Tim Snell, Agroforestry Specialist
Kerr Center Publ. F2000
Agroforestry is the deliberate integration, in space or time, of woody perennials with herbaceous crops and/or animals on the same land management unit (Steppler and Nair, 1987, p. 265). This can be simplified to the practice of growing trees with agricultural crops and/or livestock on the same piece of land (Anderson, et al., 1991).
For agroforestry practices to be widely accepted and integrated into existing agricultural enterprises, farmers must be able to accomplish them safely, efficiently, and with tools already available on the farm. Agroforestry practices must be friendly to the farmer, budget, and land.
Many tree species are used in a variety of shapes, forms, and configurations and produce benefits as agroforestry components to adjacent crops or livestock. Trees provide many benefits including lumber and forest products; shade and wind protection for crops, livestock, and buildings; erosion control; water and nutrient cycling; and wildlife food and habitat.
Windbreaks are not a new idea. The planting of windbreaks has a long and successful history in this country. Between 1934 and 1943, as part of a conservation program conceived and vigorously promoted by Franklin D. Roosevelt, about 19,000 miles of windbreaks were planted on 33,000 farms and ranches for soil and water conservation.
Windbreaks provide benefits to downwind agricultural areas and dwellings and are present in some form on large numbers of farms and ranches today. A windbreak can be as simple as an overgrown fencerow or a few rows of trees left in place after a land clearing effort or forestry harvest. Many farmers and ranchers use natural boundaries of forest blocks and strips or patches of trees as windbreaks without planning or planting and still appreciate increased yields they provide to crops and livestock.
Many agricultural enterprises can profit from the addition of a strategically placed windbreak. Windbreaks are effective wherever wind or sun is reducing yields of crops or livestock. In winter, windbreaks assist livestock by reducing the stress of windchill. They also collect snowdrift which later melts and provides additional moisture for early spring pasture growth. Without windbreaks to provide shelter from blizzards, animals can lose weight or even die from the chilling and drying effects of wind. During summer, windbreaks provide shade to cool soil, air, and water for livestock and crops. Some windbreak trees, like persimmon, mulberry, and honey locust, provide forage or concentrated foods, such as fruits or seeds. Diverse species of trees will provide a variety of wood products, including firewood and lumber. Other trees used in windbreaks fix nitrogen, most notably black locust, which not only increases crop, pasture, or orchard growth but helps other trees in the windbreak to grow better.
Orchards and croplands benefit from the slower wind speed and decreased damage and from the effects of the windbreak on soil conditions. When wind speed is reduced, evaporation and transpiration are lessened. Soil loss from wind erosion is reduced by windbreaks, and wind-transported soil particles from other areas are intercepted and added to the soil under the windbreaks. The leaf fall from trees in windbreaks provides organic matter and nutrients to adjacent crop areas, contributing significantly to soil fertility, moisture retention, and tilth. Vegetation in windbreaks hosts insects, birds, snakes, and other animals that help control crop pests.
In addition to being advantageous for crops and livestock in the field, windbreaks save energy and increase comfort in human and animal housing. The energy required to moderate or maintain temperatures in buildings protected by windbreaks can be reduced by more than 20 percent when compared to unprotected structures (Wenger, 1984).
Using cover crops well ahead of a tree planting reduces weed competition, builds organic matter and nutrients, and improves soil moisture and soil air. Cover cropping helps the trees in windbreaks grow better and reduces maintenance during the establishment period.
Mulching heavily is an excellent way to establish agroforestry trees. The Kerr Center has developed a method of establishing trees for windbreaks which uses on-site forages and standard hay equipment (Snell, et al., 1994). This method can also be used to establish trees for silvipastures and alley cropping enterprises.
Like any farm component, windbreaks must generate a return on the investment of time, energy, materials, and land. The return on investment with a windbreak comes from multiple benefits including increased yield of crops and livestock; soil and water conservation; wildlife improvements; energy savings; and production of tree crops, firewood, and lumber.
Silvipasture is widely practiced in various forms. Silvipasture is the grazing of livestock and growing of trees on the same piece of land. Silvipastures can be developed by establishing trees in existing pastures or by establishing pastures within or under existing tree stands.
Silvipasture systems can be arranged in unlimited combinations of livestock and tree components, enabling farmers to use all types of areas not easily farmed by more structured or mechanical methods.
Alley cropping is the growing of trees in rows or other configurations while growing crops between the tree rows. High-value, short-duration crops can be grown in the alleys, while orchard or nut trees are growing. As the trees mature and require the entire growing space, the crops are not replanted in the alleys, and an orchard is established with little or no time or land out of production.
Establishing Agroforestry Trees
Currently, most of the trees that have been harvested were started by natural regeneration with no help or planning from mankind. In natural regeneration, the choice of species is left to nature, as only the trees suitable for each site will survive and thrive. Sun-loving, aggressive species favor previously maintained areas. After the forest cover becomes established, shade-loving species will naturally succeed the initial forest. The diversity of trees in natural regeneration areas is a product of the surrounding trees and the growing site. The shape, size, and location of forest cover is determined by the continued maintenance of nonforested areas.
Using natural regeneration to establish trees is cost-effective and conserves resources. This method saves the costs of site preparation, planting, and weed control. A savings in labor and equipment is achieved by not having to maintain the areas on a yearly basis by brushhogging or other means. Decreased maintenance increases safety as back fencerows, corners, rocky spots, and steep areas are the most dangerous to maintain with a tractor and brushhog.
Now that both the human population and our ability to harvest, process, and use trees are increasing geometrically, mankind is having a tremendous impact on the amount of naturally regenerated timber. There are methods of harvesting and timber management that enhance natural regeneration, but it does not always produce trees that are suitable for society’s needs and wants. Harsh or unusual weather conditions can delay or prevent successful natural regeneration for many years. With the present emphasis on the environment and the role trees play in a healthy environment, it is increasingly important to reforest harvested areas as soon as possible.
Tree planting is used more frequently for reforestation than in the past. Planned tree plantings are economically viable and environmentally sound. There have been many examples of successful plantings, such as the Southern Pine Plantation system and the shelterbelt plantings of the 1930s and 1940s.
Planting the right species on appropriate sites provides trees that are suitable for human wants and needs and can also shorten the time it takes to get the trees up and growing. Proper planning and aftercare can overcome many harsh or unusual weather conditions.
Proper selection of tree species and their placement are key factors. This differs from natural regeneration, which relies on natural diversity and survival of the fittest to determine what trees will grow where. Choosing the wrong trees for a site will doom the planting in spite of best intentions and aftercare.
Site and tree selection are the most important decisions to make and should be the first decisions made. It is possible to determine what trees are wanted or needed and then to locate a suitable site for planting. Usually, because of limited land or other restraints, the site is selected first, then the trees that are needed or wanted are chosen from those species that will thrive on the site.
After an area has been selected, the first thing to do is a site inspection. A lot of information can be obtained from maps and aerial photographs, but a physical site inspection can produce vital information unavailable from any other source.
Look at the trees growing on the site. If there are no trees, search for evidence of past tree growth. Explore around the edges of the site and investigate areas with similar soil types and growing conditions. From all the tree species present, determine which ones are doing the best. If any of these will satisfy the wants and needs of the landowner or land manager, they should be included as a substantial component of the planting.
The next step is using maps, aerial photos, soil surveys, and lists of trees showing their preferred habitats and suitability on different soil types. All of these planning aids and other information can be found in the County Soil Survey published by the U.S. Department of Agriculture (USDA) and available at most Natural Resource Conservation Service offices. This book is a valuable planning tool for tree plantings and other forestry and agriculturally related pursuits. Included in the survey are species recommendations for tree plantings which take into account a wide range of factors related to the success of the planting. Tree information and identification books list soil types, conditions, and habitat types that each species thrives in.
Before the final decision is made as to which species to plant, availability of suitable planting stock must be investigated. State-operated nurseries offer good-quality seedlings at modest prices. Private nurseries sometimes sell species unavailable from state nurseries. Competition for available planting stock can be severe close to or during planting season. Order early to beat the rush, and order extra to be able to pick through the planting stock. Avoid using poor quality seedlings.
After selecting the species, the number per acre and the spatial configuration must be determined. When planting solid blocks of trees, the distance between trees in the row and the distance between rows will determine the number of trees per acre (Table 1).
|Table 1. Spatial configuration
for pines and hardwoods
|Ft between trees||Ft between rows||Seedlings/acre|
When planting single rows of trees, the total length of the row divided by the distance between the trees in the row equals the number of trees required.
Example: 6000 … 6 = 1000; Length of Row … Ft. Between Trees = No. of Trees
Trees can be planted when dormant at temperatures above freezing and when sufficient soil moisture is available. Plan ahead for a cool, moist storage area in case conditions are not right for planting when seedlings arrive. Seedlings must be kept cool and moist until planted. If planting will be delayed, heel-in the seedlings, preferably in cool, moist garden soil. Proper care during storage and in the field will greatly increase survival rate.
Seedlings must be planted with no air at the roots and just slightly deeper than at the nursery. Whether using dibble bars, hoedads, mattocks, shovels, rods, or planting machines, do as much planning, training of planters, organizing of materials, and machine maintenance ahead of time as possible. Check planting crews constantly and adjust methods as needed.
The list of big trees in Table 2 gives you an idea of the final size trees may reach. Your trees probably will not get any larger than this. This information is especially useful in alley cropping and silvipastural systems when you are trying to keep grass from being shaded out from between the trees.
|Table 2. A list of Oklahoma champion
trees suitable for planting in the southeastern part of the state
|Species||Height (ft)||Crown spread (ft)|
|Blackgum, Nyssa sylvatica||108||89|
|Black Locust, Robinia pseudoacacia||37||31|
|Common Persimmon, Diospyros virginiana||60||41|
|Eastern Cottonwood, Populus deltoides||78||99|
|Green Ash, Fraxinus pennsylvanica||82||62|
|Honey Locust, Gleditsia triacanthos||84||32|
|Loblolly Pine, Pinus taeda||90||55|
|Northern Catalpa, Catalpa speciosa||83||66|
|Osage-Orange, Maclura pomifera||36||59|
|Pecan, Carya illinoensis||93||72|
|Pin Oak, Quercus palustris||110||100|
|Red Mulberry, Morus rubra||61||76|
|Shortleaf Pine, Pinus echinata||120||46|
|Southern Red Oak, Quercus falcata||114||119|
|Sweetgum, Liquidambar styraciflua||116||57|
|White Oak, Quercus alba||77||68|
|Willow Oak, Quercus phellos||79||86|
|Source: Little, E. L., Jr. 1991. Forest Trees of Oklahoma.
13th ed. Oklahoma State Dept. Of Agric., Forestry Div.,
Oklahoma City, OK
Tree plantings will continue to be a vital tool for the future of forestry. Project planning and correct decisions about tree species, coupled with a good understanding of the landowner or land manager’s desires, will help ensure that the effort and expense of planting will pay off as trees grow and mature.
Planting of Seed
The planting of tree seeds is another method of establishing agroforestry trees. Seeding is more uncertain and takes longer than planting seedlings in most cases. The advantages are low costs and the ability to collect locally adapted seed from superior phenotypes. Considerable care, especially weed and pest control, is often required to successfully grow trees from seed.
MANAGEMENT OF AGROFORESTRY ENTERPRISE
Agroforestry enterprises require differing degrees of management depending on the number of components and variations in the time and space constraints of each component. Some well-established agroforestry systems, such as pecans and cattle, are managed by traditions handed down through generations. Others are being developed right now and serve as outdoor agricultural laboratories where management plans are based on observation, continual change, and improvement based on past success.
Agroforestry is successful when more production is obtained by the trees and crops or livestock than could be obtained on the same piece of land with only a single cropping system. As in all of agriculture, costs, inputs, and adverse environmental effects must be minimized for the enterprise to remain healthy and productive.
Anderson, S., T. G. Bidwell, and L. Romann. 1991. Introduction to Agroforestry Alternatives. Ext. Facts 5033. Oklahoma State Univ. Ext. Serv., Stillwater, OK.
Snell, T. K., Horne, J. E., Lathrop, W. J., and A. E. Kalevitch. 1994. Large Scale Agroforestry Tree Establishment. p. 249Ü252. In Proceedings of the Society of American Foresters Annual Convention, Indianapolis, IN. 7Ü10 Nov. 1993. Society of American Foresters, Bethesda, MD.
Steppler, H. A. and P. K. R. Nair. 1987. Agroforestry: A Decade of Development. ICRAF, Nairobi, Kenya.
Wenger, K. F. 1984. Forestry Handbook. 2nd. ed. John Wiley and Sons, New York, NY.
Moore, D. M. 1986. Trees of Arkansas. 4th ed. Arkansas Forestry Commission, Little Rock, AR.
Murray, T. 1991. How to Plant Bare Root Conservation Seedlings. Oklahoma Dept. of Agric. Forestry Serv. Oklahoma City, OK.
Atkins, K. 1991. Recommendations for Windbreak Plantings in Oklahoma. Oklahoma Dept. of Agric. Forestry Serv., Oklahoma City, OK.
Mollison, B. 1990. Permaculture: A Practical Guide for a Sustainable Future. Island Press, Covelo, CA.