The research conducted at Wil-O-Way Woods examined tree diversity along the major
trails, yielding a total of 368 trees encompassing ten different taxa, such as elm or hard maple.
By the Shannon-Wiener Diversity Index, the data generated a score of 1.864, a fairly good tree
diversity number. The Shannon-Wiener Diversity Index is a mathematical tool used by
ecologists in order to evaluate species richness and evenness within an ecosystem (Molles 2010).
With this information, researchers are able to understand the steps that need to be taken in order
to improve the ecosystem of interest. In the case of Wil-O-Way, a low diversity number indicates
that there is relatively good tree diversity within the forest. An urban forest with high tree
diversity allows the ecosystem to stabilize a healthy nutrient supply in the soil, slow water runoff
in the urban setting, improve water quality, support a beneficial assortment of wildlife, and
reduce decimation to the entire forest if any one disease or introduced organism entered the
system. With these benefits, the ecosystem will be able to thrive.
Comparing the results of this investigation with those of a previous tree inventory at WilO-Way Woods provides valuable information about the validity of our methods. A tree inventory
taken in 2003 also recorded ten taxa. The major tree taxa were the same in each of the studies;
both inventories found sugar maples, ash, white oaks, elm, ironwood, basswood, and red/black
oaks. The proportions of the major tree species were also similar between the two inventories,
suggesting comparable species evenness. This degree of similarity suggests that the inventorying
method that was used in this study is comparable in effectiveness to the point-centered quarter
method used by the 2003 inventory (WLC 2004). There are two reasons why this could be true.
First, our method would yield a much larger sample size. We documented 368 trees in our
inventory, while the 2003 inventory only included 192 trees using the point-centered quarter
method. Our sample size was 192% of the 2003 inventory’s sample size (92% larger). Second,
we expected our inventory method to function much like a belt transect or strip transect
sampling. These widely accepted methods of sampling use the same basic principles as our
method. They both document all the individuals of interest that are found within a band of
uniform width (Avery and Burkhart 2002). Each study is expected to yield results that represent
the overall population with a fair degree of accuracy because the belts/strips transect the forest in
such a way that the tree diversity within them would not differ significantly from that of the total
population. Therefore, we assumed that the areas of the forest that are transected by the major
trails of Wil-O-Way Woods would not differ significantly in species diversity from the rest of
the forest (WLC 2004). Although the inventory results were quite similar with regards to the
kinds and proportions of major species, there were some very important differences between
them. The 2003 investigation was able to identify all their elm trees as slippery elms and all their
oaks as red, white, or bur oaks. This difference in taxon designation could present a major
problem if we tried to compare the two inventories using a biodiversity index, such as the
Shannon-Weiner index, which would rely on the number of species found and the proportion of
the total sample represented by each species. The studies also differed in the rarer species found.
The 2003 investigation identified four red maples, three bur oaks, and a box elder tree, but our
inventory did not find any of those species in the forest. Meanwhile, our investigation came
across seven wild cherry, two beech, and one birch, which were not species seen in the 2003
inventory. Three out of ten species found in each inventory were not even seen in the other.
Species evenness varied by 30% between the two studies.
This variability in tree taxa between the two studies carries a few important implications.
First, it suggests that the forest may have more biodiversity than either of the two inventories
estimated. Together these two inventories identified at least 13 species of trees in the forest, as
compared to ten species identified by each independently. Second, such a high degree of
difference in species identified might question the significance of the numerical differences
between the inventories with regards to the species found in both. If there is that much chance
variation in species richness, it could very well be that there is an equal degree of chance
variation in species evenness. Lastly, 30% variation in species represented suggests that neither
sampling effort was intensive or effective enough to provide an accurate representation of the
entire forest population.
When examining the results of the study, one can note that the forest size, along with
species richness and evenness, assists resource managers with indications of the relationships in
this area. Animals use the forest for shelter to build their nest and den sites, and also rely on
native vegetation as a source for food. This affiliation implies that native wildlife is affected by
the composition and variety of the trees in the forest. For example, forests without oak trees are
likely to not house squirrels or wild turkeys, and a lack of dead trees within the forest will reduce
the inhabitation of woodpecker species. For example, forests without oak trees are likely to not
house squirrels or wild turkeys, and a lack of dead trees within the forest will reduce the
inhabitation of woodpecker species. In some situations, the age of the forest is additionally also
beneficial for some wildlife species. A 1969-82 study of ruffed grouse in central Wisconsin
found that the density of grouse more than doubled when the proportion of the aspen-oak forest
under 25-years increased from 13% to 55% (Cumming et al. 2007). All of these interactions
within the forest are important to biodiversity. However, there are many types of threats that can
reduce the biodiversity.
Wil-O-Way Woods, and other surrounding urban forests, are threatened by the accidental
introduction of various pathogens and invasive insect species. The most prevalent of which are
the oak wilt disease, Emerald Ash Borer (EAB), and the Dutch elm disease, which affect the oak,
ash, and elm respectively.
The fungus Ceratocystis fagacearum, whose origin is unknown but was introduced to the
United States from Mexico, is the cause of oak wilt. It is now confined to the borders of the U.S.,
but is most common in the Midwest. Oaks in the red/black category are more susceptible to
contract oak wilt, and will generally die in the course of a single summer. Symptoms of oak wilt
are easy to identify with physical signs of leaf and vascular discoloration, wilt, defoliation, and
death. Oaks in the white category share similar symptoms, but they generally live a few years
after contracting oak wilt. The fungus is primarily spread by dark beetle vectors (carriers from
diseased to healthy trees) and from diseased to healthy trees through root graphs, or connections
(Rexrode and Daniel 1993).
The most devastating and widespread tree disease to date in the U.S. is the Dutch elm
disease caused by the vascular wilt fungus, Ophiostoma ulmi. Much like the aforementioned oak
wilt disease, the Dutch elm is vectored by two species of beetles, the invasive European elm bark
beetle and the native elm bark beetle. Both spread from tree to tree through underlying root
graphs. Dutch elm disease results in a wilting and yellowing of the foliage. This is followed by
leaf death, defoliation and death of the affected branches. As the disease progresses, major limbs
die and eventually the entire tree is killed. Although Dutch elm disease is often associated with
the demise of the American elm, the majority of other elm species are affected as well (Hartman
and Eshenaur 2004).
Agrilus planipennis, Emerald Ash Borer, is an exotic beetle that was discovered in
Wisconsin in the summer of 2008. This beetle, originating in Asia, feeds on various portions of
the ash tree depending on its life stage. Adult beetles nibble on ash foliage, but cause little
damage overall. At the larvae stage, EAB’s feeds on the inner bark of ash trees, disrupting a
tree’s ability to transport water and nutrients, which leads to the tree’s demise. Although A.
planipennis prefers black and green oak, it will rapidly kill of white ash trees once green and red
ash is eliminated from the affected area. The devastating effects of the EAB, the death of 7.5
billion ash trees, rival that of the Dutch elm disease (Carlson and Karin 2006).
Within Wil-O-Way, the Emerald Ash Borer carries the most threat to the ecosystem.
Since the EAB has such a devastating effect on ash trees, it is important to understand the canopy
changes that can occur and how to prevent such loss. A previous investigation at Wil-O-Way
Woods conducted by Ahlers et. al. (2009) predicted that sugar maples would fill most of the gaps
in the canopy that would be created if emerald ash borer entered the forest. This study found that
the understory beneath the ash trees was dominated by small sugar maples. Due to the relatively
high shade tolerance of young sugar maples, this species would likely replace ash trees
throughout the forest and possibly through the entire range of ash-maple coexistence.
If remediation efforts are not made to stop the spread and destruction of these diseases,
the canopy of Wil-O-Way Woods could change drastically over the next decade or so.
Specifically in Wil-O-Way, if the EAB continues to wipe out ash trees, the canopy will have a
hard time recovering due to an overpopulated understory and the invasive buckthorn. The loss of
the oak, ash, and elm trees in the forest would directly correlate with a loss of organism diversity.
Certain organisms may depend completely on these trees, whether it be for shelter or food. The
reduction of tree diversity in Wil-O-Way could lead to the demise of these various organisms. In
order to prevent such a loss to the forest, efforts toward remediation need to be practiced.
To properly manage the urban forest, it first becomes a priority to develop a citywide
management team. Once a team is formed, the following steps need to occur: citywide funding,
gathering of assessment tools, protection of existing trees, and standards and goals for tree care.
In addition, plans need to be made in order to increase biodiversity within the urban forest. This
can be done through replanting efforts. Also, forest managers need to address the threats within
the ecosystem. One such practice done by Wisconsin is the quarantine of firewood. The DNR
restricts the movement of firewood into state parks or forests that was not from Wisconsin. The
firewood must also not originate more than 50 miles from the property that it will be taken to. In
addition to a quarantine, Wisconsin now offers an EAB pesticide. This product is injected into
ash trees in order to help control the invasive beetle (William and McNee 20008). Finally, it is
important to raise awareness in the community about the efforts that can be made in order to
protect the urban forest from decimation.
Through the use of the tree inventory performed along the major trails of Wil-O-Way
Woods, forest managers can create plans in order to increase biodiversity within the forest. If
proper managing can be done, then the overall health of the forest can be increased. With a
healthy forest, future generations will be able to enjoy the urban forest and its many gifts to the
environment.
Literature Cited
Ahlers, L., M. Sankey, and S. Hudson. 2009. Proposed gap succession of selected white ash trees
in Wil-O-Way Woods. Wisconsin Lutheran College.
Avery, T.E., and H.E. Burkhart. 2002. Forest Measurements. McGraw-Hill Higher Education,
New York.
Carlson, J. and V. Karin. 2006. Insect invasion. New York State Conservationist, New York.
Cumming, A. B., D. Nowak, D. Twardus, R. Hoehn, M. Mielke, and R. Rideout. 2007. Urban
forests of Wisconsin: pilot monitoring project 2002. Forest Service Northeastern Area,
United States Department of Agriculture. Newtown Square, PA.
Hartman, J. and B. Eshenaur. 2004. Plant pathology fact sheet: Dutch elm disease. University of
Kentucky Cooperative Extension Service. Lexington, Kentucky.
Molles, M. 2010. Ecology concepts and applications, 5th edition. McGraw-Hill, New York, New
York.
Rexrode, C.O. and B. Daniel. 1983. Oak wilt. U.S Department of Agriculture, Forest Service,
Washington, D.C.
Williams, L. and B. McNee. 2008. Emerald ash borer makes its Wisconsin debut. Wisconsin
Urban & Community Forests. 16(2): 3-7.
WLC (Wisconsin Lutheran College). 2004. Preliminary report on student investigations as WilO-Way Woods: fall 2003 and spring 2004. Wisconsin Lutheran College.