Central Tillplain Ecoregion
The greater Pigeon River ecosystem, located in northeastern Indiana,
is among the most significant biodiversity sites in the Great Lakes
watershed and is perhaps best known for its extensive wetlands which support
many imperiled plants, reptiles and amphibians. In the highly agricultural
Midwest, where most of the landscapes has been co-opted for agricultural
use, the expanse of natural habitats associated with this river
are an anomaly. Included in the Pigeon River ecosystem wetlands is one
of the largest concentrations of alkaline fen communities in the
lower Great Lakes region. Fens are influenced by a flow of highly mineralized
groundwater, water rich in calcium and magnesium carbonate. Upon
exposure to the air, these minerals precipitate into marl, which in combination
with cool temperatures and anoxic conditions, inhibits organic decomposition.
Alkaline peat deposits
dominate most fen soils. Because of these unique conditions, fens support
a variety of plants and animal that are otherwise rarely encountered
in the greater landscape.
| Other important habitats include several examples of remnant upland oak communities and the Pigeon River itself. The oak uplands surrounding the Pigeon River were originally dominated by grasslands, wetlands, and dry oak woodland and savanna communities. Scattered remnants of these communities persist in the area today. Seasonal droughts and associated fire were originally frequent in the surrounding landscape, and help shaped a series of communities influenced both byforest and prairie. The uplands surrounding the River, especially those on sandy glacial-outwash, were especially interesting and likely represented a dynamic array of successional habitats such a xeric prairie, oak savanna and oak woodlands that today are globally imperiled. |  |
The overall variety and juxtaposition of wetland and upland community types along the Pigeon River makes this system especially valuable from a conservation perspective. The system contains a wide array of wetlands adjacent to several different examples of upland oak communities. The combination of diverse wetlands and uplands in such close proximity makes the Pigeon River ecosystem an especially critical habitat for several threatened and rare animal species, many of which rely on both upland and wetland habitats at some point during their life cycles.
* One of nine Hoosier Landscape
sites, where the Conservancy works at a scale that transcends typical
protection-based conservation.
* Initial site conservation
planning was funded by EPA ’s Great Lakes Program Office. This produced
a successful planning
and research
consortium composed of various DNR divisions, Heritage, TNC and regional
universities.
* Much, but not all of the
ecologically significant habitats are already protected by IN-DNR and
most are managed for
natural attributes.
Over 12,000 acres are in conservation ownership.
Conservation Targets
The Pigeon River supports an impressive variety of globally imperiled conservation targets, both at the community level as well as individual species. Thirteen globally imperiled terrestrial plant communities are reported by the Indiana Natural Heritage Data Center from the Pigeon River ecosystem. Twelve of these community types are wetlands, emphasizing the importance of the system form the perspective of wetland conservation. The expansive forested wetlands that dominate the riverine corridor represent the most extensive forested system remaining in extreme northeastern Indiana. The concentration of open wetlands, especially of fens, is notable from a regional perspective, and represents a real opportunity for globally significant conservation in the system.
 |
Species element occurrences abound in the system. Over 120 state- imperiled species (five globally imperiled) have been reported from the greater Pigeon River Ecosystem, a strong testament to the integrity of extent of the habitats persisting in the system. These species’ habitat requirements run the entire gamut, and included are aquatic, wetland and upland dependant species. Over 70 state imperiled vascular plant species are known from the greater system. The vast majority of these are wetland dependant species, and the herbaceous fens, forested fens, floodplain forests, shrub carrs and emergent marshes are especially critical. A few species are associated with upland sites, such as oak savanna remnants and oak woodlands. |
The Pigeon River wetlands play a critical role in supporting imperiled vertebrates. Wetland habitats in the system support the bulk of the 39 state imperiled imperiled amphibians and reptiles (three are globally imperiled), as well as many of the imperiled birds and mammals. The significance of the wetlands as critical habitats, especially the herbaceous wetlands, is probably attributable to the extent and distribution of these habitats along the riverine corridor. It seems likely that these wetland habitats have created regional metapopulations of many habitat restricted species, and that has allowed several species that are experiencing regional decline, to persist in the greater Pigeon River system. Other important vertebrate habitats include the riparian extensive forests in the system, especially for neotropical migrant birds.
The insect communities of note fall out into three discrete categories, those associated with the wetlands ? especially fens, those associated with oak savanna/grassland remnants, and the aquatic species inhabiting the river. Of these habitat associated communities, the fens support the largest number of imperiled species. Significant numbers of globally/regionally rare butterflies, moths, leafhoppers, and dragonflies thrive in these specialized wetlands. The oak savanna remnant associated insect communities have not faired as well, but a handful of imperiled species still persist at scattered locations throughout the system, indicating that that other, but undetected, grassland invertebrates likely persist in the system. The Pigeon River provides habitat for several imperiled dragonflies and supports a small but important community of unionid mussels, including one species known in Indiana only from this river.
Uplands:
Oak woodlands and barrens communities once dominated much of the upland
in the project area. Quality oak communities are less common than
are wetland communities within the project area. These upland communities
have been largely converted to agriculture, but remnants remain on both
public and private lands. Oak woodlands and barrens are fire adapted,
and the communities benefit from a frequent burn cycle. Due mainly to
fire suppression, the once open barrens/woodland communities that
once characterized the surviving remnants have now converted into closed
forest. Consequently, much of the sun-loving herbaceous flora that
requires is now relatively uncommon in the area. Although the bulk
of these species are not necessarily state listed or imperiled, high-quality
oak woodlands and barrens communities are rare themselves rare, and are
a high priority conservation target.
Many of the surviving oak communities have also been degraded by livestock grazing, and have sever problems with exotic species such as Alliaria petiolata (Garlic Mustard), Elaeagnus unbellata (Autumn Olive), and Lonicera maackii (bush honeysuckle).
Wetlands:
Although still common in the project area, natural wetland communities
have also been severely impacted by past conversion to agricultural use
and by hydrologic manipulations some of which were intended to drain
the wetlands while other manipulations have inundated other wetlands.
Both types of hydrologic manipulation may entirely destroy the native
plant communities originally present. The large number of imperiled species
present in the Pigeon River system that require wetland habitats reflects
both the high-quality of remaining habitats in the system, as well as
the efficiency with which wetlands have been destroyed and altered on
a regional basis and local basis.
Fire suppression is also a threat to the wetland/fen communities. While succession is slowed under the harsh environmental conditions in these habitats, it can still proceed to the point that without natural disturbance the character of the wetland, especially herbaceous wetlands, can be lost. Originally, the combination of wildfire and intense clearing by beaver probably played a role in maintaining these open habitats. In the absence of these processes, woody species are able to encroach further in to the fen, and alter the hydrology by absorbing more water with their deeper roots. This in turn, causes the fen to become drier and consequently, the viability of fen- associated plant species diminishes. As a result, some of the fens, marshes and wet prairies have succeeded into a greater importance of woody species.
In addition to fire suppression, there are also other factors that continue to degrade the wetland and aquatic communities in the project area. Drainage from ditching and tileing in the surrounding agricultural fields has lowered water levels in many of the wetlands, especially the fens. Further, nutrient loading and siltation from agricultural runoff and increased have negatively impacted these communities. Impacts from nutrient loading are apparent at several sites in the system, especially in wetlands downslope from active and historical farms and the town of Mongo, due mainly to runoff from both agricultural and urban sources. This causes an influx of nutrients into a nutrient-poor community, altering the species composition, and nutrient levels in the community.
An issue that requires further study is the potential impact that irrigation systems may have on local groundwater levels (Appendix 1). The fens and the river itself depend on abundant surface discharge of groundwater. The uplands surrounding the project area are primarily agricultural, and most fields have pivot irrigation systems. These may be numerous enough to impact ground water levels, especially in late summer when rains are infrequent and groundwater levels are typically at their lowest. Preliminary analysis indicates that the recharge areas surrounding the project area are extensive, alleviating some concern about this potential stress. However, more detailed analysis is required to determine if pivot irrigation is a threat to the integrity of this system, and if so, what strategies may be used to moderate this impact.
There are several isolated fens on both the north and south sides of the Pigeon River. These fens lack connectivity to the central part of the ecosystem, and the species present at these fens have the potential to become isolated. Because of their isolation, the species at these sites are more susceptible to genetic drift, via the bottleneck effect. This could lead to a decline in any given population, especially for species that are more mobile and require different habitat types throughout their life cycle. For some species that have only a few remaining populations, this is a serious threat. An effort should be made to create a protected corridor from the Pigeon River to these outlying, but still high quality natural areas.
Major Science and Stewardship Activities
* Regional groundwater
flow analysis completed including hydrologic characterization of
the fens.
* Mark-recapture and
radio telemetry for analysis of imperiled reptiles - massasauga, Blanding’s
turtle and spotted turtle.
* Complete GIS developed
for the project, including presettlement vegetation, current land
cover type, extant fens, spatial analysis of
connectivity,
etc.
* Intensive inventory
of Lepidoptera, leafhoppers and Odonata.
For more information, please contact John Shuey at jshuey@tnc.org