Detailed Explanation of the Cultivation Techniques for Qinghai Spruce Seed Production Stands
Qinghai spruce (Picea crassifolia) is the main native tree species in the Qilian Mountain area, with a long history of cultivation, wide distribution and large area, and is one of the main afforestation tree species in Tianzhu and indeed the entire Northwest region. The main advantages of this tree species are cold resistance, drought resistance, tolerance of barren soil and strong resistance, and it can withstand extreme low temperatures of -30°C; it is a lateral-root tree species with good soil-fixing performance and a strong ability to conserve water sources and maintain soil and water, making it an excellent water-conservation tree species; it is evergreen in winter and summer with a graceful crown shape, and is also a main tree species for urban, courtyard, park and roadside greening; its trunk is straight and full, its wood is soft and elastic, and it is easy to process, making it an even better timber tree species. In 1983, under the guidance of the Gansu Provincial Forest Tree Seed Company, 6.67 hectares of superior Qinghai spruce forest stand were selected in Tianzhu County as the target for seed production stand cultivation. After many years of careful experimental cultivation, all indicators reached the standard requirements for seed production stand construction.
I. Basic situation of the experimental area
The experimental area is located in Compartment 5, Sub-compartment 74 of the Heigou forest area of the Wuqiaoling Forest Farm in Tianzhu County at the eastern end of the Qilian Mountains, with an area of 6.67 hectares, a northeast slope aspect, a slope of 14°, a middle-lower slope position, an average altitude of 2850 m, forest brown soil, and an average soil layer thickness of 100 cm. The average annual temperature is 1.4°C, the annual growing accumulated temperature is 1400°C, the annual rainfall is 400 mm, and the annual evaporation is 1200 mm. This seed production stand is a natural seedling-origin multi-storied uneven-aged forest, growing vigorously, developing robustly, with relatively high purity and excellent quality, of the rough-barked natural type, with a straight and full trunk, a complete and relatively narrow conical crown, a relatively low height to the first branch, relatively fine lateral branches, no pests or diseases, no mechanical damage, no large dead knots or dead tops, no forked stems, and normal flowering and fruiting; superior trees account for 21%, making it a superior forest stand. The average tree age is 61 years, the canopy density is 0.7, the average tree height is 18.7 m, the diameter at breast height is 11.6 cm, the average crown width is 3.1 m, and there are 1630 seed trees per hectare. There is no inferior forest stand within a hundred meters around, making it a relatively ideal stand for converting into a seed production stand.
II. Experimental methods and process
1. Experimental methods
For the selected target for seed production stand cultivation, through thinning and cultivation processes such as loosening the soil, weeding and fertilizing, it was brought up to the standard requirements for a seed production stand; then seed collection and determination and seedling-raising trials were carried out to compare and derive the seed production capacity of the seed production stand and the level of seed production stand cultivation.
2. Cultivation process
In 1983, the first thinning cultivation was carried out. According to the principle of retaining the superior and removing the inferior, the method was mainly fixed-tree ring thinning, combined with uniform thinning and natural thinning. The thinning targets were poorly growing inferior trees, suppressed and injured headless trees, and some intermediate trees unsuitable for retention as seed trees. The thinning intensity was 26%, and after felling 1200 trees per hectare were retained. Cultivation measures such as loosening the soil, weeding and fertilizing were carried out once a year, pests and diseases were controlled in a timely manner, and observations and records were made of growth, fruiting, phenology and other conditions; gaps in the forest were replanted with super seedlings.
In 1990, the second thinning cultivation was carried out, with an intensity of 26% of the growing stock and 30% of the number of trees; after felling, 855 trees per hectare were retained.
In 1994, the third thinning cultivation was carried out, with an intensity of 27% of the growing stock and 24% of the number of trees; after felling, the canopy density was 0.5, and 625 trees per hectare were retained, of which 338 were superior trees, accounting for 54%, and 287 were intermediate trees, accounting for 46%. The retained seed trees had an average diameter at breast height of 16.3 cm, a tree height of 11.3 m, a crown width of 3.25 m, and a height to the first branch of 1.9 m, basically meeting the standard requirements for seed production stand cultivation.
3. Seedling-raising trial
In 1999, using ordinary Qinghai spruce seeds as the control, a comparative trial was conducted in 6 replications, and observations and records were made after seedling emergence; through statistical analysis, relatively ideal results were obtained.
III. Experimental results and analysis
1. After the seed production stand was completed in 1995, cultivation and management continued. In 1998, which was a seed year, through on-site seed collection and calculation, the seed yield reached 33 kg per hectare, the seeds were plump and of high purity, and the thousand-grain weight reached 5.0 g; upon testing, the germination rate was 90%. The seed yield, thousand-grain weight and germination rate were 15%, 8% and 20% higher than those of ordinary Qinghai spruce seeds, respectively.
2. Through statistical analysis of the seedling-raising trial results: the proportion of seedlings with two rounds of leaves in the current year from seeds of the trial seed production stand was on average 21% higher than that of the control. In 2002, bed-changing cultivation was carried out, with an average seedling height of 8.3 cm, a ground diameter of 0.3 cm, and 850 seedlings per square meter, which were 33%, 30% and 21% higher than the control, respectively. In 2005, they were lifted for outplanting, with seedling height and ground diameter reaching 32 cm and 0.8 cm, respectively, 31% and 33% higher than the control.
IV. Conclusion and discussion
1. On the basis of a natural or planted superior forest stand, through thinning and transformation by retaining the superior and removing the inferior, individuals with rapid growth and good crown and stem form are retained and cultivated into a sparse stand with a thick fruiting layer and good light transmittance, promoting earlier fruiting of the trees, increasing seed yield, improving seed quality, and reducing seed production costs; moreover, the progeny grow quickly and have high yield. Producing large quantities of high-quality forest tree seeds to meet the needs of forestry production thus achieves the goal of using improved forest tree varieties, and it is also of great value in conserving germplasm resources.
2. The cultivation of Qinghai spruce seed production stands must be carried out on the basis of superior forest stands. In addition, sites with good site conditions, relatively sufficient light, relatively gentle terrain and relatively convenient transportation should be selected. Pure stands and even-aged stands are best; if a mixed stand must be selected, the target tree species must not be less than 50%, and if it is an uneven-aged stand, the ages of the seed trees should not differ too greatly. In addition, seedling-origin forests should be given priority, and the canopy density should generally be above 0.6.
3. The key to cultivating Qinghai spruce seed production stands lies in thinning and transformation. Inferior trees such as standing dead trees, windthrown trees, diseased and decayed trees, suppressed trees and trees with poor form and quality, as well as some intermediate trees, must be felled. Thinning should be carried out in 2 to 3 operations, once every 3 to 5 years, to prevent excessive thinning in a single operation. After each thinning, tree measurement and records should be made, and after successful thinning the canopy density should preferably be 0.5.