Agroforestry
Practices
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.
AGROFORESTRY PRACTICES
Windbreaks
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
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
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
Natural Regeneration
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.
Planting Seedlings
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 |
| Pine spacings |
| 6 |
8 |
907 |
| 8 |
8 |
681 |
| 6 |
10 |
726 |
| Hardwood spacings |
| 10 |
10 |
436 |
| 15 |
15 |
194 |
| 20 |
20 |
109 |
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 ENTERPRISES
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.
REFERENCES
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.
READING LIST
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.
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