Silvicultural Management Cycle for Natural Forest Stands.

The data are taken from the example of the 2nd model (Table 4.24 above). The data in rows 9 to 16 are the simulation results of the dynamic change of the diameter distribution at t=5 years until t=40 years. The data in column B (from row 9 to row 16 are calculated as follows: B9 = B8*(1-B$4-B$5-B$6) + 5*21 (in which 21 is the number of trees moving into the average smallest diameter class (calculated in Table 4.25). The data in columns C to I (rows 9 to 16) will be calculated as follows: C9= B8*B5+C8*(1-C$4-C$5-C$6). Column J is the density of trees with D 1.3 greater than 10 cm.

Table 4.28 above is a very good demonstration of the research method and

The trend of the N/D structure of natural forests. In reality, the dynamics of forests are much more complex under the influence of the regeneration process, the succession of species replacing each other by the natural struggle process. Table 4.28 is also a demonstration of the method of simulating forest dynamics according to different management scenarios. Just changing the exploitation rate at certain diameter levels (according to the intention of the business person) will calculate the results of forest dynamics. For example, in the table above, with the management method according to the 5-year cycle of the regulation plan, only selectively exploiting trees that have reached 50-60 diameter with an intensity of 25% and at a diameter of 60cm or more with an intensity of 50%, the N/D structure will return to a very stable state after about 25 years.

4.6.2. Proposing silvicultural technical solutions

4.6.2.1 Discussion of silvicultural technical solutions

Through the study of forest structure and dynamics, its application to propose specific silvicultural technical measures for forest business in the research area is very necessary. The silvicultural technical measures that the topic raises are silvicultural measures that synthesize all stages. First, it is necessary to develop a specific plan that includes the content of the work steps in order from the application of research results on forest structure and dynamics. The content of the plan is shown in Figure 4.8 and the operational work steps are shown in Table 4.29 below:

Mining design, tree felling; mining preparation

Pre-exploitation resource assessment investigation

Exploit

Post-harvest silvicultural activities:

 Forest sanitation, forest care

 Promote recycling

 Supplementary planting for enrichment

 Assess the current status of the forest

Investigation and assessment of forests after exploitation

Figure 4.8: Silvicultural management cycle for natural forest stands.

Table 4.29: Operations in the silvicultural management cycle.

Year

Operation
2 years ago mining	Investigate and evaluate forest capital with a 10% sample rate using a systematic route method to determine the amount of exploitation and plan to open export and transportation routes.
1 year ago mining	carry out exploitation design, tree felling and felling direction; clear thick vines and bushes in preparation for exploitation
Exploit	Cut down trees
0.5 years after exploitation	Investigate and determine the current status of the forest after exploitation and conduct forest cleaning.
2-5 years after exploitation	Post-harvest forest inventory with a sample rate of 10% re-determines forest status and conducts silvicultural treatments to guide the forest towards standard status.
10 years after exploitation	Check and re-determine the current status of the forest.

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4.6.2.2. Proposing silvicultural technical measures.

1) Silvicultural management cycle for natural forests.

In order to select appropriate silvicultural solutions for natural forest management, it is very important to determine a closed business cycle. In the silvicultural management cycle for forest stands, operations are determined according to the time series of a rotation, as a basis for proposing silvicultural measures to lead the forest to a standard state. The natural forest stand management cycle begins with pre-harvest, harvest and post-harvest activities until the next harvest period as described in the diagram in Figure 4.8 and Table 4.29.

2) Management planning.

Most of the rapid management plans are based on national forest inventory data that has not been updated with forest resource data of the forest enterprise. In my opinion, sustainable forest management cannot be based on rapid management plans that are developed every 5 years, without such updated forest resource data. Each forest enterprise needs a long-term management plan, at least for a business cycle (about 30 - 50 years) and must be based on detailed forest resource survey data of the forest enterprise, along with knowledge of forest development dynamics. Forest resource inventory data must be updated every 5 years through a locating OTC system established for forest statuses within the forest enterprise.

3) Mining techniques.

Logging techniques play a very important role in minimizing impacts on the remaining part and ensuring sustainable development of the forest. In logging, the design and construction of the road system, transportation and the selection of the type of transport machinery have a great influence. Currently, in Vietnam, there is no official technical guidance on logging to minimize impacts. The Forestry Handbook, chapter on logging and transporting forest products (Hanoi, 2006) describes in detail the techniques for felling, transporting and loading timber. The Ministry of Agriculture and Rural Development is drafting this document.

Tree fall direction: most designs do not specify the direction of tree fall, so the sawyer can let the tree fall in any direction that is convenient for them, resulting in many trees in the reserve layer, adjacent trees and regenerated trees being affected. The average breakage coefficient in current exploitation is 40 - 45%. If the fall direction is chosen correctly and before exploitation, vines and bushes are cleared so that the fallen tree does not overlap the canopy, the breakage coefficient can be reduced to only about 20%.

Impact reduction exploitation is the main trend of countries towards QLRBV. Vietnam cannot help but follow this trend. With the simulation results of the N/D structural dynamics presented in Table 4.28, we recommend that management

Natural forests in Kon Ha Nung area are cut selectively, every 5 years, the exploitation diameter starts from 50cm. The exploitation intensity at diameter level 50-60 is 25% (choosing trees with bad shape and poor growth). From diameter level 60 and above, 50% of the trees will be exploited (starting with the trees with the largest diameter).

4) Investigation and assessment of forest resources after exploitation.

In the current forest management planning system, there are no regulations on the investigation and re-evaluation of forest resources immediately after exploitation. However, this is an activity in the system of silvicultural technical solutions that is extremely important for QLRBV for the following reasons:

- The system of planning for the management of forest stands did not use the forest management cycle, which requires assessing forest resources immediately after the exploitation activities have ended to propose timely silvicultural measures for the forest regeneration and restoration process.

- Analyzing the 5-year planning plans of the forestry enterprises in the Central Highlands, I see that the following situations often occur: first, the implementation of the plan is not thorough and some unnecessary steps are ignored; second, the promotion of the forest recovery process after exploitation depends too much on nature; the plots that have been processed and exploited in the previous cycle are not prioritized for development but are put into the next cycle right after that...

5) Forest care

Forest maintenance activities must be planned and implemented immediately after closure.

forest gate after exploitation, as soon as possible.

- Forestry design must provide specific technical solutions for

each forest status and human and financial needs.

- Forest nurturing results must be monitored and recorded; each forest status needs control plots of about 0.5 - 1 ha (no impact) for monitoring, comparison for evaluation and improvement of forest nurturing activities later.

- Forestry technicians and workers must be trained, especially in tree identification to distinguish between purpose trees and non-purpose trees. Field guides (forest care and maintenance manuals) must be supplemented to specify the provisions of technical regulations.

Comment.

After proposing silvicultural techniques, I have the following comments:

- Guidance documents still face many difficulties in implementation among localities across the country.

- Most of the guidance documents do not have field guidance, so grassroots staff face many difficulties in implementing work and executing according to the set plan.

- There is no quantitative measurement data on forest productivity. Only based on national forest inventory data on forest types, boundaries and areas. Data on forest resources are not updated.

- In the rapid planning approach, silvicultural techniques are selected not based on the definition of the forest management cycle in a rotation. There is no detailed guidance on the method of collecting information to serve the selection of silvicultural techniques.

- Most production facilities only clean the forest, repair fallen trees and close the forest; there are no other activities.

CHAPTER 5. CONCLUSION, PROBLEMS AND RECOMMENDATIONS

5.1. Conclusion

The research results of the thesis allow to draw the following conclusions:

1. Structure of evergreen broadleaf natural forests in the Central Highlands: The study has drawn the following basic characteristics: (i) The number of species varies from 50 to 114 species. The species diversity index has a very large difference between different diameter levels. For the upper tree layer with diameter levels from (10-65), the species diversity index is highly stable and does not fluctuate as strongly as in the diameter level D1.3 < 10 cm and regenerated trees. (ii) The N/D distribution follows the distribution law of the Weibull function typical of mixed-age natural forests. The number of trees is mainly concentrated in small diameter levels, the diameter level of 10 cm ranges from 120 to 190 trees and this is usually the diameter level with the largest number of trees. The higher the number of trees in each diameter level decreases and at a diameter level above 65 cm, the number of trees ranges from 1 to 12 trees.

(iii) The distribution of species according to D is a decreasing distribution, the number of species is concentrated in small diameter levels, the diameter level of 10 cm has about 50 species, up to the diameter level of 30 cm there are about 15 species, the number of species gradually decreases as the diameter level increases, up to the diameter level of 60 cm there are only about 7 species, up to the diameter level of over 90 cm there are only 2 to 3 species. In the studied forest areas, the tree species: Xoay, Vang, De, Gioi, Coc Da reach maximum size from the diameter level of 80 cm or more, while the species: Dung, Gac Nai, Den, Hooc Quang... rarely reach a size of over 50 cm and the species De, Tram, Nhoc, Goi, Gioi Nhung... often have a common size at the diameter level of 50-65 cm. These are the dominant species and are often seen appearing in the composition of forest states.

2. Regeneration dynamics: the natural regeneration process is quite complicated, changing the composition (through the mixed species ratio index and the Shnnon-Wiener diversity coefficient in the regenerated tree layer and the tree layer with D 1.3 <10 cm. While the composition of the tall tree layer is almost unchanged after a period of five years, the change is only shown in some trees joining the first diameter class and the transitional growth in the new diameter classes changes the composition, but this change is not significant when the time is five years, the change is only clearly shown when the monitoring time is longer. For the small tree layer and the regenerated tree, there has been a very large change, the number of regenerated seedlings was very large at first, but they also died quickly due to lack of favorable light conditions. This proves that the competition for space and nutrients in these tree layers is very strong. This regeneration movement has led to the process of adding to the diameter class

minimum of the upper tree layer (ie 10-15cm); the average number of additional regenerated trees is

21 trees/year.

3. Growth dynamics: Analytical data on diameter growth show:

(i) Natural forest trees grow very slowly, in some cases individual trees may stop growing or grow extremely slowly for a long time (these are trees that are in a state of inhibition and are waiting for an opportunity to improve in terms of light). There is a huge difference between fast-growing and slow-growing trees within the same species. The growth rate of trees in natural forests can be dozens of times slower than that of trees of the same species growing in scattered plantings. (ii) Species distributed in the lower layers of the forest have the slowest growth, however they still live to a very old age even though they only reach a small final diameter. (iii) It is possible to distinguish 3 growth phases in the life cycle of a forest tree: (1) The initial phase with very slow growth and can last up to about 100 years corresponding to the period of inhibition (due to lack of light); (2) The next phase is the phase of promoting growth in diameter when the forest tree has overcome the period of inhibition. (3) The final phase is the phase of growth reduction in diameter, this phase will end when the plant dies physiologically.

4. Natural death process: the natural death rate is highest in the regenerated tree layer to the tree layer with diameter below 10; in the diameter sizes in the upper layer, the death rate also decreases gradually with the increase in diameter size; that is, when the tree has reached a larger size, the probability of death (due to competition for space) decreases.

5. Dynamic research results are a very good method to monitor the movement of forests, based on what is available to infer future forest ecosystems and vice versa to infer past forest ecosystems. Although the dynamic process is complicated, this is a very good way to control the movement, growth transition and natural death of forest ecosystems. When we understand the laws of forest movement, we will have the most appropriate silvicultural measures to achieve the most effective forest business.

5.2. Existence

- The factors that generate forest vegetation in the research area, such as geographical - topographical factors, parent rock - soil, have not been thoroughly studied, so the research results are incomplete.

- Because the OTC area is only 1 hectare, the number of trees at high diameter levels has not enough observation capacity, for example, indicators such as: level transition, spontaneous death