Technical key points for converting young Scots pine (Pinus sylvestris var. mongolica) stands into Korean pine (Pinus koraiensis) nut orchards
In recent years, the establishment of Korean pine dual-purpose nut and timber forests and Korean pine nut orchards has developed rapidly in Heilongjiang and Jilin provinces of China. In some places, developing Korean pine nut orchards has become a path to prosperity, and relatively large-scale Korean pine nut orchards have been established one after another. However, due to deviations in people's understanding, the selection of superior scions for grafting to establish orchards has been neglected, and the scions selected are rarely improved varieties that have undergone identification. Establishing Korean pine nut orchards without such selection cannot guarantee the yield and quality of seeds and nuts, let alone early fruiting, high yield, and stable yield.
Practice has proven that converting young Scots pine stands into Korean pine nut orchards results in rapid orchard establishment and good results. This article introduces the necessity, feasibility, and main orchard establishment operational techniques for converting young Scots pine stands into Korean pine nut orchards as follows.
1 Necessity
Future forestry should be high-efficiency forestry that delivers ecological, social, and economic benefits. High-efficiency forestry emphasizes targeted inputs, intensive management, and high-efficiency outputs.
Although the Scots pine forests currently established in various places have ecological significance, their social and economic benefits are relatively low, affecting economic income. If these stands are converted into nut orchards, they can both beautify the ecological environment and increase the income of workers, which is an important way for forest areas to emerge from economic difficulties.
2 Feasibility
Scots pine has strong adaptability, is cold-resistant, drought-tolerant, tolerant of poor soils, and also resistant to wind and sand. In particular, it propagates easily, has low nursery and afforestation costs, and grows rapidly. However, its economic and ecological benefits are far inferior to those of Korean pine. Using Scots pine as rootstock to graft Korean pine can indeed enable Korean pine to grow vigorously and can also advance flowering and fruiting. In the 1950s, in the southern forest-steppe zone of Omsk in the former Soviet Union, Scots pine (Pinus sylvestris) was used as rootstock to graft Siberian pine (Pinus sibirica), achieving successful afforestation and obtaining seeds, which improved the local ecological environment and economic conditions. In the Siberian region of Russia, to accelerate Siberian pine nut production, the heteroplastic grafting method was used to graft superior Siberian pine scions onto 5-7 year old Scots pine, with fruiting occurring in 3 years, and after 15 years, seeds of 110-200 kg/hectare could be obtained (maximum yield of 270-340 kg/hectare). In the 1960s, the Muling Forestry Bureau used heteroplastic grafting of Korean pine to establish timber forests, successfully obtaining fast-growing Korean pine forests that also bore fruit. In 2000, the Hongqi Forest Farm in Daqing City grafted Korean pine onto 20-year-old Scots pine, and flowering and fruiting began in 2004. Heteroplastic grafted Korean pine indeed grows faster than homoplastic grafted Korean pine. In May 2000, the Alihe Forestry Bureau in Inner Mongolia grafted Siberian pine onto Scots pine with a tree height of 3.1 m, and in 2002 the grafted branches grew an average of 37.2 cm.
Some people have suggested that grafting Scots pine with Korean pine may not heal well, or may produce a large-foot/small-foot phenomenon, affecting orchard establishment. According to surveys by Russian experts, about 25% of grafted branches show an elephant-foot phenomenon, generally appearing more than 25 years after grafting. Russia applied provenance selection and individual selection to select Scots pine varieties with good compatibility, solving this defect.
3 Orchard establishment technical regulations
3.1 Survey and planning of orchard establishment site
3.1.1 Site condition survey Before the survey, first collect stand history and meteorological and hydrological data. Survey the landform, topography, soil, and disease, insect, and rodent damage of the forest land, as well as the condition of nearby Korean pine forests. It is best to draw a topographic map of the forest land, marking roads and rivers, and to conduct a detailed survey of stand vegetation and dendrometric factors to provide reliable information for planning and design.
3.1.2 Planning and design for converting forest land According to the topography, forest form map, and stand condition, determine the positions and orientations of shelterbelts, pollen forests, and roads. According to stand condition, determine the plant and row spacing of grafted trees and the methods and means of stand invigoration. Generally, plant and row spacing is 5 x 5 m. Before grafting, it is best to mark with red paint for the convenience of grafting workers. ① Design and establishment of shelterbelts To achieve high and stable yields of Korean pine nuts, reduce wind damage, conserve water sources, and maintain soil and water, shelterbelts must be designed in the main wind direction. According to the forest land location and area size, specifically design the types and arrangement methods of shelterbelts. ② Design and grafting of pollen forests In the early fruiting stage of a Korean pine nut orchard, there is often a lack of sufficient high-quality pollen, affecting seed yield and quality. It is very necessary to graft superior pollinizer trees specifically in the main wind direction and around the nut orchard to ensure sufficient pollen within the stand, and also to block inferior pollen from entering the stand. ③ Road design Roads are an important hub connecting the nut orchard internally and externally, with functions of transport, traffic, fire prevention, ventilation, and drainage, and should be planned with a long-term perspective. The distance between roads should not be too close. Road width is generally 3-4 m. If the slope exceeds 10 degrees, a winding mountain road can be built. ④ Grafting layout diagram for Korean pine nut orchard Before grafting, first draw a grafting construction layout diagram. The female-to-male arrangement is generally 4:1, 3:1, and 2:1. We use 4:1.
3.2 Invigoration of Scots pine before grafting
One to two years before converting the orchard, invigoration management must be carried out. This mainly includes light-release tending, weeding, soil loosening, pruning, and prevention and control of disease, insect, and rodent damage, with the aim of achieving vigorous growth of the trees to be grafted and improving grafting survival rate. Design the number of grafted trees according to grafting density. If the number of rootstocks is insufficient or unevenly distributed, large Scots pine seedlings should be replanted in a timely manner to make the distribution uniform and increase seed yield.
3.2.1 Light-release tending Before light-release tending, a light-release tending survey and design must be carried out, and construction must follow the design. The method is comprehensive single-tree light-release tending, ensuring that the trees to be grafted are not squeezed by shrubs or trees, and creating convenient conditions for grafting operations. Where conditions permit, soil should also be loosened, weeds removed, and organic or inorganic fertilizer applied.
3.2.2 Pruning, shaping, and prevention and control of disease, insect, and rodent damage Pruning and shaping of trees to be grafted is an important means of improving tree resistance. Dead branches, diseased and insect-damaged branches, weak branches, dominant branches, inner-canopy branches, overlapping branches, and horizontal branches should be pruned away. Forked branches can also be pruned away. Scots pine shoot blight and red band needle blight are highly contagious and should be controlled with chemicals. Rodent damage should also be prevented and controlled in a timely manner.
3.3 Prepare sufficient scions of superior varieties
Scions of superior varieties are one of the important conditions for ensuring high and stable yields of Korean pine nut orchards. Branches from superior clones that have undergone variety identification, with high seed production and good quality, must be used as scions. Under no circumstances should inferior varieties be used casually as scions. The Qingshan Seed Orchard of the Weihe Forestry Bureau in Heilongjiang Province used 9 years of continuous surveys to evaluate Korean pine clonal mother trees. From 200 clones, 15 superior nut-type clones were selected as superior varieties for developing Korean pine nut production. High-yield and stable-yield type: No. 124, No. 56, No. 117, No. 179; large-nut high-yield pollinizer trees: No. 52, No. 58, No. 118, No. 121. These two types of superior trees have obvious phenotypic characteristics. Characteristics of the high-yield, stable-yield type: wide crown, long crown, fruiting layer thickness accounting for 3/4 of tree height, abundant fruiting, and fruiting every year; characteristics of large-nut high-yield pollinizer trees: narrow crown, short crown, obvious branching, fruiting layer thickness accounting for only 1/5 of tree height, long cones but few in number, and high pollen yield of good quality.
3.4 Grafting
Grafting technique and grafting time are related to the success or failure of orchard establishment and its cost. If grafting technique is not proficient, it affects grafting survival rate and preservation rate; different grafting methods also affect the survival rate and preservation rate of grafted branches.
3.4.1 Grafting time Grafting can be done in spring and summer. We graft in spring when sap flows (April 17-20). If grafting is too early, callus tissue forms late and the survival rate is low; if grafting is too late, the new shoots of grafted branches are prone to frost damage. Therefore, grafting time must be correctly judged. General experience is that the best grafting time is when the average day-night temperature reaches about 10 degrees C.
3.4.2 Scion collection and storage Scion storage time should be short. It is best to collect during the dormant period. The storage cellar temperature should be maintained at 0-5 degrees C. Scions should be buried in ice and snow to achieve the purpose of moisture retention and freshness preservation.
3.4.3 Grafting method The grafting method is determined according to the proficiency of the grafting workers. We use the cleft graft with cambium matching method. The grafting length should be greater than 10 cm. The grafting positions are the top of the central leader and the upper ends of the 1st to 3rd whorled branches. If the tree is relatively tall and the bark of the central leader is thick, poor matching between the grafted branch and rootstock can easily lead to low grafting survival rate, so grafting should be done at the 1st to 3rd whorled branch positions. To retain moisture and prevent late frost from damaging the terminal buds, white breathable plastic bags should be put on immediately after grafting.
3.4.4 Post-grafting management After May 6, the terminal buds of grafted branches gradually begin to sprout. Remove the plastic bags in a timely manner, cut off the terminal and lateral buds of the rootstock above the grafted branch, and apply lead paint to the wounds. From May 30 to June 10, perform the first loosening of the binding. For dead trees, completely untie the binding strips. From July 25 to July 31, perform the second loosening of the binding, and at the same time cut off the terminal and lateral buds of all whorled branches that exceed the height of the grafted branch. After current-year Scots pine branches are cut, many adventitious buds grow again, forming many small young branches. Another rootstock pruning should be done in autumn, but all nutrient branches must not be cut off at once, otherwise it will affect the survival and overwintering of the grafted branches.
3.5 Disaster and growth survey
In autumn, surveys should be conducted on diseases, insect pests, and growth conditions of grafted plants. Through the survey, 68% of scions had secondary growth, with grafted branches growing an average of 8.9 cm and a maximum of 14 cm. Because secondary growth exceeded 60%, grafted plants with secondary growth were covered with white breathable plastic bags in early November after the onset of winter to prevent frost damage to new shoots that had not fully lignified.