter, steel tape measure and laser rangefinder. The soil sampling is carried out by collecting 100g of soil at 0-20cm from the surface at the four corners and the center of the sample plot as a nutrient determination sample by the 5-point method; The stand factor calculation and measurement steps are used to calculate the dominance of top tree species, the average breast diameter of the stand, the average tree height of the stand, the degree of intermixing and the total phosphorus in the soil, wherein: The dominance of top tree species was calculated by the proportion of basal area at breast height of the zonal top tree species in the forest stand; The average breast diameter of a stand is the diameter corresponding to the average cross-sectional area of ​​the stand. The specific calculation formula is as follows: Where N is the total number of trees in the plot, di is the DBH of the i-th tree; The average tree height of the forest stand was calculated based on the measurement data of each tree in the sample plot; The intermixing degree is composed of the target tree and the four nearest adjacent trees as a spatial structural unit. The calculation formula is as follows: When the target tree i and the jth adjacent tree are of different species, vj i =1, otherwise, vj i =0; The total phosphorus in soil was determined by acid fusion-molybdenum antimony colorimetry. The determination steps are as follows: Step 1: Weigh 0.25g of air-dried soil sample that has passed through a 0.149mm aperture sieve, place it at the bottom of a nickel crucible, add 3-4 drops of anhydrous ethanol to wet the sample, spread 2.0g of sodium hydroxide on the sample, place the crucible in a high-temperature electric furnace, heat it up, and cut off the power supply when the temperature reaches 400°C, let it stand for 15 minutes, then continue to heat it up to 720°C, keep it for 15 minutes, and take it out to cool; Step 2: Add 10 ml of 80°C water to the crucible, transfer to a 100 ml volumetric flask after the melt is dissolved, and wash the crucible with 10 ml of 3 mol / l sulfuric acid solution and water. Transfer the washing liquid to the volumetric flask, cool, fix the volume, dry filter with phosphorus-free filter paper or clarify by centrifugation, and do two blank tests at the same time; Step 3: Pipette 5-10 ml of the sample solution to be tested into a 50 ml volumetric flask, dilute with water to about 30 ml, add 2-3 drops of dinitrophenol indicator, and adjust the solution to a light yellow color with 100 g / l sodium carbonate solution or 5% sulfuric acid solution, add 5.00 ml of molybdenum antimony anti-color developer, shake well, add water to make up to volume, and place at room temperature above 20°C for 30 minutes before testing; Step 4: Pipette 0, 1.00, 2.00, 3.00, 4.00, 5.00, 6.00 ml of 5ug / ml phosphorus standard solution into a 50ml volumetric flask, add a blank test solution of the same volume as the sample solution used for colorimetric determination, dilute with water to about 30ml, adjust the acidity as with the sample determination, develop color, and adjust the volume. Dilute with water to about 30ml, add 5.00ml of molybdenum antimony anti-colorimetric agent, adjust the volume, and obtain a series of solutions with phosphorus contents of 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6ug / ml, respectively. After placing at a temperature above 20°C for 30 minutes, adjust the instrument zero point with the series of solutions with zero phosphorus content, perform colorimetric determination at a wavelength of 700nm on a spectrophotometer using a 1cm light path cuvette, and record the sample concentration value; The calculation method of the stage determination factor is as follows: DF=2.403*DD+0.035*DBHa+0.106*Ha+0.65*MI-1.101*P, where DF is the stage determination factor, DD is the dominance of top tree species, DBHa is the average breast diameter of the stand, Ha is the average tree height of the stand, MI is the degree of mixed vegetation, and P is the total phosphorus in the soil.

2. The method for quantitatively dividing the succession stages of natural secondary forests according to claim 1, characterized in that: In the sample plot layout part of the forest stand survey step, the specific operations are as follows: Step 1: After selecting the origin before measurement, set up the tripod and install the compass on the tripod, and use the legs to make a rough adjustment to the level of the instrument; Step 2: Use the universal ball joint to fine-tune the level so that the two bubbles of the level on the compass box are centered; Step 3: Tighten the ball socket connection screw to make the compass in a horizontal position; loosen the set screw at the bottom of the compass housing, turn the compass horizontally, and the wire puller pulls the wire (i.e., the tape measure) from the starting position. The observer adjusts the sight above the telescope tube and directs the wire puller to move forward according to the direction; Step 4: When the wire puller reaches the specified distance, adjust the eyepiece so that the eyes can clearly see the crosshairs in the scope, and instruct the wire puller to stand in the center of the crosshairs and fix the position of the point; Step 5: Loosen the magnetic needle fixing screw to allow it to rotate freely. When the magnetic needle is stationary, read the degree dial reading pointed by the north end of the magnetic needle. Step 6: Move the tripod to this point, rotate 90° based on the azimuth of the starting point, use this as the azimuth of the next edge, repeat the previous steps to complete points 3 to 5.

3. The method for quantitatively dividing the succession stages of natural secondary forests according to claim 1, characterized in that: In the section of measuring each tree in the forest stand survey, the specific operations are as follows: The diameter at breast height is measured with a breast diameter ruler, which is accurate to 0.1 cm. The tree height is measured with an ultrasonic altimeter, with a height measurement error of 0.1 m. The crown width is measured with a steel tape measure and a laser rangefinder. The distance between the vertical projection of the farthest position of the crown in the horizontal direction in the four directions and the trunk is used as the standard. The long side of the sample plot is used as the X-axis and the short side as the Y-axis. The coordinates of each tree are recorded using a steel tape measure and a laser rangefinder.

4. The method for quantitatively dividing the succession stages of natural secondary forests according to claim 1, characterized in that: The calculation formula for the top tree species dominance calculation part of the stand factor calculation and measurement step is: Where RD is the dominance of top tree species, BA is the basal area at breast height, i is the i-th top tree species, j is the j-th tree, n and m represent the number of top tree species and the number of all tree species, respectively.

5. The method for quantitatively dividing natural secondary forest succession stages according to claim 1, characterized in that: In the stand factor calculation and measurement step, the stand average tree height calculation part is to average the tree heights of all trees based on the tree measurement data of the sample plot. The specific steps are as follows: Step 1: Select and calibrate the measuring tool. The tree height measuring tool is an ultrasonic height meter. Before measuring, calibrate it according to the instrument manual. Step 2: Tree-by-tree measurement and data recording. The height of each tree with a breast diameter greater than 5 cm in the sample plot is measured. When measuring, the operator aims the ultrasonic height meter at the top of the tree, obtains the tree height data according to the instrument operation method, and records it in meters. At the same time, the corresponding number and other identification information of each tree are recorded; Step 3: Data collation: sort the measured tree height data of each tree according to the recorded identification information, check whether there are any missing or erroneous data records, and review and correct them in time if there are any problems; Step 4: Sum calculation, add up all the sorted tree height data to get the total tree height, divide the total tree height by the total number of trees with a breast diameter greater than 5 cm in the sample plot to get the average tree height of the forest stand. The calculation formula is: Average tree height of the forest stand = total tree height ÷ total number of trees.

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