How to Build a Good Shelterbelt When Establishing a Walnut Orchard

  Shelterbelts can improve the ecological environment of a walnut orchard, serving to prevent and reduce the harm and encroachment of wind, sand, cold and drought, as well as to lower wind speed, reduce soil moisture evaporation and soil erosion, regulate temperature, weaken cold currents, increase soil water content, and ensure normal tree growth and fruiting, among other functions.

  1. The role of shelterbelt strips

  (1) Regulating the temperature and humidity of the plot. According to measurements, within the protected range of a shelterbelt strip, summer temperatures can be reduced by 0.7-2.0°C, relative humidity increased by 3.5%-14%, and soil water content increased by about 9%, narrowing the diurnal temperature difference; the frost-free period can be extended by 3-5 days. This significantly improves the orchard's ecological environment and lays a solid foundation for high yield and good quality.

  (2) Reducing wind speed and lessening wind damage. A gentle breeze is beneficial to fruit tree growth and development as well as wind pollination, while strong winds have a destructive effect on fruit trees. If strong winds occur during the walnut flowering period, they can easily cause damage to flowers, fruits and other organs, affecting pollination and fertilization and reducing the fruit-setting rate. Strong winds accelerate leaf transpiration, aggravating tree water loss and soil drought. In addition, strong winds cause soil erosion, blowing away topsoil and worsening soil infertility. Creating artificial shelterbelts can effectively reduce wind speed and alleviate wind damage.

  2. Types of windbreak forests

  Based on windbreak characteristics, shelterbelt strips are usually divided into the following two types.

  (1) Dense type. This is an impermeable shelterbelt, formed by planting multiple rows of trees and shrubs of large, medium and small heights with dense branches and leaves, creating a tight structure from top to bottom that forms a tall and dense tree wall. This type of shelterbelt has a small wind protection range but a good protective effect.

  (2) Permeable type. This type of shelterbelt consists of one layer of large trees and one layer of shrubs, composed of relatively loose trees and shrubs. The shelterbelt has a mesh-like permeable structure, so that when strong winds pass through, it is as if they are sifted through sieve holes, slowing the wind speed and providing protection. However, its windbreak effect is inferior to that of the dense type.

  3. Layout and tree species selection for shelterbelt strips

  (1) Layout of shelterbelt strips. Usually, main shelterbelt strips and secondary shelterbelt strips are set up to form a shelterbelt network. Main strips have 4-8 rows of trees, and secondary strips have 2-3 rows of trees. The middle of the strip is planted with trees and both sides with shrubs; there are also mixed plantings of trees and shrubs. For dense-type strips, the spacing between plants and rows is 0.5-0.7 m x 1.5 m; for permeable-type strips, the spacing is 1-1.5 m x 2.5-3 m; for shrubs, the spacing is 1 m x 1 m.

  When laying out windbreak shelterbelt strips, attention should be paid to the following:

  ① The main shelterbelt strip must be perpendicular to the local prevailing wind direction, and a semi-permeable shelterbelt should preferably be used.

  ② The secondary shelterbelt strips should be perpendicular to the main strips, assisting the main strips in blocking harmful winds from other directions.

  ③ The distance between two main shelterbelt strips should be 200-400 m, and that of secondary strips can be increased to 500-800 m. The distance, width and height of shelterbelt strips in different regions should be determined according to the local maximum wind speed. In the orchard, the shelterbelt on the south side should be 20-30 m from the fruit trees, and on the north side 15-20 m; roads, water channels, etc. can be placed in this space.

  ④ When a shelterbelt strip passes over the local highest point, it can be established along the watershed. When passing through a valley mouth, a gap should be left at the offset valley mouth, so as to avoid crossing the valley and trapping cold air inside the valley, which helps discharge cold air and reduce freeze damage.

  (2) Tree species selection. Shelterbelt tree species should have strong adaptability, fast growth, upright crowns and a certain economic value. In addition, the most important point is that they must not share common pests and diseases with walnuts. Tree species commonly used for shelterbelts in northern regions include: poplar, elm, early willow, tree of heaven, white ash, Chinese arborvitae, black pine, Malus baccata, hawthorn, Pyrus betulifolia, Chinese honey locust, Manchurian walnut, maple, etc.; shrubs include tamarisk, Sichuan pepper, Vitex negundo, purple-leaf pagoda tree, wild jujube, Rosa rugosa, Hibiscus syriacus, etc.