Mitchell's Grove Nature Preserve is a

nature preserve A nature reserve (also known as a wildlife refuge, wildlife sanctuary, biosphere reserve or bioreserve, natural or nature preserve, or nature conservation area) is a protected area of importance for flora, fauna, funga, or features of geolog ...

and State Natural Area located in

LaSalle County, Illinois LaSalle County is a county located within the Fox Valley and Illinois River Valley regions of the U.S. state of Illinois. As of the 2020 Census, it had a population of 109,658. Its county seat and largest city is Ottawa. LaSalle County is ...

, situated between Tomahawk Creek and the Little Vermillion River north of their confluence. It is composed of diverse terrain with over 300 plant species present. While much of the upland area is

oak savanna An oak savanna is a type of savanna (or lightly forested grassland), where oaks (''Quercus ''spp.) are the dominant trees. It is also generally characterized by an understory that is lush with grass and herb-related plants. The terms "oakery" or ...

and

prairie Prairies are ecosystems considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and a composition of grasses, herbs, and shrubs, rather than trees, as the ...

, the bottomlands consist of several different types of

mesic forest In ecology, a mesic habitat is a type of habitat with a well-balanced or moderate supply of moisture throughout the growing season (e.g., a mesic forest, temperate hardwood forest, or dry-mesic prairie). The term derives from the Greek ''mesos'' ...

with diverse plant communities. The site was given to the state of

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...

by William and Irene Mitchell in 1997.

History

Mitchell's Grove was heavily affected by glacial action during the

Wisconsin glaciation The Wisconsin glaciation, also called the Wisconsin glacial episode, was the most recent glacial period of the North American ice sheet complex, peaking more than 20,000 years ago. This advance included the Cordilleran Ice Sheet, which nucleated ...

. The movement of ice over the site lead to the presence of

Glacial erratics A glacial erratic is a glacially deposited rock (geology), rock differing from the type of country rock (geology), rock native to the area in which it rests. Erratics, which take their name from the Latin word ' ("to wander"), are carried by gla ...

and

till image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...

. The broad main valley is likely glacial in origin while the numerous small ravines are the result of erosion of the

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

bedrock. The vertical sandstone cliffs found here are also related to the presence of the Peru Monocline Fault.

Flora and fauna

A plant survey conducted from 1999 to 2000 documented 333 native plant species including several threatened species such as Burgess Forked Aster and

White Cedar White cedar may refer to several different trees: * Bignoniaceae ** '' Tabebuia heterophylla'' - native to Caribbean islands and also cultivated as an ornamental tree * Cupressaceae: ** ''Chamaecyparis thyoides'' – Atlantic white cypress ** ''Cup ...

. The deep valleys with a prevailing northern exposure and heavy tree cover make the site a

glacial refugium A glacial refugium (plural glacial refugia) is a geographic region which made possible the survival of flora and fauna during ice ages and allowed for post-glacial re-colonization. Different types of glacial refugia can be distinguished, namely nuna ...

that supports species that would typically be found in more northern latitudes such as Swamp Saxifrage. The same survey listed 21 species of

lichen A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteria living symbiotically among hypha, filaments of multiple fungus species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualism (biology), m ...

, 39 species of

moss Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...

, and 4 species of

liverwort Liverworts are a group of non-vascular land plants forming the division Marchantiophyta (). They may also be referred to as hepatics. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which cells of the plant carry ...

. No species of moss or liverwort were found in areas previously used for agriculture. 63

Invasive species An invasive species is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...

were also identified in 2000 with varying degrees of infestation. Amur Honeysuckle, an invasive plant from western Asia, was recorded as a dominant species in the shrub layer of the bottomland forest. In the open prairie and savannah, Reed Canary Grass is listed as a growing population. Without treatment, it could substantially alter the ecosystem of the preserve.

Water quality

Hydrological and

aquatic biomonitoring Aquatic biomonitoring is the science of inferring the ecological condition of rivers, lakes, streams, and wetlands by examining the organisms (fish, invertebrates, insects, plants, and algae) that live there. While aquatic biomonitoring is the most ...

was conducted for the Tommohawk Creek and Little Vermillion River from 1998 to 1999. The research concluded that the water quality was from good to fair depending on the season. Aquatic insect communities of

mayflies Mayflies (also known as shadflies or fishflies in Canada and the upper Midwestern United States, as Canadian soldiers in the American Great Lakes region, and as up-winged flies in the United Kingdom) are aquatic insects belonging to the order ...

and

caddisflies The caddisflies (order Trichoptera) are a group of insects with aquatic larvae and terrestrial adults. There are approximately 14,500 described species, most of which can be divided into the suborders Integripalpia and Annulipalpia on the basis ...

were documented and used to calculate the

Index of biological integrity An index of biological integrity (IBI), also called an index of biotic integrity, is a scientific tool typically used to identify and classify water pollution problems, although there have been some efforts to apply the idea to terrestrial environme ...

for the monitoring sites. Increased turbidity was observed in the Little Vermillion River. This was caused by runoff from agricultural fields and a limestone quarry upstream from the preserve.

References

{{authority control State Natural Areas of Illinois State parks of Illinois Protected areas of LaSalle County, Illinois 1997 establishments in Illinois Protected areas established in 1997