Some General Information on Shelterbelts

What is a shelterbelt?

A shelterbelt is a line of trees and/or shrubs planted in order to aid in protecting a given area from natural elements such as wind and snow, or for other purposes such as aesthetics, carbon sequestration and wildlife habitat. Different types of shelterbelts include farmyard, field, dugout, roadside, livestock, forest, wildlife planting and riparian buffer shelterbelts. Details on each and examples of species that are suitable to each type of shelterbelt are mentioned below. 

Image 1. A mature coniferous shelterbelt.
Source: Colin Laroque

What kind of shelterbelts are there? Different purposes for each

Farmyard shelterbelts

A shelterbelt placed in or around a farmyard is often planted for wind protection. This can benefit the farm and area by reducing snow removal costs since the shelterbelt can control blowing snow. They can also insulate the yard and therefore decrease energy consumption. Water supplies can be increased since they can trap snow in dugouts. Farmyard shelterbelts can also protect gardens due to a more controlled microclimate. They can also provide habitat for wildlife, sequester carbon, reduce dust, provide privacy and beautify the area. 

Field shelterbelts (fieldbelts)

Fieldbelts are shelterbelts planted in fields (i.e., agricultural land). The main use of these shelterbelts is for wind protection for both soils and crops. Wind can erode soil and damage crops, so wind mitigation is beneficial. They also very much help to control the snow and microclimate of the area, beautify the area and provide wildlife habitat. Fieldbelts also help increase the efficiency of irrigation since they help keep the irrigated water in its proper place; shelterbelts block the wind from evaporating the irrigation water away. These shelterbelts also protect new seeds and newly germinated plants.

In western Canada, common Caragana is the most popular species for single row field shelterbelts.

Dugout shelterbelts

Shelterbelts planted around dugouts are valuable for protecting the surrounding area from snowmelt and spring runoff, and trapping this water into a dugout area. Snow collection and runoff should be directed towards the dugout. This can be achieved by planting trees on the north and west sides of a dugout, but east and south sided shelterbelts are also beneficial for trapping snow directed east and south by wind. Also note that some deciduous trees’ roots can take water from the dugout to use for growth, so these should be planted at least 50 m from the dugout to prevent excess water loss from the dugout. Finally, the water stored in a dugout with the help of a surrounding shelterbelt can be a valuable source of water for agricultural activities. 

Roadside shelterbelts

Shelterbelts planted along roadsides are generally used to protect the road from snow in order to prevent blizzard conditions and/or improve visibility. They also reduce the need for road maintenance during the winter since there is less snow built up on the roads. Another major use for roadside shelterbelts is to reduce road dust from reaching and irritating other areas such as crops, animals, or farmhouses. They can also provide privacy. Roadside shelterbelts should be placed close to the yard, and only far enough away to allow room for snowdrift to not touch the road. As well, one must be careful to not plant shelterbelts where it will hinder visibility, such as very close to intersections. There are specific provincial regulations for these distances so check with them to learn about your specific area, but generally the distance is around 45 meters away from the centre of the main road. 

Livestock shelterbelts

Planting shelterbelts along livestock areas is beneficial for the livestock in that they protect them from wind and dust (which lowers animal stress), improves animal health, provides shade and increases efficiency of feeding. Livestock shelterbelts can also protect livestock from snow which can also decrease animal stress and increase comfort during winter months. Decreased animal stress can beneficially result in increased yields of goods such as milk from dairy cows and eggs from hens. Livestock shelterbelts also benefit nearby people in that they protect from noise and odours of the livestock and livestock operations. 

Wildlife planting shelterbelts

Shelterbelts can be planted to provide sanctuaries for animals and insects. These plantings can provide areas for feeding, nesting, breeding, and more. They can also provide shelter from weather and predators, as well as provide a food supply. In return, these animals and insects can provide pollination and help maintain a fruitful and healthy plant area. 

Multiple plant species can be planted in order to provide services for many different species. Coniferous and deciduous plants can be combined, along with herbaceous flowering vegetation to promote pollination and subsequent future growing seasons. Native plants are also very recommended for wildlife plantings since they are already adapted to the climate and soil conditions of the area. 

Note that a small planting of trees and shrubs for habitat in an otherwise baron area can result in a “predator trap” in which this small area is solely targeted by predators. Wildlife plantings should be at least 1 hectare in area in order to avoid this. 

Travel corridors between rows of the planting should also be a priority to create. These can be implemented when there are 3 of more rows of the planting. A simple 15 – 30 m spacing between rows can result in successful travel corridors for wildlife. 

Riparian buffer shelterbelts

Riparian buffer shelterbelts are put in place to divide and buffer the area between agricultural land and a body of water. These bodies of water can be wetlands, floodplains, rivers, streams, creeks, lakes, sloughs, etc. 

These riparian buffers can overall stabilize the area and improve habitat in both aquatic and terrestrial environments. They can reduce erosion, protect sensitive wetland areas, absorb excess nutrients and sediment from both aquatic and terrestrial areas, supply cover for wildlife, and more.

These buffers also very importantly aid in prohibiting flood water from reaching the nearby crops and agricultural lands, by providing distance/elevation from flood waters, slowing water entering the drainage system, and more. 

As the width of the riparian buffer increases, often its purpose is better accomplished. An effective riparian buffer generally has two to three zones (i.e., rows) of vegetation.

Forest shelterbelts

A forest belt is essentially a large field shelterbelt. To be considered a forest belt, a field shelterbelt must have at least three rows of trees and/or shrubs. The difference is they create a forest environment when the tree canopies of each row combine and close together. 

Forest shelterbelts also thereby provide the same services and serve the same purposes as field shelterbelts. These include reducing soil erosion, trapping and mitigating snow, increasing crop yields, increasing biodiversity, sequestering carbon, and providing shelter and wildlife habitat. 

  • Forest shelterbelts are special in that they can provide these services at perhaps a greater level, since there are fewer gaps in their canopies compared to field shelterbelts. 

Examples of species that can be used in each type of shelterbelt

Shrubs

  • Farmyard
    • Caragana, chokecherry, hawthorn, red-osier dogwood, sea buckthorn, silver buffaloberry, villosa lilac.
  • Field
    • Caragana, occasionally chokecherry, hawthorn, sea buckthorn, villosa lilac.
  • Dugout
    • Caragana, hawthorn, sea buckthorn, villosa lilac, chokecherry.
  • Roadside
    • Caragana, hawthorn, red-osier dogwood, sea buckthorn, villosa lilac.
  • Livestock
    • Caragana, chokecherry, sea buckthorn, villosa lilac.
  • Wildlife planting
    • Chokecherry, hawthorn, hedge rose, red elder, red-osier dogwood, sea buckthorn, silver buffaloberry, snowberry, villosa lilac.
  • Riparian buffer
    • Chokecherry, hawthorn, hedge rose, red elder, red-osier dogwood, snowberry.
  • Forest
    • Caragana, occasionally chokecherry, hawthorn, sea buckthorn, villosa lilac.

Deciduous trees

  • Farmyard
    • Bur oak, green ash, hybrid poplar, Manitoba maple, Siberian crabapple, acute willow, silverleaf willow.
  • Field
    • Bur oak, green ash, acute willow, silverleaf willow.
  • Dugout
    • Bur oak, green ash, acute willow, silverleaf willow.
  • Roadside
    • Bur oak, green ash, hybrid poplar, trembling aspen, acute willow, silverleaf willow.
  • Livestock
    • Bur oak, hybrid poplar, Manitoba maple, trembling aspen, acute willow, silverleaf willow.
  • Wildlife planting
    • Bur oak, cottonwood, green ash, hybrid poplar, Manitoba maple, pincherry, Siberian crabapple, trembling aspen, acute willow, peachleaf willow, silverleaf willow.
  • Riparian buffer
    • Cottonwood, possibly hybrid poplar, Manitoba maple, pincherry, trembling aspen, peachleaf willow.
  • Forest
    • Bur oak, green ash, acute willow, silverleaf willow.

Coniferous trees

  • Farmyard
    • Siberian larch, Scots pine, Colorado spruce, white spruce.
  • Field
    • Possibly Siberian larch, Scots pine, Colorado spruce (multiple row only), white spruce (multiple row only).
  • Dugout
    • Possibly Siberian larch, Scots pine.
  • Roadside
    • Siberian larch, Scots pine, Colorado spruce, white spruce.
  • Livestock
    • Siberian larch, Scots pine, Colorado spruce, white spruce.
  • Wildlife planting
    • Siberian larch, Scots pine, Colorado spruce, white spruce.
  • Riparian buffer
    • Possibly Siberian larch, Scots pine.
  • Forest
    • Possibly Siberian larch, Scots pine, Colorado spruce (multiple row only), white spruce (multiple row only).

Shelterbelt characteristics

Overview

Shelterbelt characteristics such as height, density, orientation and length, all affect your shelterbelt as a whole and influence how effectively it will execute its purpose(s). 

Effect of height

The height of your shelterbelt determines how much of the downwind land area will be protected by it. Height, of course, varies with each shelterbelt. Shelterbelts also change and increase height over time as the trees continue to grow. 

On the windward side, the distance of the area with reduced wind speed can be around 2 to 5 times the height of the shelterbelt. On the leeward side, the distance of the area with reduced wind speed can be around 20 times the height of the shelterbelt.

Effect of density

Naturally, a denser shelterbelt will allow less wind to pass through it. Air flow is lessened on the leeward side of a shelterbelts, and less airflow is allowed to pass through. Interestingly, the protected zone is also smaller behind denser shelterbelts. For less dense shelterbelts, more air can pass through, and this reduces wind turbulence and lengthens the downwind area of protection. This is why the less dense shelterbelts have a larger protected area. By altering the density of a shelterbelt density, different patterns of flow and protected areas are developed.

Shelterbelt density can be controlled by the number of rows planted, distance between each tree, and species used. For example, increasing the number of rows or decreasing the distance between each tree increases shelterbelt density and provides a more solid barrier. Species used will also decide the shelterbelt height, density, and influences the distance of the protected area.

Effect of orientation

Shelterbelts are most effective in protecting the nearby area when they are positioned at right angles (i.e., perpendicular) to coming winds. In the prairies, the wind often arrives from the north and west, so shelterbelts should be positioned perpendicular to these directions. Of course, wind can change direction, so at those times the shelterbelt may not provide the same amount of protection. 

The purpose of the shelterbelt can also decide the orientation of the shelterbelt. For example, farmyards and feedlots often require protection from cold winds, dust or blowing snow to protect the farm animals. Due to this, these shelterbelts should protect from multiple directions.

Fields and crops often need to be protected from hot, dry winds during summertime, abrasive particles blown in by wind, or both.

Effect of length

The length (and density) of the shelterbelt determines the amount of area to be protected. The height (and density) of the shelterbelt determines the extent of the downwind protection. To maximize the efficiency of your shelterbelt, the length should be at least 10 times the height; in other words, at least a 10:1 ratio of length to height should be implemented into your shelterbelt plan. 

Continuity of a shelterbelt, or in other words, having few to no gaps, is important since gaps can concentrate wind flow like a tunnel. This increases wind speed in those areas and therefore defeats the purpose of planting a shelterbelt! Your shelterbelt would then not be as effective. For these reasons, driving lanes or areas to access fields through shelterbelts should be positioned in areas that would avoid this consequence.

Microclimate modifications

In and around the protected zone of a shelterbelt there is a different microclimate than in the surrounding area. The specifics of temperature and humidity modifications depend on the height, density, orientation and length of the shelterbelt, as well as time of day. However, the lesser amount of wind in this area often results in this changed microclimate. This usually results in a temperature and humidity increase, which often results in decreased soil moisture evaporation as well as decreased water loss from transpiration. Higher humidity levels result in the plants having to use less water; therefore plants are more water-efficient in sheltered areas. However, increased humidity levels could potentially lead to increased diseases such as mildew.

Higher temperature and humidity of the reduced-wind area also results in summertime soil temperatures in the sheltered areas usually being higher than the areas not sheltered. This warmer soil temperature could allow earlier crop planting and aid the germination process.

However, soil temperatures close to the shelterbelt can be lower due to shading, especially in early spring. These cooler temperatures could potentially slow the rate of snow melt, and make fields difficult to access in the spring. 

Most shelterbelt benefits are indirect because of changes in the microclimate of the sheltered zone. One exception is the direct benefit of reducing wind speed to control soil erosion. A shelterbelt can reduce soil erosion on the leeward side to near zero within ten times the height of the leeward side of the tree row.

Executing goals such as reducing wind speed moderates the microclimate of the area. With diligent planning, microclimate modifications can help establish beneficial environments for agricultural crops, housing livestock, and protecting farm equipment, housing and working areas.

Image 2. An example of an understory/microclimate area of a coniferous multiple-row shelterbelt.
Source: Colin Laroque

References