Windbreaks and Shelterbelts: Are they really worth it?

Windbreaks and shelterbelts were offered to solve devastating erosion during the 1920s dustbowl across Kansas, Oklahoma, and north Texas. The idea is that wind barriers slow wind enough to reduce the lifting and movement of soil particles by strong winds. A secondary benefit is to lessen the drying effect of wind sucking moisture out of plants and soil surfaces.

Since these earliest soil conservation ideals, windbreaks and shelterbelts have proven to have many more benefits. Dense shelterbelts around homes create an oasis for wildlife, especially migratory neotropical and game birds, reduce home heating costs by about 30% and create a milder microclimate for good gardening and fruit tree habitat. Shelterbelts can reduce feed costs by as much as 30% when used to protect livestock.

For home space protection, three to five rows of shrubs and trees typically need to be planted on two to three sides of the homestead to offer maximum protection from prevailing winds (Figures 1 and 2). Shelterbelt design should create a wedge into the wind with more dense lower shrubs on the outside, deciduous, smaller trees next,followed by taller evergreens and an inside row of deciduous or ornamental trees. Drought and freeze-drying from winter winds are the biggest enemies of shelterbelt trees. To reduce frost damage, the hardiest shrubs that lose their leaves in winter should be used as the initial barrier, followed by another relatively small deciduous tree to further lift the wind. A third or fourth row is the best place for evergreen trees. Evergreen trees retain their needles all year, so they provide a dense wind block during winter, but those needles are also susceptible to winter freeze-drying damage, so they need protection from the first several outside rows. The final row can be more ornamental, but if the windbreak is facing the East, South, or West, the final row needs to be shade-tolerant or taller-growing to survive the shade from the rows in direct line with the sun.

Figure 1. A typical “tree island” shelterbelt in central Montana.

 

Figure 2. Blueprint of a functional homestead shelterbelt

Photos: Peter Kolb, MSU Extension

A spacing of 20 feet between the rows is highly recommended. Even the most drought-tolerant shrub and tree species need at least 16 inches of annual precipitation. Soil with no vegetation growing on it (fallow soil) between the planted rows acts as a water collection zone for the row of shrubs and trees. The larger the tree, the more ground area is needed to collect rain and snow for recharging soil moisture. A well-designed windbreak also traps snow (Figure 3) which further adds to the soil water recharge. Critical times, when water collection is most important, are during the initial three-year shelterbelt establishment phase and then again when the shelterbelt trees get larger and have a greater leaf area that uses more water. Any time a drought cycle hits, grasses and forbs growing within 10 feet of shelterbelt trees should be minimized because they will use the water that trees need to survive.

Crop windbreaks are planted somewhat differently than homestead shelterbelts (Figure 4). These are typically planted as a single row of a very hardy and more dense-growing shrub or tree species. Of all the species that have been tested both experimentally and experientially, it is hard to beat the Siberian Pea shrub, also known as Caragana. Although it only grows six to eight feet tall in most settings, it is one of the hardiest species and will survive for 80+ years. Lilacs, Chokecherries, and Russian Olive (the latter are no longer allowed for planting in Montana) also can form more dense single rows but typically need a little more soil moisture.

Figure 3. A well-designed and maintained shelterbelt in central Montana’s 11" precipitation zone. Row spacing, fallow ground and snow capture help keep trees that need at least 16" annual precipitation to stay alive.

Figure 4. Well-spaced single-row crop windbreaks.

Figure 5. Typical snow collection on the leeward side of a windbreak.

Photos: Peter Kolb, MSU Extension

Although valid arguments are made that crop windbreaks take up valuable space which could be cropped, studies have shown that crop productivity usually makes up for the ground lost to the windbreak. Crop windbreaks can capture significant snow on the leeward side (Figure 5). This increased moisture allows for better crop productivity that, combined with slowing transpirational water loss, has been found to increase crop productivity by an average of 30% within the wind-protected zone. Figures 6 and 7 show the differences in wheat production in a case study conducted in 2012 north of Shelby (fields in Figure 4), where the producer considered removing windbreaks. Yields were indeed 30% higher within the first 40 feet of the windbreak, increasing the overall land area crop production by 5-10%, even when lands taken up by the windbreaks were included in the productivity/acre calculations. Extensive studies of the impacts of crop windbreaks across the Midwest have shown very similar results.

Figure 6. Wheat productivity within 40 feet leeward of
a windbreak.

Figure 7. Identical crop and timing 200 yards from Figure 6 without a windbreak protection.

Photos: Peter Kolb, MSU Extension

Assistance for establishing or renovating windbreaks can be found at your local MSU Extension office or Natural Resources Conservation Service (NRCS) office. MSU Extension can offer technical assistance and facilitate contact with the Montana Department of Natural Resources and Conservation (DNRC) ‘Conservation Nursery’ for tree and shrub seedling purchases that require a conservation plan. Seedling orders are best placed in the fall to ensure seedling availability with an April delivery date for planting. NRCS can also offer technical assistance and may have cost-share opportunities, as well as at-cost weed barrier fabric and planting equipment that can be borrowed free of charge.

Peter Kolb is the MSU Extension Forestry Specialist.