Manitoba Tree Improvement Strategy:
The objectives of a tree improvement program are:
Tree improvement is a long-term investment to increase the productivity of forest plantations by providing a source of improved planting stock that will result in increased growth, better form and wood quality, and improved insect and disease resistance. Using the best quality seed source available is the first step in a series of silvicultural activities to increase productivity on the forest land base. The genetic resource is managed to ensure that genetic diversity is maintained so that the forests are able to adapt to changing conditions in the future.
In Manitoba the three main reforestation species are black spruce, white spruce and jack pine. Breeding zones have been delineated for each of these species based on climate, vegetation and physiography. The forests in these zones have adapted over hundreds of years to environmentally similar conditions. Seed collected from within the zone can be expected to perform well throughout the zone.
Species and Breeding Zones (Click on species for map of breeding zones)
Tree improvement programs are established in those breeding zones in which the predicted level of future planting justifies the cost of the program. In breeding zones with small planting forecasts that do not justify a program, efforts are made to ensure seed is collected from better stands and/or better trees within stands. In some cases seed production areas (SPA’s) are established, particularly for white spruce, as a low cost identified source for seed.
Currently there are tree improvement programs in seven black spruce, two white spruce and four jack pine zones. The Canadian Forest Service (CFS) began the jack pine tree improvement work in the early 1970’s. They also started one white spruce program in the early 1990’s. These programs were turned over to management by Sustainable Development in 1996 when the CFS Winnipeg office was closed. The provincial black and white spruce programs were initiated in the late 1980’s.
Genetic diversity is a measure of the ability of a species to adapt to changing conditions over time. It is important that while improving the genetic quality of seed to increase productivity of forests, safeguards are also put in place to ensure that the genetic diversity of the tree species is maintained. A study of genetic diversity in black spruce within two ecoregions in Manitoba was completed by Dr. Om Rajora at the University of Alberta. The study found that there are typical moderate to high levels of genetic diversity within the sampled black spruce populations. It also concluded that harvesting and forest regeneration practices currently used in the province do not appear to have reduced the levels of genetic diversity. The data from this study will be used as benchmarks to monitor the level of genetic diversity of future forests to ensure that the black spruce genetic resource of the province continues to be managed in a sustainable manner. Seed collected from orchards can be analyzed to determine if genetic diversity is being maintained relative to the levels documented in this study. This project was jointly funded by the Manitoba Forestry Branch, Tolko Manitoba, Tembec Forest Resources, LP Canada and the Manitoba Model Forest. (Genetic diversity impacts of forest fires, forest harvesting, and alternative reforestation practices in black spruce (Picea Mariana) by O. P. Rajora and S. A. Pluhar published on-line in December 2002 In Theoretical and Applied Genetics)Clone banks have been established for some of the breeding zones. These help to preserve the gene pool by maintaining genetic copies of the original plus trees. The stands from which these plus trees originated may be harvested over time, but the genetic resource of these selected trees are conserved.
Another conservation method for the genetic resource is the long-term storage of samples of most of the general collection seed lots within the province. This will also be done for seed orchard collections.
The type of tree improvement program that is initiated in a breeding zone depends on the biology of the species and forecasted planting program. For zones where forecasted planting programs is large enough a family test / orchard strategy is implemented. Where the forecasted planting program would not economically justify a family test / orchard program, a lower cost mass selection seed orchard strategy would be implemented.
The basic components of a family test / orchard program are:
The selection of plus trees from throughout the breeding zone,
The establishment of family tests to evaluate family performance, The establishment of a seed orchard to produce seed for reforestation within the zone, The assessment of family tests to provide data required for roguing the seed orchard to increase genetic gains, The controlled breeding of top performing families to begin the next generation of improvement.
The basic components of a mass selection seed orchard program are:
The selection of plus trees from throughout the breeding zone:
- The selection of plus trees throughout the breeding zone,
- The establishment of a mass selection seed orchard,
- To undertake comparative selections removing the poorer performing individual, leaving superior individual to produce seed for reforestation efforts in the breeding zone.
Plus trees are selected from stands that meet certain criteria with regards to stand composition, age, density and size. They are trees that are phenotypically superior to the surrounding trees in the stand in terms of size and form. The outward appearance of a tree (its phenotype) is determined by its genetic makeup (its genotype) and the environment in which it has grown. The outward superiority of the plus tree could be due to some environmental advantage such as a particularly fertile spot of soil. Offspring of the plus trees must be tested to determine genetic superiority.
The traits that are used to select a plus tree include height, diameter, stem straightness and form, crown size, branch diameter and angle, and natural pruning. The relative weight given to each selection trait depends on the end products that will be produced from the trees and the heritability (degree of genetic control) of the trait for that species. A plus tree is rejected for signs of insect or disease damage. There are usually 350 to 450 plus trees selected in a breeding zone.
Plus trees can be selected either by ground crews or by helicopter. Aerial selections allow trees from more remote areas to be included to get a wider distribution throughout the zone. The location, height, diameter, age, and form qualities are recorded for ground selected plus trees. Only location is recorded for trees selected by helicopter.
Cones and/or scions are collected from each plus tree. The top of the tree is accessed by cutting the tree down, shooting off the top or cutting off the top from a helicopter. Cones are collected to extract the seed to grow seedlings for the tests and/or seed orchard. Each of these seedlings is given the same family number as the plus tree from which it originated.
White spruce cones
Scions are branch tips from the top of the plus tree. They are grafted onto rootstock to produce an exact genetic copy or clone of the plus tree. This is done to establish a clonal seed orchard and/or a clone bank. Clonal seed orchards are used for white spruce because this species will not normally produce significant cone crops until about 30 years of age. The grafted tree retains its chronological age and so will produce cones much earlier. Clone banks are established to preserve the genetic resource and also to provide parents for controlled breeding.
The offspring of the plus trees (families) are planted in 3 to 4 family tests located throughout the breeding zone. The sites for the family tests are selected to sample a variety of typical plantation conditions for the species. Each site should be as uniform as possible to provide equal growing conditions for all trees; however, complete uniformity is rare due to the relatively large area (3-4 hectares) required.
A randomized complete block design with single tree plots is used for spruce family tests. One tree for each family is planted in a random location within each of 15-20 replications at each test. Trees are planted at 2-metre by 2-metre spacing to provide equal growing space. The test sites are maintained by mowing, brushing and spraying vegetative competition to keep the growing conditions as uniform as possible.
General collection seed sources are usually included in the family tests to use as benchmarks against which to compare the performance of the families. Also a few families from adjacent breeding zones are added in to check the validity of the breeding zone boundaries.
Seed orchards are usually established the year after the family tests were planted. They can be established using seedlings or clones. Seedling seed orchards are established with the same families as their associated family tests. One tree for each family is planted in random order in each of about 60 replications. The spacing in seedling seed orchards is 1 metre by 3 metres, since most of the trees will be removed over time as the orchard is rogued.
A young seedling seed orchard
Clonal seed orchards are established with clones of the plus trees. Clonal orchards are used for white spruce in order to get much earlier cone production than would be possible from a seedling seed orchard. There
can be varying numbers of trees (ramets) for each clone. The orchard layout is designed prior to planting using a specialized computer program. The position of clones relative to each other is controlled to minimize pollination amongst ramets of the same clone and maximize the mix of pollen amongst all other clones. Spacing in clonal orchards is typically wider than in seedling orchards (eg. 3.5m x 5m).
Orchards are managed to grow healthy trees with wide bushy crowns that will produce early and abundant cone crops. Orchard trees are fertilized to improve their growth and health. Fertilization also helps to increase seed yields due to larger cones and improved seed quality. Vegetative competition is controlled by mowing, brushing and spraying herbicide. Pest protection is conducted to reduce damage both to the tree and to the developing cone crop. Trees of the same species are removed from the surrounding area to reduce pollen contamination. The orchard trees are regularly topped to keep them short for easier cone collection and to encourage bushier growth with more potential cone-bearing sites. Various cone induction techniques, such as gibberellin injection, are used to increase cone production.
Injecting orchard tree with gibberellin to increase cone production
Mass selection seed orchards are a lower cost option that combine the testing and seed production functions. Orchard trees are planted at close spacing (1m x 1m) and are periodically rogued based on visual comparison with neighbouring trees. Genetic gains are expected to be lower than with the higher cost option utilizing separate family tests and seed orchard.
Mass selection seed orchard
The family tests are evaluated at 10, 15 and 20 years of age to determine the relative performance or ranking of the families and to estimate the genetic gain achieved over wild seed. At ten years of age, the family test trees are evaluated on the basis of height. At 15 and 20 years, diameter and tree quality are added to the evaluation. The data is sent to a forest geneticist for statistical analysis. The families are ranked based on their performance and this data is then used to rogue or thin the seed orchard. In most cases, the bottom 25% ranked families will have all their trees removed from the seed orchard. Then an additional 25% of trees are removed, primarily from the middle 50% ranked families, taking into account tree condition, size and spacing, as well as family ranking. This leaves the better performing families in the orchard to cross-pollinate and produce genetically improved seed for reforestation efforts.
Measuring tree height in a family test
The extent to which an orchard will be rogued will depend upon a number of factors: the number of trees remaining in the orchard; the predicted seed production/tree; the demand for seed and the genetic gain desired. Roguing more of the lower ranked families from the orchard will give a greater genetic gain, but less overall seed production. If the production of the orchard exceeds seed demand, then further roguing to increase gain can be done. The number of families left in an orchard will always be high enough to ensure that genetic diversity is not compromised.
After the 15- or 20-year measurements, the next cycle of improvement can be started if forecasted seed requirements for the zone justify the program. The strategy remains the same except that families with proven genetic quality, rather than plus trees, are now used as the genetic base. Various breeding strategies can be utilized to increase genetic gain while maintaining genetic variability and the flexibility required to adapt to changing conditions. Breeding can be done either with the original plus tree clones in the clone bank or with the best trees from the top performing families in the family tests. A tree from a highly ranked family will be bred with a tree from another highly ranked family. The seed produced will be used to grow seedlings that will be planted in family tests and a seed orchard to begin another cycle of testing and seed production. The second-generation orchard gradually takes over the provision of seed for the zone from the original seed orchard as it reaches full production.
Breeding trees involves isolating the seed cones on the female parent tree, collecting pollen from the male parent tree and then applying this pollen to the female flowers when they become receptive. The seed from each specific cross is used to grow seedlings that are collectively known as a full-sib family since both the female and male parents are known.
White spruce female flower Jack pine male pollen cone
There is currently one seed orchard in the southeast jack pine breeding zone that was established with trees produced from controlled breeding of tested families.
The three major forest companies co-operate in some of the tree improvement programs within their Forest Management Licence Areas. Sustainable Development staff plan the tree improvement programs and provide technical direction. Annual work plans are prepared for each breeding zone and meetings are held with the companies to decide the most cost-efficient way to complete the work. A Tree Improvement Trust Account has been created to provide a funding mechanism to share the costs of the programs according to an agreed upon ratio based on seed distribution.
Tembec Forest Resources is co-operating in one black spruce improvement program in the Lake Winnipeg East breeding zone. The seed orchard in this zone has been rogued once after the 10-year measurements and has started to produce seed for reforestation within the zone.
LP Canada Ltd. is co-operating in both white spruce and black spruce improvement programs in the Mountain breeding zone. The white spruce clonal seed orchard has been rogued once after the 10-year measurements (the bottom 1/3 ranked families were removed). This orchard had its first significant cone crop in the fall of 2002. The black spruce family tests and seed orchard were established in 2001.
Tolko Manitoba is co-operating in one white spruce and three black spruce programs in the Saskatchewan River, Highrock and Nelson River breeding zones. The white spruce program in the Saskatchewan River zone started off as a potted clonal seed orchard under the direction of the Canadian Forest Service. After the change in management to Sustainable Development, the clones were field planted into a seed orchard and breeding garden. A polycross breeding program is planned to produce offspring of each clone to establish family tests to evaluate their genetic worth. In the black spruce program in the Saskatchewan River zone, the seed orchard has been rogued after the 10-year measurements and is starting to produce cone crops. The black spruce programs in the Highrock and Nelson River zones were established in 1997/98 and 1993/94, respectively.
Summary of Tree Improvement Programs in Manitoba
Number of tests
(number of trees)
Number of orchards (type) –
Year of establishment
(number of trees)
2 (mass selection)
3 – 1997 (22,706)
Nelson River 2
3 – 1993 (26,100)
4 – 1989 (20,192)
3 – 1972 (12,960)
1** – 1977 (2592)
1 (selected clonal)
1 (mass selection)
2 (mass selection)
– 1986 (18,432)
1 Tembec Forest Resources
2 Tolko Manitoba Inc.
3 LP Canada Ltd.
* The jack pine programs were initiated by the Canadian Forest Service and turned over for management by the Sustainable Development in 1996.
** Two additional family tests for this zone are located in Saskatchewan.