Bulletin


STATE O F ILLINOIS 


DEPARTMENT OF REGISTRATION AND EDUCATION 


DIVISION OF THE 


NATURAL HISTORY SURVEY 

STEPHEN A . FORBES, Chj ef 

Vol. XIII. BULLETIN Article XVI. 

AN ECOLOGICAL SURVEY OF THE PRAIRIE 

VEGETATION OF ILLINOIS 


BY 

HOMER C. SAMPSON 

PRINTED BY AUTHORITY O F THE ST A TE OF ILLI N O IS 

URBANA, ILLINOIS 


August, 1921 




ERRATA
Page 97, line 17, for first larval read puital.

Page 112, in legend, for jonessi read jonesii.

Page 114, in legend, for or read of.

Page 125, line 4, for Bonosa read Bonasa.

Page 131, in legend, for Jiirundinaceus read hirudinaceus.

Page 138, last line, for coccoon read cocoon.

Plate XII, explanation page, next to last line, for acrivora read aerivora.

Plate XIII, explanation page, next to last line, for WMte-gruhs read White-gruh.

Page 293, Figure 5a was reversed in printing, and the two items of the legend

should change places.

Page 515, second table, for Pelocoris femorata read Pelocoris femoratus.



Article XVI.

—

An Ecological Survey of the Prairie Vegetation of
Illinois* By Homer C. Sampson.

Introduction f

The purpose of this survey was to determine as far as possible

the composition and ecological relation of the prairie vegetation of

Illinois. The prairie area of this state is an eastern arm of the prairie

region proper which forms a distinct formation between the grass-lands

of -the Great Plains on the west and the deciduous hardwood forest on
the east. While the origin of this prairie dates back to the changes in

climate following the uplift of the Rocky Mountains and subsequent

changes during and following the glacial period, the factors limiting its

present distribution are to be found in the present climatic and edaphic

conditions together with the biotic factors which affect succession from
prairie to forest associations.

The occurrence of all the great prairie regions of the world in

temperate climates indicates that temperature plays a role, either directly

or indirectly, in determining the general boundaries of distribution of

the prairies. For the prairie under consideration, Transeau's map (26),

comparing the ratios of rainfall to evaporation from a free water sur-

face in the three great vegetational areas noted above, shows rather

clearly that definite ratios of these two important climatic factors, with

which temperature is indirectly involved, coincide closely with the present

limits of distribution. The western boundary of the prairie is marked
by a rainfall equal to about 60 per cent, of the evaporation from a free

water surface, while on the eastern boundary of the prairie the ratio of

rainfall to evaporation is about 80 per cent. Sirnilarly the rainfall-evapo-

ration ratios marking the boundaries of the Great Plains are 20 and 60

per cent., while those of the eastern forest range from 80 to 130 per cent.

The prairie therefore lies in a region in which the ratio of rainfall to

evaporation ranges from 60 to 80 per cent. (See map on next page.)

The presence of local areas of forest together with man's ability to

carry on silviculture throughout the greater part of this range is stiffi-

cient evidence that the occurrence of prairie vegetation is not limited

by climate alone. Edaphic factors and the difficulty with which a forest

vegetation invades and succeeds that of the prairie must also be taken into

account. As the complex of climatic factors approaches the limiting

conditions for forest development, the weight of the edaphic factors be-

* Papers from the Department of Botany, Ohio State Univer.sity. No. 126.

t For non-technical summary, see page 569.
,



524

comes more and more evident and may tip the balance either in favor of

forest or of prairie. Similar conditions exist between prairie and plains

vegetation on the western edge of the prairie. But as we approach the

center of the prairie region edaphic factors become less prominent, and
it is here that we find prairie on the greatest number of edaphic habitats.

Transeau (25,2()) was the first to point out the characteristics of

the centers of distribution of the vegetation of bogs and forests of North

Map showing ratio of rainfall to evaporation expres.sed in percentages.
(After Transeau.)

America and to call attention to the meaning and use of the term "center

of distribution". As he used it the term does not imply that the plants

have necessarily spread from the present centers, but that the complex
of climatic factors most favorable to the development of the type of

vegetation characteristic of each center is localized there, and that as we
depart from such centers we find conditions more and more unfavorable

and resulting in the elimination of such species as are most rigidly



525

dependent upon climatic conditions. He also showed that the species

comprising the vegetation of any center are more abundant, attain a

greater size, and have a wider range of habitats within the limits of the

center of distribution than elsewhere. These same conditions apply to

the prairie. In addition to the climatic, edaphic, and biotic factors men-
tioned above, prairie fires are also important locally and have been va-
riously emphasized from time to time.*

To sum up, climatic factors are important in determining the gen-

eral boundaries of distribution of the prairie, while edaphic factors are

important in determining the origin and character of the prairie asso-

ciations within these boundaries. The edaphic factors become more and
more prominent toward the edges of the prairie, as in eastern Illinois.

When a prairie association is once established, biotic factors and prairie

fires are important in checking inxasion by forest vegetation.

The location of Illinois at the eastern boundary of the prairie makes
it a region of considerably more than local ecological interest. As a

prairie state it has awakened interest since the time of the first settlers,

several of whom have recorded brief but glowing descriptions of the early

prairies. Of these older descriptions, one of the most important was
written in 1857 by Frederic Gerhard (7), who greatly enriched his pub-
lication by appending a forest and prairie map of the state compiled
by Dr. Frederick Brendel of Peoria. This map shows the relative dis-

tribution of prairie and forest at that time, and a reproduction of it by
Barrows (1) is included in the present article (page 52()).

Unfortunately these pioneer writers, accustomed to life in a forested

region, were generally unfamiliar with the plants of the prairie and
failed to leave us an adequate account of the natural prairie flora. Further-

«iore, the importance of a knowledge of the relationship of plants to

the environment in which they live was not recognized until a later date.

Indeed the dynamic and genetic relationship of plant associations was not

fully appreciated until Cowles (4) pointed out its significance in 1890.

As a result of this belated appearance of modern ecological conceptions

the earlier accounts of the prairie are notably lacking in a record of the

different associations of prairie plants and of their composition and suc-

cessional relationships. The published accounts deal chiefly with asso-

ciations on the broken soil of slopes or with those along forest borders

conspicuous for their great display of coarse herbs, and leave the errone-

ous impression that the original prairie flora was a mixture of a great

variety of species. This impression, however, is offset by the occa-

sional and significant reference to the prairie as a "sea of grasses" and by

the statement of C. W. Short in 1845 that "Its leading feature is rather

the unbounded profusion with which a few species occur in certain

localities than the mixed variety of different species occurring every-

where".

Shimek (24). "The



526

Original Prairie and Forest Area in Illinois
(After Brendel and Barrows)



527

Cowles (4, 5) has shown that the plant associations and their suc-

cessions in a given region are correlated with its physiographic de-

velopment. In order therefore to determine the original prairie asso-

ciations the only feasible point of attack lies in a detailed study of the

relic associations still to be found in the various physiographic habitats

of the state. The conditions in these relic associations where least dis-

turbed by man approximate closely the conditions which existed in the

much more extensive association of only a little more than half a cen-

tury ago. The order of succession of the associations is without doubt

the same today as in the past, and the composition of the undisturbed

associations fairly representative. Some of the swamp prairies and
many of the sand prairies of the state have already been studied on this

basis by Cowles (5), Sheri? (23), Gleason (!), 10), Gates (6), and
Vestal (27, 28). The present investigation was also carried out on

this basis with special reference to primitive conditions and an attempt

to include practically all the prairie habitats of the state. The main
contribution of this report is the attempt to determine and classify the

associations of prairie vegetation in Illinois and point out the succes-

,

sions between them. The field work was entirely observational, but

experimental data of other workers have been drawn upon wherever

they appear to have a direct bearing upon the topic under discussion.

Quantitative experimental data on the physiological factors underlying

the problems of the prairie associations and their successions are too

meager at present for a full discussion of the underlying causes. A more
definite knowledge of both the ecological anatomy and physiology of

many of the plants concerned will have to be obtained before some of

the more fundamental questions can be answered.

Most of the investigations were made during the summers of 1915

and 1916 with the cooperation of the Illinois State Laboratory of

Natural History, through its director. Professor Stephen A. Forbes,

and under the direction of Dr. H. C. Cowles and Dr. (George D. Fuller,

of the University of Chicago. This report also contains many data ob-

tained previous to the above dates and from observations made in many
sections of the state during the summers of 1917 and 1918. I am par-

ticularly indebted to Professor Forbes for his cooperation in the survey

and for the aid he has given in the illustration of the report. I wish

also to express many obligations to Dr. Edgar N. Transeau, of the Ohio

State University, who first introduced me to the problems of the prairie

in the summer of 1910, and helped me with valuable data and criticisms

during the preparation of this report. To Dr. A. E. Waller, of the Ohio
State University, I am indebted for criticisms and suggestions on the

final report.

Location of Existing Virgin Prairies of the State

The location of most of the prairies studied was obtained by means
of circular letters of inquiry sent to each of the county surveyors of the



528

state. Seventy-three of a possible 102 replies were received. The fol-

lowing tabulation by counties is taken directly from the letters received.

It should be noted that these reports are not exhaustive, as no surveyor
would be expected to have a complete list of all the undisturbed areas

of his county. In some cases more definite statements are desirable, but

the ones given are included with the hope that they may be of value to

other workers in the field. Unfortunately, grazing was not suggested

as a type of disturbance in the letters of inquiry, and some of the areas

here reported have been pastured and are now generally blue-grass pas-

tures. Where this fact is known it has been added by the writer.

Asterisks refer to regions investigated in this survey.

Adams. Lowlands along the Mississippi River extending through
three townships north of Quincy.

Bond. A few small tracts in addition to numerous roadsides.

*Burcau. Several thousand acres of sand and swamp prairie along

Green River. Mostly pastured.

^Carroll. Several thousand acres of sand prairie and flood-plain

prairie south of Savanna. Most of the sand prairie and some of the

flood-plain prairie has been pastured.

*Cook. About 5,000 acres on the old lake bed of Lake Chicago and
a few small tracts on the Valparaiso moraine. There are 2,000 acres

in the vicinity of Ashburn witjiin the city limits of Chicago.

*Crawford. One hundred and sixty acres two and one-half miles

northwest of Porterville. Pastured.

De Kalb. About four acres near Maple Park. R. E. Wagner.

Dupage. Small areas along east branch of Dupage River between
Swift and Lisle.

*Effingham. A few small tracts and roadsides. An 80-acre tract of

Andropogon prairie on the farm of David Woods, 9 miles southwest of

Dietrich, was reported to the writer in 1918. Forty acres of this tract

reported plowed in 1917.

Fulton. Lowlands along the Illinois River.

*Grundy. "Hay swamps" north of Coal City ; 220 acres 5 miles

west of Morris along the Illinois River. Mostly flood-plain ; some mo-
raine and mostly pastured.

Hancock. Flood-plain along Mississippi River south of Warsaw.
*Henry. Sand and swamp land in northern part of county. Mostly

pastured.

*Jasper. Forty acres southwest of Gila and 320 acres 3 miles east

of West Liberty. Pastured. Burke's prairie of 2 acres two miles south-

west of Wheeler. Virgin. A small area northwest of Wheeler now
under cultivation.

*Jo Daviess. Some prairie in north and southwest part. Pastured.

Madison. Wet prairie in Shonteau township.



529

^Marshall. Saratoga Lake region one mile north of Camp Grove.
Another small area 6 miles east of Lacon. Mostly swamp, some upland
prairie.

Mercer. Flood-plain along the Mississippi River.

Ogle. Small tract one mile east of Polo. W. E. Eikenberry.
Peoria. Lowlands along the Illinois River.

Randolph. Flood-plain along Mississippi and Kaskaskia rivers.

*Ricliland. Fox Prairie, .j miles west of Olney. Cemetery at Noble.
Rock Island. Flood-plain along Mississippi River.

Washington. Flood-plain along Kaskaskia River.

White. Small tracts in Enfield and Hawthorn townships.
Whiteside. Prairie between Albany and Erie.

Winnebago. Small tracts along Rock River.

All of the above counties and the remaining counties with the ex-

ception of those in the southernmost part of the state were reported to

have patches of virgin prairie along railway rights-of-way, old line-fences,

and roadways. Owing to a difference in farming methods these latter

relics are somewhat more abundant in the southern half of the state

than elsewhere. Numerous relics along most of the principal railways

of the state and along hundreds of old line-fences were seen during the

survey.

This brief summary of present conditions shows that there are still

several thousand acres of virgin prairie in the state which have been so

little disturbed by man that they are of considerable value for ecological

studies. The data also show that the greater area of these relic tracts

are on flood-plains, swampy regions, and sand. Outside of the sand
prairie the upland prairies are limited to small tracts, fence-rows, and
railway rights-of-way, the latter of which were considered only after

the survey had advanced sufficiently to indicate their limitations.

Origin of the Pr.\irie Habit.\ts

The various plant habitats of the state are correlated with its recent

geological history. The accompanying glacial and soil map after Leverett

(18) and Hopkins (15) shows that nearly all of the state has been gla-

ciated. The glaciers left the state with a gently rolling topography.

The depressions, resulting from the formation of moraines across pre-

glacial valleys and the unequal deposition of the glacial drift, became
postglacial lakes and sloughs which were slowly drained. In general

the moraines became forested, but many of the lakes and sloughs through

gradual filling and draining became prairies, a process which was far

from complete when the farmer entered the state and established arti-

ficial drainage systems. The extensive areas and long duration of the

wilderness of sloughs and swamps in the Wisconsin glaciation is best

attested today by the depth and extent of the rich humus soil that accu-

mulated in them. Their estimated dimensions are not lessened by the

stories of the early settlers who swam their horses across them in early



530

III

Map of the

Glacial Geology

of Illinois



531

spring or skated for many miles across country in winter with but short

walks between the swamps. Artificial drainage has not only reduced
the swamps, but it has also caused a general lowering of the water-
table, so that wells in this region must now be dug 5-10 feet deeper than
formerly. A few of these undrained morainal depressions surrounded
by definite zones of native vegetation remain today, but most of them
have been disturbed by grazing and mowing. The swamp prairies of

the Chicago plain with their intervening lines of beaches may be in-

cluded in this group.

Postglacial drainage at first favorable for prairie formation through
the drainage of swamps ultimately became destructive through erosion

of the soil in the development of the natural drainage systems. The
invading heads of the ravines destroying the prairie turf were usually

accompanied by the development of a forest vegetation. This fact is

strikingly illustrated in Brendel's map, which shows a fringe of forest

along all the principal water courses. These belts of forest are much
narrower and the intervening prairies much larger on the youthful

topography of the Wisconsin glaciation than on the older Illinoisan

glaciation. This condition is a result partly of the difference in age of

the drainage systems of the two regions and also of the greater amount
of forest encroachment on the pre-erosion areas of the prairie in the

southern Illinoisan glaciation. Flood-plain formation has resulted in

both forest and prairie ; the prairies arising from the lagoons and swampy
regions have much in common with those arising from morainal depres-

sions. Outwash from the Wisconsin glaciers gave rise to enonnous
sand areas and sand dunes in the northern half of the state, some of

which were forested, the remainder being covered with a prairie vege-

tation and plants of the Great Plains. Rock outcrops and eroding clay

bluffs were generally forested, but the slopes of lower gradient were
frequently covered with a xerophytic prairie flora. Local areas of this

type are still to be found in the vicinity of forest borders, though many
of them must be regarded as secondary successions following deforesta-

tion.

In addition to the prairies arising from postglacial lakes and sub-

sequent erosion, there is some evidence that the sand prairies and some
of the upland prairie region of the state date back to an arid postglacial

period during which there was an eastward extension of the prairie and
plains flora. The conifer zone following the retreat of the glacier is

thought to have been succeeded immediately by a xerophytic prairie

flora extending as far eastward as Ohio. Subsequent increase in humid-
ity in the Mississippi valley was then followed by a westward migration

of a more mesophytic prairie flora and the deciduous forest of the east

which have their present tension zone in Illinois. As evidence of this

view Gleason (8) calls attention to the presence of scattered colonies

of prairie species beyond the eastern limit of the present prairie province

and to the isolated occurrence of such western plants as Cristatella



533

Jamesii, Lcsqucrclla, argentea, and Opiint'm fragilis on the sand dunes
of Illinois many miles from their nearest reported station in the west.

This brief summary of the prairie habitats of the state emphasizes
the fact that the chief prairie region reached its greatest development on
postglacial pre-erosion topography. The associations of prairie plants

found in these habitats may be placed in two distinct groups : the hydrarch
successions found on flood-plains, in morainal depressions, and on the

old lake bed of Lake Chicago ; and the xerarch successions found on sand
and xerophytic upland glacial soils.

Succession of Prairie Plant Associations

1. THE hydrarch SUCCESSIONS

The Succession (a) on the River Flood-plains

The largest and least disturbed example of this type of prairie stud-

ied is located on the flood-plain of the Mississippi River south of Sa-
vanna. The exact area of this prairie was not determined, but it is

known to include several thousand acres. The associations of prairie

plants found on this flood-plain are usually distinct and readily differen-

tiated. The list of associations found and their successional relations

are represented diagramatically in Figure 1. See also Plates XLVIII

—

LIII for illustrations of the individual associations, and pages 558—568

for a list of representative species.

The associations in the diagram are given in order from swamp to

prairie. On these Savanna prairies the plants representing the various

associations usually occupy from 85 to 95 per cent, of the area of the

association which they represent and are in every case the dominant
plants of their respective associations. The areas of the individual

associations vary from a few square rods to tens of acres. Where the

slope gradient is steep they occur as narrow strips of only a few feet

in width and some of them may be eliminated entirely. One Panicum
virgatum association was found occupying nearly a hundred acres

(Plate LII), and similar areas of Spartina Michauxiana are not infre-

quent. Andropogon fiircatns is the dominant grass of the drier portions

of the flood-plain, but owing to the fact that habitats which have
reached this stage of development are suitable for agriculture very few
such areas remain undisturbed.

Some of this prairie is now being grazed and is losing its natural

aspect. Hundreds of acres, however, are disturbed only by late autumn
mowing and occasional fires, while occasional local areas may be found
that are seldom disturbed by man. It is in these least disturbed tracts

where the dead grass remains from year to year that the dominant
plants maintain their purest stand. The secondary species become insig-

nificant, being represented only as scattered individuals here and there

throughout the association. It is in such situations also that the transi-

tion zones between the various associations are most clearly defined and
readily recognized.



Andropogon furcatus

Panicum virgatum

Carex lanuginosa

Calamagrostis canadensis

Spartina Michauxiana

Carex vesicaria

Scirpus fluviatilis

. 1. DiagTani showing: the successions of the plant associations from
swamp to prairie on the flood-plain of the Mississippi River at
Savanna. Illinois. The dotted lines, represent local exceptions of
rare occurrence. See Plates XLVIII-LIir.

The data obtained from the surveyors' reports show that the greater

amount of undisturbed flood-plain prairie occurs along the Mississippi

River. Similar areas, however, occur along the Illinois and smaller
rivers. The driest of these flood-plain prairies found, are along the
Desplaines River near Riverside, in Cook county. These areas have been



534:

modified by pasturing and are dominated by Andropogon furcatns or its

ecological equivalents.

The data in Figure 2 were obtained from a 220-acre field along
the Illinois River five miles west of Morris, in Grundy county. The
trend of associations on the unpastured portion are practically identical

with those along the Mississippi.

It is important to note that the data in Figure 2 also show the effect

of grazing upon the natural prairie flora. Practically every one of

the dominant species occurring under natural conditions is replaced by
some other species. Scirpiis fluviatilis is replaced by Typha latifolia;

Spartina Michauxiana and Calamagrostis canadensis, partly by Carex
and Junclis but mostly by Agrostis alba; Panicum virgatum, partly b)^

Andropogon furcatus . '".i^ P°^ pratensis

Panicum virgatum

Calamagrostis canadensis - . . >^ Agrqstis alba

Spartina Michauxiana—ffSl

Carex vesicaria .

Scirpiis fluviatilis - "> Typha latifolia

Unpastured

Flood-plain aiid nxoraine

Fig. 2. Diagram showing the successions of the plant associations on
pastured and unpastured areas on the flood-plain of the Illinois
River in Grundy county. The dotted lines indicate the successions
brought about by grazing.

Agrostis alba and partly by Poa pratensis; and Andropogon furcatus,

entirely by Poa pratensis. Not only are these primary species destroyed

by grazing, but practically all of the secondary species are likewise

eliminated. It may readily be seen that areas not subjected to intense

grazing or areas that had been pastured in the past and then allowed



535

to revert to natural conditions would exhibit a mixture of associations

of native and cultivated grasses impossible to decipher on an ecological

basis tmless ecological equivalents are recognized and appreciated. The
above data are important in suggesting an explanation of the conditions

existing on the Chicago plain, to be discussed later.

According to the county soil reports (3) the surface soils of these

flood-plain areas consist in the main of brown silt loam and sandy silt

loam derived from materials washed from the upland and deposited at

periods of overflow. Usually there is present a considerable amount
of sand. The subsoil as a rule is sandy silt loam, sand, or clay. In

some of the swamps peat is abundant. Enormous areas of peat occur
on the wide flood-plains of the Rock and Green rivers in Bureau,
Henry, Lee, Whiteside, and Rock Island counties. The peat beds occur
in depressions between the sand hills and in morainal depressions.

With the exception of peat all of these soils are rich in the minerals

required by plants, and their plant associations are similar. Peat, on
the other hand, is exceptionally rich in organic material and poor in

potassium, but its plant associations are dominated by the same species

that dominate wet areas on other types of soil. Calainagrostis canadensis
is particularly prominent on wet peat. The height of the water-table

and not the chemistry of the soil is the limiting factor determining the

order of associations.

Some progress toward an explanation of the order of occurrence

of the associations in the hydrarch succession has been made, but the

data at present are little more than suggestive. Miss Hayden (13, 14)

found that parenchyma and aerenchyma are more prominent in roots and
rhizomes of swamp plants than of upland plants on the prairie of central

Iowa, and that the leaves of upland plants have thinner epidermal walls,

a greater amount of palisade-tissue and more compact mesophyll, and
are more frequently hairy than leaves of plants on the lowlands. We
are greatly in need of more ecological anatomy of this type which should

be extended to include the dominant species of the prairie associations.

It should also be checked by experiments similar to those of Cannon
and Free (2) to determine the effectiveness of aerenchyma in supplying

oxygen to roots in soils of low oxygen content. It should further be

checked by actual measurements of transpiration rates to determine

the comparative effectiveness of the various modifications of leaf

structure. Transeau in some unpublished work has found that a heavy
cuticle on leaves does not necessarily mean that they have a lower trans-

piration rate than leaves with thin cuticle. Sayre (21) found that hairs

on mullein leaves do not retard transpiration under ordinary intensities

of wind and light, and that eighty per cent, of the transpiration from
these leaves is stomatal transpiration. Some of the modifications in leaf

structure, therefore, affect only the twenty per cent, of transpiration

directly froin the epidermal cells, and there is great danger of over-

emphasizing their importance in the absence of experimental data.



536

The Hydrarch Succession (b) on the Old Lake Bed of Lake Chicago

The geological history of this region has been described in detail

by Leverett (17) and Salisbury and Alden (20). The following sum-
mary is given to bring out more clearly the relation of the vegetation to

the present physiography. During the retreat of the Wisconsin ice sheet,

a temporary balance between the melting back of the glacial front and
its forward movement resulted in the formation of the Valparaiso

moraine. With further recession of the glacier this moraine served as

a dam which hemmed in the water from the melting ice, forming a lake

known as Lake Chicago. The surface of this lake was at one time 60

feet above the present level of Lake Michigan. An outlet through the

Desplaines River gradually lowered the level of the lake until the glacier

receded far enough to open an outlet to the north which resulted in the

withdrawal of the water from the Chicago plain. Three old beach
lines, sixty, forty, and twenty feet above the present level of Lake
Michigan, show that the outlet to the north was interfered with a second

and third time, and that a lake again occupied the- area in question.

With the final retreat of the glacier and subsequent drainage through

the St. Lawrence System the water was gradually drained from the region

between the Valparaiso moraine and the present beach of Lake Michigan.

The area thus exposed was a flat, level plain, poorly drained, and
abounding in lakes and swamps which have been gradually filling with

vegetation.

The old beaches and sand-dunes areas are forested, but the re-

mainder is largely prairie or swamp land. Much of the present un-

disturbed prairie is considered too wet for agricultural purposes except

in dry seasons. In some of the drier portions, however, cultivated

plants ecologically equivalent to Panicum virgatum and red top could

be grown. Roadways and ditches have recently been established along

the main section lines, and in some cases city blocks have been laid

out. This artificial drainage has reacted to some extent upon the natural

vegetation, and it is undoubtedly a partial cause of some of the dis-

turbances noted in the natural plant associations of this area.

The drainage ditches are marked by a line of cottonwoods and a few

willows,, mostly Salix amygdaloides, though in some places swamp
grasses are found refilling the ditches. These trees are growing in the

bottom of the ditches where the prairie turf has been completely de-

stroyed.

This prairie is exceptionally rich in organic matter, peat sometimes oc-

curring. The subsoil is mostly glacial till, forming poor subsoil drainage,

but local areas of sand and rock also occur. Owing to the flat surface and
the impervious clay subsoil, much of the surface soil is usually saturated

during the wet spring months. Later in the season the water content

under present conditions of drainage may drop below the wilting co-

efficient, Harvey (12) has shown that during the summer of 1911 the



537

Poa pratensis

Poa compressa

Agrostis alba

water content of this soil at a depth of 7.5 cm. was below the wilting

coefiicient during most of the period from the first of July to the last of

September, and at a depth of 25 cm. the water content was but a little

above the wilting coefficient for the same period. Plants growing
throughout the season, therefore, must be able to maintain a suitable

water balance through the two oppo-
site extremes of soil-water content.

Since the roots of many prairie plants

grow deeper than 25 cm., we need
more data on the wilting coefficient in

relation to depth of root systems of

the dominant plants in the different

associations.

More than 4,000 acres of this prai-

rie are included in this survey. Fig-

ure 3, shows the trend of associations

from a small pond near Chicago
Lawn. The prominence of the cul-

tivated grasses, Poa and Agrostis, in

this locality is very probably the re-

sult of the suburban habit of "staking

cows out to pasture", but, as will be

shown later, other factors may also

be important here.

In Figure 4 an attempt is made
to summarize the relations of the prin-

cipal associations on the Chicago prai-

rie including those of cultivated

grasses. No attempt is made to in-

clude all the associations in the deeper

swamps. These have been described

in detail by Sherff (33) and Gates

(6).

The data show that there is a far

greater complexity of associations on
this prairie than on those discussed

above. In the first place the appear-

ance of associations dominated by
Agrostis alba and by the blue grasses,

Poa pratensis and Poa compressa.

represents a condition in this prairie

not characteristic of the natural prai-

ries of the state. There is no evidence

in the older descriptions of the prai-

rie that either of these species was
present in the original prairies of the

Glyceria nervata

Calamagrostis canadensis

Carex striata

Spartina Michauxiana

Scirpus fluviatilis

Fig. 3. Diagram showing the succes-
sion of the plant associations
around a pond near Chicago Lawn
on the old lake bed of Lake Chi-
cago. Disturbance by man has
made possible the occurrence,
here, of associations dominated by
Glyceria and cultivated grasses.
See Plate LIV.



538

Andropogon furcatus ^
/v
~

Panicum virgatum ^

Spartina 'Michauxiana

Scirpus fluviatilis

Fig. 4. Diagram showing the successions of the principal associations on
the old lal^e-bed of Lalte Chicago, including those of cultivated grass-
es. See Plates LI. LIV-LXIV.

state. Their presence today is the result of their introduction and use in

cultivation. The blue grasses were apparently introduced from Europe.

Waller (30) finds that the early settlers of Virginia and Kentucky looked

upon Poa pratensis as a dangerous introduced weed and some of them
prophesied that it would some day drive the farmers out of the country.

A wealthy plantation owner, fearful lest the blue grass would ruin his

pastures, ordered his slaves to dig it out and burn it. The early settlers

of Illinois say that blue grass came into the state following the destruc-

tion of the native grasses by cultivation and grazing. The prominence
of these cultivated grasses on the. Chicago prairie is, indicative of dis-

turbance by man and raises the question as to how far this prairie may



539

be considered representative of original conditions. The data in Figures
2 and 5 show that grazing results in the coming in of cultivated grasses.

A knowledge of the amount of grazing this prairie suffered during the

early development of Chicago is wanting. During the last forty years

the grass has been cut annually in July. This is rather more detrimental

to the late fall passes than to the earlier grasses in that it destroys
their vegetative growth shortly before time for fruiting and usually pre-

vents them from seeding. In addition, fires started by trains contribute

to the disturbance of the composition of associations which obtained un-
der natural conditions of competition. Artificial drainage has lowered
the water-table and extended the seasonal period during which the water
content of the soil is below the wilting coefficient. During the slow read^

justment of the associations of native species to the disturbing condi-

tions other species have a chance to obtain a temporary foothold. These
cultivated grasses are not able to invade the undisturbed native associa-

tions, and the period of their dominance in disturbed areas is dependent
upon the continuation of the disturbances.

In the second place a number of coarse herbs become more con-
spicuous, notably Silpliiiiiii laclniatum, Cacalia tuherosa, and Liatris

spicata, which usually follow Spartina and Calamagrostis and may be
found in pure or mixed stands of various combinations now occupying
the greater part of local areas. Apocynum cannabimiim var. hyperici-

foUiim is also occasionally abundant at this stage. On the slightly drier

prairies Silpliiiim tercbluthinaceum and Eryngium yuccifolium are some-
times abundant.

Finally, the occurrence of a mixed association dominated largely

by Andropogon scoparms and Sporobolus hetcrolepis following Agrostis
alba and Panicum virgatum on the low prairies seems out of harmony
with the xerophytic nature of these grasses. The same species also

dominate a portion of the Calumet beach near Chicago Ridge where
it has been deforested. In this latter situation these species are in a
xerophytic habitat characteristic of them, but on the low prairie they

appear in the hydrarch succession which is not characteristic of them.
Isolated clumps and small patches of Andropogon furcatus occur with

them. In my opinion the above factors explain the occurrence of culti-

vated grasses in these prairies and also account for the Andropogon-
Sporobolus association in the hydrarch succession and for the notable

abundance of coarse herbs. During the period of readjustment follow-

ing disturbance, the -speed of migration becomes an important factor

which in turn depends upon the proximity of plants producing an abun-
dance of readily dispersed seeds. Andropogon furcatus is not nearly as

abundant on the hills and sand dunes near Chicago as are the other grasses,

and the latter, therefore, have a chance to obtain the first foothold on
drained and denuded areas. It appears that the composition of the

associations on the Chicago prairie is scarcely more representative of the

composition of the earlier natural associations than are those found on
railwav rights-of-wav.



540

On the other hand, if we disregard the blue grass and red top in any
given area or choose areas in which they have not gained a foothold

the order of succession of the associations of native grasses is readily

seen. With the exception of the presence of Andropogon scoparius
and Sporobolus heterolepis in some places this succession of associations

does not differ materially from that of the flood-plain prairies already

described.

Andropogon furcatus does not play a very important role on the

Chicago prairie. Under natural conditions most of this prairie was
too wet for Andropogon. As noted above, it is frequently found on the

higher ground, and it is most abundant in the neighborhood of the
artificial drainage ditches. One of the areas that shows clearly the suc-

cession from Pankiim virgatum to Andropogon furcatus on this prairie

is ^bout one half mile southwest of Oak Ridge (Plate LIX). The fact

that this particular prairie is separated from the Wabash railway by a

small stream is probably significant. The conditions on this area are

more like those in other parts of the state. Coarse herbs are present

but they occur as scattered individuals of secondary importance. Red
top and blue grasses are not abundant. Special attention should be
called to the fact that owing to their much greater height the native

grasses readily crowd out the cultivated grasses in regions undisturbed
by man. Mowing checks but does not entirely prevent the encroachment
of Andropogon furcatus in associations of Poa pratensis. This fact

was obtained from observations on carefully mapped areas about one
mile northwest of Ashburn just north of 87th Street on some of the

best drained portions of this prairie. While the observations on this

particular area were limited to a period of only three years, a slight in-

crease in the amount of Andropogon was evident. The data recorded
in Figure 6 show still more conclusively that when man does not inter-

fere too much, Andropogon furcatus will crowd out our cultivated

grasses.

Portions of the Chicago prairie have been cultivated from one to

a few years and then abandoned. In all cases so far observed these

abandoned areas have reverted again to prairie. Agrostis alba is usually

the first grass to get a foothold. Coarse herbs likewise get an early

start. Then blue grass and Andropogon follow. The reversion to prairie

is not entirely due to the absence of "seed trees". Seedlings of cotton-

wood frequently make a start, but owing to subsequent mowing and burn-

ing they are usually destroyed.

The Hydrarch Succession (c) in Morainal Depressions

The morainal depressions vary in size from the small ones found
in terminal moraines to the much more extensive ones of the ground
moraine. Many of these depressions were formerly post-glacial lakes

which became partially drained by subsequent gradation. As would be

expected, the greater area of these depressions today occurs in the less



541

eroded Wisconsin glaciated region. The horizontal or geographical suc-
cession of associations in these depressions at present is important in

showing the vertical or historical succession of associations during the
gradiial filling and draining of the sloughs since glacial times. Much
of the Andropogon furcatus prairie of the state originated in this way.

Mr. L. Wiles, of Dundas, Illinois, who plowed some of the virgin

prairie in Vermilion county before artificial drainage was established,

says that the only tillable soil between the rivers and sloughs was that

covered by tall bluestem (Andropogon furcatus), and that usually the

farmers were not able to plow quite all of the Andropogon prairie but

had to leave a narrow strip of it surrounding other grasses bordering

the sloughs in the depressions. In many places in the farming district

these depressions have not yet been completely drained, and where graz-

ing has not been too severe the successions of the native grasses are

still evident. In some places, as in the depressions near Camp Grove and
Lacon in Marshall county, all the associations up to and including Andro-
pogon furcatus may be found, while in other depressions farming has

destroyed the Andropogon, and sometimes Panicum, entirely. A sum-
mary of these associations made from observations of more than twenty
morainal depressions is given in Figure 5.

Vestal (28) has described the associations about a small depression

on the Valparaiso moraine on the boundary line of Cook and Dupage
counties. While this prairie has some indications of the influence of

civilization, such as the presence of red top and blue grass previously

mentioned for the Chicago prairies, it is of interest as a description of a

more xerophytic type of prairie characteristic of clay soils in the vicinity

of forests. The hydrarch series is somewhat similar to that already

described for the Chicago prairie, including the abundance of cultivated

grasses and herbs. On the most xerophytic areas of the upland Andro-
pogon scoparius is dominant. Silphium laciniatitm occurs in patches as

a local dominant. Several other coarse herbs are of frequent occurrence.

The effect of grazing shown in Figure 5 is the same as that already

discussed in connection with the flood-plain prairies. The conversion of

natural prairie grass-lands to blue grass and red top by pasturing has oc-

curred throughout the entire state. This fact is of interest both to

the plant ecologist and to the farmers. In the first place the natural

prairie grasses of any habitat serve as an indicator of the kind of culti-

vated grasses most suitable for that habitat. This might be further

extended to include all the agricultural crops of the region (Waller, 29,

31). In the second place it points clearly to the best method of ob-

taining permanent pastures. The data show that Kentucky blue grass

is the dominant pasture grass of all the upland prairie region, and when
once established it remains a permanent feature. On the other hand
timothy and red top pastures are in general short-lived but have the

advantage of establishing themselves more quickly. It is a well known
fact that the blue-grass pasture sod can not be obtained the first season

after seeding. This difficulty, however, is readily overcome by seeding



543

Afidropogon furcatus --

Panicum vxrgatum .. -.-l
' ' '

'

-^ Poa pratensis

-^ Carex-Tuncus-Iris

Scirpus fluviatilis -^ Typha latifolia

Unpastured

Moriinal depression.

Fig. 5. Diagram showing the plant associations and hydrarch succes-
sions in morainal depressions. The dotted lines indicate the changes
brought about by grazing.

to a mixture of blue grass with timothy and red top and allowing a few

years for the blue grass to establish itself and crowd out the other

grasses, except in low places where red top is a dominant pasture

grass. On fertile loamy soil this succession will occur within three or

four years, but on clay soils a somewhat longer time is required.

With the foregoing associations and their successional relationships

in mind it is of interest to compare them with the associations found

on the more extensive shallow depressions of the ground moraine. This

can be done at present only by having recourse to the relic patches of

prairie plants along railway rights-of-way and fence-rows (Plates LXV-
LXX). When this comparison is made, the same general associations

frequently interspersed with patches of coarse herbs and cultivated grasses

are met with again in the same order from lowlands to upland. This

comparison also shows that most of the prairie areas of the older gla-

ciated regions of the state had reached the Andropogon furcatus stage

before they were disturbed by man, while large areas in the Wisconsin



543

glaciation were still dominated by Spartina Michauxiana, Calamagrostis

canadensis, and Paniatni virgatiim. Owing to the clean farming methods
practiced in this part of the state it is now very difficult to estimate

the percentage of swamp prairie formerly occurring on the present

well-drained farms. But the postglacial history of this area is still

clearly written in the soil. The wide extent of the deep black soils points

to a long postglacial period in which swamps dominated by sedges and
swamp grasses covered large portions of this glaciation. With the gradual

filling and drainage of these extensive swamps the more mesophytic

prairies arose. Soil maps showing the comparative depth of the dark

humus soil could be used in determining the extent of associations and
also in the estimation of land values.

Mr. Wiles estimated that from 70 to 90 per cent, of the area of the

isolated prairie tracts separated by streams near his home in Vermilion

county was dominated by an almost pure stand of Andropogon furcatus,

the remainder by slough grasses, sedges, and rushes. He stated, how-
ever, that more abundant and extensive sloughs were present in the

prairie tracts northwest of Vermilion county. Farmers who helped drain

Douglas county say that the area formerly covered by sloughs and

shallow lakes greatly exceeded the area of tillable land in that county.

2. THE XERARCH SUCCESSIONS

The Succession (a) on Upland Glacial Soils

The succession of associations leading from swamp to the upland

prairie was found in every case to terminate in an Andropogon furcatus

association. This raises the questions of the amount of the upland

prairie soils dominated by this grass and the nature of the successions

from the more xerophytic areas on upland glacial soils and sand.

In this survey emphasis was placed upon the Wisconsin and the

Lower Illinoisan glaciations. On the former the most typical upland

prairie soil is a brown silt loam, on the latter it is a gray silt loam poorer

in organic matter and generally less fertile. Both of these surface soil

types are underlaid at varying depths with the typical clays of the

glacial till. Outcrops of these glacial clays are among the most

xerophytic areas of the prairie.

Owing to the value of this type of land for agriculture, it is now
practically all under cultivation. The few small relics of Andropogon
furcatus prairie in the "vicinity of morainal depressions previously dis-

cussed and similar patches near forest borders constitute the only

prairie tracts of this type found in the Wisconsin glaciation. On the

southern Illinoisan glaciation several small tracts varying in size from a

fraction of an acre to 2 acres were found. With the exception of the

exposed clay areas these are all Andropogon furcatus prairies.

Additional data were obtained from railway rights-of-way, old

line-fences, and from individuals who had lived on these prairies be-



544"

fore they were plowed. Both of these sources of information have their

limitations. The railway rights-of-way have been subjected to grading,

artificial drainage, annual cutting, and burning, and many have been culti-

vated at times. As a result the original associations have been fre-

quently greatly modified or entirely destroyed. Natural competition is

interfered with, and the observed composition of the associations and
habitat-range of individual species may not correspond to original con-

ditions. It is also of interest in this connection to call attention to the

fact that patches of natural prairie plants on these rights-of-way may
not always be relics of the original prairie but the result of secondary

successions culminating in the original prairie plants.

This fact is clearly illustrated in many places along the Indianapolis

branch of the Illinois Central Railway. This right-of-way was originally

50 feet wide. In 1897 it was made 80 feet wide by enclosing 15 feet of

farm land on each side. The diagram. Figure 6, represents the suc-

cession of associations that has occurred on a strip of this abandoned
farm land near my father's farm one mile west of Wheeler in Jasper
county.

Ajidropog^on furcatus.

Junens tenuis

Foa pratecsls

Agrostls alba

Farm weeds

Fig. 6. Diagram showing secondary successions on a railway right-of-
way formerly under cultivation near Wheeler, Illinois.

At the time of widening the right-of-way the land on one side of

the tract was a timothy pasture, on the other side it was under culti-

vation. In some places Andropogon furcatus occurs now in almost pure

stand and might well be considered original prairie if its history were

unknown. This reversion to the natural prairie plants may be seen

anywhere along this right-of-way where a sufficient number of relic

prairie plants existed on the old right-of-way.' Another instance of this,

on the Baltimore and Ohio Railway in Clay county, is illustrated in

Plate LXX. The area now covered with Andropogon furcatus was
formerly forested. The greater part of the 90 miles of this right-of-way



545

from Odin to Olney is covered by Andropogon furcatus, and much of

it is original prairie sod.

Still another type of reversion to the Andropogon furcatus prairie

may be seen on eroding banks and slopes along these rights-of-way.
Many instances were noted - where Andropogon scoparius dominated
the slopes of valleys while the upland and base of the slopes were domi-
nated by Andropogon furcatus. The successions of these associations

accompanying base-leveling in such cases is obvious. Sorghastrmn
nutans and Sporobolus lietcrolepis were also found on these slopes but
generally as secondary species. Where erosion is rapid coarse herbs are

abundant, but where erosion is slowed down by decreased gradients

and consequent greater stability of soil they become scattered secon-
dary members of the grass associations. In cases where the natural

grasses have been entirely eradicated these coarse herbs prevail perhaps
indefinitely.

In addition to railway rights-of-way in the Illinoisan glaciation old

fence-rows harboring relic patches of prairie plants are abundant. When
land adjoining these fence-rows is sowed to meadow grasses the culti-

vated grasses are gradually invaded and crowded out by Andropogon
furcatus. One instance was observed where this native grass occupied an
area of timothy meadow to a distance of 40 feet, and areas 10-15 feet in

width are common.

With regard to limitations in basing conclusions upon statements

made by the early settlers the principle that safety lies in numbers was
adhered to, and in practically all cases specimens of the plants in ques-

tion were at hand. No less than 30 individuals were questioned with
regard to the original prairies of the Southern Illinoisan glaciation.

Many of these had spent from 20 to 30 years on the virgin prairies and
on account of economic, medicinal, or esthetic reasons were familiar with
many species of prairie plants.

The data obtained from the early settlers and a careful study of

the prairie relics seem sufficient to reconstruct rather accurately the

original prairies of the Southern Illinoisan glaciation. The low prairie

was dominated mainly by Spartina Michau.viana, Calamagrostis cana-

densis, and Panicum virgatum, while the more extensive prairie was
dominated by Andropogon furcatus. Coarse herbs grew only as scattered

individuals among the grasses. On the exposed clay Andropogon scopa-
rius was abundant, and associated with it were many coarse herbs. A
mixed association consisting of the two Andropogons, Sorghastrmn nu-
tans, and Sporobolus lietcrolepis may have occurred in transition zones
on some of these clay areas.

Turning now to the Wisconsin glaciation the same sources of in-

formation exist, but they were less fruitful. From the data available

it is certain than Andropogon furcatus was the dominant grass of the

upland prairies. The points in question concern the probable role played

by coarse herbs and b)' more xerophytic grasses, particularly Andropogon



546

scoparhts, and the probable extent of mixed associations. In the Andro-
pogon furcatus prairies remaining in morainal depressions and the small
areas in the vicinity of Chicago coarse herbs occur only as scattered
individuals, as in the Southern Illinoisan glaciation. The older writers
speak of these prairies as a "sea of grasses", and it is probable that

coarse herbs did not occupy very large areas, as their presence would
certainly have called forth exclamations from the men of those days.
Wherever the prairie grasses have been greatly disturbed along railway
rights-of-way, both north and south, these coarse herbs become conspicu-
ous, and this has probably led many to ascribe to them more prominence
than they deserve. Gerhard and others report them as being abundant
on hillsides and near forest borders, and they may have been rather
prominent on the shallow soils of morainal ridges.

The xerophytic grass association dominated by Andropogon scoparius
is the characteristic association of these shallow soils. Relic patches
of this grass are most frequently found on the broken topography near
woodlands where the subsoil has been exposed by erosion. As in the

southern part of the state, Sorghastrmn nutans, Sporobolns lieterolepis,

and coarse herbs are also more conspicuous in these areas. Vestal (38)
finds that this association is not very extensively developed in the upper
Wisconsin glaciation. The data obtained in this survey agree with his

statement.

The available data bearing upon the extent of mixed associations

in this region are rather insufficient for quantitative estimates. In the

Southern Illinoisan glaciation mixed associations were of minor impor-
tance as most of that region had reached the climax stage of development
and was dominated by but one species, Andropogon furcatus. It is

probable that mixed associations representing a transition stage in suc-

cession to this climax from the drier uplands may have been more ex-

tensive on the younger topography of the Wisconsin glaciation, but
conclusive evidence is wanting.

From my records it appears evident that under the most favorable
natural conditions the dominant species shown in the previous diagrams
of this report must have occurred in almost pure stands ; that coarse
herbs were not abundant except on eroding soils and near forest borders

;

and that mixed associations were limited largely to transition zones.

This conclusion was corroborated by every early settler with whom I

talked and also by Dr. John H. Schaffner (22), who lived on the

Andropogon prairies in Kansas and had many opportunities to see them
in their natural conditions. They all report that in the best growing
seasons Andropogon furcatus grew so tall that a man sitting on a horse
could not see over it, and that the location of cattle and horses could
frequently not be determined except by the waving of the tall grass as

they passed through it. This height together with its production of a

close sod and dense vegetative growth was sufficient to exclude most
of the other prairie plants. Dr. Schaffner also reports that Andropogon
scoparius generally occurred in very pure stands, and that coarse herbs



547

were not abundant in either of the Andropogon associations but might
occur abundantly on eroding soils. Some of the plates accompanying this

report show these same features for Spartma Michauxiana. Calania-
grostis canadensis, and Panicinii virgatiim.

To sum up, both the historical data and the data obtained from relic

prairie areas lead to the conclusion that Andropogon furcatus is the

climax grass of the whole upland prairie region of the state, and that

in the successions leading to this climax from the more xerophvtic up-
lands and exposed clay soils Andropogon scoparhts is the most important
species. Figure, T shows the successions of associations that may occur
in this xerarch series.

Andropogon furcatus

Mixed xerophytic ^ Andropogon scoparius

grass asg

Coarse herbs

Fig. 7. Diagram showing the principal asi.'sociations in the xerarch suc-
cession on xerophytic upland soils.

During the long postglacial period forests' working back from the

water courses invaded these upland prairie soils. The progress of this

invasion as would be expected is much farther advanced in the Lower
Illinoisan glaciation than in the Wisconsin glaciation. While this en-

croachment of the forest on the prairie is generally considered to have

kept pace with the development of drainage and the soil erosion involved,

there are rather extensive areas in which the encroaching forest preceded

erosion. Since these forest soils bordering the upland prairie soils had the

same origin, the differences in them today are largely a result of their floral

history. In this connection the county soil reports (3) have some very in-

teresting data showing the effect of vegetation upon soil types. The or-

ganic matter of the forest soils ranges from about 25-50 per cent, of the

amount present in the adjoining prairie soils. This gives the prairie

soils a much darker color than the forest soils and is the result of a more
complete decomposition of the plant remains of a forest than of a prairie.

To quote from one of these reports : "The leaves and twigs of the trees

fall upon the surface of the ground and decay completely ; whereas the

prairie grasses form a mass of roots in the soil which, when they die,

are prevented from complete decay by the absence of sufficient oxygen.

In this way prairie grasses and other plants cause a gradual accumula-

tion of organic matter. If prairie land becomes forested the organic

matter is slowly diminished to a low point." This statement apparently

is not intended to apply to flood-plain forests, where deposition during



548

overflows is an important factor in soil fertility, nor to the occasional
small forest areas that have developed from swamps in which the slowly
decaying organic matter accumulates under water during the greater part
of the year. The conditions described above are more prominent in the
older glaciated regions, where we find the most extensive areas of forest
encroachment on pre-erosion topography.

The data in these soil reports also show a lower content of calcium
in forest soils than in the adjoining prairie soils. This difference is much
more pronounced in the subsurface soils and subsoils than in the surface
soils, rendering them more acid than the adjoining prairie soils. Forest
vegetation when compared with prairie vegetation therefore retards the
accumulation of organic matter and accelerates the drain on calcium.
Certain authors have suggested that the greater content of calcium in

prairie soils may be one of the causes of the prairie. The above facts

indicate that prairie vegetation greatly retards the rate at which calcium
leaches from the soil.

The farmers of the state have been slow in recognizing this effect

of the floral history upon the present value of soils. In my own com-
munity in the Southern Illinoisan glaciation the clearing and cultivation

of forested areas always seemed to have an alluring appeal entirely un-
related to economic values. Many of the farmers continued to clear

the forest in spite of the fact that some of the forested areas after
ten to fifteen years of cultivation yield no better crops than adjacent
prairie areas that have been cultivated for forty years. Many of the
slopes formerly protected, by forest vegetation have been cleared, farmed
for a few years, and then abandoned to the forces of erosion. An in-

telligent constructive forest policy that can be taught and convincingly
explained to the farmers is the only hope for remedying these regrettable

conditions.

The Xerarch Succession (b) on Sand

The sand prairies of the state have been described in detail by Glea-
son (9, 10) and Vestal (37) ; consequently they have received only
minor attention in this survey. The following description deals mainly
with the more general features which tend to show the relation of the
floral successions on sand to those of the soil types previously discussed.

Both of the above sources of information have been drawn upon in this

report. Evidence collected by Gleason shows that most of the sand prai-

ries were covered with a carpet of vegetation when settlements were
begun in this region. Subsequent plowing and pasturing, however, has
led to the exposure of large areas of sand to wind action and the de-

velopment of "blowouts". Owing to frequent movement of the sand
by wind, the revegetation and stabilization of these xerophytic sand areas
is a slow process, and progressive successions are often less prominent
than retrogressive ones. The most xerophytic prairies of the state occur
in these sand areas, and as Gleason has already pointed out we have
here the greatest representation of typically western plants. In fact the



549

vegetation of the more xerophytic sand areas is more representative of

the sand-hill vegetation of Kansas and Nebraska than of the Great
Plains or the Prairie.

With the establishment of a pioneer association sufificient to pre-

vent the erosive action of the wind, conditions becoine less severe and
further growth of a less xerophytic type is favored. As the vegetation

encroaches and establishes itself upon the sand, the accumulation of or-

ganic matter from decaying roots and tops of successive associations

results in physical changes in the soil which slowly approach conditions

existing on the more mesophytic prairies. The more important of these

changes is a decrease in the extremes of temperature and an increase

in humus with a consequent increase in soil stability and soil water.

Gleason (10) has shown that the evaporation rate of the air also gradually

decreases from one association to another. Each association thus im-
proves conditions and paves the way for its successor, ultimately leading

to the climax association of the region.

Observations were made on the sand areas at Hanover, between
Savanna and Albany, at Oregon, and in the northwestern part of Bureau
count}'. The succession of the principal associations leading to prairie

in these areas is given in Figure 8.

The Pamcxim pseudopiibesccns association is most frequently found
in the vicinity of blowouts, where it is a stage in the retrogressive suc-

cession from the bunch-grass association to the blowout association. Plate

LXXI represents such a stage with the blowout just beginning, and shows
the relative amount of the sand that may be occupied by this species.

The secondary species are relics of the bunch-grass associations previously

destroyed by the wind.

With the further development of the blovi'out Panicum pseudopubes-

ccns is replaced by the blowout association, which Gleason further sub-

divides into four distinct "associations." First, the basin of the blow-

out, where the sand is being removed by the wind. The vegetation of

this "association" is very meager and is composed of a few scattered

perennials persisting from the Panicum pseudopiibesccns^ association.

Chief among these are Accretes viridiflora and its varieties lanceolata

and linearis, Lithospcrmnm Gmelini, Euphorbia corollata, and Lespedeca
capitata. Second, the windward slope, where the sand is being removed
by both wind and gravity. The vegetation of this "association" consists

of relics of the Panicum pscudopitbescens and bunch-grass associations

which have been undermined at the top and have gained a foothold while

sliding down the slope. This association is limited to perennials, among
the most important of which are Panicum psciidopubesccns and Selagiuella

rupestris. Third, the lee slope, or "blowsand association," over which

the sand is being sprayed by the wind. The vegetation of this association

consists mainly of annuals characteristic of the bunch-grass association.

Gleason lists 31 species for this association, of which Aristida tuberculosa

is the pioneer. This species is common to all the areas studied. Other
important species such as Diodia teres, Paspalum sctaceum, Commclina



550

Blue grass ^• Andropogon furcatus

'j Andropogon scoparius

.-Pioneer bunch-grass

association

\

If II'
Xerophytic pasture

Bouteloua etc.
Panicum pseudopubescens

Blowout association

and blow-sand complex.

Pig. 8. Diagram showing the. interrelation of the principal associations
leading to prairie on sand. The broken lines represent retrogressive
successions resulting from blowouts. The dotted lines represent suc-

ns resulting from grazing. See Plates LXXI-I>XXV.

virginica, and Ccnchrits carolinianus are more local in their distribution.

Lastly, the "deposit association," composed chiefly of such dune-forming

species as Rhus canadensis, var. illinoensis, Ceanothus amcricanus, Tc-

phrosia virgmiana, Panicum virgatum, and occasionally Calamovilfa longi-

folia. To this list Vestal (27) proposes to add a fifth association, the

"blowsand complex", which arises from the continued growth of a large

blowout or by the confluence of a number of blowouts. The vegetation

is variable and is composed mainly of annuals as in the case of the blow-

sand association.

The meager vegetation of these five "associations" is of little conse-

quence in the stabilization of the sand. The first permanent step in the

development of vegetation on denuded areas is accomplished by the

pioneer bunch-grasses which succeed in getting a foothold in any of these

associations. Selaginella rupestris is also an important pioneer invader

in these areas at Hanover and Savanna. The order of the entrance of

the grasses is not definitely known, though, as Gleason has pointed out,

it depends largely upon the nature of the neighboring areas of the



551

bunch-grass association. Invasion may be affected by a single species

or by two or more species in common. The most important of these
pioneers observed by the writer are Panicitiii pseudopiibescens, Paspaluni
sctacciim, Sporobolus cryptandrus, Lcptoloma cognatiim, Carcx Muhlen-
bergii, and Cyperiis Sclni'dnitzii. On the deposit associations Panicum
virgatmn may serve as the starting point of the bunch-grass association.

The pioneer bunch-grass association may be dominated by a single

species or by a mixture of several species. The most important of the

grasses in addition to those listed above are Boutclona hirsnta, B. ciirti-

pendula, Eragrostis pcctinacea, Koeleria cristata, Stipa spartea, and
Andropogon scopariiis, all of which may occur as local dominants. With
decrease in xerophytism the pioneer bunch-grasses are replaced by
Andropogon scopariiis or a mixed grass association in which both species

of Andropogon and sometimes Sporobolus heterolepis are the prominent
members. Sorghastrum nutans and Panicum Scribnerianmn also in-

crease in abundance in these associations. At first the secondary species

are largely relics of the former bunch-grass association, but in the later

stages these are largely crowded out by Andropogon and partly replaced

by secondary species common to the Andropogon prairies elsewhere in

the state. In the most mesophytic stage of the Andropogon scoparius

association the open tuft-like growth characteristic of the pioneer bunch-
grass association is replaced by a close sod (Plate LXXIV). These
associations are not abundant today and were found only on low dunes,

in depressions between dunes, and on railway rights-of-way where they

had been least disturbed by agricultural practices.

The most mesophytic areas of the sand are dominated by Andropo-
gon fiircatus. Vestal (27) reports Andropogon furcatus dominating

parts of the "black-soil transition association" on sand which he finds has

reached its most advanced stage in the Havana region "in places near

Devil's Neck, in places east of the several forested dune areas, and
particularly at the eastern border of the sand plain". Most of the sand

prairies of this type have been either plowed or pastured. Plate LXXV
shows an almost pure stand of Andropogon furcatus on a low dune some
two miles south of Savanna. This dune is probably not more than 20

feet above the river. One side grades off into the flood-plain, and the

remaining three sides are bordered by small lakes. It has escaped both

plowing and pasturing. About half of the dune is dominated by
Andropogon furcat%is, the remainder by Andropogon scoparius. A simi-

lar area was found toward the base of a sand dune adjoining a swamp
preserved for hay in the northern part of Bureau county. The older

residents of this region report an abundance of tall bluestem on the low

sand hills between the swamps, and an abundance of both tall and low

bluestem, frequently mixed with other grasses, on the higher dunes.

A large part of the sand area in Bureau county has been subjected

to pasturing, and a blue-grass pasture has resulted in many cases. When
the pioneer bunch-grass association or an early stage of the Andropogon



552

scoparius association on sand is pastured, a xerophytic pasture results

in which the prominent species are Bouteloua hirsitta, Leptoloma cog-
natiDii, Panicmn pscudopubcsccus, Paspahim, sctaccuin, Eragrostis

pcctinacca, and Cypcriis Schivcinitcii. The presence of the blue-grass

pastures therefore indicates a rather advanced stage in the development
of the sand prairie, probably either a late stage of the Andropogon
scoparius or mixed grass association, or an Andropogon furcatus asso-

ciation.

Apparently this last association was rarely developed on the higher

sand areas. Gleason estimates that on the sand prairies as a whole at

least two thirds of the surface was originally occupied by a mixed
bunch-grass association varying all the way from areas dominated by
the pioneer grasses to those in which the Andropogons were abundant.

It would be of interest to both plant ecologists and farmers if a tract

of the present cultivated sand prairies of the Savanna region could be

set aside and allowed to revert undisturbed to natural conditions. The
ecologist could determine more definitely the order of succession of the

natural grasses on sand. At the same time the agriculturist would have
a means of determining how long it would be necessary to allow his

sandy farm to remain undisturbed in order to obtain a permanent blue-

grass pasture to take the place of present poor crops and shifting sand.

On the areas of pure sand many years would be required, but on most
of the area where humus has accumulated from the natural vegetation

of former years the time required might be commensurate with the re-

turns.

In Figure 9, a summary of the succession of the principal associa-

tions of the natural prairie plants is given. Associations of weeds and
cultivated grasses now present on the prairie as a result of the influence

of civilization are omitted in this summary.

Composition of the Associations

In the preceding discussion of the associations emphasis is placed

on the dominant species. Following is a list of the associations together

with some of the more frequent secondary species found on less dis-

turbed areas. This list made from small relic areas is not meant to be
complete nor to represent absolutely the composition of the more ex-

tensive associations before they were disturbed by man. Certain limi-

tations must be recognized. In the first place, the composition of an as-

sociation is usually most representative near its center of distribution,

and least representative near its boundaries where there is an over-

lapping of secondary species of adjacent associations. The centers of

distribution of some of the associatjons have been entirely destroyed by
cultivation, and Only the boundaries remain for study. Under present
conditions it is impossible in every case to list the secondary species with
the association in which they were most common. In the second place.



5
5
3



554

the habitat range of any species is more extensive when the biotic factors

of competition are removed than when they are present. The numerous
disturbances accompanying civihzation usually eliminate the influence of

biotic factors, at least in part, and admit not only a greater prominence of

secondary species but also a wider edaphic range of all species than

existed under natural conditions. Recently drained sloughs may be

found in which Spartina still persists as the dominant plant, but the

Spartina association in such cases may have as secondary species mostly

plants characteristic of the Andropogon associations. It is obvious that

a detailed account of associations under disturbed conditions is not only

valuless but is confusing to the uninitiated. Secondary species of local

prominence following drainage, grazing, or other disturbance are not in-

cluded in the list below unless they were found to occur frequently in the

same associations elsewhere. A more complete list of secondary species

of any association may be obtained from the annotated list beginning on

page 559 of this article.

The Scirpus fluviatilis Association.—Scirpus fluviatilis, S. validus,

Glyceria septentrionalis, Sparganium. eurycarpum, Acorus Calamus,

Sagittaria latifolia, Sium cicutaefolium, Pontederia cordata, Alisma

Plantago-aquatica, Rumex verticillatus, Polygonum Muhlenbergii, P.

hydropiperoides, P. amphibium, Eleocharis palustris, E. acicularis, Pen-

tiiorum sedoides, Scutellaria galericulata, Ludvigia palustris, Mimuliis

ringcns, and Ranunculus dclphinifalius.

Typha latifolia and sometimes Phragmites communis occur in this

association when there has been some disturbance, such as tramping by

grazing animals, pollution of the water, and dredging. With continued

disturbance Scirpus fluviatilis disappears, and Typha latifolia dominates

except for small colonies of Phragmites communis in some localities. The
data obtained in this survey indicate that neither Typha nor Phragmites

was abundant in the natural prairies of the state. Scirpus validus may
form an association in deeper water beyond Scirpus fluviatilis. In the

shade of trees Sagittaria latifolia usually replaces Scirpus fluviatilis.

Forest invasion of this association may occur. The principal invad-

ing species noted are Cephalanthus occidentalis, Cornus stolonifera,

Salix amygdaloides, S. nigra, S. cordata, S. discolor, and 5". longifolia.

The Carex Association.—This association needs considerable more

attention than it received during this survey. Carex vesicaria appears

to be the most important dominant species on flood-plains and in some

of the morainal depressions, but other species were also noted as domi-

nants, namely, C. lanuginosa, C. stricta, C. Sartwellii, and C. vulpinoidea.

The secondary species are : C. rostrata, C. lupulina, C. tribuloides, C.

siraminea, C. stipata, C. pennsylvanica, Scirpus atrovirens, Lobelia

cardinalis, Steironema lanceolatum, Veronia fascicidata, V. altissima,

Eupatorium perfoliatum, Asclepias incarnata, Stachys tenuifolia, Eleo-

charis palustris, E. obtusa, E. intermedia, Leersia oryzoides, and Phalaris



555

arundinacea. These last two species may occur as local dominants be-

tween Scirpus fluviatilis and Spartina Michauxiana, and they may have
been prominent in this position on the original prairies.

The Spartina Michauxiana Association.—Spartina Michauxiana,
Elymus virginicus, Phalaris arundinacea, Leersia oryzoides, Glyceria

nervata, Carex vulpinoidea, C. Bebbii, C. scoparia, C. lanuginosa, C.

tribuloides, Eleocharis palustris, E. obtusa, E. intermedia, Juncus
nodosus, J. Torreyi, J. tenuis, Cyperus strigosus, Stachys palustris,

Lythrum alatum, Vernonia fasciculata, V . altissima, Steironema lanceola-

tiim, Lycopus americanus, Aster paniculatus, Asclepias incarnata, Apocy-
nuin cannabinum var. hypericifoliuin, Hypericum ellipticum, Iris icrsi-

color, Lippia lanceolata, Senecio aureus, and 6". Balsamitac.

Forest invasion may occur in this association by the species noted

aboye and also by Populus deltoides, less frequently by P. grandidcntata

or P. tremuloides, and Cornus Aniomum.

The Calamagrostis canadensis Association.—Calaniagrostis ine.v-

pansa, Aspidium Thelypteris, and Onoclca sensibilis were found to be

more abundant in this association than elsewhere, but the remaining

secondary species consist largely of an overlapping of the secondary

species of the Spartina and Panicum associations. This condition agrees

well with the fact that the Calamagrostis association is sometimes
eliminated in the succession from Spartina to Panicum virgatum.

The Panicum virgatum Association.—Panicum virgatum, P. Lind-

heimeri, P. huachucae, P. tennesseense, Elymus virginicus, E. canadensis,

Ranunculus fascicularis, R. septentrionalis, Baptisia leucantha. Anemone
canadensis, Oxalis corniculata, Cicuta maculata, Steironema ciliatum,

Physostegia virginiana, Veronica virginica, Liatris spicata, Solidago ser-

otina, S. Riddellii, Cacalia tuberosa, Lathyrus palustris, Rudbeckia hirta,

Stachys palustris, and Gaura biennis.

Forest invasion in this association on the flood-plain at Savanna was
found occurring by three different methods: (1) by tree seedlings along

the forest borders in the shade of overhanging branches which had elimi-

nated the Panicum, (2) encroachment of Cornus and Crataegus by means
of adventitious buds from the roots extending into the prairie, and (3) by

scattered seedlings of Fraxinus americana, Ulinus amcricana, U. fulva,

and Populus deltoides on the prairie. A recent fire in a small section of

this prairie had destroyed most of the seedlings less than six feet in

height.

The Andropogon furcatus Association.—Andropogon furcatus, Sor-

ghastrum nutans, Panicum implicatum, P. praecocius, P. Scribnerianum,

Sisyrinchium angustifolium, Comandra umbellata, Fragaria virginiana,

Baptisia leucantha, Crotalaria sagittalis, Petalostemum purpureum, P.

candidum, Desmodium illinocnse, D. sessilifolium, Lespedeza capitata,

Oxalis corniculata, Polygala sanguinea, P. verticillata, Euphorbia Preslii,



556

Hypericum punctatuiii; H. Drummondii, H. gentianoides, Viola papilio-

nacea, V. pedatifida, V. sagittata, Phlox glaberrima, P. pilosa, Gatira

biennis, Eryngium. yuccifolimn, Dodccathcon Meadia, Asclepias tiiberosa,

A. Sullivantii, Acerates floridana, Pycnanthemiim flexiiosum, Veronica
virginica, Rucllia ciliosa, Vernonia illinoensis, V. missurica, Liatris

squarrosa, L. spicata, SoUdago ncmoralis, S. graminifolia, Aster multi-

Horns, Silphium laciniatum, S. terebinthinaceum, Parthenium integrifo-

liitui, Hcliopsis hclianthoidcs, H. scabra, Rndbeckia hirta, R. triloba,

Lcpachys pinnata, Helianthus mollis, H. grosscserratus. Coreopsis pal-

muta, Cacalia tubcrosa, C. atriplicifolia, Lactuca canadensis, and Prenan-
thes aspera.

Forest invasion in this association in the absence of erosion is simi-

lar to that described for Panicum virgatum (p. 555). See plates LXXVI,
LXXVII.

The Andropogon scoparius Association.—Andropogon scoparius,

Sorghastrum nutans, Panicum Scribncrianum, Stipa spartea, Aristida

oUgantha, Sporobolus hctcrolcpis, Danthonia spicata Com.andra umbcl-
lata. Cassia Chamaccrista, Tephrosia virginiana, Lespcdeza capitata. Eu-
phorbia corollata, Eryngium yuccifolium, Asclepias verticillata, Scutel-

laria parvula, Pentstcmon Iiirsutus, Rucllia ciliosa, Diodia teres, Kuhnia
eupatoriodes, Liatris scariosa, SoUdago nemoralis, S. rigida, S. gramini-

folia. Aster ericoides, A. depauperatus, A. multitlorus, Brauncria pallida,

Helianthus mollis, and Coreopsis palmata.
Most of these plants are also found as secondary species on well-

established Andropogon scoparius associations on sand such as the one
shown in Plate LXXIV. There are also certain secondary species in

this association remaining as relics from more xerophytic associations
on sand : Ambrosia, psilostachya, Callirhoe triangulata, Bouteloua hirsuta,

Helianthus occidentalis. Aster sericcus, A. linariifolius, Cyperus filiculmis,

and Koeleria cristata. Many others occur during the earlier stages of
the Andropogon associations on sand.

The secondary species of the mixed grass association on sand are
practically the same as those listed for the Andropogon scoparius asso-

ciation.

The chief grasses in the pioneer bunch-grass and Panicum pseudo-
pubescens associations on sand have already been listed. Further de-

tails regarding secondary species in these two associations may be ob-
tained from the annotated list or, better, from Gleason's paper (9) on
"The Vegetation of the Inland Sand Deposits of Illinois."

The association of coarse herbs on denuded and eroding soils is

rather variable, depending upon the water content of the soil and the
proximity of plants producing seeds. Several farm weeds and many
of the coarse herbs listed for the two Andropogon associations may
occur on these areas and in a great variety of different combinations.



557

The Relation of Prairie and Forest in Illinois.

The general relations of prairie and forest in the state have already
been noted, and some of the invading forest species were listed with
the secondary species of the prairie associations. Apparently any of the
prairie associations may be invaded by forest under the present con-
ditions. Four methods of invasion were noted: (1) forest invasion
accompanying erosion by streams, (2) growth of tree seedlings along
forest borders where the grasses are checked by the shade of over-
hanging branches, (3) the occasional establishment of isolated seedlings
farther out on the prairie, and (4) the growth of adventitious branch-
buds from the roots of certain trees and shrubs extending short distances
into the prairie. See Plates LXXVI and LXXVII.

Many of the early writers claim that wherever the prairie was
protected from annual fires the forest gradually encroached upon the

grass-land. A quotation from Gerhard is interesting in this connection

:

"The first efforts to convert prairies into forest land were usually made
on the part of the prairie adjoining the timber. A range of farms, which
girded the entire prairie along its circumference having been established,

three furrows were plowed all around the settlements in order to stop
the burning of the prairie for the whole distance of the circuit in the

neighborhood of these farms ; whereupon the timber quickly grows up
spontaneously on all the parts not burned, the groves and forests com-
mencing a gradual encroachment on the adjoining prairies, so that one
after another concentric circle springs up inside of the preceding, and
thus the entire prairie is steadily narrowed from all sides until it is

finally occupied, forming a vast region covered with timbers and farms."

Whether all of the prairie area of Illinois would have ultimately

become forested under natural conditions is a matter of speculation.

Within a few decades man has drained the sloughs and destroyed the

prairie turf through cultivation with the result that trees may now be
grown throughout the state. The development of natural drainage would
no doubt in time have reduced the area of sloughs, destroyed a limited

amount of prairie turf, and led to an increase of forested area. A basis

of fact for this conjecture is found in the older glaciated regions with
their older and better-developed drainage systems where forest occupies

a greater proportion of the area than on the youthful topography of the

more recently glaciated region. But forest invasion on the better-drained

Andropogon prairies is exceedingly slow, and the existence of rather

extensive Andropogon prairies on the older glaciated regions of the state

shows that prairie vegetation may dominate for many thousands of

years.

When the Deciduous Forest Formation comes into competition with
the Prairie Formation, the Andropogon furcatus Association may be suc-

ceeded by several of the associations of the Deciduous Forest Forma-
tion. This is not to be interpreted as saying that the Prairie Formation
is a transition between Plains Grass-land and Forest ; neither is it to be



558

understood as one of the series of successions leading to the Deciduous
Forest Climax. When the Prairie Formation is succeeded by Deciduous
Forest associations, it is exactly the same phenomenon that occurs when
the Deciduous Forest invades and succeeds the Northern Evergreen For-
est Climax—the Abies-Picea-Betula Association. Only in this sense is the
Andropogon furcatus Association a temporary climax.

We must therefore conclude that the Andropogon furcatus Asso-
ciation is the clknax association of the true prairies.

Where the prairie grades off almost imperceptibly into Plains vege-
tation there is an intermediate region in which it is too dry for Andro-
pogon furcatus and in which the Andropogon scoparius association is

the climax association of the prairie. In this intermediate region in the

hydrarch succession, Andropogon furcatus is succeeded by Andropogon
scoparius.

Annotated List of Species

No attempt was made to make a complete list of all the prairie

species in the state. The following list is added primarily to give a
more complete record of the secondary species of the different asso-
ciations, and an attempt is made to check them with reference to the
associations in which they are most usually found. Introduced species,

ruderals, and species found only on railway rights-of-way or greatly

disturbed areas are listed usually without reference to associations.

Some of the weeds and most of the species characteristic • of forest bor-
ders and small forest openings, which do not extend very far out on the
prairie, are omitted. This list, compiled from small relic areas and un-
der the present disturbed conditions, is subject to the limitations pre-
viously discussed and can only approximate the distribution under natural
conditions. Consequently reference is made only to the more promi-
nent associations. These associations are referred to in the tabulation

by initial letters as follows: S. f. a., Scirpus fluviatilis association, C. a.,

Carex association, S. M. a., Spartina Michauxiana association, C. c. a.,

Calamagrostis canadensis association, P. v. a., Panicum virgatum asso-
ciation, A. f. a., Andropogon furcatus association, A. s. a., Andropogon
scoparius association, M. g. a., Mixed grass association on sand, P.
b-g. a.. Pioneer bunch-grass association on sand, P. p. a., Panicum pseu-
dopubescens association. The nomenclature follows the Vienna Code,
as given in the seventh edition of Gray's Manual.



559

Polypodiaceae
Aspidium Thelypteris
Onoclea sensibilis

Equisetaceae
Equisetum arvense

" hyemale
" " var. inter-

medium
Selaginellaceae

Selaginella rupestris
apus

Typhaceae
Typha latifolia

Sparganiaceae
Sparganium eurycarpum

" angustifolium
Najadaceae

Potamogeton zosterifolius
Alismaceae

Sagittaria latifolia

graminea
Alisma Plantago-aquatica

Gramineae
Andropogon scoparius

" furcatus
Sorghastrum nutans
Digitaria sanguinalis
Leptoloma cognatum
Paspalum Bushii

"
circulars

Panicum capillare
" dichotomiflorum
" virgatum
" perlongum
" Llndheimeri
" huacliucae
" implicatum
" tennesseense
" praecocius
" Scribnerianum
" pseudopubescens
" Lieibergii

Echinochloa crusgalli
Setaria viridis

" glauca
Cenchrus carolinianus
Zizania palustris
Leersia oryzoides
Phalaris arundinacea



560



561



563



563



564



565



566

Boraginaceae
Lithospermum arvense

" Gmelinl
" canescens

Verbenaceae
Verbena angustifolia

" hastata
" stricta

Llppia lanceolata
Labiatae

Teucrium canadense
" occidentale

Scutellaria lateriflora

parvula
Prunella vulgaris
Physostegla virginiana
Stachys tenuifolla

" palustris
Monarda fistulosa

" punctata
Hedeoma hispida
Satureja glabra
Pycnanthemum flexuosum

" virginianum
" pilosum

Lycopus americanus
Solanaceae

Physalis heterophylla
" virginiana

Scrophulariaceae
Linaria canadensis
Pentstemon hirsutus
Mimulus ringens
Ilysanthes dubia
Veronica virginlca
Gerardia paupercula
Castilleja coccinea
Pedicularis canadensis

" lanceolata
Acanthaceae

Ruellia ciliosa

Plantaginaceae
Plantago Rugelii

" aristata
virginica

Rubiaceae
Galium boreale

" Claytoni
tinctorlum



567



568



569

Non-technical Summary

The foregoing technical report is written, in the main, for trained

botanists and agriculturists and needs no further summary. Since the

prairie region of Illinois is the greatest natural asset of the state and,

therefore, of considerable interest to the general public, it may not be
amiss to end this report with a non-technical summary of its outstanding

features.

The variations in the natixe fertilit\- of the different soils of the

state are a result mainly of the kinds of native plants that have grown
upon these soils since the recession of the glaciers th^t formerly covered
nearly the entire area of the state (map page 530). When the glaciers

melted, the surface of the state was left covered with a deposit of clay,

pulverized rock, and bowlders which the glaciers had picked up and
carried southward from the Hudson and Labrador regions. The un-
equal deposition of this glacial drift left the state with a gently rolling

topography. The depressions became shallow lakes, many of which were
several square miles in area. Streams from the melting ice left rather

large deposits of sand in some parts of the state. Thus the early post-

glacial soil, aside from these sand deposits, consisted of clay, pulverized

rock, and bowlders, practically devoid of organic matter and of general

uniformity throughout most of the state. The varying amounts of

humus in these soils today are the results of the growth and decay of

vegetation upon them during the postglacial period.

Botanists are reasonably certain that the first plants which grew
upon the glacial drift were the same as those found growing today just

south of the present glaciers in the north. The first zone of vegetation

south of these glaciers is a tundra on which mosses, lichens, grasses,

sedges, and low heath-like shrtibs are the prominent plants ; the second

zone is the northern evergreen forest of spruce and fir on the uplands

and bogs in many of the smaller lakes ; the third zone is the deciduous

hardwood forest with trees on the uplands and sedges in many of the

shallow lakes.

As the glaciers receded from Illinois the tundra was replaced by

the northern spruce-fir forest, and finally, the spruce-fir forest by the

deciduous hardwood forest. This forest, however, did not cover all of

the upland area of the state, a part of which was covered by tall grasses

characteristic of the prairie, chiefly tall bluestem (Andropogon furcatus).

Only about one third of the state became forested in contrast to the much
greater proportion of forest to prairie in Indiana and Ohio. There is evi-

dence that the prairie on the upland areas originated during a postglacial

dry period when the prairie extended farther eastward than at present.

The shallow postglacial lakes did not become forested but supported a

luxuriant growth of herbaceous water plants which decayed, but slowly,

beneath the surface water and gradually filled the lakes. In this way
enormous sloughs arose and a deep deposit of humus accumulated. The



570

depth and area of these postglacial lakes are attested today by the

depth and extent of the rich humus soils which accumulated in them.

The deeper peat deposits in some parts of the state evidently had their

origin in the postglacial bogs noted above.

As the postglacial lakes became filled and better drained through
the decay of vegetation in them and partly by the vertical cutting of

streams and the deposition of debris washed from the uplands, the pio-

neer water-plants died and were replaced by plants characteristic of the

better-drained soils. The series of this succession of plants leading to

the gradual filling of the sloughs may be seen today in areas little dis-

turbed by man. At first the bulrushes are the most abundant and promi-
nent plants accompanied by fewer individuals of many other water plants

which are unable to become abundant in competition with the luxuriant

growth of the bulrushes. The bulrushes, therefore, may be called the

dominant plants at this stage of filling of the sloughs. A miniature bul-

rush slough is shown in Plate LIV. The bulrushes begin to die as the

sloughs become drier through filling or drainage and are replaced by
sedges which dominate during a second stage of deposition (Plate

XLVIII). The sedges are followed by slough grass {Spai-tina Michan-
xiana. Plates XLIX, L). Sometimes the slough grass follows the bul-

rushes directly without an intervening sedge stage. At this stage the

sloughs may become dry for a few months during summer, but are still

too wet for cultivation. The slough grass is followed in order by blue

joint-grass {Calamagrostis canadensis, Plate LI), and tall Panicum
(Panicum virgatum) or by Panicum alone, which, in turn, is finally re-

placed by tall bluestem (Plates LXV-LXX). Tall bluestem remains as

the dominant grass of the true prairie. The early settlers found most of

the bluestem prairie dry enough for cultivation. All gradations in the fill-

ing of the sloughs were seen by the early settlers. Most of the prairie area
on the older glaciated part of the state south of the latitude of Mattoon
had become covered by tall bluestem, but a large part of the prairie re-

gion in the younger glaciated area north of this latitude was not dry
enough for tall bluestem and abounded in numerous sloughs of bul-

rush and slough grass. These drained sloughs and prairies with their

deep deposits of humus are now the most productive lands of the state.

Where the upland clay soils become covered with a prairie vegeta-

tion instead of a forest, the first abundant grass to appear upon them is

short bluestem (Andropogon scoparius). This grass, in time, becomes
crowded out and is replaced by the tall bluestem.

Some of the sand deposits of the state became forested, but a large

part of them became covered with a prairie vegetation. The first plants

that grew upon the dry moving sand-dunes were not plants of the

prairie, but short grasses more characteristic of the plants found upon
the sand hills of Kansas and Nebraska (Plate LXXI). These pioneer

plants, in time, developed a carpet of vegetation sufficient to hold the

sand against the force of the wind. Through their death and decay



571

humus was added to the sand, increasing both the stabiHty and water-
holding capacity of the sandy soils. This made conditions favorable
for the growth of plants characteristic of the prairie. Short bluestem
first became abundant and crowded out most of the pioneer plants

(Plates LXXII, LXXIV). With further increase of humus, stability, and
water content of the sandy soils tall bluestem came in and crowded out
the short bluestem (Plate LXXV). This succession of grasses, leading
ultimately to tall bluestem on the sand deposits, was not completed on
all the sand areas of the state when the first settlers arrived. All grada-
tions from the pioneer to the climax could be found.

Starting with the pioneer soil-conditions left by the melting glaciers,

the accumulation of organic matter from vegetation and the work of
erosion have been gradually changing the topography, water content,

and composition of the soils of the state. The change in water content
of the soil was the most potent factor underlying the changes in prairie

vegetation discussed above. With a decrease in water content of the

areas covered by sloughs and an increase in the water content of clay

slopes and sand accompanying the increase in humus and stability of
the soil, more and more of the prairie area became covered by tall blue-
stem. This grass was the most abundant and prominent prairie plant

on all the well-drained and sufficiently moist prairie areas of the state.

In all the successions of prairie plants accompanying the filling and
draining of sloughs, the wearing down of clay slopes, and the stabiliza-

tion of sandy soils, the ultimate vegetation of the prairie is dominated
by tall bluestem. This means that tall bluestem is the climax grass of

the prairies of Illinois. It will remain the dominant prairie plant under
natural conditions unless the water content of the soil is again seriously

changed. Where the turf is broken by eroding heads of ravines it

may be succeeded by a forest. A glance at Dr. Brendel's map (page 526)
shows that much of the forest area of the state has developed in this

way and is generally distributed along all the creeks and rivers.

None of the pictures accompanying this report give an adequate

conception of the former bluestem prairies. This grass forms a close

sod and under good growing condition may reach the height of 10-13

feet. The early settlers say that they were unable to locate cattle on the

prairie except by climbing some elevation and watching for the waving
of the tall grass as the cattle walked through it. Its growth was suf-

ficiently dense to crowd out most of the other prairie plants, among the

most prominent of which were plants of the mint, bean, and sunflower

families. On eroding clay slopes and along forest borders the yellow,

blue, and white flowers of these coarse herbs became conspicuous in late

summer and autumn. A glance at Plate L may give some impression of

the rank growth of the prairie grasses.

The humus accumulated on our prairie soils does not supply food

to our crop plants. Like all green plants they make their food chiefly

out of water and carbon dioxide. In the manufacture of carbohydrates



572

and fats no other raw material is used, but in the manufacture of pro-

tein .a supply of nitrates, sulphates, and a small amount of phosphates
are also used. Decaying organic matter, however, does greatly increase

the fertility of soils through its favorable effect on the water content

of the soil, ease of root penetration, soil aeration, and soil temperature,
checking the leaching of minerals, and being a source of carbohydrate
supply for some of the nitrogen-fixing bacteria and fungi in the soil.

The decay of forest vegetation also adds humus to the soil, but not

so rapidly nor in as great amounts as is added by the decay of prairie

plants. The glacial drift that has been forested a considerable part

of the time since the recession of the glaciers has much less humus
accumulated in it than is found on the drift covered by a prairie

vegetation. Soil surveys conducted by the Illinois Experiment Station

show that the forested soils have only from 25-50 per cent, as much
organic matter in them as is found in the adjoining prairie soils. This

is a result of the fact that most of the forest vegetation accumulates
and mostly decays on the surface of the soil, while the numerous roots

and root-stocks of the prairie vegetation accumulate and decay more
slowly beneath the surface of the soil. This difference, of course, does

hot apply to flood-plain forests, where deposition during overflows is an
important factor in soil fertility, nor to the occasional small forest areas

that have developed from swamps in which the slowly decaying organic

matter accumulates under water during the greater part of the year.

The greater amount of humus accumulated in the prairie soils increases

their fertility over that of the forest soils by increasing the check on

the leaching of minerals, such as calcium, and by increasing the other

favorable effects of humus noted above. This explains why farms for-

fnerly forested decrease in yield from year to year more rapidly than

farms on adjacent prairie soils, both of which have had the same
history except for the different kinds of native plants that have grown
upon them. Where erosion follows deforestation the cleared lands be-

come unprofitable for cultivation within a few years. Such areas should

be kept in permanent forests.

It is evident, therefore, that the variations in native fertility of

the different soils of the state are a result, mainly, of the kinds of native

plants that have grown upon them and the conditions under which these

plants grew since glacial times. Prairie and forest, alike, developed

on glacial till. Prairie vegetation has added more humus and brought

about a bigger change in the surface soil than forest. Their subsoils

are alike. It is obvious, therefore, that the cause of the original prairies

or forests in Illinois is not to be found in the different compositions of

the soils of today. Aside from climatic conditions, the water content

of the soil and not the kind of soil has been the most important factor

in determining what kind of native plants grew upon any given area

of the state. Under the present conditions of drainage, whenever the

prairie turf is broken by erosion or other means a forest vegetation may



573

develop, but this fact has no bearing upon the explanations of causes

of the original prairies and forests of the state.

The progress of civilization during the last century has not only

destroyed nearly all of the native prairies of the state but, likewise, some
of the conditions that gave rise to them. Grazing, drainage, cultiva-

tion, and stream pollution have all been destructive to the native prairie

flora. Cultivation has destroyed the prairie plants except along fences

between the farms, while grazing has destroyed even these last remnants
not reached by the plow. Intensive grazing accompanied by the introduc-

tion of blue grass and red top destroyed practically all of the native prairie

plants on the farms not cultivated. The bluestem prairies became blue-

grass pastures, and where drainage accompanied grazing the native

plants of the sloughs were also replaced by blue grass. In areas too wet
for blue grass, red top became abundant, while in still wetter areas sedges

and rushes prevailed. The bulrushes were mostly killed by the tramping
of cattle, and cattails became abundant in the undrained sloughs. Graz-
ing on the sand prairies destroyed the bluestem, and blue grass became
abundant, giving rise to blue-grass pastures on sand. But where the

sand areas were still too dry for the bluestems, grazing has increased

the number of blowouts in the sparser vegetation of plains grasses. Some
of the bluestem prairies on sand were cultivated instead of pastured.

This has led (1) to the destruction of much of the humus accumulated
for centuries by the decay of the native grasses, and (2) to the ex-

posure of loose sand to wind action through the destruction of the

prairie turf. As a result, blowouts and sand dunes become increasingly

abundant, and the farms must shortl}' be abandoned. Carefully con-

ducted experiments would undoubtedly result in the discovery of more
profitable methods of dealing with these sand areas.

The changes brought about by drainage are somewhat too com-
plicated to be discussed in detail in this summary. Artificial drainage

has lowered the water-table several feet and drained most of the sloughs.

This has led to all degrees of destruction of the natural grasses of the

sloughs and made conditions favorable for the migration into them of

plants characteristic of better-drained soils. Artificial drainage led to

a sudden disturbance of the balance that obtained under natural con-

ditions, and plants that reproduce most readily had a chance to become
prominent. As a result, many plants not prominent on the natural prai-

ries became temporarily abundant on the newly drained areas. This

condition is well represented on the railway rights-of-way today. Arti-

ficial drainage is also favorable to the development of forests on the wet
prairies.

The effect of the pollution of streams and prairie ponds received

little attention in this survey. It appears to have been destructive to

bulrushes and favorable to the growth of cattails. Its chief economic

effect is to be found in the destruction of algae, the main source of the

food of fishes.



574

This summary would not be complete without a word on the causes
of the prairie. No other question of the prairie has been discussed so
frequently or widely, and the answers to the question are as widely
variable as their authors. This is a result, largely, of the various authors
emphasizing local factors which would not apply to the prairies as a
whole, or emphasizing only one of several factors which operating to-

gether may explain the prairies, but when considered separately fall

far short of an adequate explanation. For instance, prairie fires, grazing,
and the character of the soil are factors that may afifect the local dis-

tribution of prairie and forest at their borders, but become insignificant

in any attempt to explain the prairies as a whole. In some cases they
have been reported as favorable to forest, in others as favorable to

prairie. As a matter of fact, prairie tires and grazing are an effect

rather than a cause of the prairies. As shown above, this may be true
also of the prairie soils in so far as they differ from forest soils. On the
other hand, temperature, wind, humidity, rainfall, and topography were
all important factors in causing the treelessness of the prairies, but no
one of these five factors considered alone will explain the prairies.

Omitting topography for the moment, it is possible to analyze the

effect of the remaining four factors in terms of only two factors. Tem-
perature, wind, and humidity all aft'ect the rate of evaporation of water,
and it is in this way that they operate in affecting the development of
forest and prairie. They may he dealt with as one factor, namely,
evaporation. We have to consider, therefore, only the factors, evapora-
tion and rainfall. Both rainfall and evaporation are measured in inches
per year by the Weather Bureaus. The amount of evaporation is ob-
tained by exposing standard open vessels of water and keeping the record
of water loss each day. At the end of the year this may be calculated

to terms of inches of water lost by evaporation.

If the number of inches of annual rainfall (precipitation in general)

is divided by the number of inches of annual evaporation, these two
factors may be expressed as a single factor, namely, the per cent, or ratio

of rainfall to evaporation. When the rainfall-evaporation ratios obtained

at various places in the United States are plotted on a map, we are able

to determine the combined effects of the four climatic factors—tempera-
ture, wind, humidity, and rainfall—upon the distribution of the natural

vegetation. (See map on page 524.) The region of the United

States in which the ratio of rainfall to evaporation is between 60

and 80 per cent, coincides very closely with the prairie region. In gen-

eral, where the ratio is less than 60 per cent, plains or deserts result

;

where it is more than 80 per cent, forests are found. Since the annual

distribution of rainfall is also important, these figures are not absolute

for all localities. Hence, the chief cause of the prairie lies in the

combined action of the four climatic factors named above through their

effect upon the water relations of the plants concerned.

Topography may effect the distribution of prairies through its

effect on some one or more of the climatic factors, as in the exposure



575

or protection of slopes from prevailing winds or the direct rays of the

sun. In Illinois, topography was an important factor in the origin of

prairies that developed from postglacial lakes through its effect on the

water content of the soil. Prairies also developed on some of the well-

drained upland soil. Forests were more common on the higher moraines,

flood-plains, and river bluffs.

To-sum up, climatic factors are of primary importance in determin-

ing the general boundaries of distribution of the prairies, while the

ever changing topography and water content of the soil are important

in determining where sloughs, prairies, or forests will develop withirf

these boundaries. The efifect of these soil factors is more prominent

near the boundaries of the prairie region than near its center of dis-

tribution where we find prairies growing on the greatest range of soil

conditions.

Where a prairie or swamp vegetation is once established still another

factor becomes important in keeping out the forest even after the swamps
have become well drained, namely, the ability of the tall grasses to out-

grow and over-shade the seedlings of forest trees. In the case of the

drier prairies the grasses with their well-established root system have
a monopoly of the water supply in the soil, and may prevent the de-

velopment of seedlings of forest trees.

Forest invasion of prairies however does occur. It may follow

the destruction of the prairie turf by erosion or it may precede erosion.

Forest invasion on non-eroded prairie soils in Illinois is more extensive

on the older glaciated regions of the state than on the younger glaciated

regions. On the Wisconsin glaciated region this invasion is most common
on the slightly elevated prairies, but there are natural groves of forest

on some of the non-eroded black prairie soils.

The Ohio State University,

Columbus, Ohio.



LITERATURE CITED
Barrows, H. H.

(1) 1910. Geography of the Middle IlHnois Valley. Bui. 111. Geol.

Surv., No. 15.

Cannon, W. A., and Free, E. E.

(3) 1917. The ecological significance of soil aeration. Science, new
ser., 45 (No. 1156) : 178-180.

County Soil Reports

(3) Nos. l-li, Univ. 111. Agr. Exper. Station.

Cowles, H. C.

(4) 1899. The ecological relations of the vegetation of the sand
dunes of Lake Michigan. Bot. Gaz. 27 : 95-177, 167-203,
281-308, 361-391.

(5) 1900. Physiographic ecology of Chicago and vicinity. Bot.

Gaz. 31: 73-108, 145-182.
Gates, F. C.

(6) 1912. The vegetation of the beach area in northeastern Illinois

and southeastern Wisconsin. Bui. 111. State Lab. Nat.
Hist. 9: 255-372.

Gerhard, Frederic

(7) 1857. Illinois as it is, p. 238-247, 270-278.

Gleason, Henry Allan

(8) 1909. Some unsolved problems of the prairies. Bui. Tor.
Bot. Club, 36: 265-271.

(9) 1910. The vegetation of the inland sand deposits of Illi-

nois. Bui. 111. State Lab. Nat. Hist. 9: 23-174.

(10) 1912. A comparison of the rates of evaporation in certain

associations in central Illinois. Bot. Gaz. 53 : 478-491.

Hart, Charles A., and Gleason, H. A.

(11) 1907. On the biology of the sand areas of Illinois. Bui. 111.

State Lab. Nat. Hist., 7 : 137-273.

Harvey, E. M.
(12) 1913. Evaporation and soil moisture on the prairies of Illinois.

Trans. 111. Acad. Sci., 6: 93-99.

Hayden, Ada
(13) 1919. The ecological foliar anatomy of some plants of a

prairie province in central Iowa. Amer. Jour. Bot. 6

:

69-85.

(14) 1919. The ecologic subterranean anatomy of some plants of

a prairie province in central Iowa. Amer. Jour. Bot. 6

:

87-104.

Hopkins, Cyril G., Mosier, J. G., and Baur, F. C.

(15) 1916. Summary of IlHnois soil investigations. Bui. Univ.
111. Agr. Exper. Sta., No. 193.



577

Hopkins, Cyril G., Readhimer, J. E., and Fisher, O. S.

(16) 1912. Peaty swamp lands; sand and "alkali" soils. Bui. Univ.
111. Agr. Exper. Sta. No. 157.

Leverett, F.

(17) 1897. The Pleistocene features and deposits of the Chicago
area. Bui. II, Geol. and Nat. Hist. Surv., Chicago Acad.
Sci.

(18) 1899. The Illinois glacial lobe. U. S. Geol. Surv., Vol. 38.

Mosher, Edna
(19) 1918. The grasses of Illinois. Bui. Univ. 111. Agr. Exper.

Sta. No. 205.

Salisbury, Rollin D., and Alden, W. C.

(20) 1899. The geography of Chicago and its environs. Bui. Geogr.

Soc. Chicago, No. 1.

Sayre, J. D.

(21) 1920. The relation of hairy leaf coverings to the resistance of

leaves to transpiration. Ohio Jour. Sci. 20 :
5'5-86.

Schaffner, John H.

(22) 1913. The characteristic plants of a typical prairie. The Ohio
Naturalist, 13: 65-69.

Sherfif, Earl E.

(23) 1913. Vegetation of Skokie Marsh. Bui. State Lab. Nat. Hist.

9: 575-611.

Shimek, B.

(24) 1911. The prairies. Bui. Lab. Nat. Hist., State Univ. Iowa,
6: No. 1.

Transeau, E. N.

(25) 1903. On the geographical distribution and ecological rela-

tions of the bog-plant societies of northern North
America. Hot. Gaz. 36: 401-420.

(26) 1905. Forest centers of Eastern America. • Amer. Nat. 39:

875-889.

Vestal. Arthur G.

(27) 1913. An associational study of the Illinois sand prairies.

Bui. 111. State Lab. Nat. Hist. 10 : 1-96.

. (28) 1914. A black-soil prairie station in northeastern Illinois.

Bui. Tor. Bot. Club, 41: 351.

Waller, Adolph E.

(29) 1918. Crop centers of the United States. Jour. Amer. Soc.

Agron. 10: 49-83.

(30) 1918. The grasses. Correspondence Courses in Agriculture,

Course VII, Lesson V. Extension Publications of the

Ohio State University.

(31) 1921. The relation of plant successions to crop production.

The Ohio University Publications, Vol. 25, No. 9.



P
l
a
t
e
X
L
V
I
I
I



P
l
a
t
e
X
L
I
X



P
l
a
t
e
L



P
l
a
t
e

L
I



P
l
a
t
e

L
I
I



P
l
a
t
e

L
I
I
I



P
l
a
t
e
L
I
V



P
l
a
t
e
L
V



P
l
a
t
e
L
V
I



P
l
a
t
e
L
V
I
I



P
l
a
t
e
L
V
I
I
I



P
l
a
t
e
L
I
X



P
l
a
t
e
L
X



P
l
a
t
e
L
X
I



P
l
a
t
e
L
X
I
I



P
l
a
t
e
L
X
I
I
I



P
l
a
t
e
L
X
I
V



P
l
a
t
e
L
X
V

'
2
'
*
-
?

»
4
?
^
^

/
*
%
*
*



P
l
a
t
e
L
X
\
'
I



P
l
a
t
e
L
X
V
I
I



P
l
a
t
e
L
X
V
I
I
I



P
l
a
t
e
L
X
I
X



P
l
a
t
e
L
X
X



P
l
a
t
e
L
X
X
I



T
l
a
t
e
L
X
X
I
I



P
l
a
t
e
L
X
X
I
I
I



P
l
a
t
e
L
X
X
I
V



P
l
a
t
e
L
X
X
V



P
l
a
t
e
L
X
X
V
I



P
l
a
t
e
L
X
X
V
I
I