This article describes my project to classify historical land use of the Cedarburg Bog. I worked on this as a student at the University of Wisconsin-Milwaukee.

1. DEPARTMENT OF BIOLOGICAL SCIENCES AND FIELD STATION
UNIVERSITY OF WISCONSIN - MILWAUKEE
Landscape change over 60
years surrounding
Cedarburg Bog
Jason Schroeder, Jason Mills, Erica Young, James Reinartz
5/9/2008
Cedarburg Bog, a large forested wetland that includes diverse species existing near their southerly
limits, provides a unique setting in which to study long term ecological changes in response to
land use and climate changes. Land cover changes can alter the amount and distribution of
habitat available to organisms and this could, in turn, influence the movement of organisms and
their ability to respond to a changing climate. We used a GIS to quantify patterns of land cover
change by comparing a 1941 land cover map to a recent land cover map in order to explore
patterns of land cover change within recent history. To create a historical land cover map, we
scanned 1941 aerial photos to create digital images that were then georeferenced and joined into a
photo mosaic. A simple land cover classification scheme was manually applied to the historical
and recent imagery. Our preliminary results suggest two main changes on this landscape over the
last 60 years. Suburban developments now occur on patches of former agricultural land, and
roads associated with development have increased fragmentation. It also appears that forest cover
has increased due to reduced logging and abandonment of agricultural lands. Cedarburg Bog
remains a large, undisturbed wetland in an otherwise changing landscape. Changes in the
surrounding landscape could increase the abundance of non-native species and favor the
movement of organisms, native and non-native, within forested cover types.

2. Introduction
Cedarburg Bog is a 900 hectare forested wetland in southeast Wisconsin. The
Bog originated as a postglacial lake approximately 12,000 years ago with depths over 50
ft. deep in places. Over time, the lake began to fill with sediment mainly comprised of
plant and invertebrate detritus, and silt. This basin is now mostly filled with sediment
with the exception of 6 shallow lakes that dot the surface of the Bog. On top of the
sediments grow forested wetland and sedge meadows, a stark contrast to the open lake
system that once existed.
Largely undisturbed, the Bog hosts species of plants and birds that are typically
found further north and provides a sanctuary for some rare plant species (Reinartz, 1985).
Formally protected since 1952, this unique wetland remains relatively undisturbed. Land
cover changes on this primarily agricultural landscape could influence the wetland by
altering groundwater flow and the corridors that provide native and exotic species access
to the wetland. As part of a long-term study of ecological changes in Cedarburg Bog, we
analyzed historical and contemporary land cover from aerial photographs to quantify
landscape changes between 1941 and 2000 within the 10,000 hectare area surrounding
the wetland.
Methods
The 1941 images acquired from the University of Wisconsin Madison for this
project were 9” x 9” black and white aerial photo prints at a scale of 1:20,000. The
images were scanned at 1,000 ppi resulting in a resolution of 0.5 meters. The 2000
images were acquired from the United States Geological Survey (USGS) and are 1 meter
resolution black and white Digital Orthophoto Quarter-Quadrangles (DOQQ). The aerial

3. photos were georeferenced using a minimum of 20 ground control points and mosaicked
using ERDAS Imagine 9.1 software. The images were digitized in ArcGIS 9.2 creating a
classification schema consisting of the following six classes: agriculture, forest, water,
emergent wetland, shrub/scrub wetland, and forested wetland.
To more accurately represent forested land as suitable habitat, we determined that
minimum forest patch size would be five acres with a minimum of 67% canopy cover.
For example, if a five acre or larger patch had trees on it during the digitizing process, it
was classified as forest, but lost this classification if the trees did not account for at least
67% of the area. To eliminate patch sizes smaller than five acres the raster images were
resampled to 30 m resolution using nearest neighbor assignment. At 30 m approximately
25 pixels represents five acres. At 25 pixels, there would need to be at least 16 pixels
occupied by trees to retain the forest designation. Patches that did not meet these criteria
absorbed the designation of the surrounding cover type.
Finally, the vector shapefiles were then converted to rasters for statistical analysis
with Fragstats 3.3 software. Fragstats measured changes in the land cover types for the
following five categories: total area, % of landscape area, number of patches, mean patch
area, and mean nearest-patch distance.
Results
Figure 1 illustrates the statistics in land cover change from 1941 to 2000. Mean
forest cover increased from 1941 to 2000 in both upland forest and forested wetland.
Total mean forest area increased by 58% of which 31% was forested wetland with the
remaining 27% being upland forest. Mean patch size and number of patches increased

4. among both forested wetland and upland forest. There was a decrease in overall mean
nearest-patch distance for total forest from 145 m in 1941 to 97 m (33%) in 2000.
Table 1. Results from statistical analysis of land cover classification raster.
Total mean agriculture in the area decreased 16% during the interval while mean
patch area decreased by 81%. The number of agriculture patches increased from 15 to 67
(347%) while mean nearest-patch distance decreased by 6%.
Discussion
There are several trends prevalent among the forest and agriculture statistical data.
The first trend is that between the time periods 1941 and 2000, total forest cover has
increased dramatically. As a result, mean forest patches are larger, closer together, and
more continuous. Another trend related to the increase in forest cover is the decrease of
agricultural land. As agricultural lands decrease in patch size and become more
fragmented, there are more forest patches available and at closer distances for species
dependent on upland and wetland forest.
The increase in forest cover and connectivity has several implications affecting
the ecological integrity of the Cedarburg Bog. The effect from increased and better
connected forest cover around the Bog will enhance the habitat available to native
species. This will likely increase their mobility, thus affecting their range and

5. distribution. Counter to the productivity gained from more cover is the likelihood that as
native species become more mobile, so will exotic species who sometimes possess an
extraordinary capacity to outcompete native species. Finally, as urban development in
this area continues, agricultural activity will likely continue to decrease. As this happens,
the remaining agricultural land will become further fragmented and there will be both
losses and gains to the forest cover surrounding the Bog.

6. Appendix
References
Darst, C.R. 2006. Predator learning, experimental psychology and novel predictions for
mimicry dynamics. Animal Behaviour 71: 743-748
Reinartz, J.A. 1985 A guide to the natural history of the Cedarburg Bog: Part 1. UWM
Field Station Bull. 18(2):148