March 1998 - Volume 59, Issue 3
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In this issue
Warm Cows & Cool Breezes
Too hot? Too cold? Natural windbreaks provide four-season relief.
Trees are a natural choice for moderating the extremes of our environment. They shade our homes and playgrounds, block cold winds, filter dust and pollutants from the air and make our cities nicer places to live.Trees have been called a low-tech solution to a high-tech problem. The high-tech problem is how to reduce our nation's growing demand for energy. Americans use more and pay less for energy than any other country in the world. The simple act of planting a tree can help reduce our energy demand.
Trees can save energy in several ways: through shade, reducing the need for air conditioning; as a windbreak, lowering heating costs, and by serving as a renewable source of fuel. Foresters can document energy savings of 10 to 40 percent in homes with strategically placed trees. Whether you live in the city or on a farm, planting a few well-placed trees can reduce your energy bill.
Keeping the Cows Warm
Windbreaks usually come to mind when someone mentions planting trees for energy conservation. Landowners have planted windbreaks for years to protect homes and farmsteads from winter winds in the Great Plains and Upper Midwest. Windbreaks also protect livestock, provide wildlife habitat, shelter crop fields and screen feedlots and traffic.
A 35' windbreak will slow 35 mph open wind speeds to 10 mph at 100'
and 15 mph at 200'. Buildings should be no closer than 100' to windbreak.
Trees make effective windbreaks. Their leaves and branches absorb some of the wind's energy and deflect the wind up and over a protected area. This reduces the wind velocity or wind chill effect on the downwind-or leeward-side of the windbreak. The trees' height, density and orientation determine the effectiveness of a windbreak.
Height
Windbreak height is the most important factor determining the downwind area protected by the windbreak. On the windward side of a windbreak, wind speeds are reduced upwind for a distance of two to three times the height of the windbreak. On the leeward side (the side away from the wind), the wind speed is reduced as far as 20 times the height. For example, if the tallest trees in a windbreak are 50 feet, wind speeds are reduced up to 150 feet on the windward side and 1000 feet on the leeward side.
Density
Windbreak density is the solid portion of the barrier. The number of rows, the distance between trees and species composition affect windbreak density. By adjusting windbreak density, different wind flow patterns and areas of protection are established. Windbreak densities of 25 to 35 percent are most effective for an even distribution of snow across a crop field. A density of 40 to 60 percent provides the greatest area of protection and excellent soil erosion control. High densities of 60 to 80 percent are best for protecting farmsteads and livestock areas. Surprisingly, windbreaks offer greater wind speed reductions than a solid fence.
Orientation
Windbreaks are most effective when oriented at right angles to the prevailing winds. The purpose of the windbreak will determine how it is designed. Farmsteads and feedlots typically need protection from cold winds and snow, which usually blow from the northwest in Missouri. A windbreak to protect livestock would be planted north and west of the feedlot. However, a crop field needing protection from hot summer winds would require the windbreak on the south and west, the direction of prevailing winds in summer.
Windbreaks may increase crop yields up to 20 percent. Their shelter slows hot summer winds, reducing burning and wilting of plants. Soil moisture is conserved, so the need to irrigate is decreased. With the slower winds, wind erosion is reduced, keeping the soil on your land.
A well-designed windbreak also can result in direct energy savings of 10 to 40 percent by reducing the loss of heat from homes and barns. More savings can result from livestock and crop field protection.
In the case of beef cattle, their heavy winter coat will provide protection against temperatures as low as 18 degrees. At temperatures below 18 degrees, an animal becomes stressed and requires additional feed to maintain its body temperature. With an air temperature of 0 degrees and a wind of 25 miles per hour, the wind chill is -44 degrees. The cow now needs 40 percent more feed to maintain itself, is less efficient at converting this feed into energy and is more susceptible to health problems. Although a windbreak can't raise the air temperature, it can cut the wind chill effect, resulting in warmer cows.
Windbreak BasicsPlanning Your Windbreaks
| Purpose | Minimum # of Rows | Fence | Tree Type & Configuration |
|---|---|---|---|
| Farmstead | 2 | optional |  |
| Feedlot | 2 | necessary | |
| High Traffic screen | 6 | optional |    |
| Medium-low Traffic Screen | 3 | optional | |
| Visual Screen | 2 | optional | |
| Alternative version of Visual Screen | 3 | optional |   |
| Wildlife | 5 | optional | |
Key:
best
species
option
evergreen
deciduous
- Do not place windbreaks under utility lines or use species whose mature height will interfere with the lines.
- When placing an opening through a windbreak, make openings at an angle to reduce loss of wind protection.
- Use fences to keep livestock from windbreaks.
- The most effective area of protection is two to five times the height of the tallest trees. Buildings and feedlots should be within this zone.
- Buildings should be no closer than 100 feet to a windbreak.
Choosing Your Species
| Row 1 Shrubs |
Row 2 Medium Ever- green |
Row 3 Medium Deciduous |
Row 4 Tall Ever- green |
Row 5 Tall Deciduous |
|---|---|---|---|---|
| American hazel | eastern redcedar | river birch | white pine | bald cypress |
| gray dogwood | jack pine | Osage-orange | shortleaf pine | northern red oak |
| fragrant sumac | black locust | red pine | white oak | |
| shining sumac | persimmon | tuliptree | ||
| arrowwood viburnum | green ash | hackberry |
For windbreaks with fewer rows:
- Two-row windbreak: use species from rows 2-3 or 1-3 or 1-4
- Three-row windbreak: use species from rows 1-2-3 or 2-3-4
- Four-row windbreak: use species from rows 1-2-3-4 or 2-3-4-5 or 1-2-3-5
Planting Your Windbreak
Stagger tree spacing so the trees in one row will be planted opposite the opening in the other row
| Use these spacings within the rows: | Shrubs | Evergreen Trees | Deciduous Trees |
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| Use these spacings between the rows: | Shrubs | Shrubs & Trees | Trees |
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Strategic Shade
Although city dwellers usually don't have the space to plant large windbreaks, there are still opportunities to reduce their energy consumption. The placement of trees around a home is critical to take advantage of summer shade while not blocking winter solar heat. When planning where to plant trees, remember that the sun's position in the sky changes hourly and daily. Plan for shadows that cover targeted areas during the hottest hours of the hottest weeks of summer.
Deciduous trees that provide maximum summer shade and minimum winter shade are ideal for reducing energy consumption, but they must be located properly for best year-round results.
About This Article
Authors
Bruce Palmer is a forestry education coordinator for
the Conservation Department, where he has worked for 20 years. He lives
in Jefferson City with his wife and two daughters. Bruce lists skiing,
hiking and camping as his favorite activities. He was drawn to forestry
by the prospect of being able to work outdoors, but his career now anchors
him to a desk.