1988. In: Slaughter, Charles W.; Gasbarro, Tony, eds; Lawson,
Teri, tech. ed. Proceedings.of the Alaska forest soil productivity
orkshop:
1987 April 28 -30; Anchorage, AK. Gen. Tech. Rep.
PNW-GTR-219. Portland, OR: U.S. Department of Agriculture,
Forest Service,
Pacific Northwest Research Station·, Fairbanks '
.
AK: School of Agriculture and Land Resources Management, University
of Alaska-Fairbanks.
INTEGRATING SILVICULTURE AND
GENETICS IN SOUTHEAST ALASKA
Roy Silen
Growing seasons are often truncated by
the high average elevation and in
mid-latitudes by seasonal drought.
The
strong relationship between effective
growing season and inherent growth rate
seen in farm crops has been investigated
for Do uglas-fir using growth data from
the huge genetic testing program in the
Pacific Northwest, which regularly
measures 3 million progeny. rnstances of
a virtually template-like correspondence
ABSTRACT: Southeast Alaska is surprisingly
productive for its latitude.
!ts
climate is mild for its northerly
Unlike most of western North
location.
America it has ample summer rains and
very long days.
Also, its two major
species, Sitka spruce end !!astern
hemlock, are already the.world's tallest
in each genera.
This high productivity
plus almost unfailing dense repro­
duction needs ·a special
silvicultural/genetics approach to
intensive forest management.
between local topographic features and
inherent growth rate are seen in many
examples where genetic variation has
been mapped.
Local stands are found to
have genetic structure in the sense that
their normal frequency distributions of
The environment of western North America
is far more complex than that of eastern
North America where most forest genetics
theory originated.
Environmental
As large a
gradients are often steep.
change in growing season occurs across
small areas like the Olympic Mountains
as in all eastern United States.
.
family growth rates center over the
expected mean for their position along
environmental gradients of cold or
drought.
Thus, whenever environmental
gradients are steep, such as in steep
topography or on opposite faces of major
ridges, two populations only a few miles
apart can be genetically quite
different.
Still, nearly all local
populations embrace enough inherent
growth variation to amply serve as
parentage for present tree improvement
programs.
ROY SILEN is a geneticist at the Pacific
Northwest Research Station, USDA, Forest
Service, Corvallis, Oreg.
REPRODUCED BY USDA FOREST SERVICE FOR OFFICIAL USE . 103
The suggested strategy to integrate
silviculture and genetics for most of
western North America involves first an
appraisal of how much yield improvement
is practical with fertilizer and pest or
weed control, the two widely available
techniques for site enhancement.
Then
forest geneticists should breed for
corresponding growth rate improvements
(10-50%) stand by stand. Because stands
already have genetic variation of 10 to
50 percent above their mean, there is
little point to incur the risk of
destroying local stand genetic structure
which is valuable for its buffering
against multitudinal environmental
risks.
A plan for producing essentially
local improved seed from a clinally
arranged seed orchard is already under
development in Oregon.
Agronomy and plant breeding are now
highly integrated in agriculture by a
yield strategy of simply packing more
plants per unit area.
The strategy
recognizes that yield improvement de­
pends not on growth rate alone, but upon
three other factors--harvest index,
timing of maturation, and breaking
growth contraints with agronomic
techniques ( fertilizer, irrigation, weed
and pest control ) .
Agronomic
techniques, not genetics, appear
involved in improved biomass"production.
For a crop like corn, it is agronomy
that amplified photosynthate yields-­
genetics is used to assure correct
maturation and to stiffen and shorten
the stem, provide more upright leaves
and smaller roots for closer packing of
plants.
Without agronomic improvement
of the site, the original agricultural
land races often do as well as or better
than genetically improved ones.
I
\
For southeastern Alaska, where 90+
percent of cutovers densely restock
naturally, the suggested strategy is
even simpler.
For those sites where
fertilizer and weed control can
economically amplify biomass production,
a high genetic-selection differential is
potentially possible as stands are
reduced by thinnings from about 5,000
seedlings to about 100 mature stems pe r
acre at rotation.
A land race of appro­
priately faster inherent growth rate
should then develop that is as adapted
as the native population.
The immediate
need is for research to identify and
quantify potential levels of biomass
enhancement, and to provide guidelines
for thinning that will accomplish
effective genetic selection.
Worldwide, forest genetics still
assumes, possibly erroneously, that
breeding for faster growth rates will
provide amplified yields.
Assuredly,
faster growing varieties could shorten
the part of the rotation from planting
until stand closure and between each
thinning with more rapid crown closure.
But if site cannot be improved with
seed, as agricultural breeding
demonstrates, true yield amplification
must involve a strategy that recognizes
all four components of yield.
The key
is to use silviculture to enhance
biomass, and forest genetics to match
such enhancement with an appropriate
growth rate.
Unfortunately, the
constraints of cold and drought in
western North America limit potential
gains in biomass to perhaps 10 to 50
percent, since these particular constraints are hard to alleviate. !
·I
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104