7. Sowing forests from the air.
National Academy Press, Washington, D.C., ISBN 80-83796, Third Ed., 1986, 57 p. + annex
This report discusses reforestation in which the seed is broadcast from a plane or helicopter. It relies mainly on experiences in Australia, New Zealand, Canada, and the United States.
Sowing forest seed directly on the site to be forested is known to foresters as direct seeding, broadcast seeding, or broadcast sowing. The availability of chemicals for coating seeds to repel birds, rodents, and insects has made this a practical and more reliable method of reforestation.
In many parts of the world, deforestation has reached critical proportions. Africa, Asia, and Latin America have vast areas of once-forested land that is now denuded. Many have been left largely unplanted.
These enormous areas of virtually unproductive land are increasing.
Traditional revegetation methods should be applied more extensively, but the time also seems right for examining alternative methods.
Dropping seed from planes or helicopters is a well-known and well-established technique for sowing pastures as well as agricultural crops such as soybeans, wheat, and rice. Forests have also been established in this way. However, aerial seeding of forests is largely unappreciated, even by most foresters.
When conditions and species are right, and seed supplies sufficient, aerial seeding could be an important technique for reforesting large areas. It is easy to organize and seems well suited for reforesting sites that have rough terrain, debris, or difficult access. If it can be developed for sites and objectives in developing countries, aerial seeding could offer opportunities for vastly accelerating their reforestation programs.
Aerial reforestation is not a replacement for planting seedlings by traditional methods. It is best considered as a potential complement to conventional planting and to natural seeding, an additional tool for foresters to use when the needs, sites, and species are appropriate.
Sowing tree seed directly in the field is an old technique, but it was little used until the development of repellents to protect seed from insects, rodents, and birds.
It was learned that an additional coating of commercial insecticide would guard the seed against insects and rodents. These findings signalled the beginning of large-scale aerial seeding of forests in USA.
New Zealand demonstrates its success. Some of these forests have been established despite seemingly adverse conditions - for example, on steep slopes and on overburden from strip mines.
Aerial seeding is unproven in the tropics. The panel's purpose is not to recommend it over conventional reforestation techniques but to suggest trials of aerial seeding as a possible supplementary tool.
This book is not a textbook nor a practical guide to aerial seeding: details of the operations and techniques can be found in the selected readings. The purpose is to show administrators and foresters that this fast and often economical technique can be successful on appropriate sites, at least in temperate climates. The authors hope that the report will stimulate trials with, and research into, direct seeding (with or without the use of aircraft). In particular, trials are needed in the tropics where deforestation is most severe.
Aerial seeding presents many challenges for researchers, especially those in developing countries. While technology and techniques are developed and available, they are yet to be tested and adapted for use in those Third World areas now suffering devastating deforestation.
Because experience with aerial seeding of forests in the humid tropics is limited, little is known about predators and the best species to sow.
Aerial seeding could be an expensive failure unless small-scale trials show that direct seeding can be successful for the given species and sites.
Initially, these trials do not require use of aircraft. It is necessary only to broadcast a small amount of seed (pretreated, if necessary) on a small patch of the area being tested with conventional tree-planting methods.
The existing knowledge on seed coating and pelleting should be reviewed.
Successes and failures are reported in different situations.
Seeds can be targeted accurately (often within a meter or two). Thus direct seeding might prove feasible for filling in the widely scattered breaks in the forest left by slash-and burn farmers with useful species that best protect the vulnerabale soil.
1168 92 - 7/82
Review, tropics, subtropics, developing countries, land-use systems, land-tenure, shifting cultivation, sustainable agriculture, marginal lands, fallows, alley cropping, intercropping, trees, agropastoral systems, mixed farming
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