Download Forest Genetics and Productivity: The Role of Seed Source Control

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.