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.
The panel recommends that reforestation efforts include an evaluation of the potential of aerial seeding. Researchers are encouraged to consider the more desirable timber and pioneer species growing naturally in their area, along with suitable species such as those listed in Table 2. 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. However, to evaluate fully the promise of aerial seeding in a given area, researchers must consider:
· The characteristics of species, especially the ability of
its seed to germinate without being covered;
· The choice of site and site preparation;
· Effect of season and weather on best time for sowing;
· Seed acquisition;
· Seed handling (storage, transport, care in the field);
. Seed preparation (stratification, coating with animal repellents, inoculation, testing the
coatings for toxicity to seeds or seedlings); and
· Major predators.
Existing plantations and natural stands can sometimes demonstrate how successful direct seeding is likely to be. They indicate the best season to sow the seeds and can generally foretell the seed predation and the success of natural germination (care must be taken that the natural germination being observed is occurring in conditions that approximate those on sites to be sown). The silvics of the species in question should be studied to determine its suitability for direct seeding.
Direct-seeding trials should first be implemented at sites favorable for seeding, and then, with experience, should move to the more difficult sites.
Along with all direct-seeding trials should be some seedling-planting trials. The relative costs and successes of the two techniques can be better judged when they are done in tandem.
Before aerial seeding, sites should be chosen and inspected, if possible, at least 8 months in advance. Factors to be considered include:
. Extent of grazing by livestock and wildlife;
· Infestations of ants, rodents, and seed-eating birds;
· Areas where kees are adequately reproducing naturally;
· Conditions of seedbed and need for burning the site; and
· Advantageous ridges from which aircraft can be guided.
With this information plans can be made for site preparation, seed procurement, and any seed coatings.
Researchers wishing to improve the technology and techniques of aerial seeding might pursue the following challenging research projects:
. Aerial reforestation of regions covered with Imperata and
other vigorous tropical grass species;
· Development of seed coatings for use in dry sites that absorb and hold water and yet do not disintegrate rapidly;
· Improvement of seeding equipment to provide greater control over seedling density and spacing;
. Development of less hazardous chemicals for protecting seeds from rodents, insects, and birds (some examples worth considering are methiocarb -registered in the United States as a bird repellent for use on corn- tannins, lithium chloride, extract of red squill (Urginea maritima), copper sulfate, and cyclophosphamide. Information supplied by Glenn A. Hood, U.S. Fish and Wildlife Service, Building 16, Denver Federal Center, Denver, Colorado 80225, USA. ) and
. Development of seed coatings containing spores of mycorrhizal fungi.
The existing knowledge on seed coating and pelleting should be reviewed. Successes and failures are reported in different situations.
Seed can be targeted accurately (often within a meter or two). Thus aerial 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 vulnerable soil.