savanna areas of invasive brush and trees
Because of the heavy work involved, clearing the savanna is
usually a multiple-year job. It involves a lot of chain saw
and brush cutter work. Some landowners are able to do this
work themselves. If family members or friends are willing
to volunteer, this sort of work can even become enjoyable.
Another option is to hire part-time workers (perhaps students
from a nearby University). If financial resources are available,
a private contractor can be hired. It is important to hire
a contractor who specializes in restoration work. Most such
contractors will permit the landowner to assist, and family
members and friends might contribute by helping to burn brush
piles or herbiciding cut stumps.
A conventional logger is not recommended, even if the logger
offers a substantial financial reward. Loggers have no appreciation
for the delicacy of the woods and their approach is to get
in and out as fast as possible, and leave all the cut uncommercial
wood on the ground. Small logs and brush left lying will soon
be infested with brambles, making further restoration very
Whether the understory is to be created by interseeding or
from scratch will depend on the size of the restoration, the
extent of degradation, the funds available, etc. In any case,
the critical item is the availability of a good seed mix of
savanna understory species. A restoration should not be started
until seeds are available. It is important to get the understory
started right after clearing, before invasive shrubs or brambles
from the seed bank start to flourish.
What to cut?
When restoring a savanna, all trees should be removed that
were not part of the original fire-dependent ecosystem. Woody
shrubs should be removed at the same time as the trees. Tree
species to remove include elm, black walnut, cherry, and box
elder. Woody shrubs include buckthorn, honeysuckle, and prickly
ash. If the site is a bur oak or white oak savanna, then black
oaks that are crowding white or bur oaks should also be removed.
(Black oaks are fast-growing trees that tend to grow into
the canopies of the whites or burs.) Shagbark hickories can
be left unless they are crowding white or bur oaks.
The term "daylighting"
is sometimes used to refer to the process of liberating open-grown
oaks. In a degraded savanna, weedy trees or shrubs that are
more shade tolerant generally grow up around the open-grown
oaks and crowd them. The large lower branches of an open-grown
oak get shaded and eventually killed. Careful cutting of the
invading trees and shrubs should be done so that the lower
branches of the open-grown oaks are not damaged. In some cases,
the large lower branches may be still alive and begin to thrive
again from the daylighting process.
a large open-grown oak. Before work began, this oak was
almost invisible. However, the large lower branches were
still alive and in subsequent years have leafed out, flowered,
and set seed.
Dealing with all the downed wood
A savanna restoration will result in a lot of downed wood.
The good wood can be salvaged, either for use as fire wood
or as lumber.
It is unlikely
that there will be a market for most of the wood. However,
an area with a large amount of black walnut might be salvaged.
Saw logs can be taken by cooperators with front-end loaders.
should not be used to remove logs, as this damages the understory.
If the wood can be easily transported to a town or county
road, local residents will quickly remove all this firewood.
On a ridge top, if there is motor access, the wood can be
removed by pickup truck. Since this may involve some off-road
driving, it should only be done in the winter at snow-free
times and the colder the better. Care should be taken to avoid
making ruts. Frequent off-road driving over the same track
should be avoided. Growth of savanna plants the following
season should quickly hid whatever remaining ruts are present.
of a low-impact skidder to remove large logs. Cold weather
and a thin layer of snow made it possible to skid logs
without damaging the soil.
residents who burn wood are always willing to truck away
good-sized logs. This is strictly a barter transaction.
If possible, the slash and small wood should be burned as
it is cut. If it cannot be burned then it should be placed
into large brush piles that can be burned when snow is present
(see photo below). The fewer piles that are built the better,
as the fire will sterilize the soil beneath.
Some dead trees can be left standing as habitat for woodpeckers
and other wildlife. Such dead trees can sometimes cause problems
during controlled burns, but this risk may be accepted in
the interest of creating desirable wildlife habitat. Standing
dead trees can be fireproofed. Rare bird species such as red-headed
woodpeckers prefer these trees for their nests.
Strategies for tree removal
Clearing the savanna should begin at the most accessible site
which has great oaks. A five-acre parcel of substantial open-grown
oaks will make an excellent beginning. Such a site is large
enough to have some good plants, to look great when cleared,
and to serve as a learning tool. Understory restoration should
proceed in parallel with clearing the trees and brush. There
should be a good layer of oak leaves on the ground to serve
as fuel and the restored area should be burned the same year
it is cleared. Burning will open up the bare ground so that
seeds of understory plants can germinate and grow. Planting
should be carried out immediately after burning. Do not wait
to plant for understory restoration, as it is essential to
get “good” plants started before the brambles start to take
over (which they surely will).
Even if the budget permits restoration of more than five acres,
it might be advisable to do only this small area first, in
order to get a feel for the project. This slower pace of savanna
clearing is also necessitated by the need to have seeds to
plant in the cleared areas. Since it is advisable to use only
local seeds, clearing has to continue in phase with seed collecting.
Even if the manager feels confident in the work, it may still
be preferable to clear only about 10-15 acres of savanna the
Most degraded savannas will have become infested with both
native and nonnative shrubs. This is primarily a result of
lack of fire, which top-kills shrubs and keeps them from growing
to large size. If the site was grazed, some shrubs may have
been eaten, but thorny shrubs such as buckthorn and prickly
ash are avoided by cattle.
A decision should be made about what shrubs to cut. All exotic
(nonnative) shrubs should be removed, but some restorationists
prefer leaving some or all native shrubs. The principal native
shrubs in the Midwest are hazel (Corylis americana),
gray dogwood (Cornus racemosa), prickly ash (Xanthoxylum
americanum) and two species of sumac (Rhus glabra
and R. hirta). Hazel is attractive and forms nuts
which are favorite wildlife food. Gray dogwood is attractive
and beneficial to wildlife, but is quite invasive, and left
unchecked will form large clones. Prickly ash is also clonal
but less attractive, and a menace when walking in an open
savanna. The two sumac species are also very invasive and
should be removed. Check here for details of shrub removal.
The most widespread and serious nonnative shrubs are buckthorn
(Rhamnus cathartica), honeysuckle (various Lonicera
tatarica, L. morrowii, L. X bella), but other nonnatives
sometimes encountered are multiflora rose (Rosa multiflora),
autumn olive (Elaeagnus umbellata), and Japanese
barberry (Berberis thunbergii). They should all be
completely removed from the site. (See link)
The cut stems of all shrubs should be treated with herbicide
without fail. The herbicide of choice is triclopyr (Garlon
4) dissolved in oil and sprayed not only on the cut stem but
down the sides of the stem (as a basal bark treatment). Glyphosate
is effective on honeysuckle and gray dogwood but is not recommended
for buckthorn or sumac. For that reason, triclopyr is the
herbicide of choice because it is effective against all woody
shrubs. See this link for details on control of invasive shrubs.
low-tech procedure for detailing with woody shrubs. Shown
here for honeysuckle. Each stem is cut with a lopper and
the cut surface treated with herbicide. The dye insures
that all cut stems are treated.
for spraying cut stems or basal bark spraying, using a
backpack sprayer. A dye is used to ensure that all stems
The shrubs that
are cut can be burned at the same time the trees are being
worked on, as seen in the photo at the top of this page. In
fact, the branches of the cut shrubs can be used as the base
for burn piles. Link to the fire section for a discussion
of managing burn piles in a savanna restoration.
Even if the site is relatively free of invasive shrubs, the
restoration process leads to an increase in sunlight to the
forest floor, which encourages the growth of shrubs. Brambles
(various Rubus species) are especially prone to “take
over” a restored savanna. There is always a seed bank of Rubus
species, which are held back when the site was shady, but
the increased sunlight after opening it up provides ideal
conditions for bramble growth. There is also an extensive
seed bank of other invasive shrubs such as honeysuckle and
buckthorn, as well as a seed bank of black walnuts and other
fire-sensitive trees. The new growth of these invaders may
be killed by fire but the rootstock will not be eliminated.
The restorationist should be prepared for a multiple year
job of removing invasive woody plant regrowth
Can burns be carried out without first
removing woody vegetation?
Burns can be carried out without removing the woody vegetation,
but this is not advisable. A burn will top-kill existing woody
vegetation, but will not eradicate it. Except for conifers,
most woody vegetation that has been killed will resprout from
the base, sending up new shoots the same or the following
year. Right after the burn the savanna may look good, but
this is only temporary. Unless one burns every year, the midstory
woody plants will return, usually much thicker than they were.
Since burns are much less expensive than cutting and herbicide
treatment, there may be a temptation to do so. This is really
false economy, because burns do not eradicate woody vegetation.
Eventually, it will have to be cut, and cutting shrubs and
trees that have been burned may be more difficult, because
there will be numerous resprouts that will have to be dealt
with. If funds are limited, it is advisable to work instead
on a smaller area, doing it right and getting this area in
good shape before moving on.
There are many details involved in savanna restoration. The
particular techniques used will depend upon the site, the
budget, the personnel available, the equipment available,
and a number of intangible factors. Because of differences
in climate and character across the Midwest, a savanna restorationist
should use practices that are already in use in the region.
Before undergoing a restoration, it is advisable to consult
with state agencies, conservancy groups, and other noncommercial
organizations for advice. Volunteering at a site where restoration
is already underway is strongly recommended. (This is good
advice even for professionals.)
and Brock present a case study of the restoration of a small
Sites that have not seen fire in a long time may have large
aspen clones, which should be removed. Aspen are native trees
but remain undesirable inhabitants of prairies and oak savannas.
Aspen are capable of spreading rapidly and crowding out other
vegetation. Aspen are pioneer trees on open , burned, or cut-over
land. Although important economically in the paper industry,
they are a menace in prairies and oak savannas.
Aspen cannot be simply cut like other tree species, but must
There are two species of aspen that are native to these areas:
trembling aspen (Populus tremuloides) and big-tooth
aspen (Populus grandidenta). Trembling aspen is the
most common, but both are bad and should be removed. It deserves
emphasizing that clearing aspen is a very satisfying activity,
as there very well might be “good” species underneath. Most
of these aspen areas were originally prairie remnants, and
many of the prairie plants may be able to continue maintaining
populations for some years after the aspens have started to
take over. Even if the aspen clone is very dense and there
is too much shade for satisfactory growth, good species in
suppressed form may be present. It is advisable to work hard
to get rid of these trees.
aspen clone is easy to spot in the fall of the year.
Although aspens grow from seeds, the primary spread is asexual
by underground rhizomes. The typical aspen "grove"
is a multi-stemmed clone in which all the roots are interconnected.
If an injury to a stem or root occurs, there will be a rapid
response by the clone, and new shoots ("suckers")
will be sent up all over the area. New shoots have been known
to arise as far as 50 feet from the nearest aspen tree! The
clone may expand simultaneously in several directions, as
influenced by environmental conditions. In western United
States, huge aspen clones have been found, the largest occupying
over 100 acres. In our part of the country, aspen clones are
smaller, but are often more than an acre in extent.
area where all the aspens had been removed by a commercial
logger. Massive resprouts have occurred from the dormant
buds of this clone.
Aspen clones are widespread in the Driftless area of southwestern
Wisconsin, eastern Iowa, southeastern Minnesota, and northwestern
Illinois. They are easy to spot in spring when the light green
leaves first appear, and in the fall, when the leaves take
on their distinctive fall color. Virtually every woodlot in
some areas has at least one or more aspen clones. This was
not always the case. In earlier times, aspens were uncommon.
This was because aspens are fire-sensitive, and when prairie
and savanna fires were widespread, they were held in check.
When looking at
a large aspen clone, it may be tempting to go in with a chain
saw and cut it down. Wrong! The roots remain alive and immediately
send up a huge number of new shoots. An area that had perhaps
5 or 10 large aspen trees will soon have hundreds of aspen
stems. This is one of many reasons why a commercial logger
should not be allowed on the property.
Girdling means stripping a layer of bark and the underlying
cambium and phloem in a band around the trunk. The phloem
vessels translocate sugars and other nutrients to the roots,
so if the phloem tubes are broken, the roots become starved
of food. The xylem vessels, which translocate water to the
leaves, are not affected by girdling. With girdling, the upper
part of the tree still remains alive, since photosynthesis
can continue. Eventually, however, the roots die, and the
whole tree dies. The first year after girdling, the clone
may appear almost normal, but by the second year the clone
usually dies. The dead trunks can then be cut without stimulating
For girdling to be affective the whole clone must be treated.
It is also important to make the girdle in such a way that
the underlying xylem is not damaged. Damage to the xylem sends
signals to the tree that something bad has happened, and the
tree then sends up shoots.
The photo demonstrates the technique of girdling. Girdling
is done in May or early June when the sap is running fast
and the tree is growing. At that time, the bark can be easily
cut and the girdled bark stripped off. Later in the summer,
it is virtually impossible to do a girdle properly.
of aspen girdling. The tool was made from a leaf spring
of a truck, sharpened on one side. The bark is cut with
the sharp side and then peeled off by walking around
the tree. Even large aspens can be girdled in this way.
The best time of year to girdle is when the sap is running,
usually in May or early June.
is important that every tree in the clone be girdled.
Some large clones can have over a hundred trees.
An experienced worker can girdle 100-200 trees in a day. It
takes about two years for the trees to die, and they should
not be cut until that has happened. The dead trees are then
cut, stacked, and burned.
Although girdling is very effective, small aspen resprouts
may still come up at the edge of girdled areas. These can
be handled by cutting with a hand clippers, loppers, or brush
cutter and treating the cut stems with triclopyr.
One of the invasive
tree species that comes into degraded, neglected oak savannas
is black walnut (Juglans niger). This species is
fire sensitive and was not present in original oak savannas.
It grows relatively rapidly and is able to take over any open
areas. Black walnut was originally only a minor component
of oak savannas and oak woodlands. Because its wood is a fine
straight-grained wood, it is highly prized, and there is usually
a market for it. Black walnut is intolerant of shade and it
must be a dominant or co-dominant in order to survive.
Black walnut is primarily a tree of the mid-continent of the
United States and is at the northern edge of its range in
southern Wisconsin and Minnesota. Although it occurs throughout
Iowa, it occurs only in the eastern half of Missouri, is absent
from the Dakotas, and is virtually absent from Nebraska. In
most forest situations, it is usually found in mixed forests
as single isolated specimens, although in some restricted
areas it may become dominant or subdominant.
Black walnut toxicity
produces a toxic substance called juglone (5-hydroxy-1,4-napthoquinone),
which occurs in all parts of the black walnut plant. Juglone
inhibits the growth of many other plants, a phenomenon called
allelopathy. A mature tree can have a toxic zone
of 50-80 feet in radius from its trunk. Members of the genus
Quercus have been reported to be sensitive to juglone,
which suggests that oaks might be pushed out once black walnut
becomes established. The toxic area affected extends outward
each year as a tree enlarges.
However, tests have shown that some native plants are resistant
to juglone and are thus able to grow in the presence of black
walnuts. Resistant plants include all grasses, and a number
of woodland forbs, including jack-in-the-pulpit, bellflower,
bellwort, dutchman's breeches, wild geranium, mayapple, solomon's
seal, bloodroot, and trillium. Also, spiderwort, a common
prairie plant, is resistant to juglone. Honeysuckle, an invasive
shrub, is also resistant. Lists of native plant species resistant
to juglone can usually be obtained from the County Agricultural
Agent, since juglone toxicity has horticultural implications.
Obviously, black walnut is not a tree that one would want
to have in a restored savanna.
As part of the oak savanna restoration, all black walnut trees
should be removed. Although black walnut is considered a cash
crop in forestry, in the oak savanna it is an invasive species.
Trees large enough to be used as saw logs can be saved and
marketed, or donated to a nonprofit group for a tax deduction.
If the walnut infestation is extensive, their removal may
leave behind a handsome stand of mature bur oaks that have
survived years of grazing pressure.
black walnut infestation. Some of the logs in this area
were large enough to convert to lumber.
walnut is a desirable lumber wood. If good logs can be
skidded to a road a sawmill can often be contracted to
pick them up, perhaps with no charge.
The Resprout Problem
The cut surface of a walnut trunk usually exudes a large amount
of a nutrient-rich fluid, which supports heavy mold growth.
Because of the upward flow of this fluid, penetration of herbicides
may be restricted. To prevent resprouting, herbicide treatment
of the cut stump with triclopyr followed by basal bark treatment
of the remaining trunk is recommended. When dissolved in an
oil, this herbicide has strong ability to penetrate the bark
and be translocated to the roots. Even with this harsh treatment,
the stump may still resprout. Walnuts are notoriously vigorous
resprouters and the cut stumps must be monitored for several
years following tree removal.
If the stumps do resprout, the best procedure is to cut all
new growth with a brush cutter and repeat the triclopyr/cut
stem/basal bark treatment.
The walnut seed bank
In addition to the resprout problem, there will usually be
an extensive seed bank, since walnuts are prolific seed producers.
Most of these seedlings will be difficult to find until they
have had several years growth. Monitoring in the third or
fourth year after clearing is recommended, and all walnut
saplings treated by basal bark with triclopyr alone. Alternatively,
the young tree can be cut the a brush cutter or chain saw
followed by triclopyr basal bark treatment.
Restoration work of the kind described here is expensive. Costs
in the 1990s and early 2000s ran between $3000 and $5000 per
acre. These costs were for an experienced crew who worked very
efficiently, and included cutting of trees and brush, stacking
and burning, and all herbicide treatment of cut stems. It did
not include the cost of removal of firewood except where the
wood could removed free by local residents.
The specified payment rates (dollars per acre) that the Federal
Government uses in their granting programs covers only a small
part of the operation. For instance, the per acre payment rate
for removal of heavy brush is given at $190.00 per acre, which
is only a small part of the cost. (Sites with heavy brush have
more than 40% of the area stocked with woody vegetation 0-2
inches in diameter and up to 25 stems per acre larger than 2
inches in diameter at the ground line.)
Despite the cost, oak savanna restoration is a vital activity
to carry out. As noted, the oak savanna habitat is globally
endangered and is probably one of the rarest vegetation types
in the world. Because of its broad value for wildlife and esthetics,
its restoration should be a high priority mission, and well
worthy of much more governmental support.
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