Illinois Plant Communities – Prairie Ecosystems

Influence of Fire

Native American Fires Meadows Burning by George Caitlin

Decline with spring fires Kentucky BluegrassBicknell’s Sedge

Increase with spring fires Canada Wild RyePrairie Dropseed

Fire Effects If fire is followed by adequate precipitation, biomass production will increase in the next 2 to 3 years following the fire; if precipitation is less than adequate, biomass production will decrease Species richness of plants usually increases in burned compared to unburned areas - species richness also increases when fire is combined with grazing - so fire and grazing both act to limit growth by competitive dominants and allow competitively inferior species to increase

Increase with fire - Prairie Grasshoppers

Decrease with fire BeetlesLeafhoppers

LeConte’s SparrowBobolink Return first year after fire

Savannah sparrow Requires at least two years post fire

Savanna Pembroke Savanna – Kankakee, IL

Definition Savanna is usually defined as being an area with a continuous understorey of grass and forbs with an overstorey of scattered trees, in which the tree canopy typically covers less than 60% of the ground

Types of Savanna The term savanna is applied to different types of communities in different parts of the world - being used to describe any grassland in South America whether trees are present or not; in Africa it is used to describe grasslands and open deciduous woodlands; in Australia and Asia it is applied to park-like tree studded grasslands as well as areas with tall very leafy trees with a well defined grass layer

Savanna Worldwide – in Purple

Types of Savanna In fact many authors restrict the term savanna to tropical communities - however in recent years, the term has been expanded to include any open woodland with a grass- forb understorey - hence the use of the term for plant communities once fairly common in Illinois and the Midwest

Savanna in the Midwest Savanna in the Midwest basically occurs as an ecotone region between eastern deciduous forest and tallgrass prairie Ecotone - a region where two different ecosystems grade into one another This ecotone extends in an eastward arc from Minnesota to Texas and projects into Illinois, Indiana and Kentucky

Oak Savanna in North America

Savanna vs. Prairie

More North American Savannas

Factors governing Savanna formation in North America 1. Precipitation to evaporation ratio drops below 1 (remember that in tallgrass prairie P/E ratio is typically between.6 and.8) 2. Annual precipitation varies between 60 and 100 cm 3. Yearly variability in precipitation increases relative to forest ecosystems; the frequency of drought increases - drought cannot be the whole reason for forest to give way to grasslands, however, because grassland borders further west support trees under even more arid conditions (Rocky Mountain front) 4. Fire frequency increases, favoring grasses

Factors governing Savanna formation in North America 5. Finer, deeper prairie soils favor fibrous roots of grasses 6. Tree mycorrhizal fungi are absent in prairie soils and tree saplings are at a competitive disadvantage without mycorrhizae 7. Heavy grazing by bison and elk until the late 19th century may have eliminated tree saplings – along with grazing by with rabbits 8. The tree line may have been pushed east by Xerothermic period of 6,000 years ago, and tree line has not yet regained its climatic limits

Wet-dry cycles and savanna

Savanna in Wisconsin

Savanna Restoration

Fire in Savannas - Wisconsin

Fire in Savannas - Minnesota

Fire Effects The presence of oak species in midwestern savanna is due to their having thick bark which resists fire and insulates the growing cambial layer of the tree from damage by fire - thus well established oaks could survive fire In the absence of fire, some studies in Wisconsin have shown that woody species invade prairie at an average annual rate of expansion of 3 m per year Fire in savannas stimulates the growth of grasses, increasing productivity (biomass) and flowering 2 to 3 times that in absence of fire - this is primarily in response to removal of litter layer

Oregon Oak Savanna

Forest In Illinois

Forests Forests are usually defined as areas with relatively dense and extensive growth of woody plants which are at least 20 feet (6 m) in height growing closely together; It is usually possible to distinguish layers of vegetation below the top canopy of dominant (overstorey) trees; the layers include understorey trees, lianas (woody vines), shrubs and herbaceous ground-layer vegetation

Temperate Deciduous Forest Layers

Change in Forest Acreage In 1820, an estimated 38% of Illinois, some 13.8 million acres, was forest. Within a century only slightly more than 8% of this original forest remained and today only 11,600 acres, or 0.9%, of the pre-settlement forest is left. Most forest in Illinois today (4.27 million acres) is second or third growth

Beall Woods

Illinois Woodlots

Only 11% of the 214 Grade A and B forest sites cataloged by the Illinois Nature Areas Inventory are greater than 100 acres in size. Each of the more than 169,000 private forest owners is estimated to hold only 21.5 acres on average. An analysis of 13 counties in south central Illinois found that the vast majority of forests in the region were smaller than one acre in size – the equivalent of a large backyard with trees.

Animal Diversity and Forest Area Deer and squirrels increased – like edge habitat and woods near fields Bobcats – decreased; wolves and cougar – gone but may come back Songbirds – species diversity high but numbers of individuals are down