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Highly productive seed sources of western hemlock and Douglas-fir have been developed through selection, breeding and testing. Offspring from parent trees selected in wild stands during the 1960s and early 1970s have been evaluated on many test sites. Better parent trees have been included in seed orchards for the production of fast- growing seedlings for reforestation. Trials planted to evaluate seed from these better parents show early height growth superiority averaging 15 percent for western hemlock and 22 percent for Douglas-fir, relative to wild-.seed.
Tree improvement is the application of knowledge of genetic variation in nativespecies, coupled with appropriate application of genetic principles, reproductivephysiology and seed-orchard management, to produce trees capable of betterperformance in a specified biological zone. Our goal is to understand andmaintain an adequate genetic resource while improving our trees' growth rate,disease resistance, stem, wood and fibre quality. B.C.'s Forest Practices Coderecognises the benefits of genetic improvement by requiring the use ofseed-orchard seed when available, and of resistant stock when forest-healthconcerns (insect or disease threat) exist.
In 1993, more than 225 million seedlings wereplanted on publicly owned forest lands. In the following year, planting exceeded 250 million seedlings. Thisfigure indicates the projected annual planting requirements for four main species(currently 93% of trees planted) in the year 2000 and the supply of seed-orchardseed in that year. Breeding and selection programs in these species willcontribute significantly to their potential performance.
The tree-improvement process is best portrayed in the accompanying figure showinga continuous cycle of selection, testing and breeding. In this continuous cycle,the genetic quality of a species is improved and those improvements are deliveredto the forest as seedlings from seed orchards or as plants fromvegetative-propagation systems. Tree improvement takes time; it may be 6-8 yearsbefore useful results are obtained from testing and another 10 years before seedorchards begin to produce significant quantities of improved seed forreforestation. Production of vegetative propagules (rooted cuttings ortissue-cultured plants) will take less time but is expensive and not appropriatefor all species.
The first step in the tree- improvement cycle is the selection of parent trees innatural stands. Selection is made on physical characteristics, such as superiorgrowth, form, reduced disease or insect damage. The breeder ensures that enoughtrees are selected to provide a level of genetic diversity that will buffer thefuture forest from extremes in the environment and attacks of insects anddiseases.
In order to preserve the genotype (unique combination of genes) of each parent,twigs are collected and grafted or rooted, producing a clone from each parent.These are planted in clone "banks," breeding gardens and perhaps seed orchards,where they can be the source of flowers for breeding programs or of scions(shoots) for vegetative propagation.
Parent-tree selection is based on physical appearance, which is a result ofgenetic complement and environment. Testing is required to determine the geneticworth of each parent, that is, the ability to pass on its superiority to itsprogeny (its offspring).
Progeny testing entails growing seedlings of each parent and evaluating them,along with the progeny of other parents selected from the same geographic zone,in tests that may last many years. Each test will be repeated on several plantingsites appropriate to the species in that zone so that more-reliable results areobtained.
Picking the best: measuring trees in a progeny testto identify parents of superior genetic value.
Breeding (the controlled mating of trees) begins when flowers appear on theparent trees in the forest, or on their clones in cultivation. Great care istaken to isolate young flowers so that unwanted pollen cannot "contaminate" theoffspring, from which future parent trees will be selected. Seeds from breedingprograms are sown and evaluated in new progeny tests, normally including abattery of studies, such as frost resistance, growth periodicity, insect anddisease resistance and wood quality, before results are interpreted to selecttrees for seed orchards or future breeding programs.
A breeders harvest: cones from mating betweenselected parents are ready for picking.
Active improvement programs are established for 10 species: coastal and interiorDouglas-fir, western hemlock, Sitka spruce, western redcedar, yellow cypress,interior spruce, lodgepole pine, western white pine and western larch.
Managed delivery systems are the vital link between the tree- breeding programsand reforestation. Genetic gain, resulting from years of selection, testing andbreeding, is delivered to the field forester through seed orchards orvegetative propagation programs.
Producing the best seed orchard of selected parentsplanted and managed to produce regular seed crops for a specified explanting zone.
Managed seed production is the most-economical way to deliver improved seed formost species. However, differences in flowering performance among trees andcontamination by outside pollen can reduce genetic gain from seed orchards.Research into flowering physiology, pollen dynamics, seedling adaptability,insects and diseases is leading to new practices to induce and manage seed cropsin current orchards on a regular schedule. Designs for more cost-effectiveorchards are being refined.
Seed-production planning in British Columbia is based on 24 seed-planning zones.Zonal boundaries are based on ecological information and, where possible, onlong-term field testing of many seed sources. Within each zone, long-term seedrequirements are determined for each species and evaluated to plan and establishdelivery systems.
Current seed orchards include the 10 species listed above. As well, rootedcuttings are produced for yellow cypress and some hybrid and native cottonwood.
The many components of the tree improvement system are dependent on research.Studies are directed at solving problems to increase the efficiency, quality andcost effectiveness of all phases of tree-improvement programs, and of theconsequences of planting improved seedlings. Furthermore, provenance studies (toassess geographic variability in performance) are conducted on species not yet inimprovement programs. Such work makes definition of seed zones possible, which isvital when planning reforestation programs. Studies are conducted by scientistsfrom the B.C. Forest Service, the Canadian Forest Service, Forintek Canada, B.C.Research Corp., universities and private companies.
A government-industry tree improvement program for coastal B.C. was establishedin 1979 under the direction of the Coastal Tree Improvement Council. A similarprogram began for interior forests in 1981 with the formation of the InteriorTree Improvement Council. The role of the Councils is to provide recommendationsto the Chief Forester to:
The primary goal is the annual production by the year 2000 of seeds to produce 34million genetically improved trees for the coast and 91 million for the interior.
Membership in the Councils includes the Ministry of Forests (B.C. ForestService), industrial cooperators, and the Canadian Forest Service, all of whomare involved actively in tree improvement. Additional participants includeForintek Canada, B.C. Research Corporation and the University of BritishColumbia.
Rapid advances have been made in biotechnology research with conifers. Whilebiotechnology will not replace traditional breeding methods, it offersincreasingly valuable tools to enhance breeding and delivery of genetic gain.Work is in progress to locate genes responsible for features of tree performance,such as disease or insect resistance, toward the chance of transferring them toour trees via biotechnology.
Forty years of effort in tree improvement have taught us the importance ofdelivering genetically improved plants as rapidly and consistently as possible.Research is focussing on ways to reduce the time between tree selection and seedproduction, and on ways to protect trees, cones and seeds from damaging agents,such as adverse weather, insects and diseases. Early results show promise ofmajor gains. Improved techniques will enable orchard managers to "tailor make"seedlots for specific planting sites and to capitalise on the latest selections.
Tree Improvement, Gene Conservation and Genetic Variability
Maintenance of high genetic variation in each of our forest trees species isimportant because genes represent the raw material for present and future trees.Climates surely will change in the future, as they have in the past, and highgenetic diversity is the surest way for future generations of trees toaccommodate that change.
Somatic cultures of white spruce can be generatedfrom seed embryos. The resulting in vitro culture will proliferate rapidly and spontaneously to producelarge numbers of early embryos or 'proembryos" per seed. By manipulating thehormonal balance in the medium, the proembryos will develop into mature embryos,which will 'germinate' and produce seedlings.
Genetic resources of our forest trees are being maintained in a variety of ways.For 23 tree species, surveys have been conducted to confirm that each species isrepresented by substantial numbers of trees in protected forests, such as parks.As well, thousands of individual genotypes from our native species have beenretained in genetic tests and gene archives at Provincial Research Stations.
Tree Improvement and Genetic Diversity
One result of tree-improvement programs will be a shift in gene frequencies inplantations compared to natural stands. The greatest immediate change will be abroadened gene pool from seed orchard crops, since mating in the orchards occursamong seed parents spaced too far apart in nature to cross pollinate.
By selecting the "best from the best" after breeding, genetic variation could bereduced strongly. Agricultural crops have very restricted genetic bases due totheir long history of selection, short rotations and the pressure to generateuniform crops. Forest crops, however, must remain genetically broad to withstandthe vagaries of nature during their long life span. Therefore, breeders designmating schemes to maintain genetic diversity while delivering acceptablelong-term gains.
Tree improvement in British Columbia entails the cooperative efforts of people from many disciplines. Their continued efforts will be necessary to advance toward our goal of increasing tree performance and value from a diverse land base providing a variety of social goals, while maintaining broad genetic diversity inour forests.
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