(Siberian elm)

Scientific name: Ulmus pumila L.. Also known as elm tree and home elm tree. Ulmaceae, Ulmus genus.

Form and use

Deciduous tree, up to 25 meters high and 1 meter in diameter at breast height. The leaves are oval-ovate, or elliptical-lanceolate, 2 to 8 cm long, with irregular compound serrations and single serrations, hairless or with clusters of pubescence in the vein axils below; the petiole is 2 to 6 mm long. Flowers in clusters. The fruit is nearly round or obovate, 1 to 2 cm long, yellow-white when ripe, hairless, and the core is located near the middle. The flowering period is from March to April, and the fruit matures in May.

Elm wood has straight texture, clear and beautiful patterns, slightly hard, specific gravity 0.57~0.66, elastic, moisture-resistant, corrosion-resistant, and good mechanical properties. It can be used for vehicles, sleepers, construction, agricultural tools, furniture, etc. Materials. The branches can be used as firewood and weaving materials. The young leaves are edible and can be used as feed. The bark fiber is tough and can be made into rope or artificial cotton; it also contains mucilage and is an adhesive for making incense and mosquito coils. The seeds can be squeezed for oil and eaten. It has strong anti-pollution ability. Planting elm trees in factories and mines where sulfur dioxide, lead, and chlorine are the main pollutants can achieve good air purification effects.

(Tang Wuqing)

Geographical distribution and biological characteristics

It is distributed in North China, Northwest China, Northeast China, East China and Central China. The vertical distribution is generally below 1,000 meters above sea level, with the Loess Plateau in central Gansu at 2,100 to 2,400 meters, and the Qinling and Qilian Mountains reaching 2,500 meters.

It likes light and has the highest growth rate under full sunlight. It can withstand hot and high temperatures and has strong cold resistance. The adaptability to temperature varies greatly. In the elm distribution area, the annual absolute maximum and minimum temperature difference reaches 97.6℃ (47.6~-50℃), the annual accumulated temperature is 1600~3200℃, and the growth period is 213~268 days. Within the distribution range of China, elms grow rapidly and have tall trees in the eastern humid areas (including the North China Plain, eastern Northeast China, and the Huaibei Plain) with annual precipitation of 500 to 700 mm; followed by the semi-humid areas in the central part; and the arid and semi-humid areas in the west. In arid deserts and desert steppes with low annual rainfall (less than 200 to 500 mm), elm trees can still grow normally. It likes fertile soil but can tolerate poor soil. It has strong salt tolerance. Generally, it can tolerate a salt content of 0.35 on chloride saline soil (coastal saline-alkali soil); it can tolerate a salt content of 0.38 on soda saline soil; it can tolerate a salt content of 0.6 on sulfate soil (inland saline-alkali soil). Elm trees grow quickly and have a long lifespan, usually taking 20 to 30 years to become useful.

(Zhang Dunlun)

Breeding

Cultivation of fast-growing, straight-stemmed, pest-resistant varieties is the main task of elm breeding. The German M. Klotzch conducted a hybrid experiment between U. campestris and U. effusa in 1845. When the hybrid was 8 years old, its height and thickness were 1/3 larger than that of the parent. The elm tree was first discovered in the Netherlands in the early 20th century. Dutch disease quickly spread to European and American countries. The Netherlands began disease-resistant breeding in 1926 and has selected several disease-resistant varieties. In recent years, the United States has also selected excellent disease-resistant and fast-growing lines through hybridization. In the Soviet Union, Ulmus tree species were divided into five categories: highly susceptible, susceptible, weakly susceptible, disease-resistant and highly disease-resistant based on their resistance to elm Dutch disease. The Central Asian ecotype of the white elm is the only highly susceptible. Disease resistant.

Chinese elm selection and cross-breeding began in the 1970s, and a number of excellent clones have been selected. The volume of a single plant is more than 30% larger than the control. Elm trees are easy to reproduce asexually, and excellent clones have large gains. Therefore, breeding excellent clones is an important way for elm trees. Asexual propagation of elm trees can be done by grafting, twig cuttings and root seedlings. Cross-breeding has also achieved some results. For example, the Shandong Forestry School in China selected the Luyu (Za) No. 1 clone from the combination of Ulmus elegans × Ulmus trichocarpa. It has a narrow crown, a round and straight trunk, fast growth, and a single plant volume exceeding Control 50, already used in production.

China organized a national white elm provenance test in 1980. After 6 years of testing, the results showed that: ①The height, diameter at breast height, side branch length, and trunk straightness of white elm trees are significantly related to the latitude of the place of origin, and are related to longitude. The relationship is not significant; ② the growth ability of various sources is greatly different; ③ the overwintering ability is greatly different. For example, if the sources from the middle and lower reaches of the Yellow River are introduced to Heilongjiang Province and Xinjiang, the dieback is more serious.

(Pang Jinxuan)

Afforestation technology

① Seed collection: Elm trees begin to bear fruit when they are 4 to 5 years old, and enter the peak fruiting period in 8 to 10 years, with no size years. The samara matures from April to May and is yellow. They begin to fall off about 3 to 4 days after maturity. They can be manually picked from trees or collected after being shot down. After collection, they should be dried in a ventilated place for sowing or storage. The weight of one thousand seeds is 5 to 8.2 grams. The germination rate is 70-85. If stored under sealed low-temperature conditions (below 5°C), the seed germination rate can still remain around 70% after one year. ② Seedling cultivation: Choose sandy loam or loam soil with deep and fertile soil, irrigation conditions, and good drainage as the nursery land. Avoid low-lying land prone to waterlogging. The nursery land should be plowed 30 centimeters deep and finely, and sufficient base fertilizer should be applied. Bed-type seedlings are often used, but field-type seedlings can also be used. Generally, drill sowing is used, with a strip spacing of 25 cm, a sowing width of 5 cm, and a trench depth of 2 cm. After sowing the seeds, cover the soil with about 0.5 cm, so that the seeds are no longer visible, and then press gently to make the seeds closely connected with the soil. Generally, it takes 3 to 5 days to germinate and emerge, and all the seeds can emerge in about 10 days. The seeding rate is 20 to 22.5 kilograms of samara per hectare. One-year-old seedlings, with a height of 1 to 1.5 meters and a ground diameter of 0.5 to 1 cm, there are 225,000 to 270,000 plants per hectare. 2-year-old transplanted seedlings, 2.5 to 3.0 meters high, 1.3 to 2 cm in diameter, 67,500 to 90,000 plants per hectare. In saline-alkali land, choose lightly saline-alkali soil with a salt content of no more than 0.2 in the 0 to 60 cm soil layer for seedling cultivation. It is necessary to prepare the land in autumn and apply sufficient base fertilizer to avoid spring drought. After the first drenching rain in June or July, the soil can be sown with sufficient moisture. The seeding rate is 30 to 38 kilograms per hectare. Use double-row drills in large ridges, with a strip width of 3 cm, a strip depth of 3 to 5 cm, a strip spacing of 20 cm, and mulching of 0.5 to 1.0 cm of soil, with slight suppression. When the seedlings grow 2 to 3 true leaves, start thinning. When the seedlings are 5 to 6 centimeters tall, the seedlings will be planted. About 450,000 seedlings will be left evenly per hectare. After thinning, the seedlings will be properly irrigated. During the growth stage of seedlings, soil should be loosened and weeded frequently, and top dressing should be combined with irrigation between June and August. ③Afforestation: To build timber forests, high-quality seedlings should be used for afforestation. Select deep, fertile, well-watered loam and clay loam with a water table below 1.5 meters, and carry out large pit preparation (80 cm square). The initial planting density is 1200 to 1650 plants per hectare. After 3 to 4 years, the forest stand will be closed and the lower layer will be tended and cut. The density of 405 to 600 plants per hectare can also be used for one-time planting. Mixing elms and locust trees in strips or between rows can promote forest growth. To build a farmland shelterbelt, you can use a narrow forest belt composed of 2 to 5 rows of elms, or you can mix it with narrow-crown poplars or shrubs such as Acacia acacia and Elaeagnus elegans to form a forest belt with a sparse and low-ventilation structure. When the forest stand is closed, that is, it is thinned multiple times, and the thinning intensity generally does not exceed 15 to 20 based on the volume. The elm tree has a heavy ground threat. Other tree species with light ground threat can be reasonably arranged on the edge of the field protection forest belt, and root cutting trenches can be dug to reduce the adverse impact of the elm forest belt on crops. For afforestation of arid grasslands, it is necessary to choose areas with good moisture conditions such as inter-hill flats, wide shallow depressions, terraces along rivers where water flows gather, and soils with sandy parent material. The land was prepared two years in advance and plowed 30 to 40 centimeters deep to facilitate water storage and moisture conservation. Select strong seedlings with well-developed root systems and plant trees at a spacing of 1 to 1.5 meters and a row spacing of 3 to 4 meters for afforestation in autumn. Soil improvement before afforestation. Build terraced fields in low-lying areas where the groundwater level is about 1 meter. In places where the groundwater level is deeper than 1.5 meters all year round, build strips of fields to increase the height of tree planting areas. On higher-lying alkaline wasteland without a drainage system, the fields can be surrounded by ditches to store rainwater for natural leaching and promote soil desalination; it is appropriate to plant deeply in inland saline-alkali land and shallowly in coastal saline-alkali land. The appropriate initial planting density is 3,300 to 4,950 plants per hectare. Mixing between rows of elm trees and acacia acacia can improve soil fertility in the forest and prevent salt return. In the Loess Plateau area, afforestation should be done at the foot of the slope and the lower part of the slope with good water and soil conditions, and at the bottom of the erosion ditch. In the first rainy season and autumn, reverse slope terraces should be used to prepare the land, with a depth of 40 to 60 centimeters.

Plant according to 1.5 plant spacing and 1.5 to 2.5 meter row spacing. It can be mixed with black locust, acacia acacia, etc. in strips or between rows. ④Tending and management: Carry out soil loosening and weeding 2 to 3 years after afforestation. Thinning begins when trees are 7 to 8 years old when their canopy is closed, and the canopy density remains at about 0.6 after cutting.

The main pests include elm green leaf beetle (also known as elm gold flower beetle), elm yellow leaf beetle, elm purple leaf beetle, elm geometrid, elm four-striped woolly aphid, elm poison moth, elm green hornworm, and elm wood beetle moth, Mongolian woodworm moth, glabri-shouldered star beetle, etc.

(Zhang Dunlun)

Bibliography

Zhang Dunlun et al.: "White Elm", China Forestry Press, 1984.