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FOREST GENETICS AND PRODUCTIVITY: THE ROLE OF SEED SOURCE CONTROL Rick Klevorn1 ABSTRACT.—The application of forest genetics in Minnesota is focused on the production of genetically improved seed. When the deployment of improved seed is not possible or desirable, it is important to deploy the most appropriate material. Research suggests reduced productivity from seedlings not adapted to the environment where they are planted. Jeffers and Jensen (1980) found significant differences in height growth among seed sources from several geographic sources in tests of jack pine (Pinus banksiana). Bresnan, Rink, Diebel, and Geyer (1994) found significant differences in height growth and survival among geographic sources of black walnut (Juglans nigra). These studies and others emphasize the importance of returning seedlings to their geographic origin. Natural selection favors tree genotypes best suited for a given environment. Seed source control captures environmental adaptation resulting from natural selection. Production losses and seedling mortality are reduced by deploying seedlings adapted to the environment where they will be planted. Minnesota has been divided into six zones based on prevailing climatic conditions. The Minnesota State Forest Nursery Program (SFNP) procures seed and deploys seedlings, cuttings and transplants based on these zones. SFNP seed source control guidelines cover all operational stages including seed procurement, nursery production and seedling deployment. As fiber production land base shrinks and per capita fiber consumption swells, natural resource managers must use all available tools to increase fiber production. Of the tools available, one most overlooked is seed source control. Seed source control is the operational process of returning reproductive materials—seeds, seedlings, cuttings, or transplants— to an environment that closely resembles the ones from which they originated. Although many forest genetics programs focus on the production of genetically improved seed, seed source control is a direct application of population genetics and should be the foundation of any tree improvement program. Where seed production results in genetic gain, seed source control prevents production losses by avoiding the use of nonadapted materials in artificial regeneration. Zobel and Talbert (1984), in Applied Forest Tree Improvement, view seed source control this way: “No matter how sophisticated the breeding techniques, the largest, cheapest and fastest 1 Tree Improvement Specialist, Minnesota Department of Natural Resources, State Forest Nursery Program, General Andrews Nursery, Willow River, MN, 55795. gains in most forest tree improvement programs can be made by assuring the proper use of species and seed source within species.” Phenotypic Model When we look at a tree, we are looking at the tree phenotype. However, phenotype goes further than what a tree looks like—phenotype includes everything we can observe about a tree. Height, caliper, and branch angle are obvious characteristics of phenotype. Fiber length is an obvious characteristic but we may not see it. Disease resistance, drought hardiness and timing of bud break and bud set, although not always obvious, are also characteristics of phenotype. Phenotype is a result, or product, of genotype and environment, and is illustrated in a simple model: Phenotype = Genotype + Environment All characteristics of phenotype are expressions of genotype. A genotype is a collection of genes. Genes are the biological instructions for the development of all characteristics of phenotype. No two genotypes are exactly alike. The expression of genotype varies depending on the environment. Environment is where the tree is; the soil, the climate, the position of the tree in the stand. No two environments, although possibly very similar, are exactly alike. Environmental effect on phenotype is cumulative. In other words, phenotype results from all the environmental conditions and events over the life of the tree. For example, a dominant tree and a suppressed tree may have the same genetic value for height growth, but the suppressed tree may have been damaged during planting, resulting in slower growth. A tree is the result of its genotype and all the environmental conditions it has experienced. Adaptation Trees may be exposed to large variation in climatic conditions which may be damaging. Extreme record cold temperatures seem to occur every few years. Drought years, although infrequent, can be successive and, depending on drought severity, rewatered trees may or may not return to normal. Cold hardiness and drought resistance are only a few characteristics necessary for growth and survival. It is important that trees are equipped to survive and grow in a range of environments because trees are long lived and may be exposed to environmental extremes. Trees that can survive and grow to reproductive maturity in a range of environments are adapted. Adaptation is the adjustment of an organism to an environment. Adaptation characteristics are part of phenotype; phenotype is a product of a tree’s genotype and its environment. Selection No two trees are exactly alike. In fact, all trees are different because they all are the result of different genotypes and different environments. Characteristics that are part of adaptation also are different from tree to tree. Some trees are better adapted than others. Trees that are not adapted will exhibit poor growth and in some cases will not survive. Adapted trees have been selected. Selection is the choosing of individuals (including their genes), with desirable characteristics. Nonadapted trees (and their genes) are selected against and are removed from the population. Parents pass their genes on to their progeny during reproduction. This is why progenies resemble their parents. It is not an exact resemblance. There is more resemblance in some characteristics than in others. Selected parents can pass on adaption to their progeny. Trees that are not adapted do not reach reproductive maturity and do not pass their genes on to the next generation. Seed Source Control Regeneration success is measured by the number of trees that survive and grow to rotation age. To insure maximum survival and growth the best suited seed (for broadcast) or seedlings must be used. Seed source control satisfies this requirement by returning reproductive materials to an environment that closely resembles the one from which they originated. Seeds are collected from healthy, mature trees. This captures adaptation characteristics for the environment from which the tree is located. The seeds are kept separate and labeled to reflect their origin. After the seeds are sown in the nursery, the nursery bed is monumented to identify the material by seed source. The seedlings are lifted and packed into shipping containers labeled with the seed source. The source identified seedlings are deployed as closely as possible to the regeneration site. Materials determined inappropriate are not deployed. Studies have measured the impact of seed source on seedling survival and growth. Bresnan, Rink, Diebel, and Geyer (1994) tested 66 black walnut (Juglans nigra) sources at seven test plantations. Twenty-two years after planting, survival, height and diameter at breast height (dbh) were measured on all trees. Local sources (within 100 miles) showed average or above average growth at all plantations. This study concluded black walnut seed source selection can effectively increase survival and height growth. Jeffers and Jensen (1980) tested 26 sources of jack pine (Pinus banksiana) on 14 test sites. Height and dbh were measured 20 years after planting. This test revealed trees from the local source (within 50 miles) at each test site exceeded the average plantation tree height by 2 to 19% at all test locations. Survival was related to similarity between climate and length of growing season at the seed origin and the plantation location. It is tempting to label increased performance as gain when comparing local sources with nonlocal sources. While the performance of local sources is better than nonlocal sources, this does not mean that using local sources results in gain in productivity. It means that using nonlocal sources results in a loss in productivity. Seed source control must be high priority in regeneration projects. The Minnesota SFNP is committed to deploying the most appropriate species and seed source for all planting objectives. Seed source control in Minnesota is based on six seed zones, organized by prevailing climatic conditions. These zones have been defined using several seed collection guides, such as Department of Agriculture Plant Hardiness Zone Maps, and climate data from the National Oceanic and Atmospheric Administration. Environmental conditions such as soil type are met by deploying the most appropriate species for a site. For example, jack pine would not be prescribed for planting on wet, organic soils. Seed source information is further recorded using Division of Forestry administrative area boundaries. Material is deployed as closely as possible. Every effort is made to deploy the best source within a species for the environment in which the trees will be planted. Seed source control is key to maximizing productivity. References Bresnan, D. F., G. Rink, K. E. Diebel, and W. A. Geyer. 1994. Black walnut provenance performance in seven 22-year-old plantations. Silvae Genetica 43:246-252 Jeffers, R. M., and R. A. Jensen. 1980. Twenty-year results of the Lake States jack pine seed source study. USDA For. Serv. Res. Pap. NC-181. 20 p. Zobel, B., and J. Talbert. 1984. Applied Forest Tree Improvement. John Wiley & Sons.