Mention oak trees and people may think of their lobed leaves, acorns, durable wood and long life. Th

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Mention oak trees and people may think of their
lobed leaves, acorns, durable wood and long life.
These majestic members of our hardwood forests
are an extremely valuable asset, but high quality
oaks are declining in numbers. Plant succession
and past timber harvesting practices have favored
regeneration of other tree species rather than
oaks. This program describes how to increase the
number of oaks and maintain fast tree growth when
managing hardwood stands that have a mixture of
tree species.
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Management recommendations are based on
experiences in Minnesota, Wisconsin and Iowa.
But, woodland conditions can vary widely. Always
contact a forester to inspect your woodland and
provide management suggestions before
implementing any woodland management practices.
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Oaks are useful for a wide variety of wood
products. Tree value depends largely on the
quality and size of a tree. Trees with large
diameter, high quality logs may be suitable for
flooring or for veneer used in wall paneling,
doors and furniture.
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Trees that are sound but have knots, cracks or
other defects, may be suitable for lumber,
dimension stock or railroad ties.
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Recently, small diameter, but good quality oaks
have been used to produce shiitake mushrooms.
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Poor quality trees, branches, and logging residue
make excellent firewood.
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Oak woodlands also provide habitat and acorns--an
extremely valuable food--for turkeys,
white-tailed deer, squirrels, ruffed grouse and a
host of other animals.
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Oaks and other trees often grow on slopes too
steep to farm. This woodland absorbs chemicals
and silt that wash off agricultural fields, thus
protecting water quality.
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Forests, croplands and pastures create an
attractive landscape appreciated by residents and
visitors. Forest management is necessary to
satisfy the many demands for wood, wildlife,
water, and recreation.
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There are really six oak species in this area.
The red oak group, characterized by pointed lobes
on their leaves, includes northern red oak, black
oak and northern pin oak.
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The white oak group, with rounded lobes on their
leaves, includes bur oak, white oak and swamp
white oak.
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The natural ranges of all these species overlap
but are not identical. Their site requirements
also differ. Northern red oak and white oak
prefer moist, fertile sites. Black oak and
northern pin oak tolerate drier sites. Bur oak is
the most drought tolerant. Swamp white oak
prefers moist bottomland sites.
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Oaks grow well in coves and on middle and lower
slopes facing north or east. Timber growth rate
and quality are generally best on sites with
silt, loam or clay soil at least 3 feet deep,
that is moderate- to well-drained. Tree growth
and quality is poorest on sites with soil less
than 20 inches deep or deep porous sands. Oaks
also grow poorly on narrow ridges, upper slopes
and steep slopes facing south and west. Oaks
regenerate easily on poor sites, but are
difficult to regenerate on good sites, because
they must compete with many other tree species.
Here are some points to consider when
regenerating oaks.
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Oaks commonly reproduce from acorns. Northern red
oaks produce good acorn crops at 2 to 5 year
intervals. Acorn production varies widely from
year to year. Total production may range from
just a few thousand acorns per acre in a poor
year to more than 250,000 per acre in a good
year. But these numbers are deceiving.
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Acorn weevils may destroy up to one-half of the
acorns in a good seed year and nearly all in a
poor seed year. Wildlife also eat large
quantities of acorns. Seedling numbers,
therefore, are high only following years of good
seed production, when there are excess acorns not
damaged by weevils or consumed by wildlife.
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The best seed producing trees are likely to have
large crowns and be at least 14 inches in trunk
diameter.
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Acorns are usually disseminated by squirrels,
blue jays and gravity.
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Best germination and survival occurs in mineral
soil under a light covering of leaves, just the
way squirrels plant them. Acorns exposed on top
of the leaf litter will dry out or be eaten by
mammals and birds.
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Stump sprouts are also a source of oak
reproduction following a harvest. Stump sprouts
grow fast because they begin life with a large
root system. Sprouts arising at or below ground
level are not likely to decay.
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Stump sprouts that originate high on the stump
are subject to breakage and to decay introduced
from the parent stump or from dead companion
sprouts.
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Small diameter stumps are more likely to sprout
than large diameter stumps. Sprouting is minimal
for trees larger than 17 inches diameter.
Northern red oaks sprout more frequently than
white oaks.
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Northern red oak and white oak are intermediate
in shade tolerance. They need less sunlight than
aspen, black walnut and paper birch, but they
require more sunlight than ash, basswood, elm,
hickory, maple and most other species.
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To give oak seedlings adequate sunlight, group
selection, clearcutting or shelterwood harvests
are recommended. These harvesting systems will
regenerate a mixture of tree species with oaks as
an important component. In a large managed
forest, only about 1 to 2 percent of the woodland
is regenerated each year.
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Harvesting selected trees scattered throughout
the woodland will regenerate shade tolerant
species, but not oaks. Selection harvests all too
often remove the largest and highest quality
trees. The poor quality trees left behind occupy
valuable growing space and become the seed source
for future generations. This high-grading does
not develop quality hardwood timber.
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Oaks may live for several hundred years. But,
managed stands on moderate to good sites can
produce harvestable trees, 18 to 24 inches in
trunk diameter, in 60 to 90 years.
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A stand also may be ready for harvest and
regeneration if it is greatly understocked or
most trees are of poor quality or undesirable
species.
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The most reliable method for insuring oak
regeneration is to develop plenty of advance
regeneration. Before harvesting, a forester
should count the tree seedlings and potential
stump sprouts in sample plots to determine if
regeneration is adequate.
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The number of oak seedlings needed to
successfully stock the next stand depends on
seedling size prior to the harvest and the
percentage of oaks desired in the next stand. For
example, if a pure oak stand were desired and all
the oak seedlings were 1 foot tall, you would
need 11,000 per acre to insure survival of a
sufficient number to fully stock a new stand. If
they were all 8 feet tall, you would need just
275 per acre. The larger the seedlings, the more
likely they are to survive and outgrow competing
vegetation. Fewer oak seedlings are needed if
other tree species are present and desirable as
growing stock.
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Oak stands are most likely to build up
satisfactory advance regeneration on dry sites
because oaks are more drought hardy than most
other tree and shrub species. Dry sites will not
support fast growing, high quality oaks, but they
can produce firewood and do have wildlife value.
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Oaks are more difficult to regenerate on sites
that are moist, but well-drained and have good
fertility. Many tree species grow well on these
sites and provide too much competition for oak
seedlings to survive. When such stands are
harvested, some oaks may reproduce from stump
sprouts, but there will be few oak seedlings.
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Stands that are well-stocked with advance oak
seedlings and that have little competition from
undesirable trees, shrubs or herbaceous
vegetation may be clearcut. A clearcut should be
at least one-half acre and preferably at least
two acres in size. Otherwise shade from the
surrounding timber will suppress oak seedling
growth. For regeneration purposes there is no
maximum size for clearcuts. Some landowners,
however, limit clearcut size for scenic or
wildlife purposes.
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If advance oak regeneration is not adequate, a
forester should analyze why. If there is a seed
source present, but few seedlings, the problem
often is too much shade. Acorns will germinate,
but in shade, the oak seedlings will survive for
only a few years. Large quantities of oak
seedlings will not accumulate. Shade could be
from a dense overstory of large trees.
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Shade is also created by a dense understory of
shade tolerant hardwood trees or shrubs such as
sugar maple, ironwood and prickly ash.
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Herbaceous vegetation, especially ferns and
nettles, also creates dense shade and may produce
toxins that kill oak seedlings. If oak seedlings
are to survive longer and accumulate in the
understory, it will be necessary to remove part
of this shade.
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Your first consideration should be to remove the
understory of shade tolerant hardwood trees or
shrubs. Undesirable small trees and shrubs may be
killed by felling, girdling, basal spraying a
herbicide, applying herbicide to foliage, or very
careful bulldozing. A forester can recommend
appropriate methods for your woodland.
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Ferns may be killed by a herbicide application in
late summer. Contact a forester for herbicide
recommendations, and always follow label
directions.
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Understory control is most important, but if
dense shade is produced by a high canopy, then
you should also remove approximately 20 to 40 of
this canopy, leaving 60 to 80 crown cover. This
shelterwood canopy provides seed, intermittent
sunlight needed by small seedlings, and enough
shade to discourage growth of competing
vegetation.
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Leave a seed source of species and individual
trees which you want to provide seed for the next
generation. For example, leave oaks and other
desirable species, such as ash and black walnut
with large, well-formed crowns, tall straight
stems, and no signs of severe damage.
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Remove trees which are undesirable species or
that have poorly formed stems, small crowns, or
substantial damage. Logging should be done
carefully to avoid damaging residual timber which
will be harvested later.
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Unmerchantable trees may be felled or girdled. To
prevent undesirable tree species from producing
stump sprouts or root suckers, treat cut surfaces
with an approved herbicide.
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Following the shelterwood harvest and understory
removal, you may need to wait several years until
you have a satisfactory number of seedlings
before clearcutting the stand. During that time,
a forester should inspect the stand annually to
determine the adequacy of oak regeneration and to
monitor re-growth of undesirable trees, shrubs
and ferns. Additional understory control may be
needed if the oaks require more than five years
to regenerate. Clearcutting must follow the
shelterwood harvest to provide full sunlight that
oak seedlings need to outgrow shade tolerant
species.
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There are several potential problems with a
shelterwood harvest. There may not be a
sufficient timber volume to justify two
commercial harvests spread several years apart.
The first harvest may damage residual
trees--lowering their value. And understory
vegetation treated at the time of the first
harvest may quickly re-grow, thus suppressing oak
regeneration.
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An alternative to the shelterwood harvest that
may avoid those problems is to delay harvesting
until a year when there is a very good acorn
crop. This crop can be assessed in mid-summer.
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If the stand has an abundance of undesirable
trees or shrubs in the understory that are likely
to re-sprout after cutting, you may want to kill
them with a herbicide treatment in late summer
before harvesting. Usually this competition can
be knocked down or uprooted by logging equipment
during the harvest.
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Then clearcut the stand soon after the acorns
drop in the fall. Harvesting should occur before
the ground freezes and in a manner that scarifies
the site, thus covering the acorns with soil and
leaves. Good scarification is achieved by
dragging whole trees over the ground, by
bulldozing the site with a toothed blade that
runs on the surface, or by disking. This
regeneration method has worked in a few trials
but needs further testing before results can be
predicted more accurately.
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The risk in clearcutting without advance
regeneration is that acorns, even after a good
seed year, may fail to germinate in satisfactory
numbers, or competing trees and shrubs may
outgrow oak seedlings. Then the site may revert
to less desirable species.
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Because of the risk and possible delay involved
when relying on natural regeneration, you may
want to consider planting seedlings of desirable
species such as oak, ash and walnut. Planting
enables you to supplement natural regeneration,
to plant genetically superior stock when it is
available, and to plant the species you want.
Seedlings may be planted before or immediately
following a clearcut, group selection or
shelterwood harvest. However, planting under a
shelterwood is preferred because it gives planted
trees time to become well established before they
are exposed to the surge of competition that
develops after clearcutting.
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In any case, before planting you may need to
control undesirable trees and shrubs by cutting,
bulldozing, or herbicide treatment.
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The most desirable oak seedlings have a fibrous
root system and a stem at least 3/8 inch in
diameter 1 inch above the root collar. Discard
smaller diameter seedlings because they are less
likely to survive and grow rapidly. Planting
large seedlings will reduce the total number
needed to insure a successful planting. Choose
seedlings from a seed source known to thrive in
your area and use seedlings from genetically
superior stock when available.
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The number of seedlings to be planted depends on
their size and quality, as well as the amount and
size of advance regeneration and potential stump
sprouts in the stand. You may need to plant about
200 oak seedlings per acre to supplement natural
regeneration, and possibly 600 or more per acre
where there are no seedlings present.
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Just before planting, clip the tops and roots of
the seedlings, leaving both about 8 inches long.
Clipped seedlings develop a more fibrous root
system, are easier to handle, and may grow faster
than unclipped seedlings.
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Plant oak seedlings in moist soil early in the
spring soon after the frost leaves the ground.
Plant these seedlings in the soil deep enough to
bury the root collar. Pack the soil firmly to
eliminate air pockets.
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Control weeds around the planted oak seedlings
for one to two years. Herbicides are usually
effective and economical for weed control.
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After the regeneration stage, well-stocked oak
stands should be thinned at about 10-year
intervals in order to concentrate growth on the
best trees. If less valuable species have
outgrown the oaks, thinnings should start as soon
as 10 years after regenerating the new stand. You
should select potential crop trees on a spacing
of about 15 to 20 feet. Choose crop trees that
are desirable species with crowns in or above the
main canopy, straight stems, and no signs of
severe damage.
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Remove less desirable species and trees that have
poor form or are damaged. Do not eliminate all
undesirable stems, only those touching the crowns
of crop trees. Small understory trees are not
significant competitors. Reduce stump sprout
clumps to one or two stems when the sprouts are
still less than three inches in diameter. Leave
sprouts that are vigorous, straight and attached
low on the stump. A forester can mark the trees
to be removed in a thinning.
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Before thinning, a forester will usually take
measurements in the woodland to determine the
stocking, size and quality of trees in the stand.
By referring to specially designed charts, the
forester can determine the ideal stocking for
your woodland to encourage fast growth. If too
many trees are cut during a thinning, future wood
growth and tree quality will be reduced. If too
few trees are cut, the final harvest may be
delayed many years or crop trees will be smaller
than desired when they are harvested.
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If you plan to regenerate oaks when a mixed
hardwood stand is harvested, then remember these
alternatives. If advance oak regeneration is
adequate, the stand may be harvested by
clearcutting or group selection. If regeneration
is not adequate you have three options. First,
you can conduct a shelterwood harvest. Begin by
eliminating understory competition, remove
undesirable seed producers, reduce crown cover by
means of the shelterwood harvest, then clearcut
when advance regeneration is adequate. A second
option is to wait for a good acorn crop, then
immediately after the acorns drop, harvest by
clearcutting or group selection and scarify the
site. The third option is to plant oak seedlings
in conjunction with a shelterwood harvest,
clearcut or group selection.
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Your woodland should be inspected periodically,
preferably during the growing season, to look for
damage caused by storms, insects or diseases.
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Keep fire out of woodlands. Fire may kill small
trees or damage the bark on large trees and
permit the wood to be invaded by decay organisms.
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Heartwood decay is one of the most serious
diseases. Although trees are seldom killed, decay
often renders the entire stem unusable for timber
products. Decay fungi usually enter the stem
through wounds or through dead branch stubs and
stump sprouts. To prevent decay, keep fire out of
woodlands, prevent wounding trees during
thinnings, and thin stump sprouts when they are
less than three inches in diameter.
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Oak wilt kills both red and white oaks. It
spreads mainly through root grafts between
adjoining oak trees, but insects may also spread
spores from infected trees to fresh wounds on
other trees. Oaks usually die in pockets in the
woodland. Avoid pruning oaks or wounding their
bark from April through July when spores are
being produced. If an oak wilt infection is
present, harvest infected trees within four weeks
of wilting, and harvest non-infected oaks for a
distance of 100 feet beyond the infected trees.
In high value stands, cutting root grafts with a
vibratory plow or by chemical means may stop the
disease from spreading.
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Insects also attack oaks. Various wood boring
insects may severely damage and degrade wood.
Several leaf feeding insects may defoliate oaks,
reducing their growth, encouraging root rot, and
occasionally killing stands of trees. A single
defoliation is usually not serious, but repeated
defoliations can cause mortality.
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To minimize damage by insects and subsequent
disease problems, maintain stocking levels that
permit rapid tree growth, and avoid damaging
trees during thinnings. Encourage mixed species
stands because they resist pest damage better
than single species stands. Salvage dying or
damaged trees before their wood is unfit to use.
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Livestock generally should be fenced out of
woodlands. Cattle, pigs, horses, goats and other
domestic livestock will eat seedlings, trample
and disfigure small trees, rub the bark off
trees, and compact the soil.
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Woodland management practices we have discussed
are aimed primarily at regenerating and growing
timber for wood products. Some modifications will
benefit certain wildlife species. Wildlife
diversity is fostered by creating a mix of stand
ages since some wildlife require young dense
stands and other wildlife need old growth forests.
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Songbird diversity is encouraged by maintaining
several canopy layers within a stand. Periodic
thinning of the main canopy will permit sunlight
to penetrate and stimulate the understory.
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Acorns are an important food for squirrels,
white-tailed deer, turkeys, ruffed grouse, and
other wildlife. Normal timber management
practices aimed at maintaining well-stocked
stands that are thinned at regular intervals will
produce oaks with moderately large, healthy
crowns needed for acorn production. Oaks start to
bear acorns at about age 25 and become good
producers at age To provide food for wildlife,
maintain 40 to 60 percent of the woodland in
stands of acorn-bearing age.
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During thinning operations, leave den trees to
provide homes for birds, squirrels, raccoons and
other cavity dwellers. Leaving den trees with
small crowns will not significantly reduce timber
production.
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During thinnings or clearcuts, instead of felling
unmerchantable trees, kill the trees standing in
order to provide snags for birds that feed on
insects beneath the bark or that hollow out the
wood for nesting holes. Snags are useful to the
largest variety of wildlife when they are at
least eight inches in diameter.
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The clearcut and shelterwood methods have been
recommended for releasing oak seedlings, but such
cuttings may be objectionable for aesthetic
reasons. The appearance of newly regenerated
stands can be improved by cutting stumps low,
lopping tree tops and felling all trees in the
harvest area. But remember, dead standing trees
are useful to wildlife.
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Break up straight woodland edges by creating
irregular shaped edges or by thinning into the
adjacent stand.
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Design the clearcut to blend into the topography.
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Large clearcuts should be irregular in shape so
that only small portions are visible from one
observation point.
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Seed temporary logging roads and landings to
clover and grass to reduce soil erosion and
provide forage for wildlife.
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Before implementing any woodland management
practice, contact a forester to inspect your land
and provide specific advice tailored to your
situation. You might start by contacting your
local county extension service. Their agents have
access to forestry specialists that may be able
to answer specific questions or provide
publications to help you analyze your situation.
State forestry agencies have foresters that will
inspect your woodland, explain management options
and help you plan specific activities. Consulting
foresters are available to help you with all
phases of woodland management including timber
marketing, reforestation and damage appraisal.
Some large forest products firms also have
foresters that will assist you in planning timber
harvesting and reforestation.
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Oak woodlands are one of the Midwest's greatest
natural resources for wood, wildlife, water and
recreation. But they demand careful management to
perpetuate the species and quality of trees in
demand. Plan now to invite a forester to your
woodland and investigate how to manage it for
your objectives.
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