In: New forests for a changing world;
1983 October 16-20; Portland, OR.
Bethesda,
MD:
Society of American
Foresters; 1983:
TRENDS IN STAND MANAGEMENT PRACTICES FOR U.S.
1
D. S. DeBell ,
W.
Research Foresters,
2
Harms ,
R.
1
WA , Charleston,
ABSTRACT
southern pine,
and Douglas­
Silvicultural
activities attained greater importance in
many forest management organizations during
the past 10-15 years;
growing-stock control
and fertilizer application have become
common practices in some forest types.
the future,
In
prescriptions for stand
management practices will become more
wood quality and nontimber resources.
Practices appropriate for
new forests will vary greatly by forest type
As it is not possible to
cover all forest types in this presentation,
we will approach the topic by discussing
current management practices in:
hardwood forests of the Northeast,
(1)
mixed
(2)
pine
and (3) Douglas-fir
forests of the Pacific Northwest.
These
forests were selected for illustration
because they have wide geographic
distribution and they provide examples of
progressive practices in the re pective
Next,
we will examine some recent
trends and advances in silviculture and
identify some of the factors associated with
such changes,
Finally,
PA
3
shade tolerance.
They occur in both
uneven-aged stands,
which developed
following selective removal of the larger,
more valuable trees in the past;
and in
even-aged stands which originated following
clearcutting for fuel,
timbers,
and pulpwood,
charcoal wood,
mine
Existing stands
commonly contain a high proportion of
poor-quality stems and cull trees.
There
scarce,
high-quality sawtimber or veneer
logs and material suitable only for pulp,
and low-grade sawlogs.
material from the large areas of unmanaged
applied between stand establishment and
regions.
sc2, Warren,
particle board,
Our topic concerns management practices
forests of the South,
Forestry Sciences Laboratories,
There is an excess supply of low-quality
INTRODUCTION
and ownership.
1
and R. o. c urt . s
are great differences in value between the
site-specific and more concerned with both
final harvest,
3
Marqu . s ,
FORESTS
Species differ markedly in growth rate and
Current stand management practices in
fir forests are described.
A.
USDA Forest Service,
Olympia,
mixed hardwood,
D.
47-51.
we will discuss our
perceptions of apparent future directions
and also mention some considerations that we
think will be important in selecting
management regimes for the forest stands of
tomorrow.
second-growth forest.
Planned management is
limited primarily to public and industrial
ownerships,
and stands are usually managed
by some form of even-aged silviculture,
Management is not intensive,
and cultural
measures are aimed primarily at increasing
the proportion of quality sawtimber and
veneer.
New stands in the mixed hardwood forests
are regenerated naturally from seed,
seedlings and seedling sprouts,
from cut stumps.
advance
and sprouts
Young stand densities of
many thousand trees per acre are common.
Hardwood stands seldom stagnate,
and initial
high density encourages a dominant leader
and rapid natural pruning.
therefore,
Stands are,
generally left to develop at high
density until commercial thinning becomes
feasible--at least 25 years and often 50 to
60 years.
Once merchantable size is reached,
commercial thinning is used to reduce stand
density and modify stand structure and
CURRENT PRACTICES
Mixed Hardwood Forests of the Northeast
The northeastern hardwoods form a
complex forest in which many stands consist
species composition.
Thinning may be
repeated at 10- to 20-year intervals until
final harvest.
Stocking guides that relate
stand density to average maximum basal area
of undisturbed stands of similar species and
diameter are often used to control thinning.
of mixtures of several commercial species.
47
Cull trees ar: usually killed by girdling
or by applying he= icides to individual trees
Early thinning
following commer :al sales.
of hardwood stan:s is sometimes done precom­
Cleanings and
mercially by si :ar means.
precommercial thi
ing in very young stands
and other cultura: practices, such as broad­
scale vegetation control and fertilization,
are rarely used ': present.
regeneration is
Because natural
d almost exclusively,
selective remova: of poor trees is the
principal means c: genetic improvement.
merchantable sizes.
Six- to 12-foot wide
strips are cut with a rotary brush cutter or
drum chopper making the leave strips as
narrow as possible.
Stocking control in
plantations is achieved at establishment.
Seedlings are spaced at 6- x 10-feet or at
some other combination that provides about
60 square feet of growing space per tree.
Thinning is a standard practice on
National Forests and some other ownerships
under natural stand management.
Rotation leng:hs for hardwood forests
vary from 40 or Sj years for short-lived
species to as muc as 150 years for sugar
Trees are
removed from the lower crown classes at
about 10-year intervals to maintain growth
rates and develop large,
high-quality stems
at a rotation age of 50-60 years.
Residual
maple and beech.
Rotations also vary with
ownership objecti7es, but 80- to 100-year
basal areas vary from 70 to 100 square feet,
rotations are comnon.
seldom used in pulpwood rotations of 20-25
increase total wood yields.
cially in the shade­
tolerant norther.: hardwoods.
Partial cuts
remove trees throaghout the merchantable
size classes,
bu
larger trees.
S
tend to remove mostly the
h cuts may be repeated
indefinitely at 10- to 30-year intervals.
Stand improvement operations to remove culls
and unmerchantable trees are often included.
third-growth stands.
Most
ownerships are of natural origin.
Forests
owned by industry are established almost
By the end of this
essentially all industry land will
be converted to ?lantations of genetically
improved seedlings as will many of the sites
on National Forests in the South.
are serious problems on many sites.
Some
type of vegetation control is commonly
needed throughout the rotation in both
Within 2 to
5 years following establishment of the
stand,
it is often necessary to release
seedlings from o·1ertopping herbaceous and
sprouting hardwood vegetation.
This is done
with herbicides, either by broadcast or
individual stem treatment.
rotation,
Later in the
prescribed fire used at 5- to
7-year intervals is the common control
method.
Fire also eliminates fuel buildup
and reduces the risk of destructive wildfire.
In overstocked natural stands,
precom­
mercial thinning is done early (ideally at
about age 3) to reduce the number of stems
to 500 to 750 trees per acre and thereby
accelerate the growth of trees to
48
rotation aimed at producing sawlogs.
thinning,
Row
individual tree thinning, or a
combination of the two are the most common
methods.
Row thinning with selection
generally removes rows or corridors at
and uncut rows are
Addition of phosphorus and nitrogen
fertilizers to pine sites deficient in these
nutrients has been a common cultural practice
in the Atlantic Coastal Plain since about
1969.
Phosphorus fertilization at time of
planting or soon after has become an
operational practice on large industrial
holdings and on National Forests.
Forty to
50 pounds of phosphorus per acre are
Hardwood co ?etition and encroachment
plantations and natural stands.
to as many as three thinnings in a 35-year
selectively thinned.
stands on public and small private
century,
ownership and objective and range from none
for feller-bunchers,
The southern pine forests are
entirely by planting.
Thinning
strategies in pine plantations vary by
predetermined intervals to provide access
Pine Fcrests of the South
second-growth a
Thinning is
years because it does not significantly
There is some use of uneven-aged
silviculture, es
depending on species and site.
applied; trees on poorly drained soils show
the greatest response to fertilizer.
Fertilization of established stands is
primarily with nitrogen in the Piedmont,
and
nitrogen plus phosphorus in the coastal
plain.
Response to nitrogen is generally
short term with greatest growth occurring
during the first 2 years following
application and at moderate stocking
levels.
Current application rates range
between 100 and 150 pounds nitrogen per acre
and 0 and SO pounds phosphorus per acre.
Coastal Douglas-Fir Forests of the Pacific Northwest Prior to the mid-1950's,
the prevailing
silvicultural system was clearcutting with
natural regeneration, and there are now many
young-growth stands of natural origi.n.
Some
direct seeding was done in the 1950's and
early 1960's ,
but planting has been the most
common practice for the past two decades,
to 300 p¢unds of nitrogen per acre.
Retreatnent is anticipated at 5- to 10-year
intervals.
Species control problems in Douglas-fir
Poor sites respond more than
good sites.
On an individual stand basis,
forests differ from those in the East and
econ02ic gains are probably highest when
South in that they are confined primarily to
fertilizer is applied 5 to 10 years before a
the early years of stand development.
Only
co
ercial thinning or final harvest,
rather
a few hardwood tree species (mainly red
than carrying costs for a longer period.
alder) invade regenerating areas,
Because of the recession, there has been a
and none
become established beneath existing stands.
There are,
however,
many aggressive brush
species that can create serious competition
problems,
especially along the coast and in
southwestern Oregon.
Control is mainly by
slump in fertilizer application, w hich is a
postponable operation.
Other changes
include more site-specific prescriptions
based on soils and stocking level.
Managers
are shoving interest in and some are
aerially or hand-applied herbicides.
prescribing the retention of nitrogen-fixing
Opposition to herbicides has led to
species (e.g.,
increased emphasis on spot treatments and
plantations on some soils.
red alder) in Douglas-fir
ground applications (including some manual
control)
rather than relying primarily on
In the future,
broadcast spray treatments.
Anticipated rotation ages for Douglas­
fir vary from 40 to 50 years on some
the need for intensive brush control may be
industrial ownerships to more than 100 years
reduced because of improvements in site
on some National Forest sites.
preparation,
nursery stock,
and planting
practices,
ADVANCES AND TRENDS
Most planting is done at spacings of 8 x
We were asked to identify major advances
8 to 10 x 10 feet, but many plantations fill
in stand management practices.
in naturally with Douglas-fir and associated
been difficult because the basic practices
species.
Precommercial thinning is
and methods now used in stand culture have
generally needed to achieve desirable
been used,
growth,
decades.
especially on poor sites,
and is a
common practice on publicly owned lands and
major industrial ownerships.
Such thinning
This has
or envisioned,
for several
But there has been a great change
during the past lQ-15 years in the use of
known practices,
and there have been many
is best done when stands are 10-15 years old
refinements in actual prescriptions and
or 10-15 feet tall.
applications.
Most managers thin to
300 to 400 trees per acre, aiming at about a
9-inch tree at time of first commercial
thinning.
There is,
however,
increasing
The increased use of cultural practices
is related to several factors.
One is the
interest in wider spacings to avoid or delay
change in age structure of many forests.
the need for commercial thinning,
Much of the hardwood forest in the Northeast
was regenerated in the early decades of this
Many organizations anticipate two or
century and can now sustain commercial
more commercial thinnings during the
thinning.
rotation.
plantations established in the 1950's and
Timely thinning is especially
important on long rotations,
and may be
In the South,
large areas of
1960's are now overstocked and need to be
essential to capture maximum gains from tree
thinned.
improvement and fertilization programs.
growth has largely disappeared from private
Interest in commercial thinning has varied
lands, and there is need to accelerate
o ver the past decade.
This is due partly to
In the Pacific Northwest,
old
growth of young stands on all ownerships in
fluctuating markets for small logs; partly
order to avoid a sharp decline in future
to difficulties encountered in thinning
harvest levels.
small-diameter stands,
terrain,
particularly on steep
and partly to shortening of
Another factor associated with expanded
rotations and the realization that timely
management activity was a steady increase in
precommercial thinning can delay the need
timber values during the early and
for commercial thinning.
mid-1970's.
Little or no
commercial thinning is anticipated in stands
This was especially evident in
the Pacific Northwest export market.
on steep unstable slopes and easily
Development of the southern pine plywood
compacted soils.
industry placed new premiums on size and
stem quality.
Nitrogen fertilization has been widely
Increased stumpage returns
provided cash for investment in stand
applied on the larger industrial and public
management and a favorable outlook on future
ownerships in the past decade--usually by
profitability of such investments,
aerial application of urea at dosages of 150
49
In addition to changes in age st ructure
and increased stumpage returns,
good
regimes in coming yea rs.
Public land
managers particularly, and others to some
quantitative estimates of growth responses
degree,
to many cultural practices became
wildlife, watershed,
available.
In part this will be the result of increased
Realistic economic evaluations
became possible.
Stocking control was shown
to have major effects on volume and/or value
yields of many species.
A substantial data
will give increasing attention to
and aesthetic values.
knowledge and awareness,
and in part a
response to outside public and political
pressures.
base indicated widespread opportunities for
economic responses to fertilizer application
in the southern pine and Douglas-fir forests.
Increasing diversity in stand management
goals and a better understanding of site and
ecological differences will lead to a much
During the past 10-15 years,
marked
wider range of silvicultural options than
improvements have also been made in stand
are used today.
prescriptions and application of cultural
hardwood forests may be grown for conversion
measures.
Better management and decision­
making tools are available,
and foresters
In some areas,
to energy or chemical products.
coppiced
In regions
where nitrogen deficiencies limit growth,
have obtained more experience with the use
nitrogen-fixing species may be grown in
of these tools in many forest types.
mixture or in rotation with crop tree
Better
stocking guides provide generally applicable
species.
guidelines for control of density in
in management of tree species now considered
thinning.
Some fertilizer prescriptions now
include use of soil and foliar nutrient
levels,
stand characteristics,
and/or soil
Much greater interest will be seen
secondary.
Also,
cultural practices that
depart from the traditional pure even-aged
and all-aged systems may receive wider use,
groupings to preaict growth response.
especially in mixed hardwood stands and some
Greater use is being made of habitat-type,
western conifer types.
site,
and soil classification systems in
many kinds of silvicultural decisions.
We expect more site-specific
prescriptions for all of the above reasons
A major development of the past decade
and because we may not have the margin for
has been the improvement of computer-based
error provided by the high stumpage values
stand simulators and the increased
of the recent past.
accessibility of computers.
of site and ecological classifications will
The simulators
have now become practical tools for managers
and silviculturists.
Continued development
assist in silvicultural decision making.
They are being used
increasingly to evaluate alternative stand
treatments and to make other growth and
yield predictions.
Forests managed primarily for industrial
wood production will become more
homogeneous,
particularly with expansion of
pine plantations of genetically improved
Another very important trend has been in
the training and status of silviculturists.
Not long ago,
silviculture ranked far below
stock in the South and continued conversion
of much of the Douglas-fir forest to
plantations.
In the South,
particularly,
harvesting and fire control in the priorities
owners will be increasingly concerned with
of many forest management organizations:
tailoring stands for efficient mechanized
Not so today.
Part of this change is a
thinning and harvesting.
response to the controversy over clear­
cutting and public opposition to other
forest management practices,
Economic
The
changes also have had some influence.
increased importance of growth in relation
to standing inventory has enhanced the
position of silviculture within many organi­
zations.
The USDA Forest Service introduced
Along with these changes will come
further development of stand simulators,
improved economic analyses,
g uides.
and mana ement
These will be extended to secondary
species and a wider range of conditions.
Such tools will have general applicability
and will permit more objective analyses and
training and certification programs for the
prescriptions of silvicultural treatment for
agency's silviculturists, and a considerable
individual stands.
number of state, other public, and
industrial foresters have enrolled in and
benefitted from these programs.
FUTURE DIRECTIONS
Considerations other than wood
production will have increased influence on
silvicultural prescriptions and management
50
Future trends in rotation lengths and
regulation of stand density are far more
Obviously, the
difficult to predict.
inherent traits of species determine the
range of possible management regimes;
Douglas-fir,
for example,
has slow initial
growth as compared with many other species
(such as loblolly pine) but it also has a
much longer period of sustained growth in
value.
height and volume.
information about effects of pruning when
equal,
Other things being
rotations should be substantially
longer for Douglas-fir than loblolly pine.
Within the range of regimes which are
biologically reasonable,
management ideas
For example,
done in young,
there is little
rapidly growing Douglas-fir
stands.
4.
Site productivity is another
important consideration.
Logging damage,
appear to be changing for some forest
soil-borne diseases,
types.
erosion, and nutrient status can be affected
During the past decade interest has
soil compaction,
increased in sawlog regimes for southern
by decisions on stand treatments and
pines; such regimes involve somewhat longer
rotation length.
rotations and more thinnings than were
magnitude of these effects and their
envisioned for the plantations established
significance for long-term production.
We know little of the
15-30 years ago by the pulpwood industry.
In the Pacific Northwest,
the current trend
appears to be toward shorter rotations with
5.
Management regime,
rotation length,
especially
also has an effect on real
wider spacings and reduced emphasis on
and perceived conflicts with other forest
commercial thinning.
uses.
Much of the difficulty
The shorter the rotation,
the greater
in predicting future trends in .rotation
the proportion of the forest in highly
length and stand density is the result of
visible clearcuts.
our inability to predict some consequences
real and perceived conflicts with nontimber
of various management regimes.
uses and associated political and public
We recognize
that recent trends for southern pine and
Hence,
the greater the
relations problems.
Douglas-fir forests are based on much
thought and economic analyses by various
owners.
We also believe,
however,
that some
Decisions on rotation length and
treatment regimes have so far had relatively
important factors in such decisions cannot
minor effects on overall timber production
yet be evaluated adequately or considered in
and corporate or agency goals.
present economic analyses--because either
will change rapidly as the nation's forest
needed information is lacking or it is not
products industry becomes more dependent on
readily expressed in dollar values.
The
But this
timber from young managed stands.
Much
specific factors and their relative
better information will be needed to make
importance will vary among forest types, but
decisions that are biologically and
economically sound over the long term.
some examples for Douglas-fir include:
1.
SUMMARY
Stand growth patterns may vary
greatly with choice of management regime.
Current information suggests that the period
The last 10-15 years has been a period
of maximum growth may be lengthened with
of rapidly expanding use of cultural
commercial thinning; consequently,
practices.
culmination of mean annual increment will
activity was a response to a favorable
occur at a later age than in unthinned
economic situation in the early and
stands.
Moreover, most estimates of gains
from commercial thinning are based o n
Such increased management
mid-1970's and also to changes in age
structure of many fore ts.
experimental data from late thinning o f
older,
unmanaged stands.
I t seems likely
that the gains expected are lower than those
In the future,
prescriptions must become
more site and stand specific and the quality
that will be obtained in stands having early
of wood produced must become a more
stocking control,
practices.
important consideration.
fertilization, and other
Nontimber
resources will increasingly influence
management practices, especially on public
2.
Gains from tree improvement and
lands.
Management and decision-making tools
fertilization will also be affected by
will continue to improve and so will the
management regime.
capability and experience of foresters using
To achieve maximum
benefits from these "growth enhancement"
them.
practices,
application of cultural practices will be
growing-stock levels must be
controlled throughout the rotation.
Gains
The impact of the greatly expanded
felt to,a much greater degree in the mills
Will probably be greatest in stands
and market place, and our silvicultural
maintained at some intermediate density that
knowledge and decisions will have increasing
allows room for continued crown expansion
influence on the economy.
without substantial unoccupied growing space.
3.
For Douglas-fir and many species,
there is inadequate information on effects
of management regimes on wood quality and
51