Method for measuring age of forest window

Abstract

The invention discloses a method for measuring the age of a forest window, and the method comprises the steps: 1, selecting a sample wood: selecting a suitable forest window edge wood from a target forest window as the sample wood; 2, collecting and processing tree cores, namely drilling one tree core sample on the tree trunk at the position 1.3 m away from the sample wood by using a tree core sampler at an angle of 90 degrees along the direction from the center of the forest window to the radiation direction of the sample wood, placing the tree core sample in a sampling tube, and taking the tree core sample back to a room, and 3, placing the obtained tree core sample in a shade place for natural air drying, and taking out the tree core sample. And sequentially polishing to be smooth and flat by using coarse-to-fine abrasive paper. According to the method and the device, the forest window formation time range is accurately measured by analyzing the environmental change caused by forest window formation, utilizing the environmental sensitivity of the stable carbon isotope and combining tree ring growth, so that the forest window age is determined, and the precision is improved. According to the method, the sample size demand is low, the forest window age can be accurately estimated by only needing a tree core sample of one sample tree, the requirements for the variety and the number of the sample trees are remarkably reduced, and the applicability is higher.

Description

Technical Field

[0001] The invention relates to the technical field of measuring forest gap characteristics, and in particular to a method for measuring the age of a forest gap. Background Art

[0002] Forest gaps refer to discontinuous gaps formed after the death of trees in the forest canopy. They are small-scale disturbances that are common in different forest types and significantly affect the regeneration and succession of forests. As one of the most important basic characteristics of forest gaps, the age of forest gaps directly affects the tree species composition and structure of forest gap regeneration, and reflects the stage of the forest gap in the entire closing process.

[0003] Therefore, in near-natural forestry management, clarifying the age of forest gaps is a prerequisite for using forest gaps to promote directional forest regeneration and succession. At present, the methods for estimating the age of forest gaps include observing the degree of wood decay in forest gaps, counting the branches of forest gaps, and releasing the growth rings of trees at the edge of forest gaps. Among them, the method of observing the degree of wood decay in forest gaps can only roughly divide the age of forest gaps into several levels, and the classification results are greatly affected by subjective factors, especially not suitable for the age estimation of old forest gaps. The method of counting the branches of forest gaps is limited in accuracy due to the time and young age effect of forest gap regeneration trees entering the forest gaps. The method of releasing the growth rings of trees at the edge of forest gaps is generally unable to exceed 5 years due to factors such as the sensitivity of trees to forest gap interference, their own annual ring characteristics, and the interaction between adjacent trees.

[0004] Especially in natural secondary forests with diverse tree species and complex age structure, it is usually impossible to improve the accuracy of forest gap age determination by collecting a large number of samples of the same forest gap edge wood. Traditional methods rely on experience and have great arbitrariness. Therefore, a method that can accurately measure forest gap age is needed. Summary of the invention

[0005] In order to solve the problem that it is usually impossible to improve the accuracy of forest window age determination by collecting a large number of forest window edge wood samples of the same species in natural secondary forests with diverse tree species and complex age structure, the present invention provides a method for measuring forest window age. The technical scheme adopted is as follows: A method for measuring forest gap age, comprising the following steps: Step 1: Sample tree selection: select a suitable tree at the edge of the forest gap in the target forest gap as the sample tree; Step 2: Collect and process the tree core. From the center of the forest window to the sample tree, at 1.3m away from the sample tree, use a tree core sampler to press it on the tree trunk at a 90-degree angle, drill a tree core sample, place it in a sampling tube and bring it back to the room. Step 3: After the obtained tree core sample is placed in a cool place to dry naturally, it is polished with sandpaper from coarse to fine in sequence until it is smooth and flat; Step 4: Use a tree-ring analyzer to measure the annual ring width of the tree core, and use the relative growth method to calculate the percentage growth change (PGC) of the tree ring sequence: PGC = (M2-M1) / M1×100%, where M1 and M2 are the average widths of the first five years and the last five years, respectively. The time period when PGC is greater than 10% and lasts for more than five years is used as the time range for forest gap formation determined by the growth release method.

[0006] Preferably, the method further comprises step 5, determining the time of forest gap formation by stable carbon isotope analysis: taking annual ring tree cores within a determined time range, dividing, crushing and mixing them according to one group per year, taking 5 mg from each group, and using a mass spectrometer to measure the stable carbon isotope ratio (δ 13 C), calculate the carbon isotope resolution (∆ 13 C) value, ∆ 13 C = δ 13 C a - δ 13 C tree - ring / δ 13 C tree - ring +1, where the atmospheric stable carbon isotope ratio (δ 13 C a ) is the internationally accepted value of -9.37‰, and the time range of forest gap formation is ∆ 13 The year when the lowest value of C occurs is the year when the forest gap is formed.

[0007] Preferably, the length of the tree core is 10 mm-30 mm, and the length of the tree core drilled by the tree core sampler should exceed the center of the tree by 2 to 4 centimeters.

[0008] Preferably, the order of using sandpaper from coarse to fine is 150 mesh, 300 mesh, 600 mesh, and 800 mesh.

[0009] Preferably, the radiation direction from the center of the forest gap to the sample tree is between 45 degrees and 315 degrees.

[0010] Preferably, after the tree core sample is naturally air-dried in step 2 and before polishing, the tree core sample is soaked in a chemical decontamination solution for 24 hours, wherein the chemical decontamination solution is composed of 5% sodium hydroxide solution and 3% hydrogen peroxide solution, and is mixed in a ratio of 1:1. After soaking, the tree core sample is rinsed with clean water for 3 times, and then the tree core sample is placed in an environment with a temperature of 40°C and a relative humidity of 30% for stabilization treatment for 48 hours.

[0011] Preferably, before the four-year growth-release method is used to determine the time range for forest gap formation, the physiological indicators of the sample trees are measured, and leaves from the top, middle and bottom of the crown of the sample trees are selected to measure physiological indicators such as chlorophyll content, photosynthesis rate and stomatal conductance of the leaves. At each measurement time point, the leaves in each part are repeatedly measured multiple times and the average value is taken.

[0012] Preferably, after determining the formation time of the forest gap, long-term environmental data of the target forest gap area are collected, including data such as light intensity, temperature, precipitation, and soil nutrients, and the changing trends of these environmental data before and after the formation of the forest gap are analyzed. The data are then compared with the changes in the annual ring width and stable carbon isotope ratio of the tree core samples to establish a comprehensive analysis model, and the formation time of the forest gap and the impact on tree growth are analyzed based on the model.

[0013] Preferably, the suitable forest gap edge trees should be light-loving species with straight trunks, small taper, well-developed crowns, vigorous growth, and no diseases or insect pests.

[0014] Compared with the prior art, the present invention has the following technical advances: 1. In the method of determining the age of forest gaps, the present invention analyzes the environmental changes caused by the formation of forest gaps, utilizes the environmental sensitivity of stable carbon isotopes, and combines the growth of tree rings to accurately determine the time range of forest gap formation, thereby determining the age of forest gaps and improving accuracy.

[0015] 2. In terms of sample size, the present invention requires less sample size. Only one tree core sample is needed to accurately estimate the age of the forest gap, which significantly reduces the requirements for the type and quantity of sample trees and is more applicable. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0017] In the attached picture: Figure 1 A schematic diagram of a method for measuring forest gap years according to the present invention; Figure 2 A schematic diagram of the steps for measuring the forest gap years of the present invention; Figure 3 A diagram showing the steps for calculating the percentage of growth change of the annual ring sequence of the present invention; Figure 4 A bar graph showing the percentage of growth change of each sample of the present invention; Figure 5 Parameter diagram of each sample of the present invention.

[0018] In the picture: 1. Sample wood; 2. Tree core sampler; 3. Core extractor. DETAILED DESCRIPTION

[0019] The following specific embodiments may be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments. The embodiments of the present invention will be described below in conjunction with the accompanying drawings. Embodiment 1

[0020] Secondary forests formed by the degradation of primary forests have become the main body of my country's forest resources. Taking the secondary forests in Northeast China as an example, the original top-level community broad-leaved Korean pine forests have been transformed into natural secondary forests composed of various maple species, Juglans mandshurica, maple birch, Tilia amurensis, and Mongolian oak after complex disturbances. The diverse tree species composition further increases the difficulty of determining the age of forest windows, limiting the near-natural management of secondary forests with forest window regeneration as the core. In order to test the effectiveness of the invention, eight artificial forest windows established in winter were selected from the typical secondary forests in the Dahu Work Area of ​​Dasuhe State Forest Farm in Dasuhe Township, the southern end of Qingyuan County, Liaoning Province, for forest window age determination.

[0021] Embodiment 2: A method for measuring forest gap age, comprising the following steps: like Figures 1 to 5 As shown, the steps are as follows: a suitable forest gap edge tree is selected from each of the eight sample forest gaps as sample tree 1. The species of the selected forest gap edge trees include light-loving Juglans mandshurica, Quercus mongolica or Betula acer truncatum. Sample tree 1 requires a straight trunk with a small taper, a well-developed crown, vigorous growth, and no diseases or insect pests.

[0022] Step 2: Tree core collection and processing: Figure 1 The following are the steps to measure the age of a forest gap: Figure 2 As shown in A and B, along the height direction of the sample tree 1, at the height dimension of each sample tree 1 of 1.3m, along the radial direction from the center of the forest window to the sample tree, use a 22mm tree core sampler 2 to press it on the trunk at a 90-degree angle, as shown in Figure 2 As shown in C, turn the handle to take the sample, keep it at a flat angle while turning, and insert the core extractor 3 after the length of the drilled core exceeds the center of the tree by 2 to 4 cm. Figure 2 As shown in D and E in the middle, after reversing twice, the core extractor 3 is taken out to obtain a tree core sample 1.

[0023] Step three is to take samples, polish them, and place them in sampling tubes and bring them back to the room, and finally obtain eight sample tree cores. For the obtained tree core sample 1, place it in a cool place to air dry naturally. After it is naturally dried, use 150 mesh, 300 mesh, 600 mesh, and 800 mesh sandpaper in sequence to polish it until it is smooth and flat.

[0024] Procedure Four-year growth ring release method to determine the time range of forest gap formation: Use LINTAB 6 tree ring analyzer (Rinntech, Germany) to measure the width of its annual rings, such as Figure 3 and Figure 4 As shown in the figure, the relative growth method of tree rings is used, that is, the growth rate in a certain year or years is compared with the previous year or years, with a step of five years, to calculate the percentage growth change (PGC) of the tree ring sequence, PGC = (M2-M1) / M1×100%, where M1 and M2 are the average widths of the tree rings in the first five years and the last five years, respectively. The PGC changes of each sample tree core can be found in Figure 4 As shown in Figure 2, the time interval when PGC is greater than 10% and lasts for more than 5 years is taken as the time range of forest gap formation determined by the growth release method. The time range of forest gap formation determined by each sample tree core is as follows: Figure 5 shown.

[0025] Step 5: Determine the formation time of forest gaps by stable carbon isotope analysis: Take annual ring samples within the time range, divide them into groups for each year, crush and mix them, and take 5 mg of them to measure the stable carbon isotope ratio (δ 13 C), calculate the carbon isotope resolution (∆ 13 C) value, ∆ 13 C = δ 13 C a - δ 13 C tree - ring / δ 13 C tree - ring +1, where the atmospheric stable carbon isotope ratio (δ 13 Ca) is -9.37‰, an internationally accepted value. 13 The year when the minimum value of C appears is the measured forest gap formation year, and the time interval between the forest gap formation year and the forest gap age measurement year is the forest gap age. The forest gap formation time range and forest gap age measured by each sample tree core are as follows: Figure 5 shown.

[0026] In one example, after the tree core sample in step 2 is naturally air-dried, before polishing, the tree core sample is soaked in a chemical decontamination solution for 24 hours, the chemical decontamination solution is composed of 5% sodium hydroxide solution and 3% hydrogen peroxide solution, and is mixed in a ratio of 1:1. After soaking, the tree core sample is rinsed with clean water for 3 times, and then the tree core sample is placed in an environment with a temperature of 40°C and a relative humidity of 30% for stabilization for 48 hours, and then polished. Before the annual ring growth release method is used to determine the time range of forest gap formation, the physiological indicators of the sample trees are measured, and the leaves at the top, middle and bottom of the crown of the sample trees are selected to measure the physiological indicators of the leaves, such as chlorophyll content, photosynthesis rate and stomatal conductance. At each measurement time point, the leaves in each part are repeatedly measured and the average value is taken.

[0027] After determining the time of forest gap formation, long-term environmental data of the target forest gap area are collected, including data on light intensity, temperature, precipitation, soil nutrients, etc., and the changing trends of these environmental data before and after the formation of the forest gap are analyzed. They are then compared with the changes in the annual ring width and stable carbon isotope ratio of the tree core samples, and a comprehensive analysis model is established. Based on the model, the time of forest gap formation and its impact on tree growth are analyzed.

[0028] The results of the embodiment show that the method for measuring the forest gap age provided by the present invention has the advantages of high precision and low sample quantity requirement compared with the commonly used forest gap age determination methods, and is particularly suitable for the determination of forest gap age in secondary forests with diverse species composition.

[0029] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the claims of the present invention.

Claims

1. A method for measuring forest gap age, characterized in that: The following steps are involved: Step 1: Sample tree selection: select a suitable tree at the edge of the forest gap in the target forest gap as the sample tree; Step 2: Collect and process tree cores. From the center of the forest window to the sample tree, at 1.3m away from the sample tree, use a tree core sampler to press it on the tree trunk at a 90-degree angle, drill a tree core sample, place it in a sampling tube and bring it back to the room. Step 3: After the obtained tree core sample is placed in a cool place to dry naturally, it is polished with sandpaper from coarse to fine in sequence until it is smooth and flat; Step 4: Use a tree-ring analyzer to measure the annual ring width of the tree core, and use the relative growth method to calculate the percentage growth change (PGC) of the tree ring sequence: PGC = (M2 - M1) / M1 × 100%, where M1 and M2 are the average widths of the first five years and the last five years, respectively. The time period when PGC is greater than 10% and lasts for more than five years is used as the time range for forest gap formation determined by the growth release method.

2. A method for measuring forest gap age according to claim 1, characterized in that: The method also includes step 5, determining the time of forest gap formation by stable carbon isotope analysis: taking annual ring tree cores within a determined time range, dividing, crushing, and mixing them according to one group per year, taking 5 mg from each group, and using a mass spectrometer to measure the stable carbon isotope ratio (δ 13 C), calculate the carbon isotope resolution (∆ 13 C) value, ∆ 13 C = δ 13 C a - δ 13 C tree - ring / δ 13 C tree - ring +1, where the atmospheric stable carbon isotope ratio (δ 13 C a ) is the internationally accepted value of -9.37‰, and the time range of forest gap formation is ∆ 13 The year when the lowest value of C occurs is the year when the forest gap is formed.

3. The method for measuring forest gap age according to claim 2, characterized in that: The length of the tree core is 10 mm to 30 mm, and the length of the tree core drilled by the tree core sampler should exceed the center of the tree by 2 to 4 centimeters.

4. The method for measuring forest gap age according to claim 1, characterized in that: The order of using sandpaper from coarse to fine is visually 150 mesh, 300 mesh, 600 mesh, and 800 mesh.

5. The method for measuring forest gap age according to claim 1, characterized in that: The radiation direction from the center of the forest gap to the sample tree is between 45 degrees and 315 degrees.

6. The method for measuring forest gap age according to claim 1, characterized in that: After the tree core sample is naturally air-dried in step 2, before polishing, the tree core sample is soaked in a chemical decontamination solution for 24 hours, wherein the chemical decontamination solution is composed of 5% sodium hydroxide solution and 3% hydrogen peroxide solution, and is mixed in a ratio of 1:

1. After soaking, the tree core sample is rinsed with clean water for 3 times, and then the tree core sample is placed in an environment with a temperature of 40°C and a relative humidity of 30% for stabilization treatment for 48 hours.

7. The method for measuring forest gap age according to claim 1, characterized in that: Before determining the time range of forest gap formation by the four-year growth-release method in the steps, the physiological indicators of the sample trees are measured, and leaves at the top, middle and bottom of the crown of the sample trees are selected to measure physiological indicators such as leaf chlorophyll content, photosynthesis rate and stomatal conductance. At each measurement time point, the leaves in each part are repeatedly measured multiple times and the average value is taken.

8. The method for measuring forest gap age according to claim 1, characterized in that: After determining the formation time of the forest gap, long-term environmental data of the target forest gap area are collected, including data on light intensity, temperature, precipitation, soil nutrients, etc., and the changing trends of these environmental data before and after the formation of the forest gap are analyzed. They are then compared with the changes in the annual ring width and stable carbon isotope ratio of the tree core samples, and a comprehensive analysis model is established. Based on the model, the formation time of the forest gap and its impact on tree growth are analyzed.

9. The method for measuring forest gap age according to claim 1, characterized in that: The suitable forest gap edge trees should be light-loving species with straight trunks, small taper, well-developed crowns, vigorous growth, and no diseases or insect pests.

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