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Plant Communities of the Forest Preserves of Winnebago County

Prairie Communities

The original prairie landscape of Illinois as a mosaic of different prairie types that evolved in response
to variations in climate, soils, fire, and hydrology.  Some prairies were very wet and dominated by sedges and other wetland plants capable of tolerating saturated conditions.  Other prairies were extremely dry and supported short-statured grasses and prickly pear cactus.  In between these extremes were several other prairie types, the most widespread and diverse of them all was the mesic black-soil prairie. This fertile prairie was transformed into an agricultural landscape seemingly overnight.  The mesic prairie type is now considered among the rarest prairies in Illinois. Native plants and animals are still responding to the dramatic landscape changes that occurred as prairies were plowed under and drained for agriculture; and many species are not responding well.  So, all prairie types are important when we consider native wildlife populations and FPWC works to protect and restore as many of these prairies as possible and at a scale capable of supporting viable populations of birds, mammals, insects, and reptiles. READ MORE>>

Savanna Communities

The oak savanna was once one of the most common vegetation types in the Midwest but is today highly endangered. Intact oak savannas are now one of the rarest plant communities on earth. However, many degraded oak savannas still remain and can be restored.

A savanna is generally defined as a plant community where trees are a component but where their density is so low that it allows grasses and other herbaceous vegetation to become the actual dominants of the community. Savannas are often defined in terms of the openness of the tree canopy. Thus, the upper limit between savanna and forest is generally considered to be a tree canopy with 50% coverage. Therefore, if more than one-half of the ground area is in the sun at noon in midsummer, the vegetation is classed as a savanna. It the canopy has greater than 50% tree canopy coverage, the vegetation is called a woodland or forest. The lower canopy coverage, between savanna and prairie, is generally considered to be 10% tree coverage, although these upper and lower limits are only approximate.

Forest Communities

Northern Illinois’ woodlands have decreased by 80% since settlers cleared most of this region for farming. The various woodland habitats that once defined this region are now limited to a few relicts that provide the last refuges for the insects, birds and animals that depend on them. Not only has the number of forested acres generally diminished over the decades, but the biodiversity of the forested communities has suffered. Unfragmented, landscape-scale forest is of vital importance to a long list of plants and animals dependent upon this habitat.

The largest threats to our remaining forests are fragmentation and clearing for farming and development, both commercial and residential. Size is as important as ecological quality to the woodland’s ability to support native plant and animal communities. Interior woodlands are a rare ecosystem, especially in our area of the country. Many plants and animals require the woods they live in to be large and continuous without edge effect. The ground nesting warbler, for example, must have large tracts of forest ecosystem to successfully nest. Edge effect is the term used to describe a small natural area’s vulnerability to negative impacts that assault its extensive outer borders. Forest fragmentation negatively impacts the long-term sustainability of plant and animal communities. Migratory pathways, food sources and breeding grounds are lost or divided. Fragmentation harms many woodland birds, by making them more susceptible to predators like jays, crows, raccoons and cats – creatures not typically abundant in extensive forests.

Probably the greatest concern is the status of healthy upland oak woodlands and savannas. In their natural evolution, our oak woodlands were large. Even those oak groves surrounded by prairie tended to be rather extensive. Large woodlands provide a wide range of habitats for plants and animals and can be resilient. Conversely, small woodlands provide relatively little habitat and are very susceptible to disease, storms and other disturbances. A tornado could wipe out a 20-acre woodland, but if that woodland were 500 acres or more, such a disturbance would likely add to the diversity of the woodland ecosystem. Large tracts of upland oak woodlands, 100-plus acres, are becoming exceedingly rare. READ MORE>>

Wetland Communities

Wetlands are parts of our landscape that are defined by the presence of water. More specifically, wetlands are areas where the presence of water determines or influences most, if not all, of an area’s biogeochemistry—that is, the biological, physical, and chemical characteristics of a particular site.

The amount of water present in a wetland can vary greatly. Some wetlands are permanently flooded, while others are only seasonally flooded but retain saturated soils throughout much of the unflooded period. Still other wetlands may rarely flood, but saturated soil conditions still are present long enough to support wetland-adapted plants and for hydric soil characteristics to develop. Hydric soils develop when chemical changes take place in the soil due to the low-oxygen conditions associated with prolonged saturation.

Different plant communities may be found in different types of wetlands, with each species adapted to the local hydrology (the quantity, distribution, and movement of water throughout a given area). Wetland plants are often referred to as hydrophytes because they are specially adapted to grow in saturated soils. Many bird, insect, and other wildlife species are completely dependent on wetlands for critical stages in their life cycles, while many other species make use of wetlands for feeding, resting, or other life activities. The wetland plant communities in Winnebago County include marsh, graminoid fen and sedge meadow. READ MORE>>

Dolomite Cliff

This type of cliff supports the most vegetation, and for the most part it faces north or east.  Shading from adjacent forests play an important role in determining the composition of the vegetation.  The bedrock in this community is more resistant to weathering than in other cliff communities and it has the higher pH than sandstone.

Representative Areas:  Indian Hill, Kishwaukee Gorge North & South, Rockford Rotary, Severson Dells, Seward Bluffs