CN113383689B - Method for promoting artificial forest update - Google Patents

Abstract

The invention discloses a method for promoting the update of an artificial forest, which comprises the following steps: to promoteCleaning the dead and falling objects on the forest land to expose part of the forest land surface; and sowing woodland tree seeds on the bare ground. The invention can obviously improve the natural updating grade, the updating density and the sowing germination rate of the artificial forest, and experiments prove that the updating density of the method can reach 8633.33 strain hms at the highest ^‑2 The germination rate of the seeds can reach 1.79 percent, and the germination rate is realized under the ditch-shaped treatment. Compared with the existing artificial forestation, the optimal method for cleaning the dead objects, namely trench-shaped treatment, facilitates updating, realizes updating of the forests, and greatly reduces the workload and the updating cost.

Description

Method for promoting artificial forest update

Technical Field

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

Background

Larix Gmelini (Larix pritis-ruprechtii), the special tall trees of Larix genus of Pinaceae in China are native to the mountain area of North China, and the highest distribution elevation can reach about 2800m, which is one of the main colonisation tree species of Ji, jin and other provinces of mountain needle woods. In the main distribution area, larch appears in pure forest, or is mixed with needle-leaved trees such as white (Picea meyeri), green (Picea wilsonii), white birch (Betula platyphylla), aspen (Populus davidiana) and white willow (Salix pseudotangii).

As one of the important pioneer tree species for forest community succession in the suitable area, larch is a strong positive conifer, light loving and shade intolerance. Meanwhile, the cold resistance is quite excellent, the winter can still be carried out under the condition of 50 ℃ below zero, and the resistance to bad weather is strong. The larch has strong soil adaptability, but has shallow root system distribution, is favorable for deep, fertile, wet and well-drained acidic or neutral soil, has certain tolerance to salt and alkali, and also has certain moisture resistance, drought resistance and barren resistance. In addition, larch 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 texture, and has better performance in the aspects of compression resistance and bending resistance. Because of being rich in resin, the wood is 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 used for preparing resin, tannin extract, etc. Therefore, the larch can bring good ecological benefit to each distribution area and simultaneously bring huge economic benefit to the local area. Because of this, it is widely introduced into northeast, northwest and China, and other areas, such as Shaanxi, ganning, ning and other provinces, and the existing introduction cultivation is adopted.

As an important indigenous tree species, larch has unique advantages and great protection, research and utilization values. So far, a set of complete larch research system has been constructed in China. The method has various aspects of seed morphology identification, seedling cultivation, forest culture and forest growth and accumulation, species diversity, respiratory carbon sink and the like.

Naturally, the research on the natural updating of larch is one direction and difficulty. Forest updating is significant to any healthy forest ecosystem, and the quality of the updated condition determines the future trend and trend of the whole forest community. Forest is a land ecosystem that is largely extended in space-time by the updating of individual plant populations represented by woody plants and is generally represented by the succession and development of forests themselves. The natural updating is one of 3 modes of forest updating, and compared with the method, the method has the advantages of saving cost, meeting the natural law and the like. Under the current theoretical prevalence of near natural management and the like, the method is widely applied to forestry production around the world, and is likely to become a main mode of artificial forest updating in the future, so that the method is paid attention to.

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

1. at present, natural updating or poor updating cannot be realized under larch forests in all distribution areas represented by larch artificial forests in the North China in the Serhan dam area;

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

3. the density of the updated seedlings of the larch is low, the survival rate of the updated seedlings in the forest is low, and the number of young trees is small;

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

5. there is a very large age fault between the North China She Songmu tree and the young tree.

6. By the research of the invention, the current situation of poor natural updating of the larch is not changed, and the artificial forestation technology is still the main mode, even the only mode, of the updating of the artificial forest stand of the larch. Large-area manual afforestation can increase the production burden of the forest farm in terms 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 update of artificial forests, which can achieve a significant improvement in update density and seeding germination rate, and the update cost is far lower than that of the artificial forestation technology. The inventor continuously reforms and innovates through long-term exploration and trial and repeated experiments and efforts, and in order to solve the technical problems of the above parts, the technical scheme provided by the invention is that a method for promoting the update of artificial forests is provided, which comprises the following steps:

Step 1) cleaning the dead and falling objects on the forestation promotion ground to expose part of the forestation ground;

step 2) sowing woodland forest seeds on the cleaned bare ground.

According to a further embodiment of the method for promoting the renewal of artificial forests according to the present invention, in the step 1), the forests are larch forests, and the stand density of the forests is controlled to be 1000-3000 hms ^-2 。

According to a further embodiment of the method for promoting the renewal of artificial forests according to the invention, said step 1) is carried out for a period of time of 5 late month each year for cleaning up the withered objects on the forests.

According to a further embodiment of the method for promoting the renewal of artificial forests according to the invention, in said step 1), the means of cleaning the withers are belt-like cleaning or gutter-like cleaning.

According to a further embodiment of the method for promoting the renewal of artificial forests according to the invention, the strip cleaning is performed by cleaning a plurality of strips 10-100 cm wide on the ground of the forests. Further, the strips are arranged in parallel, and the distance between two adjacent strips is 80-100 cm.

According to a further embodiment of the method for promoting the updating of the artificial forest, the ditch-like cleaning is to clean up the dead and falling objects at the ditching position and simultaneously open up a sowing ditch; the sowing ditch has a ditch width of 5-15 cm, a depth of 0.5-2 cm and a ditch spacing of 80-100 cm.

According to a further embodiment of the method for facilitating the renewal of artificial forests according to the invention, said sowing grooves are arranged in a grid.

According to a further embodiment of the method for promoting the renewal of artificial forests according to the present invention, in the step 2), the sowing time is from the end of the current year of seed rain to the middle of 6 months after the removal of the withered objects, and the sowing is carried out in the rainy day.

According to a further embodiment of the method for promoting the renewal of artificial forests according to the present invention, in the step 2), the sowing density is 220 to 280. Mu.m ^-2 。

According to a further embodiment of the method for promoting the renewal of artificial forests according to the present invention, in said step 2), the seeds selected for sowing are seeds treated with outdoor natural snow reserves; in the step 2), soil covering or leaf covering treatment is carried out after sowing.

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

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

b) Compared with the existing artificial forestation technology, the workload and the updating cost are greatly reduced. The ditch-shaped cleaning promotion accounts for no more than 45.35 percent of the forestation cost of the bare root seedlings, and accounts for no more than 19.72 percent of the forestation cost of the container seedlings. The band-shaped cleaning promotion accounts for no more than 96.10 percent of the forestation cost of the bare root seedlings, and no more than 41.78 percent of the forestation cost of the container seedlings.

Drawings

FIG. 1 is a schematic diagram of the design of a cleavage zone in example 1.

FIG. 2 is a schematic diagram of belt-like cleaning and gutter-like cleaning in example 1 of a method of facilitating manual forest renewal according to the present invention. The left graph is strip cleaning and the right graph is gutter cleaning.

FIG. 3 is a graph showing the ratio of seedlings of different ages in 2 years in example 1.

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

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

FIG. 6 shows the change in seedling growth index in the growing season in example 1.

FIG. 7 is an updated seedling density over 2 years in example 1.

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

FIG. 9 is a comparison of seed germination rates in various treatments under artificial sowing in example 1.

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

Detailed Description

The following description is made with reference to specific embodiments.

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, based on the embodiments of the invention, which are apparent to those of ordinary skill in the art without inventive faculty, are intended to be within the scope of the invention. Thus, the following detailed description of the 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 updating of the artificial forest described in the embodiment takes the artificial pure forest of larch 31a in the region of the Sehan dam as a test object for promoting the research.

1. North China larch sowing test process

1.1 Pre-preparation

(1) Test seed

The test seeds are purchased from a mountain forest fine-variety nursery stock breeding field of the management bureau of the forest farm in the magnolia enclosure of Hebei province in the beginning of 2019 in 11 months, and are stored in a refrigerator and a freezer after being purchased, wherein the storage temperature is (-15.31 +/-1.70). The detailed parameters of the purchased fine seeds are shown in Table 3, and the measurement method is referred to GB2772-1999 and forest seedling quality inspection technology, and the measurement time is 2019 and 12 months.

TABLE 3 essential parameters of improved larch variety

Note that: mean ± standard deviation. The following is the same.

1.2 study of the better promotion Effect under different stand Density, subtraction treatment methods and seed sources

1.2.1 test sample selection

31a, artificial pure forest of larch is selected as a research object for the research. 5 months 2019, the samples under 3 m-val intensities in the artificial forest were selected as test samples according to the application. The design mode and the interval time of the interval intensity of the sample area are the same. The sample size was 20m×20m, the number of test repetitions was 3, and a total of 9 fixed test samples were used.

The basic forestation information of the fixed pattern is obtained by inquiring the prior forestation data and pattern investigation, and is shown in table 4. Wherein, for convenience of the following description, the fixed test plots are sequentially used with the numbers TN from small to large according to the forest stand density size principle _a 、TN _b And TN (TN) _c And (3) representing.

Table 4 basic stand information table for fixed test samples

。

1.2.2 crack zone test design

(1) Variable design

The test design is adopted by the more advanced research to design a cracking zone, and the test variables are 3 types of forest stand density, a dead drop treatment mode and a seed source.

The main treatment is stand density, 3 kinds are all taken, and the detailed values are shown in table 4.

The secondary treatments were a total of 4, no any litter clean blank (CK) and 3 treatments containing litter clean: complete Clearance (CC), belt Clearance (BC), gutter clearance (SC). The 4 different kinds of disposal modes of the dead drop are randomly arranged in any 10m multiplied by 10m auxiliary area in the same fixed sample area, the design schematic diagram of the split area is shown in figure 1, and the different orders of the 4 kinds of disposal modes of the dead drop in figure 1 show that the disposal modes are randomly arranged in the auxiliary area. Seed source differences were achieved experimentally in different years using the same block. After the 2019 plot is cleaned, the stand is naturally updated only by the seeds which naturally seed; the seeds updated in 2020 were derived from manual sowing.

Thus, a total of 12 treatment combinations.

(2) Standard for cleaning up dead and fallen objects

Since CK groups do not treat any of the litter, only 3 criteria for litter cleaning are set forth herein.

The cleaning time is carried out in the last 5 months of the year, when the seeds have not germinated. Because uncontrollable factors occur in 2020, the cleaning time in the current year is postponed to the last ten days of 6 months.

The tools used for cleaning the dead and falling objects are 3 types of steel forks, iron hoes and iron rakes.

CC cleaning with cleaning area of 100m ² The soil on the surface of the forest after cleaning is clearly visible, the thickness of the residual dead and falling matters on the surface is not more than 1cm, and the raked dead and falling matters are accumulated outside the sample area. BC cleaning, wherein each cleaning belt has the specification of length multiplied by width of 10m multiplied by 1m and the belt spacing of 1m, so that 5 cleaning belts are arranged in one auxiliary area, and the cleaning area is 50m which is half of the overall cleaning area ² The soil on the cleaning belt is exposed obviously, the thickness of the residual dead and falling matters on the ground surface is controlled below 1cm, and the cleaned dead and falling matters are accumulated on the untreated belt. SC cleaning, namely cleaning the withered objects at the ditching position, simultaneously, opening a sowing ditch with the depth of about 1cm, wherein the ditch length is 10m, the ditch width is about 10cm, the ditch spacing is 90cm, and 20 cleaning ditches are formed in a total in one auxiliary area: 10 longitudinal and 10 transverse, the total cleaning area is 19m ² . The schematic diagrams of the effects of BC cleaning and SC cleaning are shown in fig. 2, in which the gray area is a stacking area of the dead objects in the secondary area, the white area is a cleaning area of the dead objects in the secondary area, and the marked values in the figures are only the test parameters and recommended parameters of the embodiment, and are not limited uniquely.

(3) Sowing standard

The artificial sowing time is in the middle of 6 months of 2020, and the sowing is performed in the last rainy day after the processing of the dead and falling objects is finished. The seed sowing quantity is 1.50 g.m ^-2 The sowing density is about 254.15 m by the conversion of thousand seed weight of improved seeds ^-2 . The seed mass is kept consistent by a weighing method, and an instrument used for weighing is an electronic balance with the precision of 0.001g. In summary, details of the split zone design after each treatment are shown in table 5.

TABLE 5 sample handling details of the fracture design

。

1.2.3 update seedling investigation

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

(I) Investigation mode

In view of the current situation of poor natural renewal under larch in the northland of the Serhan dam, the renewal seedlings in the sample land are comprehensively investigated in two growing seasons from 2019 to 2020.

(II) investigation content and method

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

(1) Updating seedling hierarchy

The updated seedling hierarchy is defined according to the forest layer division standard issued by the national forestry agency in 2003 (national forestry agency, 2003). The updated seedlings in this standard comprise seedlings and saplings at 2 levels, and the defined standard is shown in table 1.

TABLE 1 forest layer division criteria

Note that: in the table, "H" represents seedling height or tree height; "DBH" means the chest diameter.

(2) Update frequency

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

Update frequency (%) =number of updated seedlings appearance/total number of survey samples×100 (1-1)

(3) Distribution of seedling age

The seedling age is judged according to the accumulated She Hen, and the principle is equal to that of a method for judging the age of branches through bud scale marks. 1 year old, 2 year old and higher seedling are respectively expressed by 1a, 2a and 3a+, the seedling age distribution is calculated according to the formula (1-2), and the calculated result is reserved in units.

Seedling age distribution (%) = number of updated seedlings of a certain seedling age/total number of updated seedlings in the plot x 100 (1-2)

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

(4) Growth status

Growth conditions include both ground diameter and seedling height. Considering that larch grows in the region of the Sehan dam in a shorter season and seedlings grow slowly, the measurement of the ground diameter and the seedling height is only carried out at the beginning and the end of the growth. The initial growth data is measured shortly after germination of the seedlings, the end-of-growth data is measured uniformly while the seedlings are dormant in the end of the growing season, and the difference between the two sets of data indicates the growth of the seedlings in the whole growing season. The ground diameter and the seedling height are measured by using a vernier caliper, and the unit of the ground diameter and the seedling height is respectively mm and cm when the position is accurate to the position behind the decimal point during reading.

(5) Updating seedling number and density

At the end of each month of the growing season, the number of live updated seedlings, the number of new seedlings and the number of dead seedlings in the test sample area are respectively investigated. And accordingly, calculating the density of the updated seedlings, evaluating the update grade, drawing update dynamics and calculating the survival rate. The new seedlings are marked in time, so that repeated statistics is avoided; and the death seedlings preliminarily judge the death reasons according to the field investigation. The update density is calculated according to the formula (1-3), and the result is reserved to the last two bits of the decimal point.

Update Density (plant. Hm) ^-2 ) =updated number of seedlings/sample area×10000 (1-3)

(6) Updating the level

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

TABLE 2 Natural forest update rating criteria (Unit: plant. Hm) ^-2 )

Note that: "ρ" in the table indicates the update density.

(7) Updating dynamics

In the past, in the description of update dynamics of other tree species, update dynamics are generally represented by the number of update seedlings of different ages or heights. For example, updated seedlings are classified into 3 ranks according to Miao Gao cm, 50cm < Gao cm, and seedling height >100cm, and the update dynamics under the forest are represented by the 3 ranks update seedling number ratio. The number of larch seedlings has a greater extinction between different months in the growing season, but dynamic changes in this respect are rarely described. Accordingly, dynamic changes of the densities of the surviving seedlings of the larch between different months under various underground conditions in the growing season are drawn.

(8) Updated seedling survival rate

The survival rate of the growing season and the overwintering survival rate can be calculated according to formulas (1-4) and (1-5), and the calculated result is reserved to the percentile. It should be noted that, the defining criteria for survival of seedlings before winter in the test are: 100% of the established dead seedlings, counted as dead seedlings, were judged as viable seedlings for all the uncertainly viable and 100% of the established viable seedlings.

Growth season survival rate (%) = number of surviving seedlings before overwintering/total number of seedlings in current annual plot x 100 (1-4)

Survival rate over winter (%) = number of surviving seedlings after winter/number of surviving seedlings before winter x 100 (1-5)

(9) Seeding germination rate

The method is added with the calculation of the germination rate of the seeds under each treatment combination in the manual sowing in 2020, and aims to explore the utilization efficiency of the seeds after the manual sowing under each treatment. The calculation is controlled in the percentile by referring to the formulas (1-6) and the calculation accuracy is also controlled in the percentile. The seed germination amount in the formula is 1a seedling number measured in 2020, and the seed sowing amount can be seen in table 5.

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

1.3 study of the effect of promoting the more in different seed treatment modes

1.3.1 test sample selection

31a, artificial pure forest of larch is selected as a research object for the research. 5 months 2019, the plots under 1 m-val intensity (TN) in the artificial forest were selected as test plots of the present application. The design mode and the interval time of the interval intensity of the sample area are the same. The sample size was 20m×20m, the number of test repetitions was 3, and a total of 3 fixed test samples were used. The basic stand information for the fixed plots is shown in table 6.

Table 6 basic stand information table for fixed test samples

。

1.3.2 Single factor test design

The test method was to uniformly divide a 20m×20m sample area into 4 equal-sized 10m×10m sample areas. 1 time of comprehensive cleaning is carried out on the dead and falling matters in the fixed sample plot in the middle of 6 months in 2020, and the method and the standard are the same as 1.2.2. After cleaning, the seeding density is 1.50 g.m ^-2 。

The test variables were seed treatments, totaling 4 classes, as shown in table 7. And, each treatment regimen is randomly arranged into any one of the parties within the same fixed pattern.

Table 7 4 seed treatment method

。

1.3.3 update seedling investigation

(1) Investigation mode

With 1.2.3, the updated seedlings in the plot were thoroughly investigated in the year 2020.

(2) Survey content and method

The investigation content only comprises the quantity of the larch updated seedlings, and the updated dynamic diagram is drawn by evaluating the updated grade, calculating the updated density and the germination rate. Specific investigation methods and calculation formulas are referred to 1.2.3.

2 results and analysis of different stand densities, modes of processing dead and falling matters and research on promotion effect under seed sources

2.1 seedling update frequency at each level

The artificial forests with 3 densities in the near-maturing forests M still have limited natural updating capability after the withered objects are cleaned, and natural updating of different degrees exists under the forests. And the updated seedling layers are seedlings, no North China She Songyou tree is planted, and the updating frequency of the young tree is 0. The seedling group mainly consists of seedlings below 5 years old, mainly comprises 1a seedlings, and the ages of the perennial seedlings are 2 years old. The natural update frequency of the seedlings of each stage of the larch in the promotion test is calculated statistically and shown in table 8.

TABLE 8 update frequency of seedlings of larch stages

Note that: the presence of updated pattern-annotating symbols "; the samples without update are not marked; the update frequency of the saplings in each plot is 0, and is omitted from the table.

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

First, at the update frequency of 1a seedlings. Even when the young plants naturally seed in 2019, young seedlings appear in 3-density forests, namely, the near-maturing forests have certain setting and natural updating capacities. Therein TN _a And TN (TN) _c The 1a seedlings were updated at 100% density, and the only 1a seedlings that did not appear were TN _b CC treatment at density, 1a seedlings updated only 75% frequently. On the one hand, this may be due to the smaller number of seeds in the local area of the secondary zone in which the treatment is located; on the other hand, the seeds under the forests in the auxiliary area can be cleaned along with the layer of the withered and fallen objects. In the next year of artificial sowing, 1a seedlings are updated in all treatments of each density, and the updating frequency reaches 100%.

In terms of the update frequency of perennial seedlings, the table at the first year is due to the large disturbance of the ground At present slightly worse, TN only _b And TN (TN) _c 2a seedlings remained in CK treatment at density, and no perennial seedlings were present in the remaining auxiliary area. This is probably due to the fact that perennial seedlings present in the original zero-delta in the plot are also removed incidentally in the ground disturbance with extensive litter cleaning. The update frequency of 2a seedlings at each density is only 25% at maximum, and the update frequency of 3a+ is 0%. Thus, the large-scale cleaning of the surface litter layer is bad for the original update condition. But in 2020, due to TN _a CK and BC treatment at Density, TN _b CK treatment under density and TN _c The successful overwintering of 1a seedlings in BC treatment under density causes 2a seedlings to appear in the treated plots in the second year, and the update frequency is increased to be in the range of 25-50 percent, which is improved compared with the first year. At the same time TN _c CK treated 2a seedlings at density also promoted successfully to 3a seedlings with an up-to-25% frequency of renewal. In the rest of the treatments, the frequency of the update of the perennial seedlings in the treatments was not changed in the second year, since the seedlings all died after one growing season and the seedling age stopped increasing.

In terms of the overall update frequency of seedlings, due to TN _b CC treatment at Density was not naturally updated in 2019, no seedlings of any age were present, TN _b The overall update frequency is only 75% at a minimum. The overall frequency at each density at each other period is 100%.

In summary, in terms of update frequency, the 3-density artificial forest update capability is not greatly related to the forest stand density as a whole; however, in the stand with strong updating capability, the overall updating frequency of the stand is improved due to a certain degree of disturbance on the ground and manual seed sowing.

2.2 seedling age distribution

In this promotion test, the seedling age distribution of seedlings in various plots over 2 years is shown in FIG. 3. As can be seen from FIG. 3, TN was not added to that in 2019 _b In addition to the absence of updates in CC treatment under density, seedlings are mainly 1a seedlings in the same way in all samples with the updates in 2 years, and the ratio of the seedlings is at least over 90 percent. And alsoIn the plot at 2019, no 3a+ seedlings exist, and 2a seedlings account for a relatively low proportion of no more than 10%. The case where seedlings were all 1a seedlings was also more frequent. The main reason is that the number of perennial seedlings is indirectly influenced due to the cleaning of the dead and falling matters.

In the information conveyed in table 8, the frequency of the update of perennial seedlings at 2020 tended to rise, but natural update in the second year was greatly promoted due to artificial sowing, and the proportion of 1a seedlings was rapidly increased to at least 98%. Correspondingly, the proportion of perennial seedlings is greatly reduced, and the proportion of the perennial seedlings does not exceed 3 percent. From these results, in the research of future growth promotion experiments, attention should be paid to how to further increase the survival rate of these updated seedlings under forests and promote the growth of the seedlings under forests.

2.3 growth conditions

In the analysis of the growth conditions, the seedlings of the respective seedling ages in the plots are likewise discussed as a whole. Since no update exists in part of the secondary area after 2019 is cleaned, the seedling growth data is lost. Thus, the comparison of growth conditions is only performed between forests of different densities.

(1) Seedling ground diameter

Comparing the ground diameters of seedlings under artificial forests with different densities respectively at the initial stage and the final stage of growth in 2 years, wherein in fig. 4, uppercase letters indicate differences between densities, lowercase letters indicate differences between years; the letter differences represent a significant difference, with a difference significance level of 0.05. TN for 2 years _a 、TN _b And TN (TN) _c The seedling ground diameters under the density forest are 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. The analysis shows that the seedling ground diameters in 3 density forests in 2 years are not obviously different from each other at the beginning and the end of growth (p>0.05 Overall exhibiting a law of TN _a Or TN _c The seedling with larger ground diameter and the smallest ground diameter are TN _b At a density (p)>0.05)。

The seedling ground diameters under the same density forest are different when compared in the same period of different years. The initial growth period of seedlings in 2019 was slightly longer than 2020, but the difference was small (p >0.05 As in 2019 TN) _a The seedling ground diameter at the initial growth stage under the density is 0.81mm, and the seedling ground diameter is not remarkably reduced to 0.77mm by the initial growth stage of 2020. Whereas the difference of seedling ground diameters at the end of growth reached a significance level between two years, the ground diameters of 3 density woods seedlings were all bigger at the end of growth at 2019 (p<0.05 As well as TN _a The density is exemplified by the seedling ground diameter at the end of 2019 growth being 0.62mm, which is significantly greater than the seedling ground diameter (p) at the end of 2020 growth of 0.47mm<0.05)。

(2) Seedling height of seedling

Comparing the seedling heights of artificial forests with different densities respectively at the initial stage and the final stage of growth in 2 years to obtain a figure 5, wherein capital letters in the figure 5 indicate differences between densities, and lowercase letters indicate differences between years; the letter differences represent a significant difference, with a difference significance level of 0.05. TN for 2 years _a 、TN _b And TN (TN) _c The seedling heights under the density forest are respectively 2.69cm, 2.75cm and 2.83cm and 2.87cm, 3.12cm and 3.35cm at the initial stage of growth, and respectively 3.03cm, 3.08cm and 3.16cm and 2.96cm, 3.23cm and 3.37cm at the final stage of growth. The analysis shows that the seedling heights of 3 density forests in 2 years are not obviously different at the beginning and the end of growth (p)>0.05 And the seedling height in 2 years shows positive correlation with the stand density at the beginning and the end of growth.

The seedling height under the same density forest is compared between different years at the beginning and end of growth, and TN is only _a The seedling height at the end of growth at density was 2.96cm in 2020 and slightly less than 3.03cm in 2019 (p>0.05 While the seedling heights of other forest stand densities at various periods are slightly increased in the next year (p)>0.05 And TN) _c The seedling height at the initial growth stage at density was 3.35cm in 2020 and significantly greater than 2.83cm in 2019 (p<0.05)。

(3) Growth index variation

The results of the comparison of the growth index of Lin Fenxia seedlings of different densities for 2 years in this promotion test at the beginning and end of the growing season are shown in fig. 6.

It was found that the seedling ground diameter at the end of growth was smaller at each density than at the initial stage of growth, and the growth amount was negative. After inspection, it was found that the decrease in seedling ground diameter was not obvious in 3 forests at 2019 (p>0.05 As in 2019 TN) _a Seedling ground diameter at density did not significantly decrease from 0.81mm at the initial stage of growth to 0.62mm at the final stage of growth (p>0.05). The decrease in seedling ground diameter was significant in the forest at 2020 (p<0.05 As well as TN _a For example, the seedling ground diameter was significantly reduced from 0.77mm at the initial stage of growth to 0.47mm at the final stage of growth (p) in 2020 <0.05). Atrophy of ground diameter may be due to lignification of the stems, dehydration atrophy. In comparison, the seedlings which just germinate are saturated with water, and the ground diameters are also plump and thick, which is the possible reason that the ground diameters of the seedlings do not rise and fall in the growing season.

In terms of seedling height, the seedling heights in all forests were larger at the end of each year than at the initial stage of growth, but the growth of seedling heights was not significant (p>0.05 As in 2019 TN) _b The seedling height of seedlings at density increases from 2.75cm at the initial stage of growth to 3.08cm at the final stage, TN in 2020 _c The seedling height of the seedlings increases from 3.35cm at the initial stage to 3.37cm at the final stage of growth under the density, and the growth amount is very limited. This suggests that there is some growth of seedlings by accumulation of photosynthetic material in one growing season, but that the accumulation of material in 1 growing season is very limited.

2.4 update level and update Density

In analyzing differences in natural update promoting effects among treatments under different measures, similarly, in view of the fact that there is a large variation in the number of seedlings in the growing season, all seedlings appearing in the plot in the growing season are also explicitly used herein for measuring the overall effect of the promotion measure.

(1) Updating the level

In the artificial promotion test, the natural update grade of the northfalling larch in 2 years is judged according to the natural forest update grade evaluation standard established by the national forestry agency. Details of the respective processing update levels are shown in table 9.

Table 9 2 North China larch update rating

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In the observation in 2019, since the seeds updated in the current year mainly originate from the natural planting of the forest, and with various cleaning of the withered objects, the seeds distributed on the surface of the forest are greatly disturbed, and under the comprehensive influence of various factors, the natural update levels in the sub-areas under the forests of 3 densities are in a poor state, without exception.

In 2020, because a large number of seeds with vitality are artificially scattered, the obstacle factor of insufficient number of seeds required for natural updating in the woodland is solved, and therefore, the updating grade under various treatments is greatly improved as a whole. In particular in the secondary zone where the 3 treatments CC, BC and SC are located, after the cleaning of the withered and fallen objects, the disseminated seeds can be directly contacted with the soil, the natural renewal level of which is at least raised to a medium level and mainly to a good level. But in TN _a And TN (TN) _b In the CK process under density, the update level may be in a poor update state. The reason why the update level is still not improved under the condition that the seed source available for update is sufficient can be attributed to the huge physical barrier caused by the heavy layer of the litter.

It follows that the removal of the dead junk is a crucial step for improving the natural renewal grade under larch.

(2) Update density

The comparison results of the update densities in this promotion test are shown in fig. 7 by analysis of variance. FIG. 7 shows the updated seedling density over 2 years, with capital letters in FIG. 7 indicating differences between the modes of litter treatment and lower case letters indicating differences between densities. The letter differences represent a significant difference, with a difference significance level of 0.05. In 2019, under the condition of natural seeding, only the withered object treatment mode is updatedThe effect of the degree reaches a very significant level (p<0.01 Less influence of stand density and interaction on update density (p>0.05). The density of the forest stand is TN as a whole _c 191.67 strain hm at density ^-2 Maximum update density, TN _b 141.67 strain hm at density ^-2 Is the least (p)>0.05 A) is provided; when compared under the same measure of treating the withered objects, the updated densities of different stand densities are high and low, but the difference does not reach the significance level (p>0.05). Taking CC processing as an example, TN _a ～TN _c The updated density under the forest stand density is 66.67 strain hms respectively ^-2 0.00 strain hm ^-2 And 33.33 strain hm ^-2 The overall difference is not great (p>0.05)。

In the way of treating the withered object, the whole was treated with CK to 400.00 strain hms ^-2 The update density of (c) is significantly greater than the update density (p) under 3 kinds of litter cleaning<0.05 While the update density difference between the 3 kinds of litter cleanings is smaller (p>0.05 155.56 strain hm under the subregion where BC treatment is located ^-2 The overall update density of (1) was maximized, and CC treatment was 33.33 strain hms ^-2 The update density of (2) is the smallest; when comparing under the forest of the same density, TN is removed _a The updated density of CK treatment is higher besides the forest stand of density, but only TN _c The difference of updated density among different treatment modes under the forestation of density reaches the significance level, and 566.67 strain hms under the CK treatment ^-2 The update density of (3) is significantly higher than 33.33 strain hms under 3 kinds of dry falling object cleaning ^-2 66.67 strain hm ^-2 And 100.00 strain hm ^-2 Update density (p)<0.05 At TN) _a In the case of the density of the forest, 300 strain/hm was treated with BC ^-2 The update density of (a) is the highest and slightly higher than that of CK-treated 266.67 strain hms ^-2 Update density (p)>0.05)。

In 2020, in the case of manual sowing, the same effect on the update density was significant only in the manner of disposal of the litter (p<0.01 The effect of stand density and interaction on update density is also smaller (p>0.05). The different forest stand densities are TN as a whole _b 5808.33 strain hm at density ^-2 Maximum update density, TN _c 5516.67 strain at Densityhm ^-2 Is the least (p)>0.05 A) is provided; when comparing between forests with different densities under the same measure of treating the dead objects, the update density has different rules, but the difference also does not reach the significance level (p>0.05 Under SC treatment, TN _a ～TN _c The updated density under the forest stand density is 7200 strain hm ^-2 11100 strain hm ^-2 And 7600 strain hm ^-2 The differences from each other did not reach significant levels (p>0.05)。

In the method of treating the litter, the average of 8633.33 strain/hm under SC treatment is used ^-2 The update density of (2) was 6633.33 strain/hm after BC treatment ^-2 And both treatments were identical to CK treatment 2166.67 strain hm ^-2 Forms a significant difference between the update densities (p<0.05 While only the differences between CC and CK were small in 3 litter washes (p>0.05 While the average update density in CC treatment was 5100.00 strain hms ^-2 At the same time, the overall difference in update density between the 3 cleaning modes is also small (p>0.05 A) is provided; while the order of updating density is about the same among different modes of processing the dead objects under the same density of forests, but in TN _a Under the forestation of density, 7466.67 strain hms are treated with BC ^-2 The update density of (1) is slightly higher than that of SC treatment 7200 strain hms ^-2 Update density (p) >0.05 And only in TN _b The difference between the updated densities of the different treatments reached a significant level at which the density of seedlings in the sub-zone where the SC treatment was located was 11100.00 strain/hm ^-2 Is significantly larger than CK treatment 1833.33 strain hm ^-2 Update density (p)<0.05 6000.00 strain hms in BC and CC treatments) ^-2 4300 strain hm ^-2 Not significant in update density difference (p>0.05)。

(3) Updating density changes

Since the above analysis does not quantitatively analyze the update density differences between the same and different years, it is summarized here. As shown in Table 10, it was found after examination that the updated density of larch was substantially increased in the second year (p<0.05 The effect of artificial sowing on improving the update density under larch forest is obviousOf, e.g. TN _a Update Density in CC Density treatment was from 66.67 strain hms in 2019 ^-2 5700 strain hms which is remarkably improved to 2020 ^-2 ，TN _c Update Density in SC treatment under Density from 100.00 plant.hm in 2019 ^-2 The strain 7600 hm of 2020 is obviously improved ^-2 Etc. However, there are exceptions to the individual process, which may be caused by large inter-granule differences. The reason for the difference may be due to multiple factors such as late sowing time, vegetation under the forest, and artificial interference, and further research is required.

Table 10 comparison of update density over 2 years

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2.5 update dynamics

Dynamic changes in this further experiment are shown in fig. 8, in which the large fluctuation of the surviving seedlings of larch in the growing season is reflected in fig. 8, and because of the differences of the processing mode of the dead object and the source of the seeds, some differences exist among the dynamic diagrams.

After 2019 withered and fallen matter is cleaned, the seeds naturally planted in the forest are germinated from the bottom of 6 months, and seedlings in the sample land under various treatments are very rare at the moment, and only TN exists _b 、TN _c 1a seedlings appeared in the CK treatment under two densities of forests, at which point the densities of surviving seedlings were only 66.67 strain hms, respectively ^-2 33.33 strain hm ^-2 . And in the last two months, the under-forest update density increases rapidly. And the slope of the broken line in the figure reflects the period from the end of 6 months to the end of 7 months as the peak period of germination, and the germination rate is reduced from the end of 7 months to the end of 8 months. Meanwhile, it can be seen that the updated density under CK treatment is always kept at a higher level under the basic density forest, and particularly a larger gap is kept between the updated density under CC treatment. As in TN _b The density of the survival seedlings at the end of 7 months in 19 years in Lin Fenxia CK treatment is 366.67 strain/hm ^-2 The density of live seedlings in CC treatment is Lin Fenxia at the same timeHas strain 0.00 hm ^-2 . By 9 months, there was no more seed germination in the woodland as growth Ji Moqi was entered, and the seedlings in the plot died largely, from which the viable seedling density decreased continuously.

In 2020, since the number of living seeds in the woodland is greatly increased by artificial sowing, the under-forest update is not limited by the number of seeds, and the promotion effect of each of the litter treatment measures can be released, so that the litter may be one of the main obstacle factors in the update process in 2020. But because of uncontrollable factors, the seeding time in the current year is late, and TN is only when the seeding time is at the end of 6 months in 2020 _b Density Lin Fenxia SC treatment, etc. 1a seedlings appear in minor regions, TN _b -BC、TN _b SC and TN _c The density of the seedlings in the SC at this time is only 100.00 hm ^-2 600.00 strain hm ^-2 And 100.00 strain hm ^-2 The update density is still relatively poor. While other treated seeds should remain dormant or germinated at this time, only the seedlings that die from the failure to live through the winter are now treated, so the number of surviving seedlings drops to a very low value again.

Similarly, the germination peak of the seeds in the other withered matters except the SC treatment is delayed by about 1 month in 2020 due to the later sowing time, and the seeds in the other 3 treatments are germinated between 7 months and 8 months, so that the germination quantity is small at 7 months. As in TN _c The density of the survival seedlings at the end of 8 months in BC treatment under the density reaches 6200.00 strain hms ^-2 The density of the survival seedlings at the end of 7 months is only 1300 strain hms ^-2 . SC treatment was largely germinated by 7 months of age and was consistent with 19 year update dynamics. In addition, SC treatment remains substantially at the highest level in renewal density during the growing season, TN _a ～TN _c The density of the survival seedlings at the end of 8 months in SC treatment under the density of forest stand reaches 6600.00 strain hms respectively ^-2 7900.00 strain hm ^-2 And 5800.00 strain hm ^-2 . In contrast, the least updated density in 2020 was CK treatment, and the surviving seedlings at 8 months of CK treatment at 3 densities had only one density each1933.33 strain hm ^-2 1133.33 strain hm ^-2 And 2133.33 strain hm ^-2 . Thus, in addition to improving the update density and the update grade, the SC treatment can be beneficial to promote the early germination and the prolongation of the growing season of larch seeds; the inference that the withered object may be a major obstacle factor in the update process in 2020 is also verified to some extent. At the end of 9 months in 2020, a large number of seeds still germinate in part of the woodland, and the germinated seedlings in the last growing season cannot safely overwintere. The method can cause great waste of seedlings when the late sowing is harmful to natural updating. And the research on the related aspects in future should combine with the updated dynamic results of the test to advance the sowing time by about 1 month. However, the seedlings should be kept away from the harm of night frost as much as possible.

2.6 survival rate

The survival rate comparison in the promotion test is 2 aspects, namely the survival rate comparison of the growth season under the forest with each density in 2 years and the survival rate comparison of the growth season under the forest with different densities and treatment modes in 2020.

In comparison of growth season survival rates under each density forest over 2 years, TN was as shown in Table 11 _a ～TN _c The survival rates of the forests with the 3 densities in the season of 2019 and 2020 respectively have 70.28%, 77.22% and 49.65% and 73.93%, 62.11% and 62.26%, and no obvious difference exists between the survival rates (p>0.05 And the survival rate of the growing season is also less different among woods with different densities in the same year (p>0.05). It can be seen that the stand density has less effect on the survival rate of seedlings in the growing season, while seeds from different sources show comparable quality in terms of the survival rate in the growing season.

Table 11 comparison of survival rates of Lin Fenxia growth seasons at various densities over 2 years

Note that: capital letters indicate differences between densities, and lowercase letters indicate differences between years. The letter differences represent a significant difference, with a difference significance level of 0.05.

The results of comparing the survival rate of seedlings in growing season for different density stands and treatment modes in 2020 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). On the density of forest stand, TN _a Average growth season survival rate of 73.93% at density is maximum, while TN _b The survival rate of 62.11% of the growing season at density was minimal (p>0.05 A) is provided; the difference in survival rate of the growth seasons under different densities was also insignificant with the same mode of treatment of the litter (p>0.05 Under CC treatment, TN _a 、TN _b And TN (TN) _c The growth season survival rates under density forests were 65.85%, 85.22% and 60.60%, respectively, with the differences not reaching significant levels (p>0.05). In comparison with the method of treating the withered objects, the survival rate in the growing season is the highest with the average survival rate of 71.75% in BC treatment and the lowest with the average survival rate of 56.18% in SC treatment (p)>0.05 A) is provided; when the survival rates of the seedlings in the growing season are compared among the various withered object treatment modes in the same forest stand, the difference does not reach significance (p>0.05). As in TN _b The growth season survival rates from CK treatment, CC treatment, BC treatment, and SC treatment were 57.30%, 85.22%, 62.22%, and 43.68% respectively at the densities, and the differences between the treatments did not reach significant levels (p>0.05)。

Table 12 2020 comparison of survival rates of different density forests and growing seasons in treatment mode

Note that: capital letters indicate differences between the modes of treatment of the litter, and lowercase letters indicate differences between densities. The letter differences represent a significant difference, with a difference significance level of 0.05.

2.7 germination percentage

Each item under manual sowing in 2020The germination rates of the seeds in the treatments were compared to fig. 9. Fig. 9 shows a comparison of seed germination rates in each treatment under artificial sowing, and in fig. 9, capital letters indicate differences between the modes of treatment of the litter, and lowercase letters indicate differences between densities. The letter differences represent a significant difference, with a difference significance level of 0.05. The analysis shows that the whole method only has a large influence on the germination rate of seeds by a method of treating the withered matters, and reaches a very significant level (p<0.01 The influence of the density factor of the stand on the germination rate of seeds under the stand is smaller (p)>0.05). The density of the forest stand is TN _b The average 0.75% seed germination rate under forests of density was slightly higher (p>0.05)，TN _c And TN (TN) _a Average 0.60% and 0.59% seed germination rate under the forests of the density is lower; when comparing germination rates among forests with different densities in the same way of processing the dead objects, the germination rates are not greatly different (p)>0.05 As in CC treatment, the germination rates of 3 density woody seeds were 0.22%, 0.17% and 0.21%, and the levels of the differences from each other did not reach significance (p>0.05)。

In the mode of the withered object treatment, the germination rate of the seeds under the forest, which is 1.79 percent on average under the SC treatment, is extremely obviously higher than that of the seeds under the other three treatments (p <0.01 While the germination rates of the BC, CC and CK treated seeds decreased in order, the average germination rates were 0.52%, 0.20% and 0.08%, respectively, but the differences from each other were small (p>0.05 A) is provided; when seed germination rates are compared among different modes of seed treatment of withered objects under the same stand density, the rules are the same, and the difference of the seed germination rates in SC treatment and other treatments is at least above a significance level (p)<0.05 As in TN) _c Under a woody condition of density, the germination rate of the seeds in the SC treatment at 1.57% is significantly higher than that in the BC, CC and CK treatments at 0.50%, 0.21% and 0.11% (p<0.05 No significant difference between germination rates of the seeds of the last 3 treatments (p)>0.05)。

Results and analysis of the Effect-promoting Studies under different seed treatment modes

The previous data analysis showed that: under the condition of artificial sowing, the updating frequency is increased to 100%, the 1a seedling ratio is close to 1, the difference of the growth conditions of the seedlings under different stand densities and different sources is smaller, and the like, and the research results in the part of the promotion experiment are similar, so that the description is omitted. The analysis results of the data are developed in the aspects of update density, dynamic state and the like, so that the differences of different experiment-promoting research results are shown.

3.1 update grade, update Density and germination Rate

All seedlings appearing in each sample area in the growing season are used for measuring the lifting effect of the update grade under different seed treatment modes, and the update grade evaluation standard of the natural forest formulated by the national forestry agency is based on the standard. Table 13 shows that after the surface layer of various subsurface soil is thoroughly cleaned in 2020, the natural update level of Larix Gmelini in 4 seed treatment modes is at least at a medium level and is mainly at a good level.

Analysis of variance shows that the 4 seed treatment modes reach significance level (p) for the difference of the improvement effect of the natural update density under the forest<0.05 Seed treatment mode ST) ₁ 13400.00 strain hm ^-2 The update density of (1) is highest, and is equal to ST ₃ 13266.67 strain hm of the Chinese patent ^-2 Update density, ST of (1) ₄ 10833.33 strain hm of the Chinese patent ^-2 Is significantly greater than ST ₂ Under treatment 4733.33 strain hm ^-2 Update density (p)<0.05 But ST ₁ And ST ₃ 、ST ₄ The difference in update density between the two is small (p>0.05)。

It follows that in the case of using the same batch of seeds, the appropriate sowing time and germination accelerating measures are more helpful to increase the update density than direct sowing, while the determination of the appropriate sowing time is slightly better for the increase of the update density. In addition, because in ST ₃ And ST ₄ The update density difference between the two seed treatment modes is not large, so that the omission of the snow accumulation program can be properly considered in actual production, and the labor cost is saved.

In the test, the seed quantity is completely equal because the cleaning modes of the withered and fallen objects are all overall cleaning. And only 1 seedling of 2a was used in all the plots, the comparison of the germination rates of the seeds in each plot was substantially equivalent to the comparison of the updated densities. 4 seed treatment modes for seed germinationThe effect of the rate thus also reaches a level of significance (p<0.05 For ST) ₁ 0.53% of seeds with the highest germination rate under the treatment mode and ST ₃ 0.52% seed germination rate under treatment mode, ST ₄ The germination rate of 0.43% of seeds in the treatment mode is obviously higher than ST ₂ 0.19% seed germination (p)<0.05)，ST ₁ And ST ₃ 、ST ₄ The difference in seed germination rate is small (p>0.05). Therefore, the content is not separately described in section 1.

TABLE 13 update grade and update Density of larch under different seed treatments

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3.2 update dynamics

Dynamic changes in density of surviving seedlings in various plots under different seed treatments were made figure 10. From FIG. 10, it can be seen that ST ₂ The density of the survival seedlings is always kept at the minimum level in the growing season, and the density of the survival seedlings in the growing season is 0-4100.00 strain hms ^-2 In a relatively low range, and with a seed germination trend different from that of the other 3 treatments, the concentrated germination time of the seeds ranges from 7 months to 8 months, ST being within 1 month ₂ The density of the survival seedlings in the treated sample area is 1366.67 strain hms ^-2 Rapidly rise to 4100.00 strain hm ^-2 This is in substantial agreement with the CC, BC and CK treated seed germination dynamics at 2020 in 2.5. The other 3 treated seeds germinated mainly within 1 month after the end of 6 months, which was more similar to the update dynamics of 2019 in 2.5, i.e. the sowing time in the middle of 6 months did not affect the on-time germination of the seeds in the 3 groups.

ST ₂ The delay in seed germination is due to the late sowing time, while the other 3 groups of seeds germinate earlier for different reasons. ST (ST) ₃ And ST ₄ The treated seeds are concentrated at the end of 6 months and germinate, and the seeds are germinated before sowing, so that the seeds can quickly enter a germination state after sowing; and ST is ₁ The treated seeds are thenThe seed in 2019 is sowed in the end of rain, so that a series of early preparation work of seed germination such as water swelling can be completed before the end of 6 months, and a large amount of seeds can be germinated on time after the end of 6 months, which is similar to the seeds naturally planted.

The beneficial effects are that:

North China larch is weak in natural updating capacity, and human intervention is necessary for promoting updating. The application tries to break the limitation of the seed quantity and the withered matters on the natural updating of the larch, and manually promotes the natural updating under the forest. The promotion effect of each measure mainly improves the quantity of updated seedlings under the forest, and the best mode of manually promoting natural updating under the test condition is evaluated and screened by comparing the promotion effect differences of different measures.

A. Promotion of seedling number by means of promotion of improvement

In the forest stand of 3 densities in the larch forest in the region 31a of the Sehan dam, the updating is realized in the sample land under each promotion measure, but the updating conditions are different among different promotion treatments. When the forest is naturally planted in 2019, the natural update grades under various treatments can be seen to be in a bad state, but when the tree is artificially planted in 2020, 100% update frequency of 1a seedlings is realized in various plots, the update grade is greatly improved, and the update density is greatly improved. This further explains that seed quantity may be one of the major factors limiting the under-forest renewal of larch in the region of the stopper hamburg. While in 2019 under-forest updates occur more in CK treatment of uncleaned litter, and TN _b Under density forestation, CC treatment for comprehensively cleaning up the dead objects does not even occur. It was also confirmed that the litter layer was the primary location for storage of larch seeds in the seed pool.

However, in addition to the updated density aspect, compared with the updated characteristics of other aspects between two years, the method can find that the density, the withered object treatment mode and the seed source of different stand densities have no obvious difference basically, and particularly the difference among the stand densities is smaller. That is, various measures are not helpful for improving the quality of the updated seedlings under the forest, and only the quantity of the updated seedlings under the forest is affected. Even if the ground diameter value of fine variety seedlings at the end of 2020 is significantly smaller than that of seedlings naturally planted at the end of 2019, the artificial sowing time is probably late, and the seed germination is slow, so that the growth condition at the end of the growing season is poor, and the sowing time is extremely important. Whether the seeds are naturally planted or purchased improved seeds, the quality difference of the seeds in the under-forest updating process is not large, which means that when artificial sowing promotes natural updating in future, general seeds can be purchased to replace improved seed sowing so as to further reduce the promotion and update cost.

B. Evaluation of the best mode for human promotion

The effect of the treatment such as the cleaning mode of the dead and falling matters and the artificial sowing in the promotion test on the quantity of seedlings in the natural updating of the larch forest in North China is obvious, but the promotion effect of the seedling is slightly different. On the premise of ensuring good updating, the important purposes of saving manpower and funds are simultaneously considered, and the optimal treatment mode can be selected from the promotion measures in the test so as to provide reference basis for subsequent researchers and provide reference for forest production practice application.

First, this difference in pro-effect is manifested in update density. Under the condition that the sowing quantity in unit area is the same, the CC treatment with the largest area of the dead drop and the largest total sowing quantity is cleaned, the update density is smaller than the CK, and the SC and BC treatment with the smallest area of the dead drop and the smallest total sowing quantity is far inferior. It can be seen that the larger the area that is not cleaned, the better the effect on promoting natural renewal by cleaning up the litter. The withered and fallen matter layer also bears important functions of water and soil conservation, earth surface temperature maintenance, nutrient circulation and the like in the whole forest ecological system, and the functions can play a role in forward promotion to a certain extent in the natural updating process, and the withered and fallen matter with a certain thickness is kept to help to lighten the frost damage of seedlings in winter and improve the moisture condition of soil in dry seasons. From practical investigation, the seeds scattered in the CC treatment also have a large number of traces of feeding by rodents in the plot. This in turn explains the reason why the update density of the CC process is the smallest among the 3 kinds of litter cleaning. If effective measures could be taken to reduce to some extent the negative effects of feeding by animals, it would be possible to contribute to an increase in the renewal density of CC processing.

Second, this difference is manifested in the update dynamics. In 2020, the germination dynamics of SC treated seeds can be consistent with that of naturally planted seeds, and the germination time of the treated seeds is advanced by about 1 month compared with that of CK, CC and BC treated seeds. If the result is reasonably applied and sowed in advance on the basis of the test, the 1a seedling growing season can be prolonged, the new-born seedlings can be promoted to accumulate more dry matters in the first year, the new-born seedlings can be promoted to develop to the perennial seedlings and saplings, and natural updating can be finally and successfully realized. The reason why the germination of seeds is promoted in advance and the germination time is shortened under the SC treatment is probably because the seeds are in the withered and fallen matter ditches, so that the seeds can be directly contacted with soil, and the benefit that the withered and fallen matter layer provides water retention and heat preservation can be obtained. In the experiment of promoting the seed treatment mode, the germination accelerating measures can be found to remedy the negative influence of germination delay caused by sowing in the ten days of 6 months, and the update dynamics of the treated seeds can be consistent with that of 2019. But compared with the prior art, the proper sowing time is more time-saving and labor-saving. The seeds are sown after germination, so that the process of obtaining germination conditions in the forest land is omitted, and the reasons for keeping the update dynamic consistency are probably the reason. It should be noted, however, that the germination stage of the seeds relies on continuous and stable moisture conditions. Therefore, the seed scattering in the experiment of promoting the germination, especially the seed scattering after the germination, is carried out in rainy days, thereby avoiding the occurrence of the conditions of unfavorable updating such as flash germination and the like. Meanwhile, the research also indicates that the soil cover has the advantages of cold prevention, animal feeding prevention, moisture preservation and the like. The addition of the soil covering measure is the place where the value in the test is improved, the thickness of the soil covering is 0.3-1 cm, and the thickness of the recommended soil covering is 0.3-0.5 cm.

Finally, the pro-growth differences also manifest themselves in the germination rate of the seeds. One of the greatest advantages of natural updates over manual updates is the low cost. Improved variety purchasing is one of the main fund consumption ways in seeding promotion natural updating process. However, by calculating the germination percentage of improved seeds in the woodland in the promotion test, the utilization efficiency of seeds under the woodland can be found to be extremely low. Except for the SC treatment, the germination rate of the seeds under the forest of each treatment is not more than 1 percent. In particular, under CC treatment, the germination rate of seeds is still inferior to that of SC treatment even if measures such as germination acceleration are used. Meanwhile, the germination rate of improved larch seeds measured in laboratory conditions can reach about 88.89%. How to increase the germination rate of seeds in a woodland is significant for a promotion test. On one hand, the germination rate is improved, the seed sowing quantity can be reduced, and the seed purchase cost can be saved; on the other hand, the mass germination of seeds can offset the adverse effect of consumption in the updating process, and can fundamentally ensure good under-forest updating grade.

In conclusion, when artificial promotion is carried out in larch forest in North China in the Serhan dam area, necessary artificial sowing measures are adopted. The optimal sowing time is the end of the current year of seed rain after the withered objects are cleaned, and the time before and after the end of 5 months in the year is more proper. In the case of a false sowing time, a germination accelerating measure is necessary. As for the under-forest litter treatment, the best cleaning mode is SC treatment, followed by BC treatment, it is not recommended to directly spread seeds on heavy litter, nor to completely clean litter in the forest land to promote natural renewal.

The foregoing is merely a preferred embodiment of the present invention, and it should be noted that the above-mentioned preferred embodiment should not be construed as limiting the invention, and the scope of the invention should be defined by the appended 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 such modifications and adaptations are intended to be comprehended within the scope of the invention.

Claims (6)

1. A method for facilitating the renewal of an artificial forest comprising the steps of:

step 1) cleaning the dead and falling objects on the forestation promotion ground to expose part of the forestation ground; the method for cleaning the dead and falling objects is strip-shaped cleaning or trench-shaped cleaning;

the strip cleaning is to clean a plurality of strips with the width of 10-100 cm on the ground of a woodland;

the ditch-shaped cleaning is to clean up the withered and fallen objects at the ditching position and simultaneously open up a sowing ditch; the width of the sowing ditch is 5-15 cm, the depth is 0.5-2 cm, and the interval between ditches is 80-100 cm;

step 2) sowing woodland tree seeds on the cleaned bare ground; the sowing time is from the end of the current year of seed rain after the withered objects are cleaned to the middle ten days of 6 months of the second year, and sowing is carried out in a rainy day; and (5) carrying out soil covering or leaf covering treatment after sowing.

2. The method for promoting the renewal of artificial forest according to claim 1, wherein the woodland is larch, and the woodstand density of the woodland is controlled to be 1000-3000 strain hm ^-2 。

3. The method for promoting the renewal of artificial forests according to claim 1 or 2, wherein said step 1) is carried out for a period of time of 5 late month each year for cleaning up the dead and falling matters on the forests.

4. The method of promoting the renewal of artificial forests according to claim 1, wherein said sowing grooves are arranged in a grid.

5. The method for promoting the renewal of artificial forests according to claim 1 or 2, characterized in that in said step 2), the sowing density is 220-280 · m ^-2 。

6. The method for promoting the renewal of artificial forests according to claim 1 or 2, wherein in said step 2), the seeds selected for sowing are seeds treated with outdoor natural snow reserves.