Change in Savanna Land
Cover in
the Oak Openings Region
of Northwest Ohio
1984-2000
by Elizabeth A. Mather
Abstract
Introduction
Data Description
Methodology
Results
Conclusions/Future Directions
References
Elizabeth A. Mather
Graduate Student
Department of Geography & Planning
University of Toledo
[email protected]
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Change in Savanna Land Cover in
the Oak Openings Region of
Northwest Ohio
1984-2000
Abstract
The Oak Openings Region of Northwest Ohio is a unique ecosystem harboring a number
of rare and endangered plant and animal species. Many of these plants and animals rely
on savanna habitats. The degradation of this ecosystem has had a significant impact on
these species. In recent years, there has been an effort not only to conserve this
ecosystem but also to restore degraded areas within it. This study seeks to evaluate the
change in savanna coverage within the Oak Openings from 1984 to 2000 by analyzing
Landsat satellite data. To evaluate this change, I performed two land cover
classifications (one of 1984 and one of 2000). I then did a change detection highlighting
the areas where savanna coverage has changed. This research show a 10% increase in
savanna cover from July 13,1984 to July 1, 2000. This was done by performing hard
classifications. In the future I will be evaluating the change in savanna cover though the
use of fuzzy classifications.
Index Introduction Data Methodology Results Conclusions References
Change in Savanna Land Cover in
the Oak Openings Region of
Northwest Ohio
1984-2000
Introduction
What is the Oak Openings?
The Oak Openings Region of Northwest Ohio in present day, is located southwest of
Toledo in Lucas, Henry, and Fulton Counties (TNC, 1997). It covers between 130
(Brewer et al., 1993) and 160 square miles (Leach et al., 1995) and is roughly 40 miles
long by 5 miles wide. Historically, the area was larger, covering up to 300 square miles
and reaching as far as Detroit, MI to the north and into Wood County to the south (TNC,
1997).
The term oak openings is another word for oak savanna. R. Henderson is quoted from a
1995 publication of the Wisconsin Department of Natural Resources as describing the
North American Midwestern oak savanna as follows:
Fortunately for us in the Midwest, the term “savanna” has a relatively narrow definition.
Here it is generally used to describe an ecosystem that was historically part of a larger
complex bordered by the prairies of the west and the deciduous forests of the east. This
complex was a mosaic of community types that represented a continuum from prairie to
forest. Savannas were the communities in the middle of this continuum. The mosaic was
maintained by frequent fires and possibly by large ungulates such as bison and elk (Kline,
1997).
In Northwest Ohio, the Oak Openings are found on a sand belt deposited as beach ridges
formed by post glacial lakes (Lakes Warren I, II, III, and Lake Wayne) about 12,700
years ago (TNC, 1997). The ecosystem, which has formed on this sand belt, makes the
region unique.
The Oak Openings is currently home to one third of all Ohio endangered plant species
including among others, prickly pear cactus (Opuntia humifusa), Hairy pinweed (Lechea
villosa), and Canada frostweed (Helianthemum canadense) (Leach et al., 1995). The
variety of ecosystems within the region creates the diversity of habitats that allow such
large numbers of endangered species to exist in such a small area. “Prior to EuroAmerican settlement, they (the Oak Openings) consisted of 43% oak savanna (4-43
trees/hectare), 27% wet prairie (<1 tree/hectare), 23% oak woodland (44+ tress/hectare)
and 6.7% oak barrens (1-3 trees per hectare) (Brewer et al., 1993).”
“The Oak Openings, however, has persisted as one of the few landscape scale oak
savanna/prairie complexes left in the Midwest (TNC, 1997).” Up to 30 million acres of
oak savanna was once spread throughout the Midwest (class notes, 12/04/00). In 1985 a
survey of high-quality oak savanna estimated that only 0.02 percent of the original oak
savanna community (from presettlement time) remained (Leach et al., 1995).
The two main processes that maintained the Oak Openings of Northwest Ohio were the
impermeable glacial till topped by sandy soil (which discouraged typical surface drainage
patterns) and fire. These two processes worked together to discourage woody vegetation
(TNC, 1997). When Euro-American settlers moved into the region they altered the
hydrologic structure and suppressed fire thereby affecting the ecosystem functions in the
region.
What is a savanna?
Savannas (Midwestern oak savannas) lie within the continuum of land cover from prairie
to forest. Below is a diagram and definitions from the book, A Tallgrass Prairie
Restoration Handbook (see references).
Prairie: a fire-maintained natural community dominated by grasses and with few or no
trees
Savanna: a fire-maintained natural community dominated by grasses or sedges but with
scattered fire-tolerant species of trees
Woodland: a fire-maintained natural community with a grassy turf dominated by trees
Forest: a closed-canopy, wooded natural community that is not dependent on frequent
fire. There are typically one or more layers of shade-tolerant trees or shrubs below the
canopy trees and no grassy turf
Below is a historical map of the Oak Openings. It primarily shows Lucas County, Ohio
but it indicates how the region extends up into Monroe County, Michigan and down into
Fulton and Henry Counties, Ohio.
Index Abstract Data Methodology Conclusions References
Change in Savanna Land Cover in
the Oak Openings Region of
Northwest Ohio
1984-2000
Data
Landsat 5 Thematic Mapper
30 meter spatial resolution
7 spectral bands
The primary data used in this study is remotely sensed data. I have analyzed two Landsat
images. One from July 13, 1984 and another from July 1, 2000. The 1984 image is a
Landsat 5 Thematic Mapper image. It has a spatial resolution of 30 meters and seven
spectral bands. The 2000 image is a Landsat 7 Enhanced Thematic Mapper image. It
Landsat 7
30 met
7
also has a spatial resolution of 30 meters and I used seven spectral bands which
corresponded to the seven Landsat 5 spectral bands.
Some data preparation was necessary before I could begin classifying and analyzing these
images. I had to georectify the 1984 image to the 2000 image. It was a systematic
georectification error and therefore fairly easy to correct. I chose 35 ground control
points to perform the georectification. Because the 1984 image was just slightly shifted
from the position of the 2000 image, there was little error after georectification. I also
needed to subset the image to make it easier to analyze. I did that by converting an
ArcView shapefile into an AOI (area of interest) within Erdas Imagine. I then used to
AOI to subset the image.
As you can see in the 2000 image above, there are some popcorn cumulus clouds that
could cause classification problems. Luckily, most of the clouds are outside my area of
interest (the Oak Openings). You can see the Oak Openings fairly clearly in both images
because of the large number of trees which are present. In the false color infrared images
above, the trees and other vegetation appear in red.
I also used a digital orthophoto of Lucas county (1997) (ARIES CD) as a reference when
I did the accuracy assessment.
Index Abstract Introduction Methodology Conclusions References
Change in Savanna Land Cover in
the Oak Openings Region of
Northwest Ohio
1984-2000
Methodology
Steps in Data Processing:
1. Obtain data
2. Delineate the Oak Openings Boundary
1. Defined the boundary based on sandy soils - from Ohio GIMS data
2. Created a polygon in ArcView to use as and AOI (area of interest) in
Erdas Imagine - I then performed the land cover classification within the
boundary
3. Locate good savanna sites to use as training sets
1. Talked to Gary Haase at the Nature Conservancy's Kitty Todd Preserve
2. Consulted the 1997 digital orthoquad of Lucas County
3. Performed an unsupervised classification
1. This allowed me to identify 15 spectrally distinct classes in the
2000 image to use for training sets in the supervised classification
1984
Unsupervised
Classification
2000 Unsupervised Classification
4. Create the training sets
1. Located Kitty Todd preserve and the savanna areas within it on the
Landsat image and on the aerial photo
2. Performed an unsupervised classification using 50 classes to identify other
areas with similar spectral signatures - see links above
5. Run the classification on each image
1984 Supervised
Classification
2000 Supervised
Classification
6. Aggregate the classes into more basic classes
1984 Final
Classification
2000 Final Classification
7. Evaluate the validity of the classification
1. Chose 50 stratified random points per land cover class (except for water
and clouds - for each of those I chose only 20 points to prevent them from
biasing my accuracy assessment
2. Compared the classification to the Landsat images themselves as well at to
the 1997 digital orthoquad (only the 2000 classification) determining
whether each pixel was correctly classified.
1984 with Savanna
Class
Unclassified Water Forest Savanna Agriculture/Grass Residential Urban/Tran
Unclassified
Water
Forest
Savanna
Agriculture/Grass
Residential
Urban/Transportation
0
0
0
0
0
0
0
0
20
0
0
0
0
0
0
0
50
17
1
0
0
0
0
0
30
0
0
0
0
0
0
3
46
2
10
0
0
0
0
1
48
0
0
0
0
0
2
0
40
Column Total
0
20
68
30
61
49
42
Class
Producer's Accuracy
(omission)
Water
100%
Forest
73.53%
Savanna
100.00%
Agriculture/Grass
75.41%
Residential
97.96%
Urban/Transportation 95.24%
User's
Accuracy
(commission)
100%
100%
60%
92%
96%
80%
Overall Classification Accuracy
86.67%
1984 without Savanna
Class
Unclassified Water Forest Agriculture/Grass Residential Urban/Transportation
Unclassified
Water
Forest
Agriculture/Grass
Residential
Urban/Transportation
0
0
0
0
0
0
0
20
0
0
0
0
0
0
50
1
0
0
0
0
0
46
2
10
0
0
0
1
48
0
0
0
0
2
0
40
Column Total
0
20
51
58
49
42
Class
Producer's Accuracy
User's
Accuracy
(omission)
(commission)
Water
Forest
Agriculture/Grass
Residential
Urban/Transportation
100%
98.04%
79.31%
97.96%
95.24%
100%
100%
92%
96%
80%
Overall Classification Accuracy
92.73%
2000 with Savanna
Classes
Unclassified Water Forest Savanna Agriculture/Grass Residential Urban
Cloud/C
Shadow
Unclassified
Water
Forest
Savanna
Agriculture/Grass
Residential
Urban
Cloud/Cloud
Shadow
0
0
0
0
0
0
0
0
20
0
0
0
0
1
0
0
50
12
3
0
0
0
0
0
21
1
1
0
0
0
0
17
48
1
10
0
0
0
2
1
48
4
0
0
0
0
0
1
32
0
0
0
0
0
1
4
0
3
0
0
0
0
0
17
Column Total
0
24
65
23
76
55
33
22
Classes
Producer's Accuracy
(omission)
Water
83.33%
Forest
76.92%
Savanna
91.30%
Agriculture/Grass
63.16%
Residential
87.27%
Urban
96.97%
Cloud/Cloud Shadow 77.27%
Overall Classification Accuracy
User's
Accuracy
(commission)
100%
100%
40.38%
90.57%
92.31%
63%
85%
79.19%
2000 without Savanna
Classes
Unclassified Water Forest Agriculture/Grass Residential Urban Cloud/Cloud Row
Shadow
Tota
Unclassified
Water
Forest
Agriculture/Grass
Residential
Urban
Cloud/Cloud
Shadow
0
0
0
0
0
0
0
20
0
0
0
1
0
0
50
3
0
0
0
0
0
49
1
10
0
0
0
1
48
4
0
0
0
0
1
32
0
0
0
0
1
4
0
20
50
53
51
51
0
3
0
0
0
0
17
20
Column Total
0
24
53
60
53
33
22
245
Classes
Water
Forest
Agriculture/Grass
Residential
Urban
Cloud/Cloud Shadow
Producer's Accuracy
User's
Accuracy
(omission)
(commission)
83.33%
94.34%
81.67%
90.57%
96.97%
77.27%
100%
100%
92.45%
92.31%
62.75%
85%
Overall Classification Accuracy
87.80%
8. Run a change analysis
1. Before doing this it was necessary to aggregate the classes again so that I
was performing the change analysis on one class at a time. This allowed
me to see where each class decreased in land area, remained the same or
increased.
2. I used the Change Detection Model within Erdas Imagine to perform this.
Change in Savanna
Change in Forest
Change in Forest & Savanna
Change in
Agriculture
Change in Urban & Residential
9. Evaluate the change in savanna coverage for NW Ohio from 1984-2000
Index Abstract Introduction Data Results Conclusions References
Change in Savanna Land Cover in
the Oak Openings Region of
Northwest Ohio
1984-2000
Results
Savanna has increased 10%
Forest has decreased 2.33%
Savanna & Forest combined have increased 7.8%
Agriculture/Grass has decreased 8.27%
Residential has decreased 3.99%
Urban/Transportation has increased 3.66%
The decrease in forest cover could be due, in part, to the increase in savanna cover.
When savanna and forest cover were combined, they show an overall increase in cover.
The increase in savanna cover is due in part to the decrease in agriculture. The decrease
in residential appears unusual in a region that is suffering from urban sprawl but that may
be due to the maturation of trees within older neighborhoods as well as possible misclassification of residential as savanna. The clouds in the 2000 image may also have
affected these results.
Index Abstract Introduction Data Methodology Conclusions References
Change in Savanna Land Cover in
the Oak Openings Region of
Northwest Ohio
1984-2000
Conclusions/Future Directions
There are a number of things I would like to do to improve this study in the future. I will
be performing a fuzzy classification of the Oak Openings. This would more accurately
classify savanna and forest due to the continuous nature of the cover types. Another way
I could improve this study is through the use of more in situ data collection both for
creating more accurate training sets as well as for the accuracy assessment. It is very
difficult to distinguish savanna cover from forest cover from the Landsat images visually
so the accuracy assessment of the 1984 image may be particularly weak. Obtaining aerial
photos for 1984 would greatly aid both training set selection as well as accuracy
assessment.
Index Abstract Introduction Data Methodology Results References
Change in Savanna Land Cover in
the Oak Openings Region of
Northwest Ohio
1984-2000
References
Brewer, L.G., Grigore, M.T. (1993). Restoring Oak Savannas in Northwest Ohio – Monitoring the
Progress. Proceedings of the Midwest Oak Savanna Conference 1993 Chicago.
http://www.epa.gov/grtlakes/oak/oak93/brewer.htm
Dobson, A.P., Bradshaw, A.D., Baker, A.J.M. (1997). Hopes for the Future: Restoration Ecology and
Conservation Biology. Science 227: 515-522.
Kline, V.M. (1997). Orchards of Oak and a Sea of Grass. The Tallgrass Restoration Handbook for Prairies,
Savannas, and Woodlands. Island Press, Washington, D.C.
Leach, M.K., Ross, L. (1995) Midwest Oak Ecosystems Recovery Plan: A Call to Action. 1995 Midwest
Oak Savanna and Woodland Ecosystem Conference. http://www.epa.gov/grtlakes/oak/oak95/call.htm
The Nature Conservancy (1997) Oak Openings Site Conservation Plan. U.S. Environmental Protection
Agency Webpage. http://www.epa.gov/grtlakes/ecopage/oakopen.html
Packard, S., Mutel, C. (1997) The Tallgrass Restoration Handbook for Prairies, Savannas, and Woodlands.
Island Press, Washington, D.C.
Index Abstract Introduction Data Methodology Results Conclusions