SEED PRODUCTION AREA
WHAT IS A SEED PRODUCTION AREA?
A seed production area is defined as "a natural or planted stand or group of stands, set aside, periodically rouged, and treated to stimulate seed production. The genetic quality of the seed is not known (11)". The purpose of a seed production area is to provide, in quantity, seed of known origin from the best phenotypes available. The establishment of seed production areas is a stop-gap measure, designed to provide seed of the best possible quality until our seed orchards begin to bear.
WHY SEED PRODUCTION AREA?
The establishment of SPAs represents an innovative solution to:
ü Securing much needed understorey species and improving regional biodiversity
ü Ensuring a continued supply of known provenance seed
ü Providing opportunities for alternative land use and income
ü Planting multi functional vegetation
- windbreaks, soil improvement
ü Increase the availability and genetic diversity of local native seed
ü Providing land managers with a guaranteed purchaser and distributor of seed
HOW TREES ARE SELECTED FOR A SEED PRODUCTION AREA?
Desired attributes of the trees left in a seed production area are similar to, but less rigorous than, the qualifications required for a select tree to be used in an intensive tree improvement program. For existing mature stands that will be converted, trees showing potential for good seed production are given preference, although the evidence of past seed production is not essential if the trees have been growing in a tightly closed stand. Excellent seed crops are often produced after heavy thinning by trees that showed little seed production prior to thinning.
Selection criteria may be different between species and end products but the following characteristics are typical in the case of timber species.
I. Fast growth
II. Relatively straight single cylindrical bole
III. Good crown development
IV. Thin branches with wide branch angle
V. Good self pruning
VI. Free from insects and diseases
No tree below the desired standard should be kept, regardless of spacing. It is essential that the crowns of the trees be exposed to full sunlight of at least three sides if good seed production is to be realized. When several good phenotypes occur in a group, enough of them must be removed so that the remaining trees will receive enough light. In spots where the only trees available are inferior phenotypes, all trees must be removed, even if this results in a fairly large gap in the stand.
ESTABLISHMENT OF A SPA:
The quickest way to make a seed production area is to convert existing mature stands of good quality trees for this purpose. A seed production area can also be developed from a progeny or provenance trial. There are no specific age limitations but the stand should be old enough to produce seed.
A planted stand suitable for conversion to a seed production area should have the following specifications.
(1) Details of the seed source used to establish the stand should be known.
Knowledge of the geographic origin and genetic base, which ideally will be broad, is important in determining the suitability of the stand for development into a seed production area.
(2) The trees should be mature for seed production, but not too old.
There are no age limitations, other than that the stand must be old enough for reliable selection and be sexually mature to produce seed. Individual trees must have sufficient crown density to potentially produce large seed crops.
Seeds from very young or very old trees often are of inferior quality compared to those from middle age trees. In addition, old trees tend not to respond to thinning by further crown development.
(3) The stand should be near full stocking and contain a large number of trees of good phenotype.
A suitable stand before conversion should be near full stocking to increase the selection intensity. The final stocking of a seed production is usually 150-200 stems per ha. An initial survey should reveal that the number of trees of good phenotypes is equivalent to that.
(4) Free from pests and diseases.
Evidence of pests or diseases may be an indication of inferior adaptability of the seed source. If the stand shows widespread symptoms of attack by insects or diseases it should not be used for conversion.
(5) The trees should have proven capacity to produce flowers and seeds in the area.
To avoid failure, a detailed survey of the candidate species’ ability to flower and seed in a particular environment should be a prerequisite to establishing seed production area. This is especially important for exotic species where flowering may fail or seeds are not produced due to incompatibility with the site. Non-favorable environments, such as drought prone areas, may be unsuitable for seed production area. Availability of pollinators can also be important.
(6) The area should be easily accessible.
The conversion of a stand into a seed production area and subsequent management operations, such as harvest of seeds, requires that the area is accessible throughout the year. This implies that it should be relatively flat but well drained. Ideally it should not be in a very remote area or too far from available labor for ease of maintenance and management.
(7) The selected stand should not be subject to commercial harvesting.
Seed production areas will be maintained for many years. It is necessary, therefore, to ensure that the stand in question is safe from commercial harvesting operations. Good communication with the forest managers will help avoid the accidental loss of valuable seed production areas.
(8) Size of seed production areas.
In general a minimum of 4 ha is recommended for practical management of seed production areas for most tree species. Managing small stands is inefficient, and there is a great danger of contamination from outside pollen. However, for some species such as eucalypts an area as small as 0.5 ha may be sufficient, due to prolific seed production. The area should be as close to square as possible, rather than a long linear block to facilitate more cross pollination among the trees.
(9) Isolation.
Poor isolation will be a common disadvantage of seed production area developed from existing stands. Usually such stands are selected from mature plantations of the same species. It is virtually impossible to eliminate completely contamination by stray pollen. However, an isolation zone or pollen dilution zone surrounding the seed production area can reduce it. The dilution zone may be an open area of some 200 m. If trees are to be grown in the dilution zone they must be of a species that does not hybridize with the species of interest for seed production.
MANAGEMENT OF SEED PRODUCTION AREAS:
There is some management practices specified for the better maintenance and to get maximum amount of good quality seeds from Seed Production Area. They are as follows:
1. Removal of cut material:
After thinning, it is necessary to remove all cut material that has accumulated on the ground. Removing the residue allows for easier access into the area for management activities, and reduces the potential dangers from pests and wildfires.
2. Weeding:
If the seed production area is to function efficiently, vegetative growth under the seed trees must be controlled. Weed growth can be controlled by regular hand weeding and/or careful application of herbicides. Trees should not have their growth checked by competing weeds. Seed production areas will require ongoing weed control throughout their working life as selective thinning will leave large gaps between trees. Once the trees attain sufficient height (around 10 m) it may be possible to control weeds by grazing livestock within the areas.
3. Control of coppice growth:
For strong coppicing species like eucalypts, it is necessary to kill the stumps of cut trees to discourage re-growth. Glyphosate herbicides, such as Round-up, have proved to be effective if they are painted or sprayed onto the cut surface immediately after felling. Multiple applications may be necessary to ensure a 100% kill.
4. Fertilization:
Fertilization should be used in conjunction with the opening of the stand by thinning. The increase in tree vigor resulting from thinning and fertilization enables the development of heavier and denser crowns that will produce more flowers. N containing fertilizers are usually applied only to promote vegetative growth. Prior to and during flowering, PK containing fertilizers with micronutrients should be applied.
5. Stand demarcation:
The external boundaries of the seed production area should be marked with large permanent markers. A prominent sign should be constructed to explain the purpose of the stand and the agency responsible for its management.
6. Protection:
Adequate fire breaks (10 m wide or more) should be established surrounding each seed production area and continually maintained. It may be necessary to fence the area if foraging domestic stock, wildlife or human activities are likely to cause damage to the trees.
7. Record Keeping:
It is important that full records on all aspects of seed production areas are maintained. The following information should be included:
· Species
· Seed origin
· Location
· Year of establishment
· Climate (rainfall, temperature)
· Soil
· Silvicultural operations (time of thinning, weeding, fertilizer applications, etc)
· Flowering characteristics
· Annual seed collection (amount of seed, number of trees from which seed is collected
Conclusion:
A seed production area must be managed properly and scientifically, as it serves as the source of future plantation. If we do not manage our seed production area properly, we may get inferior quality seed from the seed production areas. That will effect in our future plantations. So, management of seed production area plays a significant role.
References
1. Society of American Foresters; 1958 ;Forest Terminology
2. Donald E. Cole ; y ; Establishment and Management Seed Production Areas
3. Donald E. Cole ; y; Management of Pine Seed Production Areas
4. Guidelines of Seed Production Areas for woody
5. Khongsak Pinyopusarerk; y; Seed Production Areas: Guidelines for Establishment and Management Practices
6. Zabala, N. Q. 1990. Principles and Practice of Silviculture
7. Hiroshi Nakata & Keiya Isoda, 2005; is teak improving?
