Preservation
Needs of the
Prairie
Path Glacial Ridge Natural Area
Marlin Bowles, The Morton
Arboretum, Lisle, IL.
Pat Armstrong, Prairie Sun
Consultants, Naperville, IL
SUMMARY
The
Prairie Path Glacial Ridge Natural Area is a unique geological and vegetation
feature bordering the Illinois Prairie Path.
It is situated on a remnant of one of the largest kame areas in DuPage
County, between the Illinois Prairie Path and the Chicago & North Western
railroad in unincorporated Glen Ellyn.
The site harbors an unusual assemblage of oak woodland vegetation on
gravel soils, including over 100 native plant species and a population of the
Illinois threatened pale vetchling.
This important site is threatened by development and by soil erosion
caused by bicycle use, and should be protected by a local conservation
organization.
INTRODUCTION
Because
the foresight of DuPage County conservation groups and agencies, most of the
natural areas of DuPage have been protected.
However, the Prairie Path Glacial Ridge Natural Area is a unique but
unprotected geological and vegetation feature that is threatened by development
and misuse. This area contains the only
known DuPage County population of the Illinois threatened pale vetchling (Lathyrus
ochroleucus). The tract of land
lies west of Hill Avenue and north of the Glen Oak Country Club. It is between the Chicago & North
Western Railroad on the north and the Illinois Prairie Path on the south, in an
unincorporated area of Glen Ellyn, Illinois.
Churchill Woods Forest Preserve is located to the north. The area appears to have escaped destruction
because it is located on a narrow triangle of land located between two railroad
rights-of-way. The railroad on the
south has been abandoned and converted into the Illinois Prairie Path, while
the Chicago & North Western is active.
However, unsupervised bicycle use of the area has caused severe erosion,
and a proposed housing development now threatens to significantly impact the
site. Action is needed to prevent
development of the site and to place it in ownership of a conservation
organization.
This
report describes the important geological and vegetation features of the area,
and suggests strategies for its protection.
GEOLOGY
In a 1912 study of the
geology of the Wheaton Quadrangle (Trowbridge 1912), which incorporates much of
DuPage County, two large kame areas were identified, one in the vicinity of
Bloomingdale, and the second at Glen Ellyn.
Kames are isolated glacial features that comprise mounds of water-sorted
gravel and sand left by melting ice along the front margins of glacial
moraines. The kame area at Glen Ellyn
comprised several hundred acres of gravel and sand overlying glacial till. The Illinois Prairie Path and the adjacent
right of way of the Chicago & North Western railroad now cross this
kame. The gravel substrate appears to
have been quarried and excavated to grade level for these railroad tracks,
resulting in steep gravel slopes that parallel the north edge of the prairie
path. However, the adjacent upper
slopes and top of the kame do not appear to have been heavily disturbed and
slope naturally to the east and west.
The soils developed in these gravels are extremely fragile and erode
quite easily.
VEGETATION
Because the kame remnant is
situated between two railroad rights-of-way, it appears to have escaped
extensive damage from over-grazing and agriculture. As a result, it harbors a diverse collection of native
vegetation, and parts of it appear to represent a rare intact example of oak
woodland vegetation. Over 100 native
plants occur at the site. The gravel
substrate and slopes of the kame contribute to the plant diversity of the site
in two ways. First, the site supports
plants that prefer dry gravel soils, such as the Illinois threatened pale
vetchling (Herkert 1991, Swink & Wilhelm 1994). Second, the slope gradient provides a range of soil-moisture
conditions that support a large number of plant species.
The lower and mid slopes of
the kame are wooded. Red and white oak
are common canopy trees on lower slopes, while big-tooth aspen, black oak, and
hills oak occur on the upper more well drained soils. Maple-leaved arrow-wood and American hazelnut, both uncommon
shrubs are also present, as well as a wide variety of typical woodland spring
wildflowers. The lower west slope of
the kame supports a colony of wild hyacinth, an indicator of former savanna
conditions, along with bracken fern, which is usually restricted to sand and
gravel soils. Other unusual or uncommon
woodland plants include few-flowered panic grass, hoary tick trefoil, the
loose-headed oval sedge, and Short’s aster.
Prairie plants such as big bluestem, rigid goldenrod, and prairie violet
occur on the highest exposed slopes of the kame, and the several patches of the
pale vetchling occur along shaded upper slopes.
PROBLEMS AND RECOMMENDATIONS
Uncontrolled use of the site
for bicycle paths has caused severe soil erosion to the upper slopes of the
kame, and is impacting the pale vetchling colonies. Current plans for a housing development on the site could result
in large-scale damage to the natural area.
To prevent these impacts, the site should be acquired and protected by a
local conservation organization.
Protection options might include incorporating the site into the
Illinois Prairie Path or including it within the Glen Ellyn Park District. Another option might be to include it as
part of the nearby Churchill Woods Forest Preserve. Once protected, unsupervised use of the site for a bicycle trail
should be halted. There is no need for
this use because of the adjacent official bicycle trial. Some restoration management will be needed
to restore vegetation on the eroding slopes and to control alien shrubs.
REFERENCES
Trowbridge,
A. C. 1912. Geology and geography of the Wheaton Quandrangle. Bulletin No. 19
of the State of Illinois State Geological Survey, University of Illinois
Urbana.
Herkert,
J. R. (editor). 1991. Endangered and Threatened Species of Illinois: Status and
Distribution. Volume 1 – Plants. Illinois Endangered Species Protection Board,
Springfield.
Swink,
F. & G. Wilhelm. 1994. Plants of the Chicago Region. Indiana Academy of
Science.
ATTACHMENTS
Species list
Site location map
Photographs