Stevens Pond: A postglacial pollen diagram from

a small Typha Swamp in Northwestern Minnesota,

interpreted from pollen indicators

and surface samplesII

2 C.R. Janssenr

Limnological Research Center, University of Minnesota, Minneapolis

TABLE OF CONTENTS

Introduction 145 Zone 4, Spectra 9 through 27; Pinus strobus

Assemblage Zone 155 Methods 148

Zone 5, Spectra 1-8/9: Ambrosia Assemblage Sampling and processing 148 Zone 157 Pollen diagrams 148 The development of the local vegetation 158

Site and Present-Day Vegetation 149 Zone 1 159

Stratigraphy 150 Zone 2 159

Zone 3 160 Palynology 150

Zone 4 161 The development of the regional vegetation 150

Zone 5 161 Zone 1, Spectra 63 through 91: Pinus bank-

siana/resinosa■Pteridium Assemblage Zone . . 150 The Local Lowland Vegetation and Its Rela-

the Upland Vegetation 161 Zone 2, Spectra 48 through 62: Quercus-Gra- tion to

Regional Pollen Rain 163 mineae-Artemisia Assemblage Znoe 151 Local, Extkalocal, and . ,

Summary 163 Zone 3, Spectra 28 through 47: Quercus-Ostrya

Assemblage Zone 152 Literature Cited 164

INTRODUCTION

The present study comprises a pollen-analytical of from investigation a peat core Stevens Pond, a

small depression situated in the coniferous-deciduous

forest belt in northwestern Minnesota, about 40 mi

east of the present prairie/forest margin (Figs. 1, 2).

Fig. 2. Photograph of Stevens Pond from the west.

A detailed picture of the development of the regional Fig. 1. Location of Stevens Pond and Itasca State vegetation is already available from the work of Me- Park (A) and Clearwater-Lake Sylvia area (B) in relation to major vegetational formations of Minnesota Andrews (1966), who analyzed sediments from lakes and adjacent regions. along an east-west transect across the principal plant

1 Contribution No. 31, Limnological Research Center. Mede- formations present today in northwestern Minnesota. delingen van het Botanasch Museum en Herbarium vam de For the Itasca Ri.jksuniversiteit te Utrecht No. (276). State Park area he identified, above 2 Present address: Botanical Museum and Herbarium, the a Pinus Utrecht, Netherlands. Accepted for publication March 14, 1967. late-glacial sediments, banksiana/resinosa- 146 C. R. Janssen Ecological Monographs Vol. 37, No. 2

which has modern of Stevens the mats Pteridium assemblage zone, no Pond, modern forests and Carex

in surface-sam- in the Itasca State Park equivalent Minnesota, according to region were studied (Janssen Details ple analyses. Following this in turn is a Quercus- 1967). of this vegetation study are irrelevant.

Gramineae- Artemisia It will suffice to note from zone, a Quercus-Ostrya zone, that species vegetation

strobus and a Pinus zone, which represent respec- plots (releves) were arranged according to presence,

the the deciduous and so that that tend to tively Quercus savanna, forest, species grow together are tabu-

the coniferous-deciduous forest. The indi- lated in so-called sequence together sociological groups (Sca- of the towards the east moni & cates an expansion prairie Passarge 1959; Doing 1962). Vegetation

and that the in mid-postglacial time a subsequent return of plots are characterized by same sociological

the forest. At the the Ambrosia top assemblage zone groups are placed together and mark a vegetation

reflects agriculture developed by white man late in type. This is essentially an ordination of plots along the 19th environmental in- century. some gradient, and one would be

to also McAndrews analyzed the sediments of moderately clined call a sociological group an ecological the The difference is large lakes, so the pollen rain reflected primarily group. that an ecological group

regional vegetation. He thus interpreted his as- is characterized by all environmental factors except

in terms at the and the includes semblage zones of vegetation or- competition, sociological group the

level the formation. ganizational of plant Now, in factor of competition. The sociological group thus

formation not indicates which to each the vegetation is homogeneously species tend grow together in a

distributed. There is a mosaic of plant communities certain climate, on a certain type of soil, and with a certain largely dependent on topography and soil differences. regional reservoir of seed sources. A floristic

The present study had the objective to examine the ordination of vegetation plots naturally includes the factor of detailed history of a small segment of this mosaic. competition, and groups of species that are

Therefore Stevens Pond was selected to reveal such derived from such an ordination must be termed so- a history, because of two reasons: ciological, although most of the characterization of the is based factors groups on other than competi- 1. In a peat bog the vegetation at the sampling tion. site itself can be studied in detail because of the over- nature The of a sociological group is illustrated representation of the local pollen types. These types in Figure 3, which shows a simplified ordination of include several characteristic herbs, as is shown by lowland vegetation plots in the Itasca State Park pollen analyses of surface samples from plant com- region. munities prominent in the various stages of recent If a stratigraphic pollen diagram is drawn with lake filling (Janssen 1966). Peat thus provides an | the pollen types arranged according to these socio- opportunity to examine the succession in the local in environment logical groups, then changes the can bog vegetation. be more easily traced. In one of the main pollen from the 2. In a small depression the pollen types diagrams for Stevens Pond (Fig. 5), the lowland immediately adjacent upland should be better rep- pollen types found in Stevens Pond have been so of the short resented than in a larger basin, because and the arranged, succession shows more clearly. distance of dispersal (compare also Tauber, 1965). discussion A of the vegetation types involved is con- introduced for In an earlier paper Janssen (1966) tained in the section on lowland vegetation. such a rise in pollen percentage the concept of ex- In comparing pollen assemblages with recent plant tralocal pollen and, for the vegetation that produces communities it is that the of not implied on same type it, the extralocal vegetation. The small size of the soil the past vegetation should have had completely basin result in extralocal effects for one may or the same composition as do the communities today. more pollen types. If such pollen types represent This might be true if climate and accessibility for species characteristic for the type of upland forest, the species to an area were the same as today, but to nature it may then be possible determine the of such was not the case. Under quite different condi- the forest surrounding the basin. Finally, after the tions found species now widely separated may once local and the extraloeal effects have been determined, have been associated. This might be true especially the remainder of the pollen content represents the for the vegetation units of lower rank (associations). regional vegetation. Units of higher rank (alliances), however, represent Throughout the discussion the terms local, extra- types of vegetation that are floristieally and eco- local, and regional pollen deposition are used as de- well-defined logically and often show a typical physi- fined earlier (Janssen 1966). in the recent had the ognomy. Probably past they To reveal to what extent extralocal effects occur combinations. same general species Moreover, in the in present-day basins of the size of Stevens Pond, late Holocene the competition was not too different basins surrounded were analyzed from small samples from that of today, because the same species were by various types of deciduous and coniferous-decidu- in the On the of present region. same type soil and ous forests. under similar climatic conditions this would there-

To evaluate the ecological significance of species fore result in species combinations similar to those whose pollen grains could be expected in the samples of today. Thus, for the late Holocene, reference to Diagram Typha 147 Spring 1967 A Postglacial Pollen from a Small Swamp

Triglochin maritima

Chamaedaphne calyculata

Menyanthes trifoliata

Comarum (Potentilla)

Utricularia vulgaris

Betula pumia

Larix laricina

Sarracenia purpurea

Sphagnum sp.

Ledum groenlandicum

Oxycoccus quadripetalus

Picea mariana

Sagittaria latifolia

Sparganium eurycarpum

Campanula uliginosa

Cicuta bulbifera

Rumex orbiculatus

Galium labradoricum

Dryopteris thelypteris

Stellaria longifolia

Gaultheria hispidula

Typha latifolia

Lysimachia thyrsiflora

Alnus rugosa

Lycopus sp.

Scutellaria epilobiifolia

Impatiens capensis

Bidens cernua

Caltha palustris

Rhamnus alnifolia

Fig. 3. Arrangement of recent plant communities in vegetation unit B. For explanation, see text under

Local Vegetation.

be recent plant communities of a fairly high rank is diagram, it should realized that many have sharp

useful. boundaries with neighboring ones.

in the discussion reference will The more we go back time, however, more In the following frequent

we find a quite different competition, even with con- be made to plant communities that were delimited different of stant climate and soil, because a set as a result of the vegetation study in the Itasca State

the The result be Park species was on stage. may a species region. Although the arrangement of the vege-

composition unknown today anywhere (c/. Iverson tation plots in this region is not strictly according to

1960). For the early Holocene and before, one might the methods developed by the Ziirich-Montpellier

ask whether a purely floristic comparison with recent school of phytosociology (Braun-Blanquet 1951), the communities informative. These difficulties plant is field methods and the identification of vegetation

can be avoided use of auteeological data rather by units are in the tradition of continental European

than floristic. However, the autecology of many plant ecology, and the plant communities have been knowl- species is still poorly known. But much of our named in the tradition of the Z-M school. An addi- edge about the ecology of species has been increased floristie tional advantage is that it stresses the con- considerably by the study of the floristics of whole cept of these communities. Classes, orders, alliances, vegetation types, accompanied by studies of the and associations recognized according to this method environment. An arrangement of recent plant com- are identified respectively by their suffixes -etae, munities much about re- may tell us as ecological -etalia, -ion, -etum. quirements of the species as does an auteeological does not of The present paper give a full account study. the floristie of the communities the composition plant By method of establishing sociological groups, investigated (Janssen 1967). Only those data deal- briefly described above, it was difficult to classify hierarchic of ing with the various stages of lake filling are repro- groups of vegetation plots in a system duced. A of the plant formations vegetation units. Although vegetation units are use- description present

in in the Itasca State Park region and their relation- ful for reference to pollen assemblages a pollen 148 C. R. Janssen Ecological Monographs Yol. 37, No. 2 ships with physiography, geology, climate, and soil ent in the marginal bog zones. An exception, how-

has been made for Ulmus because al- appear in MeAndrews (1966). ever, itself,

tree in is Laboratory work was done at the Limnological though this occurs this lowland forest it

Research Center, University of Minnesota, with the more frequent in upland forest communities.

Betula has been financial support of the Hill Family Foundation. I retained in the pollen sum, al- of the Betula be of am much indebted to Dr. H. E. Wright for his help- though some pollen grains may

ful discussions and interest in the work, to Dr. E. J. lowland origin. There are three Betula species in the

•Cushing for his help in identifying pollen types, and region: B. papyrifera is an upland tree, B. pumila

to Dr. J. H. MeAndrews for introduction to the var. glandulifera is a lowland shrub, and B. lutea

to the flora and vegetation of northwestern Minnesota. is confined bogs but is rare in area today

The for Betula vegetation work was done during the tenure (Christ 1959). Size-frequency curves in 4 beside the Betula of National Science Foundation summer fellowships pollen are shown Figure

at the Lake Itasca Biological Station. curve. Size measurements on the two main Betula

in the in the section Recalculation of the data according to different species region today are given

pollen sums was carried out by computer according on pollen morphology and in Table 1 and Figure 6.

to has distribution. P. the DHALL 3 program, designed by K. S. Def- Picea also dual ecological

feyes and E. J. Cushing. glauca is confined to uplands, whereas P. mariana

a tree. Most of the Picea grains Pollen counts are on file with the American Docu- is typical bog pollen

mentation Institute, Auxiliary Publications Project, at Stevens Pond probably are of lowland origin, and Picea included in the Photoduplication Service, Library of Congress, Wash- for that reason was not pollen

not ington 25, D. C. sum. Picea grains were measured, because pre- liminary analysis of reference material of the two

METHODS species showed too much overlap in size.

Other pollen types usually included in the pollen Sampling and processing because of sum, but here excluded a possible local

Stevens Pond was sampled with a Davis corer in origin, are Salix, Alnus, Poaceae, and Cyperaceae. when the frozen December, 1962, peat was to a

depth of only 2 cm. The core was divided longi-

tudinally, and samples for pollen analysis were

taken from the inside. Sample treatment included

boiling with 10% KOH for 1 min, sieving through

fine and at 95C for 10 min. For a screen, acetolysis

microscopic investigation the material was mounted

in silicone oil (2000 csk), without stain.

Nomenclature

Nomenclature is that of Fernald (1950) except

Comarum palustris L., Melandrium Roehl, Ephedra

fragilis Desf., E. distachya L., and Eriogonum hera-

cleoides Nutt.

Pollen Diagrams

Main Pollen Diagrams. The main pollen diagram has

been divided into two parts. Figure 4 shows the

upland pollen types that are included in the pollen

sum. Figure 5 shows lowland pollen types as well

as those from ecologically indeterminate habitats, all

from the excluded pollen sum; the percentage base

for each taxon is the pollen sum of Figure 4.

in both Percentages diagrams are shown on two

scales; the scale with lOx exaggeration permits the

accurate plotting of minor curves and minor fluctua- tions. The is pollen sum so large (generally more than that minor inflections in 1000) many the curves

have statistical significance. For example, a contin-

table shows that the in Pieea at the gency drop zone

4/5 boundary is highly significant.

Lowland types include pollen from species of the Fig. 6. Size-frequency curves of recent pollen of

Ulmus americana-Fraxinus often Betula and B. See Table nigra forest, pres- papyrifera pumila. 1. Spring 1967 A Postglacial Pollen Diagram from a Small Typha Swamp 149

Table 1. Data for collections of Betula papyrifera Marsh. and B. pumila L. var. glandulifera Regel used for size-frequency studies. All the collections were treated with 10% KOH (2 min at 100 C), acetylated (1 min at 100 C), and mounted in silicone oil.

Mean SizeSize

Slide No. Ave. and

Limnolog. No. Size Median Standard

Research Mea- (mi- (ocular Deviation

Species Collector Locality Center sured crons) units) (oc.(oc. units)

C. O.0. Goodhue Co.,

Betula pumila Rosendahl, Minnesota 2881 100 20.5 15.5 17.517.5±1.2+ 1.2

var. glandulifera F. K. Butters

JJ. WW. Moore,\Joor0 B. O.0. Phinney Fillmore Co., 2886 100 22.0 17.5 18.5±1.418.5+ 1.4

12483 Minnesota

J. H. Dakota Co.,

McAndrews Minnesota 2898 100 22.6 16.5 17.5±17.5+ 1.2

O.0. Lakela Anoka Co.,

554 Minnesota 670 100 21.2 14.5 17.5±2.017.5+ 2.0

E. J. Cushing Hennepin Co.,

Minnesota 2080 110 26.726.7 21.5 21.5 + 1.6 BetulaBetula papyrifera

M. Fries Ottawa,

Ontario 1676 100 28.6 21.5 22.5 + 1.2

O.0. Lakela Lake Co.,

21263 Minnesota 2911 7474 29.5 22.5 23.5 + 1.5

O.0. F. Zech Becker Co., 157157 Minnesota 2905 7070 28.0 21.5 22.5+1.622.5 + 1.6

the The Auxiliary diagrams. Figures 6 and 7 are diagrams adjacent to pond. steep marginal slopes

2 that show certain pollen types recalculated on the support a ruderal vegetation. In a 64 m releve made basis of different in 1962 the herb of the a pollen sum. These diagrams are vegetation, covering 90%

for the included the The first especially designed two uppermost assem- ground, following species. refers combined of blage zones to allow comparison of Stevens Pond symbol to a 6-point scale cover with surface samples and with McAndrews’ sites in and abundance, the second to sociability on a 5-point

the Itasca State Park region. The differences re- scale (Braun-Blanquet 1951) :

flect sediment lake and type (peat, sediments) dif- Festuca ovina 4.2

ferences in cultivation and long-distance transport. Trifolium pratense 3.2 The assumptions made in the establishment of these Trifolium hybridum 1.2

sums are discussed with the of 2.2 pollen descriptions Trifolium repens

the involved. assemblage zones Vicia sativa +.2

Erigeron strigosus +.1

SITE AND PRESENT-DAY VEGETATION Senecio pauperculus +.1

1.1 Solidago sp. Stevens Pond is the eastern of two ponds north Tragopogon pratense r of Itasca State Park along the south side of Minne- Agropyron repens 2.1 sota Highway 31 between the village of Lake Itasca Liatris ligulistylos +.1 and the Mississippi River (Fig. 2). Its longest axis Achillea millefolium r measures about 80 m. It is one of many ice-block Berteroa incana +.1 depressions in a small outwash valley train of the Agastache foeniculum +.2 Mississippi River. Phleum +.1 terrain pratense Much of the flat was cleared in the early Bromus inermis +.1 20th century and is now used mainly for the culti- Melilotus officinalis +.1 vation of Avena. The woods remaining have a com- Rosa acicularia +.2 position typical for sandy soils. Pinus banksiana

is dominant. Populus tremuloides is codominant, and On the side where the angle of slope is the least, Pinus resinosa and P. strobus less Ex- are common. Avena fields border the pond. The marginal zone

for Pinus between the cept narrow strips of young planted pond and the upland is characterized by

banksiana along Highway 31, there is no forest Salix shrub (mainly S. gracilis). Where the Salix 150 C. R. Janssen Ecological Monographs Yol. 37, No. 2

Fig. of deciduous for 7. Comparison average recent pollen percentages of some trees surface samples

at Clearwater and Lake Sylvia with zone 3 and the upper part of zone 2 of three sediment cores, based

upon the deciduous-tree pollen sum.

shrub is is the silt and below the less dense or lacking, the vegetation is pond, clay occurs Typha

dominated by Scirpus and Carex, with the following mat. The clay and silt apparently is slopewash

composition: that penetrates beneath the mat during times

of high water. In the core from the center of Shrubs taller than 80 cm 40% the pond the silt layer is absent. Salix gracilis +.2 5-55 cm Woody peat, gradually more decomposed Herbs shorter than 80 cm 30% toward the top. Sphagnum leaves present at

Scirpus atrocinctus 2.2 6-12 cm

Glyceria grandis +.1 56-73 cm Completely decomposed black amorphous

Poa palustris +.1 peat Same Carex projecta +.1 73-77 cm as above, but less humified 77-114 with various Carex riparia 2.2 cm Drepanocladus peat amounts

of rather humified Lysimachia thyrsiflora r moss,

Rumex crispus +.1 114- cm Calcareous till

Stachys palustris r

Solidago graminifolia +.1 PALYNOLOGY

Sium suave +.1 General Statement

Aster puniceus +.1 Despite the fact that the core is only 114 cm long,

The pond itself is covered by a floating Typha lati- the pollen diagrams (Figs. 4, 5) show basically the with the folia mat following composition : same assemblage zones as established by McAndrews

the lowest Typha latifolia 5.5 (1966). Only (Picea-Populus) zone might

be absent. Lysimachia thyrsiflora +.1 Gaps may go unnoticed because of the uniform in the Carex rostrata +.3 sediment, especially Quercus-Grami-

Lemna trisulca +.1 neae-Artemisia zone, representing a time when the

invaded of the state that now Bidens cernua 1.1 prairie parts are

Cicuta bulbifera +.1 forested. Lake levels were probably lower (Cushing Winter this 1963) or fluctuating (Watts & 1966) at

STRATIGRAPHY and time, at Stevens Pond peat accumulation may

have ceased during dry periods. The abrupt rise and Peat types are shown on the left side of the pollen

fall of the upland-herb curves at the beginning and diagrams (Figs. 4, 5). Symbols follow Troels-Smith end of the mark which do how- zone might gaps, not, (1955). Although no caloric measurements on the

eliminate an entire humification have been made, the state of humifica- ever, assemblage zone. tion is roughly indicated in the symbols to show the Development Regional Vegetation relative differences. of the

63 91: Pinus banksiana/ 0-5 cm Undecomposed Typha peat. At the time of zone 1, spectra through resinoga-Pteridium Zone sampling of the core (Dee., 1962) this thin Assemblage

zone was resting directly but Zone 1 is characterized of upon woody peat, by very high percentages

in and summer the mat is Pinus and continuous spring early Typha (80-90%) a rather high level

floating. In cores taken along the periphery of of Pteridium. Spring 1967 A Postglacial Pollen Diagram from a Small Typha Swamp 151

As in the diagrams of MeAndrews, most of the frequent fires. This vegetation includes Pteridium pine pollen grains for this zone at Stevens Pond and Gaultheria procumbens (Curtis 1959) and, ac- the belong to P. banksiana/resinosa type. According cording to Yogi (1964), several prairie elements as

to MeAndrews Pinus banksiana is the species more well. Pollen grains of Shepherdia argentea found in the likely involved because of its more northerly dis- zone suggest prairie, but otherwise prairie

tribution absence indicators absent for Artemisia today. MeAndrews noted that the are or rare; example, of Tilia and Acer rubrum from this zone is an indi- shows a value of 5%, only slightly higher than the cation of the boreal character of the forest. found in upland percentages the forest zones later in the

At Stevens Pond, zone 1 has scattered Tilia and Holocene. But it is definitely much lower than the Acer well in Artemisia in rubrum, as as Carya and Juglans, per- percentages the next zone above, which

centages much the same as in surface samples in the was deposited during the prairie expansion eastward.

conifer-hardwood formation of the Itisca Park re- Moreover, the genus Artemisia includes boreal species

gion (Janssen 1966). Although Tilia and Acer rub- (Ritchie 1964).

assumed character rum occur in the area today, Carya and Juglans do Thus, in spite of the open of

not. It is therefore difficult to decide whether these the pine forests for zone 1 at Stevens Pond, prairie

4 1 elements not to pollen types in zone reflect the regional vegeta- were very important. In addition

southern the tion or come from Minnesota, e.g. the Pteridiura, understory must have consisted of

Anoka erieaceous shrubs sandplain, where they are more consistently that usually are very underrepre-

found in the correlative pollen zone (Cushing 1963). sented, even in small bogs in forested regions (Jonas-

Pteridium is Janssen which in Canada recognized as characteristic for pine sen 1950; 1966). Lichens,

of woods (Butters & Abbe 1953). Cushing (1963) com- may cover large areas Pinus banksiana savanna

the this with the pares upland vegetation of zone the (Thieret 1964), may fill a gap in vegetation yet

northern dry forest of Curtis (1959). In the Itasca not contribute to the pollen rain.

State Park region of today, Pteridium is present in Davis (1963) concludes from her comparison with

almost every type of upland forest but is most recent pollen spectra in Vermont that Pinus played

abundant on moderately good soils in vegetation a subordinate role in the forest of zone B, and that

types that have been called Corno canadensis-Pine- the vegetation must have been dominated by Larix,

talia (Janssen 1967). Abies, Acer, and Populus, all of which are under-

Zone 1 at Stevens Pond has several grains of Shep- represented in the pollen record. Absence of pine is his herdia canadensis, a shrub characteristic of the accepted by McAndrews for the western part of

but transect. boreal forest today (Ritchie 1960, 1964) absent At Stevens Pond, however, the pine per-

from at the Itasca Park area. The Gaultheria pro- centages for zone 1 are such a high level that

cumbens toward a Pinus banksiana role in the grains point pine presumably played a major vegeta- forest rather than toward a P. reginosa forest, as tion.

judged by its present occurrence in the region in Perhaps the closest analogues for the vegetation

F. banksiana forests 1 poor on outwash soils (Arcto- of zone are the jack pine stands on sandy-gley staphylo-Pinetalia; Janssen 1967). Unfortunately, Podzols and Grey Wooded soils studied by Ritchie in in southeastern Manitoba. however, the present forests Pteridium is rare or (1961) These stands con-

where most absent Gaultheria occurs. Moss (1953) de- tain of the species found in our zone, e.g.

scribes Pinus banksiana forests in northwestern Pteridium aquilinum, Gaultheria procumbens, and

Alberta that include Shepherdia canadensis, Vac- Vaccinium angustifolium, although Shepherdia is

cinium angustifolium, and Gaultheria procumbens, absent.

but not In the Pteridium. Stevens Pond diagram a division may be

The Pteridium percentages found in zone 1 are made between spectra 72 and 73. In zone la, Ulmus,

higher than those in recent surface samples from Alnus, Larix, Comarum type, Betula, and Menyan- pine forests and from small bogs surrounded by pine. thes reach higher percentages than in zone lb. here Probably shading prevents fruiting, as fruiting The size-frequency curves for Betula indicate that

of Pteridium in these of is involved rather specimens types vegetation in zone la, Betula papyrifera

are In Pteridium very rare. western Europe is part than the smaller-sized B. papyrifera at Martin Pond

of the regeneration pattern of the vegetation on in this zone. The same species has been reported for soils after Often poor clearing. the occurrence of the correlative zone in southern Minnesota by Watts

spores of Pteridium is an indication of land occupa- & Winter (1966).

tion on these soils (Smith 1958; Iversen 1964). In

the Itasca State zone 2, spectra 48 THROUGH 62: Quercus- Gramineae- Park region Pteridium is more abun- dant in Artemisia Assemblage Zone open situations (such as windblown areas)

than in closed forests. Zone 2 represents the time in which the prairie/

The rather high percentages of Pteridium thus forest border moved east in Minnesota (Wright

indicate an open rather than a closed forest, possibly et al. 1963). At Stevens Pond it is characterized by

even a barrens—a in jaekpine savanna which herbs a sharp decrease of Pinus and a rise of Quercus, forbs and are dominant and which is maintained by Corylus, Ambrosia type, and Chenopodiaeeae/Amar- 152 C. R. Janssen Ecological Monographs Vol. 37, No. 2

of anthaceae, and by a concentration occurrences of not dispersed readily (Jonassen 1950). For that the herbs the be result prairie Artemisia, Amorpha, Petalostemum, reason high Corylus percentages may a cf. of Lilium philadephicum, and Zizia aurea. For a the short distance to the upland (extralocal effect) similar McAndrews that the rather than a assemblage, postulated more widespread regional occurrence now forested uplands of his transect were covered of Corylus. by prairie in the structure of a Quereus savanna. It is not certain whether the Ambrosia type and the

Because the sediment at Stevens Pond is peat, most Chenopodiaceae/Amaranthaeeae originate from the of the non-arboreal from pollen (Poaceae, Cyperaeeae, upland or dry lake beds. McAndrews empha-

have been Ambrosia and Tubuliflorae) may of local lowland sizes the occurrence of sp., Chenopodium

,,- cannot evaluation Amaranthus soils igin, and thus it be used for an hybridum, C. rubrum, and sp. on of the character of the upland vegetation. Some near lake shores. Wright et al. (1963) and Watts of the & Winter grass pollen may have an upland origin, (1966) favor, for Lake Carlson and Kirch-

because various within of however, types this taxon can ner Marsh, the local occurrence these plants on be found the bare lake beds in sediments. The same applies for the or in a broadened shore zone. Indeed

Tubuliflorae; of for the Ambrosia shows in some species Aster, example, type very high percentages be may very abundant in a prairie vegetation, but diagrams from these sites. At Stevens Pond, how- others can be found in Carex mats. the sediment form ever, peaty may not such a well-

2 suited In the regional diagram, zone may be divided seed bed for these plants. Accordingly the into subzones 2a (spectra 55-63) and 2b (spectra values for Ambrosia type and Chenopodiaceae/Amar-

48-55). In Zone 2b, Corylus shows a maximum, and anthaeeae are relatively subdued. At Thompson Pond, McAndrews Rhus glabra type, Symphoricarpos occidentalis, and found a peak in the curve of Ambrosia

Rosa type are present. These plants are abundant type at a silt layer in the gyttja. He assumed that

in a Ambrosia was into today Quercus macrocarpa savanna, a forma- type pollen washed this pond tion that is maintained between prairie and forest from the upland. However, the Ambrosia type pollen as a result of the suppression of Quercus seedlings in the silt was well preserved in contrast to most of it arrived air rather by fire (MeAndrews 1966). Ewing (1924) describes the other types, so must have by for northwestern Minnesota than inwash from the with the de- a Populus tremuloides by slopes along

the brush prairie, bordered on east by Quercus macro- graded pollen. carpa brush prairie with Corylus americana, Rhus

Rosa zone 3, spectra 28 through 47 : Quercus-Ostrya glabra, Amorpha canascens, sp., Petalostemum, Assemblage Zone and Symphoricarpos occidentalis.

Aikman (1928) found a “Rhus-Corylus chapparal” The base of zone 3 at Bog D in Itasca Park has

at the “xerophytic edge” of the Quercus macrocarpa a radiocarbon age of 3930±100 yr (Y-1328), and

2730±75 forest in Iowa. Curtis (1959) describes for Wis- the upper part (Y-1156) (McAndrews consin the of “oak same type vegetation as opening.” 1966).

and & also de- rise in the Bray (1960) Buell Facey (1960) Zone 3 is characterized by a curves for scribe such savanna vegetation. Pinus and Betula and a fall in the curves for Corylus,

Sedvey Lake, a typical site in the Quercus savanna Artemisia, and Chenopodiaceae/Amaranthaceae. At of northwestern Minnesota, has mesic forest on the first Quercus remains constant, hut then its curve

northeast-facing slopes around the lake, but the south- starts to drop. Pollen curves of mesic forest elements XJ1- east-facing slope and the crest support a shrub (Acer saccharum, A. rubrum, Ostrya/Carpinus,

and Fraxinus savanna with open-grown Quercus macrocarpa and mus, pennsylvanica) reach maxima in which this dense shrub in Corylus americana is dominant zone.

Cornus Rhus (McAndrews 1966). racemosa, glabra, McAndrews concluded from his surface-sample

and transects this deciduous forest Symphoricarpos occidentalis, Artemisia sp. are that for zone a must also present. The south-facing slopes support a have been present on the uplands, where Pinus and

trees to him prairie with e.g. Amorpha canescens, Aster sp., Abies were virtually absent. According

Artemisia and Petalostemum the tree was different on the two sp., sp. (1966), vegetation

Corylus americana was flowering abundantly at main till types in the area. On the sandy till of the

Sedvey Lake in April 1964. In the summer of the Wadena Lobe Quercus and Ostrya virginiana would

Lilium a from the have dominated on the Ulmus on the more same year philadelphicum, plant uplands, mesic prairie (Curtis 1955) represented in the Stev- mesic sites, and Fraxinus nigra and Abies balsamea

ens Pond diagram by several pollen grains, flowered along bog margins. On the silty till of the Des Moines

The the Stone in the east- at the base of the southern slopes. higher per- Lobe, occupying Big Moraine

found centages of Corylus at Stevens Pond (25%) ern part of Mahnomen County, the uplands con-

not have been matched in any other diagram from tained more Quercus rubra, together with Ulmus

Minnesota. In of MeAndrews’ and some diagrams, es- americana, Tilia americana, Ostrya virginiana, those the of his whereas Acer confined the pecially at easternmost part transect, saccharum was to more

a slight rise of Corylus is noticeable in this zone. mesic sites.

Corylus is a good pollen producer, hut its grains are In connection with these assumptions made by Spring 1967 A Postglacial Pollen Diagram from a Small Typha Swamp 153

the basis of the exclusion therefore is effective in the MeAndrews, largely on present an not very ecology of the tree species, it would be interesting to adjustment of the other pollen curves. However, know what kind of forest is and Am- particular present on Artemisia, Chenopodiaceae/Amaranthaceae, the upland immediately surrounding Stevens Pond. brosia type may show considerable percentages in Because of the Ambrosia shows of the heterogeneity of the vegetation it is some samples. Especially type and by no means certain that such a forest has the same high irregular percentages in recent surface

in this facilitates species composition as the overall forest present samples. Excluding type the com- the region. The small size of Stevens Pond, combined parison of recent surface samples with pre-settle- with the surface-sample studies along transects in ment pollen spectra.

deciduous forest Lake and 2. The forest is deciduous of forest two types of (the Sylvia upland a type

in which conifers are Clearwater sites of Janssen, 1966), offers an oppor- absent.

tunity to determine the character of the extraloeal Pollen types of upland conifers comprise 3 genera, vegetation. If, for instance, Tilia occurred around Pinus, Picea, and Larix:

Stevens Pond then this might be reflected by higher a. Pinus. Pollen grains of Pinus are a result of percentages (extralocal percentages) than Me An- long-distance transport from coniferous forests drews found in his larger basins. to the east. Several studies show that the Pinus A comparison thus can be made between the pollen percentages may depend on the distance from Stevens those of percentages at Pond, at a number such a forest belt. Pinus percentages in surface MeAndrews sites, and those found in surface samples samples are lower in the present deciduous forest at the distance from approximately same upland belt in the St. Cloud region than in that of the deciduous forests as the core of Stevens Pond is Itasca State Park region (Janssen 1966). Also from the upland. The surface samples were taken McAndrews found Pinus (1966) decreasing per- in bogs surrounded by two strongly contrasting types centages in the outer portion of the present of deciduous forest. The forest around the Lake conifer-hardwood forest belt and in the adjacent Sylvia Pond is of the Big Woods type, in which deciduous forest belt. The general rise of pine Acer saccharum is dominant and Ulmus americana, through zone 3 therefore might be a result of Tilia and codomi- americana, Ostrya virginiana are the approaching coniferous forest from the east, nant. It contains small amounts of Quercus rubra, rather than a change in composition in the Populus tremuloides, Betula papyrifera, and Carya regional deciduous forest. cordiformis. The Clearwater Pond is surrounded by b. Abies. Most of the pollen grains of Abies also a xerophytic forest in which 4 species of Quercus may not have originated in the regional vegeta- are dominant, Betula papyrifera, Acer rubrum, and tion. Although Abies occurs in the present de- Prunus serotina and are common, Populus tremu- ciduous forest belt, it is more abundant in the

loides, Ulmus americana, and Tilia americana are recent and subrecent conifer-hardwood forma- only minor components (Janssen 1966). tion.

All available data not without are comparable ad- Picea. As will c. he shown later Picea pollen grains justment of the pollen percentages, because: also probably came from the conifer region to

the Picea is 1. samples come from different sediment types east. absent from the present de- ciduous 2. recent surface samples show the disturbing effects forest belt. of cultivation, and 3. Finally, because some of the samples consist of 3. pollen transported from outside the region varies. peat and some of lake sediment, pollen types that

therefore have been recalculated have from Pollen percentages might originated local bog or lake vege-

basis deciduous forest includ- tation must be excluded from the sum be- on the of a pollen sum pollen

ing Populus, Fraxinus pennsylvanica type, Ulmus, cause their overrepresentation in only part of the

Quercus, Ostrya/Carpinus, Tilia, Acer saccharum, A. section would prevent a comparison of all data. The

A. A. most negundo, rubrum, spicatum, Celtis, Corylus, conspicuous representatives of this group are Humulus, Pteridium, Carya, Juglans nigra, J. cinerea, values Stevens a. Poaceae, Cyperaceae. Local at and Platanus. Several pollen types commonly in- of the surface Pond and some samples; pos- cluded in the pollen sum are absent. They fall into sibly also at Bog D. 3 The 2 excluded because groups. first groups are of b. Larix. Local values at Stevens Pond. assumptions derived from surface-sample analyses e. Betula. Some of the pollen grains might be and the work of McAndrews. Betula pumila, especially at Stevens Pond and 1. The low percentages of herbs in zone 3 at Stevens surface This some of the samples. pollen type Pond forest Pollen that point to a vegetation. types the was not excluded from the pollen sum of may have originated from non-forest vegetation main diagrams. therefore have been excluded from the pollen sum.

2 This applies in principle to all herbs and forbs Table shows an average pollen percentage for

and of the trees the except Pteridium Humulus. Most pollen some based upon deciduous-tree pollen sum.

types that fall in this category show low values, and Although it is a hazardous procedure to integrate 154 C. R. Janssen Ecological Monographs Vol. 37. No. 2

Table 2. Average pollen percentages based upon the deciduous-tree pollen sum for the Quercus/Ostrya assem-

for and blage zone and surface samples. Larix Picea are excluded from the pollen sum.

Surface samples

in deciduous Quercus/Ostrya Quercus/Ostrya

Zone 3 in forest formation assemblage zone assemblage zone

confier-hardwood near St. Cloud in conifer- in deciduous

formation in in small ponds hardwood forma- forest formation

Lake Itasca comparable to tion in Lake west of Lake region Stevens Pond Itasca region Itasca

Stevens Clear- Lake Bog D Martin Terhell Reichow Pond water Sylvia Pond Pond Pond Pond

Ulmus 7.3 4.7 43.9 7.0 5.1 9.7 13.7

Quercus 75.2 88.2 37.1 50.5 58.6 55.0 52.0

Ostrya' 8.6 1.2 3.7 32.8 22.5 20.2 22.0

Tilia 1.4 1.0 4.3 1.8 1.7 4.7 2.7

Acer saccharum 0.4 0.2 4.1 1.2 0.9 1.1 0.8

Corylus 5.2 0.3 0.4 3.1 6.1 4.6 6.1

Pollen sum 6948 1735 870 4537 1842 2084 2235

Larix 15.2 0.2 0.14 2.1 1.5 0.9 0.6 Picea 2.8 0.1 0.2 1.1 1.8 3.3 3.3

Spectra 29-47 4,5,6. 3-13 200- 125- 40- 15-97 used for 11-17 380 cm 275 cm 510 cm cm

Picea; cm

32-47

for

Larix

into an is spectra average value from a zone that lasted ens Pond in zone 3. That Corylus was close by a time long (it denies changes that certainly took indicated by its peak at the single sample Xr. 28, place), still this value will when found. be useful the varia- where also clusters of Corylus pollen were tions of the Tilia at pollen percentages are not too large. The percentages of Acer saccharum and This is in a general way one of the very character- Stevens Pond are much the same as those at Clear- istics of a pollen zone. water. Because at Clearwater Acer and Tilia are

At the based the de- also must have but any rate, percentages upon essentially absent, they played eiduous-tree of individual pollen sum the spectra for a minor part in the vegetation at Stevens Pond.

Stevens and Martin Pond in Pond, Bog I), compared I was unable to match surface samples the per- with the from the for average percentages recent sur- centages found for Ostrya/Carpinus in zone 3 face samples at Lake Sylvia (S) and Clearwater all the sites in the Itasca State Park region. Ostrya

are shown 7. (C) in Figure For Terhell and Reichow must have taken a much bigger share in the vegetation ponds no adjusted curves have been included in than in the present forest at Clearwater.

Figure 7, mainly because the time-stratigraphic iden- In Figure 6 the Ulmus and Quercus values start tity that in a exists between the level Clearwater, but general way spectra at the same percentage as at of Stevens Martin and D is rise at Pond, Pond, Bog pond Ulmus and Ostrya the expense of Quercus between these and the Rei- towards the of the tendency certainly lacking ponds top zone, indicating a chow and Terhell Ponds. For these latter two ponds towards more mesic conditions. Ulmus, however, does the reference at only to the recalculated percentages is not reach the values found for the Big Woods found in Table 2. Lake Sylvia. Accordingly it must have been sub-

2 and 6 From Table Figure it appears that the ordinate to Quercus in the vegetation at this time- pollen percentages of Stevens Pond resemble most Thus, in spite of the fact that pollen grains from 3 those of the xerophytic Quercus forest at Clear- mesic forest elements reach higher values in zone water. Both sites show high percentages of Quercus than elsewhere in the profile, the general impression

and low values of Ulnms, Tilia, and Acer saccharum. of the forest around Stevens Pond during deposition The at Stevens Pond is of 3 is that it forest. average Corylus percentage zone was a xerophytic Quercus about the in Mc- same as MeAndrews sites. The very This is in agreement with the assumption of low values for Corylus at Lake Sylvia and Clear- Andrews that Quercus forests dominated the up- water are a result of its absence in the surrounding lands in the Itasca State Park area. The average forest. The conclusion is that are Corylus (either C. percentages at Stevens Pond for pollen types americana C. Pond, or cornuta or both) was part of the the same as those for Bog D and Martin understory of the forest Quercus surrounding Stev- except for Ostrya/Carpinus, which is much lower, Spring 1967 A Postglacial Pollen Diagram from a Small Typha Swamp 155

and Quercus, which is higher. The lower percentages grains, suggesting that indeed Betula papyrifera is of Ostrya/Carpinus may result from a difference in involved. soil: Stevens Pond is situated on a level outwash If Pinus was absent during zone-3 time, then the plain, which today carries a xerophytic Pinus bank- rise of pine pollen throughout the zone is a reflection siana forest, in contrast to the tills around Bog D of the approaching coniferous elements from the

and Martin Ponds, which are covered by less xero- east. A majority of the determinable pine pollen found also phytic Populus tremuloides or Pinus resinosa forests. belongs to the Pinus strobus type, as was

The higher Quercus values at Stevens Pond may also by McAndrews. be a result of these soil difffferenees, although they 27 Pinus strobus be extralocal effect. zone 4, spectra 9 through : may an Zone Itasca Assemblage In contrast to the State Park area, Terhell

tills of the Des Moines lobe value and Reichow Ponds on In zone 4 Pinus reaches a maximum exceed- show higher values of Tilia and Ulmus in the Quer- ing 80%. Quercus, Ambrosia, Artemisia, and Cheno- but still far cus/Ostrya assemblage zone, they are podiaceae/Amaranthaeeae have their lowest percent- lower than in the Woods of forest Big type near ages in the diagram.

on these rich St. Cloud, indicating that even here The lower boundary of the zone is characterized of soils no Big Woods type existed during the time by the following features: zone 3. 1. Quercus, Ulmus, and Ostrya/Carpinus complete Sanieula pollen grains are scattered in zone 3. of their steady decrease from the upper part According to the vegetation studies in the Itasca the previous zone. State Park region Sanicula marilandica, though 2. Pinus exceeds 80%. present in most of the upland forest types, reaches 3. The Tilia curve becomes interrupted. its optimum in Quercus forests (the so-called Dier- 4. The Abies percentages show a small hut con- villeto-Quercion), not in the highly mesie Acer-Tilia- sistent rise. well Ulmus communities. This agrees with conclu-

of the sions based upon the percentages tree-pollen In Table 3 and Figure 8 all the pollen data were

grains. recalculated on a sum that includes the deciduous of Betula Although not primary concern here, pollen types of the previous table plus Pinus and

have been an papyrifera may important component Abies, on the assumption that the regional vegeta- in the lower in the Quercus forest, especially part tion during this time had the character of a conifer-

of the zone. At the boundary between zones 2 and hardwood forest (McAndrews 1966). Picea and

3 to then because of the Betula curve abruptly jumps up 35%, Larix, however, were excluded probable

drops off slowly. McAndrews found a prominent local origin.

D rise in the curve of Betula at Bog and Martin The surface samples used for comparisons with

Ponds and concluded on the basis of fruits that the zone 4 of Stevens Pond were taken at 4 sites of species primarily represented was Betula papyrifera. similar size surrounded by different types of upland

It would have been the earliest invader. At Stevens forest. That at Floating Bog has Tilia americana

of 3 sudden and americana Fraxinus Pond we find at the base zone a shift dominant Ulmus and penn- in the size frequencies towards the larger-sized Betula sylvanica codominant. At Bohall Pinus resinosa is

Table 3. Average pollen percentages for some trees, based upon the coniferous-deciduous pollen sum (exclud- ing Picea and Larix)

Recent

Extra- Stevens Stevens Bog A Bog D Cindy Martin Extra- local,local, Pond Pond Pond Pond Pond Pond local,local, French Extra- Extra- Regional,

— Floating Creek local, local,local, ItascaItasca

Zone 4 5 4 4 4 4 Bog Bog Bohall Beauty areaarea

Abies 1.2 3.6 0.65 0.32 0.32 0.390.39 2.62.6 5.6 1.6 0.32 1.40

82.2 64.2 78.4 93.2 74.5 80.8 PmusPin us 92.0 85.7 81.1 82.7 83.4 82.2 64.2 78.4 93.2 74.5 80.8

Acer saccharum 0.09 0.11 0.35 0.35 0.05 0.23 0.2 0.07 0.04 0.13 —

OstryaOstrya 0.63 0.24 3.93 2.4 3.3 4.4 0.95 0.18 0.19 0.29 0.39

Oorylus 0.91 0.63 0.95 1.47 1.46 1.04 1.9 0.93 1.9 3.8 0.75 0.13 4.8 0.16 0.15 0.09 0.16 Tilia 0.08 0.1 0.17 0.03 0.09

Ulmus 0.760.70 1.1 1.581.58 1.77 1.10 1.26 4.5 1.5 0.35 1.3 1.61

Quercus 3.68 6.6 10.2 8.26 8.26 8.23 11.6 9.3 2.4 15.2 8.30

Pollen sum 19161 8337 1681 3211 3103 2443 2526 54716471 2606 3157

Picea 3.85 1.6 0.45 2.4 1.14 1.42

Larix 0.11 0.26 3.42 3.5 0.55 0.74

Spectra used 10-27 1-9 20-60 40-180 20-90 20-105 4-12 17-22 1-5 3-10 5-10 1-3 Ecological Monographs 156 C. R. Janssen Vol. 37, No. 2

Fig. 8. Comparison of average recent extralocal pollen percentages of some tree for surface samples

4 of 3 of three sediment based coniferous-decidu- with zone and 5 and the upper part zone cores, on the

tree ous pollen sum.

and rise in the bracket dominant and Abies balsamea Betula papyrifera high percentage means a larger codominant. At French Creek Bog, Pinus resinosa increase of actual pollen numbers deposited than in the lower bracket and P. banksiana are dominant and Abies, Betula, percentage (law of diminishing and Populus codominant. The Beauty traverse is returns; Faegri & Iversen 1964). The differences characterized by dominant Populus tremuloides and between the sites are better demonstrated in Figure

Betula and papyrifera frequent Quercus macrocarpa. 9, which shows the Pinus curves based upon a pollen

The best correlation is found with Bohall, which sum of deciduous trees (the pollen sum used in Fig.

7 that the has the same high values for pine and same low for zone 3). If we assume total pollen values for Quercus. Deciduous elements such as deposition of deciduous-tree pollen remained fairly

Acer saccharum, Ostrya virginiana, Tilia americana, constant throughout zone 3, then the gradual rise of in this reflects the Ulmus americana, and Quercus sp. are completely pine zone approach of the lacking in the forest at Bohall. Because the pollen conifer-hardwood belt from the east. Alternatively, the percentages of these trees are approximately pines already slowly migrated into the region dur- Bohall and in 4 of Stevens these time and deciduous same at zone Pond, ing zone-3 actually replaced trees, forest elements were probably lacking in the pine thus resulting in a decline of the total pollen deposi- around Stevens Pond at that time. tion of the deciduous elements and a rise in pine

The mature Pinus resinosa forest at Bohall locally values in zone 3 to levels consistently higher than

scattered Abies balsamea. For Stevens those at D and Martin Pond. It is not has young Bog very the Pond in zone 4, the values for Abies are about likely that this difference reflects different distances

are conifer belt in the because Stevens same as the regional recent percentages. They from a east,

values found at the and D to higher than the regional sites of Pond Bog are very close each other. Per-

McAndrews, but the differences are small, so extra- haps the regional vegetation on the outwash plain

not occurred Stevens Stevens Pond included local Abies may have around around already some pine

Pond. The rise of Abies in zone 4 must have been during zone-3 time. Today we And Pinus banksiana

in largely a regional feature. on such sandy areas the Itasca State Park region

The values for pine at the 4 sites investigated by as well as in the deciduous forest of the Twin Lakes of the Stone Moraine. McAndrews all are slightly lower than those at drainageway east Big of deciduous Stevens Pond. They are about the same as the Certainly actual replacement elements

9 average regional recent percentage. Apparently by pine took place in zone 4. Figure shows in size that Pinus fails 4 Pinus between 300 and these ponds are of such a to zone percentages 900% show at and an extralocal value, even though they may have Bog D, Bog A, Martin, Cindy ponds. Stevens been surrounded by pine forests. One might ask Pond however, shows Pinus percentages between whether the difference of ca. 10% that exist between 1100 and 1800%, reflecting extralocal values. The rise transition Stevens Pond and the 4 sites of McAndrews is sig- steep of pine at the of zone 3 to zone

realize 4 Stevens Pond mean that that level nificant. It is, if we that a same percentage at may at Spring 1967 A Postglacial Pollen Diagram from a Small Typha Swamp 157

sites in the Itasca State Park for Fig. 9. Curves for Pinus at 5 region zones 3, 4, and 5, based upon

the deciduous-tree pollen sum. For explanation see text.

Finns arrived shore of Stevens of Ambrosia Above at the Pond, re- type (Fig. 10). spectrum 5 the placing the xerophytic Quercus forest of the previous extralocal addition of pine pollen to the total pollen zone. Such a replacement nearby explains why such deposition ceases, and as a result a relative rise in of a steep rise is absent at the other sites. The Pinus percentage other pollen types is possible. Above curve here merely ends its steady increase of zone 3, spectrum 5 Finns thus shows regional values again. and above this it remains at a constant level. The Betula pollen grains in zone 4 continue to be

forest around Stevens Pond have been of the Betula size. pine may largely papyrifera either Pinus banksiana or P. resinosa rather than zone 5, spectra 1 through 8: Ambrosia P. strobus, according to the ratio of pine pollen Zone types (Fig. 4). The increase is present also at Bog Assemblage

D and Martin but there it is less Zone 5 is Ponds, important, characterized by a rise in the curves for the soils perhaps because are on till rather than on Ambrosia type, Chenopodiaceae/Amaranthaceae, and outwash sand. Between 5 and 6 at Stevens and the spectra Abies appearance of pollen grains of culti- Pond the Pinus values decrease the level to same vated cereals (Avena type, Zea mays). Pollen grains at the other sites. At this level Pinus have as may of cf. Melilotus, Trifolium pratense type, and Tri-

from around Stevens Pond as a result disappeared folium repens, all introduced from Europe and of clearance by white settlers at the turn of the present today in disturbed sites, have been found in

event also marked the rise in the Other century, an by pollen samples. pollen grains from plants ac- 158 C. R. Janssen Ecological Monographs Vol. 37, No. 2

Fig. 10. Selected curves in the upper part of the Stevens Pond diagram

the other the rise reflect of companying cultivation are Melandrium type, An- hand, may the expansion

themis type, and (not exclusively) Asteraceae (Liguli- Abies balsamea trees with suppression of fires in the 50 & Cantlon florae). The logging and cultivation of the area past yr (Buell 1951). around Stevens Pond resulted in a complete change of the local vegetation to the Typha latifolia mat of Development of the Local Vegetation today. The development of the local vegetation is repre- Figure 10 shows enlarged some of the events of sented in Figure 5, which shows the pollen curves of 8 sediment the transition. Between spectra and 9 the the lowland In the types. general, pollen types are from forest to reflected in changes peat Typha peat, to arranged according their stratigraphic appear- the diagram by the drop in Pieea, the disappearance ance, which is closely related to the floristic com- of Ledum, and the strong increase of Typha latifolia. position of plant communities representing the Pollen grains from cereals and from plants accom- in lake stages filling. In Figures 3 and 11 some of cultivation above this level Am- panying occur only. brosia and Chenopodiaceae/Amaranthaceae show their highest percentages. Apparently above this level

(zone 5) the pine forest around Stevens Pond was burned transformed logged or and to the present fields. Indeed we find in this zone the decrease of pine from extraloeal values to regional values (see

Figs. 9, 10) at the level where the percentage of

Bidens type rises. Historic records show that this happened about 1900. Between spectra 8 and 12, before the stratigraphic change, the curves of Am- brosia and Chenopodiaceae/Amaranthaceae rise (zone 11. Fig. General occurrence of main sociological groups that 4b), indicating cultivation was approaching, 3 1,2, and in three major lowland vegetation types. For

Red River to west text for the Valley the was settled for explanation, see under Local Vegetation. 1880. Also shows farming by Typha latifolia a slight rise. Around Stevens Pond forest was still present, the results of a study (Janssen 1967) of the recent but logging and cultivation elsewhere in the area vegetation in the Itasca State Park region are sum- resulted in a regional rise of these 3 pollen types. marized. Only species that disperse recognizable Pollen of Ambrosia type and Chenopodiaceae/Ama- pollen grains have been included. The height of ranthaceae are easily carried by the wind, and sur- the curves on Figure 3 represent steps in the Braun- is face-sample studies showed that Typha among the Blanquet scale for cover and abundance. At the few lowland that in types occur the regional pollen top of the figure are the vegetation plots (releves). rain in forested regions (Benninghoff 1960; Janssen Releves and species have been arranged according to 1966). As mentioned in the presence. introduction, plant No trees occur at present around Stevens Pond, communities have been established on the basis of the rise Abies and of pollen therefore must be a sociological groups, each group including species that feature. It be regional may explained partly by the show the approximately same sociological (ecological) decrease of pine in the pollen rain, resulting in amplitude. higher of the other To percentages pollen types. On facilitate comparison of the local succession Spring 1967 A Postglacial Pollen Diagram from a Small Typha Swamp 159 at Stevens Pond with the recent vegetation types in thus represent the wettest communities in the low- lowland short of the results of land labeled habitats, a summary vegetation. Sociological groups b, c, the in in State drier vegetation study lowlands the Itasca etc., represent ones. Figure 3 thus shows a Park follows. For reference to the of division of the 3 main region species sociological groups along a the 3 moisture 3 sociological groups, Figure may be used, al- gradient roughly on levels of nutrient though it contains only some of the species of the content of the substrate. recent vegetation. The communities heading Figure 3 have been es- The be divided flo- tablished lowland vegetation types can arbitrarily by combining sociological groups. ristically into 3 major units, each characterized by a The pattern of lake filling typical for the not-too- combination basins of the is typical of species. Figure 11 shows, large region easily seen. At the

3 simplified, how sociological groups are distributed margin of a floating Carex mat, especially near a in these 3 units. major creek, a eutrophic vegetation of Typha latifolia,

Unit A a Bidens and Later (Kalmio-Chamaedaphnetea) comprises cernua, Impatiens capensis occurs.

of east- group communities especially present in the stages are represented by Betula pumila shrub,

Larix laricina ern arm of the Lake Agassiz basin, 200 km north- forest, and Picea mariana forest. In east of Stevens Pond, covered mostly by Picea this succession the Typha mat represents the wettest, Larix and mats of Carex. As is most The mariana, laricina, eutrophic stage. later stages represent com- munities shown in Figure 11, species from sociological groups found in a drier, more mesotrophic environ- 2 and 3 absent there. Unit B ment. are comprises a group of communities The local at characterized by sociological group 2. diagram from Stevens Pond shows

These the of to are types vegetation that are very almost every level plants belonging sociological

distributed 3 widely in the very small depressions of groups 1, 2, and and thus is a typical example of the Itasca State Park region and elsewhere. Species the pattern of succession found today in vegetation 1 and 3 also unit B. This is because of the small belonging to sociological groups are not surprising size present in some of the communities of this vegeta- of the basin. tion unit. Unit C (Fraxinetalia nigrae) represents communities ZONE 1 found in the marginal zones between upland and hogs in the Itasca State Park region. In the lower half of zone 1 several pollen types

indicate water: Species from sociological group 3 occur in these shallow open Nuphar, Nymphaea, communities, as well as species that are found ex- Lemna, Myriophyllum, and the alga, Pediastrum.

The is not but clusively here (sociological group 4, not mentioned sediment, however, gyttja Drepano- in Figs. 3, 11). eladus peat. It was impossible to identify the moss several To summarize: to species, but among the possible species

In of occur in a submerged habitat. the upper part in soc. group 1 may be found vegetation types and the zone these pollen types are gone Equisetum belonging to units A and B reaches high percentages. In the lower part of the 2 found soc. group may he in vegetation type and zone pollen grains of Menyanthes are present, belonging to unit B the values for Alnus and Sagittaria are higher than soc. group 3 may he found in vegetation types in the All the upper part of zone. 3 species may belonging to units B and C the water Alnus and have grown along edge. Sagit- units reflect habitat. how- Because these 3 vegetation in a rough taria suggest a eutrophie Menyanthes,

the content of nutrients in the socio- indicates more conditions. way substrate, ever, mesotrophic Myrio-

1 logical group thus contains mainly oligotrophio phyllum is also mesotrophic. It thus remains diffi-

and 3 contains the cult to a of the local in species, group species adapted get fitting picture vegetation to 2 to more eutrophic conditions. Accordingly group zone 1. Perhaps it may be compared the Myrio-

be called The from an association may a mesotrophic group. trophic phyleto-Nupharetum Europe, is in designations are of course relative and are used in a that the starting point of the succession meso- loose here. water. The the thus sense trophic Equisetum at top may “reed” It should he emphasized that the characterization represent an equivalent of the stage. of communities the main groups of by sociological ZONE 2 groups does not mean that all species from such a of the of sociological group are found in all communities of The composition local vegetation zone unit. In each 2 is clearer than in Pollen the vegetation major sociological group previous zones. grains

to a further floristic division is possible. In vegetation from plants belonging sociological groups 2a, 3a, division maximum This units A and B such a reflects a moisture 2d, and 2f show percentages. com- bination gradient. Figure 3 shows some of the subdivisions of species, the high values for Typha lati-

the main he and the of in sociological groups that can made in folia, presence Bidens type point to-

vegetation unit B. The various stages along the wards a vegetation camparable to the Bidenteto-

moisture gradient have been indicated by the letters Typhetum latifoliae.

to of the alphabet. Sociological groups la, 2a, and 3a However, Salix increases up 40%; surface sam- 160 C. R. Janssen Ecological Monographs Yol. 37, No. 2

indicate that of pies relatively high percentages as well. The curves of pollen types belonging to

Salix can be found where Salix shrubs are only sociological groups 2a, 3a (part), 2d, and 2£, char- in the local in actually present vegetation, even tree- acteristic for the Typha latifolia vegetation of the less (Welten not mentioned regions 1950). Though previous zone, decrease strongly or discontinue. in 3, Salix (e.g. Salix candida) are Figure spp. However, several pollen types that occur in zone 2b abundant in the Cariceto-Betuletum The do not decrease well pumilae. (sociological group 2c, as as abundance of of pollen Cyperaceae and Betula pumila Alnus, Scutellaria type, and Lycopus type from also to a to the point vegetation comparable present group 3a). Alnus shows a slight rise at the base of Cariceto-Betuletum This contains pumilae. plants the zone. from sociological 1 ( Comarum palustre and Additions the group to pollen assemblage are plants

Menyanthes the shows to and trifoliata) ; pollen diagram belonging sociological group la, lb, 1c, Id,

low Comarum a percentage of palustre type but no 3b. From 3 Figure it appears that this assemblage to Menyanthes. According Figure 3, Menyanthes fits best that of a Larix laricina forest. The con-

trifoliata is absent where Typha latifolia is very tinuous presence of pollen types from sociological abundant. Surface from samples a Typha latifolia 2c and 3a is in with groups perfectly agreement this, mat (Lake Sylvia: Janssen 1966) show relatively because the plants involved are also present in the of the high percentages same pollen types as found recent vegetation of the Larix laricina forests as at Stevens Pond in zone 2: Typha latifolia, Sagit- as in mats. well Carex Pollen of Sarracenia purpurea taria, Lysimachia thyrsiflora, Sparganium type, Bid- also occurs—this plant is found today mostly in ens type, cf. Stellaria longifolia, and Dryopteris type. Larix forests where its pollen shows up in surface

Salix reaches a value of 10% in one of these sam- samples (French Creek Bog). ples in a narrow band of low Salix shrub. Pollen Larix pollen reaches a value of 10%, or 15.2% grains of Impatiens found at Lake Sylvia are if based upon the deciduous-tree pollen sum (Table lacking at Stevens Pond, however, and the values for 2), much higher than the more regional values found Cyperaceae are much lower. We thus conclude may at Martin and Bog D Ponds. Larix must have -oc- from the pollen record that the local vegetation for curred in the local bog vegetation.

zone 2 at Stevens Pond was basically a Typha mat A good agreement exists between the pollen as-

with much Salix but with some of the ele- shrub, found in surface sam- semblage in zone 3 and that

ments of a Carex mat. recent ples in a Larix laricina bog (French Creek In many pollen diagrams from Minnesota in the Bog). However, some important constituents of correlative with Stevens Pond assemblage zone zone not French Creek Bog were probably very abundant 2, the percentages for aquatic plants are slightly at Stevens Pond (e.g. Ledum, Sphagnum, Erieaeae). higher than below or above, indicating lower water Also, the percentages of Cyperaceae pollen are higher levels and the of marsh thereby expansion plants at Stevens Pond, perhaps reflecting the Carex-mat and shallow-water plants (e.g. Bog D and Martin character of the local vegetation. Altogether, the Ponds of McAndrews 1966; Kirchner Marsh and Larix forest in zone 3 shows a vegetation different Lake Carlson of Wright et al. 1963 and Watts & from that of recent Larix laricina forests. This dem-

Winter 1966). At Stevens Pond these features are stated in onstrates clearly that, as the introduction, much exaggerated because of the local occurrence recent vegetation types are not fully comparable a of The these marsh plants. same applies for Salix, fossil in the late Holocene. priori to types, even which also shows a slight rise in some of the other The percentages of the Poaceae pollen are much Minnesota mentioned above. diagrams with 2. This is in diminished compared zone agree- Spores of Dryopteris type show an abrupt rise at ment with the change from savanna vegetation,

the base of the but then a decrease toward the zone, to where grasses play a large role, forest vegetation. top. Such a rise is present at Cedar Bog Lake The percentages are higher, however, than those

1963). At both localities with a (Cushing spores in found in surface samples upland forests. In con- preserved perisporium were present and thus could trast to zone 2, the pollen grains belong to one type identified be as Dryopteris thelypteris. Cushing con- only. Probably most of the Poaceae pollen thus is of siders this the time of maximum in zone as dryness, local origin. which and Carex in Typha latifolia mats expanded shows than in Picea pollen a higher percentage former as a result of lake levels. bays falling 2. the de- zone The average for Picea based upon As at Cedar Bog Lake, the pollen grains tend to ciduous-tree pollen sum (Table 2) is slightly higher be corroded in zone 2a (see below), especially to- than that found at Bog D and Martin Pond. There ward the base. at Stevens Pond in of Possibly part is not much difference, however, from the values at

the assumed time of dryness no accumulated, peat Terhell and Reiehow Ponds, where Picea is absent. and a sharp break at the boundary between 1 and Picea therefore must have come from the local vege- 2 resulted. tation at Stevens Pond at the time of Zone 3, and

ZONE 3 its rise in zone 2 is a regional feature, perhaps a The abrupt change from zone 2 to zone 3 in the result of the approaching coniferous forests from the

upland diagram is present in the lowland diagram east (compare also Pinus). A Postglacial Spring 1967 Pollen Diagram from a Small Typha Swamp 161

The survey of the recent lowland vegetation (Fig. a change in the vegetation surrounding the pond

indicates that Betula is does not from 3) pumila an important appear until zone 5. Pollen grains

in the Larix laricina to component shrub layer of plants belonging sociological group 3b and 1, forests. Stevens Although at Pond most of the including Larix, are absent in zone 5. Picea drops Betula pollen grains belong to the larger B. papyri- to regional values, and Typha latifolia and Bidens the fera type, some of size-frequency curves for type rise to maximum values. The sediment changes both zones 3 and 4 show a small peak at the smaller from woody peat to Typha peat. This pollen se-

the of the from the size, reflecting occurrence local Betula pumila. quence suggests transformation oligo-

Recent surface samples in comparable vegetation trophic bog forest to the recent eutrophic Typha

seem to indicate an equally small share of local latifolia vegetation. The pollen assemblage resembles

Betula in the that in 2 pumila pollen rain when Betula found zone but is much in papyri- poorer types, is the fera present on upland. lacking pollen grains from sociological groups 2a, A change in the pollen assemblage of zone 3 oc- 2d, and 2f.

curs between spectra 31 and 32. Larix, Salix, and Comarum type decrease, and other pollen grains all THE LOCAL LOWLAND VEGETATION AND

to belonging sociological groups la, lb, and 1c ITS RELATION TO THE UPLAND disappear. The for is still curve Dryopteris type con- VEGETATION tinuous. Picea rises. Figure 3 shows that these The succession of the local vegetation at Stevens are reflection changes a of a replacement of the 5 Pond from zone 2 up to zone resembles that of Larix laricina forest by a Picea mariana forest. the recent of lake It starts with a The process filling. percentage of Picea pollen points in the same pollen assemblage comprising typical Carex mat direction. Table 3 shows that spe- the average Picea per- forest cies, then proceeds through a Larix laricina based centage upon the coniferous-deciduous pollen into a mariana forest. Each successional stage is Picea sum 3.85%, well above the regional presettlement is accompanied by the same associates found today percentages for that tree, in spite of the fact that it in comparable vegetation. The succession proceeded is depressed by the high extralocal pine values. This drier from a eutrophic wet habitat to a mesotrophie indicates that from spectrum 31 upward Picea environment. Ecologically this is a succession com- locally occurred at Stevens Pond; on account of its suffi- mon in most parts of temperate regions with ecology, it was mainly Picea mariana. cient precipitation. The increasing thickness of ac-

matter results in the exclusion ZONE 4 cumulating organic

of nutrient-rich groundwater and thus in an acidifi- At the base of zone 4 Sphagnum rises to distinct cation of the environment. local values, and Ledum and the other ericaceous

Indications of the same can be found The development types appear. curve for the Dryopteris type in other diagrams from various regions in Minnesota ends. From this level upward the local bog forest D Pond of Cedar Lake of shows (Bog McAndrews; Bog the pollen assemblage that is typical for the Cushing 1963; Weber Lake of Fries 1962), which recent Picea forest. mariana There is also a good show after the prairie period a rise in Larix and agreement with the local pollen assemblage found after that at Bog D a rise of Picea. The pollen in surface samples in the Picea mariana forest at assemblages at these sites, however, do not contain French Creek Bog. There are also pollen grains of forest local. bog herbs, because there the bog was not Arceuthobium, a parasite on Picea mariana. The The present bog vegetation of the Larix and Picea size frequencies for Betula continue to indicate that with lowland forest shows a strong floristic affinity only a small part of the Betula pollen rain is from both lowland and upland vegetation of the boreal Betula The Larix pumila. percentages are very low, forest. This not for shrubs such as lower than the applies only even average regional values for the Ledum but also for the trees Larix tree found at and groenlandicum Martin Cindy Ponds. The average laricina and Picea mariana. to Transeau values D and A According at Bog Bog ponds are higher be- (1903), after the retreat of the ice the bog species cause of the probable extralocal occurrence of Larix

were widely distributed all over the region just as at these sites. These low values at Stevens Pond in the north. Since then these indicate that Larix absent they are today plants was in the local vegeta- have in where other tion. the disappeared except bogs, species However, continuous scattered occurrences invading the area during the Holocene could not of pollen grains of Utricularia and, especially in the follow account of the extreme environment there. and on upper part of the zone, the rise of Salix Com- to him the bog forest thus is a relic from indicate According arum palustre type that still Larix was late-glacial time. The diagrams of Stevens Pond, present, so the local vegetation must have been a and Cedar Lake show that char- mixed Larix laricina-Picea mariana forest. Bog D, Bog plants

acteristic for the bog communities, at least in these

ZONE 5 of the relics from wide- parts state, are not a once

The in boreal forest. the time of 2 regional diagram shows the upper part of spread During zone

zone 4 (zone 4b) the approaching cultivation, but these species were absent. They have been re-intro- 162 C. R. Janssen Ecological Monographs Vol. 37, No. 2

Table 4. Relation of local to extralocal vegetation in a low content of exchangeable bases (Zinke 1962).

Stevens Pond sequence, after the prairie period. It is quite conceivable that because of these differ-

ences the of from forest chemistry the runoff a pine

Pollen InterpretationInterpretationof the InterpretationInterpretation of the is quite different from that of a deciduous forest,

zone extralocal vegetation local vegetation influencing the nature of the local vegetation in the

pond. In the present vegetation of the Itasca State Cultivated fields after Typha latifolia mat Park exists. the 5 logging of the pinepine region such a relationship often In

forest. contact zone between bogs and a deciduous type of

forest, usually a broad belt of Fraxinus Pinus forest Picea mariana forest with eutrophie Between Larix. Ericaceae in the nigra-Ulmus americana forest is present.

4 understory. Sphagnum and bogs pine forest, however, such a belt is narrow important in the moss or lacking. This mechanism would explain why at layer the Stevens Pond there was a delay in introduction

Picea mariana forest with of Sphagnum, Ledum, and the other Ericaceae, com- Larix. No Ericaceae pared to the usual succession in the lake Ailing.

These elements are in the recent Larix lari- Xeric Quercus forest, Larix laricina forest present

33 increasingly mesic without Ericaceae andand cina and Picea mariana forest, but they were intro- towards the of the Salix im- towards top the Sphagnum. earlier duced at Stevens Pond no than the postulated zone portant in understoryunderstory change in the extralocal vegetation from Quercus runoff Quercus savanna with Salix shrub with much forest to Pinus forest (base of zone 4). The 2b Corylus understory. Typha latifolia from the pine forest would stop the inflow of nu- Prairie vegetation trients into the pond, allowing the introduction of present locally species highly adapted to an acid environment.

The same mechanism would perhaps account for

duced in the lowland vegetation after the prairie the drop of Fraxinus nigra type at the base of zone period. 4, for Fraxinus nigra occurs especially in the mar-

between and deciduous of The diagram of Stevens Pond reveals a close re- ginal zone bogs types

lationship between the development of the local and forest.

the extralooal vegetation. In the upland diagram The recent distribution of Pinus, Picea mariana,

the top boundaries of zones 2a, 2b, 3, and 4 are all Ledum groenlandicum, and Larix laricina point to- reflected in the local diagram. The regional pollen wards the same relationships. Of the 3 pines present assemblages for each zone are accompanied by their 4 these own local pollen assemblages. In Table relationships are summarized.

These interrelations are in the first place a result of the way the data are presented. The percentages

have been calculated the of the local components on basis of the upland pollen sum. They thus are de-

pendent on the absolute regional pollen precipita-

tion per unit surface. It is not unlikely that a

change in the absolute pollen rain occurs especially

at the transitions in the regional pollen diagram,

thus affecting the local pollen percentages.

The variations in the local diagram, however, are

too big to be attributed solely to this phenomenon.

There must be some other reason for the simultaneous

development of the extralocal and local vegetation.

factors be taken into consideration. Two may Changes

in climate are probable since the prairie period

(McAndrews 1966), and it is not unlikely that they

influenced both the upland and lowland vegetation.

The present diagram, however, does not particularly

show the influence of climate in its pollen curves, because it registers mainly local features.

In a small site like Stevens Pond the extralocal

influence the local vegetation may vegetation by

means of its runoff. The chemical properties of coni- Fig. 12. Distribution of Pinus banksiana (from fer from litter are quite different those of deciduous Schoenike 1962), Larix laricina (from Rowe 1957), trees. As result the soil a underneath a conifer for- and Picea mariana (from Heinselman 1957) in Minne-

est or even under a single tree shows a low pH and sota. Spring 1967 A Postglacial Pollen Diagram from a Small Typha Swamp 163

in Minnesota Pinus most to not banksiana ranges the on the pollen diagram is so large that correla- west and southwest and therefore has been used in tion with diagrams from larger basins becomes diffi-

the following comparison of ranges. Figure 12 shows cult. The relative unimportance of the extralocal

that the western limits of Picea mariana and P. effect at Stevens Pond from may result 2 factors:

banksiana are approximately the same. The area of 1. The dispersion curves fall very rapidly even over Larix laricina extends much more to the west, cover- short distances as was also noted in the surface- ing the deciduous forest belt in Minnesota. Distribu- sample study. tion for Picea maps mariana (Heinselman 1957), 2. The extralocal vegetation (the vegetation on the Pinus banksiana (Rudolph 1958), and Larix laricina uplands adjacent to Stevens Pond) was not (Roe that 1957) suggest the same applies for Wis- markedly different from the overall vegetation consin and Michigan. in the region. A larger extraloeal effect might The relation between local and extralocal vegeta- be expected when the extralocal vegetation is tion is most at the of evident top zone 4. The logging quite different. of the pine forest around Stevens Pond resulted in increase an of nutrients in the forest soil. Moreover, The Stevens Pond diagram does not show clearly a

cores from the of margin Stevens Pond show a cap raised percentage of upland herbs because of the

of sand that can be attributed to the sheet erosion short distance to the upland (except perhaps Sani-

caused cula most herbs by exposure of the soil after logging. The in zone 3). Apparently pollen from inflow of nutrients in the This that for small resulting to pond destroyed has short dispersal. means ponds the from mesotrophic bog forest, turning it to the present the upland forest type can not be determined

eutrophic Typha latifolia mat. the pollen of characteristic upland-forest herbs. This

The influence of the result surface upland vegetation upon the also is essentially the same as found in

lowland vegetation is of course most effective in samples from comparable small basins.

small ponds or along the margin of larger basins. A completely different picture, however, is shown

In those a non-coniferous is the Local areas vegetation a re- by local vegetation. pollen types are many"

factor in the establishment of and and each is in stricting a true bog characteristic, type represented In the of the sediment and in surface vegetation. center larger basins such an samples by relatively influence is less important, but here frequently ex- large numbers. Because of this local effect the de-

cessive moisture be the in basin might limiting factor. Thus velopment of the vegetation the can be in regions close to the prairie-forest border, which followed in detail.

saw the extermination of the early Holocene pine SUMMARY forests the during prairie period, bog plants are

new arrivals in the late Holocene and not relics from The pollen assemblages of a core in the conifer-

the late-glacial. More to the east, however, the im- hardwood formation in northwestern Minnesota are pact of the prairie expansion in the mid-Holocene compared with the floristics of the recent vegetation in was less, and Pinus is present in relatively high the region. Percentage levels of the main tree

values throughout the Holocene (Weber Lake of components have been compared first with those from

Fries 1962). Persistence of bog plants might be recent surface samples taken at the same short dis-

most likely in those regions. tance from various types of upland forests and

second with the regional values of the pollen rain

in this LOCAL, EXTRALOCAL, AND REGIONAL area (McAndrews 1966). To that end all the data POLLEN RAIN were recalculated on the basis of special

pollen sums. As mentioned in the introduction, the small-sized The regional diagram of Stevens Pond shows basi-

Stevens Pond was selected to determine the influence cally the same assemblage zones as established by of a particular type of upland forest close to the McAndrews but without the late-glacial Picea-Popu- sampling site, i.e. the extraloeal effect of pollen lus assemblage zone. The pollen in the following types. Pinus-Pteridium assemblage zone has been interpreted The Stevens Pond diagram shows 2 or 3 features as derived from a pine forest. During the mid- that may be considered a result of the extralocal postglacial expansion of the prairie eastwards the effect. In zone 2 shows high values not Corylus yet must regional vegetation have been a Quercus savan- found in diagrams from larger basins in Minnesota. na, locally with prairie. Corylus reaches relatively In zone 3 Quercus is higher in the adjusted diagrams, high percentages in this zone. Among the prairie and in 4 zone the percentage of Pinus shows a dis- elements especially the occurrence of Lilium phila- tinct rise compared with the values fróm larger In next delphicum may be noted. the zone the basins. In the latter case the Pinus rise also has the pollen diagram shows a rise of curves of mesic found in been surface samples from a small bog elements. In spite of this the comparison with recent surrounded by pine forests. surface indicates samples a xerophytic Quercus

for some tree elements an extralocal Although forest rather than a mesophytic deciduous forest. effect is the influence of this In the Pinus present, phenomenon following assemblage zone pine was 164 C. K. Janssen Ecological Monographs Vol. 37, No. 2

present along the margin of Stevens Pond and is Davis, M. B. 1963. On the theory of pollen analysis. Amer. J. Sei. 261: 897-912 therefore overrepresented in the diagram. In the H. 1962. und floristische effect Doing, Systematische Ordnung uppermost zone the pollen curves show the Zusammensetzung Niederlandischer Wald- und Ge- of of the forest about 1900. Pollen of culti- logging Wentia biisehgesellschaften. 8, 85 p. vated and introduced plants in this zone. appear Erdtman, G. 1943. An introduction to pollen analysis.

local were found, on account Chronica Many pollen types Botanica Co., Waltham, Mass. 239 p.

of local overrepresentation. This made it possible . 1952. Pollen morphology and plant taxonomy. Pond with the Angiosperms. Chronica Botanica Co., Waltham, Mass. to compare the local Stevens sequence

539 p. composition of recent lowland vegetation types. The Erdtman, G., B. Berglund & J. Praglowski. 1961. An similar a extent to the pollen was to large sequence to introduction a Scandinavian pollen flora. Almqvist recent of lake filling, starting with a pattern 92 & Wiksell, Stockholm. p. of Typha latifolia and Salix eutrophic vegetation Ewing, J. 1924. Plant succession of the brush prairie

a Larix forest in the prairie period and leading to of northwestern Minnesota. J. Ecol. 12: 238-266.

Picea mariana & Iversen. 1964. of and then to a mesotrophic forest, the Faegri, K. J. Textbook pollen

soils. There is a analysis. Munksgaard, Copenhagen. 237 p. present edaphic climax on peaty Fernald, M. L. 1950. Gray’s manual of botany, 8th delay, however, in the introduction of acidophilous ed. American Book Co., New York. 1632 p. species, the Larix forest being without Sphagnum Fries, M. 1962. Pollen profiles of late Pleistocene and and Ericaceae. This is explained by assuming an Recent sediments from Weber Lake, Minnesota. Ecol- influence of the of the surrounding slopes vegetation ogy 43: 295-308. the the local About 1900 bog M. L. 1957. Silvieal characteristics of upon vegetation. Heinselman,

and black Lake States Forest Exp. Sta. Pap. forest was destroyed by logging operations spruce. 45, 30 replaced by the present Typha latifolia mat. p. Helmich, D. E. 1963. Pollen morphology in the maples

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Univ. Minnesota. 165 p. Schoenike, R. E. 1962. The distribution of jack pine Spring 1967 A Postglacial Pollen Diagram from a Small Typha Swamp 165

Fig. 13. 1. Sanicula marilandica, fossil, spectrum 41, 2. Comarum palustre type, fossil, spectrum 47,

3. Trifolium pratense type, fossil, spectrum 2, 4. Petalostemum purpureum, fossil, spectrum 59, 5. Amorpha

canescens, fossil, spectrum 53, 6. Shepherdia canadensis, fossil, spectrum 87. Ca. 1700x. 166 C. R. Janssen Ecological Monographs Yol. 37. No. 2

Fig. 14. 7. Shepherdia argentea, fossil, spectrum 84; 8. Rhus glabra type, fossil, spectrum 86; 9. Lilium 10. Rumex orbiculatus philadelphicum, fossil, spectrum 48; type, fossil, spectrum 51; 11. Arceuthobium, fossil, spectrum 16; 12. Sarcobatus, fossil, spectrum 36. Ca. 1700x. Spring 1967 A Postglacial Pollen Diagram from a Small Typha Swamp 167

Fig. 15. 13. Lysimachia thyrsiflora, fossil, spectrum 27; 14. Bidens type, fossil, spectrum 3; 15. cf.

Stellaria longifolia, fossil, 50, 16. Melandrium fossil, 17. Sarracenia spectrum type, spectrum 3; purpurea, fossil, spectrum 40; 18. Ledum, fossil, spectrum 18; 19. Gaultheria procumbens, fossil, spectrum 84; 20. Triglochin, recent. Ca. 1700x. Monographs 168 C. R. Janssen Ecological Vol. 37, No. 2

in Minnesota. Univ. Minn. School Forest. Spec. Publ. equatorial view. Grain large (36-42 |j_). Includes

Rhus and R. both 1, 57 p. glabra (4) typhina (2), upland

Smith, A. G. 1958. Pollen analytical investigations of species.

the mire at Fallaholgy Td., Co. Derry. Proc. Eoyal Rhus radicans type. Also tricolporate and striato-

Irish Acad. 50 B(16): 329-343. reticulate, but size smaller (ca. 24 (i). Includes

Styx, E. 1960. Pollenmorphologische Untersuchungen Rhus radicans (2) and R. vernix (3), both lowland

an Compositen. Grana Palynol. 2: 41-104. species.

Tauber, H. 1965. Differential pollen dispersion and the

interpretation of pollen diagrams. Danmark Geolo- APIACEAE

giske Undersogelse, R. 2, Nr. 89, 69 p. Cicuta type. Trieolporate, shape compressed-con- Thieret, J. W. 1964. Botanical survey along the Yel- stricted, oval. Structure rather coarse. Costae colpi lowknife Highway, Northwest Territories, Canada. thick, broad. Borders of endocolpus parallel. Col- So. Methodist Univ., Sida, Contrib. Bot. 1: 187-256. pus in equatorial view visible up to the margin of E. N. 1903. On the distribution Transeau, geographic Polar axis 25-30 ratio of the grain. jj. long; length and ecological relations of the bog plant societies of of poplar to equatorial axis (P/E) 1.9-2.1. In- northern North America. Bot. Gaz. 36:401-420. cludes Cicuta bulbifera (1) and C. maculata (2). Troels-Smith, J. 1955. Karakterisering af lose jordarter. Sanicula (Fig. 13-1). Tricolporate, shape compressed- Danmarks Geologiske Undersogelse, R. 4, 3(10), oval or very slightly constricted-oval. Perprolate, 73 p. 2.0-2.3. Grain axis 50 P/E large, polar ca. p.. Yogi, R. J. 1964. Vegetational history of Crex mea- Colpus in equatorial view visible up to the margin dows, a prairie savanna in northwestern Wisconsin. of the grain. Borders of endoeolpus parallel, or Amer. Midland Natur. 72: 157-175. endoeolpus slightly oval. Endoeolpus broad, up to Watts, W. A. & T. C. Winter. 1966. Plant macrofossils ca. 6 Costae medium. Includes S. p.. endocolpi from Kirchner Marsh, southeastern Minnesota —a marilandica and S. (1) europaea (3). paleoecological study. Bull. Geol. Soc. Amer. 77: Cf. Zizia Size 28-35 Shape aurea (2). p.. strongly 1339-1360. apiculate in equatorial view. Endoeolpus oval. Welten, M. 1950. Beobachtungen viber den rezenten Exine much thicker in equatorial plane. Pollenniederschlag in alpiner Vegetation. Berichte

Geobot. Inst. Eiibel, Zurich 48-57. (1949) : ARALIACEAE

Wright, H. E., T. C. Winter & H. L. Patten. 1963. Two Cf. Aralia nudicaulis. Tricolporate, spherical, reticu- pollen diagrams from southeastern Minnesota; Prob- lum irregular with small lumina and broad muri. lems in the regional late-glacial and post-glacial vege- Borders of endoeolpus parallel. Endoeolpus rela- tation history. Bull. Geol. Soc. Amer. 74: 1371-1396. tively broad (co. 3 p.). Grains are much like Zinke, P. J. 1962. The pattern of influence of individual A. nudicaulis (1), which is the smallest of the forest trees on soil properties. Ecology 43: 130-133. species seen (ca. 24 p.), does not have well-de-

Notes on pollen morphology veloped costae colpi and costae endocolpi, and has

a slightly rugulate pattern. A. racemosa (1) has This section describes pollen-morphological features similar shape and endoeolpus, but structure is to that serve separate the pollen types mentioned. No slightly coarser. A. hispida (1) is larger and to attempt has been made give a complete morphological apiculate in equatorial view and has thick costae diagnosis of the types. colpi and costae endocolpi. In A. spinosa (1) the Most of the pollen morphological terms are from columellae are larger than in any of the preceding Faegri & Iversen (1950, 1964) and Iversen & Troels- species. Smith (1950).

Pollen types described by Cushing (1963) have been ABTERACEAE instance omitted, for Aceraceae, many Fabaceae types, Pinus, and Populus. Anthemis type (Stix 1960). Tricolporate, tectae,

echinate. For the sake of unity the conventions on identifica- Spines equilateral triangular. Intercolpi

limb with 12 Exine thick tion used by Cushing are also applied here. Names along equatorial spines. in intereolpium with often branched without any suffix indicate a reasonably certain identi- coarse, colum- ellae. Includes Achillea borealis lanulosa fication within the flora of the Midwest. The suffix (1), A.

‘ ‘ ’ ’ when A. sibirica (1), Chrysanthemum leucanthemum type is added there are alternatives; in the (1),

that (1), Matricaria matricarioides (1), M. chamomilla description the taxa are included within the pollen ” (1) Tanacetum huronense (1), T. vulgare type are mentioned. “Cf. indicates an uncertainty in (1), Anthemis the identification, resulting from insufficient reference arvensis (1), Achillea ptarmica (1), A. material. The number of collections studied for the millefolium (1).

Bidens Helianthus Stix separation of the pollen types is stated in parentheses. type (Fig. 15-14) ( type p.p.; 1960). Tricolporate, teetate, echinate. Spines Microphotographs (Figs. 14-16) were taken with a long, triangular, in fossil material often Leitz Orthomat camera and Orthodox microscope with bent. Columellae fine. apochromatie objective x63 and eyepiece xlO. Sizes Intereolpium along equatorial limb with 15-17

acuminate. apply to acetolyzed grains mounted in silicone oil. spines. Colpus long, Endoeolpus short.

Includes Bidens cernua (3), B. connata (3), B.

ACERACEAE. For morphology see Cushing (1963) comosa (1), B. discoidea (1), B. coronata (2), and

and Helmich (1963). Acer spicatum and A. negundo Echinacea angustifolia (1). In Bidens frondosa

occur scattered in all zones. (2) and B. tripartita (3) the number of spines is larger (up to 20 along equatorial limb). The Hel- ANACARDIACEAE

ianthus species seen (H. laetiflorus, H. petiolaris,

Rhus striato- H. glabra type (Fig. 14-8). Tricolporate, tuberosus) have shorter oolpae and an oblate

reticulate, distinct costae endocolpi, apiculate in shape. Diagram Spring 1967 A Postglacial Pollen from a Small Typha Swamp 169

it improbable that it occurred during the post-

glacial in the Itasca State Park region. The same

may be true for all the species of Betula with east-

western ern or ranges. Possible exceptions are

B. with northern that species ( glandulosa) ranges

might have been present in the region in the early

Holocene. The size-frequency curves for B. pumila

and B. papyrifera and for a mixture of the two

species show that the peaks are sufficiently far

result apart to in a bimodal frequency curve for a

mixture (Pig. 3). The most striking change in

size of Betula pollen grains occurs at the boundary

between zones 2 and 3, where the sediment changes

from amorphous peat to woody peat. Because of

the possible effects of sediment type on pollen size

(Wenner 1953), the interpretations based on size

not are completely conclusive.

Alnus. The grains are similar to A. rugosa. Ostrya/Carpinus. See Cushing (1963).

BRASSICACEAE

Tentatively a separation has been made between:

Cardamine type. Brassicaceae with large lumma. In-

cludes Brassica (2 spp.), Cardamine (3 spp.),

Dentaria (1 sp.), and Erucastrum (1 sp.).

Cf. Lepidium densiflorum (2). Size extremely small

(14-17 p) but columellae relatively large.

Brassicaceae. All Brassicaceae pollen grains not in-

cluded in the types mentioned above.

CAMPANULACEAE

Campanula. The number of spines and pores agrees well with Campanula uliginosa (2).

CAPRIFOLIACEAE

Lonicera hirsuta type. Tricolporate, eohinate, with

short and small 1.5 colpi endocolpi. Spines ( ca. p

long), ca. 15 along the equatorial limb. Columellae

larger than in the following type. Includes L.

hirsuta (1), L. prolifera (1), L. sempervirens (1),

L. oblongifolia (1), and L. dioica yar. glaucescens (1).

Fig. 16. 21. cf. Ephedra fragilis type, fossil, spectrum Lonicera canadensis type. Differs from the previous 37; 22. Pinus banksiana/resinosa type, fossil, spectrum type by its verrucate-echinate structure, its stout 87 23. Pinus strobus fossil, spectrum 29. Ca. 1200x. ; type, spines (often obtuse at the top), fine columellae,

and not very distinct composite aperture. Includes

Lonicera canadensis (1). Diervilla lonicera (1) is Ambrosia type (Cushing 1963). Includes Ambrosia triporate with thick annuli and few and (9 spp.), Franseria (8 spp.), and Iva axillaris (1). very spines

verrucae. Iva ciliata (Cushing 1963). Includes Iva ciliata Symphoricarpos occidentalis. Resembles Lonicera hir- (2), I. microcephala (1), I. frutescens (1), I. suta type but is densely echinate (30-40 spines imbricata (1), and I. angustifolia (1). along equatorial limb) and has much smaller col- Iva xanthifolia type (Cushing 1963). Includes I. umellae. S. albus is psilate. xanthifolia (2), I. dealbata (1), and I. ambrosiae- (1) folia (1). Viburnum lentago and Viburnum trilobum (Cushing 1963). Asteraceae tubuliflorae. All Asteraceae tub. types not Cf. Viburnum (1). Lumina and col- included in the types described above. Includes rafinesquianum umellae larger than in V. trilobum. especially the genera Aster (10 spp.), Solidago (6 spp.), Erigeron (6 spp.), and Eupatorium (2 spp.). CARYOPHYLLACEAE

Melandrium type (Pig. 15-16) (Chanda 1962). Grain BETULACEAE rather large with distinct (1 p) spines. Includes

Melandrium album (2). Betula. Size measurements were made of recent pollen

of B. pumila and B. papyrifera (Table 1). Betula Cf. Stellaria longifolia (Pig. 15-15). Periporate,

lutea omitted from 30 Pores with distinct was these studies because of subangular, ca. p. narrow

its rarity in the present flora. It has its main area annulus. Pore membrane with 6-10 granules. Tec-

in the eastern United recent tum 1 States. Its range makes with microechini (smaller than p). Fossils Ecological Monographs 170 C. R. Janssen Vol. 37. No. 2

and S. FABACEAE are closest to S. longifolia (1) longipes

(2). Petalostemum purpureum (Fig. 13-4) (Cushing 1963). Caryophyllaceae. All the other Caryophyllaceae types Petalostemum candidum (Cushing 1963). not described above. Amorpha (Fig. 13-5) (Cushing 1963).

Cf. Amorpha. Corresponds closely with Amorpha but COKNACEAE has no operculum in the eolpus.

Cf. Reticulum Cornus stolonifera type. Trieolporate, grain large, Amorpha nana (1). coarser than in

Structure Costae Amorpha canescens. 40-70 (x. coarse. colpi broad, Trifolium pratense type (Fig. 13-3). Trieolporate, thick, interrupted in equatorial plane. Shape pro-

late, apiculate in equatorial view. Includes Cornus prolate, large (32-45 p.). Endoaperture circular, without costae. Supra-reticulate, heterobrochate. alternifolia (2), C. obliqua (1), C. racemosa (3), Colpi with costae. Includes T. (3), T. C. rugosa (1), C. stolonifera (3). Cornus canaden- pratense

procumbens (1), and T. hybridum p.p. (2), but sis is much smaller (20-25 jx), with narrow costae colpi. the latter two tend to be smaller and have smaller

lumina.

Lumina often ELEAGNACEAE Trifolium repens type. very small,

often indistinct. Includes T. repens (2). Shepherdia canadensis (1) (Fig. 13-6) (Erdtman Vida type (Faegri & Iversen 1964). Tricolporate, axis 27-35 1952). Trieolporate, prolate, polar jx. depressed oval-prolate. Structure almost psilate or Colpus membrane psilate, without costae, ca. 3 (x faintly reticulate. Costae endocolpi well-developed, wide. Endoaperture circular, within the colpus, with endocolpus oval. Includes Lathyrus venosus (1), small costae. Structure scabrate. L. ochroleucus (1), L. palustris (1), and Vicia Shepherdia argentea (1) (Fig. 14-7). Oblate, api- americana (1). Most grains are probably Lathyrus culate. circular with distinct fasti- Endoaperture account venosus on of shape and costae endocolpi. gium. In polar view semi-triangular-semilobate, Cf. Melilotus. Perhaps synonymous with Ononis type polar area small. of Faegri & Iversen (1964). Tricolporate, prolate,

compressed at the poles, finely reticulate. Endo- to EPHEDRACEAE. Distinctions according Beug circular. of aperture Colpus narrow with one row (1961). granules. Polar axis 30-37 u.. Fossil grains agree

well with M. alba and M. Ephedra distachya type. Longitudinal furrows (1) officinalis (1).

branched. Synonym: E. viridis type (Cushing 1963). HYDROCHARITACEAE Includes E. viridis (2), E. cutleri (1), E. funera

(1), E. antisyphilitica (1), and E. nevadensis (1). Sagittaria. Periporate, echinate with numerous spines.

Ephedra fragilis type (Fig. 16-21). Longitudinal fur- Pores without annulus. Spines also present on

E. membrane. rows unbranched. Synonym: trifurca type (Cush- pore Sagittaria latifolia (1).

ing 1963). Includes E. trifurca (2), E. californica JUGLANDACEAE (1) and E. torreyana (2).

Juglans nigra (Cushing 1963). Pore number greater

ERICACEAE than 10.

Juglans cinerea (Cushing 1963). Pore number 10 or Ledum-Chamaedaphne complex. Tetrads subtriangular, less. than 3 with distinct costae. ca. 35 jx. Colpi longer |x, Ledum (Fig. 15-18). Inner walls of tetrad (5) LAMIACEAE thicker than outer walls. (Cf. Beug 1961; Erdtman sub- 1943). Agastache type. 6-eolpate, supra-reticulate, spheroidal. Synonyms: Prunella type (Faegri & Chamaedaphne type (5). Inner walls of tetrad usual- Iversen 1964), Dracocephalum type (Cushing 1963). ly not thicker than outer walls. Costae colpi tend Includes Agastache foeniculum (1), A. Urticoides to be broader, and colpi ends are often more obtuse (1), A. nepetoides (1), Dracocephalum parviflorum than in Ledum. Includes Chamaedaphne calyculata (1), Nepeta cataria (1), and Prunella vulgaris (5) and Kalmia polifolia (3). (1). Ledum/Chamaedaphne. Grains of the complex for Lycopus type. 6-colpate, intectate, reticulate. Synonym: which no distinction could be made. Mentha type (Faegri & Iversen 1964). Includes Gaultheria procumbens (2) (Fig. 15-19). Tetrads Blephilia (1 sp.), Salvia, Hedeoma (1 sp.), Ly- globular-shaped with long colpi (14 u.). Size ca. copus 5 spp.), Mentha (3 spp.), Monarda (2 spp.), 40-45 Structure scabrate to jx. faintly rugulate. Satureja (2 spp.), Pycnanthemum (2 spp.). structure Arctostaphylos uva-ursi (3) has a finer (Faegri Scutellaria type. Stachys type p.p. & Iver- and broader costae colpi. Gaultheria hispidula (3) sen 1964). Tricolpate, subspheroidal, finely supra- is smaller and has a different structure. reticulate. Lumina size decreases towards the pole. Vaccinium angustifolium (2). Tetrads globular- Includes S. epilobiifolia (1), S. parvula (1), S. shaped, 40-45 but colpi short without distinct (x, lateriflora (1). costae. Structure coarsely seabrate-rugulate. Stachys type. Tncolpate, reticulate, lumina uniform. Other tetrads. Includes all the other Erica- ericaceous Includes Stachys (3 sp.) and Galeopsis (3 spp.). and and ceae Pyrolaceae except Chimaphila (2) In Lamium the reticulum is almost indistinct at

Arctostaphylos (3). Includes Pyrola asarifolia (2), 600X.

P. elliptica (2), P. rotwndifolia (3), P. virens LILIACEAE (2) Vaccinium myrtilloides (2), V. vitis-idaea

V. Gaul- Lilium (2), oxycoccus (2), Moneses uniflora (2), philadelphicum (1) (Fig. 14-9). Monoeolpate,

theria hispidula (3) and Epigaea repens (1). reticulate, prolate-perprolate. Muri width variable, Spring 1967 A Postglacial Pollen Diagram from a Small Typha Swamp 171

to 6 towards the and small often up [j,, decreasing poles colpi. endoporus (ca. 4 longitudinally

Polar axis 60-75 Lilium michi- the width. Ektexine Duplibaeulate. p.. elongated, exceeding colpus and ganense (1) is less prolate has a different thick. Capita united in small groups or united in

pattern. a coarse broken rugulate pattern. Resembles Fago-

Includes pyrum. Erigonum heracleoides (2) and LORANTHACEAE E. microthecum (1). E. umbellatum has a coarser

Arceuthobium (Pig. 14-11). 6-colpate, eehinate with structure.

blunt spines. Three eolpi are long, with psilate POLYPODIAOEAE colpus membrane; 3 colpi are short, with granulate-

echinate colpus membrane. Grain intertriangular in Dryopteris type. Monolete spores with perisporium

polar view, suboblate in equatorial view. Size ca. incomplete or absent. Includes Cystopteris, Athy-

35 Includes Arceuthobium A. (j.. pusillum (1), rium, Onoclea, Dryopteris, Woodsia, and Matteucia. americanum (1), and A. (1). douglasii Dryopteris thelypteris. Perisporium wrinkled, with

small spines. LYCOPODIACEAE (Cf. Erdtman et al. 1961). Dryopteris spinulosa type. Perisporium folded, with

Lycopodium annotinum (2). Reticulate, lumina ca. numerous small spines. Includes D. spinulosa (1)

6 in distal view. and D. cristata (2). (a. Triangular Lycopodium inundatum (1). Irregularly rugulate, Dryopteris filix-mas (1). Perisporium folded, without circular in distal view. spines. Lycopodium clavatum type. Reticulate, lumina smaller

6 PRIMULACEAE than ia, triangular in distal view. Includes L.

clavatum (3), L. complanatum (2), L. tristachyum Lysimachia thyrsiflora (Fig. 15-13). Tricolporate, (1) Perhaps from the local Picea-Larix forest, bog subspheroidal, small (ca. 22 [«.), reticulate with broad muri. Granulae not easily resolvable at 600 x. OLEACEAE. Distinctions according to Cushing (1963). Endocolpus oval, often constricted in eolpus area.

Fraxinus pennsylvanica type. Colpus margin irregu- Colpus provided with a broad margo. Lysimachia Includes F. lar, usually 4-colpate. pennsylvanica ciliata (1), L. lanceolata (1), L. quadrifolia (1), F. Americana (6), (2). and L. terrestris (1) show differences in distinct- Fraxinus nigra distinct, type. Colpus margin usually ness of the structure and in width of the endo- Includes Fraxinus 3-colpate. nigra (2), F. quad- colpus. rangulata (2).

Fraxinus undiff. No reliable distinction between the RANUNCULACEAE

above two types was possible. Caltha type (Faegri & Iversen 1964). Tricolpate, microeehinate. Includes Caltha palustris (2), Aquil- OSMUNDACEAE egia canadensis (2), A. coerulea (2), Delphinium Osmunda. Includes O. regalis (2), O. claytoniana virescens (1), and D. nelsonii. (2) Material very variable ( cf. Andersen 1961). Ranunculaceae. Synonym: Ranunculus type (Cushing

1963) Includes all the other Ranunculaceae with PIN ACEAE. Distinctions according to Cushing (1963). scabrate-verrucate structure.

Pinus the strobus type (Fig. 16-23). Ventral face of Thalictrum has been left undivided.

grain coarsely verrucate.

Pinus banksiana/resinosa type (Fig. 16-22). Ventral ROSACEAE

face of the grain scabrate-psilate. The Pinus stro- Comarum palustre type (3) (Fig. 13-2). A subtype bus type also tends to be larger, but this character of the Potentilla type (Faegri & Iversen 1964) has not been used here. Not all of the pine pollen characterized by its protruding operculum and

grains could be assigned to a type. Fig. 4 shows lack of anastomosing vallae (Reitsma 1966). Fas- ratio two the of the pine types based upon a sum tigium sharply protuberant, which together with of determinable pine pollen grains. size and structure serve to distinguish the type

from other Potentilla species. POACEAE (CEREALIA) Rosa type. Tricolporate, operculate, costae colpi dis- Zea mays (2). Grain more than 45 larger, ja. tinct. Fastigium large. Grain distinctly striate. Avena (1) (c/. 1961). type Beug Shape almost spheroidal. The difference from

Potentilla lies in the shape, the well-defined endo- POLYGONACEAE colpus and the presence of costae colpi. Includes Rumex orbiculatus type (Fig. 14-10). Synonym: R. macounii (1), R. arkansana (2), R. blanda (1), Rumex aquaticus-hydrolapathum (Andersen 1961). R. acicularis (1). Pore Periporate, large ( ca. 35 (a). relatively small. Spiraea type {of. Filipendula in Faegri & Iversen Includes R. orbiculatus (2), R. hydrolapathum 1964) Grain small, spheroidal to slightly prolate.

(1), and R. fenestratus (1). Endocolpus margins parallel. Structure microechi-

Rumex undiff. All other Rumex types, smaller than nate. Includes S. alba (3), S. tomentosa (2), Fili-

30 |a. pendula ulmaria (3).

Polygonum persicaria type. Synonym: P. lapathi- Prunus-Amelanchier complex. Tentatively divided

folium type (Cushing: 1963). Periporate, reticulate. into:

Includes P. P. P. arifolium, careyi (1), hydropiper Prunus type. Synonym: Geum type (Faegri & Iver- (1), P. sagittatum, P. (1), P. persicaria hydro- sen 1964). Not operculate, distinctly striate, dis- P. P. piperoides (1), lapathifolium (1), pennsyl- tinct costae colpi. Includes Prunus (6 spp.), Geum

vanicum (1), P. punctatum (2). aleppicum (2), G. canadensis (1), G. macrophyllus

heracleoides. Eriogonum Tricolporate. Colpi narrow, (1). 172 C. R. Janssen Ecological Monographs Vol, 37, No, 2

Amelanchier type. Not operculate, indistinctly striate endoporus present. Slightly depressed-oval in equa-

Amelanchier Sarracenia or psilate. Includes (9 spp.), Sorbus torial view. purpurea (1).

(2 spp.), Pyrus (1 sp.). SCHEUCHZERIACEAE

EUBIACEAE Triglochin (Fig. 15-20). Inaperturate, reticulate,

homobroehate. Columellae not easily resolvable ( cf. Houstonia. Trieolporate, reticulate with broad muri Beug 1961, Faegri & Iversen 1964). Triglochin and distinct capita. Lumina of variable size, up maritima ag 9- (2), Triglochin palustris (1). to 2.5 Colpus membrane Polar axis 35 jx. psilate. jx.

Polar area small. Typical are the double costae of SPARGANIACEAE

the endoaperture; one set borders a wide, more or Sparganium type ( cf . Beug 1961). Monoporate, less oval endocolpus with diffuse ends; the second annulus reticulate, no around pores. Includes Typha set is much thicker and borders a smaller endo- angustifolia (3) and Sparganium (2 spp.). porus. Houstonia longifolia (1).

Galium labradoricum type. 5-7-colpate, small, rela- ULMACEAE Galium tively coarse structure. Includes boreale (Cushing 1963). (1), G. labradoricum (2), G. longifolia (1). Celtis

Galium undiff. Stephanocolpate grains with structure VITACEAE finer than in the previous type. 40 often Parthenocissus. Tricolporate, prolate, ca. p,

SALICACEAE slightly apiculate in equatorial view. Intectate,

reticulate, elements much fused. Muri thick, lumina Populus tremuloides type (Cushing 1963). Includes small. Endoporus provided with thick costae, ca. P. tremuloides, P. grandidentata, and P. deltoides. the membrane 3 (i, slightly exceeding colpus. Colpus and psilate, with costae margo. Polar area small. SARRACENIACEAE Exine 2.5 thick. Parthenocissus inserta (1) ca. p.

Sarracenia (Fig. 15-17). Grain small (ca. 20 jx), and P. quinquefolia (1).

tectate, psilate, 7-colporate. Colpus in equatorial Vitis (Faegri & Iversen 1964). Vitis riparia (1),

V. aestivalis plane irregular or interrupted. Sometimes a small V. rotundifolia (1), and (2).