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Paleoecology of an early Holocene faunal and floral assemblage from the Dows Local Biota of north-central Iowa
QUATERNARY
RESEARCH
21, 351-368 (1984)
Paleoecology of an Early Holocene Fauna1 and Floral Assemblage from the Dows Local Biota of North-Central Iowa CURTIS
M. HUDAK
Department of Geology, The University of Iowa, Iowa City, Iowa 52242 Received January 28, 1983 The faunas and floras from the Dows Local Biota provide an opportunity to compare Holocene taxa without a cultural bias. The Dows Local Biota is located in a large depression on the back side (north) of the Altamont I Moraine complex within the Des Moines Lobe. The Dows Silt Fauna/Flora (=DSF; ca. 9380 ? 130 yr B.P.), one horizon of the Dows Local Biota, was collected for plant macrofossils, mollusks, and micromammals. DSF terrestrial gastropods are upland mesic forest dwellers although one species, Strobilops afinis. is characteristic of more xeric forests and may represent open woods. The aquatic gastropods reflect both permanent and periodic waters. DSF micromammals prefer an open, mesic, deciduous forest. The micromammal sympatry is restricted to a small area within the tension zone and deciduous forest belt of west-central Wisconsin. DSF plants are characteristic of upland forests, moist meadowlands or disturbed areas, and aquatic habitats. The DSF plant sympatry is large but restricted to the conifer-hardwood and deciduous forests along the Great Lakes-New England regions. Quantitative climatic data for the combined DSF sympatries suggest that Dows (ca. 9380 yr BP.) was cooler than at present, and is nearly identical to that achieved by pollen analyses at the Cherokee Sewer-Lake West Okoboji sites (ca. 9000 yr BP.) in northwest Iowa. Based on common habitat interpretations and sympatries, about 9380 vr B.P. north-central Iowa was cooler and moister than at present and was occupied by an open deciduous forest.
INTRODUCTION Few Holocene paleoecological interpretations, from nonarchaeological sites in the United States, are based upon plant macrofossils, mollusks, and vertebrates from a single locality. The Dows Silt Fauna/Flora (DSF), a 9380 2 130 yr B.P. (Beta-5001) horizon of the Dows Local Biota, yields information without a cultural bias on the early Holocene of north-central Iowa. Iowa, during the early Holocene, was occupied by a deciduous forest as interpreted by numerous pollen analyses. The Dows Local Biota provides an opportunity to test (1) whether or not mollusks, small mammals, and plant macrofossils from the same horizon in a noncultural site have similar paleoecologic interpretations, and (2) whether these paleoecologic interpretations concur with pollen analyses in the same region. This will be accomplished by comparing common habitats for each taxonomic group and by constructing
sympatries (areas where the taxa ranges currently overlap). The Dows Local Biota, near Dows, Iowa, was discovered during construction of Interstate 35 in March 1974, when part of a prairie wetland and creek was destroyed. Remains of bison, elk, deer, small vertebrates (including amphibians, reptiles, birds, and mammals), mollusks, plant macrofossils, insects, and wood were found in the spoil. Construction activity prevented establishment of a section at the time, even though peat and other sediments were exposed. Recently, a drainage ditch constructed in the Dows depression (Fig. 1) exposed silts, sands, and a peat. Preliminary studies have not revealed any pollen. The depression with the Dows Local Biota is located on the backside (north) of the Altamont I moraine complex of the Des Moines lobe (Fig. 2 in Kemmis et al., 1981) in Sec. 28 and W’h Sec. 27 T91N R22W (Fig. 1). The Altamont moraine, characterized by hummocky topography near the
351 0033-5894184 $3.00 Copyright 0 1984 by the University of Washington. All righIs of reproduction in any form reserved.
CURTIS M. HUDAK
352
study area, is next to the oldest of the Des Moines lobe moraines and dates at approximately 13,500 yr B.P. (Kemmis et al., 19Sl).
iippmximate Depthcm> HOrIm”1. Verydarkt.3blackmucky silt loam. O-
STRATIGRAPHY
Six vertical sections measured and described along the side of the newly excavated ditch (Fig. 1) provided sufftcient data to develop a composite stratigraphic settion (Fig. 2). Six lithic horizons were identified and are here described from top to bottom to accommodate addition of units that may be discovered with deeper sampling. Horizon 1 has abundant mollusks, seeds, and microvertebrates. The seeds are primarily sedges (Carex spp.), the mollusks are dominated by aquatics, and nearly all the microvertebrates are anurans (frog). The interpreted depositional environment is a marshy wetland that spans the entire depression north of the Altamont moraine. The wetland accumulated into historic time. Horizon 2 varies from fibric to nonfibric
FIG. 1. Map showing county ditch and measured sections (A-F). The Dows Silt Fauna/Flora was collected from Sec. E. Contour interval = 7.5 m (25 ft).
rarecross-bedding. lag fragments in fragment dated at 9650 upper 20(Beta-mm: cm. : logabundant 130yrB.P nearDDWS section c in+ Graytoquartz darkgray silty sands. N410 610:mostly grains. Grayto darkgraysilts, 244106/O. FIG. 2. Composite stratigraphic section for the Dows Local Biota. The Dows Silt Fauna/Flora was collected from Horizon 3.
peat and is discontinuous along the ditch because it only tills in depressional areas in the underlying Horizon 3 sediments. The peat contains microvertebrates, including small mammals, reptiles, and amphibians, plus abundant mollusks, plant macrofossils, insects, and bison. This unit was probably deposited in a prairie wetland environment. Radiocarbon dates on the peat were not obtained because of modern root contamination and the absence of wood. Horizon 3 is an olive-green silt and contains the DSF. Oak (Quercus) wood, collected near the bottom of this unit, was dated at 9380 + 130 yr B.P. (Beta-5001). This sedimentary unit exhibits constant thickness except over older topographic highs. Three silt lithofacies are present that change abruptly both laterally and stratigraphically. Of the three facies one is primarily silt, one is slightly richer in coarse to medium sand, and the other consists of subhorizontal, thin, discontinuous, organic
EARLY
HOLOCENE
PALEOECOLOGY
silts. Horizon 3 may have originated under a low energy fluvial environment, or possibly a lake with differential influxes of hillside sediments creating the facies changes. Horizon 4 grades up from gravelly sands to laminated silty sands. The surface of this unit is often iron cemented, and contains abundant wood fragments and horizontal logs up to 58 cm (23 in.) in diameter. One wood fragment was identified as elm (Ulmus) and another was dated at 9650 + 130 yr B.P. (Beta-3048). Two cross-bedded gravels, one occurring near Section C (Fig. 1) and the other near the junction of the ditches, indicate deposition from currents flowing toward the south-southeast. Horizons 4, 5, and 6 are fluvial silts or sands. Hoyer (1980) and Walker (1966) noted that Holocene and late Wisconsin sediments in Iowa may record changes in paleoclimates. Walker (1966) emphasized a consistency in stratigraphic sequences from five bogs on the Des Moines lobe in Iowa as follows: Upper Muck Zone, O-3000 yr B.P.; Upper Silt Zone, 3000-8000 yr B.P.; Lower Muck Zone, 8000-10,500 yr B.P.; Lower Silt Zone, 10,500-13,000 yr B.P.; Cary sediments, >13,000 yr B.P. He interpreted the muck zones to represent periods of relatively slow hill-slope erosion because of increased vegetation, which is a function of high precipitation; the silt zones represent intervals of relatively rapid slope erosion resulting from reduced vegetation during periods of low precipitation. Walker’s stratigraphy does not correlate with that at Dows. For instance, the Dows wood dates of 9650, and 9380 (this report) and 9180 rt 90 yr B.P. (DIC-1131; R. S. Rhodes, 1982, written communication), respectively, from the top of Horizon 4, the bottom of Horizon 3, and a sand unit 20 cm (8 in.) below the peat put these mineral deposits time- stratigraphically in the middle of Walker’s lower muck zone. There are a number of reasons why the stratigraphy of Walker’s bogs differs from that of the Dows depression. Walker’s bogs, as opposed to Dows, were in small
OF NORTH-CENTRAL
IOWA
353
closed depressions that trapped the mineral sediments during periods of low precipitation and sparse vegetation. The Dows depression is larger and the interpretation of sedimentary environments through time is hindered by limited exposure and by limited control on the time of deposition for the lowermost horizons. Sands and gravels in Horizon 4 clearly indicate deposition in some type of high energy fluvial environment in the Dows depression prior to or ca. 9650 yr B.P. The sandy silt of Horizon 3 could be indicative of a number of sedimentary environments, and sand lenses in Horizon 2 may indicate periodic influx of hill-slope sediments (from the surrounding uplands) into a marshy environment. The overall record of the depression thus appears to be one of decreasing energy through time. Two possible depositional environments might produce a sedimentary sequence similar to that found in the Dows depression. The first possibility is one of deposition on a floodplain. Under this model, Horizon 4 would represent an active channel, Horizon 3 might represent one or several episodes of flooding of an abandoned channel area, and Horizon 2 might represent the organic accumulation of a marsh on a poorly drained floodplain. Major problems with this interpretation are that the Dows depression is not associated with any present river system, there is no clear indication of any past association with known river systems, and present day gradients along the depression are opposed to each other, rather than in the same direction along a well-defined former channel. A second possibility is that Horizon 4 represents glaciofluvial deposition associated with stagnant ice in the Altamont I moraine complex. This would explain the opposing gradients along the depression. Horizon 3 would then represent the initial infilling of areas between sand bars of Horizon 4, possibly as a lake formed in the depression following deglaciation. The peat in Horizon 2 would be generated in the
354
CURTIS
shallow lake or marsh that formed as a result. In any case, both of the above theories would require extensive coring and trenching but do offer explanations for differences with Walker’s (1966) closed depressions and the fauna1 and floral habitats discussed below. EXCAVATION AND LABORATORY PROCEDURES Excavations at Dows showed that Horizon 3 would yield approximately 20 mollusks, 9 seeds, and 1 mammal tooth per 4 liters of silt. Approximately 727 kg of Horizon 3 matrix was washed in l-mmmesh box screens to produce the biotic sample used in this report. Drainage from a farmer’s tiles was sufficient in the county ditch to remove most of the silt with minimum agitation. Samples, at first, were collected in IO-cm stratigraphic units. This was later abandoned and the data combined because the specimens were recovered in roughly the same proportions from the different levels and lithofacies. Fossiliferous burrow fillings of organic silts and clays, intruded from the overlying peat, were removed as best as possible to reduce contamination. The laboratory work involved picking, measuring, and identifying specimens using a Bausch and Lombe binocular microscope equipped with a micrometer scaled to the nearest 0.05 mm. Identifications were based upon comparative material in the University of Iowa Museum of Natural History Geological Repository (SUI) and the University of Kansas Museum of Natural History (KUMNH). All specimens described herein have been cataloged into the University of Iowa Geological Repository. DOWS
SILT FAUNA
AND FLORA
A. Invertebrates
The DSF invertebrates comprised mollusks and insects. In the former, 27 genera
M.
HUDAK
and 35 species are present (Table 1). Many bivalves were heavily damaged and were not picked from the residue, however, it is estimated that the Bivalvia comprised about 25-30% of the molluscan fauna. The snails, comprising approximately 75% of the molluscan fauna, included both aquatics (58%) and terrestrials (18%). The taxonomy follows those of Clarke (1981) and La Rocque (1970). The insects for the Dows Local Biota are currently under study by Dr. Donald P. Schwert of the North Dakota State University, Fargo, North Dakota. B. Vertebrates General. The vertebrates are the least abundant group in both numbers of taxa and individuals. In all, remains of five classes (fish, amphibians, reptiles, birds, and mammals) have been recovered, but only the latter (Table 2) are specifically identified and considered in the paleoecologic analysis. Shrew taxonomy. All of the micromammals were readily identified by standard taxonomic procedures except for one of two left soricid dentaries. Dentary SUI No. 49221a (Table 2) clearly falls into the Sorex cinereus category based on dentary width versus depth (Fig. 3) and mandibular condyle morphology. The other Sorex dentary (SUI No. 49223; Table 2) has a more robust ml (Fig. 4 in Hudak, 1982, unpublished thesis, University of Iowa) and mandible (Fig. 3) than the S. cinereus group (S. cinereus group includes all S. cinereus subspecies and S. haydeni; Junge and Hoffman, 1981). In general SUI No. 49223 does not fit within either the S. cinereus or S. fumeus clusters (Fig. 3). However, the unknown is closer to either of these than to the smaller Microsorex or the extremely larger S. arcticus and S. palustris. A bivariate plot of ml-m2 length versus ml dentary depth clearly separates the S. cinereus group from S. fumeus biometrically and places the specimen in the S. cinereus group.
EARLY
HOLOCENE
PALEOECOLOGY
The members of the S. cinereus group are clustered but with a characteristic overlapping pattern found in subspecies (see Hudak, 1982, unpublished thesis, University of Iowa). The size of SUI No. 49223 is much larger than the S. cinereus dentary (SUI No. 49221a) mentioned above and the pair lay outside of the range of variation expected for a single population. This suggests that SUI No. 49223 is significantly different than SUI No. 49221a but not assignable on a single specimen. Because the presence of two distinct subspecies is not expected in a single faunule, SUI No. 49223 must either be aberrant or represent a distinct species. Dentary SUI No. 49223 may be related to S. haydeni (recently elevated to species; see van Zyll de Jong (1980), and Junge and Hoffman (1981)), a plains species, and distinguished from S. c. cinereus, a woodland form, or reflect an abnormally large individual more characteristic of a glacial population. C. Flora
Approximately 650 plant macrofossils were examined, of which 626 were identified (Table 3). The flora is comprised of 19 families, 26 genera, and a minimum of 42 species. Those listed as “type” were inseparable from one or more other species based on morphology; the chosen name was made for ecological or plant geographical reasons. Taxonomy was based on Gleason and Cronquist (1963). PALEOECOLOGY
Paleoecologic reconstructions assume that common habitats of organisms have changed little from the present day to those of 9380 yr ago. The degree of confidence is based on the knowledge of the living organism. Molluscan
Fauna
Table 1 lists the land snails and their common habitats. The most common associations are with moist woods (nonri-
OF
NORTH-CENTRAL
IOWA
355
parian or upland woods) and alluvial woods (riparian and floodplain woods). Sixteen of the seventeen DSF species are also listed under the more general category of mesic (moist) environments. Only Strobilops affinis, represented by four specimens, is restricted to dry forests (relative to Strobilops labyrinthica), which suggests that these specimens were transported from drier upland woods. Eleven species are common to both moist and alluvial woods. One species, Discus cronkhitei, is restricted to alluvial woods or moist prairie grasslands. Four species, Vallonia parvula, Punctum minutissimum, S. labyrinthica, and Carychium exiguum, prefer moist woods over alluvial woods. C. exiguum is of special note because it is largely restricted to cool forests (T. Frest, 1982, oral communication). No DSF land snails are restricted to prairie environments. Table 1 also lists the Dows Silt aquatic mollusks and their common habitats. All of these aquatics can be found in lentic (quiet) waters. Half of the aquatics can be found under lotic (moving water) conditions, but none are restricted to this environment. Thus, quiet water was characteristic of the depression ca. 9380 yr BP. Two other distinct habitats are represented by the DSF aquatic mollusks. Seven species are restricted to permanent waters and four species are more common to periodic waters that dry up at least once a year. This division suggests that permanent water occurred at Dows, but that adjoining areas did dry up on occasion. This would support both the floodplain and lake environments interpreted from the sedimentology and stratigraphy. The author interprets the molluscan paleoenvironment at Dows (ca. 9380 yr B.P.) as a cool, moist forest along the water’s edge and hillsides, with a drier, possibly open forest on the hilltops. The Dows depression probably held either a permanent lake or a slow flowing river with impermanent ponds on a floodplain. Sympa-
49234 49235 49236 49237 49238 49239 49240 4924 1 49242 49243 49244 49245 49246 49247 49248 49249 49250
Land snails Carychium exiguum (Say) Catinella avara (Say) Deroceras laeve (Muller) Discus cronkhitei (Newcomb) Gastrocopta contracta (Say) G. tappaniana (C. B. Adams) Hawaiia minuscula (Binney) Helicodiscus parallelus (Say) Punctum minutissimum (Lea) Retinella electrina (Gould) Strobilops afinis (Pilsbury) S. labyrinthica (Say) Succinea ovalis (Say) Triodopsis multilineata (Say) Vallonia parvula (Sterki) Vertigo ovata (Say) Zonitoides arboreus (Say)
Total land snails
SUI No.
274
9 34 7 3 7 31 7 12 1 5 4 16 94 39 2 1 2
MN1
1. MOLLUSKS
Taxon
TABLE
17.9
0.6 2.2 0.5 0.2 0.5 2.0 0.5 0.8 0.1 0.3 0.3 I.0 6.1 2.5 0.1 0.1 0.1
Est. % of molluscan fauna
FROM THE Dows
23.4
0.8 2.9 0.6 0.3 0.6 2.6 0.6 1.0 0.1 0.4 0.3 1.4 8.0 3.3 0.2 0.1 0.2
% of total snail fauna
SILT FAUNA
5
* * * * *
Moist prairie grassland
12
* * * * * * * * -
Alluvial
AND THEIR COMMON
15
* * * * * * * * * * * * * * *
Moist
Woods
HABITATS
7
* * * * * * *
Dry
16
* * * * * * * * * * * * * * * *
Mesic
7
*
Xeric
General
2 2 t; 5
Iimosa exigua dejlectus
(Say) (Lea) (Say)
1545
Total mollusks
Total Bivalves >375 1271
49266a 49266b 49266~
Total aquatic mollusks
Pisidium compressum Sphaerium occidentale S. rhomboideum (Say)
(Prime) (Prime)
1170
Bivalves
896
(Say)
40 15 7 446 2 9 14 2 217 5 5 47 1 7 79
Total snails
tricarinata
49262 49263 49264 49265
4925 1 49252 49253 49254 49255 49256 49257 49258 49259 49260
MN1
Total aquatic snails
Valvata
S. reflexa (Say)
Helisoma antrosa (Say) H. trivolvis (Say) Physa gyrina (Say) P. jennessi skinneri (Taylor) Planorbula campestris (Dawson) Promenetus exacuous (Say) Somatogyrus subglobosus (Say) Stagnicola catascopium (Say) S. elodes (Say)
G. parvus (Say)
Amnicola Fossaria Gyraulus
Aquatic snails
Taxon
SUI No.
1-Continued
100.1
82.2
24.3
75.8
57.9
2.6 1.0 0.5 28.9 0.1 0.6 0.9 0.1 14.0 0.3 0.3 3.0 0.1 0.4 5.1
Est. % of molluscan fauna
TABLE
Est. % of bivalve fauna 50 10 40
99.9
76.5
3.4 1.3 0.6 38.0 0.2 0.8 1.2 0.2 18.5 0.4 0.4 4.0 0.1 0.6 6.8
% of total snail fauna
18
* * *
* * * * * * * * * * * * * * *
Lentic
9
* * * * * * * *
Lotic
14
* *
* * * * * * * * * * * *
Permanent
Waters
11
* *
* * * * * * *
Periodic
palustris
Sorex
sp.~
Bison
49230d
49230b 49230~
49230a
49229b
49228a 49228b 49229a
in ecologic
analysis.
23
1
1 1
8
-
5
-
5
-
-
*
*
4
10
* -
*
*
*
10
* -
*
*
*
*
*
*
*
*
*
*
*
*
* -
*
Open woods
*
* -
*
“OUS
Decid-
-
* -
*
Coniferdeciduous
*
*
* -
*
Conifer
*
*
*
*
*
*
*
*
10
* -
-
*
Forest edge
Dows SILT FAUNA AND THEIR COMMON
1
1
1
1
1
1 1
1
MN1
FROM THE
L. maxillary and zygomatic plate Rm2 LM3 L. edentulous dentary 1 Lml, 4 Lm2, 3 Lm3,l Rml, 1 Rm2,2 LMl, 2 LM2,l LM3 and 2 RMl Palate with Ml s and M3s Palate edentulous R. dentary with ml and m2 8 Lml, 2 Lm2, 2 Lm3,3 Rml, 5 Rm2,3 Rm3, 6 LMl, 4 LM2, 1 LM3,6 RMl, 6 RM2 and 1 RM3 1 Lml and 1 LM2 R. radius Caudal vertebra 3rd phalanx 2nd phalanx (juvenile)
L. ulna
Lml or m2
L. edentulous dentary L. maxillary and Ml RI1 L. dentary with ml and m2 LIl, Lil
Element
2. MAMMALS
not included
4923 1 49232a 49232b 49232~ 49233
a Genera with wide habitat tolerance
Total
Bison
Pine vole Muskrat
M. pinetorum Ondatra zibethicus
vole
Meadow
Microtus pennsylvanicus
49227
49225
Mouse
49224
49226
shrew
49222 49223
49221b
49221a
WI No.
Short-tailed shrew Franklin’s ground squirrel Red squirrel
Southern hog lemming Red-backed vole
sp.
shrew
Masked
Water shrew Long-tailed
name
Common
Synaplomys cooperi Cleithrionomys gapperi
Tamiasciurus hudsonicus Peromyscus
Blarina brevicauda Spermophilus franklini
Sorex sp.”
cinereus
Sorex
BX0n
TABLE
*
*
*
*
5
-
-
-
-
*
Prairiegrasslands
HABITATS
*
*
*
*
6
*
-
-
-
-
*
Wetlands
*
7
*
-
*
*
*
c
*
Riparian
11
* *
*
*
*
*
*
*
*
*
*
Mesic
0
-
-
-
-
-
-
-
-
-
-
-
Xeric
EARLY
HOLOCENE
PALEOECOLOGY
OF NORTH-CENTRAL
IOWA
359
grass. The Franklin’s ground squirrel, because of its current eastward pioneering 2.8 _ * into recently opened forests of northwest * * 2.7Minnesota (Hazard, 1982), may well represent the first mammalian evidence of an 2.6 open forest during the postglacial of 2.5 * i northern Iowa. z Tamiasciurus hudsonicus (red squirrel) is ; 2.4 ** * ** E chiefly restricted to conifer or mixed cob 2.3 *** niferous-deciduous forests, but it can oc9 cupy pure stands of deciduous trees, parE 2.2 * )14F q t 8 ticularly if in a wet terrain (Jackson, 1961). ? Bc 2.1 O o%Dp Hazard (1982) contends that the species is d more at home in mature and continuous for2.0 #F f$ s* ests than in open woodlands or small iso1.9 8&d% 0 lated stands. Cleithrionomys gapperi (red-backed 1.s 0 •~m~o 0’ vole), like the red squirrel, occurs com1.7 lO ln monly in moist coniferous and mixed forI 1.0I 1.1I 1.2I 1.31 I.4I 1.51 1.6I 1.7, ests of the northern states. In Iowa it is .9 presently limited to the north-central part Dentq width under m2 f X 2mm I of the state, just north of Dows (Bowles, FIG. 3. Bivariate plot of dentary width versus depth 1975). However, Semken (in press) records in Sorex fumeus, S. cinereus, and S. haydeni. Measpecimens from 2000-yr-old Rockrun surement = X 2 mm. Shelter deposits in southeastern Iowa and from Holocene portions of the Peccary Cave in Arkansas. Bardwell (1981, unpubtries were not constructed because reliable lished thesis, University of Iowa) also redata on current molluscan ranges do not ports a single specimen of C. gapperi from exist. an earth lodge (13MLl24) in the 1215 AD Glenwood Local Fauna of southwestern Small Mammal Fauna Iowa. Bardwell explained that 13MLl24 is The DSF small mammals represent many situated in a more protected, steeperdifferent habitats although 10 of the 11 taxa walled valley than any of the other Glenconsidered are common to the deciduous wood lodges and speculates that a cooler forest (Table 2). The same 10 species can and moister microenvironment, suitable to also be found in an open forest (parkland) support a relict population of C. gapperi, and/or forest-edge environment. The elev- must have been preserved in the valley. The enth mammal, Ondatra, is restricted in red-backed vole had a more widespread range only by permanent water, but it is distribution in the late Holocene, but has in recommonly associated with those in Table 2. recently become more restricted, All of the DSF mammals prefer mesic con- sponse to either agricultural or postglacial ditions. climatic changes. Spermophilus franklini (Franklin’s The DSF mammalian sympatry (Fig. 4) ground squirrel), the most prairie-like DSF is based on the modem distributions in Burt mammal, climbs more than any other North and Grossenheider (1976). The sympatry, American ground squirrel and prefers the which lies in the deciduous forests of westcentral Wisconsin, is bound on the south open forest-forest-edge habitateh tall 2.9-
* Cl 0 0 8 + 0
S fumwr s haydent S c cinoreu s t leeuri S c ohicenru SUI 492210 SUI 49223
racemosa
Wild.
cf.
Walt
ciliata
biflora
rugosum
stolonifera
sp. Mill
L. cf.
L.
L.
Balbis
type P. spp. L. Potamogeton
P. lapathfolium P. pennsylvanicum P. ramosissimum
L. type
alpinus
L.
Juglans cinerea L. Menyanthes trfoliata L. Polygonurn hydropiper
Iva
Impatiens
Houtt
Eupatorium
Michx.
Cirsium Cornus
Aellen
C. bushianum
Ceratophyllum demersum Chenopodium album L.
Cares spp. L.
Aralia
Ambrosia artemisiifolia A. trifida L.
Taxon
L.
4928 1 49282 49283
49284 49285
Smartweed Smartweed Smartweed
Smartweed Smartweed
49286
49280
Buckbean
Pondweed
49278 49279
49277
49276
49274 49275
Marsh elder Butternut
Touch-me-not
White snakeroot
Lamb’s quarters Thistle Red osier dogwood
49273
49272
quarters
Lamb’s
49269 49270
49268
49267
49271
name
PLANT
SUI No.
3.
Homwort
Ragweed Giant ragweed Spikenard Sedge
Common
TABLE
4
7
13
10
35 108
4
9 1
1
7
1 13
29
9
1
17 63
28 12
MN1
0.6
2.1 1.1
5.6 17.3 1.6
0.6
1.4 0.2
0.2
1.1
0.2 2.1
4.6
1.4
0.2
2.7 10.1
4.5 1.9
Est. % of Dows Silt Flora
MACROFOSSILS
-
-
-
-
*
*
*
-
-
-
-
-
-
-
Rich
-
-
-
-
-
-
-
-
-
-
-
-
-
-
*
*
-
-
* -
* -
-
-
-
-
-
-
-
Dry
-
-
*
-
* *
* *
*
* * *
* * *
-
-
-
-
-
* -
-
-
*
*
-
Lentic waters
-
* *
* * *
* * * * *
-
*
-
-
* -
-
-
*
* *
* -
-
-
-
-
* -
-
-
-
*
-
Wetlands
-
-
-
-
*
-
*
-
-
-
-
-
-
-
* -
-
-
* *
-
-
-
Prairie
-
-
* *
areas
turbed
Dis-
HABITATS
Moist meadows
AND THEIR COMMON
-
-
*
-
* *
-
-
-
Riparian
SILT FLORA
-
-
Open
-
Moist
Woods
FROM THE Dows
-
* *
* * *
-
* *
*
*
* *
*
*
-
-
-
*
-
-
*
*
*
-
* * -
* *
Xeric
* *
Mesic
General
*
*
-
*
-
-
-
-
-
-
*
*
-
dric
HY-
Rydb.
L.
Note.
All are seeds except for Quercus
ash
sp. (wood)
49303
Prickly
Total
Mill.
49302
Forest grape
Zanthoxylum americanurn
49291
Great bulrush
49298 49299 49300 49301
49296
49295
49294
49293
Bulrush
Common
Red raspberry Willow
Used for ‘T date
Bur reed Bur reed Hedge nettle Violet
americanurn
elder
49291
Pin-cherry
49292
49289 49290
Pondweed Pondweed
Wild crabwle Oak
49287 49288
Pondweed Pondweed
Engelm. Stachys palustris L. Viola sp. L. Vitis ripnria Michx. type
S. ewycarpum
Nutt. type
Sparganium
we
Sambucus canadensis L. Scirpus jhwiatilis (TOIT.) Gray S. validus Vahl.
Salir sp. L.
Rubus cf. strigosus
Quercus sp.
Pyrus cf. corenaria L.
P. spp. L. Prunus cf. pennsylvanica L.f.
(Berm.)
P. pulcher ‘Ibckerm P. pusillus L. P. richardsonii
100.3
3.7
1.3
0.3 1.0 0.5 1.4
3.2
3.7
14.2
0.6
8.3
4
-
*
12
4
-
-
* *
*
*
4
-
-
*
-
-
-
-
-
-
-
*
*
-
-
-
-
-
*
*
-
-
*
-
*
*
*
*
-
*
-
-
-
-
-
-
-
and Salti sp. (bud scales).
23 626
8
20
23
89
4
52
0.2
0.2
0.2
0.2 0.5
0.2 1.1
*
*
*
12
-
-
-
19
-
-
*
* *
*
* -
*
*
-
-
-
-
* *
* *
-
-
-
-
-
15
-
-
* * * *
*
*
*
-
-
-
-
-
12
-
-
-
-
-
*
-
*
-
-
-
-
-
6
-
-
-
-
-
-
-
-
-
-
-
-
-
1
-
-
-
-
-
-
-
-
-
-
-
-
*
*
27
*
*
* *
-
-
*
*
*
*
-
-
*
8
-
-
-
-
-
-
-
-
-
-
*
-
* *
* *
362
CURTIS M. HUDAK
MINNESOTA S. DAKOTA
L
* JO
Dawr
NEBRASKA
FIG. 4. Dows Silt Fauna micromammal sympatry (ca. 9380 ? 130 yr BX); Wisconsin tension zone (after Curtis, 1959); Dows Silt Flora sympatry (inset B); recent original vegetation (inset A; after Wright et al., 1963); and selected early Holocene site locations of the upper Midwest (localities defined in Table 5).
by S. palustris, the northeast by S. franklini, and the northwest by Microtus pineforum. The sympatry covers parts of Jackson, Clarke, Marathon, and Wood counties in Wisconsin. Long (1970) reported 58 native mammals (including bats) from central Wisconsin with Peromyscus leucopus, Microtus pennsylvanicus, C. gapperi, S. cinereus, and Blarina brevicauda being the most abundant. All, with the possible exception of P. leucopus, are found in the DSF with M. pennsylvanicus and C. gapperi being the most abundant in
the DSF. The rarest species in central Wisconsin are Napeozapus insignis, Mustela nivalis, and Microsorex hoyi; none of which were found in the DSE Locally distributed, but rare, are M. pinetorum, Synaptomys cooperi, S. palustris, S. franklini, Microtus ochrogaster, Reithrodontomys megalotis, Glaucomys sabrinus, and, today at least, Eutamias minimus. The first four of the
above locally distributed species are found in the DSF. The DSF micromammals, using both the common habitat chart (Table 2) and the
EARLY
HOLOCENE
PALEOECOLOGY
present sympatry (Fig. 4), infer a moist decidous forest environment for north-central Iowa ca. 9380 yr B.P. However, the possibilities of isolated conifer stands cannot be ruled out because of the strong affinities of Tamias and Cleithrionomys toward this vegetation. S. franklini strongly indicates that the forest was open, or that a forestedge tall-grass habitat was present. Flora
The most recent vegetation in north-central Iowa consisted largely of tall-grass prairie and prairie wetlands prior to cultivation. The DSF plant remains are dominated by aquatic and forest taxa, and none are limited to prairies or moist meadows (Table 3). Most of the aquatic plant macrofossils are associated with lentic waters. Ambrosia and Zva are meadowland forms but can be found with Chenopodium on disturbed ground. The forest species include two trees, Quercus and Juglans, both of which are upland genera. Three of four shrubs, Prunus pennsylvanica, Pyrus coronaria, and Zanthoxylum americanum, are understory shrubs, and the fourth, Mix, is riparian. Aralia racemosa is an upland herb restricted to a rich woods and not usually found in riparian forests. The current floral sympatry (Fig. 4) is large and encompasses the distribution of the conifer-hardwood and deciduous forests in the Great Lakes-New England regions. Although several species are currently rare in Iowa, only Potamogeton alpinus is not found in Iowa today, and it defines the western boundary of the sympatry. The northern boundary is defined by Polygonum lapathifolium and P. pennsylvanicum in Minnesota, and by Ceratophyllum demersum, densis,
Vitis
riparia,
Sambucus
cana-
and Sparganium eurycarpum across Canada and New England. The southern boundary is defined by P. alpinus and Cornus stolonifera. The western edge of the sympatry approximates the deciduous vegetation zone defined in Wright et
al. (1963).
OF
NORTH-CENTRAL
IOWA
363
The common habitats (Table 3) and sympatry (Fig. 4) for the DSF plant macrofossils infer a moister and cooler climate, as do both mollusks and micromammals, than currently found in north-central Iowa. They also suggest lentic waters in close proximity to an upland deciduous forest. An open environment (e.g., meadow or disturbed area) could exist among the woods or possibly on the perimeter of the water body. Comparisons of Climatic Vegetational Data
and
The combined sympatry for the 40 DSF species of plants and mammals is limited by the small mammal sympatry (Fig. 4). This sympatry coincides largely with a “tension zone,” described by Griggs (1914) and Curtis (1959) as a place where many plants and animals from two biotic provinces overlap. The tension zone of Wisconsin and Minnesota includes the southern limits of many northern species and the northern limits of many southern species. Curtis (1959) plotted the zone by the densest concentration of individual range lines to cross Wisconsin (Fig. 4). Northeast of this zone the vegetation is coniferous and contains pines, hemlock, spruces, and fir. To the southwest conifers are replaced by prairies and several species of oaks. Within the tension zone, the vegetation is dominated by oak savannas (bur and white oak with blue stem grasses), southern oak forests (white, black, and red oaks), and the southern mesic forests (sugar maple, basswood, and elm; Cottam and Loucks, 1965). This tension zone (or ecotone) is high in biotic diversity, which is also reflected in the DSF (for discussion on ecotones, see King and Graham (1981)). Climatic data for the DSF sympatry in Wisconsin and present day Dows, Iowa, are averaged from three nearby weather stations at Eau Claire, Marshfield Experimental Farm, and Hatfield Dam, in Wisconsin, and Iowa Falls, Hampton, and Webster City, in Iowa. The data for these
364
CURTIS M. HUDAK TABLE
4. CLIMATIC
SUMMARY
DATA RELATED
TO THE Dows
SILT FAUNA/FLORA
Dows, Iowa
Dows Silt sympatry (ca. 9380 yr B.P.)
Cherokee Site (ca. 9000 yr BP)”
Cherokee Site (ca. 8400 yr B.I?)b
9 (48)
7 (44
-
9 (48)
20 (68)
18 (65)
18(64
-
777 (30.6)
785 (30.9)
800 (31.5)
864 (34.0)
X annual temperature, “C (“F) X growing season temperature (MaySept.), “C (“F) X annual precipitation, mm (in.) X number of days with snow cover ji frost-free days
90
120
-
60
150
140
-
165
a Wendland (1980). b Semken (1980).
areas come from NOAA (1978) and Visher (1954). Climatic data (Table 4) for Dows today is compared to that of the Dows Silt sympatry (approximately 282 km NE of Dows), and the Cherokee Site (Semken, 1980, WendTABLE Symbol
5. SELECTED EARLY HOLOCENE Site name
Ch
Cherokee
co ct CC HM .I KM
Co10 Bog Chatsworth Bog Disterhaft Farm Bog Graham Cave Hudson-Meng Jewel1 Bog Kirchner Marsh
LWO
Lake West Okoboji
Ma MC MRS OF PL RR
Madelia McCulloch Bog Modoc Rock Shelter Old Field Pickerel Lake Raddatz Rock Shelter Rodgers Shelter Sumner Bog Volo Bog Woden Bog
D
RS S V W
land, 1980) in northwestern Iowa (approximately 169 km west of Dows). Temperatures within the Dows Silt sympatry are approximately 2°C (4°F) cooler annually and 2°C (3°F) cooler during the growing season than that presently at Dows. The mean anSITES OF THE UPPER MIDWEST Source
Semken, 1980; Wendland, 1980; Baerreis, 1980 Brush, 1967 King, 1981 Webb and Bryson, 1972 McMillan and Klippel, 1981 Agenbroad, 1977 Brush, 1967 Wright ef al., 1963; Watts and Winter, 1966 Baker and Van Zant, 1980; Van Zant, 1979 Jelgersma, 1962 Brush, 1967 Fowler, 1959; Parmalee, 1959a King and Allen, 1977; King, 1981 Watts and Bright, 1968 Cleland, 1966; Parmalee, 1959b McMillan and Klippel, 1981 Van Zant and Hallberg, 1976 King, 1981 Durkee, 1971
EARLY
HOLOCENE
PALEOECOLOGY
nual precipitation in the sympatry is nearly identical to that of Dows today. However, cooler temperatures undoubtedly reduced evaporation and increased available ground moisture at the time of deposition of the DSF. The number of days with snow cover averages 1 month longer in the sympatrv than currently at Dows, and there are approximately 10 fewer days per year that are frost free. The closest site to the Dows Local Biota, in age and geographic affinity, that contains mammals, mollusks, and plant macrofossils is the Cherokee Sewer Site in Cherokee County, Iowa (Fig. 4; Table 5; Anderson and Semken, 1980). Wendland (1980) based the climatic reconstruction from the Cherokee Site on the pollen analysis from Lake West Okoboji (Baker and Van Zant, 1980; Van Zant, 1979). He considers the climatic episode between 10,000 and 9000 yr B.P. to represent a more moist and cooler interval than is presently found in northwestern Iowa. The average growing season temperature during deposition of the DSF is estimated to be nearly identical to that at Cherokee while the annual precipitation averaged 15 mm (0.6 in.) less than at the Cherokee Site at 9000 yr B.P. (Table 4). Although the DSF climatic data are restricted primarily by mammal distribution, and the Cherokee climatic data are based on pollen analyses, the climatic conditions at Dows (ca. 9380 yr B.P.) and Cherokee (ca. 9000 yr B.P.) were very similar. Dows and Cherokee are currently on the same east-west isotherms that traverse Iowa (NOAA, 1978), and it is tempting to speculate that the two sites were also on similar east-west isotherms during the early Holocene. Mammals and mollusks have been reported from the 8400 yr B.P. cultural Horizon III at Cherokee (Semken, 1980; Baerreis, 1980). The pollen and plant macrofossils have been recorded for this period from nearby Lake West Okoboji (Baker and Van Zant, 1980, Van Zant, 1979). The paleo-
OF
NORTH-CENTRAL
IOWA
365
ecologic interpretations for Cherokee Horizon III largely confirm the DSF reconstruction that a moist, deciduous forest to open woodland was present across northwest Iowa ca. 9380-8400 yr B.P. McMillan and Klippel (1981) noted that Rodgers Shelter (ca. 10,500-9500 yr B.P.) and Graham Cave (estimated lO,OOO-9000 yr B.P.) in Missouri had deciduous forest and forest-edge mammals. At approximately 9000 yr B.P. both sites experienced an influx of grassland species from which McMillan and Klippel conclude that the forests were being replaced by prairie. The Modoc Rock Shelter (Fowler, 1959) in southwestern Illinois had a fauna that favored cool, moist woodlands throughout the Holocene. From the fauna1 data, Parmalee (1959a) concluded the local habitat remained relatively unchanged except in the early Holocene, which was apparently cooler and damper. The Raddatz Rockshelter fauna (Parmalee, 1959b), located in southwestern Wisconsin, was representative of a deciduous-conifer forest from ca. 9000 to 5500 yr B.P. (Cleland, 1966). Semken (1983) summarized the Holocene mammalian faunas from Missouri, Illinois, and Wisconsin and concluded that they were inhabiting cool, moist forests between 10,000 and 8400 yr B.P. West of Dows and Cherokee the molluscan fauna from the Hudson-Meng Site led Agenbroad (1977) to conclude that prior to 9000 yr B.P. a cooler grassland environment existed across northwestern Nebraska. Vegetation studies from Lake West Okoboji (Baker and Van Zant, 1980; Van Zant, 1979), Madelia (Jelgersma, 1962), Jewell, Colo, and McCulloch bogs (Brush, 1967), Woden Bog (Durkee, 1971), Pickerel Lake (Watts and Bright, 1968), Kirchner Marsh (Wright et al., 1963; Watts and Winter, 1966), Old Field (King and Allen, 1977), and Chatsworth Bog (King, 1981) all reflect a deciduous forest environment with oak and/or elm being the dominant pollen at some time between 10,000 and
366
CURTIS M. HUDAK
8500 yr BP (Fig. 4; Table 5). Sumner Bog (Van Zant and Hallberg, 1976) pollen indicated that conifer forests were still occupying northeastern Iowa at ca. 9270 yr B .P., but the authors have interpreted this date is too young and is undoubtedly caused by the hiatus directly on top of the dated horizon. The pollen analysis of R. G. Baker (in Webb and Bryson, 1972) on Disterhaft Farm Bog of east-central Wisconsin supported Cleland’s (1966) interpretation from Raddatz that a deciduous-conifer forest was still present in Wisconsin ca. 8600 yr B.P. King’s (1981) interpretation of Volo Bog in northeastern Illinois suggests that pine was still present in low abundance among the oaks and elms ca. 9000 yr B.P. The DSF fits in the general scheme of a cool and moist climate across the Midwest during the early Holocene. It also confirms that a deciduous forest biome was present across southern Minnesota and northern Iowa ca. 9000 yr B.P. At that time conifers were growing to the northeast in central Wisconsin, open deciduous woods were present to the south and immediate west, and grasslands were developed further west. CONCLUSIONS
(1) The plants and mammals of the Dows Silt Fauna/Flora are sympatric in west-central Wisconsin, an area of similar precipitation to that presently at Dows, but cooler mean annual temperatures. This cooler temperature suggests greater effective precipitation at Dows ca. 9380 yr B.P. (2) The area of sympatry for the small mammals lies in the Wisconsin tension zone, an area of open deciduous woods that contains an overlap for species from the northern forest province and the southwestern prairie province. Independent analyses of the mollusks, plant macrofossils, and small mammals in the Dows Silt Fauna/Flora, or Horizon 3 (ca. 9380 yr B .P.), all indicate a cool, moist, deciduous forest with open woods possibly on the hilltops.
(3) The Dows Silt Fauna/Flora reconstruction fits the regional vegetation setting based on other fauna1 and floral analyses of similar age. ACKNOWLEDGMENTS Mr. and Mrs. Emory Fitz and Mr. and Mrs. Vem Peterson from Dows, Iowa, allowed me to track across their land. Holmes Semken, Jr., Richard Baker, Timothy Kemmis, George Hallberg, Russell Graham, and Frances King reviewed and made excellent suggestions on the text. Lon Drake, Terrence Frest, and Richard S. Rhodes helped by discussing certain problematic areas. Terrence Frest identified the mollusks. Jane Junge and the University of Kansas Museum of Natural History provided valuable information toward identifying certain mammals in this paper. Frances B. King from the Illinois State Museum at Springfield, Illinois, identified the wood fragments. The University of Iowa Geology Department and the Iowa Geological Survey each provided funds for one radiocarbon date. The University of Iowa Geology Department (Littlefield Fund) helped to defray field expenses.
REFERENCES Agenbroad, L. D. (1977) Climatic change and early man in northwest Nebraska. In “Paleoindian Lifeways” (E. Johnson, Ed.). Museum Journal 17, 117-125. Anderson, D. C., and Semken, H. A. (Eds.) (1980). “The Cherokee Excavations: Holocene Ecology and Human Adaptations in Northwestern Iowa,” Academic Press, New York. Baerreis, D. A. (1980). Habitat and climatic interpretation from terrestrial gastropods at the Cherokee site. In “The Cherokee Excavations: Holocene Ecology and Human Adaptations in Northwestern Iowa” (D. C. Anderson and H. A. Semken. Eds.), Chap. 4; pp. 101-122. Academic Press, New York. Baker, R. G., and Van Zant, K. L. (1980). Holocene vegetational reconstruction in northwestern Iowa. In “The Cherokee Excavations: Holocene Ecology and Human Adaptations in Northwestern Iowa” (D. C. Anderson and H. A. Semken, Eds.), Chap. 5; pp. 123-138. Academic Press, New York. Bowles, J. B. (1975). Distribution and biogeography of mammals of Iowa. Texas Tech University, The Museum,
Special
Publications
9.
Brush, G. S. (1967). Pollen analyses of late-glacial and postglacial sediments in Iowa. In “Quarternary Paleoecology” (E. J. Cushing and H. E. Wright, Eds.), pp. 99-115. Yale Univ. Press, New Haven, Conn. Burt, W. H., and Grossenheider, R. P. (1976). “Field Guide to Mammals.” Houghton Mifflin, Boston. Clark, A. H. (1981). “The Freshwater Molluscs of
EARLY
HOLOCENE
PALEOECOLOGY
Canada.” Natl. Museums of Natural Sci./Natl. Museums of Canada, Ottawa, Canada. Cleland, C. E. (1966). The prehistoric animal ecology and ethnozoology of the upper Great Lakes region. Museum of Anthropology, Anthropological Papers
University
of Michigan.
29.
Cottam, G. and Loucks, 0. L. (1965). Interpretation of the vegetation of Wisconsin. From the early vegetation of Wisconsin map. Wisconsin Geological and Natural History Survey, G. F. Hanson, Director. Curtis, J. T. (1959). “The Vegetation of Wisconsin.” Univ. of Wisconsin Press, Madison. Durkee, L. H. (1971). A pollen profile from Woden Bog in north-central Iowa. Ecology 52, 837-844. Fowler, M. L. (1959). Summary report of Modoc Rock Shelter 1952, 1953, 1955, 1956. Illinois State Museum Report
of Investigations
8.
Gleason, H. A. and Cronquist, A. (1963). “Manual of Vascular Plants of Northeastern United States and Adjacent Canada.” Van Nostrand, Princeton, N.J. Griggs, R. E (1914). Observations on the behavior of some species on the edges of their ranges. Bulletin of the Torrey Botanical Club 41, 25-49. Hazard, E. B. (1982). “The Mammals of Minnesota.” Univ. of Minnesota Press, Minneapolis. Hoyer, B. E. (1980). The geology of the Cherokee sewer site. In “The Cherokee Excavations: Holocene Ecology and Human Adaptations in Northwestern Iowa” (D. C. Anderson and H. A. Semken, Eds.), Chap. 2, pp. 21-66. Academic Press, New York. Jackson, H. H. T. (1961). “Mammals of Wisconsin.” Univ. of Wisconsin Press, Madison. Jelgersma, S. (1962). A late-glacial pollen diagram from Madelia, south-central Minnesota. American Journal
of Science
260,
522-529.
Junge, J. A., and Hoffman, R. S. (1981). An annotated key to the long-tailed shrews (genus Sorex) of the United States and Canada, with notes on middle American Sorex. Occasional Papers of the Kansas Museum of Natural History 93, l-48. Kemmis, T. J., Hallberg, G. R., and Luttenegger, A. J. (1981). Depositional environments of glacial sediments and landforms on the Des Moines lobe, Iowa. Iowa Geological Survey Guidebook Series 6. King E B., and Graham, R. W. (1981). Effects of ecological and paleoecological patterns on subsistence and paleoenvironmental reconstructions. American Antiquity 46(l), 128-142. King, J. E. (1981). Late Quaternary vegetational history of Illinois. Ecological Monographs 51(l), 43-62. King, J. E., and Allen, W. H., Jr. (1977). A Holocene vegetation record from the Mississippi River Valley, southeastern Missouri. Quarternary Research 8, 307-323. La Rocque, A. (1966-70). Pleistocene Mollusca of Ohio. Ohio Geological Survey Bulletin 62 (4 parts).
OF NORTH-CENTRAL
IOWA
367
Long, C. A. (1970). Mammals of central Wisconsin. Museum of Natural History, Wisconsin State Vniversity, Reports on the Fauna and Flora of Wisconsin 3.
McMillan, R. B., and Klippel, W. E. (1981). Post-glacial environmental change and hunting-gathering societies of the southern prairie peninsula. Journal of Archaeological Science 8, 215-245. National Oceanic and Atmospheric Administration (NOAA) (1978). ‘Climate of the United States, with Current Tables of Normals, 1941-1970, and Means and Extremes to 1975” (J. A. Ruffner and F. E. Bair, Eds.), Vols. 1, 2. U.S. Weather Bureau and National Oceanic and Atmospheric Administration Data. Gale Research Co., Detroit. Parmalee, P. W. (1959a). Animal remains from the Modoc Rock Shelter site, Randolph County, Illinois. In “Summary Report of Modoc Rock Shelter” (M. L. Fowler, Ed.). Illinois State Museum Reports of Investigations 8, 61-65. Parmalee, P. W. (1959b). Animal remains from the Raddatz Rockshelter, SK5, Wisconsin. Wisconsin Archaeologist
40(2),
83-90.
Semken, H. A., Jr. (1980). Holocene climatic reconstructions derived from the three micromammal bearing cultural horizons of the Cherokee sewer site, northwestern Iowa. In “The Cherokee Excavations: Holocene Ecology and Human Adaptations in Northwestern Iowa (D. C. Anderson and H. A. Semken, Eds.), Chap. 3, pp. 67-99. Academic Press, New York. Semken, H. A., Jr. (1983). The Holocene mammalian record of the eastern and central United States. In “Late Quaternary Environments of the U.S. and the U.S.S.R.,” Vol. 2, “Holocene Environments of the United States” (H. E. Wright, Jr., Ed.) Univ. of Minnesota Press, Minneapolis. Van Zant, K. L. (1979). Late- and postglacial pollen and plant macrofossils from Lake West Okoboji, northwestern Iowa. Quarternary Research 12, 358380. Van Zant, K. L. and Hallberg, G. R. (1976). A lateglacial pollen sequence from northeastern Iowa: Summer Bog revisited. Iowa Geological Survey Technical
Information
Series
3.
van Zyll de Jong, C. G. (1980). Systematic relationships of woodland and prairie forms of the common shrew, Sorex cinereus cinereus Kerr and S. c. haydeni Baird, in the Canadian prairie provinces. Journal
of Mammalogy
61, 66-75.
Visher, S. S. (1954). “Climatic Atlas of the United States.” Harvard Univ. Press, Cambridge, Mass. Walker, P. H. (1966). Postglacial environments in relation to landscape and soils on the Cary Drift, Iowa. Iowa State University Agricultural and Home Economics
Experimental
Station,
Research
Bulletin
549, 839-875. Watts, W. A., and Bright, R. C. (1968). Pollen, seed. and mollusk analysis of a sediment core from Pick-
368
CURTIS M. HUDAK
erel Lake, northeastern South Dakota. Geologicnl Society of America Bulletin 19, 8554376. Watts, W. A., and Winter, T. C. (1966). Plant macrofossils from Kirchner Marsh, Minnesota-A paleoecological study. Geological Society of America Bulletin 77, 1339-1360. Webb, T., and Bryson, R. A. (1972). Late- and postglacial climatic change in the northern midwest. USA: Quantitative estimates derived from fossil pollen spectra by multivariate statistical analysis. Quaternary Research 2, 70-115.
Wendland, W. M. (1980). Holocene climatic reconstruction of the prairie peninsula. In “The Cherokee Excavations: Holocene Ecology and Human Adaptations in Northwestern Iowa” (D. C. Anderson and H. A. Semken, Eds.), Chap. 6, pp. 139-148. Academic Press, New York. Wright, H. E., Jr., Winter, T. C., and Patten, H. L. (1963). Two pollen diagrams from southeastern Minnesota: Problems in the regional late-Glacial and post-Glacial vegetational history. Geological Society of America Bulletin 74, 1371-1396.
RESEARCH
21, 351-368 (1984)
Paleoecology of an Early Holocene Fauna1 and Floral Assemblage from the Dows Local Biota of North-Central Iowa CURTIS
M. HUDAK
Department of Geology, The University of Iowa, Iowa City, Iowa 52242 Received January 28, 1983 The faunas and floras from the Dows Local Biota provide an opportunity to compare Holocene taxa without a cultural bias. The Dows Local Biota is located in a large depression on the back side (north) of the Altamont I Moraine complex within the Des Moines Lobe. The Dows Silt Fauna/Flora (=DSF; ca. 9380 ? 130 yr B.P.), one horizon of the Dows Local Biota, was collected for plant macrofossils, mollusks, and micromammals. DSF terrestrial gastropods are upland mesic forest dwellers although one species, Strobilops afinis. is characteristic of more xeric forests and may represent open woods. The aquatic gastropods reflect both permanent and periodic waters. DSF micromammals prefer an open, mesic, deciduous forest. The micromammal sympatry is restricted to a small area within the tension zone and deciduous forest belt of west-central Wisconsin. DSF plants are characteristic of upland forests, moist meadowlands or disturbed areas, and aquatic habitats. The DSF plant sympatry is large but restricted to the conifer-hardwood and deciduous forests along the Great Lakes-New England regions. Quantitative climatic data for the combined DSF sympatries suggest that Dows (ca. 9380 yr BP.) was cooler than at present, and is nearly identical to that achieved by pollen analyses at the Cherokee Sewer-Lake West Okoboji sites (ca. 9000 yr BP.) in northwest Iowa. Based on common habitat interpretations and sympatries, about 9380 vr B.P. north-central Iowa was cooler and moister than at present and was occupied by an open deciduous forest.
INTRODUCTION Few Holocene paleoecological interpretations, from nonarchaeological sites in the United States, are based upon plant macrofossils, mollusks, and vertebrates from a single locality. The Dows Silt Fauna/Flora (DSF), a 9380 2 130 yr B.P. (Beta-5001) horizon of the Dows Local Biota, yields information without a cultural bias on the early Holocene of north-central Iowa. Iowa, during the early Holocene, was occupied by a deciduous forest as interpreted by numerous pollen analyses. The Dows Local Biota provides an opportunity to test (1) whether or not mollusks, small mammals, and plant macrofossils from the same horizon in a noncultural site have similar paleoecologic interpretations, and (2) whether these paleoecologic interpretations concur with pollen analyses in the same region. This will be accomplished by comparing common habitats for each taxonomic group and by constructing
sympatries (areas where the taxa ranges currently overlap). The Dows Local Biota, near Dows, Iowa, was discovered during construction of Interstate 35 in March 1974, when part of a prairie wetland and creek was destroyed. Remains of bison, elk, deer, small vertebrates (including amphibians, reptiles, birds, and mammals), mollusks, plant macrofossils, insects, and wood were found in the spoil. Construction activity prevented establishment of a section at the time, even though peat and other sediments were exposed. Recently, a drainage ditch constructed in the Dows depression (Fig. 1) exposed silts, sands, and a peat. Preliminary studies have not revealed any pollen. The depression with the Dows Local Biota is located on the backside (north) of the Altamont I moraine complex of the Des Moines lobe (Fig. 2 in Kemmis et al., 1981) in Sec. 28 and W’h Sec. 27 T91N R22W (Fig. 1). The Altamont moraine, characterized by hummocky topography near the
351 0033-5894184 $3.00 Copyright 0 1984 by the University of Washington. All righIs of reproduction in any form reserved.
CURTIS M. HUDAK
352
study area, is next to the oldest of the Des Moines lobe moraines and dates at approximately 13,500 yr B.P. (Kemmis et al., 19Sl).
iippmximate Depthcm> HOrIm”1. Verydarkt.3blackmucky silt loam. O-
STRATIGRAPHY
Six vertical sections measured and described along the side of the newly excavated ditch (Fig. 1) provided sufftcient data to develop a composite stratigraphic settion (Fig. 2). Six lithic horizons were identified and are here described from top to bottom to accommodate addition of units that may be discovered with deeper sampling. Horizon 1 has abundant mollusks, seeds, and microvertebrates. The seeds are primarily sedges (Carex spp.), the mollusks are dominated by aquatics, and nearly all the microvertebrates are anurans (frog). The interpreted depositional environment is a marshy wetland that spans the entire depression north of the Altamont moraine. The wetland accumulated into historic time. Horizon 2 varies from fibric to nonfibric
FIG. 1. Map showing county ditch and measured sections (A-F). The Dows Silt Fauna/Flora was collected from Sec. E. Contour interval = 7.5 m (25 ft).
rarecross-bedding. lag fragments in fragment dated at 9650 upper 20(Beta-mm: cm. : logabundant 130yrB.P nearDDWS section c in+ Graytoquartz darkgray silty sands. N410 610:mostly grains. Grayto darkgraysilts, 244106/O. FIG. 2. Composite stratigraphic section for the Dows Local Biota. The Dows Silt Fauna/Flora was collected from Horizon 3.
peat and is discontinuous along the ditch because it only tills in depressional areas in the underlying Horizon 3 sediments. The peat contains microvertebrates, including small mammals, reptiles, and amphibians, plus abundant mollusks, plant macrofossils, insects, and bison. This unit was probably deposited in a prairie wetland environment. Radiocarbon dates on the peat were not obtained because of modern root contamination and the absence of wood. Horizon 3 is an olive-green silt and contains the DSF. Oak (Quercus) wood, collected near the bottom of this unit, was dated at 9380 + 130 yr B.P. (Beta-5001). This sedimentary unit exhibits constant thickness except over older topographic highs. Three silt lithofacies are present that change abruptly both laterally and stratigraphically. Of the three facies one is primarily silt, one is slightly richer in coarse to medium sand, and the other consists of subhorizontal, thin, discontinuous, organic
EARLY
HOLOCENE
PALEOECOLOGY
silts. Horizon 3 may have originated under a low energy fluvial environment, or possibly a lake with differential influxes of hillside sediments creating the facies changes. Horizon 4 grades up from gravelly sands to laminated silty sands. The surface of this unit is often iron cemented, and contains abundant wood fragments and horizontal logs up to 58 cm (23 in.) in diameter. One wood fragment was identified as elm (Ulmus) and another was dated at 9650 + 130 yr B.P. (Beta-3048). Two cross-bedded gravels, one occurring near Section C (Fig. 1) and the other near the junction of the ditches, indicate deposition from currents flowing toward the south-southeast. Horizons 4, 5, and 6 are fluvial silts or sands. Hoyer (1980) and Walker (1966) noted that Holocene and late Wisconsin sediments in Iowa may record changes in paleoclimates. Walker (1966) emphasized a consistency in stratigraphic sequences from five bogs on the Des Moines lobe in Iowa as follows: Upper Muck Zone, O-3000 yr B.P.; Upper Silt Zone, 3000-8000 yr B.P.; Lower Muck Zone, 8000-10,500 yr B.P.; Lower Silt Zone, 10,500-13,000 yr B.P.; Cary sediments, >13,000 yr B.P. He interpreted the muck zones to represent periods of relatively slow hill-slope erosion because of increased vegetation, which is a function of high precipitation; the silt zones represent intervals of relatively rapid slope erosion resulting from reduced vegetation during periods of low precipitation. Walker’s stratigraphy does not correlate with that at Dows. For instance, the Dows wood dates of 9650, and 9380 (this report) and 9180 rt 90 yr B.P. (DIC-1131; R. S. Rhodes, 1982, written communication), respectively, from the top of Horizon 4, the bottom of Horizon 3, and a sand unit 20 cm (8 in.) below the peat put these mineral deposits time- stratigraphically in the middle of Walker’s lower muck zone. There are a number of reasons why the stratigraphy of Walker’s bogs differs from that of the Dows depression. Walker’s bogs, as opposed to Dows, were in small
OF NORTH-CENTRAL
IOWA
353
closed depressions that trapped the mineral sediments during periods of low precipitation and sparse vegetation. The Dows depression is larger and the interpretation of sedimentary environments through time is hindered by limited exposure and by limited control on the time of deposition for the lowermost horizons. Sands and gravels in Horizon 4 clearly indicate deposition in some type of high energy fluvial environment in the Dows depression prior to or ca. 9650 yr B.P. The sandy silt of Horizon 3 could be indicative of a number of sedimentary environments, and sand lenses in Horizon 2 may indicate periodic influx of hill-slope sediments (from the surrounding uplands) into a marshy environment. The overall record of the depression thus appears to be one of decreasing energy through time. Two possible depositional environments might produce a sedimentary sequence similar to that found in the Dows depression. The first possibility is one of deposition on a floodplain. Under this model, Horizon 4 would represent an active channel, Horizon 3 might represent one or several episodes of flooding of an abandoned channel area, and Horizon 2 might represent the organic accumulation of a marsh on a poorly drained floodplain. Major problems with this interpretation are that the Dows depression is not associated with any present river system, there is no clear indication of any past association with known river systems, and present day gradients along the depression are opposed to each other, rather than in the same direction along a well-defined former channel. A second possibility is that Horizon 4 represents glaciofluvial deposition associated with stagnant ice in the Altamont I moraine complex. This would explain the opposing gradients along the depression. Horizon 3 would then represent the initial infilling of areas between sand bars of Horizon 4, possibly as a lake formed in the depression following deglaciation. The peat in Horizon 2 would be generated in the
354
CURTIS
shallow lake or marsh that formed as a result. In any case, both of the above theories would require extensive coring and trenching but do offer explanations for differences with Walker’s (1966) closed depressions and the fauna1 and floral habitats discussed below. EXCAVATION AND LABORATORY PROCEDURES Excavations at Dows showed that Horizon 3 would yield approximately 20 mollusks, 9 seeds, and 1 mammal tooth per 4 liters of silt. Approximately 727 kg of Horizon 3 matrix was washed in l-mmmesh box screens to produce the biotic sample used in this report. Drainage from a farmer’s tiles was sufficient in the county ditch to remove most of the silt with minimum agitation. Samples, at first, were collected in IO-cm stratigraphic units. This was later abandoned and the data combined because the specimens were recovered in roughly the same proportions from the different levels and lithofacies. Fossiliferous burrow fillings of organic silts and clays, intruded from the overlying peat, were removed as best as possible to reduce contamination. The laboratory work involved picking, measuring, and identifying specimens using a Bausch and Lombe binocular microscope equipped with a micrometer scaled to the nearest 0.05 mm. Identifications were based upon comparative material in the University of Iowa Museum of Natural History Geological Repository (SUI) and the University of Kansas Museum of Natural History (KUMNH). All specimens described herein have been cataloged into the University of Iowa Geological Repository. DOWS
SILT FAUNA
AND FLORA
A. Invertebrates
The DSF invertebrates comprised mollusks and insects. In the former, 27 genera
M.
HUDAK
and 35 species are present (Table 1). Many bivalves were heavily damaged and were not picked from the residue, however, it is estimated that the Bivalvia comprised about 25-30% of the molluscan fauna. The snails, comprising approximately 75% of the molluscan fauna, included both aquatics (58%) and terrestrials (18%). The taxonomy follows those of Clarke (1981) and La Rocque (1970). The insects for the Dows Local Biota are currently under study by Dr. Donald P. Schwert of the North Dakota State University, Fargo, North Dakota. B. Vertebrates General. The vertebrates are the least abundant group in both numbers of taxa and individuals. In all, remains of five classes (fish, amphibians, reptiles, birds, and mammals) have been recovered, but only the latter (Table 2) are specifically identified and considered in the paleoecologic analysis. Shrew taxonomy. All of the micromammals were readily identified by standard taxonomic procedures except for one of two left soricid dentaries. Dentary SUI No. 49221a (Table 2) clearly falls into the Sorex cinereus category based on dentary width versus depth (Fig. 3) and mandibular condyle morphology. The other Sorex dentary (SUI No. 49223; Table 2) has a more robust ml (Fig. 4 in Hudak, 1982, unpublished thesis, University of Iowa) and mandible (Fig. 3) than the S. cinereus group (S. cinereus group includes all S. cinereus subspecies and S. haydeni; Junge and Hoffman, 1981). In general SUI No. 49223 does not fit within either the S. cinereus or S. fumeus clusters (Fig. 3). However, the unknown is closer to either of these than to the smaller Microsorex or the extremely larger S. arcticus and S. palustris. A bivariate plot of ml-m2 length versus ml dentary depth clearly separates the S. cinereus group from S. fumeus biometrically and places the specimen in the S. cinereus group.
EARLY
HOLOCENE
PALEOECOLOGY
The members of the S. cinereus group are clustered but with a characteristic overlapping pattern found in subspecies (see Hudak, 1982, unpublished thesis, University of Iowa). The size of SUI No. 49223 is much larger than the S. cinereus dentary (SUI No. 49221a) mentioned above and the pair lay outside of the range of variation expected for a single population. This suggests that SUI No. 49223 is significantly different than SUI No. 49221a but not assignable on a single specimen. Because the presence of two distinct subspecies is not expected in a single faunule, SUI No. 49223 must either be aberrant or represent a distinct species. Dentary SUI No. 49223 may be related to S. haydeni (recently elevated to species; see van Zyll de Jong (1980), and Junge and Hoffman (1981)), a plains species, and distinguished from S. c. cinereus, a woodland form, or reflect an abnormally large individual more characteristic of a glacial population. C. Flora
Approximately 650 plant macrofossils were examined, of which 626 were identified (Table 3). The flora is comprised of 19 families, 26 genera, and a minimum of 42 species. Those listed as “type” were inseparable from one or more other species based on morphology; the chosen name was made for ecological or plant geographical reasons. Taxonomy was based on Gleason and Cronquist (1963). PALEOECOLOGY
Paleoecologic reconstructions assume that common habitats of organisms have changed little from the present day to those of 9380 yr ago. The degree of confidence is based on the knowledge of the living organism. Molluscan
Fauna
Table 1 lists the land snails and their common habitats. The most common associations are with moist woods (nonri-
OF
NORTH-CENTRAL
IOWA
355
parian or upland woods) and alluvial woods (riparian and floodplain woods). Sixteen of the seventeen DSF species are also listed under the more general category of mesic (moist) environments. Only Strobilops affinis, represented by four specimens, is restricted to dry forests (relative to Strobilops labyrinthica), which suggests that these specimens were transported from drier upland woods. Eleven species are common to both moist and alluvial woods. One species, Discus cronkhitei, is restricted to alluvial woods or moist prairie grasslands. Four species, Vallonia parvula, Punctum minutissimum, S. labyrinthica, and Carychium exiguum, prefer moist woods over alluvial woods. C. exiguum is of special note because it is largely restricted to cool forests (T. Frest, 1982, oral communication). No DSF land snails are restricted to prairie environments. Table 1 also lists the Dows Silt aquatic mollusks and their common habitats. All of these aquatics can be found in lentic (quiet) waters. Half of the aquatics can be found under lotic (moving water) conditions, but none are restricted to this environment. Thus, quiet water was characteristic of the depression ca. 9380 yr BP. Two other distinct habitats are represented by the DSF aquatic mollusks. Seven species are restricted to permanent waters and four species are more common to periodic waters that dry up at least once a year. This division suggests that permanent water occurred at Dows, but that adjoining areas did dry up on occasion. This would support both the floodplain and lake environments interpreted from the sedimentology and stratigraphy. The author interprets the molluscan paleoenvironment at Dows (ca. 9380 yr B.P.) as a cool, moist forest along the water’s edge and hillsides, with a drier, possibly open forest on the hilltops. The Dows depression probably held either a permanent lake or a slow flowing river with impermanent ponds on a floodplain. Sympa-
49234 49235 49236 49237 49238 49239 49240 4924 1 49242 49243 49244 49245 49246 49247 49248 49249 49250
Land snails Carychium exiguum (Say) Catinella avara (Say) Deroceras laeve (Muller) Discus cronkhitei (Newcomb) Gastrocopta contracta (Say) G. tappaniana (C. B. Adams) Hawaiia minuscula (Binney) Helicodiscus parallelus (Say) Punctum minutissimum (Lea) Retinella electrina (Gould) Strobilops afinis (Pilsbury) S. labyrinthica (Say) Succinea ovalis (Say) Triodopsis multilineata (Say) Vallonia parvula (Sterki) Vertigo ovata (Say) Zonitoides arboreus (Say)
Total land snails
SUI No.
274
9 34 7 3 7 31 7 12 1 5 4 16 94 39 2 1 2
MN1
1. MOLLUSKS
Taxon
TABLE
17.9
0.6 2.2 0.5 0.2 0.5 2.0 0.5 0.8 0.1 0.3 0.3 I.0 6.1 2.5 0.1 0.1 0.1
Est. % of molluscan fauna
FROM THE Dows
23.4
0.8 2.9 0.6 0.3 0.6 2.6 0.6 1.0 0.1 0.4 0.3 1.4 8.0 3.3 0.2 0.1 0.2
% of total snail fauna
SILT FAUNA
5
* * * * *
Moist prairie grassland
12
* * * * * * * * -
Alluvial
AND THEIR COMMON
15
* * * * * * * * * * * * * * *
Moist
Woods
HABITATS
7
* * * * * * *
Dry
16
* * * * * * * * * * * * * * * *
Mesic
7
*
Xeric
General
2 2 t; 5
Iimosa exigua dejlectus
(Say) (Lea) (Say)
1545
Total mollusks
Total Bivalves >375 1271
49266a 49266b 49266~
Total aquatic mollusks
Pisidium compressum Sphaerium occidentale S. rhomboideum (Say)
(Prime) (Prime)
1170
Bivalves
896
(Say)
40 15 7 446 2 9 14 2 217 5 5 47 1 7 79
Total snails
tricarinata
49262 49263 49264 49265
4925 1 49252 49253 49254 49255 49256 49257 49258 49259 49260
MN1
Total aquatic snails
Valvata
S. reflexa (Say)
Helisoma antrosa (Say) H. trivolvis (Say) Physa gyrina (Say) P. jennessi skinneri (Taylor) Planorbula campestris (Dawson) Promenetus exacuous (Say) Somatogyrus subglobosus (Say) Stagnicola catascopium (Say) S. elodes (Say)
G. parvus (Say)
Amnicola Fossaria Gyraulus
Aquatic snails
Taxon
SUI No.
1-Continued
100.1
82.2
24.3
75.8
57.9
2.6 1.0 0.5 28.9 0.1 0.6 0.9 0.1 14.0 0.3 0.3 3.0 0.1 0.4 5.1
Est. % of molluscan fauna
TABLE
Est. % of bivalve fauna 50 10 40
99.9
76.5
3.4 1.3 0.6 38.0 0.2 0.8 1.2 0.2 18.5 0.4 0.4 4.0 0.1 0.6 6.8
% of total snail fauna
18
* * *
* * * * * * * * * * * * * * *
Lentic
9
* * * * * * * *
Lotic
14
* *
* * * * * * * * * * * *
Permanent
Waters
11
* *
* * * * * * *
Periodic
palustris
Sorex
sp.~
Bison
49230d
49230b 49230~
49230a
49229b
49228a 49228b 49229a
in ecologic
analysis.
23
1
1 1
8
-
5
-
5
-
-
*
*
4
10
* -
*
*
*
10
* -
*
*
*
*
*
*
*
*
*
*
*
*
* -
*
Open woods
*
* -
*
“OUS
Decid-
-
* -
*
Coniferdeciduous
*
*
* -
*
Conifer
*
*
*
*
*
*
*
*
10
* -
-
*
Forest edge
Dows SILT FAUNA AND THEIR COMMON
1
1
1
1
1
1 1
1
MN1
FROM THE
L. maxillary and zygomatic plate Rm2 LM3 L. edentulous dentary 1 Lml, 4 Lm2, 3 Lm3,l Rml, 1 Rm2,2 LMl, 2 LM2,l LM3 and 2 RMl Palate with Ml s and M3s Palate edentulous R. dentary with ml and m2 8 Lml, 2 Lm2, 2 Lm3,3 Rml, 5 Rm2,3 Rm3, 6 LMl, 4 LM2, 1 LM3,6 RMl, 6 RM2 and 1 RM3 1 Lml and 1 LM2 R. radius Caudal vertebra 3rd phalanx 2nd phalanx (juvenile)
L. ulna
Lml or m2
L. edentulous dentary L. maxillary and Ml RI1 L. dentary with ml and m2 LIl, Lil
Element
2. MAMMALS
not included
4923 1 49232a 49232b 49232~ 49233
a Genera with wide habitat tolerance
Total
Bison
Pine vole Muskrat
M. pinetorum Ondatra zibethicus
vole
Meadow
Microtus pennsylvanicus
49227
49225
Mouse
49224
49226
shrew
49222 49223
49221b
49221a
WI No.
Short-tailed shrew Franklin’s ground squirrel Red squirrel
Southern hog lemming Red-backed vole
sp.
shrew
Masked
Water shrew Long-tailed
name
Common
Synaplomys cooperi Cleithrionomys gapperi
Tamiasciurus hudsonicus Peromyscus
Blarina brevicauda Spermophilus franklini
Sorex sp.”
cinereus
Sorex
BX0n
TABLE
*
*
*
*
5
-
-
-
-
*
Prairiegrasslands
HABITATS
*
*
*
*
6
*
-
-
-
-
*
Wetlands
*
7
*
-
*
*
*
c
*
Riparian
11
* *
*
*
*
*
*
*
*
*
*
Mesic
0
-
-
-
-
-
-
-
-
-
-
-
Xeric
EARLY
HOLOCENE
PALEOECOLOGY
OF NORTH-CENTRAL
IOWA
359
grass. The Franklin’s ground squirrel, because of its current eastward pioneering 2.8 _ * into recently opened forests of northwest * * 2.7Minnesota (Hazard, 1982), may well represent the first mammalian evidence of an 2.6 open forest during the postglacial of 2.5 * i northern Iowa. z Tamiasciurus hudsonicus (red squirrel) is ; 2.4 ** * ** E chiefly restricted to conifer or mixed cob 2.3 *** niferous-deciduous forests, but it can oc9 cupy pure stands of deciduous trees, parE 2.2 * )14F q t 8 ticularly if in a wet terrain (Jackson, 1961). ? Bc 2.1 O o%Dp Hazard (1982) contends that the species is d more at home in mature and continuous for2.0 #F f$ s* ests than in open woodlands or small iso1.9 8&d% 0 lated stands. Cleithrionomys gapperi (red-backed 1.s 0 •~m~o 0’ vole), like the red squirrel, occurs com1.7 lO ln monly in moist coniferous and mixed forI 1.0I 1.1I 1.2I 1.31 I.4I 1.51 1.6I 1.7, ests of the northern states. In Iowa it is .9 presently limited to the north-central part Dentq width under m2 f X 2mm I of the state, just north of Dows (Bowles, FIG. 3. Bivariate plot of dentary width versus depth 1975). However, Semken (in press) records in Sorex fumeus, S. cinereus, and S. haydeni. Measpecimens from 2000-yr-old Rockrun surement = X 2 mm. Shelter deposits in southeastern Iowa and from Holocene portions of the Peccary Cave in Arkansas. Bardwell (1981, unpubtries were not constructed because reliable lished thesis, University of Iowa) also redata on current molluscan ranges do not ports a single specimen of C. gapperi from exist. an earth lodge (13MLl24) in the 1215 AD Glenwood Local Fauna of southwestern Small Mammal Fauna Iowa. Bardwell explained that 13MLl24 is The DSF small mammals represent many situated in a more protected, steeperdifferent habitats although 10 of the 11 taxa walled valley than any of the other Glenconsidered are common to the deciduous wood lodges and speculates that a cooler forest (Table 2). The same 10 species can and moister microenvironment, suitable to also be found in an open forest (parkland) support a relict population of C. gapperi, and/or forest-edge environment. The elev- must have been preserved in the valley. The enth mammal, Ondatra, is restricted in red-backed vole had a more widespread range only by permanent water, but it is distribution in the late Holocene, but has in recommonly associated with those in Table 2. recently become more restricted, All of the DSF mammals prefer mesic con- sponse to either agricultural or postglacial ditions. climatic changes. Spermophilus franklini (Franklin’s The DSF mammalian sympatry (Fig. 4) ground squirrel), the most prairie-like DSF is based on the modem distributions in Burt mammal, climbs more than any other North and Grossenheider (1976). The sympatry, American ground squirrel and prefers the which lies in the deciduous forests of westcentral Wisconsin, is bound on the south open forest-forest-edge habitateh tall 2.9-
* Cl 0 0 8 + 0
S fumwr s haydent S c cinoreu s t leeuri S c ohicenru SUI 492210 SUI 49223
racemosa
Wild.
cf.
Walt
ciliata
biflora
rugosum
stolonifera
sp. Mill
L. cf.
L.
L.
Balbis
type P. spp. L. Potamogeton
P. lapathfolium P. pennsylvanicum P. ramosissimum
L. type
alpinus
L.
Juglans cinerea L. Menyanthes trfoliata L. Polygonurn hydropiper
Iva
Impatiens
Houtt
Eupatorium
Michx.
Cirsium Cornus
Aellen
C. bushianum
Ceratophyllum demersum Chenopodium album L.
Cares spp. L.
Aralia
Ambrosia artemisiifolia A. trifida L.
Taxon
L.
4928 1 49282 49283
49284 49285
Smartweed Smartweed Smartweed
Smartweed Smartweed
49286
49280
Buckbean
Pondweed
49278 49279
49277
49276
49274 49275
Marsh elder Butternut
Touch-me-not
White snakeroot
Lamb’s quarters Thistle Red osier dogwood
49273
49272
quarters
Lamb’s
49269 49270
49268
49267
49271
name
PLANT
SUI No.
3.
Homwort
Ragweed Giant ragweed Spikenard Sedge
Common
TABLE
4
7
13
10
35 108
4
9 1
1
7
1 13
29
9
1
17 63
28 12
MN1
0.6
2.1 1.1
5.6 17.3 1.6
0.6
1.4 0.2
0.2
1.1
0.2 2.1
4.6
1.4
0.2
2.7 10.1
4.5 1.9
Est. % of Dows Silt Flora
MACROFOSSILS
-
-
-
-
*
*
*
-
-
-
-
-
-
-
Rich
-
-
-
-
-
-
-
-
-
-
-
-
-
-
*
*
-
-
* -
* -
-
-
-
-
-
-
-
Dry
-
-
*
-
* *
* *
*
* * *
* * *
-
-
-
-
-
* -
-
-
*
*
-
Lentic waters
-
* *
* * *
* * * * *
-
*
-
-
* -
-
-
*
* *
* -
-
-
-
-
* -
-
-
-
*
-
Wetlands
-
-
-
-
*
-
*
-
-
-
-
-
-
-
* -
-
-
* *
-
-
-
Prairie
-
-
* *
areas
turbed
Dis-
HABITATS
Moist meadows
AND THEIR COMMON
-
-
*
-
* *
-
-
-
Riparian
SILT FLORA
-
-
Open
-
Moist
Woods
FROM THE Dows
-
* *
* * *
-
* *
*
*
* *
*
*
-
-
-
*
-
-
*
*
*
-
* * -
* *
Xeric
* *
Mesic
General
*
*
-
*
-
-
-
-
-
-
*
*
-
dric
HY-
Rydb.
L.
Note.
All are seeds except for Quercus
ash
sp. (wood)
49303
Prickly
Total
Mill.
49302
Forest grape
Zanthoxylum americanurn
49291
Great bulrush
49298 49299 49300 49301
49296
49295
49294
49293
Bulrush
Common
Red raspberry Willow
Used for ‘T date
Bur reed Bur reed Hedge nettle Violet
americanurn
elder
49291
Pin-cherry
49292
49289 49290
Pondweed Pondweed
Wild crabwle Oak
49287 49288
Pondweed Pondweed
Engelm. Stachys palustris L. Viola sp. L. Vitis ripnria Michx. type
S. ewycarpum
Nutt. type
Sparganium
we
Sambucus canadensis L. Scirpus jhwiatilis (TOIT.) Gray S. validus Vahl.
Salir sp. L.
Rubus cf. strigosus
Quercus sp.
Pyrus cf. corenaria L.
P. spp. L. Prunus cf. pennsylvanica L.f.
(Berm.)
P. pulcher ‘Ibckerm P. pusillus L. P. richardsonii
100.3
3.7
1.3
0.3 1.0 0.5 1.4
3.2
3.7
14.2
0.6
8.3
4
-
*
12
4
-
-
* *
*
*
4
-
-
*
-
-
-
-
-
-
-
*
*
-
-
-
-
-
*
*
-
-
*
-
*
*
*
*
-
*
-
-
-
-
-
-
-
and Salti sp. (bud scales).
23 626
8
20
23
89
4
52
0.2
0.2
0.2
0.2 0.5
0.2 1.1
*
*
*
12
-
-
-
19
-
-
*
* *
*
* -
*
*
-
-
-
-
* *
* *
-
-
-
-
-
15
-
-
* * * *
*
*
*
-
-
-
-
-
12
-
-
-
-
-
*
-
*
-
-
-
-
-
6
-
-
-
-
-
-
-
-
-
-
-
-
-
1
-
-
-
-
-
-
-
-
-
-
-
-
*
*
27
*
*
* *
-
-
*
*
*
*
-
-
*
8
-
-
-
-
-
-
-
-
-
-
*
-
* *
* *
362
CURTIS M. HUDAK
MINNESOTA S. DAKOTA
L
* JO
Dawr
NEBRASKA
FIG. 4. Dows Silt Fauna micromammal sympatry (ca. 9380 ? 130 yr BX); Wisconsin tension zone (after Curtis, 1959); Dows Silt Flora sympatry (inset B); recent original vegetation (inset A; after Wright et al., 1963); and selected early Holocene site locations of the upper Midwest (localities defined in Table 5).
by S. palustris, the northeast by S. franklini, and the northwest by Microtus pineforum. The sympatry covers parts of Jackson, Clarke, Marathon, and Wood counties in Wisconsin. Long (1970) reported 58 native mammals (including bats) from central Wisconsin with Peromyscus leucopus, Microtus pennsylvanicus, C. gapperi, S. cinereus, and Blarina brevicauda being the most abundant. All, with the possible exception of P. leucopus, are found in the DSF with M. pennsylvanicus and C. gapperi being the most abundant in
the DSF. The rarest species in central Wisconsin are Napeozapus insignis, Mustela nivalis, and Microsorex hoyi; none of which were found in the DSE Locally distributed, but rare, are M. pinetorum, Synaptomys cooperi, S. palustris, S. franklini, Microtus ochrogaster, Reithrodontomys megalotis, Glaucomys sabrinus, and, today at least, Eutamias minimus. The first four of the
above locally distributed species are found in the DSF. The DSF micromammals, using both the common habitat chart (Table 2) and the
EARLY
HOLOCENE
PALEOECOLOGY
present sympatry (Fig. 4), infer a moist decidous forest environment for north-central Iowa ca. 9380 yr B.P. However, the possibilities of isolated conifer stands cannot be ruled out because of the strong affinities of Tamias and Cleithrionomys toward this vegetation. S. franklini strongly indicates that the forest was open, or that a forestedge tall-grass habitat was present. Flora
The most recent vegetation in north-central Iowa consisted largely of tall-grass prairie and prairie wetlands prior to cultivation. The DSF plant remains are dominated by aquatic and forest taxa, and none are limited to prairies or moist meadows (Table 3). Most of the aquatic plant macrofossils are associated with lentic waters. Ambrosia and Zva are meadowland forms but can be found with Chenopodium on disturbed ground. The forest species include two trees, Quercus and Juglans, both of which are upland genera. Three of four shrubs, Prunus pennsylvanica, Pyrus coronaria, and Zanthoxylum americanum, are understory shrubs, and the fourth, Mix, is riparian. Aralia racemosa is an upland herb restricted to a rich woods and not usually found in riparian forests. The current floral sympatry (Fig. 4) is large and encompasses the distribution of the conifer-hardwood and deciduous forests in the Great Lakes-New England regions. Although several species are currently rare in Iowa, only Potamogeton alpinus is not found in Iowa today, and it defines the western boundary of the sympatry. The northern boundary is defined by Polygonum lapathifolium and P. pennsylvanicum in Minnesota, and by Ceratophyllum demersum, densis,
Vitis
riparia,
Sambucus
cana-
and Sparganium eurycarpum across Canada and New England. The southern boundary is defined by P. alpinus and Cornus stolonifera. The western edge of the sympatry approximates the deciduous vegetation zone defined in Wright et
al. (1963).
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363
The common habitats (Table 3) and sympatry (Fig. 4) for the DSF plant macrofossils infer a moister and cooler climate, as do both mollusks and micromammals, than currently found in north-central Iowa. They also suggest lentic waters in close proximity to an upland deciduous forest. An open environment (e.g., meadow or disturbed area) could exist among the woods or possibly on the perimeter of the water body. Comparisons of Climatic Vegetational Data
and
The combined sympatry for the 40 DSF species of plants and mammals is limited by the small mammal sympatry (Fig. 4). This sympatry coincides largely with a “tension zone,” described by Griggs (1914) and Curtis (1959) as a place where many plants and animals from two biotic provinces overlap. The tension zone of Wisconsin and Minnesota includes the southern limits of many northern species and the northern limits of many southern species. Curtis (1959) plotted the zone by the densest concentration of individual range lines to cross Wisconsin (Fig. 4). Northeast of this zone the vegetation is coniferous and contains pines, hemlock, spruces, and fir. To the southwest conifers are replaced by prairies and several species of oaks. Within the tension zone, the vegetation is dominated by oak savannas (bur and white oak with blue stem grasses), southern oak forests (white, black, and red oaks), and the southern mesic forests (sugar maple, basswood, and elm; Cottam and Loucks, 1965). This tension zone (or ecotone) is high in biotic diversity, which is also reflected in the DSF (for discussion on ecotones, see King and Graham (1981)). Climatic data for the DSF sympatry in Wisconsin and present day Dows, Iowa, are averaged from three nearby weather stations at Eau Claire, Marshfield Experimental Farm, and Hatfield Dam, in Wisconsin, and Iowa Falls, Hampton, and Webster City, in Iowa. The data for these
364
CURTIS M. HUDAK TABLE
4. CLIMATIC
SUMMARY
DATA RELATED
TO THE Dows
SILT FAUNA/FLORA
Dows, Iowa
Dows Silt sympatry (ca. 9380 yr B.P.)
Cherokee Site (ca. 9000 yr BP)”
Cherokee Site (ca. 8400 yr B.I?)b
9 (48)
7 (44
-
9 (48)
20 (68)
18 (65)
18(64
-
777 (30.6)
785 (30.9)
800 (31.5)
864 (34.0)
X annual temperature, “C (“F) X growing season temperature (MaySept.), “C (“F) X annual precipitation, mm (in.) X number of days with snow cover ji frost-free days
90
120
-
60
150
140
-
165
a Wendland (1980). b Semken (1980).
areas come from NOAA (1978) and Visher (1954). Climatic data (Table 4) for Dows today is compared to that of the Dows Silt sympatry (approximately 282 km NE of Dows), and the Cherokee Site (Semken, 1980, WendTABLE Symbol
5. SELECTED EARLY HOLOCENE Site name
Ch
Cherokee
co ct CC HM .I KM
Co10 Bog Chatsworth Bog Disterhaft Farm Bog Graham Cave Hudson-Meng Jewel1 Bog Kirchner Marsh
LWO
Lake West Okoboji
Ma MC MRS OF PL RR
Madelia McCulloch Bog Modoc Rock Shelter Old Field Pickerel Lake Raddatz Rock Shelter Rodgers Shelter Sumner Bog Volo Bog Woden Bog
D
RS S V W
land, 1980) in northwestern Iowa (approximately 169 km west of Dows). Temperatures within the Dows Silt sympatry are approximately 2°C (4°F) cooler annually and 2°C (3°F) cooler during the growing season than that presently at Dows. The mean anSITES OF THE UPPER MIDWEST Source
Semken, 1980; Wendland, 1980; Baerreis, 1980 Brush, 1967 King, 1981 Webb and Bryson, 1972 McMillan and Klippel, 1981 Agenbroad, 1977 Brush, 1967 Wright ef al., 1963; Watts and Winter, 1966 Baker and Van Zant, 1980; Van Zant, 1979 Jelgersma, 1962 Brush, 1967 Fowler, 1959; Parmalee, 1959a King and Allen, 1977; King, 1981 Watts and Bright, 1968 Cleland, 1966; Parmalee, 1959b McMillan and Klippel, 1981 Van Zant and Hallberg, 1976 King, 1981 Durkee, 1971
EARLY
HOLOCENE
PALEOECOLOGY
nual precipitation in the sympatry is nearly identical to that of Dows today. However, cooler temperatures undoubtedly reduced evaporation and increased available ground moisture at the time of deposition of the DSF. The number of days with snow cover averages 1 month longer in the sympatrv than currently at Dows, and there are approximately 10 fewer days per year that are frost free. The closest site to the Dows Local Biota, in age and geographic affinity, that contains mammals, mollusks, and plant macrofossils is the Cherokee Sewer Site in Cherokee County, Iowa (Fig. 4; Table 5; Anderson and Semken, 1980). Wendland (1980) based the climatic reconstruction from the Cherokee Site on the pollen analysis from Lake West Okoboji (Baker and Van Zant, 1980; Van Zant, 1979). He considers the climatic episode between 10,000 and 9000 yr B.P. to represent a more moist and cooler interval than is presently found in northwestern Iowa. The average growing season temperature during deposition of the DSF is estimated to be nearly identical to that at Cherokee while the annual precipitation averaged 15 mm (0.6 in.) less than at the Cherokee Site at 9000 yr B.P. (Table 4). Although the DSF climatic data are restricted primarily by mammal distribution, and the Cherokee climatic data are based on pollen analyses, the climatic conditions at Dows (ca. 9380 yr B.P.) and Cherokee (ca. 9000 yr B.P.) were very similar. Dows and Cherokee are currently on the same east-west isotherms that traverse Iowa (NOAA, 1978), and it is tempting to speculate that the two sites were also on similar east-west isotherms during the early Holocene. Mammals and mollusks have been reported from the 8400 yr B.P. cultural Horizon III at Cherokee (Semken, 1980; Baerreis, 1980). The pollen and plant macrofossils have been recorded for this period from nearby Lake West Okoboji (Baker and Van Zant, 1980, Van Zant, 1979). The paleo-
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NORTH-CENTRAL
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365
ecologic interpretations for Cherokee Horizon III largely confirm the DSF reconstruction that a moist, deciduous forest to open woodland was present across northwest Iowa ca. 9380-8400 yr B.P. McMillan and Klippel (1981) noted that Rodgers Shelter (ca. 10,500-9500 yr B.P.) and Graham Cave (estimated lO,OOO-9000 yr B.P.) in Missouri had deciduous forest and forest-edge mammals. At approximately 9000 yr B.P. both sites experienced an influx of grassland species from which McMillan and Klippel conclude that the forests were being replaced by prairie. The Modoc Rock Shelter (Fowler, 1959) in southwestern Illinois had a fauna that favored cool, moist woodlands throughout the Holocene. From the fauna1 data, Parmalee (1959a) concluded the local habitat remained relatively unchanged except in the early Holocene, which was apparently cooler and damper. The Raddatz Rockshelter fauna (Parmalee, 1959b), located in southwestern Wisconsin, was representative of a deciduous-conifer forest from ca. 9000 to 5500 yr B.P. (Cleland, 1966). Semken (1983) summarized the Holocene mammalian faunas from Missouri, Illinois, and Wisconsin and concluded that they were inhabiting cool, moist forests between 10,000 and 8400 yr B.P. West of Dows and Cherokee the molluscan fauna from the Hudson-Meng Site led Agenbroad (1977) to conclude that prior to 9000 yr B.P. a cooler grassland environment existed across northwestern Nebraska. Vegetation studies from Lake West Okoboji (Baker and Van Zant, 1980; Van Zant, 1979), Madelia (Jelgersma, 1962), Jewell, Colo, and McCulloch bogs (Brush, 1967), Woden Bog (Durkee, 1971), Pickerel Lake (Watts and Bright, 1968), Kirchner Marsh (Wright et al., 1963; Watts and Winter, 1966), Old Field (King and Allen, 1977), and Chatsworth Bog (King, 1981) all reflect a deciduous forest environment with oak and/or elm being the dominant pollen at some time between 10,000 and
366
CURTIS M. HUDAK
8500 yr BP (Fig. 4; Table 5). Sumner Bog (Van Zant and Hallberg, 1976) pollen indicated that conifer forests were still occupying northeastern Iowa at ca. 9270 yr B .P., but the authors have interpreted this date is too young and is undoubtedly caused by the hiatus directly on top of the dated horizon. The pollen analysis of R. G. Baker (in Webb and Bryson, 1972) on Disterhaft Farm Bog of east-central Wisconsin supported Cleland’s (1966) interpretation from Raddatz that a deciduous-conifer forest was still present in Wisconsin ca. 8600 yr B.P. King’s (1981) interpretation of Volo Bog in northeastern Illinois suggests that pine was still present in low abundance among the oaks and elms ca. 9000 yr B.P. The DSF fits in the general scheme of a cool and moist climate across the Midwest during the early Holocene. It also confirms that a deciduous forest biome was present across southern Minnesota and northern Iowa ca. 9000 yr B.P. At that time conifers were growing to the northeast in central Wisconsin, open deciduous woods were present to the south and immediate west, and grasslands were developed further west. CONCLUSIONS
(1) The plants and mammals of the Dows Silt Fauna/Flora are sympatric in west-central Wisconsin, an area of similar precipitation to that presently at Dows, but cooler mean annual temperatures. This cooler temperature suggests greater effective precipitation at Dows ca. 9380 yr B.P. (2) The area of sympatry for the small mammals lies in the Wisconsin tension zone, an area of open deciduous woods that contains an overlap for species from the northern forest province and the southwestern prairie province. Independent analyses of the mollusks, plant macrofossils, and small mammals in the Dows Silt Fauna/Flora, or Horizon 3 (ca. 9380 yr B .P.), all indicate a cool, moist, deciduous forest with open woods possibly on the hilltops.
(3) The Dows Silt Fauna/Flora reconstruction fits the regional vegetation setting based on other fauna1 and floral analyses of similar age. ACKNOWLEDGMENTS Mr. and Mrs. Emory Fitz and Mr. and Mrs. Vem Peterson from Dows, Iowa, allowed me to track across their land. Holmes Semken, Jr., Richard Baker, Timothy Kemmis, George Hallberg, Russell Graham, and Frances King reviewed and made excellent suggestions on the text. Lon Drake, Terrence Frest, and Richard S. Rhodes helped by discussing certain problematic areas. Terrence Frest identified the mollusks. Jane Junge and the University of Kansas Museum of Natural History provided valuable information toward identifying certain mammals in this paper. Frances B. King from the Illinois State Museum at Springfield, Illinois, identified the wood fragments. The University of Iowa Geology Department and the Iowa Geological Survey each provided funds for one radiocarbon date. The University of Iowa Geology Department (Littlefield Fund) helped to defray field expenses.
REFERENCES Agenbroad, L. D. (1977) Climatic change and early man in northwest Nebraska. In “Paleoindian Lifeways” (E. Johnson, Ed.). Museum Journal 17, 117-125. Anderson, D. C., and Semken, H. A. (Eds.) (1980). “The Cherokee Excavations: Holocene Ecology and Human Adaptations in Northwestern Iowa,” Academic Press, New York. Baerreis, D. A. (1980). Habitat and climatic interpretation from terrestrial gastropods at the Cherokee site. In “The Cherokee Excavations: Holocene Ecology and Human Adaptations in Northwestern Iowa” (D. C. Anderson and H. A. Semken. Eds.), Chap. 4; pp. 101-122. Academic Press, New York. Baker, R. G., and Van Zant, K. L. (1980). Holocene vegetational reconstruction in northwestern Iowa. In “The Cherokee Excavations: Holocene Ecology and Human Adaptations in Northwestern Iowa” (D. C. Anderson and H. A. Semken, Eds.), Chap. 5; pp. 123-138. Academic Press, New York. Bowles, J. B. (1975). Distribution and biogeography of mammals of Iowa. Texas Tech University, The Museum,
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HOLOCENE
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Cottam, G. and Loucks, 0. L. (1965). Interpretation of the vegetation of Wisconsin. From the early vegetation of Wisconsin map. Wisconsin Geological and Natural History Survey, G. F. Hanson, Director. Curtis, J. T. (1959). “The Vegetation of Wisconsin.” Univ. of Wisconsin Press, Madison. Durkee, L. H. (1971). A pollen profile from Woden Bog in north-central Iowa. Ecology 52, 837-844. Fowler, M. L. (1959). Summary report of Modoc Rock Shelter 1952, 1953, 1955, 1956. Illinois State Museum Report
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Gleason, H. A. and Cronquist, A. (1963). “Manual of Vascular Plants of Northeastern United States and Adjacent Canada.” Van Nostrand, Princeton, N.J. Griggs, R. E (1914). Observations on the behavior of some species on the edges of their ranges. Bulletin of the Torrey Botanical Club 41, 25-49. Hazard, E. B. (1982). “The Mammals of Minnesota.” Univ. of Minnesota Press, Minneapolis. Hoyer, B. E. (1980). The geology of the Cherokee sewer site. In “The Cherokee Excavations: Holocene Ecology and Human Adaptations in Northwestern Iowa” (D. C. Anderson and H. A. Semken, Eds.), Chap. 2, pp. 21-66. Academic Press, New York. Jackson, H. H. T. (1961). “Mammals of Wisconsin.” Univ. of Wisconsin Press, Madison. Jelgersma, S. (1962). A late-glacial pollen diagram from Madelia, south-central Minnesota. American Journal
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McMillan, R. B., and Klippel, W. E. (1981). Post-glacial environmental change and hunting-gathering societies of the southern prairie peninsula. Journal of Archaeological Science 8, 215-245. National Oceanic and Atmospheric Administration (NOAA) (1978). ‘Climate of the United States, with Current Tables of Normals, 1941-1970, and Means and Extremes to 1975” (J. A. Ruffner and F. E. Bair, Eds.), Vols. 1, 2. U.S. Weather Bureau and National Oceanic and Atmospheric Administration Data. Gale Research Co., Detroit. Parmalee, P. W. (1959a). Animal remains from the Modoc Rock Shelter site, Randolph County, Illinois. In “Summary Report of Modoc Rock Shelter” (M. L. Fowler, Ed.). Illinois State Museum Reports of Investigations 8, 61-65. Parmalee, P. W. (1959b). Animal remains from the Raddatz Rockshelter, SK5, Wisconsin. Wisconsin Archaeologist
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Semken, H. A., Jr. (1980). Holocene climatic reconstructions derived from the three micromammal bearing cultural horizons of the Cherokee sewer site, northwestern Iowa. In “The Cherokee Excavations: Holocene Ecology and Human Adaptations in Northwestern Iowa (D. C. Anderson and H. A. Semken, Eds.), Chap. 3, pp. 67-99. Academic Press, New York. Semken, H. A., Jr. (1983). The Holocene mammalian record of the eastern and central United States. In “Late Quaternary Environments of the U.S. and the U.S.S.R.,” Vol. 2, “Holocene Environments of the United States” (H. E. Wright, Jr., Ed.) Univ. of Minnesota Press, Minneapolis. Van Zant, K. L. (1979). Late- and postglacial pollen and plant macrofossils from Lake West Okoboji, northwestern Iowa. Quarternary Research 12, 358380. Van Zant, K. L. and Hallberg, G. R. (1976). A lateglacial pollen sequence from northeastern Iowa: Summer Bog revisited. Iowa Geological Survey Technical
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Visher, S. S. (1954). “Climatic Atlas of the United States.” Harvard Univ. Press, Cambridge, Mass. Walker, P. H. (1966). Postglacial environments in relation to landscape and soils on the Cary Drift, Iowa. Iowa State University Agricultural and Home Economics
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erel Lake, northeastern South Dakota. Geologicnl Society of America Bulletin 19, 8554376. Watts, W. A., and Winter, T. C. (1966). Plant macrofossils from Kirchner Marsh, Minnesota-A paleoecological study. Geological Society of America Bulletin 77, 1339-1360. Webb, T., and Bryson, R. A. (1972). Late- and postglacial climatic change in the northern midwest. USA: Quantitative estimates derived from fossil pollen spectra by multivariate statistical analysis. Quaternary Research 2, 70-115.
Wendland, W. M. (1980). Holocene climatic reconstruction of the prairie peninsula. In “The Cherokee Excavations: Holocene Ecology and Human Adaptations in Northwestern Iowa” (D. C. Anderson and H. A. Semken, Eds.), Chap. 6, pp. 139-148. Academic Press, New York. Wright, H. E., Jr., Winter, T. C., and Patten, H. L. (1963). Two pollen diagrams from southeastern Minnesota: Problems in the regional late-Glacial and post-Glacial vegetational history. Geological Society of America Bulletin 74, 1371-1396.