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
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
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
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
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.
6 = 1000; Length of Row
Ft. Between Trees = No.
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
||Crown spread (ft)
|Blackgum, Nyssa sylvatica
|Black Locust, Robinia pseudoacacia
|Common Persimmon, Diospyros virginiana
|Eastern Cottonwood, Populus deltoides
|Green Ash, Fraxinus pennsylvanica
|Honey Locust, Gleditsia triacanthos
|Loblolly Pine, Pinus taeda
|Northern Catalpa, Catalpa speciosa
|Osage-Orange, Maclura pomifera
|Pecan, Carya illinoensis
|Pin Oak, Quercus palustris
|Red Mulberry, Morus rubra
|Shortleaf Pine, Pinus echinata
|Southern Red Oak, Quercus falcata
|Sweetgum, Liquidambar styraciflua
|White Oak, Quercus alba
|Willow Oak, Quercus phellos
|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.
Anderson, S., T. G. Bidwell, and L. Romann. 1991. Introduction to Agroforestry
Alternatives. Ext. Facts 5033. Oklahoma State Univ. Ext. Serv., Stillwater,
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.
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