Myrtle Lake:
post-glacial pollen diagram from northern
late- and
a
Minnesota
1
C.R. Janssen
Botanical
and
Museum
Herbarium, Utrecht, Netherlands,
and
Limnological
Research
Center, University of Minnesota, Minneapolis,
Received
A
pollen diagram from
sota records a
(or)
vegetation
P. resinosa
and
prairie
at 10 000
(or) Quercus
then
B.P.,
savanna
followed
Abies and
Slightly later,
forest
prior
Betula
types.
to 3000
migrated
8000-7000
Dryopteris thelypteris,
B.P.
and
conspicuous peaks
The time
of
lowland
formation
in its
bogs
Canada.
into
came
when
the
sublobe
Ruhe
existence
arrival of white
Des
Alborn
marked
the
its
and
pro-
beach)
the
St.
ago
Louis
and
River
Lake
lake,
lake
Wright
Red
and
(Fig.
1).
and
Ontario,
Lake
about
arose
the
1961).
Agassiz
rim
outlet
not
vegetational
Because of
in
a
strong
northwestern
reach
The
eastern
rupted
'Contribution
nisch
of
Museum
No.
en
climatic
the lake
gradient
Minnesota
54, Limnological
Herbarium
by
consist of
tern
shift
by
the rise
of Am-
species composition
van
de
and aspen
patterned
sandy
fens,
Agassiz
raised
covered
varies
by
surficial
an
In
upland
peatlands
bogs, string bogs,
in
clay
inter-
are
The
1963).
arranged
by
recent
parkland.
peatlands
beaches
islands
the
area
part of the basin has
(Heinselman
determined
between
zone
the
thins
out
(Fig.
1).
et
al.
and
is
swamps,
intricate pat-
drainage.
prairie
from
to
the
Research
Center,
het
period
the
Myrtle
B.P.
bogs began
base
Lake
(Heinselman
peat
Since
prairie
an
in
return
1967a).
Lindford
A
bog,
revealed
an
C-14
west
to
the
this
date
of
the
age of 4360
1963), indicating that
according
of the
development after
accumulated after
then,
by
toward
formation
of northwestern Minne-
their
peatland,
parkland
aspen
followed
area
forest.
Minnesota (Wright
1966) point
the
(Janssen
of
by
in
McAndrews
of
deciduous
deciduous forest belt
replaced
extension
sota the
and
studies
mid-postglacial time,
(McAndrews
van
prairie
north this
Pollen
1963;
eastern
prairie
Heinselman,
most
of
period.
most
of
Bota-
Riiksuniversitet
te
the
vast
resulted
j
trees
Lake
the
colonization.
Minnesota; Mededelingen
Utrecht
are
deciduous
by prairie
part
and spruce
the
University
gave
There
began, indicating a
in the
western
soils covered
the
the
forest. In the Itasca
B.P.
and the lake with-
Campbell beach, leaving
west
outlet
eastern
lowland. About 9200
began,
when
B.P.,
bed
for
peatland
different soil types,
as
in
to
(Campbell
drew from the
open
minima of
and fens
well
as
vegetation
low-level
a
an
II
10 000-10 500
final retreat of the ice
Typha latifolia,
occidentalis.
Agassiz I,
At this time the lake did
Red Lake
Thuja
of
of the
Much of Minnesota is situated in the tension
eastern
After
ice readvanced and closed the
(Zoltai
to
in
conditions
in the lake waters.
large
years
its
of
phase
southern
the Herman beach
east
Quer-
of deciduous
prairie
of fens
pollen and
vegetation
12 000
stage resulting from the opening of
the
pollen
man in the area is reflected
Towards
by
and
rugosa,
strobus
greatly.
large
occupied
retreated from the
along
sheet in late-
northern Minnesota
Moines lobe
the
(of
1965)
of
expansion
clearly accompanied by changes
are
Minnesota this
about
Red Lake lowlands. This
is
wake
In
consisted
and poor swamps
1966),
which
Agassiz,
adjacent
decline
1397 (1968)
46,
in northwestern and
areas
and
time left
Lake
glacial
and
Between 8000 and 7000 B.P.
of a return to
and lateral
laricina, Alnus
much Pinus
by
of raised
peatland types
of the Mankato ice
waning
gradual
a
Minne-
banksiana
deciduous forests ofmainly
by
vegetation
paludification
Introduction
The
of Pinus
sp.
indication
an
Myrtle Lake, indicating correspondingchanges
Canadian Journal of Botany,
Wisconsin
in
in northern
Agassiz
pollen diagram.
wetter conditions. The
The shifts in overall
of Pediastrum in
the
is characterized
lowlands,
in climate towards
the
Later
mariana, Larix
Myrica in
after 3000 B.P.
and herbs. In the
brosia.
followed
resulting
and there is
interval
dry
Cyperaceae.
rise to rather rich swamps of Picea
some
still later Alnus.
possibly Populus
into the area,
pollen, however, rises,
of Lake
B.P.
the
During
Pinus strobus
uplands,
and
arm
by immigration successively
Pteridium,and
on the
prevailed
Ostrya virginiana, Fraxinus pennsylvanica,
cus,
of the eastern
lake in the former bed
a
of spruce forest
Minnesota
1968
February 5,
peatlands
from
of
the
Red
paludification
Lake
rather
lowlands
than
lake
1398
CANADIAN JOURNAL
Fig.
1.
of
Map
southeastern
after Leverett
Minnesota
Agassiz
Lake
(1932),
McAndrews
filling, especially along
the
however,
what
occupied
the
before
on a
area
large
The present
on
the
work
can
of
of these
Lake
One
close
to
the
pollen
of the
Myrtle Lake,
40
latest
types, and
(1963),
question
The
of
vegetation
few
miles
eastern
ice
and
pollen
sented in this
lobe
on
an
lakes
east
since the
Before
of the
Ruhe
beaches
in the text.
of
Modified
(1965).
diagram
from this lake
is
pre-
paper.
of
a
Lake Peatland
Fork
Rivers
(Fig.
types
of the
entire
must
be
lake sedi-
Lake
margin of the Lake
Lake
Myrtle
is
is
peatland
divide between the
the
peatland
Red
water
detailed
cores,
area
in the
of
The
investigation
peat
analysis
the area,
in
sites mentioned
Wright
A
1968
recorded
pollen
and
basin.
46,
accumulation
peatlands
Agassiz.
regional vegetational history
ment.
Schoenike
of the
VOL.
Myrtle
undertaken
determined from
(1966),
peat
work is part
of
be
vegetation
BOTANY.
scale ?
development
withdrawal
kind
the border
recent
margin.
remains,
started
showing
major
OF
2).
of
Most
Lake
gentle slope
According
and
basal
Agassiz
peat,
to
to
north
Heinselman
sedge peat
and
the
then
is
typically
by
either
to
on
and
peatland
accumulate
(Heinselman
(1963,
the
Big
vegetation
the
Agassiz
found there. The peat started
a
situated
Little Fork
Sphagnum
by
on
1968).
1968),
overlain
are
the
forest
peat
or
JANSSEN:
Fig.
2.
mixed
see
the
and
absent
locally
center
the forest
Lake
Myrtle
deep pit
in
history
is
the
before the
measures
about
situated
1.5
peatland
peatland
graphy of
(1963,
of
west
forest
miles
and
locally
from
the
It forms
therefore its
developed.
inflowing
by peat
The lake
and
across
is
sur-
At the southern
by peatland.
an
peatland.
the cedar
the
to
stream
is
found,
The
growth.
strati-
string bog
The
19676).
forest
bog
Kalmia-spruce
sented
or
Janssen
the
rich
Thuja
northern
described
north.
Along
for the
State
a
area
Park area,
(Janssen
may be
classification
19676).
described
by
by
grouped (Fig. 2)
developed
100 miles
Thus
Heinselman
the
Heinselman,
to
the
poor
and
for
black
(Janssen
spruce
-
leather-
Sp6ag«MW-leatherleaf-
both of which
1968),
topo-
are
are
repreThe
Piceto-Chamaedaphnetum.
the
along
-
(Heinselman
forest
of
unit
Heinselman is
labeled
Most of the
(19676).
found
one
heath,
the
by
swamp
Piceion,
is
fens, belong floristically
and
raised
graphically
rich
and
Sphagnum
to
to
For
(1968).
Lariceto-Chamaedaphnetum
grades
1968)
after Heinselman
Modified
the lake sediment is listed in Table I.
vegetation types
according
Itasca
is
the
forest
regional vegetation
half mile
a
almost obliterated
The
layer
(Fig. 3B).
substratum,
rounded on all sides
a remnant
Lake
leaf
sediments should record the
end
along
with
starts
(Fig. 3A).
southern end of the
a
but
sedge peat,
sequence
peat, and in the
Myrtle
1399
MINNESOTA
FROM
text.
Sphagnum
margin
map of the
Simplified vegetation
explanation
POLLEN DIAGRAM
the
margin
margin
stand
of the
vegetation
poorer
the
poor swamp forest
by
swamp forest
peatland,
occurs
lake.
types
other sides
Copti-
“transition”
rich
of the
occidentalis
the
It
gradually
toward
of the
but
along
lake
the
only
occurs.
the
southswamp
probably
Methods
Sampling
The
and
Myrtle
Processing
Lake
core
was
taken
through
the
frozen
1400
CANADIAN JOURNAL
TABLE
OF BOTANY.
scale
I
this
Sediment
of
stratigraphy
Myrtle
Lake
the
Dark-brown
medium-detritus
almost
is
identical
440-505
Fine-detritus
505-525
Coarse-detritus
gyttja
2.
Medium-detritusgyttja
570-595
Coarse-detritus
595-695
Medium-detritus
695-725
Detritus
725-735
Medium-detritus
gyttja
735-825
Medium-detritus
gyttja
gyttja
finer
gyttja, slightly
800
the
cm, marl
825-852
Marl
852-863
Dark-brown
with
863-867
Marl
867-875
Dark-brown
875-895
Gyttja,
than
made
with
with
marl
increasing
bottom;
between
795
is small
content
Upland Pollen
an
also
left
were
out
Silt
gyttja
increasing
included
wood
925-975
Silt with
wood
975-1000
Grey-blue clay
are
much marl
although
it
shown
for
detritus towards
the
of the lake
and
some
Ulmus,
and
Pollen
len
with
through
the
the
the
ically
Within
pollen
sam-
core
The
pollen
pollen
sums
is
The
pollen
numbers
addition
show
of the
mounted
period,
This is
places
cannot
of
Research
follow
in
the
below
and
Quercus
pected
show
on the
basis
from
in
but
No.
sum
total
of the
and
lake
of two
for
pollen diagram
and
the
the shores
of the
where
the
that
only.
sum
might
(Scirpus),
indeterminate
curves
and
have
local
above
The
the
pollen
and
aid
of the
iden-
Iversen
(1967a). The identiPrescott
(1951).
available at the Limnoof Minnesota.
Analysis
been
are
useful
a
divided into
traceable
lakes
scheme
at
(Wright
zones
al.
et
tion
development
that
elsewhere
as
As
discuss
to
that
1968).
to
in
The
thus
can
and Kotiranta
regional vegeta-
be
sarily
Minnesota,
pollen assemblages
time-stratigraphic
zones
by
as
of Minnesota.
show,
similar
of forest dominants may result
synchronous
that
implication
the initials of the
1967).
The
list
are
To
everywhere.
the convention of
boundaries,
with
compared
the discussion of results will
rates
extent
great
a
northeastern
in other parts
parts
pollen diagram has
Weber, Jacobson,
for
not neces-
avoid
the
any
zone
designating pollen
site is
followed here
below
shows
these
indices and their literature references.
Weber Lake
WL
Kortiranta Lake
KL
in
Fries
1962
ex-
pollen
grown
the
Wright
et
al.
1968
Jelgersma)
Jacobson Lake
JL
Wright
et
al.
1968
Poaceae
types,
algae
lined
are
are
values:
open-water
types.
the
many
spectra
pollen
(Zizania), Cyperaceae
are
sequence, the
pollen
(Cushing
at
Picea, Betula, Pinus,
No. 60
show
postglacial
curves
percentages
time
Janssen
Center, University
of the lake.
regional
might
peatland.
upland pollen types
for most of the
the
and
of the
Faegri
species follows
pollen counts
provide
in similar
on
of
criteria
with
pollen grains
GENERAL
throughout. Many
spectrum
black
upland
basis
of
and
The
the
made
were
occurrences
the
taxa that at any
excluded.
is
B.
as
upland pollen
and
of recent
Pollen
well
in the
especially
60,
lake
ecologically
of
on the
sediment
values
the trend
exactly
thus
parts,
upland pol-
trends.
of the
size
types from
itself
as
(without exaggerated
Center. Most
the
in
Sum
lake
diagram
spectrum
Excluded
is
of the
migration
occurred
recognizable
and
bog
herbs, Pteridium,
pollen grains
collection
Research
logical
arranged stratigraph-
coincidence
species that,
have
in two
in the
left outside the
been
applies mostly
from
the
curves
Quercus, Pinus,
of
ecological-physiognomic
are calculated
regional
large
of course,
originating
in the
well
which
Betula,
occurred
upon
as
For
1966).
Pollen
type
divided
were
have
greatest
(Janssen
Regional
types
because
that
the successional
The sediment
is
exception
that
types
minute,
1
10 minutes.
was
Copies
To
certain
curves
the
to visualize
pollen types
are the
stain.
types included
pollen
other those
show
to
An
based
of Pediastrum
of the
the
sum.
groups
This,
for
material
pollen diagram (Fig. 4)
sum,
1.
for
screen,
°C
without
csk),
x
KOH
fine
a
Livingstone
Treatment of the
10%
at 95
acetolysis
(2000
showing
pollen
and
2-in.
Diagram
The
one
may
Poaceae,
regional pollen sum,
(including prairie
reference
Limnological
Wright 1965).
boiling
mixture
oil
the
of
up
snails
tifications
a modified
by
microscopic investigation
silicone
and
of
ex-
which
Identifications
fication
and
herbs
species
Excluded
supplemental
as
herbs
upland
is made
might have
(1964), Cushing (1963),
the
An
curve,
Sum
of the
pumila. Percentages
of the
with
10% HC1,
upland
upland
sum
types.
Identifications
905-925
sieving
regional pollen
diagram.
the Poaceae
that of
upland origin.
and fen
bog
scale)
without
gyttja,
with
Silty gyttja
included
the
Sarcobatus).
895-905
pler (Cushing
for
record
upland pollen
that have
the
bottom
samples
from
side of the
right
above
snails
some
mostly
The
The
gyttja
content towards
upon
rather than Zizania.
gyttja
525-570
and
therefore
gyttja
based
percentages
excluded
the
on
Water
145-440
surface
show
x)
thus
types
shown
ception, however,
is
10
exaggerated
All
0-145
1968
46,
regional pollen sum.
sum are
Strata
cm
VOL.
are
curves
(W.
and
also
(with
Bog
D
Thompson
Pond
A.
Watts)
BD
McAndrews 1966
TP
McAndrews
1966
(S.
Plate I
Fig.
3A.
Heinselman,
Fig.
3B.
Cross section
through
the
Myrtle Lake peatland, showing the
main
stratigraphic features.
After
1963.
Aerial view
of
Myrtle Lake, looking
northwest. Patterned
fen
is
light area
in
background.
JANSSEN: POLLEN
Andree
DIAGRAM FROM
AB
Cushing
1964
zone
CBL
Cushing
1963
Schroevers,
Horseshoe Lake
HL
Cushing
Kirchner Marsh
KM
Wright
Cedar
Bog
Lake
Bog
1967
1963
(T.
Winter)
C.
According
1.
Also
locations
of these
sites
in
relation to
formations in
vegetation
recent
is
shown
In the
will
in
Lake
Myrtle
all sites in
and
the
with
species
temperate
pollen
of the
together
zone,
south of the 14 °C
only
used
elsewhere
in
for
number
a
the
throughout
of sites
occurrences
result
of
of this
Cedar
Cyperaceae.
following
dicate
a
the
by
zone,
treeless
they
date from the
B.P.
Weber and
at
and
la is
that,
from
clay
Also
is
silt
11
120 +
la/lb
zone
may
seems
Myrtle Lake,
zone
before
11 740
drawal of Lake
the
the
at
gram
the
by
now
south end
the
of
parallel
that
Myriophyllum,
abundant
is
of
and
Possibly
at
(1967).
1965).
Lake,
stream
In the
at
pollen
by
JL-1,
the base of the
for
as
are
Equisetum
they
Pediastrum
a
zone.
striking
Ranunculaceae,
Sparganium
also
dia-
redeposited
of ML-1 shows
present
and
to
group
have been called
simplex
is
at
Lemna,
this
of
occurrences
well
of
as
of Abies and
break
rently
dary
in the
all
Pteridium,
imply
region
late-glacial
as
Wright
tree
trans-
aquatic types,
the present
al.
Appaboun-
(climatic?)
today.
(1968)
line of Picea
and
trees
vegetational
a
near
it does
et
of
distance.
of coniferous forests.
a
the
to
occurrences
dispersal
deciduous
constituted
where
Myrtle, Weber,
present
of these
thermophilous
area
species (Iversen
at
is
short
by
1966). Nuphar,
single
for
a
pollen
boundary
this
it
Marsh the
confirmed
Typha, long-distance
that time in the
at
southern
It is also
postulated
during
the
time
of zone 1 a.
confined
by
to
ML-2
zone
With-
Myrtle
Myrtle Lake, belong
pioneer aquatics,
Watts
lake.
of
as
a
Andree
an
obliterated
indicated
vegetation
with
both sites.
south
largely
pollen grains
The local
Shay
beach,
resulted in erosion from
of the
erosion
Cretaceous
of
Agassiz
immediately
area
possibly
(Y-1327;
B.P.
The
has
1b
but
account
which
northern
that occurred in northwestern Minnesota
Herman
cannot
Nuphar,
aquatic
zone
lakes,
contrast to
area
event
the
south. In
is
and Winter
(Watts
Kotiranta
port
itself
plant
thermophilous
the
Agassiz
from
and
the
and at Kirchner
is also absent in
1954),
the
Lake
I
another
lake
withdrawal
a
macrofossils
shift
pollen-free
stratigraphic
reflect
the
A C-14
high.
layer
time
The
deposited.
to
at
that
lacking. During
were
too
are
younger than the
assume
in-
Kotiranta
KL-la).
Kotiranta Lake. It therefore
at
reasonable to
clays
low to
too
in
of the
type indicated
base of the silt
(Y-1782),
transition
Chenopodiaceae,
still
are
values of Larix and Picea
210
values of
slightly higher than
vegetation
WL-la
(zones
by high
Although Cyperaceae
are
basal sediments
Lakes
are
and Kirchner Marsh it is
Bog Lake,
of
At
transport.
discussion.
and moderate values
Pinus,
and Artemisia values
the
some
plain
pollen type, probably
long-distance
ML-1
Artemisia, Larix,
and
Myrtle,
at
in and north of the Anoka sand
Bog,
characterized
low values of
Poaceae,
late-glacial
and Kotiranta lakes. At
the
presence
Quercus,
a
Scandinavia
in
of
Weber, Jacobson,
those
zone
of
of
July isotherm (Iversen
the
1954), is absent from
correlation
found
now
consistently present,
Picea,
pollen
latifolia,
available C-14 dates. Table II
on
Zone ML-1 is
sediments
no
Typha
trees.
of the
development
The
synchroneity
be
may
Ostrya- type
late-glacial
ML-1 has
Minnesota,
thermophilous
single
shows
and
Ulmus,
found in
are
features
regional
sites
is based
state
the
peatlands.
features
regional
but this
ubiquitous.
Quercus,
which
other
following sections,
interpretation
sediment type.
boryanum,
1.
Fig.
be discussed for each
with
the
J.
its
Minneat
sota
with
P.
species;
the
pollen,
major
polysaprobic
Pediastrum
is
is almost
species
information from
to
a
consistent
present
Except for
The
is
it
is
presence
al.
et
1401
MINNESOTA
At the transition from
is
a
zone
resinosa
type.
increase,
and
occur
and
Quercus
now-exotic
to
zone
regularly.
Picea
Equisetum
Nuphar
transition;
matic
and
has
a
decreases
Ranunculus
short
these
2 there
as
which is indicated also
organic
pure
vascular
astrum
species
simplex,
as
by
a
matter. The
and the
which
to
decline,
to
just
above
improving
a
and
the
cli-
quieter
lake water,
change
in sediment
occurrence
disappearance
is
types
gradually
type
point
well
also
type
tree
simplex disappears,
maximum
trends
conditions
Ostrya
deciduous
small percentage, Pediastrum
to
1
sharp increase of Ulmus and Pinus banksiana/
the
most
of these
of Pedi-
planktonic
1402
of
CANADIAN
all
A
of
most
of this
arrive
not
pine
pollen
distance
duced
the
at
pine pollen
a
the
B.P.
the
rise
this
over
Zone
2a
elements;
type. In
has
zone
2b
and Abies and
out
2
zone
occurs
remain
relatively
sition from
A
in
several
deciduous
and
but
Ostrya
Pteridium,
Throughof
most
the
fall
a
the
at
tran-
is
values of mesic
higher
present
other
at most
Weber
at
eastern
Lake,
Minnesota
a
pine
a
is
period
division
on
the
short,
too
same
basis
In
the
the
and
described
Abies
rise and
by Wright
appear
lowland
may have
the
pine
the
rise:
pine rise;
the
postdate
relative
at
and
pine
position
JL, WL,
at
swamps
at
the
Alnus follows the
CBL, HL,
and
come
with
Myrtle Lake they decidedly
of the Abies
at
and
north.
and HL before
they
rise. There is also
and ML it
delayed
and WL
south
the
pine
shift in the
maximum. In the
rise
or
earlier,
According
pattern, but its maxito
AB
of Alnus
rise
before the appearance of Abies.
the Alnus maximum
at
are
even
Abies. At
is
KM,
to
zone.
occur
however,
there
point
Another
lowland
much
to
area
until
in
on
tremuloides
are
have
former lake
herdia
been
of
between
oldest
peats
diagram,
covered
covered
was
in boreal
On
forest
and
zones
between
is
a
Populus
such
1957)
of the
areas
but
not
ShepAbies
the present difference
Picea
the
is
soils
especially
two
wide
or
richer
Ritchie
America,
a sense
boreal
forest
palu-
not
similar
the first
over
by
exposed
(beaches)
types.
1935;
by
now;
bed. In all these forest types
the
that
of fens.
Pinus banksiana
soil,
soils
sandy
occurred
occurs
between
the
1963).
America
sorts
in
as
sedge
the
on
and that it
common,
and Pteridium. In
and
area
(Heinselman
floodplains (Raup
may
well
pollen
glauca, Populus balsamifera,
Picea
as
assemblage
have
might
other soil
on
Picea mariana
smaller than it is
boreal
all
on
types that
Sphagnum,
occurrence
that the
was
Agassiz,
later
grow
fire climax
as
is
are
are
In the
pollen
no
of
Typha
percentages
(1963),
area
widespread
little
1957;Thieret 1964).
floodplain vegetation
of Lake
dified
is
a
possibility
and
their
uplands
Ritchie
is
of
grains
regions
on
peats.
vegetation
of the
there
only pollen
Heinselman
rather than forest
on
but
the
Lake, finally,
composition
Pollen
Lake Agassiz
forest
same
as
and
the
the
tem-
difference
2a and 2b in northern Minnesota,
zones
found
Minnesota.
The
The differences
comigration
of
greater. At JL
the
at
rise
assemblage
from the lowland
to
in the
peats
perate pine
with respect
the
but
later.
comes
same
a
giving
diagram
present,
(Raup 1935;
to
towards
Lake
and Larix laricina
grow
from the
It
the
be absent.
and Larix. In boreal
Picea,
tends
KM, CBL,
AB, JL,
south it is about
is
later
this
to
towards
Abies;
character and
Actually
come
migration pattern
to
its
Pteridium.
At Weber
to
vegetation.
are
types
(1968). According
came
progressively
Abies first appears
al.
et
seems
Myrtle
Betula,
maxima of
follows the
them these elements
in
zone
Although
order of the
Alnus,
mum
Pinus-Pteridium
latifolia
exists.
The
is
and Pinus,
Abies
indication of the
clays
lower
before
even
belong
may
group
Anoka sand plain it appears
as
Pteridium
Minnesota the
Stevens Pond
that
the Alnus and Abies rise.
upland
at
at the end
expected:
At JL and ML it is later: it appears there with
sites. In most of the Itasca sites in northwestern
but
KM
at
time
would
2.
to
forest elements also
but it is absent
la and
it
Betula maximum
intermediate between
migratory
Cushing’s
a
2a. The Larix percentages
2 with
zone
in
shows
zones
Corylus,
stable after
1
species
Another
southern
appears
be
might
thus
Lake
Myrtle
at
The
zone.
Jacobson Lake and Weber Lake.
at
remain low.
decreases,
zone
zones
similar
also
1968),
increase of Ambrosia.
an
decline
gyttja
10 310+260
at
maxima of Pinus,
Picea
of
counts
level.
Quercus,
are
proin the
rise
pure
dated
maxima of
Ulmus,
great
a
locally
Zone ML-2 may be divided into
2b.
position
but
2b,
zone
next
ML-26,
zone
same
then
case,
in
the
north in the
to
Heinselman
at
pine
in the northern part of
bog
peatland,
(GX-0498;
pine
in
time everywhere
sharp
sandy gyttja
Lake
WL it is
is the
the
the
large
a
of
The
that
Preliminary pollen
curve.
from the raised
Myrtle
same
in
resulting
transition from
core
such
over
If this
that
(Table II).
state
overshadows
clearly
pollen,
and
1968
46,
is the level where it
tran-
age
hitherto-dated
easily dispersed
so
an
perfectly possible
in northern Minnesota.
the
the
feature
It is
is striking.
did
mean
this
places
cm
(Y-1781),
pine throughout the
synchroneity
trees
890-895
at
with
consistent
area
also
may
BOTANY. VOL.
comes
10 150+160 B.P.
at
rises in
species,
OF
levels.
water
C-14 date
sition
is
Pediastrum
the
falling
JOURNAL
1
and
2
explanation
at
forest communities.
least
the
toward
may
southern
lie
dominant
in
trees
the
of
JANSSEN; POLLEN DIAGRAM
questionable
It remains
deciduous
elements
their
extent
to
were
pollen
what
extent
mesic
to
what
present
or
contributed
was
by
abundant
very
Myrtle
at
trees has been found at the
in the
Agassiz
Therefore it
of the
part
They
that these
likely
seems
the
on
of Lake
edge
valley (Love
vegetation
have occurred with
may
Populus
Assiniboine
regional
and
at
1959).
trees
were
Lake.
Myrtle
Picea,
KL.
At
Lake
Myrtle
and
Abies,
Zone 3a
may be
with
period
postglacial
the
considered
A
prairie period.
Myrtle
and,
Lake.
(Zizania type)
implies
trees
are
Features
Zone
values
ML-3
of
zone
In
3a
zone
suggest
and Salix
maximal for the
are
tages
Ambrosia,
Quercus,
at
the
and
top
reach
Pinus
the
Pinus
abruptly.
of the
type.
base
Picea
zone
a
a
Larix
Ostrya
maximum
entirely
remain
3c Picea and Larix
but there is
with
minimal
a
type. Upland
zone
JL, WL,
herbs reach
4 instead of in
and
there
KL,
rise of Abies,
arguments,
the
JL
nosa
a
is,
Picea,
which
following
1. At
a
slight
type
rises
the
at
top
strobus
Pinus
a
are
Quercus
zone
at
3c
the
and 8000 B.P.
All these
to
3
include zone
because,
and Larix. The
as
at
zone
counter-
include
persuasive,
rise of Pinus
banksiana/resi-
is shown at the upper
and KL
Myrtle
3. There is still
must
part
Quercus,
Ulmus,
and
a
zone
4. This is
not
so
in
zone
Lake.
Picea
sota
the
be
upland
herbs
at
Myrtle Lake.
4. Alnus shows low values in
in
slight
zone
4
at
JL, WL,
its
curves
of raised
B.P.
herb
(U-163),
decrease of
Quercus
dated
7120 +110
at
Winter
1966).
Also,
Quercus-Grami-
zone
of MeAndrews
dated somewhere between 7000
the
traceable
result of
It may
such
over
major
a
serve
the
a
large
shift
as
a
to
a
second
diagrams,
rise at 10 000 B.P. Simul-
pine
northern and northeastern Minne-
its
lowest
percentages.
Lake the Pinus values
Poaceae and
according
west
(McAndrews
grains
BP.
at
the top of
go down to less than 20%, and it would
means,
areas
the
Lake
Myrtle
of the
140
still lower when calculated
ably
at
Quercus
7210 + 80
at
in the
zone
assemblage
reaches
Myrtle
zone
a
level in Minnesota pollen
being
taneously in
Myrtle
maximum of
and
warmer, drier climate.
the first
a
were
changes,
synchronous
subzone.
but
thin,
horizon
a
Marsh
peak
be
with
Lake
Bog
Dryopteris
3a is very
maximum
Watts
be
together
must
area,
Cedar
at
7300 +
at
level,
(Y-l 140;
Ambrosia
is 7850 ±
upland herbs, along with evidence
low lake
a
B.P.
Pinus,
type have completed their decrease
the base of
at
for
including
JL, WL,
Ostrya
and increase of
At
type clearly
Kirchner
at
zone
synchronous
the rise and therefore should be
dated
was
deciduosu
JL-3 there is
the
on
on
neae-Artemisia
of zone 3.
2. At
values
is
dated
later. At Weber Lake
ones.
slight
it is
rather than
(1966)
maximum.
zone
maximum
levels. A dis-
This date is later than the
but
date,
This
of JL-2 and
herb
(Y-1690).
of the
cause.
Y-l 197) in his
120,
increase,
from the base of
more
and
banksiana/resinosa
new
+
Typha latifolia
water
the base of the
At Jacobson Lake
level for
water
sharp peak
a
mid-
features that likewise
low-water stage
Cushing’s
(7880
at
(Y-1780).
to
start
A few arguments may be made
3c in
percen-
low,
minimum of
new
rise of the Pinus
slight
B.P.
and
3b
almost
and
and
type.
zone
reaches
Fraxi-
increase,
and Tilia makes its first appearance.
decreases,
In
of
it is
zone;
Artemisia,
diagram.
120
transition
show values
of the subzone. There is
increase of Pinus strobus
At
entire
Corylus
and
pennsylvanica
a
more
three subzones.
Typha latifolia,
Picea, Larix,
3c,
high pollen
values of deciduous
by high
divided in
be
may
Poaceae,
nus
which
herbs,
and
by
and low values of coniferous elements. The
trees
that
characterized
upland
vegetation,
open
A C-14 date
is
the
Myriophyl-
herbs and
upland
climatic
a
of
of
the abundant
Also,
the base of the zone,
at
represent the
peak
lum andLemna may indicate a low
tinct maximum of
ML-3
to
impact
greatest
may be connected with low
Regional
a
Zone ML-3a
Poaceae
floodplains.
zone
Alnus shows
maximum.
Lake. Wood of these
western
1403
MINNESOTA
long-
distance transport. Pollen of Ulmus and Fraxinus
is
FROM
Lake
came
of
the
to
region,
into
pollen
This
Pinus
was
easternmost
region
absent in the
and that the pine
long-distance
sum
prob-
samples
coniferous
increase of Pinus strobus
migration
a
recent surface
present
1966), that
from
on
Cyperaceae.
pollen
transport. The
type may reflect
Minnesota.
1404
CANADIAN JOURNAL
The
recent
pollen assemblage
resembles that of sub-
vegetation
Quercus
came
prairies
although,
present,
and
pollen
Pond of
Quercus
bog
8560 ±
at
there
is
120
This
(Y-1780).
140 B.P.
is
with
in
species
happens
at
At
to
east.
120
+
Weber Lake
Jacobson
at
Lake
B.P.
7300 +
the
date
known but it is before 7210
not
this
the
eastward
is
migration
penetration
time. At
mid-postglacial
the southern parts of Minnesota
the
by
and
CBL)
Quercus began well before
8000
resulted
B.P.
This
Minnesota
eastern
and
later,
also
of Picea.
the
at
a
thus that the
as
reaches
its
Quercus
after
interval
of
Quercus
arrived
thin
a
the
much
lowest
It
postglacial.
is similar
that of Pinus,
to
At Weber Lake in the
today.
north-
distribution of Picea in this
of Minnesota there is
east
and
arrived
the
total
early
an
savanna
later time in
part of the postglacial
just
in
northern
Picea
accordingly
percentages
seems
In
only
there
the
representing
zone
prairie
far north-
slight rise of
a
It
period.
late
too
seems
climatic interval unfavorable for its
that
from
profit
to
dry
a
competitors.
and
vanica,
values in
But
level
the
the
where
ratio of
overall
fails
Wright
al.
et
of
pression
First there
related
(1968)
wards
the
west
be
a
never
is
clearly
absent
was
accordingly
an
direct
a
Pinus strobus. At
a
later in
mostly
by pine,
a
this
at
3b.
Quercus
feature that
of
pine
to-
time.
zone
although
sup-
Myrtle
zone
of
replacement
Pinus
it
strobus reaches
that it
high percentage (60 %)
been present,
thus
general migration
At the top of the
such
pennsyl-
type of soils.
emphasized
but
true
the
seems
show up. At Jacobson Lake
to
seems to
to
stro-
Ulmus and
Fraxinus
and
other hardwoods and
by
is
perhaps
Quercus by
Lake this is also
little
a
of Pinus strobus. At
migration
pine
seem
same
deciduous forest
to
this
at
this time P.
replace
and
the
type
If so, then it
to
the
on
postglacial,
zone
a
sudden
a
Although
at
area.
began
Ostrya
determined by the
Lake
is
strobus
Pinus
type.
that
mean
later also
The fate of the
Ostrya
reaches
decrease at
there
pine percentages
vania, for it thrives
the
forest,
pennsyl-
after minimal
zone
starts to
curve
48)
that P. strobus
during
vegeta-
of
3a.
migrated into the
Weber
upland
pollen
the
much
in the deciduous
Fraxinus
Ulmus
banksiana/resinosa
slightly
shows
The
Tilia,
base of
low, it still might
bus
Pinus still
assemblage
deciduous type
a
Ulmus.
Ulmus
in
increase
level
forest
samples
Ostrya,
(spectrum
Pinus
deciduous
zone
pollen
Itasca.
was
the
a
zone
the
likely
D and in
bog
(KM
+
con-
the rise of herbs and
suppression
of Lake
west
maximum
rise
Lake
Myrtle
7850
at
forest
Quercus,
the
the
resembles that of recent
with
of Picea started
At
(Y-1419).
Quercus
and
values,
Thompson
west
to
savanna
In the lower half of the
low
apparently
prairie,
suppression
from
about 4000 B.P.
at
tion
of the
1968
46,
continuous
dates
from
of the
(Y-1690). Clearly
nected
prairie
of
(U-163).
for the rise
80 B.P.
a
C-14
migration
a
B.P.
rise
a
prairie
also
(cf.
The
expansion
and the
Quercus,
the
bog D, Myrtle Lake, and Jacob-
at
the
D
from
however,
type
McAndrews).
rise
Lake suggest
son
of
ciliata
Iva
from
apart
Chenopodiaceae,
grains
remains small. There is,
for
west
savannas
(McAndrews 1966). Possibly local
Artemisia,
of
number
in
samples
were
Ambrosia,
At
BOTANY. VOL.
surface
of Lake Itasca
curve
OF
not
may
must
have
have
been
very abundant.
Zone ML-3b
Zone 3b is
land herbs
The
characterized by
and
an
elements ( Quercus,
strobus.
In
resembles
iod
at
zone
herbs.
the
where
follows
But
a
a
follows
zone
whereas
Bog
pollen
in
of Pinus
assemblage
prairie
and
per-
western
Quercus-Ostrya assemblage
of
Quercus
north,
Lake
the
and
upland
strong impact of
this
immediately,
the
Lake
the
(CBL)
because of the less
B.P.,
deciduous
and
type)
postdate
zone
interval in the
blage
Cedar
that
of mesic
the
southern
more
dry
Ostrya
principle
those
(BD) sites,
increase
decrease of up-
a
sort
at
Itasca
of
assem-
about 7000
area
transformation
and
of
at
the
arrival of
early
eastern
deciduous forest
the
B.P.
not
type
is
zone
JL-3
and 7210 ±
but
3b
northern and
to
Jacobson
the
fall
of
3920 ±
80 B.P.
(Y-1690).
area
the
D: 2730
coniferous
+ 75
(Janssen
At
is
again,
between
(bog
argued
zone
low
At
(Y-1779).
known,
in the
quite early.
transition from
Ostrya
pine
of Minnesota thus
suppresses
parts
forest
Lake
120
the
depends
forest. The
relationships
on
120
date
is
type is
in
BP.
(Y-1691)
In the Lake Itasca
arrives
that
where
±
the
Ostrya
Picea in lowlands
same
4840
B.P., Y-1156).
1967a)
3c,
zone
at
the
Lake
Myrtle
the
much
later
It has
been
occurrence
type
exist
of
at
of
upland
most
of
JANSSEN; POLLEN DIAGRAM
the
other sites in the
mation:
when
for-
coniferous/hardwood
arrives
pine
Picea
also
returns
in
FROM
1405
MINNESOTA
3
zone
indicate the kind
clearly
vegetation.
In
ML-3a there
zone
and thus appears earlier in the northeast than in
Typha latifolia followed in
the south.
mum
in
zone
are
Zone ML-3c
In
which
Betula,
birch.
bog
is
decrease
slight
a
based upon the regional
curve
of the decline is
most
sum,
of
ML-3c there
zone
In the
pine.
a
But if Betula is
Insectiferous
pollen
do
in the
for the
as
the total
these
upland
pollen
decrease of
the
upland
type.
their
is
It
is
the
again
the
slight
a
and
deciduous
not
Ulmus
shows
very
forests
forest fires
pine. Perhaps
upon
ratio
whatsoever
Ostrya type
therefore
based
pine
in
the
final dethat
probable
upon
Pinus
through
strobus stands, and semiprairies and Betula
of Pinus
banksiana/resinosa type
The Jacobson Lake
at the expense of
largely
time there is
a
a
increase
slight
of
The base of
2680 +
is 3920 B.P.,
et
al.
And
indeed,
and Abies
occurred
area
at
although
Myrtle
at
the
have
date
In
after
humid
may
climatic
a
zone
in
ML-3c
having
been
striking parallel
the
3
previous
by
a
and
the
zone
4.
Picea, Larix,
of
the Lake
2800 B.P.
a
Itasca
If both
to
error.
saccharum
absent
for
reappears
time,
In contrast
of
to
Lake
Itasca
2,
the
local
the
these
There-
next zone.
vegetation
swamp
is
species
and
string bogs.
sedge vegetation
in
reflected
Cyperaceae;
drop
the
and
of the
diagram
some
of
out.
the
under the raised
this
during
from
at
bog)
may have
then
amorphous
+
160
bog
the northern end of
at
this
so
most of the
pollen
west
Today
a
occurs
may
forest
of Myrtle
1963),
hypothesis.
have
to
the
come
stand of
the northern
end
sur-
from
of the
periphery
conspicuous
at
and
C-14
Myrtle Lake, forest
rather than from the
area
peatland.
A
Heinselman
which is in agreement with this
But
originated
underlying
peat
(W-562;
Sphag-
peatland
paludification
peatland had started.
the base of Lindford
Lake is 4360
of the
perimeter
time. If so,
of the
expansion
peat
at
a
Thuja
of the
area.
the Peatland in Zone ML-3
zone
also
(e.g.
lake. In
Development
of the
sedge peat
occidentalis
the
of
Much of the forest peat that underlies
face,
some
In
occur.
grains
peats overlie sedge peats almost up
with the succession of deciduous
forest elements in
fens,
swamps,
decrease of the
fen
the
recent
Poten-
richer character than the
present
num
date
then the Jacobson Lake
Acer
a
zone
bogs
change
until in the
from
swamps,
in these
trifoliata,
pollen
show
come
poor
However,
that
thickets).
which
at
Wright
to
expansion
triggered by
conditions,
be
zone
the
increase,
and
grains,
Ericaceae
likely
swamping
with
for
Larix
typical of
and
not occur
seems
same
dated
cause
in the north
Lake
been
it
poor Larix
Jacobson Lake it
at
time, about
same
phenomena
more
Lake is
Myrtle
earlier,
return
fore
banksiana/resinosa
the transition form
at
the
and
woods
diagram,
must have had
than 1000 years earlier.
stressed
Lake
the rich
at
originated during
a
synchroneity problem.
a
areas.
Myrtle
Menyanthes
types
pine is
upland herbs,
Pinus
(Y-1778);
more
(1968)
changes
4
zone
120 B.P.
at
unless
the base of the
zone, may have
today
palustris,
Myrtle
The
maximum of
type. There is, however,
and
Betula,
unless
or
large
pollen
and fens.
strings bogs,
essentially
of
at
of
Betula
pumila,
plants do
decrease
a
very low
unusually
Picea
numbers in this
high
were
transport.
shows
diagram
relationships:
same
usually
maxima of Alnus and Osmunda (a
species
the
vegetation
then would be
result of an intensified long-distance
the
are
mesotrophic
Part of
The increase
regeneration stages.
is
have
must
vegetation:
and there
tilla
involved in the
rich fen.
3c there is evidence for formation of
zone
swamp
Betula
encroached
swept
In
shifts
continue
a
sedge peats
peatland
a
time of zones 3a and 3b.
banksiana/resinosa
Pinus
Quercus
Lake
is
(Ambrosia)
curve
The
reaction
no
and
decline,
crease.
in
sum.
of
types.
tree
herbs
upland
favor
There
other
of
pollen
in
slightly
remains
covered
types
Most of the
noticeable
especially
still
fen
uli-
type,
these
regional pollen rain,
pollen deposition
pine.
increase
An
there
sum,
occur
like
grains
the
pumila,
excluded,
not
maxi-
a
Rumex orbiculatus
Bidens type, and Cicuta type, indicating
result of the increase
have been B.
might
of
pollen
of
peak
by
thyrsiflora, Campanula
type, Impatiens,
ginosa
3b
zone
peatland
a
Scattered throughout the
Dryopteris type.
Lysimachia
of
is
pollen
types
zone
3
Thuja
centages remain low
tinuous.
is
not
and
absent, but its
its
curve
is
per-
discon-
1406
CANADIAN
shows
Myrica
continental
is
three
Gates
1968;
soils
along
shores
even
today
there is
two
stream
(Fig.
lake
remnants
3A).
in
Myrica
is
lity
may
the
dust
in
Myrica
The
of
of
pollen
the
astrum
for the
which
is
Development
Pediastrum
In
after three
but
they
3c.
zone
maxi3c.
zone
phenomena
related
clearly
are
3b,
varieties,
striking
of these
f.
and Pedi-
abundant in
most
are
duplex
vegetation of
the
increases and
of the
at
species
and
area
to
peatlands.
the
a
had
became
but
percen-
minor
a
then,
change
type
much earlier
migrated
had remained
climatic
the
strobus
relatively high
result
raised
and
the
land
perhaps
postulated
important.
a
by
Abies
Also,
Pinus
come
tion),
not
deciduous
their lowest level in the
in
stands,
in.
a
after
According
ago
on a
of
which
Abies
one
(and
Heinselman
to
to
herbs
happened
zone
the
of
Fagus
was
in
Betula)
Myrtle
Lake
there
are
increase
east of Minnesota in
grain
fires
(conversa-
Abies
rock island in the
Tsuga, reflecting
Tsuga canadensis
Also,
in the
bog
leading perhaps
the
this
a
new
of
Wiscon-
found in this
the
At the top of the
zone
Ambrosia, Chenopodia-
have
and
impoverishment
a
suitable
but
areas
its
result of
margin
of the
but
available,
at
rise
an
in-
lake.
At the
a
the
peatland
the
from
vegetation
perhaps
decreases,
of
peatland,
Osmunda. Larix shows
to
swamp
new
also
margin. Thuja
been
At the
became
rich
and around
area
the northern end of the
apply
may
the
at
the
on
peatland
of the entire peat-
expansion
impoverished.
became
of
top
same
3
zone
the
zone
of continued
result
formation
of
raised
bogs.
There is
continuous decrease of
a
for
Fraxinus
low
to
panied
a
to
zones
3
occurs
The
Myrtle
to
4,
the
lake
sediments
levels.
Pollen
mainly
in
in
Lake.
At
Pediastrum
on
except
the
accom-
species
of
the transition
boryanum
Pediastrum is
for
type
from
the lower
events are
change
occur, and from then
Alnus,
Dryopteris
regional
striking
in
Pediastrum
from
percentage
zone.
by
and
nigra,
pollen types
fens.
minerotrophic
herbs
minerotrophic
part of the
ceases
rare
in
Pediastrum inte-
grum, which decreases but still remains present.
According
trum
is
raised
zone.
at
slight rise.
areas
time
only
not
availability
might
Thuja
same
Osmunda.
result of the increase
occurs
of the
margin
zone
of
and
Thuja,
a
1963) provided potential
from the
profited
decline
perhaps
In the upper part of the
occurrences
upland
diagram.
detail, reflecting
succession from Pinus
long
and
of Pinus and Abies faintly mirror
curves
peatland.
sin.
trees
It
for colonization
Salix,
other
at
Sphagnum peat
raised
islands in the
spruce
but lateral
tages of the
The
late in
Ericaceae appear,
and also
clearly
(Heinselman
areas
Larix
com-
the
on
lake,
characteristic
each
of lum-
Peatland
in the northern part of the
bog
reaches maximal values. In contrast, the percen-
at
and
of Picea,
of suitable habitats.
crease
Pinus
zone
vegetation,
are
Lake
present
peatland
strong rise
a
along
ML-4
ponent in the
it
Lake
the
to
The rise of Picea is
only
stays
level. The
Wright,
Myrtle
the
Sphagnum
began, leading
Features
of
topmost
relatively
was
that the formation of
favored
duplex
strongly halfway through
the base
the
4
zone
The
tage
the
effect
Zone ML-4
of
indicating
3a and
to zones
longicorne,
var.
zone
into
the
state.
of
the Time
in
At
which
area,
this part of the
Myrtle
Pediastrum
boryanum
known,
Regional
in the
bering
core,
in
pine
perhaps
is
integrum
in
have
may
decrease of
a
of the
possibi-
areas.
ecological significance
not
There is
sample
of
prominence
Another
synchronous
level in Minnesotadiagram.
all
before
time,
result of the arrival
a
to the formation of poor swamps and fens. There
other
changes
occurred
3
as
This is the third
man.
Pediastrum.
decreases
The
the
Poaceae rise
of the white
greater exposure
areas,
account
Pediastrum boryanum,
ma,
In fact
have
cohaerens is almost restricted
whereas
mineral
ceae, and
1968
46,
zonation is reflected in the behavior
alga
Pediastrum
on
rivers.
zone
pollen diagram.
peatland
swamps
Myrica along
may
during
large
storms,
Myrica
the southern end of the
at
Myrica
paludification
of beaches
belt of
a
and
and
OF BOTANY. VOL.
In
zone.
in
occurs
1942)
of lakes
around the lake. Also
the
but it
bog species,
(Heinselman
this
in northern America
regions
not a true
in
peaks
JOURNAL
a
to
bogs,
integrum
Schroevers
genus
that
but,
is the
(conversation)
generally
if present,
most
is
then
likely species.
Pedias-
absent
from
Pediastrum
On
the other
JANSSEN: POLLEN
the
hand,
from
trum
of the lake
surprisingly high pH
(Heinselman
should
1968)
DIAGRAM FROM
today
prevent Pedias-
not
occurring.
influenced
of
result
Remarks
Several sites
Weber
the
increased
the
at
prairie period,
greatly
forest
decreased,
the
subsequent
where
(bogs),
in lowland
2
areas
disappeared
the
of
type
and
west
in favorable
these
cannot
last
the
pointed
out
the
east
tion between the lowland succession
the
upland
easily
stressed. In
was
basin (Stevens
explained
the
runoff
types of upland forests. For
Myrtle Lake Peatland,
less
such
and here
probable,
by
tation
to
in the
in
zone
4
the
a
small
is
most
chemical
from different
like
relationship
there is
the
proportion
most
and the
of
of its
the
seems
a more
peatland
the overall character
soligeneous peatland,
pines
on
For
evaporation.
however,
ment,
a
change
a
of
a vast area
a
perhaps
direct influence of climate
tation
case
water
rela-
and that of
relationship
differences in
by
of the
composition
this
Pond),
vege-
precipi-
develop-
was
that of
of the
expansion
the uplands may have changed
on
the chemical composition
of the inflow into the
would
likely
of
bogs
more
The available radiocarbon dates
raised
started
bogs
to
initiated
perhaps
climate
Flint
be
not
the
of the
(end
Of
1957).
In older
form
by
a
suggest
about
3000
that
years
worldwide change in
most
start
problems
C-14
dates
needed.
state are
investigation
of
University
Hill
interest in
peatland
introduced
Dr.
trum.
the
across
kindly provided
E.
script.
The
nished
by
data
J.
Cushing,
in
to
me
the
that
bog.
Dr.
Lake
interesting
J.
criticized
were
my
Heinsel-
Myrtle
Schroevers
of Pedias-
ecology
radiocarbon dates
H. E.
ignited
some
Dr. P.
the
on
the
had
Cushing
the
manu-
kindly
fur-
Dr. Minze Stuiver of the Yale Univer-
Radiocarbon
sity
the
and Dr. M. L.
and with whom I
excursions
and
Among
were
spark
to
National
GB-3814)
(St. Paul).
the
provided
the
by
involved
were
bog ecology,
who
raan,
that
who
Wright,
(Grant
Foundation
people
many
supported by grants
was
Minnesota
Foundation
Family
E. J.
1963.
east-central
Laboratory.
Lake-Wisconsin
Minnesota.
pollen stratigraphy
Univ.
Minnesota
Ph.D.
Thesis.
1964.
from
in
pollen
Redeposited
pollen spectra
1967.
the
east-central
upland
Deevey
trees
and
also
are
Late-Wisconsin
glacial
sequence
paleoecology.
Edited
in
late-Wisconsin
Minnesota.
E.
J.
pollen
Am. J.
E.
J.
,
Yale
and
operated piston
Univ.
Press,
Wright,
corer
where
glauca pollen
on
1948),
a
and
distinction
was
longer
period, perhaps
from Indiana
made
than
in
(Potzger
between
on
P.
bogs.
Maine
(Griffin 1950),
Picea
the basis
glauca
of
during
and
Michi-
Friesner
mariana and
size,
the
P.
P.
mariana
lower
pine
stratigraphy
Minnesota.
by
__
Jr.
Wright,
Cushing,
Hypsithermal:
course,
diagrams
(Potzger
stays
start of
with the
and
cores
to
out-
Acknowledgments
The
for
H.
and
Quaternary
Cushing
pp.
lake
In
and
H.
E.
59-88.
Jr.
E.,
1965.
sediments.
Hand-
Ecology,
46:380-384.
Deevey,
1948),
con-
drainage
feature and
E.
S.
and
Flint,
R. F.
1957.
2
gan
been
who
so, then the
synchronous
from peat
more
has
intensified
an
local
a
expan-
regions
in other regions. To solve these
analyses
across
is
expansion
Jacobson
bog
(1968),
for
responsible
a
and the
date for the
at
possibility
Heinselman
a
Sci. 262:1075-1088.
area.
ago,
by
was
caused
area
4
than in
Another
that the
area
this would mean that
west.
was
bog
Science
the
1967a),
Lake
zone
flow of nutrients. If this is
the
glacial.
earlier paper (Janssen
to
smaller
a
that
sidered that increased erosion and
the
an
3
started earlier here
towards
Itasca
event
If the C-14
bog expansion.
pine
returned
Spruce
Lake
Myrtle
zone
to
possibility
a
climatic
in the
Lake is
correct,
sion
the
same
transition from
with the reintroduction of pine in the late post-
In
in
pine
of the
of
start
although
rem-
when
destroyed
uplands.
of
late-glacial
hardwoods
Finally,
were
of the
start
visualize relics
of
and
east-
conifer/hardwood
pine period
from the
disappeared
the
may
pine
compete with spruce.
nants
the
deciduous
a
forest
spruce
entered
and Larix
first in the south and
north. One
original
during
as
replaced
2,
zone
later in the
sites
time. At
Lake,
time of
Picea and Larix had
or savanna
forests of
the
Bog
bog vegetation
mid-postglacial
same
Jacob-
(bog D,
prairie expansion. Pinus, Picea,
ward
or
the
during
climate,
pine expansion
Cedar
Pond,
show that
Lake)
area
Minnesota
across
Stevens
Lake,
son
by
1407
There is therefore
degree.
arrival
Concluding
MINNESOTA
thermal
Faegri,
K.
interval. Science,
and
Iversen,
J.
125:
1964.
Postglacial hypsi-
182-184.
Textbook
of
pollen
analysis. Copenhagen, Munksgaard.
Fries,
M.
Recent
1962. Pollen
sediments
Ecology,
profiles
from
43: 295-308.
of late
Weber
Pleistocene
Lake,
and
Minnesota.
1408
CANADIAN
Gates,
C. 1942. The
F.
Ecol.
C.
Griffin,
D.
1950.
Randolph
Minnesota.
1968.
its
in
the
area, Minnesota.
C.
R.
Ecology,
Minnesota:
toba.
and
Shay,
Geol.
in
of
in
pollen
T.
indicators
37:
and
Quaternary
geology
states.
U.S.
Watts,
Minnesota
1964.
1967.
In
W.
A.
postglacial development
discussion.
Can.
J.
Prof.
Wright,
H.
E.,
H.
United
survey
Wright,
savanna,
Mem.
Potzger,
J.
H.
and
Torrey
J. E.
of lower
1966.
forest
Botan.
1948.
A
Michigan.
Postglacial history
in
northwestern
Club,
22
of
prairie,
E.,
Minnesota.
in the tension
Butler Univ.
Botan.
Contr.
and H. E.
Wright,
Jr.
T.
Winter,
Kirchner
Jr.
Botan.
Friesner,
R.
C.
coast of southern
C.
Studies,
of the
by
Press,
macro-
paleo-
a
77:1339-1360.
early postglacial
in the Great Lakes
region. Ecology,
Aspects
and
Ruhe,
Iowa.
In
by
R. V. 1965. Glaciation
The
H. E.
Jr., Winter,
E.,
pollen
Two
S.
E., Jr.,
Wright,
pp.
T.
Fig.
4
the
of
the
Jr. and D. G.
29-41.
and
C,
Patten,
from
diagrams
in
of
H. L.
southeastern
regional late-glacial
Geol.
Soc.
and
Am.
and
W.
A.,
and
vegetationalhistory
Glacial
Geol.
follow.
Watts,
Jelgersma,
S.
of northeastern
Unpublished manuscript.
1961.
Ontario.
II and
Quaternary
74:1371-1396.
H.
Minnesota.
Zoltai,
8:178-190.
Table
from
of the
problems
Bull.
Butler Univ.
Plant
1966.
vegetational history.
Wright,
Note:
So.
184-256.
Edited
Minnesota:
Marsh,
Minnesota:
zone
1948. Forests
Maine.
1;
Jr. Yale Univ.
Geol. Soc. Am. Bull.
1964.
and
1968. Glacial
J. E. and
past along the
the Yellow-
Canada.
Botany,
postglacial
Studies, 8:
161-177.
Potzger,
M.S.
Late-glacial plant macrofossils
States. Edited
H.
1963.
(2).
pollen study
along
Territories,
Princeton Univ. Press,
Frey.
547-
585.
McAndrews,
Minnesota,
45:439-448.
Wright,
of the flora
Botany, 37:
in
for
implications
Univ.
,
a
pine
Sta. Sci. J.
Quaternary paleoecology.
and
from
Minnesota
1959. The
Botanical
Northwest
ecological study.
161.
Manitoba:
of Jack
Agr. Expt.
and its
ecology.
Univ., Sida,
Cushing
fossils
and
Surv.
Mani-
lowlands.
Bay
distribution
Minnesota
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