Method for restoring low-quality Cryptomeria fortunei plantations into coniferous and broad-leaved mixed forests

Abstract

The present invention relates to the technical field of degraded forest land restoration, and discloses a method for restoring low-quality Cryptomeria fortunei plantations into coniferous and broad-leaved mixed forests. The specific steps include the selection of restoration target tree species, the division of degradation types, and restoration and transformation measures. According to different degraded community structures, development laws and habitats, the present invention classifies the degradation types of Cryptomeria fortunei forests, selects target tree species with reference to the composition of the climax community of subtropical zonal vegetation, and takes appropriate restoration and transformation technical measures, which promotes the restoration growth of alpine coniferous and broad-leaved multi-layered mixed forests, reduces the silvicultural risks caused by improper selection of traditional transformation tree species, has clear restoration targets, strong pertinence, and is easy to operate.

Description

Technical Field

[0001] The present invention belongs to the technical field of degraded forest land restoration, and particularly relates to a method for restoring a low-quality Cryptomeria fortunei plantation into a coniferous and broad-leaved mixed forest. Background Art

[0002] In the early 1960s, a large number of pure Cryptomeria fortunei plantations were established in the subtropical region to green barren mountains, and currently, they have all entered the near-mature forest stage. However, due to frequent typhoons, snow pressure, low-temperature stress, and ineffective tending measures, trees in the forest are prone to lodging or breaking, vines and bamboos grow in clusters, and pests and diseases occur frequently. As a result, the growth of forest trees is slow, the stand structure is simple, the trunks are hollow, there are many rotten woods, the wood quality is poor, the soil fertility declines, and it is difficult to regenerate the stand.

[0003] The following are the main problems existing in the traditional forestry technology for the transformation of degraded Cryptomeria fortunei: 1) Since Cryptomeria fortunei mostly grows in harsh habitats with high altitudes, strong winds, and cold, the degradation types are diverse, and it is difficult to select replacement tree species for regeneration and transformation. Often, the tree species are selected improperly, resulting in failed forest management; 2) There are few broad-leaved tree species in the Cryptomeria fortunei forest, and natural regeneration is scarce. The biodiversity is very poor. After logging, the ground cover in the forest land is low, the loose surface materials are few and the thickness is shallow, soil erosion is serious, the soil degenerates, and the cost of restoration and regeneration is relatively high, which affects the growth and sustainable development of the Cryptomeria fortunei forest; 3) After logging, there are many Cryptomeria fortunei root stumps on the cutover land, and the decomposition and decay time is long, which brings difficulties to the subsequent site preparation, regeneration, and tending.

[0004] The tree species for afforestation and density are two important factors affecting the growth and harvest of forest stands, and are also the key measures to improve the productivity of artificial forests. Therefore, the configuration of tree species and density management for different site types are not only one of the key technologies to be solved in the production of artificial forest establishment and low-quality forest transformation, but also become a hot topic in forestry science. Although there are more and more articles on low-quality forest transformation test forests, there are few articles on the impact of different degraded Cryptomeria fortunei forest transformations on the growth and structure of forest stands, especially the reports on the rapid restoration of different site-type degraded Cryptomeria fortunei forests into zonal climax forests are extremely scarce.

[0005] After retrieval, CN108464176B discloses a transformation technology for a pure Pinus massoniana plantation in the south subtropical region into a pine and broad-leaved uneven-aged multi-layered mixed forest. By thinning to form forest gaps and replanting native broad-leaved tree species under the forest gaps, the pure Pinus massoniana plantation with the same age and single layer is transformed into a pine and broad-leaved multi-layered mixed forest in the early stage. However, it does not scientifically establish tree species allocation and forest cultivation technical schemes corresponding to different sites and pine forest structure types, and cannot meet the needs of large-scale transformation of Cryptomeria fortunei forests with different degraded community structures and habitats. Summary of the Invention

[0006] The present invention discloses a method for restoring low-quality Cryptomeria fortunei plantations into coniferous and broad-leaved mixed forests, which solves the problems that the prior art fails to construct according to the dominant species of regional climax vegetation. More importantly, there is no scientific establishment of tree species allocation and forest cultivation technical schemes corresponding to different site conditions and pine forest structure types, and it cannot meet the needs of large-scale transformation of Cryptomeria fortunei forests with different degraded community structures and habitats.

[0007] A method for restoring low-quality Cryptomeria fortunei plantations into coniferous and broad-leaved mixed forests specifically includes the following steps:

[0008] (1) Selection of target tree species for restoration

[0009] According to the subtropical vegetation climax forest model, the target tree species for restoration are Cyclobalanopsis myrsinifolia, Cyclobalanopsis gilva, Cyclobalanopsis sessilifolia, Castanopsis carlesii, Schima superba, and Machilus thunbergii. Among them, two or more target tree species are combined, and the planting proportion of the target tree species is greater than 20% of the total tree species quantity;

[0010] (2) Division of degradation types

[0011] According to the community structure, development law, and site type conditions of degraded Cryptomeria fortunei forests, the degraded Cryptomeria fortunei forests are divided into three degradation types: Cryptomeria fortunei sparse forests on ridges, Cryptomeria fortunei - Indocalamus tessellatus degraded forests on slopes, and low-quality old-growth Cryptomeria fortunei degraded forests;

[0012] (3) Restoration and transformation measures

[0013] S1. Transformation of the degradation type of Cryptomeria fortunei sparse forests on ridges: From December to February, through winter sanitary felling and tending, keep the density of the tree layer at 10 - 15 plants per mu, and replant Cyclobalanopsis myrsinifolia, Cyclobalanopsis gilva, and Cyclobalanopsis sessilifolia in spring, with a density of 230 - 250 plants per mu. Conduct continuous tending for 4 years after replanting;

[0014] S2. Transformation of the degradation type of Cryptomeria fortunei - Indocalamus tessellatus forests on slopes: From December to February, through winter stand thinning, use strip and block land preparation, and replant Cyclobalanopsis myrsinifolia, Castanopsis carlesii, Schima superba, and Cyclobalanopsis gilva in spring, with a density of 150 - 160 plants per mu; Conduct continuous tending for 4 years after replanting;

[0015] S3. Transformation of the degradation type of low-quality old-growth Cryptomeria fortunei forests: From December to February, through winter sanitary felling and tending, keep 25 - 30 Cryptomeria fortunei plants per mu in the tree layer; Keep seedlings and saplings of broad-leaved trees; Replant Cyclobalanopsis gilva, Castanopsis carlesii, Schima superba, and Machilus thunbergii in spring, with 150 - 160 plants per mu; Conduct continuous tending for 4 years after replanting.

[0016] Preferably, the degradation type division described in (2) is as follows in the table:

[0017]

[0018] Preferably, when transforming the degraded type of sparse Cryptomeria fortunei forests on ridges in S1 of (3), site preparation and hole digging are carried out on the forest clearings in early December, and supplementary planting is carried out in spring; the specifications of the holes are 0.5×0.5×0.3 m, backfill with topsoil, and the plant spacing is (1.6 - 1.8 m)×(1.6 - 1.8 m).

[0019] Preferably, 10 years after transforming the degraded type of sparse Cryptomeria fortunei forests on ridges in S1 of (3), there are 10 - 13 trees per mu in the arbor layer of the community; the height of the shrubs is 2 - 3 m, and the density is 200 - 210 plants.

[0020] Preferably, when transforming the degraded type of Cryptomeria fortunei - Indocalamus tessellatus forests on slopes in S2 of (3), during the thinning of the forest stand, blow - down, standing dead, weak, diseased and pest - infested trees and bamboo shrubs are removed.

[0021] Preferably, when transforming the degraded type of Cryptomeria fortunei - Indocalamus tessellatus forests on slopes in S2 of (3), site preparation and hole digging are carried out on the forest clearings in early December, and supplementary planting is carried out in spring; the specifications of the holes are 0.5×0.5×0.3 m, backfill with topsoil, and the plant spacing is (1.8 - 2 m)×(1.8 - 2 m).

[0022] Preferably, 10 years after transforming the degraded type of Cryptomeria fortunei - Indocalamus tessellatus forests on slopes in S2 of (3), there are 30 - 35 Cryptomeria fortunei trees per mu in the arbor layer; the height of the shrubs is 2 - 3 m, and the density is 140 - 150 plants.

[0023] Preferably, when transforming the degraded type of low - quality old - growth Cryptomeria fortunei forests in S3 of (3), the specific method of sanitary felling and tending is as follows: fell hollow, standing dead, blow - down and weak trees, clean up the logging residues, and prepare the removed residues into organic matter with 180 kg of logging branches and leaves residues, 18 kg of fresh grass, and 2 kg of compound fertilizer, cover it under the crowns of the well - growing retained trees, and cover it with soil with a thickness of 3 cm; drill holes in the stumps, apply 0.5 kg of compound fertilizer per tree, and cover with mud.

[0024] Preferably, when transforming the degraded type of low - quality old - growth Cryptomeria fortunei forests in S3 of (3), site preparation and hole digging are carried out on the forest clearings in early December, the specifications of the holes are 0.5×0.5×0.3 m, backfill with topsoil, and the plant spacing is (1.8 - 2 m)×(1.8 - 2 m).

[0025] Preferably, 10 years after transforming the degraded type of low - quality old - growth Cryptomeria fortunei forests in S3 of (3), the density of the arbor layer is 20 - 25 trees per mu; the height of the shrubs is 3.5 - 4 m, and the density is 140 - 150 plants.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1) The present invention classifies the degradation types of Cryptomeria fortunei forests according to different degraded community structures, development laws, and habitats. Referring to the composition of the climax community of subtropical zonal vegetation, target tree species are selected and appropriate restoration and transformation technical measures are taken, which promotes the restoration growth of the alpine needle-broadleaved multi-layered mixed forest, reduces the silvicultural risks caused by improper selection of traditional transformation tree species, has a clear restoration goal, strong pertinence, and is easy to operate.

[0028] 2) The present invention plants Cyclobalanopsis glauca in the Cryptomeria fortunei forests on the ridges. Since Cyclobalanopsis glauca is tolerant of barrenness, has strong adaptability, has a large wood density, is tough, and has functions of wind resistance, ice and frost resistance, and snow pressure resistance, the survival rate of the planted saplings is high, the growth is good, the restoration is fast, and it is beneficial to promoting the restoration growth of the alpine needle-broadleaved multi-layered mixed forest.

[0029] 3) The present invention covers the crowns of the remaining trees with organic matters such as Cryptomeria fortunei branches, leaves residues and fresh grass on the logging sites of old-growth Cryptomeria fortunei forests. This not only clears a large amount of logging residues on the forest land, solves the inconvenience of tending and cultivation operations, but also can increase soil nutrients and moisture, improve soil structure, maintain soil fertility, uses local materials, makes comprehensive utilization, is easy to operate, and is economical and practical.

[0030] 4) The present invention applies fertilizer and presses mud on the stumps of old-growth Cryptomeria fortunei forests, which can accelerate the decay of the stumps, can not only increase the forest land utilization area, but also promote the natural regeneration of broad-leaved seedlings, reduce the production cost, and improve the economic benefits. Detailed implementation manners

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0032] In each embodiment of the present invention, the experimental methods are all conventional methods unless otherwise specified. The materials, reagents, etc. used can be obtained from commercial channels unless otherwise specified.

[0033] The implementation location of the embodiments of the present invention is located in Yinzhou District, Ningbo City, Zhejiang Province in the coastal mountainous area, with an altitude of 350 - 500 m. The low-quality Cryptomeria fortunei degradation types are classified according to Table 1.

[0034] Table 1 Classification of degraded Cryptomeria fortunei forest types

[0035]

[0036]

[0037] Example 1

[0038] (1) Selection of target tree species for restoration

[0039] Determine the constructive tree species according to the climax forest pattern of subtropical vegetation in East Zhejiang.

[0040] (2) According to the community structure, development law and site type conditions of the degraded Cryptomeria fortunei forest in Table 1, the degraded Cryptomeria fortunei forest is divided into three degraded types: Cryptomeria fortunei sparse forest on the ridge, Cryptomeria fortunei - Indocalamus tessellatus degraded forest on the hillside, and low - quality old - growth Cryptomeria fortunei degraded forest.

[0041] (3) Select corresponding restoration and transformation measures according to the degraded types of low - quality Cryptomeria fortunei plantations.

[0042] S1. Transformation of the degraded type of Cryptomeria fortunei sparse forest on the ridge:

[0043] First, analyze the results of the 20×20m fixed - plot survey. It is determined that the degraded forest stand was originally a pure Cryptomeria fortunei plantation. Due to its location at the mountaintop with harsh site conditions, the Cryptomeria fortunei forest has a simple structure, a large amount of depreciated heliophytic resources, a small tree density, and a declining growth trend. This type of forest stand is determined as Cryptomeria fortunei sparse forest on the ridge. The recent restoration goal is a multi - layer, uneven - aged mixed forest of coniferous and broad - leaved trees, quickly establishing the dominant target tree species of the climax forest, adjusting the forest stand structure, and promoting the growth of young forests.

[0044] Secondly, the restoration measures are as follows: Through sanitary felling and tending of the forest stand, fell dead standing, wind - thrown, weak, and broken - topped trees, and retain 10 Cryptomeria fortunei trees per mu with growth prospects; then, on December 1st, conduct block - shaped land preparation and digging of holes in the forest clearings. The hole specifications are 0.5×0.5×0.3m, backfill the topsoil, and the plant spacing is 1.6×1.6m. Since Cyclobalanopsis glauca has strong wind and cold resistance, strong adaptability, high economic value, and is a climax species of the community, it is selected as the target tree species for restoration. On March 11th, replant 130 two - year - old bare - root seedlings of Cyclobalanopsis gilva with local provenance, strong growth, full apical buds, and high lignification degree, 50 bare - root seedlings of Cyclobalanopsis myrsinifolia and Cyclobalanopsis sessilifolia respectively per mu, with a density of 230 plants per mu. After replanting, loosen the soil and remove weeds within 1m of the young trees in May and September of the same year, and conduct tending for 4 consecutive years.

[0045] Thirdly, the positive effect is that 10 years after the transformation, the height of Cryptomeria fortunei trees in the tree layer reaches 9m, with a density of 10 plants per mu; in the shrub layer, a large number of trees such as Cyclobalanopsis glauca with the function of resisting snow, wind, and ice appear, with a height of 2m and a density of 200 plants per mu, showing good growth. It shows that the technology of the present invention can quickly improve the community structure, form an updated structure dominated by the dominant species of the climax community, and promote the growth of the forest stand.

[0046] S2. Transformation of the degraded type of Cryptomeria fortunei - Indocalamus tessellatus on the hillside:

[0047] First, from the sample plot survey, it is known that the height of Cryptomeria fortunei in the existing forest stand of the tree layer is 11 m, and the density is 33 trees. Due to the long-term closing of the mountain for forest cultivation, Indocalamus tessellatus and vines are overgrown in the forest stand, and the competition among trees is intense. Therefore, this type is determined as the degraded type of Cryptomeria fortunei and Indocalamus tessellatus on the hillside. The restoration goal is to establish Cyclobalanopsis glauca and Schima superba forest, and the short-term management goal is to cultivate a multi-layered and uneven-aged mixed forest of coniferous and broad-leaved trees, remove bamboo shrubs and vines as soon as possible, repair the regeneration layer composed of the dominant target tree species, and improve the forest stand structure.

[0048] Secondly, the restoration measures are as follows: through intermediate cutting and tending of the forest stand, 30 Cryptomeria fortunei trees are reserved per mu, a large amount of Indocalamus tessellatus, shrubs and herbs are removed, the tree tops and branches are cut off below 1 m, and they are covered with organic matters such as logging residues and fresh grass under the crowns of the reserved trees, and then covered with about 3 cm thick soil; block soil preparation is adopted, the reclamation hole specification is 0.5×0.5×0.3 m, the topsoil is backfilled, and 60 Cyclobalanopsis myrsinifolia, 60 Schima superba and 30 Cyclobalanopsis gilva are replanted per mu at a plant spacing of 1.8×1.8 m, with a total of 150 trees per mu. After replanting, the young trees are loosened and weeded once in May and September of the same year respectively for 4 consecutive years; in February of the following year after replanting, 0.3 kg of compound fertilizer is applied to each young tree by ditch digging, and then covered with soil for 3 consecutive times.

[0049] Thirdly, the positive effects are as follows: after 10 years of transformation, due to the improvement of the light and nutrient resources of the reserved trees after tending, the competition is reduced, thus improving the growth of Cryptomeria fortunei and the replanted young trees. The average height of tree species such as Cryptomeria fortunei in the tree layer is about 12 m; the average breast diameter is 14 cm, and the density is 30 trees per mu; the average height of Cyclobalanopsis myrsinifolia, Cyclobalanopsis gilva and Schima superba growing in the shrub layer is 3.5 m, the average breast diameter reaches 3.1 cm, and the density is 150 trees per mu. The forest stand density has increased significantly, and the important value has exceeded 38%, improving the community structure and showing the important construction role of the target species replacing the community.

[0050] S3. Transformation of the degraded type of low-quality and old-aged Cryptomeria fortunei:

[0051] First, through quadrat survey, it is found that the forest history of this type is similar to that of the degraded type of Cryptomeria fortunei and Indocalamus tessellatus on the hillside. Due to the older age, there are a small number of medium and young individuals of Sassafras tzumu and Machilus thunbergii mixed in the forest stand, but the number of updated individuals in the forest land is small. Due to the ineffective long-term tending measures and disease damage, many Cryptomeria fortunei trees are hollow and decayed, and the quality of standing trees is poor. Therefore, this forest stand is determined as the low-quality and old-aged degraded Cryptomeria fortunei forest, the restoration goal is the zonal evergreen broad-leaved forest at a relatively high altitude, and the short-term management goal is to restore it to a mixed forest of uneven-aged coniferous and broad-leaved trees;

[0052] Secondly, the restoration measures are as follows: In December, through sanitary felling for tending and removing hollow, standing dead, windthrown, weakened, diseased and pest-infected trees, and shortening the removed branches and rotten wood to a length less than 1 m, prepare organic matter composed of 180 kg of harvested tree tops and residues, 18 kg of fresh grass and 2 kg of compound fertilizer according to the weight ratio, cover it under the crowns of the well-growing reserved trees, and cover with soil with a thickness of about 3 cm and compact it; this is beneficial for removing logging residues and improving soil nutrients to promote the growth of forest trees; drill holes in the stumps, apply about 0.5 kg of compound fertilizer to each stump, and cover with mud to promote the decay of the root stumps; use strip or block land preparation methods to dig holes with specifications of 0.5×0.5×0.35 cm; backfill the topsoil; in mid-March, replant 60 Cyclobalanopsis gilva, 60 Schima superba and 30 Machilus thunbergii per mu, a total of 150 trees; after replanting, carry out tending for the young forest once in May and early September of the same year, and continue tending for 4 years. In early February of the following year, open shallow trenches in the uphill direction of the replanted young trees, apply 0.3 kg of compound fertilizer to each tree, and cover with soil after application;

[0053] Thirdly, the positive effects are as follows: Due to measures such as clearing and burying windthrown and hollow trees, the light transmittance in the forest is enhanced, the forest environment is unobstructed, and the competition among forest trees is reduced, so that the young trees left or replanted grow rapidly, the stand structure is improved, and the stand volume is increased. After 10 years of transformation, the average tree height of broad-leaved tree species such as Cryptomeria fortunei reserved in the tree layer is 13 m, the average breast diameter is 16.5 cm, and the density per mu is 25 trees; the average tree height of the target tree species for renewal and restoration in the shrub layer is 3.6 m, the average breast diameter is 4.0 cm, the density per mu is 150 trees, and the coverage is 50%. It shows that the community structure of the present invention has been significantly improved, and a mixed coniferous and broad-leaved uneven-aged multi-layer community structure has been formed. More importantly, the abundance and community status of the target tree species have been improved, shortening the community succession time by at least 20 years, and the effect is obvious.

[0054] Example 2

[0055] (1) Selection of target tree species for restoration

[0056] Based on the top forest pattern of subtropical vegetation in East Zhejiang, determine the constructive tree species.

[0057] (2) According to the community structure, development law and site type status of the degraded Cryptomeria fortunei forest in Table 1, divide the degraded Cryptomeria fortunei forest into three degraded types: ridge Cryptomeria fortunei sparse forest, hillside Cryptomeria fortunei - Indocalamus tessellatus degraded forest and low-quality old-aged Cryptomeria fortunei degraded forest.

[0058] (3) According to the degraded types of low-quality Cryptomeria fortunei plantations, select corresponding restoration and transformation measures.

[0059] S1. Transformation of the ridge Cryptomeria fortunei sparse forest degraded type:

[0060] First, the analysis of the results of the 20×20m fixed plot survey was adopted to determine that the degraded forest stand was originally a pure Cryptomeria fortunei plantation. Due to its location on the mountaintop with harsh site conditions, the Cryptomeria fortunei forest not only had a simple structure, a large amount of depreciated resources with heliophytic characteristics, a small tree density, and a declining growth trend, but also was determined as a sparse Cryptomeria fortunei forest on the ridge. The recent restoration goal was a multi-layered and uneven-aged mixed forest of coniferous and broad-leaved trees, to quickly establish the dominant target tree species of the climax forest, adjust the forest stand structure, and promote the growth of young forests.

[0061] Secondly, the restoration measures were as follows: Through the sanitary felling and tending of the forest stand, dead standing, wind-thrown, weak, and broken-top trees were felled, and 13 Cryptomeria fortunei trees with growth prospects were retained per mu; then, in early December, block land preparation and hole digging were carried out in the forest clearings. The hole-digging specifications were 0.5×0.5×0.3m, and the topsoil was backfilled. The plant spacing was 1.7×1.7m. Since Cyclobalanopsis glauca had strong wind and cold resistance, strong adaptability, high economic value, and was also the climax species of the community, it was selected as the target tree species for restoration. In mid-March, 130 two-year-old bare-root seedlings of Cyclobalanopsis gilva with local provenance, robustness, plump terminal buds, and high degree of lignification, and 50 bare-root seedlings of Cyclobalanopsis myrsinifolia and Cyclobalanopsis sessilifolia were planted and matched, with a density of 230 plants per mu. After planting, in May and September of the same year, the soil within 1m of the young trees was loosened and weeded respectively, and tending was carried out continuously for 4 years.

[0062] Thirdly, the positive effect was that after 10 years of transformation, the height of Cryptomeria fortunei trees in the tree layer reached 9m, with a density of 13 plants per mu; in the shrub layer, a large number of trees such as Cyclobalanopsis glauca with the function of resisting snow, wind, and ice appeared, with a height of 2-3m and a density of 210 plants per mu, showing good growth. It indicated that the technology of the present invention could rapidly improve the community structure, form an updated structure dominated by the dominant species of the climax community, and promote the growth of the forest stand.

[0063] S2. Transformation of the degraded types of Cryptomeria fortunei and Indocalamus tessellatus on the hillside:

[0064] First, from the plot survey, it was known that the height of Cryptomeria fortunei trees in the existing forest stand's tree layer was 11m, and the density was 33 plants. Due to the long-term closure of the mountain for forest cultivation, the Indocalamus tessellatus vines were overgrown in the forest stand, and the competition among trees was fierce. Therefore, this type was determined as the degraded type of Cryptomeria fortunei and Indocalamus tessellatus on the hillside. The restoration goal was set as a forest of Cyclobalanopsis glauca and Schima superba, and the recent management goal was to cultivate a multi-layered and uneven-aged mixed forest of coniferous and broad-leaved trees, quickly remove the bamboo shrubs and vines, repair the updated layer composed of the dominant target tree species with climax advantages, and improve the forest stand structure.

[0065] Secondly, the restoration measures are as follows: in December, through thinning and tending of the stand, 30 Cryptomeria fortunei trees are retained per mu, a large amount of Indocalamus tessellatus, shrubs and grasses are removed, the tree tops and branches are cut off below 1 m, and they are covered with organic matters such as logging residues and fresh grass under the crowns of the retained trees, and then covered with about 3 cm thick soil; block site preparation is adopted, the specifications of the reclamation holes are 0.5×0.5×0.3 m, the topsoil is backfilled, and 60 Cyclobalanopsis myrsinifolia, 60 Schima superba and 30 Cyclobalanopsis gilva are replanted per mu at a plant spacing of 1.8×1.8 m, with a total of 150 trees per mu. After replanting, the young trees are loosened and weeded once in May and September of the same year respectively for 4 consecutive years; in February of the next year after replanting, 0.3 kg of compound fertilizer is applied to each young tree by trenching, and the soil is covered after application for 3 consecutive times.

[0066] Thirdly, the positive effects are as follows: after 10 years of transformation, due to the improvement of the light and nutrient resources of the retained trees after tending, the competition is reduced, thus improving the growth of Cryptomeria fortunei and the replanted young trees. The average tree height of tree species such as Cryptomeria fortunei in the tree layer is about 12 m; the average breast diameter is 14 cm, and the density per mu is 30 trees; the average tree height of Cyclobalanopsis myrsinifolia, Cyclobalanopsis gilva and Schima superba growing in the shrub layer is 3.5 m, the average breast diameter reaches 3.1 cm, and the density per mu is 150 trees. The stand density has increased significantly, and the important value has exceeded 38%, improving the community structure and showing the important construction role of the target species replacing the community.

[0067] S3. Transformation of the degraded type of low-quality old Cryptomeria fortunei forest:

[0068] Firstly, through quadrat surveys, it is found that the forest history of this type is similar to the above case. Due to the mixture of a small number of medium and young individuals of Sassafras tzumu and Machilus thunbergii in the stand with older ages, but the number of forest land renewal individuals is small. Due to the ineffective long-term tending measures and disease hazards, many Cryptomeria fortunei trees are hollow and decayed, and the quality of standing trees is poor. Therefore, this stand is determined as a low-quality old degraded Cryptomeria fortunei forest, the restoration goal is the zonal evergreen broad-leaved forest at higher altitudes, and the short-term management goal is to restore it to a needle-leaved and broad-leaved uneven-aged multi-layered mixed forest;

[0069] Secondly, the restoration measures are as follows: in December, through sanitary felling for tending and removing hollow, standing dead, windthrown, weak, and pest-damaged trees, and shortening the removed branches and rotten wood to a length less than 1 m, prepare organic matter composed of 180 kg of harvested tree tops and residues, 18 kg of fresh grass, and 2 kg of compound fertilizer according to the weight ratio, cover it under the crowns of the well-growing reserved trees, and cover with soil to a thickness of about 3 cm and compact it; this is beneficial for removing logging residues and improving soil nutrients to promote the growth of forest trees; drill holes in the stumps, apply about 0.5 kg of compound fertilizer to each stump, and cover with mud to promote the decay of the root stumps; use strip or block land preparation methods to dig holes with specifications of 0.5×0.5×0.35 cm; backfill the topsoil; in mid-March, replant 60 Cyclobalanopsis gilva, 60 Schima superba, and 30 Machilus thunbergii per mu, a total of 150 trees; after replanting, conduct young forest tending once in May and early September of the same year, and continue tending for 4 years. In early February of the following year, open shallow trenches in the uphill direction of the replanted young trees, apply 0.3 kg of compound fertilizer to each tree, and cover with soil after application;

[0070] Thirdly, the positive effects are as follows: due to measures such as clearing and burying windthrown and hollow trees, the light transmittance in the forest is enhanced, the forest environment is unobstructed, and the mutual competition among forest trees is reduced, thus enabling the young trees left or replanted to grow rapidly, improving the stand structure, and increasing the stand volume. After 10 years of transformation, the average tree height of broad-leaved tree species such as Cryptomeria fortunei retained in the arbor layer is 13 m, the average breast diameter is 16.5 cm, and the density per mu is 25 trees; the average tree height of the updated and restored target tree species in the shrub layer is 3.6 m, the average breast diameter is 4.0 cm, the density per mu is 150 trees, and the coverage is 50%. This shows that the community structure of the present invention has been significantly improved, and a heterogeneous multi-layer community structure of coniferous and broad-leaved mixed forest has been formed. More importantly, the abundance and community status of the target tree species have been improved, shortening the community succession time by at least 20 years, and the effect is obvious.

[0071] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0072] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for restoring low-quality Cryptomeria fortunei plantations into coniferous and broad-leaved mixed forests, characterized in that, Specifically, it includes the following steps: (1) Selection of target tree species for restoration According to the climax forest pattern of subtropical vegetation, the target tree species for restoration are Cyclobalanopsis myrsinifolia, Cyclobalanopsis gilva, Cyclobalanopsis sessilifolia, Castanopsis carlesii, Schima superba, and Machilus thunbergii. Among them, two or more target tree species are combined, and the planting proportion of target tree species is greater than 20% of the total tree species quantity; (2) Classification of degradation types According to the community structure, development law, and site type conditions of degraded Cryptomeria fortunei forests, the degraded Cryptomeria fortunei forests are divided into three degradation types: Cryptomeria fortunei sparse forests on ridges, Cryptomeria fortunei - Indocalamus tessellatus degraded forests on slopes, and low - quality old - growth Cryptomeria fortunei degraded forests; (3) Restoration and transformation measures S1. Transformation of the degraded type of Cryptomeria fortunei sparse forests on ridges: From December to February, through winter sanitation felling and tending, retain 10 - 15 trees per mu in the tree layer. In spring, replant Cyclobalanopsis myrsinifolia, Cyclobalanopsis gilva, and Cyclobalanopsis sessilifolia, with a density of 230 - 250 trees per mu, and continuously tend for 4 years after replanting; S2. Transformation of the degraded type of Cryptomeria fortunei - Indocalamus tessellatus forests on slopes: From December to February, through winter stand thinning, use strip or block - shaped land preparation. In spring, replant Cyclobalanopsis myrsinifolia, Castanopsis carlesii, Schima superba, and Cyclobalanopsis gilva, with a density of 150 - 160 trees per mu; Continuously carry out young forest tending for 4 years after replanting; S3. Transformation of the degraded type of low - quality old - growth Cryptomeria fortunei forests: From December to February, through winter sanitation felling and tending, retain 25 - 30 Cryptomeria fortunei trees per mu in the tree layer; Keep the seedlings and saplings of broad - leaved trees. In spring, replant Cyclobalanopsis gilva, Castanopsis carlesii, Schima superba, and Machilus thunbergii, with 150 - 160 trees per mu; Continuously carry out young forest tending for 4 years after replanting; The degradation types described in (2) are as follows in the table: 。 2. The method according to claim 1, characterized in that, When transforming the degraded type of Cryptomeria fortunei sparse forests on ridges in S1 of (3), prepare land and dig holes in the forest gaps in early December, and replant in spring; The specifications of the dug holes are 0.5×0.5×0.3 m, backfill the topsoil, and the plant spacing is (1.6 - 1.8 m)×(1.6 - 1.8 m).

3. The method according to claim 2, characterized in that, Ten years after the transformation of the degraded type of Cryptomeria fortunei sparse forests on ridges according to S1 of (3), there are 10 - 13 trees per mu in the tree layer of the community; The height of the shrub layer is 2 - 3 m, and the density is 200 - 210 trees per mu.

4. The method according to claim 1, wherein When transforming the degraded type of Cryptomeria fortunei - Indocalamus tessellatus forests on slopes in S2 of (3), during the stand thinning, remove wind - fallen, standing dead, weak, pest - infested, and bamboo and shrub trees.

5. The method according to claim 4, characterized in that, When transforming the degraded type of Cryptomeria fortunei - Indocalamus tessellatus forests on slopes in S2 of (3), prepare land and dig holes in the forest gaps in early December, and replant in spring; The specifications of the dug holes are 0.5×0.5×0.3 m, backfill the topsoil, and the plant spacing is (1.8 - 2 m)×(1.8 - 2 m).

6. The method according to claim 5, wherein Ten years after the transformation of the degraded type of Cryptomeria fortunei - Indocalamus tessellatus forests on slopes in S2 of (3), there are 30 - 35 Cryptomeria fortunei trees per mu in the tree layer; The height of the shrub layer is 2 - 3 m, and the density is 140 - 150 trees per mu.

7. The method according to claim 1, wherein When transforming the degraded type of low-quality old-growth Cryptomeria fortunei in S3 of (3), the specific method of sanitary felling and tending is as follows: fell the hollow, standing dead, windthrown, and weak trees, clean up the logging residues, and prepare the removed residues into organic matter consisting of 180 kg of logging branches and leaves residues, 18 kg of fresh grass, and 2 kg of compound fertilizer, and cover it under the crowns of the well-growing reserved trees, and then cover with soil with a thickness of 3 cm; drill holes in the stumps, apply 0.5 kg of compound fertilizer to each stump, and cover with mud.

8. The method according to claim 7, characterized in that, When transforming the degraded type of low-quality old-growth Cryptomeria fortunei in S3 of (3), in the early ten-day period of December, prepare the land and dig holes in the forest open space. The specifications of the holes are 0.5×0.5×0.3 m, backfill the topsoil, and the plant spacing is (1.8 - 2 m)×(1.8 - 2 m).

9. The method according to claim 8, wherein Ten years after the transformation of the degraded type of low-quality old-growth Cryptomeria fortunei in S3 of (3), the density of the tree layer per mu is 20 - 25 plants; the height of the shrub layer is 3.5 - 4 m, and the density is 140 - 150 plants.

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