THE FRAGMENTATION OF TERRESTRIAL HABITATS ALONG THE
UPPER MISSISSIPPI RIVER CORRIDOR  

Craig, Mary R.1

1U.S. Geological Survey - Biological Resources Division, Environmental
Management Technical Center, Onalaska, WI 54650.  

Major landscape transformations related to rowcrop cultivation, deforestation,
navigation, and urbanization may all directly contribute to the fragmentation of
terrestrial habitats within riverine landscapes.  I present the results of my analyses
of the fragmentation of terrestrial habitat types (forests, "grasses/forbs", and
"sand/mud") within six landscapes along the Upper Mississippi River corridor. 
Traditional models of habitat fragmentation include processes such as habitat
loss, increases in patch density, diminution in patch size, and increases in
interpatch distance.  The results of my analyses, however, do not entirely
conform to traditional models.  Habitat loss over the past 100 years has indeed
been extensive.  Losses of forested habitat range from 19.11 percent to 64.37
percent; losses of "grasses/forbs" habitat range from 26.76 to 47.09 percent;
losses of "sand/mud" habitat range from 62.7 to 96.37 percent.  Although the
density of forested patches and "grasses/forbs" patches has increased in each
landscape, the density of "sand/mud" patches has decreased dramatically.  The
average size of forest patches has decreased  (p< .05) in each landscape; the
average interpatch distance (edge to edge) has, however, decreased (p< .05). 
Although the average size of "grasses/forbs" patches has decreased (p < .01) in
four landscapes, the average interpatch distance has decreased (p < .0001) in each
landscape.  The average size of "sand/mud" patches has not changed appreciably
in five landscapes, and changes in interpatch distance vary among all landscapes. 
My analysis of patch dispersion shows that shortly before the turn of the century
patches of forest and of "grasses/forbs" were randomly distributed within each
landscape; today, however, they exhibit an aggregated distribution.  Patches of
"sand/mud" once exhibited and still maintain an aggregated distribution.  Within
riverine landscapes, the effects of the fragmentation of terrestrial habitat types
may be offset by the aggregation of terrestrial habitat patches which confers a
degree of habitat connectivity that has not been observed in other landscapes.

Keywords: habitat fragmentation, forests, sand/mud, grasses/forbs, Mississippi
River

Mary R. Craig.  U.S. Geological Survey - Biological Resources Division,
Environmental Management Technical Center, 575 Lester Avenue, Onalaska, WI
54650.  Phone: (608) 783-7550, ext. 710., FAX (608) 783-8058,  e-mail:
Mary_R_Craig@nbs.gov.  

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