Transcript Document

Summary
Ground Beetles and Butterflies of Corn and Old Field Areas Along a
NE Iowa Trout Stream Before Riparian Habitat Reconstruction
Waterloo Creek is one of the premier trout streams in
NE Iowa. In August 2004, a major habitat reconstruction
project involving stream bank stabilization and
rehabilitation, and conversion of corn fields, grassy old
fields, and wooded riparian areas to tallgrass prairie is
occurring at the confluence of Waterloo Creek and Duck
Creek in NE Iowa. Beginning in 2003 prior to the
reconstruction, we sampled ground beetle assemblages
with pitfall traps and butterflies with a visual survey to
provide baseline data beginning in 2003. As of 2005,
25 species of butterflies (an increase from only 11
species in 2003 and 8 species in 2004) have been
found during July transect surveys. Currently, 29
species of ground beetles have been found on site by
pitfall trapping (2005 samples are still being processed).
We hypothesize that as the tallgrass prairie planting this
winter (2005-06) becomes established in former old
field, corn field, and riparian areas, both butterfly and
ground beetle diversity (richness and abundance) will
continue to increase. Future monitoring will quantify
long-term changes and correlate plant species richness
and productivity with insect community diversity.
Kirk J. Larsen
Department of Biology, Luther College, Decorah, Iowa
Ground Beetle Survey Results
Why Remove Trees from the Stream Banks?
Tree cover along Waterloo
Creek hides extensive
stream bank erosion. The
banks were eroding due to
inadequate root support
from the box elder trees
with shallow roots and the
reed canary grass that
dominated the banks.
Following removal of the
box elder trees and reed
canary grass, tallgrass
prairie plants on the newly
stabilized banks such as
prairie cordgrass grow
thick, deep root networks
that stabilize and hold the
banks, reducing erosion
and improving reproductive
habitat for the trout.
Ground beetles (Coleoptera: Carabidae) have been
sampled using 18 oz cup pitfall traps. Twelve pitfall
traps have been placed in each of the former corn field
and old field riparian areas for one-week sampling
periods in June, July & August beginning in 2003. In
the corn field in 2003, only 8 species were found, but in
2004, these areas were fallow with a more diverse
annual weed community beginning to develop and
hosted 17 species of ground beetle with a reduction in
the abundance of common agricultural species typically
found in corn such as Poecilus chalcites and Scarites
quadriceps. Thus there was a significant change in the
ground beetle assemblage in corn field areas from 2003
to 2004 (t=16.56; df=316; p<0.001). In the grassy old
field areas dominated by brome grass, there was no
significant change from 2003 to 2004 in the abundance
or diversity of ground beetles (t=1.65; df=213; p=0.09)
but there also was little observed change in the plant
community composition.
Pitfall trap in corn field in 2003.
This 98-acre site located at the confluence of Waterloo
Creek and Duck Creek, 1 km NW of Dorchester in
Allamakee County, Iowa, includes valley bottom
formerly planted to corn and soybeans, and overgrown
oak savanna forest. Since 2003, we have been
monitoring aquatic insect communities in the streams,
and butterfly populations and ground beetle
communities in the former corn and old field riparian
areas as the habitat reconstruction has began. Future
monitoring will continue as the prairie and savanna
areas become reestablished.
Conclusions
Pitfall trap in fallow corn field in 2004.
Butterfly Survey Results
A 1,500 m long sampling transect across the riparian
area of the property has been established, and
monitored for butterfly activity each July since 2003. All
butterflies observed or collected in an approx. 5 m wide
band along the transect were identified to species and
counted. Before any work was done, the site was
dominated by corn, box elder trees, and reed canary
grass. Only 11 species of butterflies were found on-site
in 2003. In 2004, following removal of the box elder
trees and spraying of reed canary grass with the corn
fields left fallow, annual weeds were just beginning to
emerge after extensive earthmoving. The butterfly
populations took a hit in 2004, with only 8 species being
present, and only 6 of those species being found in both
2003 and 2004. This did result in a significant change
in this small butterfly community from 2003 to 2004
(t=2.13; df=52; p=0.04). In 2005, after some prairie
areas had been planted, and many native prairie plants
appeared from the seed bank, we had a significant
change (t=1.99; df=51; p=0.049) in the butterfly
community with a jump to 25 species and a 10X
increase in butterfly abundance over previous years.
The ongoing reconstruction of a more diverse riparian
habitat along Waterloo Creek has reduced erosion into
the stream, improved trout habitat, and is changing the
terrestrial insect communities along the stream. The
prairie reconstruction is increasing butterfly and ground
beetle species diversity and abundance. As the prairie
seeding on most of the site becomes established during
2006, we expect to see an even greater jump in overall
terrestrial species diversity and insect abundance as
evidenced by these indicator groups. Ongoing studies
carried out by the Luther College biology department
will continue to monitor ongoing changes in the plant
and insect communities at this site.
Pitfall trap in grassy old field in 2003 or 2004.
Acknowledgements
Generous financial support for this project has come
primarily from Dr. Michael Osterholm. Additional funds
for summer undergraduate research positions were
provided by the R.J. McElroy Trust Student/Faculty
Research Fund and Luther College Summer
Undergraduate Student-Faculty Collaborative Research
Program. Collaborators include the Iowa DNR, USDANRCS, Trout Unlimited, and Driftless Land Stewardship.
Luther biology students Katie Hopp, Deneb Wood,
Derek Broman, Mike Thompson and other students
have contributed to the ongoing collection and analysis
of data for this project.