Afforestation method for improving defense capability of betula alnoides to extreme low-temperature weather

Abstract

The invention belongs to the technical field of afforestation, particularly relates to an afforestation method for improving the defense capability of betula alnoides to extreme low-temperature weather, and provides a scheme aiming at the phenomenon that the defense capability of typical precious tree species in south China to extreme low-temperature weather cannot be improved in the prior art, and the method comprises the following steps: S1, constructing a uniform forest stand environment; constructing a locally uniform forest stand environment through uniform intermediate cutting with different intensities; and S2, constructing a heterogeneous forest stand environment. According to the method, the defense capacity of the typical precious tree species betula alnoides in the south China to extreme low-temperature weather is improved, meteorological characteristics in the extreme cold wave occurrence period and the cold resistance difference between the tree species in different afforestation modes are found out, the appropriate afforestation mode is selected, growth health and cold resistance are synchronously improved, and the method is suitable for large-scale popularization and application. The method promotes healthy and sustainable development of man-made forests of main precious tree species in South China, and is an important technology for actively coping with the influence of extreme low-temperature weather in the field of precious tree species cultivation.

Description

Technical Field

[0001] The invention relates to the technical field of afforestation, and in particular to an afforestation method for improving the defense capability of birch trees against extreme low temperature weather. Background Art

[0002] my country is rich in precious tree species, which are important natural resources and an important part of the country's strategic timber reserve resources. Precious tree species have the characteristics of good material, high density, deep color, beautiful texture, high commercial value, and artistic, collection and inheritance of historical culture, which exceed the general use value. With the development of social economy and the improvement of people's living standards, the demand for precious timber is strong, and the development of precious tree species resources must be strengthened.

[0003] The scientific development of the cultivation of precious tree species is an important part of realizing the transformation of the forestry development model to one that prioritizes quality and emphasizes both quantity and quality in the new era. It is an important practice to adapt to economic and social development, optimize the composition of forest resources, and realize the sustainable development of forest resources.

[0004] Betula alnoides is a precious fast-growing native broad-leaved tree species in tropical and subtropical areas of my country. Its trunk is straight and round, and its wood is diffuse-porous, light reddish brown, slightly shiny, with no obvious distinction between heartwood and sapwood, no special smell, beautiful texture, moderate wood density, and has excellent properties such as no warping or cracking, and easy processing. It can be used to make wooden floors and high-end furniture. It is also an ideal material for interior decoration and veneer veneer, and has high economic value. The air-dry density of its wood can reach 0.60g·cm when it is 15 years old. －3 According to the analysis of the growth process, processing and utilization methods and market factors of Betula alnoides, it is recommended that the main felling age is 20 to 25 years. The price of logs of Betula alnoides >20cm is 2,000 yuan / m 3 About 30cm, the price of knot-free material is 5000 yuan / m 3 About. The bark of birch contains 6.96% tannin and 57.60% purity, which can be used as tannin raw material. The main component of bark essential oil is methyl salicylate, with a content of up to 98.2%. In general, birch is one of the fastest growing precious tree species in southern my country and has great development potential.

[0005] The frequent occurrence of extreme weather under the background of climate change has a more serious impact on the composition, structure, health and stability of forest ecosystems. In the past, research on forest frost damage focused on the northern region. After the major rain, snow and freezing disasters in the south, the impact of extreme low temperature weather has gradually attracted attention from all parts of the south. In recent years, it is more common for winter temperatures to be higher in the south. When extreme cold currents occur, the temperature is low and the temperature difference is large, which leads to aggravated disaster impacts. Timber forests, ecological public welfare forests, economic forests and urban greening tree species are damaged to varying degrees or even die.

[0006] In addition to the influence of low temperature, cold currents are often accompanied by drastic changes in meteorological factors such as strong winds, frost, rain, snow and ice. The impact is related to tree species, development stage, planting pattern, etc., and is affected by terrain factors such as altitude, slope direction, and slope position. In the case of frequent extreme weather, forestry ecological construction should not only analyze its occurrence characteristics and impacts, but also scientifically select tree species and forest land to reduce afforestation risks. For example, scientific site selection, suitable trees for suitable sites, construction of mixed forests, optimization of forest structure and density measures can effectively improve the adaptability and resistance of forest stands to extreme weather. Northern Guangdong is an important ecological barrier area in Guangdong Province. The problems of poor forest health and quality caused by the composition and simple structure of artificial forests are more prominent. In recent years, large-scale forest quality precision improvement projects have been carried out, and the path of realizing the transformation of the two mountains by introducing precious tree species has been actively explored. The frequent cold currents in northern Guangdong are one of the main limiting factors for the development of local precious tree species. The existing technology cannot improve the ability of typical precious tree species in South China to prevent extreme low temperature weather. Therefore, we propose a afforestation method to improve the defense ability of southwestern birch against extreme low temperature weather to solve the above problem. Summary of the invention

[0007] The purpose of the present invention is to solve the shortcoming that the prevention ability of typical precious tree species in South China to extreme low temperature weather cannot be improved, and to propose a afforestation method for improving the defense ability of southwestern birch to extreme low temperature weather.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather comprises the following steps:

[0010] S1. Uniform forest environment construction: construct a local uniform forest environment through uniform thinning of different intensities;

[0011] S2. Construction of heterogeneous forest stand environment: building forest windows through block thinning of different areas to form a heterogeneous forest stand environment;

[0012] S3. Analysis of meteorological factors of cold waves: by analyzing the changes in temperature, humidity, wind speed, and sunshine hours during the cold wave period, we can find out the characteristics and occurrence patterns of different types of cold waves;

[0013] S4. Evaluation of tree species' responses to extreme low temperatures to provide a basis for future tree species selection;

[0014] S5. Evaluation of afforestation models: comparative analysis of the damage degree of Betula alnoides in different afforestation models, and selection of afforestation models with comprehensive cold resistance and healthy growth.

[0015] Preferably, in S1, thinning includes two modes of uniform thinning and block thinning to construct forest windows. The uniform thinning includes three intensity uniform thinning modes. The stand retention density after thinning is 375 trees / hectare, 300 trees / hectare, and 225 trees / hectare, respectively. Each treatment is about 5 mu, with 3 repetitions. The tree species planted under the forest are Betula alnoides and Elaeagnus chinensis, with 2 rows of mixed strips. The interplanted tree species are tended 5 times in 3 years. The interplanted species without thinning are used as the control for severe light deficiency, and the pure forest constructed on the clear-cut site is used as the control for full light.

[0016] Preferably, the block thinning includes three types, and the forest window areas are approximately 250㎡, 500㎡, and 750㎡ respectively, all of which are set to be approximately square, and the forest window interval is not less than the tree height, and is actually greater than 20m, repeated three times, with the retention belt interplanting as a control, and the planting method is to plant two rows of light-loving southwestern birch in the area with good light conditions in the middle of the forest window, and plant shade-tolerant euphorbia cerasifera on both sides.

[0017] Preferably, in S4, the evaluation of tree species' responses to extreme low temperatures is specifically as follows: 20m×30m sampling plots are set up in uniformly thinned and intercropped stands for spot checks, and forest gap intercropping patterns are comprehensively investigated to investigate the symptoms and degree of damage to tree species, the number of affected trees, and the differences in the degree of damage to tree species are analyzed mainly from the aspects of cold current characteristics and afforestation patterns.

[0018] Preferably, the damage level of tree species is divided as follows: within 1-3 days after each cold wave, the frost damage situation of the test forest is inspected, and the damage level of tree species is determined according to the analysis of the damage situation of tree species and the previous frost damage / cold damage level classification method of southern tree species. A re-inspection is carried out after 6-8 days. Since the test tree species have been planted for 1-2 years, the tree height of 1-year-old Phoebe nanmu, Castanopsis hystrix, and Betula alnoides is 0.5-0.8m, and that of Betula alnoides is 1.1-1.8m; the tree height of 2-year-old Betula alnoides is 0.8-1 .4m, Betula alnoides is 1.9-4.1m, which belongs to the young forest stage. The degree of damage to the tree species is divided into three levels. Mild damage means that the leaves on the upper crown dry up and are less than 1 / 4 of the crown length, and the damaged length of young shoots within the frost damage range is less than 10cm; moderate damage means that the leaves on the upper crown dry up and are less than 1 / 2 of the crown length, and the damaged length of young shoots is less than 30cm; severe damage means that the leaves on the upper crown dry up and are greater than 1 / 2 of the crown length to the leaves of the whole plant dry up, and the damaged length of young shoots is less than 50cm.

[0019] Preferably, in said S5, a comparative analysis of the damage degree of Betula alnoides in different afforestation patterns is carried out as follows: collect damage degree data of different tree species under each afforestation pattern, including damaged area, number of damaged plants, and damage degree level; clean the collected data, remove outliers and incomplete data, and ensure the accuracy and consistency of the data; classify and count: classify and count the damage degree data according to afforestation pattern and tree species, and calculate the average damage degree and proportion of damaged plants under each pattern; comparative analysis: compare and analyze the damage degree of each tree species under different afforestation patterns through charts and statistical test methods.

[0020] Preferably, in S3, the analysis of cold wave meteorological factors is as follows: data collection: temperature: record the daily maximum and minimum temperatures before and after the cold wave; humidity: monitor changes in air humidity to understand the water vapor content; wind speed: measure wind speed and record changes in wind direction; sunshine hours: count the daily sunshine duration to reflect the lighting conditions; data analysis: compare the changes in various factors before and after the cold wave to find out significant differences; analyze the correlation between temperature, humidity, wind speed, and sunshine hours; type classification: divide different types of cold waves according to the characteristics of factor changes; analyze the frequency, intensity and duration of each type of cold wave; rule summary: summarize the occurrence rules of various types of cold waves, including seasonal distribution and geographical distribution; predict the possible types and occurrence trends of future cold waves.

[0021] Preferably, in S1, improving the stress resistance of tree species is specifically as follows: formulating scientific cultivation and management measures: including reasonable pruning, fertilizing and watering; pruning to remove pests and dead branches, fertilizing to enhance immunity, and watering to keep the soil moist; targeted measures: cold resistance: strengthen winter fertilization, cover with thermal insulation materials, and select cold-resistant tree species; disease and pest resistance: strengthen observation, timely prevention and control, and use biological control to reduce harm; improve the growth environment: protect the soil, pay attention to drainage, and provide suitable growth conditions.

[0022] Preferably, in S1, after thinning, ensure that the forest stand is in good sanitary condition and stable state to prevent the increase of light due to the reduction of the number of trees, which may lead to the growth of weeds and the harm of wind breakage and snow pressure; adjust the forest stand density: reasonably adjust the forest stand density according to tree species, site conditions, and afforestation density factors to create the most suitable growth conditions for the retained trees; monitor and adjust: regularly monitor the growth of trees, and adjust the nurturing measures according to actual needs, such as replanting and pruning, to promote the healthy growth of trees.

[0023] Preferably, regular monitoring of forest growth is as follows: Observation and measurement: Regularly observe the growth status and performance of trees, including crowns, branches, leaves, and trunks, and use measuring tools such as height gauges and measuring rulers to accurately measure tree height and breast diameter; Data analysis: The collected data needs to be analyzed to find the patterns and problems of tree growth and provide a basis for management; Image and soil analysis: Use drones or remote sensing technology to obtain tree images for quantitative analysis, and sample and analyze the soil at the same time to understand the tree growth environment.

[0024] Compared with the prior art, the advantages of the present invention are:

[0025] The present invention improves the ability of typical precious tree species in South China to prevent extreme low temperature weather, finds out the meteorological characteristics and differences in cold resistance of tree species during extreme cold waves, and selects appropriate afforestation models to achieve one tree one model, thereby improving growth health and cold resistance simultaneously, promoting the healthy and sustainable development of artificial forests of major precious tree species in South China, and is an important technology in the field of precious tree species cultivation to actively respond to the impact of extreme low temperature weather. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A uniform forest stand environment and a heterogeneous forest stand environment construction diagram of a afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather proposed by the present invention;

[0027] Figure 2 Characteristic diagram of meteorological factors of four cold waves from the end of 2020 to the beginning of 2021 for a afforestation method proposed by the present invention to improve the defense ability of southwestern birch against extreme low temperature weather;

[0028] Figure 3 A comparison diagram of the damage rate of Betula alnoides in different afforestation modes of a afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather proposed by the present invention;

[0029] Figure 4 A growth comparison diagram of Betula alnoides in a uniform thinning afforestation model of a afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather proposed by the present invention;

[0030] Figure 5 A growth comparison diagram of Betula alnoides in a forest gap afforestation model of a afforestation method proposed by the present invention to improve the defense capability of Betula alnoides against extreme low temperature weather;

[0031] Figure 6 This is a technical research and development flow chart of a afforestation method proposed by the present invention for improving the defense capability of southwestern birch against extreme low temperature weather. DETAILED DESCRIPTION

[0032] The technical solution of this embodiment will be clearly and completely described below in conjunction with the drawings in this embodiment. Obviously, the described embodiment is only a part of this embodiment, rather than all of the embodiments.

[0033] Embodiment 1

[0034] Reference Figure 1-Figure 6 , a afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather, comprising the following steps:

[0035] S1. Uniform forest stand environment construction: construct a local uniform forest stand environment through uniform thinning of different intensities;

[0036] S2. Construction of heterogeneous forest stand environment: building forest windows through block thinning of different areas to form a heterogeneous forest stand environment;

[0037] S3. Analysis of meteorological factors of cold waves: by analyzing the changes in temperature, humidity, wind speed, and sunshine hours during the cold wave period, we can find out the characteristics and occurrence patterns of different types of cold waves;

[0038] S4. Evaluation of tree species' responses to extreme low temperatures to provide a basis for future tree species selection;

[0039] S5. Evaluation of afforestation models: comparative analysis of the damage degree of Betula alnoides in different afforestation models, and selection of afforestation models with comprehensive cold resistance and healthy growth.

[0040] In this embodiment, in S1, thinning includes two modes: uniform thinning and block thinning to construct forest windows. Uniform thinning includes three intensity uniform thinning modes. The stand retention density after thinning is 375 trees / hectare, 300 trees / hectare, and 225 trees / hectare, respectively. Each treatment is about 5 mu, with 3 repetitions. The tree species planted under the forest are southwestern birch and euphorbia cerasifera, with 2 rows of mixed strips. The interplanted tree species are tended 5 times in 3 years. The interplanted species without thinning are used as the control for severe light deficiency, and the construction of pure forest on clear-cut sites is used as the control for full light.

[0041] In this embodiment, block thinning includes three types, and the forest window areas are approximately 250㎡, 500㎡, and 750㎡ respectively. All of them are set to be approximately square. The interval between forest windows is not less than the tree height, and is actually greater than 20m. It is repeated three times, with intercropping of retention strips as a control. The planting method is to plant two rows of light-loving southwestern birch in the area with good light conditions in the middle of the forest window, and plant shade-tolerant euphorbia cerasifera on both sides.

[0042] In this embodiment, in S4, the response evaluation of tree species to extreme low temperatures is specifically as follows: 20m×30m sample plots are set up in uniform thinning and intercropping stands for spot checks, and the forest gap intercropping patterns are comprehensively investigated to investigate the symptoms and degree of damage to tree species and the number of damaged trees, and the differences in the degree of damage to tree species are mainly analyzed from the aspects of cold current characteristics and afforestation patterns.

[0043] In this embodiment, the damage level of tree species is divided as follows: within 1-3 days after each cold wave, the frost damage situation of the test forest is inspected, and the damage level of the tree species is determined according to the analysis of the damage situation of the tree species and the previous frost damage / cold damage level classification method of southern tree species. A re-inspection is carried out after 6-8 days. Since the test tree species have been planted for 1-2 years, the tree heights of the one-year-old Phoebe nanmu, Castanopsis hystrix, and Oleander are 0.5-0.8m, and the southwestern birch is 1.1-1.8m; the two-year-old Oleander is 0.8- 1.4m, Betula alnoides is 1.9-4.1m, which belongs to the young forest stage. The degree of damage to the tree species is divided into three levels. Mild damage means that the leaves on the upper crown dry up and are less than 1 / 4 of the crown length, and the damaged length of the young shoots within the frost damage range is less than 10cm; moderate damage means that the leaves on the upper crown dry up and are less than 1 / 2 of the crown length, and the damaged length of the young shoots is less than 30cm; severe damage means that the leaves on the upper crown dry up and are greater than 1 / 2 of the crown length to the leaves of the whole plant dry up, and the damaged length of the young shoots is less than 50cm.

[0044] In this embodiment, in S5, a comparative analysis of the degree of damage of each tree species in different afforestation patterns is performed as follows: collect damage degree data of different tree species under each afforestation pattern, including the damaged area, the number of damaged plants, and the degree of damage; clean the collected data to remove outliers and incomplete data to ensure the accuracy and consistency of the data; classify and count the damage degree data according to the afforestation pattern and tree species, and calculate the average degree of damage and the proportion of damaged plants under each pattern; compare and analyze: compare and analyze the degree of damage of each tree species under different afforestation patterns through charts and statistical test methods.

[0045] In this embodiment, in S3, the analysis of cold wave meteorological factors is as follows: data collection: temperature: record the daily maximum and minimum temperatures before and after the cold wave; humidity: monitor changes in air humidity to understand the water vapor content; wind speed: measure wind speed and record changes in wind direction; sunshine hours: count the daily sunshine duration to reflect the lighting conditions; data analysis: compare the changes in various factors before and after the cold wave to find out significant differences; analyze the correlation between temperature, humidity, wind speed, and sunshine hours; type classification: divide different types of cold waves according to the characteristics of factor changes; analyze the frequency, intensity and duration of each type of cold wave; rule summary: summarize the occurrence rules of various types of cold waves, including seasonal distribution and geographical distribution; predict the possible types and occurrence trends of future cold waves.

[0046] In this embodiment, in S1, improving the stress resistance of tree species is specifically as follows: formulating scientific cultivation and management measures: including reasonable pruning, fertilizing and watering; pruning to remove pests and dead branches, fertilizing to enhance immunity, and watering to keep the soil moist; targeted measures: cold resistance: strengthen winter fertilization, cover with thermal insulation materials, and select cold-resistant tree species; disease and pest resistance: strengthen observation, timely prevention and control, and use biological control to reduce harm; improve the growth environment: protect the soil, pay attention to drainage, and provide suitable growth conditions.

[0047] In this embodiment, in S1, after thinning, ensure that the forest stand is in good sanitary condition and stable state to prevent the increase of light due to the reduction of the number of trees, which may lead to the growth of weeds and the harm of wind breakage and snow pressure; adjust the forest stand density: according to the tree species, site conditions, and afforestation density factors, reasonably adjust the forest stand density to create the most suitable growth conditions for the retained trees; monitor and adjust: regularly monitor the growth of trees, and adjust the nurturing measures according to actual needs, such as replanting and pruning, to promote the healthy growth of trees.

[0048] In this embodiment, regular monitoring of tree growth is specifically as follows: Observation and measurement: Regularly observe the growth status and performance of trees, including crowns, branches and leaves, and trunks, and use measuring tools such as height gauges and measuring rulers to accurately measure tree height and breast diameter; Data analysis: The collected data needs to be analyzed to find the patterns and problems of tree growth and provide a basis for management; Image and soil analysis: Use drones or remote sensing technology to obtain tree images for quantitative analysis, and sample and analyze the soil at the same time to understand the tree growth environment.

[0049] In this embodiment, the cold current overview and frost damage investigation and analysis

[0050] Overview of cold currents: In recent years, cold currents have occurred frequently in northern Guangdong. Within 5 years after afforestation (2019-2023), an average of 2-3 severe cold currents occurred each year. Among them, the cold currents from December 2020 to January 2021 were the most frequent and had the greatest impact on afforestation tree species. According to the data from the Shaoguan National Basic Meteorological Station, the changing characteristics of temperature, humidity, light intensity, etc. during the four cold currents during this period were analyzed in detail to analyze the relationship between the degree of damage to tree species and the characteristics of the cold currents.

[0051] Investigation and analysis methods: 20m×30m sample plots were set up in uniform thinning and interplanting stands for spot checks, and forest window interplanting patterns were comprehensively investigated. The symptoms and degree of damage to tree species, the number of damaged trees, etc. were investigated, and the differences in the degree of damage to tree species were analyzed mainly from the aspects of cold current characteristics and afforestation patterns. 2.3.3 Classification of damage levels Within 1-3 days after each cold current, the frost damage situation of the experimental forest was investigated. According to the analysis of the damage to the tree species, the damage level of the tree species of the present invention was determined by referring to the previous frost damage / cold damage level classification method for southern tree species, and a review was conducted after 6 to 8 days. Since the participating tree species have been afforested for 1-2 years, the tree heights of the one-year-old Phoebe nanmu, Castanopsis hystrix, and Betula alnoides are 0.5-0.8m, and the southwestern birch is 1.1-1.8m; the two-year-old Betula alnoides is 0.8-1.4m, and the southwestern birch is 1.9-4.1m, which belongs to the young forest stage. The degree of damage to tree species is divided into three levels: mild damage (I) refers to the drying up of leaves on the upper crown and the length being less than 1 / 4 of the crown length, and the damaged length of tender shoots within the frost damage range being less than 10 cm; moderate damage (II) refers to the drying up of leaves on the upper crown and the length being less than 1 / 2 of the crown length, and the damaged length of tender shoots being less than 30 cm; severe damage (III) refers to the drying up of leaves on the upper crown and the length being greater than 1 / 2 of the crown length to the drying up of all leaves of the plant, and the damaged length of tender shoots being less than 50 cm.

[0052] 1. Results and Analysis

[0053] Relationship between the damage degree of tree species and the characteristics of cold current

[0054] Analysis of cold current characteristics: According to the data from the Shaoguan National Basic Meteorological Station (Qujiang District, Shaoguan City, 24°40′22″N, 113°37′13″E, 120m above sea level), four major cold currents occurred in South China from December 2020 to January 2021 ( Figure 1 ). The first time was from December 13 to 23, 2020. The extreme low temperature occurred on the 21st, which was 2.2℃, with a temperature difference of 12.9℃, 9.2 hours of sunshine, a maximum wind speed of 7.6 m / s, and a relative humidity of 63.8%. The second time was from December 30, 2020 to January 3, 2021. The extreme low temperature occurred on January 1, which was -1.7℃, with a temperature difference of 14.1℃, 9.8 hours of sunshine, a maximum wind speed of 5.8 m / s, and a relative humidity of 58.3%. The third time was from January 7 to 14, 2021. The extreme low temperature was on the 12th, which was -2.8℃, with a temperature difference of 17.6℃, 1.8 hours of sunshine, a maximum wind speed of 8.7 m / s, and a relative humidity of 59.3%. The fourth time was from 18th to 20th, 2021. The extreme low temperature was 0.3℃ on the 19th, the temperature difference was 18.6℃, the sunshine hours were 9.3 hours, the maximum wind speed was 4.2 m / s, and the relative humidity was 86.8%.

[0055] Analysis on the impact of cold current characteristics on frost damage of tree species

[0056] According to the survey on the impact of four cold waves on tree species, Betula alnoides was the most affected, with mild frost damage symptoms in the third cold wave, and the leaves of a small number of plants turned brown locally; the damage rate and degree increased dramatically in the fourth cold wave, the pure forest died seriously, and there were differences in the degree of damage in the transformation model. The leaves of the pure forest of Euphorbia cerasifera died only in the fourth cold wave, and the terminal buds were not damaged. Phoebe fujianensis and Castanopsis hystrix were not damaged by frost in the four cold waves. Based on this, it can be seen that Phoebe fujianensis and Castanopsis hystrix have strong cold resistance, followed by Euphorbia cerasifera, and Betula alnoides has the lowest cold resistance.

[0057] According to on-site investigations, the impact of the fourth cold wave was the most obvious, so we focused on analyzing the differences between the characteristics of this cold wave and the previous three, the relationship between the degree of damage to tree species and afforestation patterns, etc. We took the southwestern birch, which was the most obviously damaged, as an example to analyze the relationship between the characteristics of the cold wave and the degree of damage to tree species. The first two cold waves had not yet reached the minimum temperature for damage to southwestern birch; the third extreme temperature was the lowest, reaching -2.8°C, but only slight leaf frostbite symptoms appeared, and the terminal buds were not damaged, which was close to its low temperature tolerance limit. It is worth noting that the fourth cold wave had a minimum temperature of only 0.3°C, which was higher than the second and third cold waves, but the temperature difference was large, the humidity was high, the sunshine hours were long, and the wind speed was low ( Figure 1 ), and obvious frost phenomenon occurred, and the degree of damage to Betula alnoides increased seriously, indicating that the lowest temperature is not necessarily the only factor causing the damage to Betula alnoides. Temperature difference, humidity, wind speed, sunshine hours, etc. also have a great impact.

[0058] Relationship between tree species damage degree and afforestation pattern

[0059] Relationship between the damage degree of tree species and forest reserve density: The survey results of the reserve density test forest in Dongfeng Work Area showed that the damage of Betula alnoides was more serious than that of Euphorbia cerasifera, and there were obvious differences among the reserve densities. As the reserve density increased, the damage degree of the tree species decreased ( Figure 2 ). The damage rate of Betula alnoides in the lowest stand retention density treatment (225 trees / ha) reached 100%, which was the same as the pure forest in the clear-cut site (CK), but the degree of damage was lower than that in the pure forest, with no severely damaged individuals and mainly lightly damaged. The control stand and the two treatments with higher retention density (300 trees / ha and 375 trees / ha) were not damaged. The damage rate of the pure forest of Euphorbia cerasifera (CK) was about 70%, of which about 43% were lightly damaged and about 27% were moderately damaged. There was no severely damaged individual. The degree of damage to Euphorbia cerasifera in the forests of various retention densities was extremely low. Only 2% of the individuals were lightly damaged in the lowest stand retention density treatment, and there was no damage in the other treatments.

[0060] The relationship between the degree of damage to tree species and the area and shape of forest gaps The results of the investigation on forest gap planting patterns in the Dongfeng area of ​​Shaoguan Forest Farm showed that the degree of damage to Betula alnoides was higher than that to Euphorbia cerasifera, and the degree of damage increased with the increase of forest gap area ( Figure 3). In the unthinned area (CK) and the smaller forest (250㎡), both were not damaged. In the medium-sized forest gap (500㎡), the proportion of mild and moderate frost damage to Betula alnoides was about 20% and 10%, respectively. In the larger forest gap (750㎡), the proportion of mild frost damage to Betula alnoides was similar to that of the medium-sized forest gap, but the proportion of moderate frost damage increased to 30%, and the proportion of severe frost damage was about 20%, and the overall damage rate was about doubled. The wood of Euphorbia cerasifera was only slightly damaged in both the medium and large forest gaps, with the proportions of about 5% and 9%, respectively.

[0061] 2. Conclusion and Discussion

[0062] The impact of extreme low temperature weather on forests under global climate change is becoming more and more serious. It is particularly important to adopt a forestation model that adapts to climate change for forest quality and stability. Most of the low-quality and low-efficiency forest transformation in South China adopts the introduction of a certain proportion of precious tree species. This paper explores the afforestation model to cope with cold currents from the aspects of tree species, forest stand structure adjustment method and site.

[0063] Northern Guangdong is a region seriously affected by cold currents. Among the 4 tree species selected by the present invention, Phoebe fujianensis and Castanopsis hystrix are in the natural distribution area, have strong frost resistance, and are not harmed in 4 cold currents; the damage degree of Phoebe fujianensis is relatively light, and Betula alnoides is more seriously harmed, especially the clear-cut afforestation plot. Phoebe fujianensis and Betula alnoides belong to the tree species introduced northward from the natural distribution area, and the introduction purpose of Phoebe fujianensis is to increase the precious tree species of nitrogen fixation, and Betula alnoides is the rare precious tree species of the middle rotation period (25-30 years) in the south, and the introduction in this area is about 10 years and 20 years respectively, and in the past, only the top tip was slightly harmed during the cold current, and mainly the new leaves were more harmed, and no serious frost damage was seen, and it was preliminarily believed that it can adapt to the local climate environment. During the major rain and snow freezing disaster that occurred in southern my country in 2008, Betula alnoides was only slightly harmed, and it was faster to recover growth after being harmed, and the impact was less.

[0064] The serious damage to the southwestern birch is related to its biological characteristics and cold current characteristics. Southwestern birch is a semi-deciduous tree species. In winter, it is in the budding period. The branches and leaves are relatively young. In addition, the leaves are papery, which leads to its low cold resistance. The extreme low temperature that the southwestern birch can tolerate is -5.7°C. In the present invention, the lowest temperature of the third cold current was -2.8°C, and only the leaves were slightly damaged. According to the analysis of previous damage, southwestern birch is not frost-resistant. The lowest temperature of the fourth cold current was 0.3°C, but it had a serious impact, which was mainly related to the cold current characteristics such as low wind speed, high humidity, and frost phenomenon ( Figure 1). Therefore, before breaking the extreme low temperature that the tree species is adapted to, a single cooling is not as significant as the effects of frost and strong winds that accompany the low temperature. In the closed forest stands of Betula alnoides over 10 years old around the test site, only a small number of leaves on the top of the crowns of some individuals on the windward side were damaged. Therefore, from the perspective of the forest stand development process, the degree of lignification of young trees is low, the forest stand environment is unstable before closure, and the anti-interference ability is poor, resulting in a higher risk of frost damage in the young forest stage. Generally, the degree of damage to the forest stand after closure is relatively light, not only because the degree of lignification is improved, but also the relatively neat forest stands form a relatively flat underlying surface, which can reduce wind speed, reduce turbulence, avoid drastic temperature changes, etc., and reduce the impact of cold currents.

[0065] From the perspective of afforestation mode, clear-cut afforestation may face higher risks than thinning and intercropping. Open areas have sufficient sunlight, fast forest growth and early phenology. In addition, warm winters can lead to increased accumulated temperature and change the phenology of tree species. The sprouting of new leaves and branches in winter will increase the risk of frost damage. Open woodlands have no upper forest protection, and when cold currents come, the wind speed is high, the temperature drops quickly, the temperature difference is large, and frost is easy to form. Therefore, the selection of tree species should take into account meteorological factors such as tree species characteristics, average temperature of the introduction site, and extreme temperature. In particular, the introduction of tree species to the north should consider the impact of extreme low temperatures under the background of warm winters.

[0066] Compared with the high damage rate of clear-cut afforestation ( Figure 2 ), the risk of damage to tree species in various thinning and intercropping patterns was low. In the thinning and intercropping patterns, the degree of damage to Betula alnoides and Elaeagnus chinensis generally increased with the decrease of stand retention density ( Figure 2 ) increases with the increase of forest gap area. Compared with the square forest gap planting pattern, the uniform thinning planting pattern has a high damage rate, but the moderate and severe damage is relatively low ( Figure 2 , Figure 3 ). The thinning and intercropping mode maintains part of the forest stand structure and environment, which is beneficial to reduce wind speed, slow down the degree of frost in the forest stand, etc. It can effectively reduce the impact of extreme cold weather on tree species, and indirectly improve the ability of young forests planted under the forest to resist low temperature frost damage. The higher the degree of preservation of the original forest stand environment, the stronger the defense against extreme weather. In addition, in the forest window mode, a forest window with an area that is too large is prone to form "frost holes", which may reduce the protective effect. In the present invention, obvious frost was found in the middle of the large forest window (750㎡). The degree of damage to individuals in the middle of the forest window is relatively high, while the degree of damage near the edge of the forest window is extremely low. Therefore, the forest window area should be reasonably selected.

[0067] Frequent extreme weather has become an important factor affecting forest health and stability, especially for new afforestation. It is necessary to give full play to the protective role of forest stand structure on young forests. First, retaining some of the original trees is conducive to maintaining the forest stand structure and environment, and improving the resistance of interplanted tree species to extreme weather. Secondly, in terms of transformation models, although the uniform thinning and interplanting model suffers less damage, the forest gap model has a high degree of directional control over internal environmental factors relative to uniform thinning without causing lethal damage. It can select matching forest gap shapes and areas for tree species and sites with different ecological characteristics, and is easier to operate, which is conducive to the thinning management of upper forest stands in the middle and late stages, and reduces the mechanical damage caused by interplanting in the later stages, and has a high application value.

[0068] On the whole, through reasonable tree species selection and site matching combined with scientific forest stand structure control measures to improve tree species resistance, forest quality improvement and ecosystem restoration can be carried out scientifically and rationally. However, further strengthening of relevant theoretical and technical research is needed before it can be widely used in production practice.

[0069] Embodiment 2

[0070] The difference from the first embodiment is that a afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather comprises the following steps:

[0071] S1. Forest stand environment construction: through thinning, a forest stand environment suitable for tree species growth and improving the tree species' resistance to adversity is constructed;

[0072] S2. Tree species selection: Select representative precious tree species with different cultivation cycles according to local climate conditions, cultivation goals, and management entities. Irrigate the soil two days before the arrival of frost to keep the soil moist, which helps to increase soil temperature.

[0073] S3. Analysis of meteorological factors of cold waves: by analyzing the changes in temperature, humidity, wind speed, and sunshine hours during the cold wave period, we can find out the characteristics and occurrence patterns of different types of cold waves;

[0074] S4. Evaluation of tree species' responses to extreme low temperatures to provide a basis for future tree species selection;

[0075] S5. Evaluation of afforestation patterns: comparative analysis of the degree of damage to each tree species in different afforestation patterns is conducted to screen out suitable afforestation patterns for each tree species, especially those for low-temperature sensitive species.

[0076] The above description is only a preferred specific implementation manner of this embodiment, but the protection scope of this embodiment is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of this embodiment within the technical scope disclosed in this embodiment, and they should be covered by the protection scope of this embodiment.

Claims

1. A afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather, characterized in that: The following steps are involved: S1. Uniform forest stand environment construction: construct a local uniform forest stand environment through uniform thinning of different intensities; S2. Construction of heterogeneous forest stand environment: building forest windows through block thinning of different areas to form a heterogeneous forest stand environment; S3. Analysis of meteorological factors of cold waves: by analyzing the changes in temperature, humidity, wind speed, and sunshine hours during the cold wave period, we can find out the characteristics and occurrence patterns of different types of cold waves; S4. Evaluation of tree species' responses to extreme low temperatures to provide a basis for future tree species selection; S5. Evaluation of afforestation models: comparative analysis of the damage degree of Betula alnoides in different afforestation models, and selection of afforestation models with comprehensive cold resistance and healthy growth.

2. The afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather according to claim 1, characterized in that: In S1, thinning includes two modes: uniform thinning and block thinning to construct forest windows. The uniform thinning includes three intensity uniform thinning modes. The stand retention density after thinning is 375 trees / hectare, 300 trees / hectare, and 225 trees / hectare, respectively. Each treatment is 5 mu, with 3 repetitions. The tree species planted under the forest are Betula alnoides and Elaeagnus chinensis, with 2 rows of mixed strips. The interplanted tree species are tended 5 times in 3 years. The non-thinning and interplanting are used as the control for severe light deficiency, and the construction of pure forest on clear-cut sites is used as the control for full light.

3. The afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather according to claim 2, characterized in that: The block thinning includes three types, with forest gap areas of approximately 250㎡, 500㎡, and 750㎡ respectively, all of which are set to be approximately square. The interval between forest gaps is not less than the tree height, and is actually greater than 20m. It is repeated three times, with intercropping of retention strips as a control. The planting method is to plant two rows of light-loving southwestern birch in the area with good light conditions in the middle of the forest gap, and plant shade-tolerant euphorbia cerasifera on both sides.

4. The afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather according to claim 3, characterized in that: In S4, the response evaluation of tree species to extreme low temperatures is specifically as follows: 20m×30m sampling plots are set up in uniform thinning and intercropping stands for spot checks, and the forest gap intercropping patterns are comprehensively investigated to investigate the symptoms and degree of damage to tree species and the number of damaged trees. The differences in the degree of damage to tree species are mainly analyzed from the aspects of cold current characteristics and afforestation patterns.

5. The afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather according to claim 4, characterized in that: The damage levels of tree species were divided as follows: within 1-3 days after each cold wave, the frost damage situation of the experimental forest was inspected, and the tree species damage level was determined based on the analysis of the tree species damage situation and referring to the previous frost damage / cold damage level classification method for tree species in the south. A re-inspection was conducted after 6-8 days. Among them, the one-year-old southwestern birch was 1.1-1.8m; the two-year-old southwestern birch was 1.9-4.1m, which belonged to the young forest stage. The degree of tree species damage was divided into 3 levels. Mild damage meant that the leaves on the upper crown dried up and were less than 1 / 4 of the crown length, and the length of damaged young shoots within the frost damage range was less than 10cm; moderate damage meant that the length of dried leaves on the upper crown was less than 1 / 2 of the crown length, and the length of damaged young shoots was less than 30cm; severe damage meant that the length of dried leaves on the upper crown was greater than 1 / 2 of the crown length to the whole plant leaves dried up, and the length of damaged young shoots was less than 50cm.

6. The afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather according to claim 5, characterized in that: In S5, a comparative analysis of the damage degree of Betula alnoides in different afforestation patterns is carried out as follows: collect damage degree data of tree species under each afforestation pattern, including damaged area, number of damaged plants, and damage degree level; classification statistics: classify and count the damage degree data according to afforestation pattern and tree species, and calculate the average damage degree and proportion of damaged plants under each pattern; comparative analysis: compare and analyze the damage degree of each tree species under different afforestation patterns through charts and statistical test methods.

7. The afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather according to claim 6, characterized in that: In S3, the analysis of cold wave meteorological factors is as follows: Data collection: Temperature: record the daily maximum and minimum temperatures before and after the cold wave; Humidity: monitor the changes in air humidity to understand the water vapor content; Wind speed: measure wind speed and record changes in wind direction; Sunshine hours: count daily sunshine hours to reflect lighting conditions; Data analysis: compare changes in various factors before and after the cold wave to find significant differences; analyze the correlation between temperature, humidity, wind speed, and sunshine hours; Type classification: classify different types of cold waves according to the characteristics of factor changes; analyze the frequency, intensity and duration of each type of cold wave; Rule summary: summarize the occurrence rules of various types of cold waves, including seasonal distribution and geographical distribution; predict possible types and occurrence trends of future cold waves.

8. The afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather according to claim 7, characterized in that: In S1, a uniform forest environment is constructed locally through uniform thinning of different intensities to improve the resistance of tree species to adversity, as follows: Formulate scientific cultivation and management measures: including reasonable pruning, fertilization and watering; pruning to remove pests and dead branches, fertilization to enhance immunity, and watering to keep the soil moist; targeted measures: cold resistance: strengthen winter fertilization, cover with warm materials, and select cold-resistant tree species; disease and pest resistance: strengthen observation, timely prevention and control, and use biological control to reduce harm; Improve the growing environment: protect the soil, pay attention to drainage, and provide suitable growing conditions.

9. The afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather according to claim 8, characterized in that: In S1, after thinning, ensure that the forest stand is in good sanitary condition and stable state to prevent the increase of light due to the reduction of the number of trees, which may lead to the growth of weeds and the harm of wind breakage and snow pressure; adjust the forest stand density: reasonably adjust the forest stand density according to the tree species, site conditions, and afforestation density factors to create the most suitable growth conditions for the retained trees; monitor and adjust: regularly monitor the growth of trees, and adjust the tending measures according to actual needs to promote the healthy growth of trees.

10. The afforestation method for improving the defense capability of Betula alnoides against extreme low temperature weather according to claim 9, characterized in that: Regular monitoring of forest growth is as follows: Observation and measurement: Regularly observe the growth status and performance of trees, including crowns, branches, leaves, and trunks, and use measuring tools such as height gauges and measuring tapes to accurately measure tree height and breast diameter; Data analysis: The collected data needs to be analyzed to find the patterns and problems of tree growth and provide a basis for management; Image and soil analysis: Use drones or remote sensing technology to obtain tree images for quantitative analysis, and sample and analyze the soil at the same time to understand the tree growth environment.

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