Design of roadside vegetative barriers

Preparing the soil

The soil must be prepared to facilitate growth of seedlings. The soil must be loose enough and have adequate pore space to allow roots to penetrate and absorb sufficient water and oxygen. In many instances, the highly compacted soils that often result from roadside construction do not have suitable characteristics for tree planting. Moreover, people and animals tend to walk along the roadsides, compacting the soils even more. adding materials (compost, manure, or other soil) is not recommended unless the existing soil is of very poor quality. If existing soil quality is very poor, the volume of organic matter added to it should not exceed 25 percent of the planting bed. Ultimately, it is better to select plants that can tolerate existing conditions than to improve a large area of soil to suit less well-adapted species.

Several actions can be undertaken to loosen the soil and make it suitable for planting. Tilling can increase porosity in the rooting zone, increase infiltration rates, and increase surface roughness. for vegetation work associated with road construction, it is important to break up deep compaction at depths of at least 0.5 meter. Soil shattering involves pulling one tine, or a set of tines, through the soil at various depths to break up compaction by the roadside.

Topsoiling should be undertaken when possible. Topsoiling involves the removal, storage, and reapplication of topsoil material to provide a suitable growing medium for vegetation. Topsoiling increases nutrient availability, water-holding capacity, and microbial activity for the planting. Topsoil should only be removed from areas that will be excavated, are highly compacted, or are buried under excavated material, such as fill slopes. When possible, laboratory tests and field surveys should be conducted to determine topsoil quality. Topsoil with high salinity, very high or very low pH, or any other condition that may obstruct plant growth should be avoided. Removal and collection of topsoil is best done when soils are relatively dry to avoid soil compaction. The depth of topsoil application depends on the amount available. Deeper topsoil generally will result in a more productive site.

Preparing planting holes

Use of planting holes improves newly planted trees’ chances of survival. Planting holes should be dug vertically rather than perpendicular to the ground surface. Preferably, the planting hole should be 5–7 centimeters deeper than the total length of the root system, and at least as wide as the root system. Species that can be rooted from cuttings can be planted deeper given that portions of the stem will root when buried. The roots of the seedlings should not be forced into the planting hole, nor damaged or broken during planting. after placing the plant in the hole, excavated soil should be placed firmly around the root system so that there is no loose soil or air pockets around the root plug. The root system must not be damaged during this operation.

DESIGN OF ROADSIDE VEGETATIVE BARRIERS

Several decisions must be made when designing roadside vegetative barriers, specifically the combination of trees and shrubs, the porosity of the barrier, and the number of tree lines.