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Producing tree seed and propagation material

Increased interest in a wide range of native and exotic tree species provides Australian farmers with the opportunity to grow seed commercially. The market covers genetically improved seed (resulting from long-term breeding trials) to selections of local indigenous varieties. Breeding programs for commercially valuable tree species involve incorporating selected wild trees into seed orchards and testing their progeny.

The lead times and costs involved in seed breeding programs mean that improved seed is currently only available for a small number of commercial species. For other species, the choice is usually between seed collected from the wild and seed collected from plantations. Wild seed collected from a particular location can be marketed as being of that provenance. With many organisations and farmers wishing to establish locally indigenous trees and shrubs there are sometimes very strong markets for locally indigenous seed. Farmers with native forest on their property may be able to take advantage of this.

Where buyers are interested in seed that exhibits fast growth or other desirable traits they may be prepared to pay more for seed of highly regarded provenance or ‘improved seed’ from seed orchards or well managed plantations. (Seed orchards are simply specially designed and managed plantations grown for seed production only.)

Common methods of enhancing the quality of any plantation for seed production include:
• encouraging out-breeding by incorporating a range of promising provenances or seedlots. Outbreeding alone can add as much as 10% to the growth rate of some tree species.
• selective culling for desirable tree characteristics such as vigour or form so that all the retained trees exhibit the desirable characteristics.
• isolating the plantation away from any native forest or plantation containing the same species or any others that may be able to interbreed.

Intensive selection and culling on the basis of growth characteristics is normal plantation practice. By eliminating the poor individuals from the stand the seed produced by the remaining trees is expected to be of higher quality. For frost sensitive species, such as Spotted Gum (Corymbia maculata), or where there are other environmental factors that lead to mortality, farmers may find that they are able to use natural selection to cull their stands. If sufficient individuals survive, the seed from these may produce trees that are more environmentally tolerant of adverse conditions. The only way to demonstrate that a particular seedlot or selection is superior is by undertaking a progeny trial. This involves a direct comparison of the growth and development of seedlings’ different sources.

Specially tending trees to reduce seed harvesting costs might also be an option. Widely spaced trees develop a larger canopy and, commonly, more seed. The use of pollinators, such as bees, can increase seed set in flowering species. Even tall native trees can be pushed or bent over to allow seed harvesting from ground level. Using horticultural hormones that induce flowering has increased seed production in native trees.

When collecting seed, farmers must be aware of the risks of inbreeding and hybridisation. A small genetic base in the original seed lot could increase inbreeding and dramatically affect seed viability and vigour. Because many eucalypt species can interbreed, seed collected from mixed species planting, or from plantations located near native forests or domestic gardens, may not be strictly true to species.

There are opportunities to sell propagation material from species that can be grafted or struck from root or stem cuttings. Many exotic timber trees—including poplars, pines and ‘cricket bat’ willows—are commonly grown from cuttings. Recent research has found that some of Australia’s promising native cabinet timber species—such as Blackwood (Acacia melanoxylon)—can also be propagated from root cuttings. This type of vegetative propagation produces genetic clones. Mass-producing well formed trees in this way can greatly reduce production costs (due to pruning, for example, which can increase production costs in species with high genetic diversity). However, developing farm forests using clones can also increase the risk of disease, so it is common to use several unrelated clones in a plantation.

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