Tree Improvement in Alberta
Updated: July 14, 2003
Position Paper – Tree Improvement in Alberta
Alberta Forest Genetic Resources Council
Tree improvement may be defined as stand yield enhancement obtained through control of parentage in combination with good silvicultural practices.
Using traditional methods employed in plant and animal breeding programs, the best individuals are selectively bred together or vegetatively propagated to produce more valuable offspring. Traits considered in selection of parents may include health, growth rate, form, and wood properties.
This process is applied in Alberta in several programs in each of several native species. Following extensive and long-term testing, several exotic species may eventually be considered for inclusion in tree improvement programs, either as parents of hybrids or as pure species.
Program development generally involves the following sequence, but programs vary considerably in intensity, speed, size and complexity.
- Choose target species on the basis of ecological suitability, economic value, expectation of variability, and societal concerns.
- Conservatively delineate initial breeding region on the basis of ecological integrity (currently bounded by 2º to 3º latitude by 2º to 4º longitude, and 400 m elevation range, as well as ecological parameters).
- Establish provenance tests and genecological studies within and outside the breeding region to confirm appropriateness of breeding region boundaries and to delineate extent and patterns of variation.
- Select a large number of parents on the basis of good phenotype (expression of traits of interest such as height, volume, stem straightness, wood density, freedom from disease) and good geographic coverage of the breeding region. Ideally, trees selected are close to rotation age and at least 1.6 km apart.
- Propagate some or all parents (typically 50-150 parents, with 10-20 copies or progeny of each) into a seed orchard (and/or clone bank and/or breeding orchard).
- Collect seed or vegetative propagules from original wild parents, or make controlled crosses among grafted ramets in an orchard, and establish progeny and/or clonal tests to:
evaluate parental genotype (genetic worth);
estimate genetic parameters, e.g. heritability;
estimate genetic gain; and
generate a new population for selection of the next generation’s parents.
- Manage orchard for regular and abundant production of high quality seed or vegetative material.
- Progressively remove (rogue) poorer parents from the orchard as progeny tests yield estimates of parental value. Limits to roguing will be determined by seed production and parental numbers.
- Evaluate tests and move to the next phase of both orchard and breeding program. Age at evaluation will depend on species and program; for conifers, it is typically 15-20 years in Alberta. Parents for the next phase can be chosen through forward selection (selection of individuals from progeny tests), backward selection (selection of original parents on the basis of progeny performance) or a combination of both. New orchards can be de novo, or can gradually replace older ones in a “rolling front” orchard, where poorer parents are removed over a period of time and replaced by new selections. Numbers of parents in an advanced phase orchard will be typically lower, in the range of 25-50. New breeding population selections are also made from progeny tests and original parents, on the same basis as new orchard parents, but in far greater numbers (typically 150 to 300).
- New material may be introduced into the breeding population at any time.
- Breeding region boundaries can be adjusted on the basis of provenance and progeny test results and genecological studies.