A method for determining a reasonable stand density based on the relationship between forest and water

Abstract

The present invention relates to a method for determining a reasonable stand density based on the forest-water relationship. Under the condition of having precipitation resource supply, according to the environmental capacity of precipitation resources, the stand density is automatically determined by a computer program. The determination process includes: (i) determining technical parameters, (ii) establishing a reasonable stand density model of the forest-water relationship, and (iii) determining the reasonable stand density. The technical parameters include: (1) the environmental capacity of precipitation resources V, (2) the water consumption v1 for understory evapotranspiration, and (3) the water consumption v2 per single tree of different tree species with different breast diameters. Starting from the water resource, which is the most important limiting factor for northern forest vegetation, the present invention comprehensively considers the environmental capacity of regional precipitation resources and the dynamic changes of transpiration water consumption, effectively solving the problem of reasonable management density for different tree species throughout their life cycles under the environmental capacity of regional precipitation resources, and playing an important role in improving forest quality and the stability of forest ecosystems.

Description

Technical Field

[0001] The present invention belongs to the technical field of forest management and production, and relates to a method for determining a reasonable stand density based on the relationship between forest and water. Background Art

[0002] Stand density is the basis for the formation of a reasonable spatial structure of a forest and also a decisive factor for the size of the growth and development space of individual trees. Determining the reasonable density at different growth stages of a stand is one of the core issues in forestry. Whether the stand density is reasonable directly affects the health, quality, stability, production structure and productivity of the stand. Correctly applying the theory and technology of reasonable density, by regulating the forest production structure, giving full play to the potential of the forest to make full use of existing environmental resources, to improve productivity and resistance to external interference, and to increase the stability of the forest ecosystem. The forest management density has always been a problem that troubles us. Exactly what kind of management density is reasonable should be different for different climates, different tree species and different diameters at breast height. Some existing methods for determining density, such as determining density according to different configuration forms and determining density according to management purposes, usually have a certain degree of empiricism and arbitrariness, and less consideration is given to the main factors restricting stand density. The relatively more scientific determination method is the comparison test method of different management densities, but this method has a long test period and is greatly affected by site conditions, and does not have universal applicability.

[0003] For the stands planted in the 1960s and 1970s of the last century, due to the excessive planting density and the lack of reasonable density management for a long time, there has been an obvious degradation trend at present. The main reason is that as the trees grow, the water consumption increases continuously, and the water resources that can be satisfied by young forests can no longer meet the growth needs of the trees after they become mature forests. Water is generally scarce in the northern region, and the available water resources will inevitably become a limiting factor for determining the reasonable stand density. Therefore, the basis for determining the stand density is the environmental capacity of precipitation resources. The so-called environmental capacity of precipitation resources refers to the tree species and their quantities that a certain amount of precipitation resources can accommodate in areas without irrigation conditions and without groundwater replenishing soil moisture, on the premise of maintaining regional ecological balance and water balance. This quantity is reflected in the stand structure as the stand density of a certain tree species at different development stages or the maximum number of trees that can be accommodated per unit area of forest land.

[0004] The determination of reasonable stand density must follow the basic principle of "determining forests based on water", which is reflected in the stand structure as determining the appropriate stand density on the premise of water balance, rationalizing the bearing capacity of precipitation resources, and thus forming a stable and sustainable stand structure. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for determining a reasonable stand density based on the forest-water relationship, which fully considers the environmental capacity of precipitation resources and the water consumption dynamics of trees with different diameter classes, improves the existing method for determining forest management density, and enhances the scientificity and applicability of forest management density determination.

[0006] The technical solution of the present invention is: a method for determining a reasonable stand density based on the forest-water relationship. Under the condition of having precipitation resource supply, according to the environmental capacity of precipitation resources, the stand density is automatically determined by a computer program. The determination process includes: (i) determining technical parameters, (ii) establishing a reasonable stand density model based on the forest-water relationship, and (iii) determining the reasonable stand density. The technical parameters include: (1) the environmental capacity of precipitation resources V, (2) the water consumption v1 of understory evapotranspiration, and (3) the water consumption v2 per single tree of tree species with different breast diameters. The reasonable stand density model based on the forest-water relationship is:

[0007]

[0008] In the formula: H is the stand density, trees / hm 2 ; a 土 is the proportion of atmospheric precipitation stored in the soil, %; V 降 is the average annual rainfall, mm; T is the number of months in the growing season; W is the understory evapotranspiration rate, kg·m -2 ·d -1 ; t is the daytime transpiration duration, h; s is the sapwood area, cm 2 , or the xylem perimeter, cm; F is the average value of the stem sap flow rate during the growing season, kg·h -1 ·cm -2 or kg·h -1 ·cm -1 .

[0009] The environmental capacity of precipitation resources V represents the amount of rainfall stored in the soil and is calculated by the following formula:

[0010] V = a 土 ×V 降 ×10 4 (2)

[0011] In the formula: V is the environmental capacity of precipitation resources, kg / hm 2 ; a 土 is the proportion of atmospheric precipitation stored in the soil, %; V 降 is the average annual rainfall, mm;

[0012] Among them, V 降 is obtained by consulting local meteorological data, and a 土 needs to be obtained through monitoring the water redistribution process of forest vegetation and atmospheric precipitation;

[0013] a 土 = V土 / V 总 (3)

[0014] V 土 =V 穿 +V 树 -V 坡 -V 壤 (4)

[0015] V 土 is the soil storage of atmospheric precipitation, kg / hm 2 ; V 总 is the atmospheric precipitation, kg / hm 2 ; V 穿 is the throughfall of atmospheric precipitation, kg / hm 2 ; V 树 is the stem flow, kg / hm 2 ; V 坡 is the surface runoff, kg / hm 2 ; V 壤 is the subsurface flow, kg / hm 2 .

[0016] To ensure the accuracy of the measurement of a 土 it is necessary to monitor at least 10 component values of atmospheric precipitation with different intensities, and take the arithmetic mean of a 土 .

[0017] The water consumption v1 of understory evapotranspiration represents the evapotranspiration of understory shrubs, herbs and soil in a forest stand, and is calculated by the following formula:

[0018] v1 = 30 × T × W × 10 4 (5)

[0019] In the formula: v1 is the water consumption of understory evapotranspiration in a growing season, kg / hm 2 ; T is the number of months in a growing season, and W is the average rate of understory evapotranspiration in a growing season, kg·m -2 ·d -1 ;

[0020] T is determined by monitoring the months with stem sap flow through the stem sap flow monitoring system; W is monitored using a small lysimeter and calculated by the following formula:

[0021]

[0022]

[0023] In the formula: W i is the evapotranspiration rate of a single evapotranspiration process, kg·m -2 ·d -1; i represents each evapotranspiration process in a growing season. Z1 is the weight of the soil column in the lysimeter at the start of an evapotranspiration process, in kg; Z2 is the weight of the soil column in the lysimeter at the end of an evapotranspiration process, in kg; M is the area of the lysimeter, in m 2 ; D is the number of days in an evapotranspiration process, in d.

[0024] The water consumption per single tree v2 with different tree diameters at breast height characterizes the transpiration water consumption per single tree of a certain tree species with a certain diameter at breast height in the whole growing season, and is calculated by the following formula:

[0025] v2 = 30×T×t×s×F (8)

[0026] In the formula: v2 is the water consumption per single tree of a certain tree species with a certain diameter at breast height in a growing season, in kg / tree; T is the number of months in a growing season, t is the daytime transpiration duration, in h; s is the sapwood area, in cm 2 , or the xylem perimeter, in cm; F is the average value of the trunk sap flow rate in the growing season, in kg·h -1 ·cm -2 or kg·h -1 ·cm -1 ; when s is the sapwood area (cm 2 ), the corresponding unit of the trunk sap flow rate is kg·h -1 ·cm -2 , when s is the xylem perimeter (cm), the corresponding unit of the trunk sap flow rate is kg·h -1 ·cm -1 .

[0027] T is determined by monitoring the months with trunk sap flow through the trunk sap flow monitoring system. t is determined by monitoring the start and end times of sap flow through the trunk sap flow monitoring system, and then taking the average value in the growing season. F is measured by the trunk sap flow monitoring system, and the average value of the daytime trunk sap flow rate in the growing season is taken. s is calculated by the diameter at breast height to obtain the sapwood area or xylem perimeter, and a large-sample model (n≥50) of the diameter at breast height and the sapwood area or xylem perimeter of the tree species to be measured is established, and then the diameter at breast height is substituted to obtain it. The application of a reasonable stand density model based on the forest-water relationship will make the water consumption of the stand less than or equal to the environmental capacity of precipitation resources.

[0028] Select plants with different diameters at breast height, and the diameter distribution should be as uniform as possible, including both large and small diameters at breast height. Measure the diameter at breast height with a girth tape, measure the sapwood thickness or xylem diameter with an increment borer, and calculate the sapwood area or xylem perimeter; establish the correlation between the diameter at breast height and the sapwood area or xylem perimeter, and the coefficient of determination R 2 should reach a highly significant correlation, and if R 2 is greater than 0.80, the calculation result will be more accurate.

[0029] The traditional density test method can only conduct tests for the same DBH (diameter at breast height). If the DBH changes, the test needs to be carried out again for that DBH. The present invention solves the problem of the management density of different DBHs of a certain tree species. The traditional density test method is equivalent to a trial-and-error method, with a relatively long test period, and the test results are greatly affected by the site conditions, lacking general applicability. The present invention applies basic research to production practice, aiming to solve problems from the root cause, and has greater promotion value.

[0030] The method for determining a reasonable stand density based on the forest-water relationship in the present invention starts from the water resource, which is the most important limiting factor for northern forest vegetation. It comprehensively considers the environmental capacity of regional precipitation resources and the dynamic changes of transpiration water consumption of different tree species and different DBHs, effectively solving the problem of the reasonable management density of different tree species throughout their life cycles under the environmental capacity of regional precipitation resources. It is more scientific, reasonable, time-saving, and labor-saving compared with the existing technical experience method and different density test methods. The present invention incorporates the understory evapotranspiration component, considering the water demand of understory shrubs and herbs while considering the management density of arbors. Reserving the water demand of understory shrubs and herbs can effectively solve the problem of understory vegetation degradation caused by excessive density in existing forest stands. The present invention can provide a method for determining the reasonable management density of different forest stands in different regions throughout their life cycles, which plays an important role in improving forest quality and the stability of forest ecosystems. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the water redistribution component and ratio of the Chinese pine forest;

[0032] Figure 2 It is the understory evapotranspiration process of the Chinese pine forest;

[0033] Figure 3 It is the daily variation (I) of the sap flow rate of Chinese pine trunks in different months;

[0034] Figure 4 It is the daily variation (II) of the sap flow rate of Chinese pine trunks in different months;

[0035] Figure 5 It is the monthly variation of the sap flow rate of Chinese pine trunks;

[0036] Figure 6 It is the model related to the circumference of the xylem of Chinese pine and the DBH. DETAILED DESCRIPTION OF THE INVENTION

[0037] The present invention will be described in detail below in conjunction with the embodiments and the drawings. The protection scope of the present invention is not limited to the embodiments, and any modifications made by those skilled in the art within the scope defined by the claims also fall within the protection scope of the present invention.

[0038] The present invention selects to be applied in Xiaowutai Mountain National Nature Reserve in Hebei Province, and the stand type is Chinese pine plantation. The test plot is selected on a relatively uniform typical slope, with a plot size of 40×50 m, an altitude of 1336 m, a slope direction of west by north, a slope gradient of 14°, and a slope position in the middle. The stand density is 915 trees / hm 2 , the stand age is 40 years, the canopy density is 78%, and the ground cover is 76%. The average DBH of Chinese pine is 17.15±5.58 cm, the average tree height is 9.26±2.42 m, and the average crown width is 4.52 m×4.12 m.

[0039] The method for determining the reasonable stand density based on the forest-water relationship of the present invention, according to the principle of water balance of water supply and consumption of forest trees, under the condition of precipitation resource supply, according to the environmental capacity of precipitation resources, uses a computer program to automatically determine the stand density. The determination process includes: (i) determining technical parameters, (ii) establishing a reasonable stand density model of the forest-water relationship, and (iii) determining the reasonable stand density; the technical parameters include: (1) the environmental capacity of precipitation resources V, (2) the water consumption of understory evapotranspiration v1, and (3) the water consumption per single tree of tree species with different DBHs v2. The formula for calculating the stand density based on the environmental capacity of precipitation resources is:

[0040]

[0041] H is the stand density, trees / hm 2 ; V is the environmental capacity of precipitation resources, kg / hm 2 ; v1 is the water consumption of understory evapotranspiration, kg / hm 2 , and v2 is the water consumption per single tree of tree species with different DBHs, kg / tree.

[0042] (i) Determining technical parameters

[0043] (1) The environmental capacity of precipitation resources V

[0044] V = a 土 ×V 降 ×10 4 (2)

[0045] Determining parameter a 土 、V 降

[0046] Through the monitoring of water redistribution in the Chinese pine forest from 2017 to 2019, a total of 23 different intensity rains were counted; since no interflow was monitored, the soil infiltration amount is the soil storage water amount, and it can be seen from Figure 1 that the soil infiltration amount accounts for 71.84% of the total precipitation amount, and parameter a 土 = 71.84%.

[0047] By measuring the annual precipitation in the Xiaowutai area, the average annual precipitation is 500 mm, and the annual and altitude differentiation characteristics are obvious. The precipitation span at different altitudes and in different years is 450 - 600 mm. Therefore, parameter V 降 is determined to be 450 - 600 mm, with each 50 mm as a gradient.

[0048] ⑵ Water consumption v1 for understory evapotranspiration

[0049] v1 = 30 × T × W × 10 4 (5)

[0050] In the formula: v1 is the water consumption for understory evapotranspiration in one growing season, kg / hm 2 ; T is the number of months in one growing season, and W is the average rate of understory evapotranspiration in one growing season, kg·m -2 ·d -1 .

[0051] ⑶ Water consumption v2 per single tree of arbor species with different DBHs

[0052] v2 = 30 × T × t × s × F (8)

[0053] In the formula: v2 is the water consumption per single tree of a certain tree species at a certain DBH in one growing season, kg / tree; T is the number of months in one growing season, t is the daytime transpiration duration, h; s is the sapwood area, cm 2 , or the xylem perimeter, cm; F is the average value of the trunk sap flow rate in the growing season, kg·h -1 ·cm -2 or kg·h -1 ·cm -1 ; when s is the sapwood area (cm 2 ), the corresponding unit of the trunk sap flow rate is kg·h -1 ·cm -2 , and when s is the xylem perimeter (cm), the corresponding unit of the trunk sap flow rate is kg·h -1 ·cm -1 .

[0054] ① Determine parameter W

[0055] By deploying small lysimeters in the Chinese pine forest plot to monitor the understory evapotranspiration process, see Figure 2 . The weight of the soil in the lysimeter bucket shows a process of rising linearly for some days and then declining along a certain slope, repeating cyclically. The linear rise is due to precipitation, and the water content in the bucket increases; the decline along the slope is due to the evaporation of the soil in the bucket and the transpiration of the vegetation in the bucket, which reduces the water content in the bucket. By statistically averaging the slopes of each descending line segment, the average understory evapotranspiration intensity of the Chinese pine forest in the entire growing season is calculated to be 1.46 kg·m -2 ·d-1 , the parameter W = 1.46 kg·m -2 ·d -1 .

[0056] ② Determine the parameters T, t, and F

[0057] Through the analysis of annual continuous observation data, it is obtained that the sap flow of Chinese pine trunks starts around April 20th and ends around October 21st, lasting for 184 days in total. As shown by Figure 3 and Figure 4 , in most months, the sap flow of Chinese pine trunks starts at 8:00 and ends at 20:00, with a daytime transpiration duration of 12 hours. As shown by Figure 4 in the monthly variation of the sap flow rate of Chinese pine trunks, the average value of the sap flow rate of Chinese pine trunks during the growth season is 0.013 kg·h -1 ·cm -1 . Therefore, the parameter T = 6 months, t = 12 h, and F = 0.013 kg·h -1 ·cm -1 .

[0058] ③ Determine the parameter s

[0059] As shown by Figure 5 , by establishing a correlation model between the diameter at breast height (DBH) and the xylem circumference of Chinese pine, the xylem circumference s can be calculated from the DBH. The correlation model is y = 2.6499x + 0.3487, with the coefficient of determination R 2 = 0.9792, reaching a highly significant correlation; n = 52 meets the requirements of a large-sample model; the diameter class span is 5 - 35 cm, meeting the requirements of the diameter class distribution. According to the diameter class distribution of Chinese pine included in the large-sample model, the xylem circumference s is calculated for each 1-cm gradient of the DBH of Chinese pine in the range of 5 - 35 cm.

[0060] ㈡ Establish a reasonable stand density model based on the forest-water relationship

[0061] The reasonable stand density model based on the forest-water relationship is as follows:

[0062]

[0063] In the formula: H is the stand density, trees / hm 2 ; a 土 is the proportion of atmospheric precipitation stored in the soil, %; V 降 is the average annual rainfall, mm; T is the number of months in the growth season; W is the understory evapotranspiration rate, kg·m -2 ·d -1 ; t is the daytime transpiration duration, h; s is the sapwood area, cm 2 , or the xylem circumference, cm; F is the average value of the sap flow rate of the tree trunk during the growth season, kg·h -1 ·cm -2or kg·h -1 ·cm -1 。

[0064] (III) Determine the reasonable stand density based on the forest-water relationship

[0065] Substitute the parameters in (I) into the reasonable stand density model based on the forest-water relationship in (II) for calculation. Among them, parameter a 土 = 71.84%; V 降 is calculated at gradients of 450 - 600 mm, with a 50 mm interval; W = 1.46 kg·m -2 ·d -1 , T = 6 months, t = 12 h, F = 0.013 kg·h -1 ·cm -1 ; s is obtained by substituting the diameter at breast height into the relevant model of xylem perimeter and diameter at breast height. The diameter at breast height is calculated at gradients of 5 - 35 cm, with a 1 cm interval. The calculation results are shown in Table 1.

[0066] As can be seen from Table 1, forest density control follows two basic laws. One is that with the increase in rainfall, the stand density shows a significant increasing trend; the other is that with the increase in diameter at breast height, the stand density shows a significant decreasing trend. This is mainly determined by the water resource carrying capacity and the water consumption law of forest trees. As rainfall increases, the water resource carrying capacity increases accordingly, and the number of forest vegetation and forest trees that can be carried naturally increases. As the diameter at breast height of forest trees increases, their water consumption per individual increases, and the number of forest trees that can be carried naturally decreases under the condition of a certain water resource carrying capacity.

[0067] The average annual rainfall in Xiaowutai area is approximately 500 mm, and in some places it can reach 600 mm. At a rainfall of 500 mm, when the diameter at breast height of Chinese pine is 10 cm, the density can reach 1,279 trees / hm 2 , when the diameter at breast height is 15 cm, the density is 856 trees / hm 2 , and when the diameter at breast height is 20 cm, the density is 644 trees / hm 2 , and when the diameter at breast height is 30 cm, only 430 trees can be retained per hectare. It can be seen that the stand density decreases rapidly with the increase in diameter at breast height. Therefore, when the diameter at breast height increases to a certain extent, selective thinning can be appropriately carried out to control the stand density and make it reach the appropriate density standard.

[0068] Table 1 Operating density table of Chinese pine forest at different rainfall levels for each diameter class

[0069]

[0070]

Claims

1. A method for determining a reasonable stand density based on the relationship between forest and water, characterized in that: in Under the condition of precipitation resource supply, according to the environmental capacity of precipitation resources, the stand density is automatically determined by a computer program. The determination process includes: (i) determining technical parameters, (ii) establishing a reasonable stand density model for the forest-water relationship; (iii) determining the reasonable stand density; the technical parameters include: (1) the environmental capacity of precipitation resources V , (2) the water consumption of understory evapotranspiration v 1 and (3) the water consumption per single tree of arbor species with different breast diameters v 2; The environmental capacity of precipitation resources V Characterizing the soil storage of rainfall, calculated by the following formula: In the formula: V is the environmental capacity of precipitation resources, kg / hm 2 ; a 土 is the proportion of soil storage of atmospheric precipitation, %; V 降 is the average annual rainfall, mm; Among them V 降 Obtained by consulting local meteorological data a 土 It is necessary to obtain through the monitoring of the water volume redistribution process of forest vegetation and atmospheric precipitation V 土 is the soil storage of atmospheric precipitation, kg / hm 2 ; V 总 is the atmospheric precipitation, kg / hm 2 ; V 穿 is the throughfall of atmospheric precipitation, kg / hm 2 ; V 树 is the stemflow, kg / hm 2 ; V 坡 is the surface runoff, kg / hm 2 ; V 壤 is the subsurface runoff, kg / hm 2 ; The water consumption by understory evapotranspiration v 1 represents the evapotranspiration of shrubs, herbs and soil in the understory of a forest stand, which is calculated by the following formula: In the formula: v 1 is the water consumption for understory evapotranspiration in a growing season, kg / hm 2 ; T is the number of months in a growing season, W is the average rate of understory evapotranspiration in a growing season, kg·m -2 ·d -1 ; W Monitoring is carried out using a small lysimeter and calculated by the following formula: In the formula: W i is the evapotranspiration rate of a single evapotranspiration process, kg·m -2 ·d -1 ; i is each evapotranspiration process in a growing season ，Z 1 is the weight of the soil column in the lysimeter at the start of a single evapotranspiration process, kg; Z 2 is the weight of the soil column in the lysimeter at the end of a single evapotranspiration process, kg; M is the area of the lysimeter, m 2 ; D is the number of days the single evapotranspiration process lasts, d; The water consumption per individual tree of different tree species with different DBHs v 2, which represents the transpiration water consumption per individual tree of a certain tree species with a certain DBH during the entire growing season, is calculated by the following formula: In the formula: v 2 is the water consumption per tree per growing season at a certain DBH, kg / tree; T is the number of months in a growing season, t is the daytime transpiration duration, h; s is the sapwood area, cm 2 , or the xylem perimeter, cm; F is the average trunk sap flow rate during the growing season, kg·h -1 ·cm -2 or kg·h -1 ·cm -1 ; when s is the trunk sap flow rate corresponding to the sapwood area, with the unit of kg·h -1 ·cm -2 , when s is the trunk sap flow rate corresponding to the xylem perimeter, with the unit of kg·h -1 ·cm -1 ; The reasonable stand density model of the forest-water relationship is as follows: In the formula: H is the stand density, plants / hm 2 .

2. The method for determining a reasonable stand density based on the forest-water relationship according to claim 1, characterized in that: The T is determined by monitoring the months with trunk sap flow through a trunk sap flow monitoring system; the t is determined by monitoring the start and end times of sap flow through a trunk sap flow monitoring system and then taking the average value during the growing season; the F is measured by a trunk sap flow monitoring system and takes the average value of the daytime trunk sap flow rate during the growing season.

3. The method for determining a reasonable stand density based on the forest-water relationship according to claim 1, characterized in that: The s is calculated by the diameter at breast height to obtain the sapwood area or the xylem perimeter, a large-sample model of the diameter at breast height and the sapwood area or the xylem perimeter of the tree species to be measured is established, and the diameter at breast height is substituted to obtain it.

4. The method for determining a reasonable stand density based on the forest-water relationship according to claim 1, characterized in that: The application of the reasonable stand density model based on the forest-water relationship will make the water consumption of the stand less than or equal to the environmental capacity of precipitation resources.

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