The results of the planting years showed that the average diameter of the experimental formulas increased with decreasing density, but the total cross-sectional area (G) increased with increasing density, which means that although the low-density plantations grew higher in diameter, the standing wood reserve of the forests was still smaller than the high-density plantations. In Malaysia in 1995, people built multi-storey mixed forests on 3 subjects: natural forests, Acacia mangium forests and Teak forests with 23 valuable native species, planted in strips of different widths (10m, 20m, 30m, 40m) and different mixed methods. The results showed good height growth in strips of 10m and 40m.
Thus, planting density has a significant impact on productivity, product quality and business cycle, so it is necessary to base on specific business goals to determine the appropriate planting density.
1.1.4. Research results on the effects of fertilization on the growth and productivity of planted forests
Fertilizing plants is one of the intensive technical measures to improve the productivity and quality of planted forests that has attracted the attention of many scientists in the world. A typical example is the research work of Mello (1976) in Brazil showing that Eucalyptus grows quite well in the formula without fertilizer, if NPK is fertilized, the productivity of planted forests can increase by more than 50%. In another research work in South Africa by Schonau (1985) on the issue of fertilizer for Eucalyptus grandis, it was shown that the formula of fertilizing 150gNPK/tree with the ratio N:P:K= 3:2:1 can increase the average height of planted forests by 2 times after the first year.
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For P. caribeae in Colombia, Bolstad et al. (1988) also found some fertilizers that had positive reactions and brought about obvious effects for the plantations such as Potassium, Phosphate, Boron and Magnesium. When studying fertilizers for P. caribeae forests in Cuba, Herrero et al. (1988) also showed that Phosphate fertilization increased the yield from 56m3 to 69m3 / ha after 13 years of planting.
1.1.5. Research results on market policy
The effectiveness of production forest plantation work, in which economic efficiency is the main factor. Planted forest products must have a market, serving both short-term and long-term goals. At the same time, the cultivation method must be suitable for local knowledge and easy to apply to the people. According to the research of Thomas Enters and Patrick B. Durst (2001), to develop production forest plantation with high economic efficiency, in addition to focusing on economic and technical investment, it is also necessary to study issues related to policy and market. Recognizing the two key issues, which play a decisive role in the production process, in developed countries such as the US, Canada, Japan..., forestry economic research at the national level is currently focused on the market and the competitiveness of products. From the viewpoint of "Market is the key to the production process", forestry economists analyze that the market itself will answer the question of what to produce and for whom to produce? When the market has demand and the interests of producers are guaranteed, it will promote production development to create goods.
Based on the analysis and assessment of the actual situation in recent years, Liu Jinlong (2004) has proposed a number of key tools to encourage private sector to develop afforestation such as:
- Forests and forest land need to be privatized.
- Sign contracts or lease state forestry land to private individuals.
- Reduce taxes on forest products.
- Financial investment for private forest planting.
- Develop cooperative relationships between companies and people to develop afforestation.
The tools that the author proposes are relatively comprehensive, from the general management of land issues, taxes, and the relationship between businesses and people. It can be said that these are not only levers to promote private participation.
afforestation but also suggests important directions for the development of production forests in developing countries, including Vietnam.
Authors around the world are also interested in forms of encouraging afforestation. Typically, there are studies by Narong Mahanop (2004) in Thailand, Ashadi and Nina Mindawati (2004) in Indonesia... Through their studies, the authors said that currently, 3 issues are considered important, encouraging people to participate in afforestation in Southeast Asian countries, namely:
- Clear regulations on land use rights.
- Regulations on beneficiaries of afforestation.
- Improve people's understanding and technical grasp.
These are also issues that countries in the region, including Vietnam, have been interested in solving to attract many sectors to participate in production forest planting, especially to open up private capital and foreign direct investment for forest planting. Therefore, the general viewpoint to develop production forest planting with high economic efficiency is to plant forests to provide raw materials for the processing and export industry with the participation of many economic sectors and diversify the forms of ownership in each type of forest plantation production business organization.
In summary: A review of related research issues in the world shows that there are many quite in-depth and elaborate research projects. Although research projects in countries around the world have solved quite fully related issues, most of the projects were researched in ecological circumstances and very different technical and economic conditions, so they cannot be mechanically applied to the specific conditions of our country in general as well as in Bao Lac, Cao Bang in particular.
1.2. In Vietnam
Our country's forestry sector has had significant innovations in recent years. Along with innovations in management, research activities
Scientific research on forest construction and development has also received attention. Large-scale afforestation projects have been implemented throughout the country with many production forest models being tested and developed, many technical measures have been drawn up and processes and regulations have been developed to effectively serve afforestation work, including production forest planting. Some research and evaluation projects related to afforestation in our country can be mentioned in the following fields:
1.2.1. Research results on site location
The issue of determining suitable site conditions for plant species in our country in recent years has been paid attention to and has been mentioned at different levels, most notably the research work of Do Dinh Sam and colleagues (1994), when assessing the potential for forestry land production in the Southeast region, the authors based on 3 basic contents that are closely related to each other: land use unit, land production potential and suitability of plants. The research results have shown that the Southeast region has a fairly large potential for forestry production and business, the land area suitable for developing forestry species accounts for 70-80%. In particular, it is suitable for developing industrial wood species such as some species of Eucalyptus and Acacia . In addition, the Southeast region is also suitable for planting large timber forests such as Teak ( Tectona grandis ), Sao ( Hopea odorata ) and Dau nuoc ( D.alatus ). When studying the standards for dividing sites for industrial plantations in some ecological regions in Vietnam, Ngo Dinh Que and colleagues (2001) also identified four main factors affecting the growth capacity of industrial plantations, including: 1) parent rock and soil types; 2) soil layer thickness and mixed rock ratio; 3) slope; 4) indicator vegetation. When studying the evaluation of commune-level forestry land for afforestation, Do Dinh Sam and colleagues (2003) also developed a set of evaluation criteria and indicators including 6 criteria and 24 indicators on natural conditions and 5 criteria on socio-economic conditions.
Researching the planting of hybrid Acacia on different types of soil in the Southeast region, Pham The Dung and colleagues (2004) pointed out that although the same intensive farming measures were applied, hybrid Acacia grew better on red-brown soil than on ancient alluvial gray soil. When evaluating the productivity of Eucalyptus ( E. urophylla ) plantations on 3 different types of soil in the Central Highlands region, Nguyen Huy Son and colleagues (2004) also had similar comments, on gray granis soil in An Khe and K'Bang, E. urophylla plantations after 4-5 years of age could reach 20-24m 3 /ha/year, but on red-brown soil developed on acid magma in Mang Yang after 6 years of age, it only reached 12m 3 /ha/year, on degraded basalt red soil in Pleiku after 4 years of age, it also only reached 11m 3 /ha/year.
Le Dinh Kha and Doan Ngoc Dao (2004) studied the plantation of hybrid Acacia varieties (BV10; BV15; BV16; TB5; TB12) at the age of 5-7 years with the control varieties of Acacia mangium and Acacia auriculiformis in some ecological regions of our country. The varieties were planted on trial in Dong Nai, Tuyen Quang, Hoa Binh, Ha Tay and Vinh Phuc with an initial planting density of 1650 trees/ha (3x2m). The results showed that under intensive planting conditions in good sites after 6-7 years, with the current density of 800 - 1200 trees/ha, hybrid Acacia can reach a yield of 40-45m 3 /ha/year, while Acacia mangium reaches a yield of 14 - 20m 3 /ha/year and Acacia auriculiformis only reaches a yield of about 10m 3 /ha/year. In poor soil areas, the productivity of planted Acacia hybrids is from 15 - 18m 3 /ha / year, Acacia mangium and Acacia auriculiformis are below 10m 3 /ha / year. The author affirms that planted Acacia hybrids have good growth, high productivity and improved soil fertility compared to some other plant varieties.
Thus, determining suitable site conditions for afforestation in general is one of the important technical measures to improve the productivity of planted forests.
1.2.2. Research results on breeds
Forest tree breeding work in recent years to serve production nationwide has achieved remarkable results, typically the research projects of the Tree Breeding Research Center.
Forests of the Vietnam Forestry Science Institute, especially the research works of authors Le Dinh Kha (1999), Nguyen Hoang Nghia (2011) have studied and selected natural hybrid Acacia and Eucalyptus lines with high productivity and disease resistance. Moreover, artificial crossbreeding has been successful for Acacia and Eucalyptus species, the results have selected to create hybrid lines with the ability to grow 1.5-2.5 times faster than the parent varieties, the productivity of experimental planted forests in some areas has reached 20-30m 3 /ha / year, in some places reaching 40m 3 /ha / year.
In the past 10 years, research on forest tree varieties in our country has achieved remarkable results, many TBKT varieties and national varieties have been recognized, the growth capacity of these varieties is 50-100% superior in volume compared to the parent varieties. In particular, recently many authors have focused on selecting varieties based on quality. Based on varieties with fast growth ability, authors continue to select varieties based on disease resistance, typically the research work of Nguyen Hoang Nghia (2000) has selected 2 Eucalyptus lines MS16 and MS23 and have been recognized as TBKT varieties. In parallel with selecting varieties, scientists have also researched asexual propagation techniques to maintain the quality characteristics of the selected mother trees to serve more effective production.
The results of testing natural hybrids between Acacia auriculiformis and Acacia auriculiformis by Le Dinh Kha, Nguyen Dinh Hai, Ho Quang Vinh (1996) showed that at the age of 4 years, F1 hybrid Acacia cuttings had a volume 1.6 - 2 times that of Acacia auriculiformis and 3 - 4 times that of Acacia auriculiformis. The growth rate of F1 hybrid Acacia cuttings was faster than that of seeds and cuttings of the fastest growing origins among the parent Acacia species and they were maintained at the age of 4 years and continued to grow rapidly after a number of years. There were clear differences in growth rate, trunk quality and wood density among the tested Acacia hybrid lines. From the testing of asexual lines, a number of hybrid Acacia lines with the highest trunk volume, the best trunk quality and relatively high wood density were selected.
According to Le Dinh Kha (1999): The results of the research on asexual varieties in the Southeast by Luu Ba Thinh (1999) concluded that different varieties grow differently. Most hybrid Acacia varieties have superior growth compared to Acacia auriculiformis and Acacia auriculiformis such as TB1 and TB8. After 5 years of testing, the two varieties have a volume of 202.3 - 202.7 dm 3 / tree, while Acacia auriculiformis is 146 dm 3 / tree and Acacia auriculiformis is 52.1 dm 3 / tree. The research on selecting superior trees, propagating and initially testing asexual hybrid Acacia varieties in the Southeast conducted by Luu Ba Thinh and Pham Van Tuan (1999) showed that Acacia hybrid shoots give the highest rooting rate if they are planted from May to July and treated with powdered IBA, concentrations of 0.7% and 1.0%. In which, different hybrid Acacia individuals have different rooting rates of cuttings. Through testing of asexual varieties, it was found that only some hybrid Acacia varieties grow faster than Acacia auriculiformis and Acacia mangium. From the research results, hybrid Acacia varieties TB03, TB05, TB06 and TB012 were selected with fast growth that can be mass-produced for production forest planting in the Southeast and localities with similar site conditions. However, from the data obtained by the above authors, it can be seen that variety TB06 really grows fast in the years, so it needs to be tested again to see their true value.
The results of the research on experimental planting and building a model for planting some high-yield forestry trees in Bac Kan province (Le Dinh Kha, associates, 2011) give the following conclusions.
- The two varieties BV10 and BV16 planted in 2002 at Cho Moi Forestry Farm had survival rates of 75% and 80% by the end of 2008, respectively, with trunk volumes of 192.98 dm3/tree and 127 dm3/tree, respectively, and actual yields of 26.53 m3/ha/year and 18.68 m3/ha/year, respectively.
- BV10 and BV16 varieties planted in 2002 (measured in 2008) had heights below the branches of 14.14 m and 9.33 m respectively, corresponding to the ratio calculated by the height of the top of the tree being 69.3% and 52.5%. BV10 is also a variety with a straight trunk and smaller branches than BV16.
- At Cho Moi Forestry (Bac Kan), although the BV10 variety has a higher rate of breakage than the BV16 variety, due to its fast growth, it still has a higher yield than the BV16 variety.
The research topic on selecting fast-growing hybrid Acacia varieties using molecular markers (Ha Huy Thinh, 2017) has selected 5 lines (BB055, BB026, BV 586 in the Quy Nhon trial and lines BV523, BV585 in the Quang Tri trial) with growth equivalent to the recognized varieties, which can reach 30m3/ha/year when combined with appropriate silvicultural measures. This is the basic source of material for further in-depth research. If implemented, the topic will be the first model using both of these methods in parallel, in which the application and development of molecular markers in selecting hybrid Acacia varieties will be a powerful tool for breeding activities to shorten the time and provide specific strategies for breeding programs. The results of the project are not only new hybrid Acacia varieties with productivity equivalent to recognized varieties but also molecular markers that can be used for further research in biotechnology application programs in forestry research.
Currently, most key economic regions have industrial nurseries with a production scale of millions of trees per year. The successes in forest tree variety research have created favorable conditions for the development of production forests in our country in recent years. However, new high-yield tree varieties are mainly tested and developed in some provinces of regions such as the Southeast, North Central, South Central and Central Highlands. For the northern mountainous region, including Bao Lac (Cao Bang), they have only been developed on a small scale. Therefore, quickly introducing new varieties and asexual propagation techniques into production is very necessary to improve productivity and efficiency of forest planting, attracting many economic sectors to build forests. This is also the desire and policy of local authorities at all levels in Cao Bang in general and Bao Lac district in particular.