Ecosystem Restoration: A Systems Approach to Exotic Plant Control
From: Exotic Pests of Eastern Forests, Conference Proceedings - April 8-10, 1997, Nashville, TN, Edited by: Kerry O. Britton, USDA Forest Service & TN Exotic Pest Plant Council
Abstract: Ecosystem restoration is a
systems approach because it relates to all of the thousands of interrelated
and interacting systems within the ecosystem. Ecosystem restoration also
changes your role in the forest from observer to participant. Some of the
goals of ecosystem restoration are to improve the health, vigor, and diversity
of the ecosystem-and these goals can and must be quantitatively measured.
The concepts and processes of ecosystem restoration will be illustrated
by a specific example with an emphasis on the application and methods of
prescribed burn, which can be very useful in the control of exotic pest
Many of you are under a mandate to provide a regular supply of timber
products and may be wondering how ecosystem restoration relates to your
situation. Some of you may be under a mandate not to interfere with the
forest except to remove the exotic pest plants and may be wondering how
ecosystem restoration relates to your situation. Some of you may be operating
under a belief system that says, "If we get rid of all the exotic pest
plants in the forest, then the forest will take care of itself and will
not need people." I am asking all of you to briefly accept that you
are part of nature, and that you are obligated to be a nurturing participant
in the forest. You may find some useful ideas in this discussion of ecosystem
restoration. Some of what you know know may be challenged by these ideas
about ecosystem restoration.
Perceiving The Need To Restore
Perceiving the need to restore requires a combination of the ability
to see the forest clearly, without prior assumptions, and a belief system
that will allow you to be a nurturing participant in the forest. For this
reason, it is useful to me to think in terms that include people as part
of nature. In this paper, I refer to them as two distinct and separate entities.
Therefore, I will use the term "the rest of nature" to mean all
living and nonliving things in the universe except people.
Our culture, and thus, our educational system, teaches that people can
only have a negative effect on "the rest of nature." Nearly all
ecologists describe the original ecosystems-meaning the ones that the first
Europeans found here-in terms of "the rest of nature" and almost
always disregard as insignificant the activities of the indigenous people
that were present. This viewpoint does not take into account the effect
of 20 million or more indigenous people who both occupied and actively cared
for the "Garden of Eden" which the settlers first found (Anderson
1997, Martinez 1996, Olson 1996, and Cronon 1983). This belief system does
not help us to understand how we can recreate that "Garden of Eden."
Again, please accept, at least for the moment, that people can be nurturing
and have a positive influence on "the rest of nature."
With these ideas in mind, I looked at the forests in the Brecksville
Reservation of the Cleveland Metroparks, Ohio. I discovered that unhampered
by the aforementioned assumptions and enabled by a belief system that allows
me to be a nurturing participant in the forest, I could see the need to
restore this forest. I could see the decline in vigor of the even age oaks
in the canopy, of the understory oak forest components, and even of all
members of the herbaceous layer. In addition, the second age class of white
oaks did not find space in the canopy and died due to the lack of proper
Writing A Quantitative Behavioral Standard
Once you have perceived the need to restore, your next step is to write
a quantitative behavioral standard (QBS) to guide you in your restoration
efforts. Having determined why the forest is unhealthy, you simply write
a description of how it will be when it is healthy and this becomes the
QBS. QBS is a term which I coined specifically to measure progress in the
restoration process. In our example of the Brecksville Reservation, the
forest is overstocked (Ginrich 1967). This means that there are too many
trees and too many square feet of basal area of trees per acre to have fully
healthy oak trees. So, the QBS in this case would be: At least 75% of the
species on the list of oak- hickory forest ecosystem indicator species will
set seed at least once in every five years. The restorative effort will
be to reduce the stocking percentage from the current 120% down to 70% and
monitor the changes in the ecosystem. The reduction of stocking percentage
will also make space in the canopy for a second age class of white oak.
Note that the QBS is quantitative. It contains measurable numbers. It
is behavioral because you are measuring changes in the behavior of plants.
It is also a standard-which means that it can be "held up" to
the existing forest to see if you are moving toward or have reached the
stated goals. Another characteristic of a QBS is that a knowledgeable person
with a day or less of training can perform measurements to determine the
forest's progress toward the specified standard. The QBS is not limited
in its quantitative standards-it can relate to percentage of flowering,
seed setting, and production of offspring; number of nesting birds; breeding
salamanders; etc. But, it must define measureable quantities-to say "the
forst is doing better" means nothing. You can and must quantitatively
define what "better" means, by translating it into a QBS.
It is often helpful to have a reference ecosystem on which to model your
QBS. In the example of the Cleveland Metroparks forest, I used the original
land survey which was conducted in 1811 for the Brecksville township. Sometimes
a nearby forest may be a useful model. A careful study of the types and
quality of ecosystems in the area in which you are working is most useful.
A recognized reference, such as The Vegetation of Wisconsin (Curtis 1959),
is useful well beyond the state of Wisconsin because it examines regional
forest types, fully characterizing their plant associations.
Planning The Restorative Efforts
Because this forest had very low vigor in all layers, (i.e., the canopy
and oak forest components of the understory and herbaceous layer), the restorative
efforts were aimed at increasing vigor of all layers. Therefore, one part
of the QBS stated: White oak and shagbark hickory will produce seedlings
more than once every 15 years. In order to achieve this, restorative efforts
were targeted at reducing the stocking percentage of the oak. The intent
was to improve the health of the individual trees, thereby increasing their
ability to produce viable acorns. Enough acorns need to be produced so that
some would remain after predation to produce seedlings. The restorative
efforts were designed to reduce the stocking level from the current 120%
down to 70%-with the target number based on Gingrich's study of oak tree
health (Gingrich 1967). In practical terms, this means that 103 trees, averaging
13 inches in diamater, were cut on 2.5 acres. This opened up space in the
canopy for the second generation of oak trees. This reduced the percentage
of canopy to well less than the 85% needed for white oak regeneration (Curtis
Another part of the restorative effort focused on the understory of this
oak-hickory forest. Sugar maple had become pervasive in the understory,
supressing the growth of other woody and herbaceous species present. This
great increase in sugar maple, as compared to its frequency at the time
of the original land survey, has been well documented (Ebinger 1986). This
pervasive sugar maple growth was limiting the amount of Photosynthetic Active
Radiation (PAR) reaching the forest floor. PAR is defined specifically as
wavelengths between 400 to 700 nanometers, and is the critical segment of
the sun's light spectrum which plants require to be able to conduct photosynthesis
(Attridge 1990). It is possible to have light reaching the forest floor,
but if it does not include the PAR segment in the proper amounts, then the
plants are essentially in the "dark." Herbaceous plants or seedlings
of the forest floor must likewise receive adequate PAR in order to flower
and seed. Therefore, another part of the restorative effort was to remove
the sugar maple understory, using prescribed burning and cutting. Together,
these actions were intended to meet the specified QBS of 75% flowering of
the oak-hickory forest species, as stated above.
The declining condition of the forest, the QBS, and the restorative efforts
are interrelated as follows: Inverting the conditions which you want to
change in the forest defines the QBS and the restorative efforts are the
means by which you bring about the desired changes and achieve the QBS.
The end result of using the QBS method is that you are assured that you
have measurably succeeded in "curing" what is wrong with the forest.
Designing A Monitoring System
In monitoring progress of the Brecksville restoration, we used 91 sets
of stratified random quadrats, with three quadrats per set. In a 0.01 hectare
circle, trees are measured and identified every three years. In a 4 x 4
meter quadrat, all woody stems under 6 inches are measured and identified
and mayapple are monitored. In a 1 x 1 meter quadrat all herbaceous plants
are monitored and acorn counts are made. The 4 x 4 and 1 x 1 quadrats are
monitored often during each growing season. Other data are also collected
on these quadrats. Forms were developed so that all data were properly collected
and all data are entered into a Paradox-based database.
Volunteer Earth Restorers established most of the quadrats and have done
over 90% of the data collection in the Brecksville Reservation. These volunteers
have done an excellent job. Please do not think of volunteers as "children
of a lesser god." The fact that they are not paid for what they do
does not mean that it must be of lesser quality (Smith 1991 and 1995).
Implementing The Restorative Efforts
As a practitioner, the implementation is the exciting part. However,
without first developing the QBS and a monitoring progam, you will never
know where you are going in the restoration process. Or, as it says in Alice
in Wonderland, "If you do not know where you are going, any road will
get you there." The order in which we implemented the restorative efforts
in Brecksville were: (1) prescribed burn, (2) understory removal of the
sugar maple and beech, and (3) canopy opening, i.e., describing the stocking
rate. Separate areas were treated with different restorative programs as
follows: (1) burn only, (2) burn and cutting of the understory only; or
(3) burn, understory cutting, and canopy opening. The monitoring of these
differing treatments enabled the evaluation of each restorative effort.
Since cutting of trees and saplings is easy to understand, I will not cover
it in this paper, and will instead go into prescribed burning in some detail.
Another part of the QBS stated that: Non-native, exotic species will
constitute less than 10 percent of the total above-ground stems. The main
restorative effort that we used to meet the exotic pest plants elimination
goal of the QBS and to begin understory removal was prescribed burning.
Prescribed burning is defined as fire (1) applied in a skillful manner,
(2) under exacting weather conditions, (3) in a definite location, (4) for
a specific purpose, and (5) to achieve certain results. By monitoring after
a small prescribed burn, we determined that the certain results that we
could obtain were to kill about 90% of all the above-ground stems of 2 inches
or less in diameter of all species without damage to trees or herbaceous
plants. We burned when all species were dormant.
The burn window that we always used was:
||less than 3 miles per hour in the forest at eye level (which means that
no leaves are changing location)
||30-55% (35-45% preferred)
||32-65° F (Dixon et al 1989)
||Pass the "bucket test"-see below (Moore 1991)
The bucket test consists of simply picking up a small portion of all
the leaf layers intact, placing them in a metal bucket, taking a leaf from
the top layer, lighting it, and dropping it into the bucket. What is left
in the bucket after the fire is similar to what will be left in the forest
after the fire. If there are two layers of leaves left in the bucket, then
there will be two layers of leaves left in the forest. Often it is necessary
to do the bucket test in different moisture situations in different parts
of the forest to get an accurate picture of what will happen. The "bucket
test" allows you plan burns that leave leaf litter or remove it all,
depending on the prescription and reason for buring.
A few points need to be kept in mind when planning a prescribed burn.
First, a prescribed burn will top kill ALL above-ground stems that are 2
inches or smaller in diameter. Yes, that includes honeysuckles, buckthorn,
and so on. Second, always remember that weather controls a fire, NOT people.
All people can do is plan and ignite a fire so that weather will control
it. In almost twenty years as fire boss, burning forests and tallgrass prairies,
we have never had any injuries. We burned only what we planned to burn and
achieved the results that we expected. Finally, please be aware that many
states and agencies have a certification or licensing requirement before
you are allowed to conduct a prescribed burn.
Herbaceous Layer Enhancement
In a study that was done in England, it was clear that adding herbaccous
species as plants maximized survival rate, but it is costly and very labor-intensive.
Use of seed came in a close second and has the important advantage of lower
cost and less labor (Francis 1995). In this study, the important factor
was seeding or planting in bare soil. My own studies have indicated the
same. When you think about putting small seed on leaf litter or under leaf
litter, you know that the seed does not have enough stored food to either
get a radicle down to soil or shoot up through the leaf litter. Prescribed
burning was used to remove the leaf litter in our study.
The Structural Health of The Soil
Just as a reminder, you need to pay very careful attention to avoid compacting
the soil or interfering in any way with the functioning of the soil microbes
or mycorrhizal fungi. Without passages in the soil for air and water to
go into the soil and carbon dioxide to come out, the plants will not be
healthy (Harris 1996).
Evaluating Restorative Efforts
This is the simplest part. You can compare the first year of data with
the second and successive years' data and see if you are moving in a direction
that will enable you to meet the goals outlined in your QBS. Be aware that
there may be some ups and downs in the progress of the restoration. If you
find that you are not accomplishing the QBS, you may need to reevaluate
your restorative efforts. Remember though, change is not sudden in a forest.
I hope each of you has found something useful in this brief discussion
of forest ecosystem restoration. For those of you that are mandated to provide
a regular supply of timber products, you may find it interesting that this
mandate can fit in with ecological restoration. The Chief Forester of the
Ohio Department of Natural Resources has outlined this idea as follows:
If we can thin the stand (which is also called reducing the stocking percentage)
of an oak forest and reliably get a second age class of oak, we can revolutionize
the gathering of timber products because we can harvest trees and not the
forest. For those of you that are mandated not to interfere with the forest,
except to remove exotic pest plants, you may have found useful ideas that
can help you modify that mandate. For those of you that operate under the
belief system that says the forest does not need nurturing people, perhaps
this discussion has challenged that belief system enough that you are now
a little uncomfortable with it. Perhaps you will try being nurturing to
the forest and see how it goes for you and the forest. I feel better about
me when I am being nurturing to both forests and people.
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