Shelterbelts: Has Their Time Come ?

by 5m Editor
7 November 2004, at 12:00am

By G.T. Tabler, Poultry Science Department at the University of Arkansas's Avian Advice - The increasing urban expansion into rural areas creates numerous challenges for livestock producers to various types of farming operations. A strong livestock industry is essential to the nation’s economic stability, the viability of many small rural communities, and the sustainability of a healthful, plentiful and high quality food supply for the American public.

Shelterbelts: Has Their Time Come for Arkansas Poultry Producers? - By G.T. Tabler, Poultry Science Department at the University of Arkansas's Avian Advice - The increasing urban expansion into rural areas creates numerous challenges for livestock producers to various types of farming operations. A strong livestock industry is essential to the nation’s economic stability, the viability of many small rural communities, and the sustainability of a healthful, plentiful and high quality food supply for the American public.


Farmers and ranchers view odors and dust associated with livestock as part of production agriculture and have come to accept them as part of their way of life. However, as urban dwellers are less likely to accept dust or odors, differences in lifestyles between farmers and city folks are becoming increasingly apparent. Although there will probably always be some odor and dust issues associated with animal production units, there are some simple, economical methods of reducing the frequency of complaints.

For poultry producers, shelterbelts offer an opportunity for poultry growers to be proactive in demonstrating good neighbor relations and environmental stewardship. Shelterbelts are typically vegetation (most often trees and shrubs) planted in purposeful rows to alter wind flow in order to achieve certain objectives. Planting trees and shrubs as screens around poultry houses will help remove them from public view (perhaps also the public’s mind) and buffer odor, dust and noise.

Livestock Production

In the United States about 130 times more animal waste is produced annually than human waste. Livestock in the U.S. produce more than 1.4 billion tons of manure annually (U.S. Senate Committee, 1997). Livestock production in the U.S. is characterized by fewer yet much larger production facilities. USDA data indicate that nationwide about 85% of estimated 450,000 agricultural operations with confined animals have fewer than 250 animal units (GAO, 1995).

Therefore, only about 15% of farms house the vast majority of the animal units nationwide. USDA estimates that only about 6,600 animal feeding operations nationwide have more than 1,000 animal units (GAO, 1995). From 1978-1992, the average number of animal units per facility increased by 56, 93, 134, 176, 148 and 129% for cattle, hogs, layers, broiler and turkeys, respectively, while during the same period the number of facilities dropped by over 40% in the cattle industry, and over 50% in the dairy, hogs and poultry industries (USDA and EPA, 1999).

Figure 1 demonstrates the increase in broiler production and decrease in broiler farm numbers from 1975 to 1995. Increased size of production facilities and greater numbers of livestock at each facility has meant larger amounts of animal waste, concentrated into relatively smaller geographic areas. This concentration of animals has increased the intensity, duration, and timing of odor events. The control of livestock odors has become of paramount concern for the public and livestock producers.

Figure 1: US Broiler production (lbs) and number of farms 1975 - 1995

Source: United States Senate Committee on Agriculture, Nutrition and Forestry, 1997

Understanding Odor Events

A recent survey of Iowa farmers found that 46% of rural residents were within a half mile or less of a livestock facility. In the same survey 71% of residents were within one mile of a livestock facility (Lasley and Larson, 1998). This finding is consistent with the average separation distances nationwide (Tyndall and Colletti, 2000). Odor compounds may be transmitted as gases, aerosols (a suspension of relatively small solid or liquid particles in gas) or dust (relatively large particles in gas or air). Efforts to control odors from animal production units fall into three basic strategies (Tyndall and Colletti, 2000):

  1. Prevent odors from forming
  2. Capture or destroy odorous compounds and
  3. Collection, dispersion or dilution of odor compound.

In most cases the third strategy is the easiest and most economical procedure to implement in animal production units. In operations without protection wind or breezes often transmit odors gases, aerosols and dust to neighbors. Shelterbelts hinder this transmission, by trapping odors, redirecting air or creating turbulence so that odor compounds are diluted.

Odor Control using Shelterbelts

The source of animal odors is near the ground and tends to travel along the ground (Takle, 1983), shelterbelts can intercept and disrupt the transmission of these odors (Heisler and DeWalle, 1988; Thernelius, 1997). Shelterbelts also reduce the release of dust and aerosols by reducing wind speed near production facilities. Wind tunnel modeling of a threerow shelterbelt quantified reductions of 35% to 56% in the downwind transport of dust. However, shelterbelt density determines the degree to which dust and aerosols are reduced.

Density is a simple ratio of the porous area (the areas wind can pass through) to the total area of the shelterbelt. A density of approximately 40-60% is the most beneficial (Brandle and Finch, 1991). The trees or shrubs chosen for the shelterbelt and the spacing of those plants will determine the overall density. Remember that deciduous species tend to be more open closer to the ground and conifers have branch cover close to the ground (Griffith, 2001).

Shelterbelts physically also intercept dust and other aerosols. A forest cleans the air of micro-particles twenty-fold better than barren land. Leaves with complex shapes and large circumference to area ratios collect particles most efficiently. Shelterbelts attract and bind the chemical constituents of odor. Volatile Organic Compounds (VOCs) have an affinity to the cuticle of plant leaves. Microorganisms on plant surfaces can metabolize and breakdown VOCs.

Finally, shelterbelts provide a visual and aesthetic screen. A well-landscaped livestock operation is much more acceptable to the public than one that is not. Shelterbelts should be designed for the specific location, according to the expected and experienced odors, so that the tree and shrub species chosen can provide year round interception of odors and aerosols (Griffith, 2001).

Why Shelterbelts Now

Although shelterbelts have been used for many years in the Midwest to modify wind flow; control wind erosion, increase crop yields, protect farm buildings, and protect livestock, few in poultry producing areas considered their use.

However, urban encroachment is forcing changes in how poultry growers manage their operations and tunnel ventilated houses have made the use of shelterbelts feasible. Few recommended planting trees around poultry facilities for fear of blocking air flow through conventionally-ventilated houses, but today, with the poultry industry shifting to tunnelventilated, solid sidewall poultry houses, restricting natural air flow is much less of a problem.

Trees have a pleasing image across a large cross section of the American population. Planting trees around poultry houses may help foster a positive image of your farming operation. In addition, as the trees mature, less of your agricultural operation will attract attention, your farm takes on a more attractively landscaped appearance, and property values increase for both you and your neighbors (Malone and Abbott-Donnelly, 2001).

Plants used in Shelterbelts

Dense evergreen trees are perhaps the best choice for the tunnel fan end for maximum filtering during summer and screening year round. For greatest emissions scrubbing, shelterbelts should be as close to the tunnel exhaust as possible. As a general rule, to not interfere with fan efficiency, no trees should be planted closer than a distance of five times the diameter of the fans (Malone and Abbott- Donnelly, 2001). Check with your integrator before constructing a shelterbelt. Take into account the width of the shelterbelt at maturity and how this may affect roads, loadout areas, or chick delivery areas.

There are a variety of trees and shrubs suitable for Arkansas conditions that would work well to screen poultry houses. White pine, properly spaced, creates a dense shelterbelt, grows rapidly and is reasonably priced. Virginia pine and loblolly pine also do well. Various cedars also form a dense mat; however, some consider certain varieties a nuisance and the berries may attract wild birds. A variety of hollies and other ornamental shrubs such as Red Tip Photinia form highly effective screens and have a beautifying effect on the surrounding landscape. The plants you choose will depend on the site, soil conditions, available space, number of plants required, growth rate of plants, personal preference for landscaping effects and cost of the plants. For more information on trees and plants that do well in your area, contact your local county Extension office, local Conservation District, Arkansas Forestry Commission or a professional landscape nursery/garden center.

Air quality issues surrounding poultry production facilities are no longer a matter of “if”, but “when.” Arkansas poultry producers should take proactive steps to plan for management changes these issues will bring. The planting of trees in strategic locations around poultry houses is one method to help address these issues before and as they arise. In addition, research has shown that shelterbelts can reduce heating costs 10-40% and reduce cooling costs as much as 20%.

Strategically placed trees can also reduce wind speeds by 50%, adding protection from spring and fall storms. The leaves of trees physically trap dust particles that may be laden with nitrogen, and root systems will absorb up to 80% of the nutrients that might escape the proximity of the poultry operation (Stephens, 2003). Cost-share assistance for planting a shelterbelt is available in some states; unfortunately, Arkansas is not one of these states at the present time.

Barriers to Shelterbelt Adoption

Although shelterbelts around the perimeter of poultry houses offer many advantages, there are some barriers to adoption and some negative aspects to consider. For example, Malone and Abbott-Donnelly (2001) indicate:

  • A limited amount of land will be taken out of production to support the shelterbelt

  • There will be cost associated with purchasing the trees, labor for planting and maintenance

  • You will encounter a restricted view of your houses access will be limited to designated roadways trees will create a potential habitat for wild birds.


Air quality issues will become an increasing concern to production agriculture with continued urban encroachment into previously rural, agricultural areas. Shelterbelts offer one method by which poultry producers can take proactive steps to address the issue; demonstrating good public relations efforts and environmental stewardship by buffering odor, dust and noise emissions from their facilities while improving farm aesthetics and property values.

Dense shelterbelts may detract attention from farming operations and help reduce air emission concerns surrounding poultry facilities by capturing dust particles and ameliorating odors. Consult your integrator concerning placement before constructing a shelterbelt. Select trees or shrubs suitable for your area. Your local Extension office, NRCS office, Arkansas Forestry Commission or local landscape nursery can be of valuable assistance on species information. If planted during warmer weather, be sure to provide plenty of water to assure successful establishment. A well-landscaped livestock operation is more pleasing to the public than one that is not.

A shelterbelt used as a pollution control device is visible proof that producers are making an effort to control what leaves their operation. This could prove valuable in the court of public opinion and perhaps reduce tension levels between farming and non-farming segments of the population.


Brandle, J. R., and S. Finch. 1991. How windbreaks work. University of Nebraska Cooperative Extension Publication EC91-1763-B.

General Accounting Office (GAO). 1995. Animal Agriculture: Information on Waste Management and Water Quality Issues.

Griffith, C. 2001. Improvement of air and water quality around livestock confinement areas through the use of shelterbelts. South Dakota Association of Conservation Districts.

Hammond, E. G., C. Fedler, and R. J. Smith. 1981. Analysis of particle bourne swine house odors. Agriculture and Environment. 6:395-401.

Heisler, G. M., and D. R. Dewalle. 1988. Effects of windbreak structure on wind flow. Elsevier Science Publishers B.V., Amsterdam. Agriculture, Ecosystems and Environment, 22/23:41-69.

Laskley, P. and K. Larson. 1998. Iowa farm and rural life poll – 1998 Summary Report. Iowa State University Extension, Pm- 1764, July, 1998

Malone, G. W., and Abbott-Donnelly, D. 2001. The benefits of planting trees around poultry houses. University of Delaware College of Agriculture and Natural Resources. Bulletin #159. 4 pages.

Stephens, M. F. 2003. Benefits of trees on poultry farms. The Litter Letter. Fall 2003. LSU Ag Center Research and Extension, Cooperative Extension Service. Calhoun, La.

Takle, E. S. 1983. Climatology of superadiabatic conditions for a rural area. J. Climate and Applied Meteorology. 22:1129- 1132.

Thernelius, S. M. 1997. Wind tunnel testing of odor transportation from swine production facilities. M. S. Thesis. Iowa State University, Ames.

Tyndall, J., and J. Colletti. No Date . Odor Mitigation. Available at: 6 pages.

Tyndall, J., and J. Colletti. 2000. Air quality and shelterbelts: Odor mitigation and livestock production a literature review.

Source: Avian Advice - Winter 2004 - Volume 6, Number 2