Method for recovering tropical degraded forest based on thinning and complementary planting of nitrogen fixation precious tree species

Abstract

The invention relates to the technical field of ecological restoration, in particular to a method for restoring a tropical degraded forest based on thinning and complementary planting of nitrogen fixation precious tree species. The method comprises the following steps: dividing a degenerated forest into three types, namely a mild type, a moderate type and a severe type according to canopy density and forest stand composition; for the light tropical degraded forest, a stand structure is built through target tree marking and interference tree felling, stand renewal is driven in cooperation with pruning work and selective felling, and a different-age double-layer forest is cultivated; for the moderate tropical degraded forest, a forest window updating unit is constructed, and survival rate and preservation rate dual monitoring is executed to maintain the forest window updating unit; for the severe tropical degraded forest, native vegetation is reserved through strip cleaning, seedlings are planted in a planting strip to construct a strip recovery substrate, synchronous complementary planting is carried out, and finally the strip succession process is stabilized in combination with continuous tending. According to the method, the problem of repairing the fragmented area is effectively solved, synergistic interaction of soil improvement and economic value improvement is achieved, and the technology generalizability is remarkably enhanced through a standardized operation system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ecological restoration, in particular to a method for restoring degraded tropical forest based on thinning and replanting nitrogen-fixing valuable tree species BACKGROUND

[0002] In the 20th century, the area of tropical forest decreased sharply, about 350 million hectares of forest were cut down, and 500 million hectares of tropical forest were degraded, resulting in serious damage to its structure and function. The goal of tropical forest restoration is to rebuild an ecological system similar to the structure and function of zonal vegetation, or gradually transition to a zonal forest ecosystem through artificial ecosystems, and achieve self-maintenance after restoration.

[0003] The restoration techniques of degraded tropical forest mainly include: forest closure, artificial promotion of natural restoration and artificial reconstruction. Due to different degrees of degradation of tropical forests in different regions, different restoration techniques should be adopted. However, the classification of different degraded forest types is not clear at present, and there is a lack of differentiated schemes for different degrees of degradation, making it difficult to meet the management needs of fragmented topography.

[0004] So far, there is no scientific mechanism for the collaborative use of valuable tree species with both ecological and economic value and nitrogen-fixing tree species that can improve soil through symbiotic nitrogen-fixing microorganisms in the management of degraded forests. SUMMARY

[0005] The present application aims to provide a method for restoring degraded tropical forest based on thinning and replanting nitrogen-fixing valuable tree species, which formulates and adopts corresponding forest restoration strategies and techniques according to the degree of forest degradation, in order to improve the level and effect of degraded forest restoration.

[0006] To achieve the above-mentioned purpose, the present application provides a method for restoring degraded tropical forest based on thinning and replanting nitrogen-fixing valuable tree species, comprising: dividing the degraded tropical forest into light, moderate and severe degraded tropical forest; the light degraded tropical forest has a canopy density greater than or equal to 0.6, and the forest stand composition includes interlayer lianas and tall trees, wherein the area proportion of the interlayer lianas and tall trees is more than that of other forest stands; the moderate degraded tropical forest has a canopy density of 0.2-0.6, and the forest stand composition includes low trees, sprouting or naturally regenerated trees and shrubs, wherein the area proportion of the low trees, sprouting or naturally regenerated trees and shrubs is more than that of other forest stands; the severe degraded tropical forest has a canopy density less than 0.2, and the forest stand composition includes sprouting and naturally regenerated bushy low trees and shrubs, and positive weeds, wherein the area proportion of the sprouting and naturally regenerated bushy low trees and shrubs and positive weeds is more than that of other forest stands; The restoration method of the mild tropical degraded forest comprises: Constructing a stand structure: selecting a nitrogen-fixing tree species in precious tree species as a target tree at a density of 90-120 trees per hectare and marking, and cutting interference trees, which are trees with canopies connected or overlapping with the target tree; Driving stand regeneration: implementing pruning operations on a section with a vertical height of less than or equal to 9 m from the ground surface reference plane of the main stem of the target tree; then selecting and cutting the target trees with a diameter at breast height greater than 60 cm to form a regeneration forest, and finally cultivating the regeneration forest into a multi-aged complex forest; The restoration method of the moderate tropical degraded forest comprises: Constructing a forest window regeneration unit: opening forest windows in the moderate degradation type tropical forest at a density of 90-120 per hectare, and digging multiple first-type planting holes at the corresponding positions of each forest window, and planting nitrogen-fixing precious tree species seedlings in the rainy season; Maintaining a forest window replacement unit: mowing off invasive vegetation, maintaining the area of the forest window to maintain a light-transmitting environment, monitoring the survival rate of the constructed nitrogen-fixing precious tree species seedlings, and replanting when the survival rate is less than 85%; investigating the preservation rate in the dry season the next year, and replanting when the preservation rate is less than 85% until it is greater than 85%, and protecting the naturally regenerated nitrogen-fixing precious tree species seedlings by implementing 2-3 times of cutting and weeding every year for 3-5 consecutive years;

[0007] The restoration method of the severe tropical degraded forest comprises: Constructing a strip-shaped restoration base: dividing the afforestation land of the severe tropical degraded forest into a planting strip and a reserved strip, removing weeds and shrubs in the planting strip and piling them into the reserved strip, keeping the planting strip consistent in the same afforestation land direction, preserving the precious tree species seedlings in the planting strip, and digging second-type planting holes in the middle of the planting strip to plant nitrogen-fixing precious tree species seedlings in the rainy season; Stabilizing the strip-shaped succession process: monitoring the survival rate of the planted nitrogen-fixing precious tree species seedlings, and replanting based on the axis of the planting strip when the survival rate is less than 85%; investigating the preservation rate in the dry season the next year, and replanting when the preservation rate is less than 85% until it is greater than 85%, and protecting the naturally regenerated nitrogen-fixing precious tree species seedlings by implementing 2-3 times of cutting and weeding every year for 3-5 consecutive years.

[0008] In the above method, in the construction of the stand structure, the selection method is a small sample circle method or a small grid method; The small sample circle method is: selecting 3-4 target trees within a 10 m radius circular range with the operator as the center; The small grid method is: selecting one dominant tree as a target tree in a 10 m x 10 m grid unit.

[0009] In the above method, in the construction of the stand structure, the nitrogen-fixing tree species includes one or more of Dalbergia hanceana, Dalbergia cochinchinensis, Schefflera actinophylla, Garcinia xanthichyloides and Xylaria intermedia.

[0010] In the method, in the driving of stand regeneration, the pruning operation includes: removing all living branches and dead branches below a vertical height of 9m from the ground level of the target tree trunk in one time; In the method, in the driving of stand regeneration, the pruning operation includes: removing all living branches and dead branches below a vertical height of 9m from the ground level of the target tree trunk in one time; In the method, in the driving of stand regeneration, the pruning operation includes: removing all living branches and dead branches below a vertical height of 9m from the ground level of the target tree trunk in one time; In the method, in the driving of stand regeneration, the regeneration forest canopy density is 0.5.

[0011] In the method, in the driving of stand regeneration, the pruning operation includes: removing all living branches and dead branches below a vertical height of 9m from the ground level of the target tree trunk in one time;

[0012] In the method, in the driving of stand regeneration, the pruning operation includes: removing all living branches and dead branches below a vertical height of 9m from the ground level of the target tree trunk in one time;

[0013] In the method, in the driving of stand regeneration, the pruning operation includes: removing all living branches and dead branches below a vertical height of 9m from the ground level of the target tree trunk in one time;

[0014] In the method, in the driving of stand regeneration, the pruning operation includes: removing all living branches and dead branches below a vertical height of 9m from the ground level of the target tree trunk in one time;

[0015] In the method, in the driving of stand regeneration, the pruning operation includes: removing all living branches and dead branches below a vertical height of 9m from the ground level of the target tree trunk in one time;

[0016] Compared with the prior art, the technical scheme provided by the present application at least has the following beneficial effects or advantages: 1. The degraded forest grading restoration method provided by the present application has the effect of solving the restoration problem in fragmented areas: by dividing the three types of degraded forests of light, medium and heavy degrees according to the canopy density and stand composition standards, and designing special restoration processes respectively, the target tree marking, interference tree removal and cultivation are implemented for the light degradation type, the time-consuming problem of the existing technology of closing the forest for cultivation is avoided, the precise supplementary planting in the forest gap is adopted for the medium degradation type, the strip cleaning planting is performed for the heavy degradation type, by uniformly formulating the key technical parameter standards of the forest gap, the standard operation and large-scale popularization feasibility of the mode in different degradation type areas and complex terrain conditions are ensured, and the treatment pertinence of the heterogeneous degraded landform is significantly improved.

[0017] 2. The nitrogen-fixing valuable tree species supplementing strategy provided by the application has the effect of synergistic increase of ecology and economy: local tree species with both nitrogen-fixing function and high economic value are selected for combination and supplementing, and through the mixed planting mode of multiple tree species, the soil nutrient circulation is improved, the risk of single tree species afforestation is avoided, and the ecological restoration benefit and the economic value of the stand are simultaneously improved.

[0018] 3. The application significantly accelerates the natural restoration process of the forest by marking target trees, accurately removing canopy interference trees, and implementing standardized pruning, combined with the control of reasonable canopy density after selective cutting, while maintaining the original vegetation and ensuring biodiversity and ecosystem stability. In addition, a dual monitoring system of seedling survival rate and preservation rate is established, and strict supplementing requirements and regular tending management are implemented to continuously optimize the stand structure, ultimately ensuring the restoration results and forming a healthy and stable multi-layer mixed forest ecosystem. DETAILED DESCRIPTION

[0019] In the following, the technical solutions of the application will be described in conjunction with examples. However, the application is not limited to the examples described below. In each example, the test method and detection method are conventional methods unless otherwise specified. The reagents and materials can be purchased on the market unless otherwise specified. In the following examples, % is the mass percentage unless otherwise specified. In the following examples, the ratio is the mass ratio unless otherwise specified.

[0020] Implementation site: Siem Reap Province, Cambodia (40°11'104''E, 35°26'13''N), altitude 50-80 m. It belongs to tropical monsoon climate, with an average annual temperature of 28.2°C, annual rainfall of 1500-2000 mm, sandy soil; Implementation scope: 50 hectares of tropical degraded forest restoration demonstration forest; among them, the light, moderate and severe degradation restoration demonstration forests are 20 hectares, 15 hectares and 5 hectares respectively; Implementation time: from January 2019 to December 2021.

[0021] Example 1 The applicant successfully created a 50-hectare tropical degraded forest restoration demonstration forest in Siem Reap Province, Cambodia through the following method of supplementing nitrogen-fixing valuable tree species based on thinning. After 3 years of ecological restoration, the stand volume of the light tropical degraded forest increased by 22%, the stand volume of the moderate tropical degraded forest increased by 57%, and the diameter class of the valuable nitrogen-fixing tree species in the severe tropical degraded forest grew rapidly, significantly higher than that of ordinary trees.

[0022] The method specifically comprises: dividing the tropical degraded forest into light, moderate and severe tropical degraded forest; The light tropical degraded forest has a canopy density of 0.6 or more, a relatively light human disturbance degree, a rich plant species, a similar forest layer structure to the original forest, a well-developed interlayer liana, and only a few large trees with high timber value are cut down, and the proportion of large-diameter trees is less than that of the original forest; The moderate tropical degraded forest has a canopy density of 0.2-0.6, a relatively large human disturbance degree, no large trees in the stand, and belongs to sparse forest land formed after forest destruction, the community is composed of a part of low trees, sprouting and natural seedling update trees and shrubs, the vegetation species is relatively rich, and the herb layer coverage is obviously smaller than that of the severe degradation type. The severe tropical degraded forest has a canopy density of less than 0.2, the most intense human disturbance, and the existing main vegetation is composed of sprouting and bushy low trees and shrubs. The sprouting tree layer is less than 5 m high, and the species is less. The herb layer coverage is large.

[0023] The recovery method of the light tropical degraded forest comprises: Construction of stand structure The nitrogen-fixing tree species such as Dalbergia cochinchinensis, Dalbergia lanceolaris, Tabebuia pentaphylla, Palaquium spp. and Xylaria spp. among the precious tree species are taken as target trees, 90-120 target trees per hectare are selected by using a small sample circle method and a small grid method, and red paint is sprayed around the trunk at a height of 1.3 m of the target trees to form a mark so that the target trees can be found in any direction in the forest. In the small sample circle method, 3-4 target trees are selected in a circular range with a radius of 10 m with the standing point of the operator as the center. In the small grid method, 1 dominant tree is selected as a target tree in each 10 m*10 m small grid range. Finally, the interference trees are cut down, the interference trees are trees with crowns connected or overlapped with the target trees, the interference trees should be cut down as soon as possible, if the interference trees have commercial utilization value, the interference trees are pulled out for utilization, otherwise the interference trees are stored in place, and the crown of the target tree should be kept free growth and kept a certain distance from the edge of the crown of the adjacent tree during the cultivation process. The interference trees, the cutting time and intensity and the like are determined according to the crown shape change of the target tree and the contact condition of the crown with the adjacent tree.

[0024] Driving stand update: after the first interference tree is cut down, the target tree is pruned in the same year, that is, the live branches and dead branches below 9 m of the main trunk of the target tree are pruned at one time. The side branches with a base diameter of less than 3 cm can be pruned by using a branch cutter, the side branches are cut flat without leaving a stump, the cut surface is smooth, and the bark is avoided to be torn. The thicker side branches are cut by using a hand saw, the sawing surface is perpendicular to the axis of the branch, the side branches are cut obliquely without leaving a stump, and the cut surface is as close to the branch collar as possible. The cut surface can be coated with a tree wound healing agent if conditions permit. The target trees with a breast height diameter of more than 60 cm are selected and cut to form an update stand, and the canopy density is kept at about 0.5 after the selection and cutting. The natural update is mainly used, and the artificial promotion of natural update is auxiliary, and a multi-species mixed and multi-aged complex forest is gradually cultivated.

[0025] The recovery method of the moderate tropical degraded forest comprises: Constructing gap renewal unit: In the place where the trees are low, the canopy density is small and the trees are sparse, gaps are built, the gap building density is 90-120 per hectare, the gap diameter is about 6 m, and the interval is about 10 m. Four first-type planting holes are dug at the corresponding positions of the gaps, with a plant spacing of 2 m x 2 m, and the planting hole specifications are 50 cm x 50 cm x 30 cm (length x width x depth). When digging, the topsoil and subsoil are placed separately, and the topsoil is backfilled first. If there are large root segments in the soil, they should be removed first. The soil is then backfilled while breaking the large soil blocks with a size of more than 5 cm in diameter. Then select 3-5 local ecologically and economically valuable native nitrogen-fixing tree species as afforestation seedlings, such as Dalbergia hupeana, Dalbergia cochinchinensis, Schefflera actinophylla, Garcinia mangostana and Xylopia aethiopica. The seedling specifications are: seedling height 35 cm, ground diameter more than 0.5 cm. Finally, in the rainy season, when the soil in the planting hole is fully moist, it can be planted when the soil can be grabbed into a ball. Remove the container bag, place the seedling into the hole, straighten the seedling, backfill and compact the soil, and finally backfill a layer of 2-3 cm thick soil to reduce soil water evaporation.

[0026] Maintaining gap replacement unit: During routine inspection, invasive vegetation is removed, the gap area is controlled to maintain a light environment, and afforestation is carried out 1 month later. If the survival rate is less than 85%, replanting is carried out in suitable weather. Before the dry season the following year, the survival rate is investigated again, and if the survival rate is less than 85%, continue to replant until the survival rate is more than 85%. Continue to cut grass and weed for 2-3 times a year for 3 consecutive years to protect the natural regeneration of nitrogen-fixing valuable tree seedlings.

[0027] The restoration method of severe tropical degraded forest includes: Constructing a strip restoration base: The afforestation land of severe tropical degraded forest is divided into planting strips (4 m wide) and reserved strips (3 m wide). The weeds and shrubs in the planting strips are completely removed and stacked in the reserved strips by taking a strip cleaning method. The direction of the planting strip is not limited, and it is subject to the convenience of operation, but the direction of the planting strip in the same afforestation land should be consistent. If there are valuable tree seedlings in the planting strip, they should be preserved. Then 2 rows of second-type planting holes are dug in the middle of the planting strip, with a plant spacing of 2 m x 2 m, and the planting hole specifications are 50 cm x 50 cm x 30 cm (length x width x depth). In the rainy season, nitrogen-fixing valuable tree seedlings are planted in the planting strip.

[0028] Stabilizing the strip succession process: The survival rate of the planted nitrogen-fixing valuable tree seedlings is monitored, and if the survival rate is less than 85%, replanting is carried out based on the axis of the planting strip. The survival rate is investigated in the dry season the following year, and if the survival rate is less than 85%, replanting is carried out until it is greater than 85%. For 3 consecutive years, 3 times of grass and weed cultivation are carried out every year.

[0029] Through the above method, the present application finally increases the proportion of high-value timber tree species in the moderately and severely degraded forests by thinning and re-planting native nitrogen-fixing valuable tree species, thereby improving the economic value of the stand. The detailed results of the restoration of moderately and slightly degraded tropical forests are shown in Table 1: Table 1: Changes in stand structure and tree growth in the tree layer of moderately and slightly degraded forests As shown in Table 1, during the three-year restoration period, the average number of trees per hectare in moderately degraded tropical forests increased from 656 to 1461, an increase of 123%, the stand density increased by 17 percentage points to 0.7, the tree species diversity increased by 18%, the average diameter at breast height and tree height increased by 5% and 3%, respectively, but the average volume increased by 57%. These core indicators prove that the present application can break through the ecological threshold to rapidly rebuild the community structure, simultaneously improve the carbon sink capacity and biodiversity under the premise of increasing the number of trees, and achieve efficient conversion from sparse forest to high-density mixed forest.

[0030] The above describes the basic principles, main features and advantages of the present application. The above examples and descriptions are only to describe the preferred embodiments of the present application, and the present application is not limited by the above examples. Any changes and improvements to the technical solutions of the present application made by those skilled in the art without departing from the spirit and scope of the present application shall fall within the scope of protection of the present application.

Claims

1. A method for restoring degraded tropical forests based on thinning and replanting nitrogen-fixing precious tree species, characterized in that, include: The aforementioned tropical degraded forests are classified into mildly degraded tropical forests, moderately degraded tropical forests, and severely degraded tropical forests; The canopy closure of the mildly degraded tropical forest is greater than or equal to 0.6, and the forest stand composition includes interlayer vines and tall trees, wherein the area of ​​the interlayer vines and tall trees accounts for more than that of other forest stands; The canopy closure of the moderately degraded tropical forest is 0.2 to 0.6; the forest stand composition includes: low trees, trees and shrubs that are regenerated by budding or natural regeneration, wherein the area of ​​the low trees, trees and shrubs that are regenerated by budding or natural regeneration is greater than that of other forest stands. The canopy closure of the severely degraded tropical forest is less than 0.2; the forest stand composition includes: budding regeneration clump-like low trees and shrubs and light-loving weeds, wherein the area of ​​the budding regeneration clump-like low trees and shrubs and light-loving weeds accounts for more than other forest stands; The restoration methods for mildly degraded tropical forests include: Establish forest stand structure: Select nitrogen-fixing tree species among precious tree species as target trees at a density of 90-120 trees / hectare and mark them. Then remove interfering trees, which are trees whose canopies are connected to or overlap with the target trees. Drive forest stand regeneration: Pruning is carried out on sections of the target tree trunk with a vertical height of less than or equal to 9m from the ground surface reference plane; then, the target trees with a diameter at breast height (DBH) greater than 60cm are selectively felled to form a regeneration forest, and finally the regeneration forest is cultivated into an uneven-aged multi-layered forest; The restoration methods for moderately degraded tropical forests include: Construct forest window regeneration units: Open forest windows in moderately degraded tropical forests, with a forest window opening density of 90-120 per hectare, and then dig multiple Class I planting pits at the corresponding location of each forest window to plant nitrogen-fixing precious tree seedlings during the rainy season; Maintaining forest gap succession units: removing invasive vegetation, maintaining forest gap area to preserve light penetration, monitoring the survival rate of nitrogen-fixing precious tree seedlings, and replanting when the survival rate is less than 85%; investigating the survival rate in the following dry season, and replanting until the survival rate is greater than 85% when it is less than 85%; carrying out 2-3 rounds of shrub clearing and weeding every year for 3-5 consecutive years to protect naturally regenerated nitrogen-fixing precious tree seedlings; The restoration methods for the severely degraded tropical forests include: Constructing a strip-shaped restoration base: Divide the afforestation area of ​​severely degraded tropical forest into planting zones and retention zones. Remove weeds and shrubs from the planting zones and pile them into the retention zones. The planting zones should be aligned in the same direction within the same afforestation area. Retain the seedlings of precious tree species in the planting zones. Then, dig a second type of planting hole in the middle of the planting zone and plant nitrogen-fixing precious tree species seedlings during the rainy season. Stabilize the zonal succession process: Monitor the survival rate of planted nitrogen-fixing precious tree seedlings. If the survival rate is less than 85%, replant based on the planting zone axis. Investigate the survival rate in the following dry season. If the survival rate is less than 85%, replant until it is greater than 85%. Implement 2-3 weeding and pruning annually for 3-5 consecutive years to protect the naturally regenerated nitrogen-fixing precious tree seedlings.

2. The method according to claim 1, characterized in that, In the construction of the forest stand structure, the selection method is either the small sample circle method or the small grid method; The small sample circle method is as follows: select 3 to 4 target trees within a circular area with a radius of 10m and the operator as the center; The small grid method involves selecting one dominant tree as the target tree within a 10m×10m grid unit.

3. The method according to claim 1, characterized in that, In the constructed forest stand structure, the nitrogen-fixing tree species include one or more of the following: Dalbergia cochinchinensis, Pterocarpus macrocarpus, Cassia obtusifolia, Aster tataricus, and Aster tataricus.

4. The method according to claim 1, characterized in that, In the aforementioned forest stand regeneration process, the pruning operation includes: removing all living and dead branches below 9m vertically from the ground surface of the target tree trunk in one go; For lateral branches with a base diameter of 3 cm or less, use branch shears to cut them flat along the base of the branch, with the cut surface flush with the trunk surface and smooth without tearing. For lateral branches with a base diameter greater than 3cm, use a hand saw to cut the branch obliquely in a direction perpendicular to the branch axis, with the cut close to the base of the branch, and apply tree wound healing agent to the cut.

5. The method according to claim 1, characterized in that, In the aforementioned forest stand regeneration process, the canopy closure of the regeneration forest is 0.

5.

6. The method according to claim 1, characterized in that, In the constructed forest window renewal unit, the diameter of the forest window is 5~7m and the interval is 9~11m.

7. The method according to claim 1, characterized in that, In the constructed forest window renewal unit, the number of the first type of planting holes is 4 to 5. The first type of planting holes are arranged in a square grid layout with a plant spacing of 2m×2m. The dimensions of the first type of planting hole are 50cm×50cm×30cm (length×width×depth).

8. The method according to claim 1, characterized in that, In the stable zonal succession process of the forest window replacement unit and type 3, the nitrogen-fixing precious tree species include 3 to 5 species from Dalbergia cochinchinensis, Pterocarpus macrocarpus, Cassia obtusifolia, Aster tataricus, and Aster tataricus; the seedlings of the nitrogen-fixing precious tree species have a height of ≥35cm and a ground diameter of ≥0.5cm.

9. The method according to claim 1, characterized in that, In the stable zonal succession process, the planting bandwidth is 3-5m, the retention bandwidth is 2-4m, and the removal method is zonal clearing.

10. The method according to claim 1, characterized in that, In the stable zonal succession process, the number of the second type of planting holes is 2 rows, the plant spacing is 2m×2m, and the length×width×depth of the second type of planting hole is 50cm×50cm×30cm.

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