does not result from self-pollination or matings (crosses) among related trees. To maintain genetic quality, it is important that leave trees remaining after partial cutting have desirable characteristics in terms of health, form and growth rate. If only slow-growing, crooked or diseased trees remain as parents of the next generation, it is likely that the quality of the resulting stand will be lower than if high-quality seed parents are left.
Forest Genetic Resources and Tree Improvement The genetic quality of reforested stands can be improved considerably when stands are regenerated using planting stock produced through selective breeding. Seed obtained from parent trees selected in a breeding program and collected in a seed orchard containing such parents is called genetic Class A seed. The selected trees are planted in an area called a seed orchard, and become the production population. A seed orchard is a plantation that is intensively managed for frequent and abundant seed production. Seed orchards are commonly established in areas with good history of seed production, close to water, infrastructure, and labour. Breeding programs range from being simple to very complicated. In most cases, the breeding method, the trait(s), and the short- and long-term goals of the program determine the level of sophistication. Most tree breeding programs share several steps in common: selection, breeding and testing (Figure 2). Selection is the act of choosing individuals that will serve as parents in the breeding program. Parents are either selected for their apparent superiority – phenotypic selection (individuals are selected based on their appearance), or based on their performance Natural Stands
Breeding Population
Production Population
Selection
Testing
Breeding
1st Generation Seed Orchard
Regenerated Stands
2nd Generation Seed Orchard
Regenerated Stands
Infusion Selection
Testing
Breeding
Figure 2: The progression of a breeding program: from selecting trees in natural populations, through successive breeding cycles, incorporating new wild selections after each cycle (infusion) and creating production populations (seed orchards).
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