(Editor's Note: This article was originally published on August 30, 2007)
While many references on trees are useful guides to trees individually, there is less information on configurations of trees. But, used collectively, trees can become ecological entities where the whole is definitely more than the sum of its individual constituents. For the home gardener planting 30 or 50 trees can also be an intimidating job, compared to planting a single shrub or tree. Therefore, careful planning is essential when you want to plant small or large groups of trees on your property.
Functions of Shelterbelts
Technically, a hedge is an arrangement of closely spaced trees or shrubs defining an edge or boundary, whereas a windbreak is a spaced row of shrubs or trees designed to protect a space by baffling and thereby slowing the speed and direction of wind. A shelterbelt is a more generic term for windbreak. . The first thing to do when planning a windbreak or shelterbelt is to decide what purposes it shall serve. Shade, wind protection, fruit and nut production, protection from drifting snow, containment of animals, shelter for wild life, shielding living spaces from obnoxious noise and even odors, are all, not mutually exclusive possibilities.
In Marlboro, Country, South Carolina, an entire community of 55 landowners cooperated to build pine windbreaks to protect more than 3500 acres from being sandblasted by windblown sand from soil erosion. In Puerto Rico windscreens were built to protect fruit crops where the flight of bumblebees and their pollination activities were impeded by winds. In Washington State, windscreens were planted to prevent snow from drifting onto highways, thereby preventing traffic obstructions in winter and saving dollars in road maintenance for snow removal. In the plain states, windbreaks are used to “keep cows warm” by modifying wind chill temperatures where cattle are being over wintered on wind-swept fields. 
Dave’s Garden members bruntongardens and resin discuss the use of shelterbelts on the Isle of Lewis, an island off the west coast of Scotland in this thread in the European Gardening forum.  In the 1830s, local advocates of fencing laws here in the Alabama Blackbelt invited northern nurseries to bring osage orange trees (Maclura pomifera) to the South where it is not indigenous. The trees were sold as whips by the thousands to Alabama planters to be used as ‘living fences’ to contain animals within the new boundaries of frontier plantations. Those same “hedge apples” are still a picturesque feature of the canebrake landscape (see thumbnail photo), many embedded with the original hogwire fencing and hand-made square nails (Personal observation).
In England, hedgerows have been used for hundreds of years to separate fields and fields from roadways. As many of the hedgerows fell into disrepair, wildlife habitats associated with them became threatened. Today, conservation groups are teaching individuals to repair and maintain historic hedgerows throughout England and also in Scotland. Possibly one of the most famous proponents of hedgerow repair and maintenance is Prince Charles, who maintains his own hedgerows on his property at Highgrove in Glouchestershire. 
Characteristic styles of hedgerow construction have developed for different areas of England. Sometimes maintenance of the traditional style is dictated by local ordinances. Usually, all hedgerows require the laying of hedges, where the shrubs are cut to one side and laid in a nearly horizontal position, all in the same direction along the fence or property line. The shrubs have to be just upright enough to allow the sap to rise and nourish the plants. The horizontal position allows the shrubs to form a thick and impenetrable thicket, which keeps farm animals from straying onto roadways. In some areas property lines were to be defined by dug ditches. The owner was to place the fill from the ditch to his own property side. Then the hedgerow was planted and layed along the raised earthen berm.  I have seen these raised berms in this country along old farm field roads in South Carolina, and in North Alabama (Franklin County).
Planning the Shelterbelt & Selecting Trees to Plant
Detailed planning is essential to the successful windbreak or shelterbelt. Selecting which trees to plant depends on what you want your shelterbelt to do. Before purchasing trees, it’s a good idea to check with your local Extension Office, State Forestry Department, or State University for recommendations. In most cases you will want to use native plant species, either exclusively, or for the main body of the plantation. Avoid planting invasive species, short-lived, or disease prone plants.
You will need to find out and record:
(1) The direction of prevailing winds in all seasons. For a windbreak, trees should be planted perpendicular to prevailing winds.
(2) The mature height of each tree to be planted. Record this next to each tree in your list.
(3) Check the shadow pattern of intended shade trees by hoisting a temporary pole where you intend to plant the tree. Record seasonal changes in the shadow cast by the pole.
You can plot all of this information on graph paper, or use landscaping software. But a rough schematic drawing of essential information should suffice.
The suggested within-row spacing of trees and shrubs is 4 to 6 feet; 10 to 16 feet for evergreen trees, and 12 to 20 feet for deciduous trees. For between row spacing, distances of 10 to 12 feet between shrubs, 15 to 20 feet between shrubs and trees, and 15 to 20 feet between trees are recommended. Windbreaks should be at least 100 feet from the nearest building . Dave’s Garden member, Equilibrium has recommended trees for me that will attract wildlife in Zone 8a in this thread in the Indigenous Plants forum. Thomas G. Barnes discusses woody plants that can be used within urban environments to attract wildlife for the State of Kentucky. 
Planting the Shelterbelt
After selecting trees and shrubs and deciding how much space should be left between them, the next consideration is actually planting them. Whether holes are mechanically or hand dug, the most important consideration is to make sure that the tree is planted no deeper than it grew in the nursery. Trees planted too deeply are not likely to thrive. Another consideration is the use of a mycorrhizae fungi root dip  to enhance the health and drought resistance of newly planted trees. Plan to mulch the trees with pine straw or weed barrier to conserve moisture and control weeds. Finally, after careful planning and consideration, there may be still questions. In this thread in the Beinner Landscaping forum, bettabug is concerned that the trees she intends to plant may not be properly spaced, because, “ … everything grows bigger in Texas.”
 http://en.wikipedia.org/wiki/Hedgerow. Definition of Hedge, Hedgerow.
 http://en.wikipedia.org/wiki/Windbreak. Definition of Windbreak, Shelterbelt.
 http://www.unl.edu/nac/insideagroforestry/2003spring.pdf. USDA. National Agroforestry Center. Inside Agroforestry. Spring 2003. Windbreaks.
 http://home-and-garden.webshots.com/album/560011272OJmhIc?vhost=home-and-garden. My Garden on the Isle of Lewis. 24 July 07. Two Gardeners.
 http://news.bbc.co.uk/1/hi/england/2691141.stm. Hedgelaying at Highgrove.
 http://en.wikipedia.org/wiki/Hedge_laying. Hedgelaying. Regional Styles.
 http://www.mdc.mo.gov/conmag/1998/03/50.htm. Missouri Conservationist online. Bruce Palmer. Warm Cows & Cool Breezes. (Planting distances for shelterbelts and windbreaks).
 http://www.mdc.mo.gov/conmag/1998/03/50.htm. Thomas G. Barnes. Trees, Shrubs, and Vines That Attract Wildlife. (University of Kentucky, Extention)
 http://agebb.missouri.edu/commag/shelterbelt/FAQ.htm. Shelterbelt Design. University of Missouri, Extention.