Chapter 2 Improved Breeding
The breeding of forest trees includes the genetic improvement of forest trees and the breeding of forest trees. The fundamental task of forest tree breeding is to breed and propagate fine varieties of forest trees. The forest tree fine varieties refer to the forest tree groups that are artificially selected in terms of quantity and quality that meet the production needs, are genetically stable and can adapt to certain natural and cultivation conditions. As a basic breeding material for afforestation, fine tree species play an important role in fully utilizing the natural production potential in forest production, improving the yield and quality of forest products, enhancing the resistance of tree species, and giving full play to the multiple benefits of forests. . In the current practice of forestry production, breeding materials that have been improved through traits and traits are generally known as improved varieties.
The main method for breeding seedlings in the forest is the scion and seed orchard. Mother trees can also be included in the breeding category, but its improvement is less than that of seed orchards. Genetic testing and improvement of genetic improvement in breeding materials is an important part of improved breeding.
Variety breeding is closely related to some basic theories and applied disciplines. In order to raise the breeding work to a new level, it is necessary to accelerate the improvement of the genetic quality of trees based on the application of other disciplines, and to accelerate the reproduction efficiency of elite species, so that improved varieties can be used in forestry. Play a greater role in production.
Section 1 Establishment and Management of Mother Trees
First, the significance of the establishment of the mother trees
The mother forest is a stand dedicated to seed collection after the genetic quality of seeds has been improved. It is also known as seed forest, and it is also one of the forms of seed breeding of forest trees. Its task is mainly to produce high quality tree seeds.
In order to improve the quality and quantity of current forest seed, in addition to establishing a seed garden and a scion nursery, the establishment of a mother tree is also indispensable. Especially for larch, although the seed garden approach can obtain high genetic gain, but from the best selection, garden construction to a large number of species, the technology is complex, the cost is high, and it takes a long time. The establishment of mother trees is simple, low-cost, early production, and quick results. Through intensive cultivation management, it can not only meet the current urgent need for seeds, but also improve the genetic quality of seeds to a certain extent. Therefore, the establishment of mother trees is an important measure to realize the large-scale production of improved varieties of primary forest trees as soon as possible.
The Mengzi Forest Management Bureau of Hebei Province, Longtoushan Planting and Seedling Farm (formerly Longtoushan Forest Farm), rebuilt 5,000 acres of Larix principis-rupprechtii mother trees in 1976. Through the selection of mother trees, thinning and tending and other measures, from 1980 to 2001, the communist genetic gains The 10% excellent seed 29565K, in addition to satisfying local afforestation species, is also exported to Liaoning, Shanxi, Shaanxi, Inner Mongolia, and Beijing.
Second, the conditions established by the mother trees
(i) Climate conditions
The annual average temperature is above 1°C, the plant growth period is not less than 100 days, and the accumulated temperature above 10°C is not less than 2500°C. Low temperatures can cause frost damage, and short growth periods affect seed development and seedling quality.
(II) Site Conditions
The site conditions mainly consider the soil fertility and the terrain and aspect closely related to the light conditions. The level of soil fertility has a great influence on the yield and quality of the mother tree seed. The best choice is I and II, and the soil type is moderate and thick humus. Acidic soils are suitable for the growth of larch.
Mother trees should be selected for open terrain, flat terrain, and non-tuyere locations. As far as possible, the mountainous area should use a semi-sunny or sunny slope with a gentle slope (a slope of no more than 20°), near the water source, and an elevation of about 1000-1200 m.
(iii) Status of stand
The establishment of fine forest stands must be selected for the establishment of the mother trees. The condition of the stand is a decisive factor for the internal conditions of the mother trees.
1. The quality and quality of the fine mother tree's fine mother tree play a decisive role in the genetic quality of the seed produced by the mother tree. The greater the proportion of good mother trees in the selected stands, the better. The proportion of elite mother trees in the seedlings and improved seedlings base of Longtoushan Mountain has reached more than 70%.
2. The degree of canopy density in the stand canopy directly affects the light conditions of the mother tree, which in turn affects the yield and quality of the seed. The general canopy closure is 0.4 to 0.6. The closure of the forest can be smaller, and the closure of the forest can be smaller.
3. Forest age: The suitable forest age of the mother trees should be the age at which the high growth reaches its peak, so that the mother tree has high seed yield and good quality. In order to produce seeds for early yield and produce more seeds, the forests that have entered the stage of fruitful growth or have already entered the stage of fruitful growth should be reconstructed. For Larix principis-rupprechtii, the best age is 7 to 10 years. The forest is young and can be cleared by multiple thinnings, leaving the mother trees that meet the requirements.
4. Growth and development status of stands: The trees in the mother trees should be made up of fast-growing and robust, dry and straight without defects, well-proportioned crowns, good natural pruning, and good forests free of pests and diseases.
5. Stand Density: The replanted forest should be selected from seedlings planted by artificial seedlings with an initial density of 222 plants per mu. Reasonable and sparse is conducive to the formation of a complete canopy of forest trees, thereby effectively increasing the solid area.
6. Other conditions: In order to facilitate mechanized management, seed collection and transportation, seedlings should be selected for convenient transportation; water should be provided for irrigation; mother trees should be concentrically connected to improve operating efficiency; there should be isolation conditions around them. To prevent poor quality pollen from invading.
Third, the division of mother trees and provenance selection
(a) The setting of the road
In order to facilitate the management and seed transportation, if there are more than 10 hectares, mountainous roads should be built along the Hengshan Mountain to a main road that is 6 to 8 meters wide, and the business area should be divided into 4 to 5 hectares, and 4 to 6 meters of roads should be widened between the operating areas.
(B) Set up isolation belts
If the isolation zone of the female forest is coniferous, its width should be more than 100m; if it is a broad-leaved tree, its width should be more than 200m; if it is a non-forestland, it should be more than 300m; if it is a stand of the same species, it should be 100m from the periphery of the mother tree. It is relatively safe to collect seeds and fireproofing belts.
(c) Provenance selection
The provenance usually refers to seeds or other propagation material collected from different locations within the same tree species distribution area. For the seeds or other propagation materials with different geographical origins, the comparative test of cultivation done together is called the provenance (origin) test. The selection of provenances with high productivity and good stability for each afforestation area is called selection of provenances. In order to achieve proper tree location and improve the productivity and stability of plantation, it is necessary to identify the most suitable species source area and better species source area according to the provenance test results to determine the applicable scope of the provenance. Transport seeds or other propagation materials should be selected within the most suitable source area. Only when the best seed source area cannot meet the needs, can seeds or other propagation materials be called in the better seed source area. If there has been experience in introducing foreign provenances and afforestation in the past, there are species or varieties that have adaptability and productivity that exceed those of the local provenances and can continue to be used. When selecting the mother tree or calling the seed, the site conditions of the seed production site must be emphasized, mainly including climatic conditions and soil conditions. The climate conditions mainly consider latitude, longitude, altitude and air temperature; soil conditions mainly consider slope, aspect, soil thickness and soil pH. Also refer to the division of the seed area of ​​Larix principis-rupprechtii in the "Chinese National Forest Tree Seed Area GB8822.1-8822.13-88".
IV. Management of mother trees
(I) Thinning Techniques of Mother Trees
Thinning is a key measure for establishing the mother trees. Thinning trees are eliminated through thinning to improve the light, water, fertilizer, and sanitary conditions of the forest. Timely and appropriate thinning and adjustment of the standing timber structure to expand the underground and spatial nutrient area of ​​the mother tree, promote the growth and development of the mother tree, facilitate the expansion of the canopy, and increase the seed yield and quality.
1, the mother tree classification: Before thinning, the forest in the stand according to their advantages and disadvantages are divided into three categories.
V1w good mother tree:
1 The type is good: it is the best type in this tree species.
2 Growth is good: Strong growth potential. It is a relatively thick and tall tree in a stand. The volume of a single plant is more than 15% of the average individual plant volume of the same age and same-level stand.
3 The tree is good: the trunk is straight, full, and the wood texture is straight, the crown is even and symmetrical, and the height of the branches is lower.
4 Good conditions of solidity: The level of solidity is above average level.
5 Health, no pests, no mechanical damage.
V2w Poor mother tree: Tree height, diameter growth is lower than the average value of the stand, and growth is declining. The trunk is curved and the lateral branches are thick. Double fork wood, flat top wood. Poor conditions. Forests that are harmed by pests and diseases.
V3w Normal mother tree: Between the above two, this kind of mother tree has the largest proportion.
2. Principles for thinning should be determined According to the category of the mother tree, the reserved wood should be determined and marked. The fine mother trees are generally all preserved. Generally, the mother tree will be partially removed and all the bad mother trees will be removed.
When it is determined whether to keep or cut, it is considered to be good or bad, but also to take care of the row spacing, so as to keep the mother tree evenly distributed. However, in the stands, sometimes 2 to 3 or 3 to 5 fine trees grow close to each other. At this time, they should be kept as the elite trees.
3. The first thinning of thinning for the first time directly affects the efficiency of seed production. If early thinning, it will increase the operating period before the seed, thus reducing the efficiency of seed supply; if the thinning is too late, it will lead to the formation of dead branches in the lower tree.
4. Reserve Density The retention density is large but the yield is low, and the density is small. Although the yield per plant increases, the total yield per mu is not high. Through years of research, it has been confirmed that the first thinning of 10-year-old stands is appropriate, and it is appropriate to keep 70-80 plants per acre.
Table 2-1 Comparison of the effects of the first thinning retention density
Number of plants per acre
Thinning strength (%)
Mu seed (pound)
ratio%
Note
45
81.2
5.8
644.4
75
68.7
10.0
1111.1
240
―
0.9
100
Control
According to Table 2-1, 75 strains per acre were preserved, and the seed yield was the highest, which was 11 times more than that of the control, and the level of standing wood was medium; 45 strains per acre were retained. Although the seed yield was 6.4 times that of the control, the seed yield was too low. Not the main business purpose.
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