Method for determining shading range and degree of farmland protection forest

Abstract

The invention relates to a quantitative evaluation method for the shading range and degree of a farmland protection forest in the technical field of forestry. In the region where the target forest belt is located, the length and orientation of the forest belt shadow in each time period of the key date are determined according to the solar altitude angle and the azimuth angle in combination with parameters such as the average height and the trend of the forest belt, and the forest belt shading range is divided into light, medium and heavy land-side degrees according to the proportion of the shading duration to the sunshine duration. The method for objectively, quantitatively and easily determining the shading range and degree of the farmland protection forest is provided for the first time, a scientific standard is provided for objectively evaluating the shading and hypochondrium range of the farmland protection forest, and a reference basis is provided for determining the buffer distance between the forest belt and the farmland interface in high-standard farmland construction.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of forestry, in particular to a quantitative method for determining the range and degree of shelter of farmland shelterbelt. BACKGROUND

[0002] In recent years, with the promotion of high-standard farmland construction and ecological restoration projects, the layout and structure of farmland shelterbelt are still being optimized. However, in the construction and management practice of farmland shelterbelt, there is a phenomenon of land encroachment near the two sides of the shelterbelt, which leads to crop yield reduction and causes conflicts between farmers and forest owners. The two main causes of land encroachment are shelterbelt shading and competition for water and fertilizer between root systems and crops. Land encroachment by root systems can be alleviated by ditching and film mulching, while there is still no effective solution to shading land encroachment. At present, most of the researches on farmland shelterbelt shading land encroachment are qualitative evaluation, and there is no quantitative evaluation method for the range of shelterbelt shading land encroachment.

[0003] The range of shelterbelt shading changes dynamically with time (season and time period), which is a difficulty in quantitative evaluation. Some studies have analyzed the daily variation of the range of shelterbelt shading by measuring solar radiation intensity for one day or adjacent days. Since the range of shading has strong seasonal variation, the observation results of a few days lack representativeness. At present, there are few reports on the seasonal variation of the range of shelterbelt shading. In practice, based on the yield measurement results of crops, the closer to the shelterbelt within the range of shelterbelt shading, the more the yield reduction. Although the yield reduction results can reflect the degree of shading land encroachment of the shelterbelt, yield measurement is time-consuming and laborious, and it is not easy to compare between different crop species, and the range of shading land encroachment of shelterbelt varies at different locations and directions. Therefore, it is not conducive to wide application. In fact, the length of the shadow of the shelterbelt mainly depends on the solar elevation angle and the height of the shelterbelt, and the direction of the shadow is exactly opposite to the solar azimuth angle. The changes of these solar parameters have obvious regularity, and it is a feasible way to calculate and simulate the variation of the shadow of the shelterbelt. Previous studies have successfully calculated and simulated the seasonal variation of the projection of individual trees. Therefore, compared with yield measurement, calculation and simulation are not only simple and easy to operate, but also can be widely applied in combination with the latitude and direction of the shelterbelt. SUMMARY

[0004] The purpose of the present application is to provide a method for determining the range and degree of shelter of farmland shelterbelt, which is objective, quantitative and easy to operate, to provide a unified and comparable standard for scientific evaluation of the shading land encroachment of farmland shelterbelt. At the same time, the present application can also display the range and degree of shelter of farmland shelterbelt in different forms such as charts or tables.

[0005] The technical scheme adopted by the present application to achieve the above-mentioned purpose is:

[0006] A method for determining the range and degree of shelter of farmland shelterbelt, comprising the following steps:

[0007] 1) Obtain the geographical data related to the area where the farmland shelterbelt is located, and preprocess it;

[0008] 2) Based on the preprocessed data, calculate the solar elevation angle, solar azimuth angle and solar direct radiation duration, respectively;

[0009] 3) Calculate the length of the forest belt shadow based on the solar elevation angle, construct the daily dynamic dataset of the length of the forest belt shadow, and further construct the daily dynamic dataset of the length of the shadow on both sides;

[0010] 4) Based on the solar direct radiation duration and the two datasets, determine the forest belt shading range corresponding to different shading durations;

[0011] 5) Visualize the obtained forest belt shading range in the form of a chart.

[0012] The step 1) comprises the following steps:

[0013] 1.1) Obtain the latitude, longitude, forest belt strike, forest belt average height and solar direct radiation data of the area where the farmland shelterbelt is located;

[0014] 1.2) Filter the obtained key date solar direct radiation data, and remove the solar radiation values at times when it is cloudy or cloudy.

[0015] The step 2) comprises the following steps:

[0016] 2.1) According to the geographical latitude of the study area, calculate the solar elevation angle corresponding to different times in the three days of the spring equinox, summer solstice and autumn equinox, respectively:

[0017]

[0018] Wherein, α is the solar elevation angle, is the geographical latitude of the study area, δ is the solar declination angle, and ω is the hour angle;

[0019] 2.2) Calculate the solar azimuth angle θ through the solar elevation angle:

[0020]

[0021] 2.3) The period when the ground surface solar direct radiation intensity is greater than the threshold value on a sunny day without clouds is regarded as the solar direct radiation period, and the total duration T is the sunshine duration.

[0022] The step 3) comprises the following steps:

[0023] 3.1) Calculate the length of the forest belt shadow L:

[0024] L=H×cotα

[0025] Among them, H is the average height of the forest belt, H = average[H1, H2, H3…, H , , , ,

[0038] , , , ,

[0036] ,

[0035] ,

[0034] ,

[0033] , Figure 1 , , ,

[0032] ,

[0037] ,…, H N , average is to take the average value, H i is the height of the i-th standard tree, and N is the number of selected standard trees;

[0026] 3.2) Calculate the shadow length of the forest belt once every set time interval, and use all the calculation results within one day to construct a daily dynamic data set of the forest belt shadow length [L1, L2, L3…, L j ;

[0027] 3.3) Calculate the shadow lengths on both sides perpendicular to the direction of the forest belt:

[0028] L ⊥ = L×sinβ

[0029] Among them, β is the included angle between the direction of the forest belt and the solar azimuth angle;

[0030] 3.4) Calculate the shadow lengths on both sides perpendicular to the direction of the forest belt once every set time interval, and use all the calculation results within one day to construct a daily dynamic data set of the shadow lengths on both sides [L ⊥1 , L ⊥2 , L ⊥3 …, L ⊥j .

[0031] The said step 4) includes the following steps:

[0032] 4.1) Divide the sunshine duration T in a day into 3 segments evenly, and the continuous shading durations t within each segment are respectively

[0033] 4.2) Obtain the upper and lower limits of the shadow length of the forest belt and the shadow lengths on both sides perpendicular to the direction of the forest belt within each shading duration segment, and use them as the boundary values of different degrees of shading ranges;

[0034] 4.3) According to the boundary values, divide the shadow areas on both sides perpendicular to the farmland shelter forest into mild, moderate and severe shading ranges.

[0035] The present invention has the following beneficial effects and advantages:

[0036] 1. The present invention objectively and quantitatively gives a method for determining the shading range and degree of the farmland shelter forest for the first time.

[0037] 2. The present invention provides a unified, comparable and easy-to-implement standard for the evaluation of the shading and land damage of the farmland shelter forest. BRIEF DESCRIPTION OF THE DRAWINGS<00001​​​​

[0039] Figure 2 It is a schematic diagram of the sunshine period (T) at key node dates in the northern region of China (north of the Tropic of Cancer);

[0040] Figure 3 Schematic diagram of the shadow range of the forest belt corresponding to different shading durations (degrees);

[0041] Figure 4 It is the specific flowchart of the processing program in an embodiment of the present invention. Specific implementation manners

[0042] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0043] In view of the fact that there is a lack of a quantitative evaluation method for the shading and land damage range of farmland shelter forests in the present invention. First, the key node dates (the Spring Equinox, the Summer Solstice, the Autumn Equinox, and the Winter Solstice) of the sun's movement trajectory are cleverly selected to reflect the entire growth season of crops. Since it is too time-consuming and laborious to observe and count the shadow length of the forest belt at each moment every day and weather changes (such as cloudy days) lead to data loss, etc., selecting key node dates for reasonable simplification is the primary link for quantitatively evaluating the shading range of the forest belt. The Spring Equinox, the Summer Solstice, the Autumn Equinox, and the Winter Solstice are the key node dates of the periodic change of the solar altitude angle in a year. At the same time, considering that shading mainly affects crops during the growth season, therefore, the present invention uses the Spring Equinox, the Summer Solstice, and the Autumn Equinox to represent the growth season of crops. Second, it is innovatively proposed to divide the land damage degree (mild, moderate, and severe) of different regions within the shading range of the forest belt according to the proportion of the shading duration to the sunshine duration. Finally, considering the characteristics such as the latitude where the target forest belt is located and the forest belt orientation, etc., a method for objectively, quantitatively and easily operating to determine the shading range and degree of farmland shelter forests is proposed. This method can provide a reference for objectively evaluating the shading and land damage degree of farmland shelter forests and determining the buffer distance between the farmland shelter forest belt and the farmland interface, etc.

[0044] The shading range of the farmland shelter forest belt determined by the present invention refers to the shadow length interval on both sides of the forest belt perpendicular to the forest belt orientation ( Figure 1 where, H is the average height of the forest belt, α is the solar altitude angle, β is the angle between the solar azimuth and the forest belt orientation, L is the shadow length of the forest belt, L ⊥(The length of the shadow perpendicular to the direction of the forest belt). Selecting the shadow length perpendicular to the direction of the forest belt facilitates a unified comparison of the shading area of ​​forest belts with different orientations. Since the length of the forest belt is much greater than its width, the shadows at both ends of the forest belt are ignored, and only the shadows on both sides are considered. This invention also simplifies the forest belt structure, setting the entire height of the forest belt as opaque. Although theoretically the trunk layer (the part below the branch height) of the forest belt can be partially transparent, in reality, most farmland shelterbelts consist of two or more rows, and the trunk layer is also shaded by the canopy of adjacent rows; therefore, the entire height of the forest belt is considered opaque. Furthermore, the target forest belt and the farmland on both sides are flat and located north of the Tropic of Cancer in my country.

[0045] The length of the shadow cast by a forest belt varies diurnally and seasonally with the Earth's rotation and revolution. Observing and statistically analyzing the shadow length every day and hour is too time-consuming and laborious, and data loss can occur due to variable weather (e.g., cloudy days). Therefore, selecting key dates for reasonable simplification is the primary step in quantitatively evaluating the shading range of a forest belt. The vernal equinox, summer solstice, autumnal equinox, and winter solstice are key dates for the periodic change of the solar altitude angle throughout the year. Considering that shading primarily affects crops during the growing season, this invention uses the vernal equinox, summer solstice, and autumnal equinox to represent the crop growing season. After selecting a key date, the diurnal variation of the length and direction of the forest belt shadow is calculated. Sunrise and sunset times are determined based on the intensity of direct solar radiation rather than the solar altitude angle, because when the solar altitude angle is very small, the direct radiation intensity is weak and does not reach the light compensation point for crop photosynthesis, making the shading effect of the forest belt insignificant. According to the International Meteorological Organization's definition of sunshine duration (defined as daily solar radiation intensity greater than 120 W·m² on a plane perpendicular to its rays),... -2 The definition of the duration of solar radiation (under ideal weather conditions, such as clear skies and transparent atmosphere) is as follows: This invention defines the direct solar radiation intensity as greater than 120 W·m⁻¹. -2 The time between sunrise and sunset is recorded as the exact moment when the sun rises, and the time before sunrise is recorded as sunset. The duration of daylight from sunrise to sunset is called the daylight period. Figure 2 A schematic diagram of the sunshine duration (T) for key dates in northern my country (north of the Tropic of Cancer) (the sun's trajectory on the vernal equinox, summer solstice, autumnal equinox, and winter solstice; under clear, cloudless skies, sunrise occurs when the direct solar radiation intensity is greater than 120 W·m⁻², and sunset occurs when it is less than 120 W·m⁻², with the time period from sunrise to sunset recorded as the sunshine duration).

[0046] like Figure 4 As shown, the specific process for calculating the length of the shadow on both sides of the forest belt perpendicular to its direction is as follows:

[0047] The first step is to calculate the length of the forest belt shadow (L, Equation 3) every half hour during the sunshine period on key dates, based on the average height of the forest belt (H, Equation 1) and the solar altitude angle (α, Equation 2). The latitude, longitude, forest belt orientation, and average height of the farmland shelterbelt area are as follows: the latitude and longitude are determined by GPS, the forest belt orientation is determined by compass, and the key dates are the spring equinox, summer solstice, and autumn equinox.

[0048] H = average[H1,H2,H3…,H…] i ,…,H N (1)

[0049] In the formula, H is the average height of the forest belt. i Let N be the height of the i-th standard tree, and N be the number of standard trees selected.

[0050]

[0051] In the formula, α is the solar altitude angle. δ represents the geographical latitude of the study area, δ represents the solar inclination angle (declination angle), and ω represents the hour angle.

[0052] L=H×cotα(3)

[0053] The second step is to calculate the shadow length (L) on both sides of the forest belt perpendicular to its direction, based on the forest belt orientation, solar azimuth angle (θ, Equation 4), and forest belt shadow length. ⊥ Equation 5).

[0054]

[0055] L ⊥ =L×sinβ(5)

[0056] In the formula, β is the angle between the direction of the forest belt and the solar azimuth.

[0057] The third step is to determine the upper and lower limits of the forest belt shadow length corresponding to different shading durations (t) based on the diurnal variation patterns of sunshine duration (T) and shadow length on both sides of the vertical forest belt.

[0058] Under ideal conditions (e.g., clear, cloudless days) with direct solar radiation greater than 120 W·m², the sunshine duration is sufficient. -2 Sunrise time less than 120 W·m -2 The number of hours between sunset and daylight. This invention artificially divides the shaded areas on both sides of the vertical forest belt into three shading levels based on the proportion of shaded time (t) to the total sunshine duration. The area was divided into lightly shaded zones. This area is currently under moderate shade. Heavy shaded areas ( Figure 3Finally, the average values ​​of the upper and lower limits of the shaded area under different shading levels on each key date are calculated to comprehensively evaluate the degree of shading provided by the forest belt to crops throughout the growing season.

[0059] As can be seen from the above steps, the degree of shading of farmland shelterbelts determined by the present invention is related to the height of the shelterbelt, the direction of the shelterbelt, the latitude, the date, and the duration of sunshine. In other words, it depends on the characteristics of the shelterbelt and the geographical characteristics of the area it is located in.

[0060] Note that this invention is applicable to areas north of the Tropic of Cancer in the Northern Hemisphere, as well as areas with relatively flat farmland shelterbelt sites.

[0061] Example

[0062] (I) Research Location and Data Acquisition

[0063] The shade range of farmland shelterbelts at two different latitudes in my country was calculated, including (1) Gannan County, Qiqihar City, Heilongjiang Province (47.87°N, 123.51°E); and (2) Changtu County, Tieling City, Liaoning Province (42.78°N, 124.09°E). The main tree species of farmland shelterbelts in these two regions are poplar, and the dominant wind is westerly. Therefore, the main shelterbelts are mostly oriented north-south, while the secondary shelterbelts are perpendicular to the main shelterbelts and mostly oriented east-west. The crop growing season is from mid-April to late September, so only the direct solar radiation data of the spring equinox, summer solstice, and autumn equinox in the target area were obtained. Since some key dates are not sunny and cloudless, the average value of the direct solar radiation data monitored over many years was used to determine the sunrise (direct solar radiation intensity greater than 120 W·m). -2 ) and sunset (when the direct solar radiation intensity is less than 120 W·m -2 The data should be analyzed at a time resolution of once every 30 minutes (or 15 minutes, 10 minutes, and 5 minutes). The average height and orientation of the forest belt to be evaluated also need to be obtained.

[0064] (II) Calculation results of the shade range of the forest belt

[0065] The sunrise and sunset times of key dates (spring equinox, summer solstice, autumn equinox) are determined based on the intensity of direct solar radiation, and the average height of the forest belt, solar altitude angle, forest belt shadow length, solar azimuth angle and vertical forest belt shadow length are calculated according to formulas (1) to (5) respectively (Tables 1 and 2).

[0066] H = average[H1,H2,H3…,H…] i ,…,H N (1)

[0067] In the formula, H is the average height of the forest belt. i Let N be the height of the i-th standard tree, and N be the number of standard trees selected.

[0068]

[0069] In the formula, α is the solar altitude angle. δ represents the geographical latitude of the study area, δ represents the solar inclination angle (declination angle, which varies with the date), and ω represents the hour angle (calculated based on true solar time).

[0070] L=H×cotα (3)

[0071] Based on the forest belt orientation (consistent with the definition of solar azimuth, i.e., 0° for true north and increasing clockwise, with the smaller angle of the forest belt orientation used in the calculation), the solar azimuth (θ, Equation 4), and the forest belt shadow length, the shadow length (L) on both sides of the forest belt perpendicular to the forest belt orientation is calculated. ⊥ Equation 5).

[0072]

[0073] L ⊥ =L×sinβ (5)

[0074] In the formula, β is the angle between the direction of the forest belt and the solar azimuth.

[0075] Table 1. Solar parameters (solar altitude angle α, solar azimuth angle θ and its angle β with the direction of the forest belt) and shadow length of farmland shelterbelts (shadow length L and vertical forest belt shadow length L) in Gannan County, Heilongjiang Province ⊥ )

[0076]

[0077]

[0078]

[0079]

[0080] Note: Negative values ​​for the length of the vertical forest belt shade indicate a change in the direction of the shade, and the same applies below.

[0081] Table 2. Solar parameters (solar altitude angle α, solar azimuth angle θ and its angle β with the direction of the forest belt) and shadow length of farmland shelterbelts (shadow length L and vertical forest belt shadow length L) in Changtu County, Liaoning Province. ⊥ )

[0082]

[0083]

[0084]

[0085] Based on the diurnal variation patterns of sunshine duration (T) and the length of shadow on both sides of the vertical forest belt, the upper and lower limits of the forest belt shadow length corresponding to different shading durations (t) were determined (Tables 3 and 4).

[0086] Under ideal conditions (e.g., clear, cloudless days) with direct solar radiation greater than 120 W·m², the sunshine duration is sufficient. -2 Sunrise time less than 120 W·m -2 The number of hours between sunset and daylight. This invention artificially divides the shaded areas on both sides of the vertical forest belt into three shading levels based on the proportion of shaded time (t) to the total sunshine duration. The area was divided into lightly shaded zones. This area is currently under moderate shade. Heavy shading areas. Finally, the average upper and lower limits of the shaded areas with different shading levels on each key date were calculated to comprehensively evaluate the shading effect of the forest belt on crops throughout the growing season. The calculation results in Tables 3 and 4 show that the higher the latitude, the larger the shading range. In Gannan and Changtu, the heavily shaded areas of the east-west oriented forest belts are within 0.79 and 0.56 times the forest belt height from the edge, respectively. Assuming a forest belt height of 15m, the heavy shading distances correspond to 11.9m and 8.4m, respectively. Because real-world farmland shelterbelts vary greatly in tree species, age, and other factors, their heights also differ. For ease of comparison, this invention uses multiples of forest belt height as the basic unit. Note that the shading directions on both sides of a vertical forest belt are different; that is, the positive and negative signs of the data indicate opposite shading directions. Furthermore, north-south oriented forest belts have no heavily shaded areas, as the shading duration on one side of the forest belt does not exceed half of the sunshine duration.

[0087] Table 3. Shading Range and Degree of Farmland Shelterbelts in Gannan County, Heilongjiang Province (Unit: Multiples of Average Shelterbelt Height H)

[0088]

[0089]

[0090] Note: Negative values ​​for the length of the vertical forest belt shadow indicate a change in shadow direction. For east-west oriented forest belts, shadow direction 1 (positive value) indicates due north and shadow direction 2 (negative value) indicates due south. For north-south oriented forest belts, shadow direction 1 (positive value) indicates due west and shadow direction 2 (negative value) indicates due east. "-" indicates non-existent. The same applies below.

[0091] Table 4. Shading Range and Degree of Farmland Shelterbelts in Changtu County, Liaoning Province (Unit: Multiples of Average Forest Belt Height H)

[0092]

Claims

1. A method for determining the shading range and degree of farmland shelterbelts, characterized in that, Includes the following steps: 1) Obtain relevant geographic data of the area where the farmland shelterbelt to be studied is located, and preprocess it; 2) Based on the preprocessed data, calculate the solar altitude angle, solar azimuth angle, and duration of direct solar radiation; 3) Calculate the length of the forest belt shadow based on the solar altitude angle, construct a daily dynamic dataset of the forest belt shadow length, and then construct a daily dynamic dataset of the shadow length on both sides; 4) Based on the duration of direct solar radiation and two datasets, determine the shade range of the forest belt corresponding to different shade durations; 5) Visualize the obtained shade area of ​​the forest belt in the form of charts.

2. The method for determining the shading range and degree of farmland shelterbelts according to claim 1, characterized in that, Step 1) includes the following steps: 1.1) Obtain data on latitude, longitude, forest belt orientation, average forest belt height, and direct solar radiation of the area where the farmland shelterbelt to be studied is located; 1.2) Filter the acquired direct solar radiation data for key dates to remove solar radiation values ​​from cloudy days or times when there is cloud cover.

3. The method for determining the shading range and degree of farmland shelterbelts according to claim 1, characterized in that, Step 2) Includes the following steps: 2.1) Based on the geographical latitude of the study area, calculate the solar altitude angle at different times during the spring equinox, summer solstice, and autumn equinox: Where α is the solar altitude angle, The latitude of the study area is δ, the solar inclination angle (i.e., declination angle) is ω, and the hour angle is ω. 2.2) Calculate the solar azimuth angle θ using the solar altitude angle: 2.3) The period when the intensity of direct solar radiation on the Earth's surface is greater than the threshold under clear, cloudless weather is taken as the period of direct solar radiation, and its total duration T is the sunshine duration.

4. The method for determining the shading range and degree of farmland shelterbelts according to claim 1, characterized in that, Step 3) includes the following steps: 3.1) Calculate the length L of the forest belt shade: L=H×cotα Where H is the average height of the forest belt, H = average[H1,H2,H3,…,H] i ,…,H N ], average means taking the average value, H i Let N be the height of the i-th standard tree, and N be the number of standard trees selected. 3.2) Calculate the forest belt shade length at set intervals, and construct a daily dynamic dataset of forest belt shade length [L1, L2, L3…, L…] using all calculation results within a day. j ]; 3.3) Calculate the length of the shadow on both sides perpendicular to the direction of the forest belt: L ⊥ =L×sinβ Where β is the angle between the direction of the forest belt and the solar azimuth angle; 3.4) Calculate the length of the shadow on both sides perpendicular to the direction of the forest belt at set intervals, and construct a daily dynamic dataset of the shadow length on both sides using all calculation results within a day [L]. ⊥1 ,L ⊥2 ,L ⊥3 …,L ⊥j ].

5. The method for determining the shading range and degree of farmland shelterbelts according to claim 1, characterized in that, Step 4) includes the following steps: 4.1) Divide the day's sunshine duration T into 3 equal segments, and the continuous shading duration t in each segment is as follows: 4.2) Obtain the upper and lower limits of the length of the shaded area of ​​the forest belt and the length of the shaded area on both sides perpendicular to the direction of the forest belt within each shaded period, and use them as the boundary values ​​of different shaded areas. 4.3) Based on the boundary values, the shaded areas on both sides perpendicular to the farmland shelterbelt are divided into light, moderate and heavy shading ranges.

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