CN113383689A

CN113383689A - Method for promoting artificial forest to be updated

Info

Publication number: CN113383689A
Application number: CN202110659211.6A
Authority: CN
Inventors: 贾忠奎; 王杰; 尹群; 崔靖亭; 司瑞雪; 王利东; 刘彦清; 朱亚丽; 陆景星; 李岩
Original assignee: Beijing Forestry University
Current assignee: Beijing Forestry University
Priority date: 2021-06-15
Filing date: 2021-06-15
Publication date: 2021-09-14
Anticipated expiration: 2041-06-15
Also published as: CN113383689B

Abstract

The invention discloses a method for promoting the updating of an artificial forest, which comprises the following steps: cleaning the litter on the forest promotion land to expose part of the forest land ground; sowing forest seeds on the bare ground. The method can obviously improve the natural updating level, updating density and sowing germination rate of the artificial forest, and experiments prove that the updating density of the method can reach 8633.33 strains hm at most^‑2The germination rate of the seeds can reach 1.79 percent, and the seeds are all realized under the ditch-shaped treatment. Compared with the existing mode of realizing forest stand updating by artificial afforestation, the optimal litter cleaning mode, namely furrow-shaped treatment promotes updating, and the workload and the updating cost are greatly reduced.

Description

Method for promoting artificial forest to be updated

Technical Field

The invention belongs to the fields of forest sustainable management, near-natural management and afforestation, and relates to a method for updating an artificial forest.

Background

Larix principis-ruprechiti (Larix principis-ruprechiti) is a special tall tree of larch genus in Pinaceae, originally produced in alpine regions in North China, has the highest distribution altitude of about 2800m, and is one of the main group-establishing tree species of alpine needle forest belts in provinces such as Ji, jin and the like. In the main distribution area, the larch of North China appears in pure forest, or forms a mixed forest with coniferous trees such as Picea wilsonii (Picea meyeri), Picea wilsonii (Picea wilsonii), white birch (Betula platyphylla), Populus davidiana (Populus davidiana) and Salix pseudochinensis (Salix pseudosangi) and other broad-leaved trees.

As one of the important pioneer tree species for succession of forest communities in the habitability area, larch is a strong positive conifer which is loving light and is not shade-resistant. Meanwhile, the cold resistance of the winter-resistance agent is very excellent, and the winter-resistance agent can still live through winter at the temperature of minus 50 ℃ and has strong resistance to adverse climate. The larix dahurica has strong soil adaptability, but has shallow root system distribution, favors deep, fertile, moist and well-drained acid or neutral soil, has certain tolerance to salt and alkali, and also has certain moisture resistance, drought resistance and barren resistance. In addition, the larch in North China also has various advantages of long service life, fast growth, easy propagation, developed root system, certain germination capacity and the like. The wood material is excellent and tough, has compact structure and straight grains, and has better performance in compression resistance and bending resistance. Because of being rich in resin, the wood is more corrosion-resistant and durable, and can be used for buildings, bridges, electric poles and the like. In addition, the trunk and bark can also be made into resin, tannin extract, etc. Therefore, the larch in North China not only can bring good ecological benefits to each distribution area, but also can bring huge economic benefits to the local area. Because of this, it is widely introduced to northeast, northwest and central China, and provinces such as Shaan, Gannan and Ning have been introduced and cultivated at present.

As an important native tree species, the larch has unique advantages and great protection, research and utilization values. So far, a complete research system for larch in North China has been established in China. The method relates to various aspects such as seed form identification, seedling cultivation, forest culture measures, forest growth and accumulation, species diversity, respiratory carbon sink and the like.

Undoubtedly, the study of the natural renewal of larch north China is one of the directions and difficulties. Forest updating is significant for any healthy forest ecosystem, and the future trend and trend of the whole forest community can be determined by the quality of the updating condition. Forests are a terrestrial ecosystem that is largely time-space-extended by the renewal of individual plant populations, represented by woody plants, and generally represents the succession and development of the forest itself. Natural updating is one of 3 ways of forest updating, and compared with the natural updating, the method has the advantages of saving cost, conforming to natural laws and the like. Under the prevailing theories such as the current natural management, the method is widely applied to the forestry production all over the world and is likely to become a main mode for updating artificial forests in the future, so that the method is concerned.

In the process of implementing the invention, the inventor finds that at least one of the following technical problems exists in the prior art:

1. the larch forest in each distribution area represented by the larch artificial forest in the China north of the Han dam area cannot be naturally updated or poorly updated at present;

2. the number of seeds in the soil under the larch forest in North China is small, and the activity is low;

3. the density of the updated seedling of the larix huabeiensis is small, the survival rate of the updated seedling in the forest stand is low, and the number of young trees is small;

4. the seedlings germinated from larch of North China die continuously with the passage of time;

5. there is a very large age fault between the parent and the sapling of the larch, north China.

6. By the research of the invention, the current situation of the natural poor updating of the larix huabeiensis is not changed, and the artificial afforestation technology is still the main mode, even the only mode, for updating the stand of the larix huabeiensis artificial forest. The large-area artificial afforestation can increase the production burden of the forest farm in the aspects of time, manpower, financial resources and the like.

Disclosure of Invention

In view of the above, the present invention aims to provide a method for promoting the renewal of artificial forests, which can significantly improve the renewal density and the sowing germination rate, and the renewal cost is far lower than that of artificial forestation technology. The inventor continuously reforms and innovates through long-term exploration and attempt, and multiple experiments and endeavors, and in order to solve the above technical problems, the technical scheme provided by the invention is to provide a method for promoting the updating of artificial forests, which comprises the following steps:

step 1) cleaning litter on the forest promotion land to expose part of the forest land ground;

and 2) sowing forest seeds on the cleaned bare ground.

According to a further embodiment of the method for promoting the renewal of the artificial forest, in the step 1), the forest land is a larch forest in North China, and the forest stand density of the forest land is controlled to be 1000-3000 h.hm^-2。

According to a further embodiment of the method for promoting the renewal of artificial forests, in the step 1), the time for cleaning the litter on the forest promotion land is 5 months in the first ten days per year.

According to a further embodiment of the method for promoting the renewal of artificial forests, in the step 1), the mode of cleaning the litter is strip cleaning or ditch cleaning.

According to a further embodiment of the method for promoting the regeneration of the artificial forest, the strip-shaped cleaning is to clean a plurality of strips with the width of 10-100 cm on the ground of the forest land. Further, the strips are arranged in parallel, and the distance between every two adjacent strips is 80-100 cm.

According to a further embodiment of the method for promoting the regeneration of the artificial forest, the ditch-shaped cleaning is to clear the litter at the ditching position and open the sowing ditch at the same time; the width of the sowing ditch is 5-15 cm, the depth is 0.5-2 cm, and the interval between the ditches is 80-100 cm.

According to a further embodiment of the method for promoting the renewal of artificial forests, the sowing trenches are arranged in a grid.

According to a further embodiment of the method for promoting the renewal of the artificial forest, in the step 2), the sowing time is from the end of the seed rain to the middle of 6 months in the current year after cleaning the litter, and the sowing is performed in rainy days.

According to a further embodiment of the method for promoting the regeneration of the artificial forest, in the step 2), the seeding density is 220-280 m^-2。

According to a further embodiment of the method for promoting the renewal of artificial forests, in the step 2), the selected seeds are sown as seeds treated by outdoor natural snow; in the step 2), soil covering or leaf covering is carried out after sowing.

Compared with the prior art, one of the technical solutions has the following advantages:

a) the method can obviously improve the update grade, the update density and the sowing germination rate of the artificial forest, and experiments prove that the update density can reach 8633.33 strains hm under the furrow-shaped treatment in the method^-2The germination rate of the seeds can reach 1.79 percent.

b) Compared with the existing artificial afforestation technology, the workload and the updating cost are greatly reduced. The furrow cleaning promotion accounts for not more than 45.35% of the bare-rooted seedling afforestation cost and not more than 19.72% of the container seedling afforestation cost. The strip-shaped cleaning agent accounts for not more than 96.10% of the cost of bare-rooted seedling afforestation and not more than 41.78% of the cost of container seedling afforestation.

Drawings

Figure 1 is a schematic of the fracture design in example 1.

FIG. 2 is a schematic diagram of band cleaning and furrow cleaning in embodiment 1 of the method for promoting forest renewal of the present invention. The left figure is a belt-like cleaning and the right figure is a gutter-like cleaning.

FIG. 3 is the proportion details of seedlings of different seedling ages in 2 years in example 1.

FIG. 4 is a comparison of the seedling ground diameter at different times in example 1.

FIG. 5 is a comparison of seedling heights at different times in example 1.

FIG. 6 is the variation of the seedling growth index in the growing season in example 1.

FIG. 7 shows the updated seedling density in 2 years in example 1.

FIG. 8 is the dynamic change in density of surviving seedlings in growing season in example 1.

FIG. 9 is a comparison of the germination rates of seeds in the respective treatments under artificial sowing in example 1.

FIG. 10 is the dynamic change in density of surviving seedlings in growing season in example 1.

Detailed Description

The following description will be given with reference to specific examples.

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the embodiments of the present invention will be described in detail and completely with reference to the accompanying drawings. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention. Thus, the following detailed description of embodiments of the invention is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention.

Example 1

The method for promoting the regeneration of the artificial forest described in this embodiment uses the artificial pure forest of larch north China in the area 31a of the sakhan as the test object for promoting the regeneration research.

1. Larix principis seeding test process

1.1 preliminary preparation

(1) Test seeds

The test seeds are purchased from a good seed seedling breeding field of the Yuanshan mountain forest of the State forest farm management office of the Loulan surrounding field of Hebei province in 11 months in 2019, and are stored in a refrigerator freezer at the temperature of (-15.31 +/-1.70) DEG C. The detailed parameters of the purchased improved variety are shown in a table 3, the measuring method refers to GB2772-1999 and forest seedling quality inspection technology, and the measuring time is 2019 and 12 months.

TABLE 3 basic parameters of the improved variety of Larix principis-rupprechtii

Note: mean ± standard deviation. The same applies below.

1.2 study of the Effect of different forest stand densities, litter treatment methods and seed sources

1.2.1 test plot selection

Selecting 31a larch artificial pure forest in North China as a research object of the research promotion. In 5 months 2019, the sample plots of the artificial forest under 3 intermediate cutting strengths were selected as the test sample plots of the present application. The way of designing the thinning intensity and the thinning time of the same are the same. The size of the sample is 20m × 20m, and the number of test repetitions is 3, for a total of 9 fixed test samples.

Table 4 shows the basic forest stand information obtained by searching the past forestation data and the sample plot survey. Wherein, for the convenience of the following description, the fixed test sample plot is sequentially numbered TN from small to large according to the principle of forest stand density_a、TN_bAnd TN_cAnd (4) showing.

Table 4 basic forest stand information table of fixed test sample plot

1.2.2 Split zone design of experiments

(1) Variable design

The study for promoting crop growth adopts a test design as a fissure area design, and test variables are forest stand density, litter treatment mode and 3 seed sources.

The main treatment is forest stand density, 3 types are counted, and the detailed numerical values refer to table 4.

The side treatments were litter treatment methods, 4 in total, and were blank Control (CK) without any litter cleaning and 3 treatments including litter cleaning, respectively: full clean (CC), strip clean (BC), and trench clean (SC). 4 different litter treatment modes are randomly arranged in any sub-area of 10m multiplied by 10m in the same fixed sample, a schematic design diagram of the splitting area is shown in figure 1, and the different sequences of the 4 types of litter treatment modes in figure 1 show that the litter treatment modes are randomly arranged in the sub-area. The difference in seed source was achieved by using the same trial plot for different years. After the sample plot is cleaned in 2019, the forest stand is naturally updated only by the seeds planted naturally; the renewed seeds in 2020 come from artificial sowing.

Thus, there are a total of 12 treatment combinations.

(2) Litter cleaning criteria

Since the CK group did not perform any treatment on the litter, only 3 kinds of the operation criteria for litter cleaning treatment are described here.

The cleaning time is carried out in the last 5 months of the year, at which time the seeds have not yet germinated. Due to uncontrollable factors occurring in 2020, the cleaning time of the year is postponed to the first 6 th of month.

The tool for cleaning the litter uniformly comprises a steel fork, an iron hoe and an iron rake 3.

CC cleaning with cleaning area of 100m²And the soil on the ground surface in the forest is clear and visible after cleaning, the thickness of the residual litter on the ground surface is not more than 1cm, and the raked litter is accumulated outside the sample plot. BC cleaning, wherein the specification of each cleaning zone is that the length multiplied by the width is 10m multiplied by 1m, the zone spacing is 1m, therefore, a sub-zone is 5 cleaning zones in total, and the cleaning area is 50m half of the overall cleaning area²And obviously exposing soil on the cleaning belt, controlling the thickness of residual litter on the ground surface to be below 1cm, and accumulating the cleaned litter on an untreated belt. SC cleaning, cleaning the litter at the ditching position, and simultaneously, ditching 20 seeding ditches with the depth of about 1cm, the length of each ditch being 10m, the width of each ditch being about 10cm, the interval between every two ditches being 90cm, and one sub-areaCleaning a ditch: 10 longitudinal and 10 transverse, the total cleaning area is 19m². Fig. 2 is a schematic diagram of the effects of BC cleaning and SC cleaning, where a gray area in fig. 2 is a deposition area of litter in the sub area, a white area is a cleaning area of litter in the sub area, and the labeled numerical values in the diagram are only test parameters and recommended parameters in this embodiment, and are not limited uniquely.

(3) Standard for sowing

The artificial sowing time is 6 middle of 2020, and the sowing is carried out in the last rainy day after the completion of the treatment of the litter. The seed spreading amount is 1.50 g.m^-2The seeding density is about 254.15 grains m through the conversion of thousand grain weight of improved seeds^-2. The seed quality is kept consistent through a weighing method, an instrument used for weighing is an electronic balance, and the precision is 0.001 g. In summary, details of the split zone design after the various treatments are shown in table 5.

TABLE 5 plot treatment details of the split zone design

1.2.3 update seedling investigation

In this embodiment, the updated seedling survey requirements are as follows:

(I) investigation mode

In view of the current situation of natural poor updating in the China North China larch forest in the Shihan dam region, the updated seedlings in the sample plot are comprehensively investigated in two growing seasons of 2019-2020.

(II) survey content and methods

The investigation content comprises the updated seedling level, the updated frequency, the seedling age distribution, the growth condition, the updated seedling quantity and density, the updated grade, the updated dynamic state, the survival rate and the germination rate.

Firstly, updating the seedling level

The updated seedling level is defined according to the forest level division standard issued by the national forestry agency in 2003 (national forestry agency, 2003). The updated seedling in the standard comprises 2 levels of seedlings and saplings, and the defined standard is shown in table 1.

TABLE 1 forest layer division Standard

Note: in the table, "H" represents the height of the seedling or the height of the tree; "DBH" means the diameter at breast height.

Update frequency

The update frequency is calculated according to the formula (1-1), and the calculation result is retained to a bit.

Update frequency (%) — number of sample plots appearing in updated seedling/total number of survey sample plots × 100 (1-1)

Distribution of seedling age

The seedling age is judged according to the gathered leaf marks, and the principle is equivalent to a method for judging the branch age through bud scale marks. Seedlings of 1 year, 2 years and higher are expressed by 1a, 2a and 3a + respectively, the distribution of the seedling ages is calculated according to the formula (1-2), and the calculation result is kept in one place.

Seedling age distribution (%) -updated seedling number per sample plot updated seedling total number X100 (1-2)

The 3-point survey was conducted only 1 time per growing season.

Growth conditions

The growth condition comprises two aspects of ground diameter and seedling height. Considering that larch in the area of the Han's dam has short growing season and slow seedling growth, the ground diameter and seedling height are measured only in the early and late growth stages. The early growth data are measured shortly after the seedlings germinate, the late growth data are measured uniformly when the seedlings are dormant at the end of the growing season, and the difference between the two sets of data represents the growth amount of the seedlings in the whole growing season. The ground diameter and the seedling height are measured by using a vernier caliper, the reading is accurate to two decimal points, and the unit of the ground diameter and the unit of the seedling height are respectively mm and cm.

Fifthly, the quantity and the density of the seedlings are updated

At the end of each month of the growing season, the number of surviving renewed seedlings, the number of newly born seedlings and the number of dead seedlings in the test plots were investigated, respectively. And calculating the updated seedling density, evaluating the update grade, drawing the update dynamic state and calculating the survival rate. Wherein, the new seedlings are marked in time to avoid repeated statistics; the death seedlings are subjected to field investigation to preliminarily judge the death reason. The updating density is calculated according to the formula (1-3), and the result is reserved to the two digits after the decimal point.

Renewal density (strain hm)^-2) Number of updated seedlings/area of sample plot x 10000 (1-3)

Update grade

The update ranking is based on the evaluation standard of the update ranking of the natural forest in the forest resource planning and design survey main technical provision made by the national forestry agency in 2003, as shown in table 2.

TABLE 2 evaluation criteria for renewal grade of natural forest (Unit: strain. hm)^-2)

Note: in the table, "ρ" represents the update density.

Seventhly, update the dynamic state

In the past research, on the update dynamic description of other tree species, the update dynamic is generally expressed by the ratio of the number of update seedlings in different age classes or height classes. For example, the updated seedlings are classified into 3 levels according to the seedling height of 50cm or less, 50cm < seedling height of 100cm or less, and seedling height >100cm, and the update dynamics under the forest is expressed by the ratio of the number of updated seedlings in the 3 levels. The number of larch seedlings in North China shows a large decrease in growth between months in the growing season, but dynamic changes in this respect are rarely described. Accordingly, the dynamic change of the density of the surviving seedling of the larch north China is drawn during different months under the ground in the growing season.

Eighty percent survival rate of renewed seedlings

The survival rate in the growing season and the survival rate in the overwintering season can be calculated according to the formulas (1-4) and (1-5), and the calculation result is retained to a percentile. It should be noted that the defining criteria for the survival of seedlings before overwintering in the test are: dead seedlings are counted as 100% determined dead seedlings, and all indeterminate and 100% determined live seedlings are judged as live seedlings.

Survival rate (%) before overwintering in growing season is the number of surviving seedlings/total number of seedlings in the same plot x 100 (1-4)

Number of surviving seedlings after overwintering/number of surviving seedlings before overwintering x 100 (1-5)

Ninthly sowing germination rate

The calculation of the germination rate of seeds under each treatment combination in the artificial sowing in 2020 is added, and the aim is to explore the utilization rate of the seeds after the artificial sowing under each treatment. The calculation is referred to the formulas (1-6), and the calculation precision is also controlled in percentile. The germination amount of the seeds in the formula is the number of 1a seedlings measured in 2020, and the sowing amount of the seeds can be seen in table 5.

Seed germination rate (%) ═ seed germination amount/seed sowing amount × 100 (1-6)

1.3 Effect study under different seed treatment modes

1.3.1 test plot selection

Selecting 31a larch artificial pure forest in North China as a research object of the research promotion. In 5 months 2019, the plots in the artificial forest under 1 kind of thinning strength (TN) were selected as the test plots in the present application. The way of designing the thinning intensity and the thinning time of the same are the same. The size of the sample is 20m × 20m, and the number of test repetitions is 3, for a total of 3 fixed test samples. The basic forest stand information for the fixed plots is shown in table 6.

Table 6 basic forest stand information table of fixed test sample plot

1.3.2 Single factor test design

The test method was to divide the 20m × 20m samples into 4 blocks of 10m × 10m samples. In 6 months of 2020, 1 complete cleaning of litter in the permanent plot was carried out, the method and standard being identical to 1.2.2. After the cleaning, the seeding density is 1.50 g.m^-2。

The test variables were seed treatment pattern, totaling 4 classes, as shown in table 7. And, each processing mode is randomly arranged in any sample in the same fixed sample.

Table 74 seed treatment

1.3.3 update seedling investigation

(1) Investigation mode

As with 1.2.3, the renewed seedlings within the plot were investigated comprehensively during the 2020 growing season.

(2) Survey content and method

The investigation content only comprises the updated seedling number of the larix huabeiensis, and the updating grade is evaluated, the updating density and the germination rate are calculated, and an updating dynamic graph is drawn. The specific investigation method and calculation formula are referred to 1.2.3.

2 results and analysis of research on effects of different forest stand densities, litter treatment modes and seed sources

2.1 update frequency of seedlings at all levels

The 3 density artificial forests in the familiar forest M still have limited natural renewal capacity after the litter is cleaned, and natural renewal of different degrees exists in the forests. And the updating seedling levels are all seedlings, no larval tree of the larch of North China exists, and the updating frequency of the larval tree is 0. The seedling group is mainly composed of seedlings under 5 years old, mainly 1a seedlings, and the age of the perennial seedlings is 2 years. The natural update frequency of each level of seedling of the Chinese larch is shown in table 8.

TABLE 8 renewal frequency of seedlings at all levels of larch forest in North China

Note: there is an updated plot designation "√"; the sample plot without update is not marked; the updating frequency of each treelet is 0, and is omitted from the above table.

As can be seen from table 8, the natural renewal status of M forest performed better in terms of renewal frequency.

First, at 1a seedling's renewal frequency. Even when the seedlings are naturally planted in 2019, new seedlings appear under 3 density forest divisions, namely the near-mature forest has certain fructification and natural renewal capacity. Wherein TN_aAnd TN_cThe 1a seedling renewal frequency under the density reaches 100 percent, and the only 1a seedling which does not appear is TN_bCC treatment at density where 1a seedling turnover frequency is only 75%. On the one hand, this may be due to the small number of seeds in the part of the sub-area where the process is located; on the other hand, it may be that the understory seeds in the sub-area are cleaned up together with the litter layer. And when the seedlings are sowed manually in the next year, 1a seedlings are updated in all the treatments of all the densities, and the updating frequency reaches 100 percent.

In terms of the frequency of renewal of perennial seedlings, the first year is slightly worse, only TN, due to the large disturbance of the ground_bAnd TN_c2a seedlings remained in the CK treatment at the density, and no perennial seedlings existed in the remaining subplants. This is probably due to the fact that with extensive litter clearing, also perennial seedlings originally present in the san are removed in the ground disturbance along. The 2a seedling renewal frequency was only 25% at the highest at each density, while the 3a + renewal frequency was 0%. Therefore, the large-scale cleaning of the surface withered material layer is damaged for the original renewal condition. But in 2020, due to TN_aCK and BC treatment at Density, TN_bCK treatment at Density and TN_cThe 1a seedlings in BC treatment under density successfully overwinter, so that 2a seedlings appear in the second year in the treated plots, and the updating frequency is increased to be in the range of 25-50%, which is improved compared with the first year. At the same time, TN_cAlso, the CK treated 2a seedlings at density had succeeded in promoting 3a seedlings with a renewal frequency of up to 25%. In the remaining treatments, since all seedlings at all ages died after one growing season and the seedling ages stopped growing, the treatments were carried out in the same mannerThe turnover frequency of perennial seedlings does not change the second year.

In terms of overall renewal frequency of seedlings, due to TN_bCC treatment at density was not naturally renewed in 2019, no seedlings of any age were present, thus TN_bThe overall update frequency is only 75% at the lowest. The overall frequency of the frequency reaches 100% in other periods and at various densities.

In conclusion, in the aspect of updating frequency, the updating capacity of the artificial forest with 3 densities is not greatly related to the density of the forest stand on the whole; but in the forest stand with stronger updating capability, the overall updating frequency of the forest stand is improved by disturbing the ground to a certain degree and manually sowing seeds.

2.2 distribution of seedling ages

In this test, the distribution of the seedling ages of seedlings in each plot over 2 years is shown in FIG. 3. As can be understood from FIG. 3, TN except in 2019_bExcept that the regeneration does not occur in the CC treatment under the density, all the seedlings are mainly 1a seedlings in any regeneration sample in 2 years, and the ratio of the seedlings is at least more than 90%. Moreover, no 3a + seedlings were present in the plots in 2019, and 2a seedlings were present at a low rate of not more than 10%. The case where all seedlings were 1a seedlings was also more frequent. The main reason is due to the cleaning of litter, which indirectly affects the number of perennial seedlings.

In the information conveyed in table 8, however, the frequency of renewal of perennial seedlings showed an upward trend in 2020, but natural renewal of the second year was greatly promoted due to artificial sowing, when the proportion of 1a seedlings was rapidly increased to a level of at least 98%. Correspondingly, the proportion of perennial seedlings is greatly reduced, and the proportion of the seedlings does not exceed 3 percent. Therefore, in the future research of the promotion experiment, attention should be paid to the aspects of further improving the survival rate of the under-forest renewed seedlings, promoting the growth of the under-forest seedlings and the like.

2.3 growth conditions

In the analysis of the growth conditions, seedlings of each seedling age in the plot were also discussed as a whole. In view of no update in part of the subzones after 2019 litter cleaning, the seedling growth data of the subzones are lost. Therefore, the comparison of growth conditions is only performed between stands of different densities.

(1) Ground diameter of seedling

Respectively making a comparison graph 4 of the ground diameters of seedlings under the artificial forests with different densities at the initial stage and the final stage of growth within 2 years, wherein in the graph 4, capital letters represent the difference between the densities, and lower case letters represent the difference between the years; letter differences indicate significant differences with a significance level of 0.05. TN for 2 years_a、TN_bAnd TN_cThe ground diameters of seedlings in the dense stand were 0.81mm, 0.76mm and 0.89mm and 0.77mm, 0.76mm and 0.82mm, respectively, at the initial stage of growth, and 0.62mm, 0.55mm and 0.57mm and 0.47mm, 0.43mm and 0.48mm, respectively, at the final stage of growth. Analysis shows that the ground diameters of seedlings under 3 density forest stands for 2 years have no obvious difference between the early stage and the late stage of growth (p)>0.05), the law expressed as a whole is TN_aOr TN_cThe seedling with the largest ground diameter under the density is TN when the ground diameter is the smallest_bAt density of (p)>0.05)。

The situation of the ground diameter of the seedlings in the same density forest stand is different when the ground diameter is compared with the ground diameter in the same period of different years. The ground diameter of the seedling in the early growth stage in 2019 is slightly larger than 2020, but the difference is small (p>0.05), e.g. 2019 TN_aThe diameter of the seedlings at the early growth stage under the density is 0.81mm, and the diameter of the seedlings at the early growth stage is not remarkably reduced to 0.77mm by 2020. The difference of the seedling ground diameter at the final growth stage between two years reaches a significance level, and the ground diameters of the seedlings under 3-density forest stands are larger at the final growth stage in 2019 (p)<0.05), likewise in TN_aFor density example, the seedling ground diameter at the end of growth in 2019 is 0.62mm, which is significantly larger than the 0.47mm at the end of growth in 2020 (p)<0.05)。

(2) Height of seedling

Respectively making a comparison graph 5 of the height of seedlings under the artificial forests with different densities at the initial stage and the final stage of growth within 2 years, wherein capital letters in the graph 5 represent the difference between the densities, and lower case letters represent the difference between the years; letter differences indicate significant differences with a significance level of 0.05. Continuous 2 years time TN_a、TN_bAnd TN_cThe heights of seedlings under the dense forest stand were 2.69cm, 2.75cm and 2.83cm and 2.87cm, 3.12cm and 3.35cm respectively at the initial stage of growth, and 3.03cm, 3.08cm and 3.16cm and 2.96cm, 3.23cm and 3.37cm respectively at the final stage of growth. Analysis shows that the height of seedlings under 3 density forest stands for 2 years does not have obvious difference at the early and late stages of growth (p)>0.05) and the height of the seedlings in 2 years is in positive correlation with the density of forest stands at the early and late stages of growth.

When the seedling height of seedlings under the same density forest stand is compared between different years in the early and late growth stages, TN is present and TN is present only_aThe height of seedling at the final stage of growth under the density is 2.96cm in 2020 and is slightly less than 3.03cm in 2019 (p>0.05), while the seedling height of seedlings at each period of other forest stand density is slightly increased in the second year (p)>0.05), and TN_cThe height of seedlings at the early growth stage under the density is 3.35cm in 2020, which is obviously greater than the height of seedlings at 2.83cm in 2019 (p)<0.05)。

(3) Change in growth indicator

The results of comparisons of seedling growth indicators at the beginning and end of the growing season for 2 consecutive years in forest stands of different densities in this promotion test are shown in FIG. 6.

It can be found that the ground diameter of the seedlings under the forest stand of each density is smaller at the final growth stage than at the initial growth stage, and the growth amount is negative. After the test, the reduction of the ground diameter of the seedlings under 3 forest stands in 2019 is not obvious (p)>0.05), e.g. 2019 TN_aThe seedling ground diameter is not remarkably reduced from 0.81mm at the early stage of growth to 0.62mm (p) at the late stage of growth under the density>0.05). While the reduction of the under-forest seedling ground diameter is significant in 2020 (p)<0.05), likewise in TN_aFor example, the diameter of the seedling is remarkably reduced from 0.77mm at the early stage of growth to 0.47mm (p) at the late stage of growth in 2020 at a density<0.05). The atrophy of the ground diameter may be caused by stem lignification, dehydration atrophy. In contrast, the newly germinated seedlings are saturated with water and have more plump and thick ground diameters, which is a possible reason for the fact that the ground diameters of the seedlings do not rise and fall reversely in the growing season.

In the aspect of seedling height, the seedling height of all the seedlings in the forest stand is within eachThe value at the end of the year growth is larger than that at the early growth, but the growth of the seedling height is not obvious (p)>0.05), e.g. 2019 TN_bThe seedling height at the density is increased from 2.75cm at the early stage of growth to 3.08cm at the end stage, and TN is TN at 2020_cThe seedling height of seedlings under the density is increased from 3.35cm at the early growth stage to 3.37cm at the terminal stage, and the like, and the increase amount is very limited. This indicates that there is some degree of growth of the seedling through the accumulation of substances from photosynthesis in one growing season, but the accumulation of substances from the seedling in 1 growing season is very limited.

2.4 update level and update Density

When analyzing differences in natural renewal promoting effects between treatments under different measures, it is also clear here that all seedlings present in the growing season are used in order to measure the overall effect of the renewal promoting measures, given that the number of seedlings varies to a greater extent in the growing season.

(1) Update level

In the manual update promotion test, the natural update grade of the larch forest in north China for 2 years is judged according to the evaluation standard of the update grade of the natural forest made by the national forestry bureau. Details of the update levels of the respective processes are shown in table 9.

Update rating of larch North China in Table 92

In the observation of 2019, since the seeds updated in the current year mainly come from the natural seeds of forest trees and the seeds distributed on the surface of the forest land are greatly disturbed along with the various cleaning of the litter, the natural updating grades in the sub-areas of 3 densities of forest lands are in a bad state under the combined influence of various factors, without exception.

In 2020, a large amount of viable seeds are artificially spread, so that the barrier factor of insufficient seed quantity required by natural updating in the forest land is solved, and the updating grade under each treatment is greatly improved on the whole. Especially in CC, BC andin the subzone where the 3 treatments of SC were located, after litter cleaning, the sown seeds could directly contact the soil, with their natural renewal grade at least raised to a moderate level, and predominantly to a good level. But at TN_aAnd TN_bIn the CK processing at density, the update level may be in a state of poor update. Under sufficient seed sources available for renewal, the renewal grade has not been raised due to the huge physical barrier caused by the heavy layer of litter.

Therefore, cleaning the litter is a crucial step for improving the natural renewal grade of the larch forest in North China.

(2) Density of update

The comparison of the update densities in this test is shown in FIG. 7 by ANOVA. Fig. 7 shows the updated seedling densities in 2 years, with capital letters in fig. 7 indicating the differences between litter treatment regimes and lower case letters indicating the differences between densities. Letter differences indicate significant differences with a significance level of 0.05. In 2019, under the condition of natural seeding, the influence of the litter treatment mode on the update density reaches an extremely remarkable level (p)<0.01), forest stand density and interaction have less impact on update density (p)>0.05). Forest stand density is TN as a whole_c191.67 strains hm at density^-2Update density maximum, TN of_b141.67 strains hm at density^-2Minimum update density (p)>0.05); when compared under the same litter treatment measure, the update densities of different forest stand densities are high and low, but the differences do not reach the significance level (p)>0.05). Taking CC treatment as an example, TN_a～TN_cThe updated density of the forest stand density is 66.67 strains hm^-20.00 strain hm^-2And 33.33 strains hm^-2The overall difference is not great (p)>0.05)。

In the litter treatment method, 400.00 strains hm were treated with CK in its entirety^-2The renewal density of (A) is significantly greater than the renewal density (p) under 3 litter cleans<0.05), whereas the difference in refresh density between 3 litter cleans is small (p)>0.05) and 155.56 strain hm under the side zone where BC treatment is located^-2Of (2)The body renewal density was the highest, and the CC treatment was 33.33 strains hm^-2The update density of (2) is minimum; when the comparison is carried out under the forest stand with the same density, TN is removed_aIn addition to the dense forest stands, the density of updating by CK treatment is higher, but only at TN_cThe difference of updated density among different treatment modes under the forest stand of the density reaches the significance level, 566.67 strains hm are treated by CK^-2The renewal density of the fertilizer is obviously more than 33.33 strains per hm under the cleaning of 3 litter^-266.67 strains hm^-2And 100.00 strain hm^-2Update density (p) of<0.05) and at TN_aUnder the forest stand with the density, 300 strains hm are processed by BC^-2Has the highest update density which is slightly larger than 266.67 strain hm treated by CK^-2Update density (p) of>0.05)。

In the case of artificial sowing in 2020, only the litter processing mode (p) with significant effect on the renewal density<0.01), forest stand density and interaction have less impact on update density (p)>0.05). The different forest stand densities are TN as a whole_b5808.33 strains hm at density^-2Update density maximum, TN of_c5516.67 strains hm at density^-2Minimum update density (p)>0.05); under the same litter treatment measures, when forest stands with different densities are compared, the magnitude rules of the updated densities are different, but the difference does not reach the significance level (p)>0.05), e.g. under SC treatment, TN_a～TN_cThe updated density of the forest stand density is 7200 plants hm^-211100 strain hm^-2And 7600 strain hm^-2Are not significantly different from each other (p)>0.05)。

In the litter treatment method, the average of 8633.33 strains hm was measured under SC treatment^-2Has the highest update density, is processed by BC, and has the update density of 6633.33 strains hm^-2And both of these treatments are similar to CK treatment 2166.67 strain hm^-2Form a significant difference (p) between the update densities of<0.05), whereas of the 3 litter washes only the difference between CC and CK was small (p)>0.05), and the average renewal density in CC treatment was 5100.00 strains hm^-2At the same time, the overall difference in refresh density between the 3 cleaning modes is also small (p)>0.05); are in the same placeIn the forest stand with density, the order of updating density is approximately the same between different litter processing modes, but TN is adopted_aThe density of the forest was determined by BC treatment of 7466.67 strains hm^-2The update density of the strain is slightly larger than that of SC treatment 7200 h.hm^-2Update density (p) of>0.05) and only at TN_bThe difference between the updated densities of the different treatments at the density at which the seedling density of the subplot where the SC treatment was located was 11100.00 h hm was significant^-2Is obviously greater than 1833.33 strain hm treated by CK^-2Update density (p) of<0.05), and 6000.00 strain hm in BC and CC treatment^-24300 strain hm^-2Does not have significant update density difference (p)>0.05)。

Update density variation

Since the above analysis does not quantitatively analyze the difference in update density between different years in the same sample, it is summarized here. As shown in Table 10, after examination, the update density of larch north China under each treatment is basically remarkably improved in the second year (p)<0.05), the effect of artificial sowing on improving the renewal density under larch forest of North China is obvious, such as TN_aThe update density in CC treatment under density was 66.67 strains hm in 2019^-2Remarkably improved to 5700 strains hm in 2020^-2，TN_cThe update density in SC treatment under density is 100.00 strains hm in 2019^-27600 strain hm which is remarkably promoted to 2020^-2And the like. However, there are exceptions to individual processing, which may be caused by large differences between granules. The reason for the difference is determined by multiple factors such as late sowing time, under-forest vegetation, human interference and the like, and further research is needed.

TABLE 10 comparison of update Density over 2 years

2.5 update dynamics

The dynamic changes in this test are shown in FIG. 8, which shows that the surviving seedlings of Larix principis have a large fluctuation in the growing season and that there are some similarities and differences between the dynamic graphs due to differences in the way the litter is treated and the source of the seeds.

After 2019, after the withered and fallen objects are cleaned, the naturally planted seeds of the forest trees start to germinate from the bottom of 6 months, at the moment, seedlings in sample plots under various treatments are very rare, and only TN is obtained_b、TN_c1a seedlings appeared in CK treatment under two densities of forest stands, and the density of the surviving seedlings is only 66.67 h.m^-233.33 strains hm^-2. And in the next two months, the under forest renewal density increases rapidly. And the slope of the broken line in the graph reflects that the time from the bottom of 6 months to the bottom of 7 months is the peak period of germination, and the germination rate is reduced from the bottom of 7 months to the bottom of 8 months. Meanwhile, it can be seen that the refresh density under the CK processing under the basic density forest division is always kept at a higher level in the period, and particularly, a larger difference is kept between the refresh density under the CC processing. Such as at TN_bThe density of the survival seedlings at the bottom of 7 months in 19 years in the CK treatment under the forest stand is 366.67 strains hm^-2Under the same-period and same-density stand, the density of the living seedlings in the CC treatment is only 0.00 strain hm^-2. By the 9 months, as seeds no longer germinated in the woodland and seedlings in the plot died in large numbers, the viable seedling density declined continuously from this point forward, due to the end of the growing season.

In 2020, because artificial sowing greatly increases the number of viable seeds in the forest land, under-forest renewal is no longer bound by the seed number, and the promotion efficiency of various litter treatment measures can be released, litter can be one of the main barrier factors in the 2020 renewal process. But only TN is obtained when the seeding time is later in the year to the end of 6 months in 2020 due to uncontrollable factors_bIn minor treated subregions such as SC treatment and the like under dense forest stand, 1a seedlings, TN appear_b-BC、TN_b-SC and TN_cThe density of the surviving seedlings in the SC is only 100.00 h.hm respectively^-2600.00 strain hm^-2And 100.00 strain hm^-2The update density is still at a relatively poor level. While other treated seeds should remain dormant orIn the germinating state, only the seedlings which die due to the failure of overwintering are present in this type of treatment, so that the number of surviving seedlings drops to a very low value again.

Similarly, the germination peak of seeds in the litter treatments other than SC treatment was delayed by about 1 month in 2020 due to the late sowing time, and the seeds of the other 3 treatments were germinated approximately in the period from the bottom of 7 months to the bottom of 8 months, and the number of germination was small at the bottom of 7 months. Such as at TN_cThe density of 8-month-bottom survival seedlings in BC treatment under the density reaches 6200.00 strains hm^-2The density of the survival seedlings at the bottom of 7 months is only 1300 plants hm^-2. SC treatment was carried out until 7 months, and the germination was largely consistent with the 19-year update. In addition, SC treatment also remained essentially at the highest level in renewal density during the growing season, TN_a～TN_cThe density of the survival seedlings at the bottom of 8 months in SC treatment under the forest stand density reaches 6600.00 plants hm^-27900.00 strain hm^-2And 5800.00 strain hm^-2. In contrast, in 2020, the lowest update density was the CK treatment, and the density of surviving seedlings at the end of 8 months in the CK treatment at 3 densities was only 1933.33 hm^-21133.33 strain hm^-2And 2133.33 strain hm^-2. Therefore, SC treatment can promote the updating density and updating grade, and is beneficial to promoting the early germination of the larch seeds in North China and prolonging the growing season; the inference that litter may be a major obstacle in the 2020 update process is also verified. At the end of 9 months in 2020, a large number of seeds still germinate in succession in a part of the forest land, and these germinated seedlings cannot be safely overwintering in the end-of-season growth period. Therefore, the late sowing can cause great waste of the seedlings to the harmful part of the natural updating. In the future, the research on relevant aspects should be combined with the updated dynamic result of the experiment to advance the sowing time by about 1 month. But also needs to be noticed that the seedling can be protected from the harm of night frost after coming out of the soil.

2.6 survival rate

The survival rate comparison in the promotion test is in 2 aspects, namely the survival rate comparison of the growing seasons under the forest stand with various densities within 2 years and the survival rate comparison of the growing seasons under the forest stand with different densities and the processing mode within 2020.

In comparison of survival rates in growing seasons for each density forest division over 2 years, TN is shown in Table 11_a～TN_cThe survival rates of 3 densities of forest stands in the growth season of 2019 and 2020 are respectively 70.28%, 77.22% and 49.65% and 73.93%, 62.11% and 62.26%, and have no obvious difference (p is the survival rate of the forest stands in the growth season of 2020)>0.05), and the survival rate difference of the growing season is smaller among the forest divisions with different densities in the same year (p)>0.05). It can be seen that forest stand density has less influence on the survival rate of seedlings in the growing season, while seeds from different sources show comparable quality in the survival rate of the growing season.

Comparison of survival rates of forest stands at various densities within 112 years

Note: capital letters indicate differences in density and lowercase letters indicate differences between years. Letter differences indicate significant differences with a significance level of 0.05.

The results of comparing the survival rates of seedlings in the growing season in 2020 with different densities of stands and treatments are shown in Table 12. Analysis shows that the influence of each factor on the survival rate of the growing season does not reach the significance level (p)>0.05). Forest stand density in TN_aThe average growth season survival rate at density is greatest at 73.93%, whereas TN_bSurvival in the growing season at 62.11% minimum at density (p)>0.05); the difference of the survival rate of the forest stands with different densities is not obvious when the same litter treatment mode is adopted (p)>0.05), e.g. under CC treatment, TN_a、TN_bAnd TN_cThe survival rate of the growing season under the density forest stand is 65.85%, 85.22% and 60.60%, respectively, and the difference between the survival rates is not significant (p)>0.05). On the other hand, in comparison with the way of treating litter, the survival rate in the growing season is the highest with 71.75% in average for BC treatment and the survival rate is the lowest with 56.18% in average for SC treatment (p)>0.05); survival rate ratio of seedling growing season between litter processing modes in same forest standIn time, the difference was not significant (p)>0.05). Such as at TN_bAt density, the survival rates of the growing seasons from CK treatment, CC treatment, BC treatment and SC treatment were 57.30%, 85.22%, 62.22% and 43.68%, respectively, and the differences between the treatment modes did not reach significant levels (p)>0.05)。

TABLE 122020 comparison of survival rates in growing season for different densities of forest stands and treatments

Note: capital letters indicate differences between litter treatment regimes, and lowercase letters indicate differences between densities. Letter differences indicate significant differences with a significance level of 0.05.

2.7 germination Rate

The germination rates of seeds in the treatments under artificial sowing in 2020 are compared with those in FIG. 9. Fig. 9 shows a comparison of germination rates of seeds in respective treatments under artificial sowing, and in fig. 9, capital letters indicate differences between litter treatment modes, and lower case letters indicate differences between densities. Letter differences indicate significant differences with a significance level of 0.05. Analysis shows that only the way of processing the litter has great influence on the germination rate of the seeds on the whole, and reaches a very significant level (p)<0.01), the forest stand density factor has little influence on the germination rate of seeds under the forest (p)>0.05). The forest stand density is TN as a whole_bThe average 0.75% seed germination under dense forest stand is slightly higher (p)>0.05)，TN_cAnd TN_aThe average germination rates of 0.60 percent and 0.59 percent of seeds under the dense forest stand are lower; when the germination rates of different density forest branches are compared under the same litter treatment mode, the difference of the germination rates is not large (p)>0.05), as in the CC treatment, the germination rates of the seeds of the forest stand with 3 densities were 0.22%, 0.17% and 0.21%, and the difference levels among them were not significant (p)>0.05)。

In the litter treatment mode, the under-forest seed germination rate of 1.79% on average under SC treatment was significantly higher than that under the other three treatments (p)<0.01) and the germination rates of the BC, CC and CK treated seeds decreased in sequence, the average germination rates of the seeds were 0.52%, 0.20% and 0.08%, respectively, but the differences among them were small (p)>0.05); when the germination rates of seeds are compared among different litter treatment modes under the same stand density, the rules are the same, and the germination rates of the seeds in the SC treatment and other treatments are different at least above the significance level (p)<0.05), e.g. at TN_cUnder dense forest stands, the germination rates of the seeds at 1.57% for SC treatment were significantly higher than those at 0.50%, 0.21% and 0.11% for BC, CC and CK treatments (p)<0.05), there was no significant difference in germination rate between the seeds of the last 3 treatments (p)>0.05)。

3 results and analysis of Effect-promoting studies under different seed treatment modes

Analysis of the previous data showed: under the condition of artificial sowing, the updating frequency is increased to 100%, the 1a seedling proportion is close to 1, the difference between the growth conditions of seedlings from different sources is small and the like, and the research results of the part in the test are similar to the above results, so that the detailed description is omitted. The data analysis results in the part are expanded in the aspects of update density, dynamics and the like so as to show different points of promoting the research results of the experiment.

3.1 renewal grade, renewal Density and Germination Rate

And (3) measuring the upgrading effect of the updating grade under different seed treatment modes by using all seedlings appearing in various plots in the growing season, and establishing the updating grade evaluation standard of the natural forest according to the standard. Table 13 shows that the natural renewal grade of larch north China was at least moderate and predominantly good in 4 seed treatments after the full cleaning of various underground surface litter layers in 2020.

As can be seen from the analysis of variance, the difference of the improving effect of the under-forest natural update density of the 4-item seed treatment mode reaches the significance level (p)<0.05), seed treatment mode ST₁Is prepared from 13400.00 strain hm^-2Has the highest update density, andand ST₃Strain Zhong 13266.67 hm^-2Update density of (ST)₄Strain Zhong 10833.33 hm^-2Has a refresh density significantly greater than ST₂4733.33 strains hm were treated^-2Update density (p) of<0.05), but ST₁And ST₃、ST₄The difference between the update densities is small (p)>0.05)。

It follows that in the case of using the same batch of seeds, suitable sowing time and germination acceleration measures contribute to an increase in the update density more than direct sowing, while the determination of suitable sowing time is slightly superior to the increase in the update density. Furthermore, because in ST₃And ST₄The difference of the updated density of the two seed treatment modes is not large, so that the snow preservation procedure can be properly considered and omitted in the actual production, and the labor cost is saved.

In the experiment, the cleaning modes of the litter are all comprehensive cleaning, and the seeding amount is completely equal. And only 1 seedling of 2a was present in all the plots, the comparison of the germination rates of the seeds in each plot was substantially equivalent to the comparison of the renewal density. The influence of the 4 seed treatment modes on the germination rate of the seeds also reaches a significant level (p)<0.05) by ST₁The seed germination rate of 0.53% under the treatment mode is highest, and is mixed with ST₃0.52% seed germination percentage, ST under treatment mode₄The 0.43% germination rate of the seeds is obviously greater than that of ST under the treatment mode₂0.19% seed germination (p) under treatment<0.05)，ST₁And ST₃、ST₄The difference in seed germination rate is small (p)>0.05). Accordingly, this content will not be separately described in section 1.

TABLE 13 update grade and update Density of Larix principis' Larix under different seed treatment modes

3.2 update dynamics

The dynamic variation of the density of surviving seedlings in each plot over the growing season for different seed treatments is shown in FIG. 10. From FIG. 10, it can be seen thatST₂The density of the survival seedlings in the growing season is kept to be the lowest level all the time, and the density of the survival seedlings in the growing season is 0-4100.00 strains hm^-2Relatively low range, and the germination trend of the seeds is different from that of the other 3 treatments, the concentrated germination time of the seeds is from the bottom of 7 months to the bottom of 8 months, and ST is in 1 month₂The density of surviving seedlings in the plot of the treatment site is 1366.67 strains hm^-2Quickly rises to 4100.00 strains hm^-2This is essentially consistent with the dynamics of germination of CC, BC and CK treated seeds in 2.5 at 2020 hand sowing. While the other 3 treated seeds mainly germinated within 1 month after the end of 6 months, which is more similar to the update dynamics of 2019 in 2.5, i.e. the sowing time in mid-6 months did not affect the timely germination of the seeds in the 3 groups of treatments.

ST₂The delay in seed germination was due to a late sowing time, but not the same reason for the earlier germination of the other 3 groups of seeds. ST (ST)₃And ST₄The treated seeds are gathered at the bottom of 6 months and germinate, because the seeds are subjected to germination acceleration before sowing, and can quickly enter a germination state after sowing; and ST₁The treated seeds are sown in the late stage of seed rain in 2019, so that a series of preliminary preparation works of seed germination such as water swelling can be completed before the end of 6 months, and further, a large amount of seeds can be germinated on time after the end of 6 months, as is common to naturally planted seeds.

Has the advantages that:

the larix dahurica forest has weak natural updating capability, and human intervention is necessary for promoting updating. The seed quantity and the litter are used as main limiting factors for natural updating of the larch in North China, and the application tries some methods to break the limitation of the two on updating and artificially promote the natural updating in the forest. The promotion effect of each measure is mainly to promote the quantity of the seedlings to be updated under the forest, and the best mode for artificially promoting natural updating under the test condition is evaluated and screened out by comparing the promotion effect differences of different measures.

A. Promotion of seedling quantity by promotion measures

For 2 years, the forest stand with 3 densities in the northern China larch forest in the region 31a of the Shihan damIn the method, updating is realized in the sample plot under each updating promotion measure, but the updating conditions are different among different updating promotion processes. In 2019, when the forest is naturally planted, the natural updating level under each treatment is in a bad state, but in 2020 artificial sowing, the 100% updating frequency of 1a seedlings is realized in each plot, the updating level is greatly improved, and the updating density is greatly improved. This further explains that seed number may be one of the major factors limiting the under-forest renewal of north China larch in the region of the sakhan dam. Whereas the under-forest renewal of 2019 mostly occurred in the CK treatment of uncleaned litter, and TN_bUnder the density forest, the CC treatment for completely cleaning the litter even does not occur. Meanwhile, the withered material layer is proved to be the main storage place of the larch seeds in the seed bank.

However, in addition to the aspects of renewal density, the renewal characteristics of other aspects between two years are compared, and it can be found that there is basically no obvious difference among different forest stand densities, litter treatment modes and seed sources, particularly the difference among forest stands with different densities is small, in terms of age distribution, growth conditions and growing season preservation rate of seedlings. Namely, each measure is not helpful to improve the quality of the updated seedlings under the forest, and only influences the quantity of the updated seedlings under the forest. Even the ground diameter value of the fine-breed seedling at the late growth stage of 2020 is obviously smaller than the ground diameter of the naturally planted seedling at the late growth stage of 2019, which may be due to the fact that the artificial sowing time is late, the seed germination is late, and the growth condition at the late growth season is poor in performance, and the sowing time is extremely important. The quality difference shown in the under-forest updating process is not large no matter the seeds naturally planted in the forest or the good seeds purchased, which means that when the natural updating is promoted by artificial sowing in future, the seeds can be purchased to replace the good seeds for scattering, so as to further reduce the cost for promoting updating.

B. Manually facilitating more optimal way of assessment

The effect of improving the number of seedlings in natural updating in the larix dahurica forest by treatment such as litter cleaning mode, artificial sowing and the like in the promotion test is obviously visible, but the respective promotion effects are slightly different. On the premise of ensuring good updating, the important purposes of saving manpower and capital are taken into consideration, and the best processing mode can be screened out from the updating promotion measures in the test so as to provide reference for subsequent researchers and provide reference for forest production practice.

First, this difference in boosting effect is manifested in the density of updates. Under the condition that the seeding rate per unit area is the same, the updating density of the CC treatment for cleaning the most withered plant area and the most seeding rate is smaller than that of CK, and is far inferior to the SC and BC treatment for cleaning the withered plant area and the least seeding rate. It can be seen that the larger the area that is not cleaned, the better the effect for promoting natural renewal by cleaning litter. The litter layer also plays an important role in keeping water and soil, maintaining surface temperature and nutrient circulation and the like in the whole forest ecosystem, and the functions can play a positive promoting role to a certain extent in the natural updating process, and the retention of litter with a certain thickness is helpful for reducing the freezing damage of winter seedlings and improving the moisture condition of dry soil. From the actual investigation, the seeds spread during the CC treatment were also found to be eaten by rodents in the plots in large numbers. This explains the reason why the update density of the CC process is the smallest among the 3 types of litter cleans, from the other direction. If effective measures can be taken to reduce the negative effects of animal feeding to some extent, this will likely contribute to an increase in the renewal density of the CC treatment.

Second, the difference is manifested in the update dynamics. In 2020, the germination dynamics of the seeds sown in the same batch can be consistent with that of the naturally planted seeds only by SC treatment, and compared with CK, CC and BC treatment, the germination time of the seeds planted by the treatment is about 1 month earlier. If the achievement is reasonably used and the seedlings are sowed in advance on the basis of the experiment, the growth season of 1a seedlings can be prolonged, more dry matters can be promoted to be accumulated in the first year by the new seedlings, the new seedlings can be favorably developed to perennial seedlings and young trees, and the natural updating can be finally and successfully realized. The SC treatment promotes the seeds to germinate in advance and shortens the germination time, probably because the seeds are in a litter trench, the seeds can directly contact with soil and can obtain the benefits of providing water retention and heat preservation for a litter layer. In the test of promoting the seed treatment mode to be more improved, the germination accelerating measure can also remedy the negative influence of germination delay caused by sowing in the middle of 6 months, and the updating dynamic performance of the treated seeds is consistent with that in 2019. But in contrast, the appropriate seeding time is more time and labor efficient. The seeds are sown after pregermination, so that the process that the seeds obtain germination conditions in forest lands is omitted, and the reason for keeping the updating dynamic consistency is probably. However, it should be noted that the germination phase of the seeds is dependent on continuous and stable moisture conditions. Therefore, the sowing of the seeds in the test, particularly the sowing of the seeds after the germination acceleration, is promoted in rainy days, so that the condition that the seeds are unfavorable for the regeneration, such as the bud flashing, is avoided. Meanwhile, the research also points out the advantages of soil covering in cold protection, animal feeding avoidance, moisture retention and the like. The increase of the earthing measures is the place with the improved value in the test, the earthing thickness is 0.3-1 cm, and the recommended earthing thickness is 0.3-0.5 cm.

Finally, the acceleration difference is also manifested in terms of the germination rate of the seeds. One of the greatest advantages of natural renewal over manual renewal is low cost. Stock procurement is one of the major capital expenditure approaches in seeding and promoting natural renewal. However, the efficiency of utilization of the seeds under the forest can be found to be extremely low by calculating the germination rate of the improved seeds in the forest land in the promotion test. The under-forest seed germination rate of each treatment did not exceed 1% except for SC treatment. In particular, in the case of CC treatment, the germination rate of the seeds is inferior to that of SC treatment even when measures such as germination acceleration are taken. Meanwhile, the germination rate of the improved variety of the larix huabeiensis measured in laboratory conditions can reach about 88.89%. How to improve the germination rate of seeds in the forest land is significant for promotion experiments. On one hand, the germination rate is improved, and the seeding quantity of the seeds can be reduced so as to save the seed purchase cost; on the other hand, the large amount of germination of the seeds can offset the adverse effect consumed in the updating process, and the good under-forest updating grade can be fundamentally ensured.

In conclusion, when the artificial promotion is carried out in the larch forest in north China in the Shihan dam area, necessary artificial sowing measures are adopted. The optimal sowing time is the late stage of seed rain in the current year after cleaning the litter, and is more appropriate before and after 5 months in the year. In the case of sowing time being missed, germination hastening measures are necessary. As for the under-forest litter treatment, the best cleaning method is SC treatment followed by BC treatment, and it is not recommended to directly spread seeds on heavy litter, nor to completely remove litter in the forest land to promote natural renewal.

The above is only a preferred embodiment of the present invention, and it should be noted that the above preferred embodiment should not be considered as limiting the present invention, and the protection scope of the present invention should be subject to the scope defined by the claims. It will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the spirit and scope of the invention, and these modifications and adaptations should be considered within the scope of the invention.

Claims

1. A method for promoting the renewal of artificial forests is characterized by comprising the following steps:

and 2) sowing forest seeds on the cleaned bare ground.

2. The method for promoting the renewal of artificial forest according to claim 1, wherein the forest land is a larch forest in North China, the forest trees in the forest land are larch in North China, and the forest stand density of the forest land is controlled to be 1000-3000 h.m^-2。

3. A method for promoting artificial forest renewal according to claim 1 or 2, characterized in that in step 1), the time for cleaning up the litter on the forest-promoting land is 5 months of the year.

4. The method for promoting the renewal of artificial forests according to claim 1 or 2, characterized in that in the step 1), the way of cleaning the litter is strip cleaning or ditch cleaning.

5. The method for promoting the renewal of the artificial forest according to claim 4, wherein the strip-shaped cleaning is to clean a plurality of strips with the width of 10-100 cm on the ground of the forest land.

6. The method for promoting the renewal of artificial forests according to claim 4, characterized in that the furrow clearing is to open the sowing furrow while clearing the litter at the furrowing position; the width of the sowing ditch is 5-15 cm, the depth is 0.5-2 cm, and the interval between the ditches is 80-100 cm.

7. The method for promoting the renewal of artificial forests according to claim 6, wherein the sowing trenches are arranged in a grid.

8. The method for promoting the renewal of artificial forests according to claim 1 or 2, wherein the sowing time in the step 2) is from the end of the seed rain to the middle of 6 months in the current year after cleaning up the litter, and the sowing is carried out in rainy days.

9. The method for promoting the renewal of artificial forests according to claim 1 or 2, wherein in the step 2), the seeding density is 220 to 280 m-m^-2。

10. The method for promoting the renewal of artificial forests according to claim 1 or 2, characterized in that in said step 2), the seeds selected are sown as seeds treated by natural outdoor snow; in the step 2), soil covering or leaf covering is carried out after sowing.