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THE IMPACT OF GENETICS ON FOREST PRODUCTIVIY
Robert J. Weir
Director, N.C. State University - Industry
Cooperative Tree Improvement Program
(From Alabama's TREASURED Forests; Spring 1996; p19-21)
Establishing a pine plantation is hard work and it is expensive.
The cost of the seedlings planted is only a small part of
the total, yet a poor choice of planting stock can frequently
reduce the productivity and value of the resulting plantation
and in extreme cases, cause outright failure (Lantz and
Kraus 1987). Conversely investing in the best available
genetic material can provide the opportunity to grow much
greater wood volume and value per acre. Good genetics is
a corner stone of the foundation on which improved plantation
productivity is constructed.
Genetics improvement of pines began in the southern region
of the United States in the early 1950's. Forward thinking
leaders of major forest products companies initiated genetics
research and development coincidental with the rapid expansion
of tree planting programs. To insure a continuous supply
of low cost raw material for the large pulp and paper mills
in the region, these leaders reasoned that they must replant
the thousands of acres of timber harvested each year with
seedlings that have the genetic potential to grow rapidly,
resist disease infection and produce desirable wood. Now
more than 1.5 million acres are planted in the southern
U.S. each year and all of these acres are planted with genetically
improved tree seedlings. The very first plantation established
with genetically improved seedings in the 1960's are now
being harvested. The promise of increased yield and higher
value per acre is being realized.
The development of genetic improvement in the southern
region has largely been accomplished through the efforts
of three major tree improvement cooperatives. These organizations
are a partnership among universities, forest industry and
government agencies. Three cooperative tree improvement
programs impact the southern region and the State of Mississippi.
The Western Gulf Tree Improvement Cooperative works on the
genetic improvement of both loblolly and slash pines. This
program is run by the Texas Forest Service, and works in
close collaboration with scientists at Texas A & M University.
The Cooperative Forest Genetics Research Program, at the
University of Florida, has a primary focus on the improvement
of slash pine. The N.C. State University - Industry Cooperative
Tree Improvement Program is the largest of the three cooperatives,
and works primarily on the genetic improvement of loblolly
pine. Members of each cooperative provide support for a
scientific/technical staff; they breed, test, and select
superior trees; develop seed orchards for the production
of genetically improved seed; and support research focused
on improving the efficiency and benefit to be derived from
future genetic improvement work.
The first level of genetic control is to plant the species
that survives and grows best, given the soils, rainfall,
temperatures and general climate in your area. In the 1950's
nearly 80% of all tree planting in the south was with slash
pine. The early fast growth of slash pine on a wide variety
of sites, along with nearly total resistance to attack from
the pine tipmoth, resulted in this species being planted
in many areas where loblolly eventually proved to be a better
choice. Today loblolly is planted on 80% of the acres reforested
(Todd, et al. 1995) and slash pine planting is properly
restricted to the wetter "flatwoods" sites in
the lower costal plain that commonly have a sandy topsoil
over a poorly drained clay subsoil. Loblolly is best suited
to the better drained soils in the upper coastal plain and
Piedmont, however it does not survive or grow well on very
dry, deep sands. Experience has also led to the conclusion
that slash pine planted in the interior regions of the south
will too often suffer severe damage from cold, ice and snow
storms.
Choosing the correct seed source within a species is absolutely
critical to the success of pine plantations. Slash pine
has very little seed source variation and most any commonly
produced source of seed is acceptable in any part of the
region where slash pine should be planted. In contrast,
loblolly pine has a very wide natural range, extending from
Delaware to southeast Texas. Eastern coastal sources of
loblolly pine, when moved into Mississippi are usually faster
growing yet can be more susceptible to fusiform rust and
have lower wood density than sources taken from west of
the Mississippi River. Western sources of loblolly may exhibit
more drought resistance (Wells 1985). Generally southern
sources of loblolly pine will grow faster than northern
sources, however care must be taken not to move southern
material too far north or cold, ice and snow will cause
major losses. Moving seed sources northward from areas with
minimum average temperatures that are 5 degrees (F) warmer
than the planting site, will give maximum growth gain over
local sources (Schmidtling 1992). Seedlings grown from the
Livingston parish, Louisiana seed source have exhibited
excellent growth rates and strong resistance to fusiform
rust when planted over much of the lower gulf coast and
south Atlantic coastal areas. Again care must be taken not
to move this source too far north.
Genetic improvement of loblolly pine has brought additional
gains in volume and value over and above those achieved
from use of appropriate wild seed sources. first-cycle seed
orchards have produced seed, that when planted in bulk mixture,
grow plantations with 8 to 12 percent more volume per acre
at harvest (age 25 to 28, depending on site quality) than
the trees grown from wild seed (Talbert et al. 1985). The
value of genetic based quality improvements (stern straightness,
disease resistance, and wood density) are more difficult
to assess, but are believed to be at least equal in value
to the improvement in growth rate. Second-cycle seed orchards
are now producing as much as 50% of the total seed harvest
in the region and these orchards are projected to add an
additional 4 to 8 percent improvement above the gains from
the initial seed orchards established in the early 1960's.
Harvest yields from second-cycle seed orchard bulk seed
mixes, the best wind pollinated families, the best specific
crosses, and the best clone selected from the best cross,
were derived from the reports of Todd et al. (1995) and
Frampton and Huber (1995) and are depicted in Figure 1,
in terms of cunits (1 cunit equals 100 cu. ft. of solid
wood) per acre. Second-cycle seed orchard mixes are projected
to produce 29 cunits per acre at harvest which is 16 percent
more wood per acre than would be expected from plantations
grown from wild seed. With increased seed orchard production,
it will be possible to plant seeds from the best wind pollinated
families and the yields from such a family block planting
system are projected to approach 32 cunits per acre. Developmental
work is underway to optimize the techniques needed to mass
produce the best specific crosses from parents in second-cycle
seed orchards. If this technique were operational today,
it is projected that yields could be as high as 36 cunits
per acre. Longer term research is focused on developing
vegetative propagation methods for the mass production of
the best individual tree in the best cross which might yield
as much as 40 cunits of wood per acre at harvest.
Figure 1. Loblolly pine plantation harvest yields expected
from several genetic improvement alternatives.
The marginal cost of developing a tree improvement program
for those organizations planting at least 10,000 acres per
year is approximately $8 per acre of plantation established.
This is true for seed produced as a seed orchard mix and
for those planting seed from the best wind pollinated mother
trees (a family block deployment system). The value return
in today's dollars for the $8 invested will range from $100
dollars per acre to as much as $300 per acre, depending
on the level of genetic improvement used. Land owners reforesting
limited acreage are not justified in developing their own
tree improvement program. However, all southern states and
many industries produce genetically improved seedlings for
sale to the public. When you buy seedlings grown from seed
produced in seed orchards developed from the best available
breeding stock, the $8 per acre is part of your seeding
costs and depending on the level of genetic development,
the benefits depicted in Figure 1 should also be realized.
The cost of more advanced technologies such as mass production
of the best 3 crosses, or vegetative propagation of the
best clone in the best cross are unknown. The technology
for these systems is still being developed as refined through
research. Yet the projected increases in yield are substantial
and they are expected to offset the costs encountered. Clearly
genetic improvement can be a very worthwhile investment.
Cultural treatments can provide yield increases comparable
to or greater than those realized from genetic improvement.
Response to intensive site preparation, fertilization, and
weed control have been well documented (Allen et al. 1990).
However, to realize the full benefit from investment in
cultural practices such as mechanical site preparation,
fertilization and weed control, one must also plant the
highest quality genetic stock. Figure 2 depicts the yield
response to intensive cultural treatments for families with
high, average, and low breeding values. The high breeding
value family is projected to have a 7.1 cunit response (age
8 volume) to cultural treatments, while the average and
low breeding value families are respectively projected to
have a 5.4 cunit and 3.6 cunit response. Clearly to get
the most from investments in stand culture, it must be coupled
with good genetics. Good genetics and good silviculture
must go together.
Figure 2. Volume growth response with intensive site preparation,
fertilizer, and herbicide treatment for low, average and
hight breeding value families.
A substantial investment by the forest science community
is being made in forest bio-technology research, in addition
to the ongoing research aimed at improving the efficiency
of traditional tree improvement, mass production of outstanding
specific crosses, and vegetative propagation. Biotechnology
research involves basic science investigation at the molecular
genetics level and may well revolutionize genetic improvement
in the years and decades ahead. Already substantial progress
is being made in describing the underlying genetic control
of economically important traits. Regions of loblolly pine
DNA have been mapped and a marker for a single gene having
major control of fusiform rust resistance has been identified
(Wilcox 1995). Work is underway to locate additional resistance
genes and to understand the frequency of these genes in
pine breeding populations. Across the nation various research
laboratories are working on lignin and cellulose production
pathways, molecular control of growth rate, water stress,
herbicide tolerance, reproductive sterility, etc. Understanding
the genetic control of economically important traits at
the molecular level can have several benefits. Initially
it may change the way tree breeders design and develop their
breeding programs. Subsequently it may be possible to develop
alternative and improved selection methods where it would
be possible to select trees in the laboratory based on their
DNA configuration rather than in long term field tests.
Such systems can only be developed if we have a greatly
improved understanding of the genetic control mechanisms
for tree growth, wood formation and disease infection.
The ultimate system would involve developing cell cultures
from pine trees into which important genes could be inserted,
and these altered cells would then be manipulated so as
to grow many thousands of tree seedlings, all having an
"engineered" change in their genetic makeup. Genetic
engineering is certainly a powerful tool that may someday
be used to make important and valuable changes in our southern
pines, yet substantial barriers exist that prevent the implementation
of this technology today. The potential for desirable change
is great, yet it may well be a long time before this technology
makes a difference in the trees we grow and how we grow
them.
Literature Cited
Allen, H.L., P.M. Dougherty, and R.G. Campbell. 1990. Manipulation
of water and nutrients - practice and opportunity in southern
U.S. pine forests. Forest Ecology and Management 30:437-453.
Frampton, L.J., Jr. and D.A. Huber. 1995. Clonal Variation
in four-year-old loblolly pine in coastal North Carolina.
Proceedings of the 23rd So. Forest Tree Improvement Conf.:
254-284.
Lantz, C.W. and J.F. Kraus. 1987. A guide to southern pine
seed sources. General Technical Report SE-43. Southeastern
Forest Exp. Station, USDA - Forest Service Asheville, N.C.
34 pp.
McKeand, S.E., R.P. Crook, and H.L. Allen, 1995. Genotype
by environment interaction effects on predicted family responses
to silvicultural treatments in loblolly pine. (Submitted
to Southern Journal of Applied Forestry, September 1995).
Schmidtling, R.C. 1992. A minimum temperature model for
describing racial variation in loblolly pine provenance
tests. North American Forest Biology Workshop, August 1992.
Sault Ste. Marie, Canada.
Talbert, J.T., R. J. Weir and R.D. Arnold. 1985. Costs
and benefits of a mature first-generation loblolly pine
tree improvement program. Journal of Forestry 83(3):162-166.
Todd, D., J. Pait and J. Hodges. 1995. The impact and value
of tree improvement in the south. Proceedings of the 23rd
So. Forest Tree Improvement Conf.: 7-15.
Wells, O.O. 1985. Use of Livingston Parish, Louisiana loblolly
pine by forest products industries in the Southeast. Southern
Journal Applied Forestry 9(3): 180-185.
Wilcox, P.L. 1995. Use of DNA markers for the genetic dissection
of breeding of fusiform rust resistance in loblolly pine.
Ph.D. Thesis, North Carolina State University, Raleigh,
N.C. 125 pp.
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