Overstory #134 - Seed Source Establishment and Management
Farmers commonly plant trees on farms or community lands to grow products that satisfy household needs and market demands. Non-government organizations (NGOs) often support farmers' tree-planting efforts. Tree seed, a key input that determines the success of any tree planting activity, is often in short supply. As a result, farmers and NGOs use whatever seed is available, regardless of its quality.
In most countries good quality tree seed is not readily available for a number of reasons, including:
- A lack of awareness concerning the importance of seed quality.
- Limited quantities of good quality seed are available; and government agencies, researchers and forest industry control access to this seed.
- Limited areas of forests and plantations exist that produce good quality seed (seed producing areas are called seed sources').
- The genetic quality of forests is often degraded because the best quality trees have been harvested, leaving only poorer quality trees available for seed collection.
- Collectors, dealers and other workers in the tree seed sector have limited training and inadequate facilities to produce, handle and store seed properly.
- A lack of cooperation between governmental agencies at the community level to improve the availability and utilization of quality seed.
- No labeling or certification systems exist to provide adequate information (to the farmers and NGOs) concerning the origin and quality of the tree seed that is available.
- No premium is paid for better quality tree seed.
Definitions for common tree seed terms
It is appropriate to define some of the basic terms related to tree seed production and management. The definitions provided here are intended specifically for farmers and NGO fieldworkers. They may differ from those used in the formal tree seed sector.
- Germplasm: Seed or vegetative material used for the purpose of plant propagation; most commonly germplasm refers to seed.
- Seed: Reproductive material of flowering plants.
- Seedling: Plants propagated from any form of germplasm.
- Seed source: Individual trees or stands, natural or planted, from which seed is collected. This manual addresses four types of seed sources: seed trees, seed stands, seed production areas and seed orchards.
- Seed trees: Trees from which seed is collected.
- Genotype: Genetic constituents of an individual tree which, in interaction with the environment, largely controls tree performance and is inheritable by its progeny. Generally, trees with good genotype produce good progeny.
- Phenotype: The observed characteristics of a tree, which result from the interaction of the genotype and environment.
- Plus trees (Selected trees): Superior phenotypic trees from which seed is collected.
Another important term is seed quality. Seed quality has a direct impact on tree growth and the success of tree planting activities. Seed quality is comprised of three components.
- Physical quality: Quality related to physical characteristics, such as size, color, age, seed coat condition, occurrence of cracks, pest and disease attacks, or other damage.
- Physiological quality: Quality related to physiological characteristics, such as maturity, moisture content, or germination ability.
- Genetic quality: Quality related to characteristics inherited from the parent trees.
Seed quality helps determine:
- The quantity of seed that should be sown to produce the required number of seedlings;
- The number, health and vigor of the resulting seedlings; and
- The characteristics of the resulting seedlings and mature trees, such as growth rate, biomass production (wood, leaves, etc), fruit and seed production, stem form (straightness, diameter, branchiness, merchantable length), general health and susceptibility to pests and diseases.
Establishment of seed trees on farm
Most farmers generally own, or have access to, only small areas of land and do not have the time or financial resources required to invest in intensive seed source management. In most cases, it is not feasible for the farmers to establish seed orchards or seed production areas. The best option for most farmers is to integrate seed trees into their existing farming systems, which often include pre-existing trees of many species. To maximize the genetic base and productivity of on-farm tree sources, the following approach for establishing on-farm seed trees is recommended.
Site selection and tree planting
- First, environmental conditions of the site - rainfall, temperature, elevation, and soils - must be appropriate for the target species.
- To improve tree survival and growth thorough land preparation should precede seed tree establishment.
- Wider spacing between seed trees and other trees enhances seed production by exposing more of the seed tree's crown to sunlight and pollination. Appropriate spacing will differ by species and site. A general recommendation is that seed trees be planted at 2x4 or 3x3 m. After these trees become large, thinning should be conducted to achieve wider spacing and remove the poorer quality trees. Additionally, seed trees should not be planted closer than 4 m to pre-existing trees, unless the pre-existing trees can be removed once they begin to impede the growth of the seed trees.
- If improved germplasm is used to establish seed trees, the seed trees should be isolated from stands of unimproved trees of the same species to avoid pollen contamination and maintain the genetic superiority of the seed produced. Because landholdings are small and farmers can not control the land management practices of their neighbors, maintaining effective isolation distances is often impossible. Therefore, farmers should realize that the seed collected from on-farm trees results from both 'improved quality mother trees pollinated by improved quality father trees' and 'improved quality mother trees pollinated by average to below average quality father trees'. To improve the pollen source from their own land, farmers should remove poor quality trees.
Seed trees management
- Active management of trees will improve on-farm seed production. Management options include: planting seed trees; weed control near seed trees; fertilizing seed trees; removing poor quality trees and trees that inhibit seed trees; pruning dead and non-productive branches from seed trees; maintaining a clean understory to facilitate seed collection (and reduce fire hazard); and implementing pest and disease protection measures. At the farm- and community-level these operations can be implemented in a cost-effective manner. However, labor is often a limiting factor for farmers. The potential positive impact of these management operations must be compared to the opportunity costs of individual farmers. The suitability of these operations will vary for each farm and situation.
- Seed tree planting on farms should be developed for multiple products and services, not solely for seed production. Seed trees can serve as living fences, border trees, hedgerows, and shade trees or to enhance soil and water conservation. Under multiple-purpose management seed trees and other trees may produce fodder, fuelwood, timber, fruit, seed and other products. Multipurpose management will increase the overall productivity of the stand, but decrease the productivity of each individual product. In other words, less seed but more products (and total value) for the farmer.
Establishment of a small-scale seed orchard
Although farm-level seed production is primarily based on seed tree management, in some cases it may be possible for farmers to establish seed orchards. As mentioned earlier, seed orchards are seed sources established for the specific purpose of seed production. They are usually established from families of improved genetic quality of either seedling or clonal origin. Seed orchards are planted at a regular spacing with a specific design. Seed orchards are not intended to produce multiple products or services. Their main objective is to maximize the production of quality seed to meet long-term needs. Because of this strong emphasis on seed production, seed orchards are usually managed intensively. Isolation distances of 200 m from unimproved stands or trees of the same species are recommended and selective thinning is conducted purposely to increase spacing as trees become larger and to remove poorer quality trees. Fertilization, pruning and intensive pest and disease monitoring are also recommended.
In most cases it is difficult for individual farmers to establish seed orchards. But farmer groups or NGOs may establish seed orchards by utilizing the lands of adjacent individual farmers or communal land. Because of the intensive design and management associated with seed orchards, it is recommended that farmer groups and NGOs seek assistance from technical experts when establishing seed orchards. The remainder of this chapter provides information on seed orchard establishment and management.
Site selection for seed orchards
Site selection is important and the first step in seed orchard establishment. Seed orchards are long-term investments. Appropriate sites should meet all of the following criteria:
- Environmental conditions - rainfall, temperatures, elevation, and soils - must be appropriate for the target species.
- Not vulnerable to natural disasters - floods, volcano, earthquake, landslide and frequent wildfires.
- Secure from wild and domestic animals.
- Isolated to avoid pollen contamination. The recommended isolation distance is 200m.
- Easy to access.
- Land tenure or land use rights are secure.
Germplasm selection for seed orchard
The seed used for seed orchard establishment should be collected from identified and improved seed sources. It may be seed from a large number of plus trees (30 or more) where the identity of the individual trees is recorded, or where the identity is not recorded (bulk seed). Seed from identified individual plus trees is good because the planting design can be developed to minimize inbreeding. However, if bulk seed is used seed orchard establishment and management is much simpler.
If the seed orchard design is intended to maintain the identity of individual mother trees, seed from each mother trees must be germinated separately in well-marked containers. The resulting seedlings must also be well marked in the nursery, during transportation and planting at the site. Before planting a detailed seed orchard map must be made that includes the identity of each tree. It is important that this map be followed during planting. If bulk seed is used to establish the seed orchard, seed can be germinated in any available and appropriate containers. The identification of individual seedlings is not necessary. The seed orchard map can be simple, showing the location of each tree, without specifying its identity.
Seed orchard size
As the area of the seed orchard increases it should be more attractive to pollinators. Even though individual farmers have limited areas of land, a farmer group approach can be used to establish a large-scale seed orchard at the community-level. With this approach individual farmer would establish small-scale seed orchard units of 0.1 - 0.25 ha on their own land. At the community-level, these small units scattered across different adjacent farms will form a large-scale seed orchard. One hectare is the minimum 'target size' of a community-level seed orchard. This would require 4 to 10 farmers to establish small-scale seed orchard units of the size mentioned above. The more farmers involved, the larger and better the community-level seed orchard. An appropriate role for NGOs in this process is to develop linkages with technical specialists and document/monitor each small-scale seed orchard unit. Each small-scale unit should contain at least 30 families/trees. The more families included the broader the genetic base of the seed produced from the community-level seed orchard.
Seed orchard design
Tree spacing will depend on tree species, site conditions, and orchard design. If the orchard is established as a hedgerow, in-row space may be 10-50 cm with spacing between hedgerows 4-10 m. A hedgerow design is common for fast growing leguminous species, such as Calliandra calothyrsus (red calliandra), Flemingia macrophylla (flemingia), Gliricidia sepium (gliricidia) and Leucaena species (ipil ipil). Most other species will be established in a block design. Initial spacing may be 2x4 m, 3x3 m, or even wider. Narrow spacing such as 2x4 or 3x3 allows for intensive thinning, see details below under Orchard spacing.
If the genetic identity of each tree is to be maintained, a detailed orchard design should be developed prior to establishment. The seed orchards should be arranged so that no individuals of the same family are planted close to each other. This precaution will minimize inbreeding. Farmers and NGOs should develop the orchard designs with assistance from a tree geneticist or tree improvement specialist who is familiar with seed orchard establishment. If the genetic identity of individual trees is not to be maintained, seed orchard establishment is easier, because there is no need to worry about the arrangement of individual trees or families. Trees can be planted in any arrangement. However, farmers and NGOs may still wish to seek assistance from a tree improvement specialist.
Seed orchard management
Pest and disease control
Because seed orchards contain many trees of the same species they are more susceptible to pest and disease problems than individual trees scattered across a farm or community. Orchards should be closely monitored for evidence of pest and disease problems. If problems occur assistance should be sought from agriculture and forestry plant protection specialists.
The importance of thinning and pruning
Wider tree spacing enhances seed production by exposing more of the tree crown to direct sunlight and pollination. If tree crowns are allowed to grow together sunlight exposure, flowering, pollination, and seed production will all decrease. As mentioned above, most seed orchards should be established at 2x4 or 3x3 m. As the trees grow, wider spacing is required. Wider tree spacing is achieved through 2-4 successive thinnings, each following an assessment of the orchard and ranking of the trees to identify inferior trees for removal. Poor quality trees may include those that are slow growing, attacked by pests or disease and produce low quantities of seed. Each thinning should remove no more then 30 to 40% of the trees. The subsequent thinning should occur when the crowns close and seed production declines. The recommended final density for a mature seed orchard of medium- to large-sized trees is 100 to 150 trees/ha (a tree spacing of approximately 8x8 to 10x10 m). Caution: Thinning should be conducted so as not to reduce the number of families below 30 per seed orchard. Pruning should be conducted periodically to remove lower branches that have grown large or no longer produce flowers. The pruning of some branches from the upper crown may be warranted to maintain full sunlight exposure to the branches that are retained.
Spacing management is different for hedgerow orchards. Hedgerows should be pruned to a 1 m height once or more per year. Every two m one tree should be retained unpruned to serve as a seed tree. After the canopies of the hedgerow seed trees begin to close, probably after 2-4 years, in-row spacing of seed trees should be increased to 4 m. In hedgerow orchards, spacing between seed trees greater than 4 m is probably not necessary. Once seed trees in the hedgerow become too large they can be cut down. Coppice growth from the seed tree, or other trees in the hedgerow, is then allowed to grow up and fill the place of the removed seed trees. To maintain high annual seed production, it is recommended that each year only a few large seed trees be removed. This will result in the hedgerow seed orchard containing seed trees of various sizes, with a relatively consistent annual seed production. The leaf and woody biomass harvested from hedgerows during pruning operations should be used as fodder, green manure or fuelwood.
Although seed orchards are intended for the sole purpose of seed production, it is possible to practices intercropping. Seed orchards can be intercropped with food crops - such as corn, upland rice, cassava, or vegetables - for 1 to 3 years after establishment. Intensive weed control and fertilizer application will benefit both the food crops and the orchard trees. Once the orchard trees become large shade-tolerant crops - such as ginger, turmeric or dwarf cardamom - may be cultivated in the understory. Covercrops may also be used to control weed growth and improve soil fertility. However, covercrops are often management intensive. Also, since covercrops do not provide a direct product, farmers and NGOs may prefer other crops.
A moderate amount of intercropping will not hinder seed orchard health and may enhance tree growth. However, intensive intercropping may damage trees and decrease seed production. All management practices should be implemented to favor the main objective of the orchard - seed production!
IFSP. 2000. Demo room poster. Indonesian Forest Seed Project (IFSP). Bandung, Indonesia.
IFSP. 2000. Visual presentation of extension material. Indonesia Forest Seed Project (IFSP). Bandung, Indonesia.
Chamberlain, J.R. 2000. Improving seed production in Calliandra calothyrsus a field manual for researchers and extension workers. Oxford University Press, Oxford, UK.
Dawson. I. and J. Were. 1997. Collecting germplasm from trees – some guidelines. Agroforestry Today 9: 6-9.
Schmidt, L. 2000. Guide to handling of tropical and subtropical forest seed. Danida Forest Seed Centre (DFSC). Humlebaek, Denmark.
Simons, A.J. 1997. Tree domestication – better trees for rural prosperity. Agroforestry Today 9: 4-6.
Stubsgaard, F. 1997. Tree climbing for seed collection. Technical Note. Danida Forest Seed Centre, Humlebaek, Denmark.
Willan, R.L. 1985. A guide to forest seed handling. FAO. Rome, Italy.
Yaacob, O. and S. Subhadrabandhu. 1995. The production of economic fruits in South-east Asia. Oxford University Press. Kuala Lumpur, Malaysia.
Mulawarman, J.M. Roshetko, S.M. Sasongko, and D. Iriantono. 2003. Tree Seed Management: Seed Sources, Seed Collection and Seed Handling. Winrock International, Morrilton, Arkansas, USA, and International Centre for Research in Agroforestry (ICRAF), Bogor, Indonesia.
Winrock International 38 Winrock Drive Morrilton, Arkansas, 72110-9370 USA Phone: 1 501 727-5435 Fax: 1 501 727-5417 Email: firstname.lastname@example.org
International Centre for Research in Agroforestry Southeast Asia Regional Research Programme PO Box 161, Bogor, 16001, Indonesia Phone: 62 251 625-415 Fax: 62 251 625-416 Email: email@example.com
Indonesia Forest Seed Project (IFSP) Taman Hutan Raya Ir. H. Juanda, Dago Pakar, Bandung, 40135, Indonesia Phone/Fax: 62 22 251-5895 Email: firstname.lastname@example.org.
About the authors
Mulawarman formerly worked as Tree farming Research Officer with World Agroforestry Centre (ICRAF) SEA to enhance smallholder tree farming systems in Indonesia, particularly in Nusa Tenggara. He is currently based in Pangkalan Kerinci, Riau, Indonesia as the Senior Silviculture Researcher with Riau Andalan Pulp and Paper, a member of APRIL Group. He can be contacted at: R&D Forestry, Riau Andalan Pulp and Paper, Pangkalan Kerinci, Riau 28300, P.O Box 1089, Indonesia; Tel: 62 761 95550 Ext. 5204, 5222; Fax: 62 761 95360; email: Mulawarman@aprilasia.com.
Jim Roshetko has worked with agroforestry systems and species for over 20 years in Southeast Asia, South Asia, the Pacific and the Caribbean. He is currently based in Bogor, Indonesia as the Trees and Markets Specialist with Winrock International and the World Agroforestry Centre (ICRAF). His work focuses on methods to enhance smallholder tree farming systems. He can be contacted at: ICRAF/Winrock, PO Box 161, Bogor 16001, Indonesia; Tel: 62 251 625-415; Fax: 62 251 625-416; email: J.Roshetko@cgiar.org.
Djoko Iriantono has been a researcher for Seed Technology of Tree Species in Seed Technology Center, Forestry Research and Development Agency in Bogor, Indonesia since 1987. He has also worked on Tree Improvement of Acacia, Mahogany, and Gmelina. He joined IFSP (Indonesia Forest Seed Project) in 2000. The project focuses on development of human, technical, and institutional resources for the tree seed sector in Indonesia. He is currently working as a Project Manager. His address is Indonesia Forest Seed Project, Taman Hutan Raya Ir. H. Juanda, PO Box 6919, Bandung 40135, Indonesia; Tel/Fax: +62 22 2515895; e-mail: email@example.com.
Related editions to The Overstory
- The Overstory #130--Seed Sources for Collection
- The Overstory #120--Seed Collection
- The Overstory #58--Guidelines for Seed Production of Agroforestry Trees
- The Overstory #43--Essentials of Good Planting Stock
- The Overstory #31--Tree Domestication