Climate change and the development of coastal plain disjunctions in the central Great Lakes region

17 Pages·1997·6.7 MB·English

by  S T Jackson

1
RHODORA,
Vol. 99, No. 898, 101-117, 1997
pp.
CLIMATE CHANGE AND THE DEVELOPMENT OF
COASTAL PLAIN DISJUNCTIONS THE CENTRAL
IN
GREAT LAKES REGION
and Darren
Stephen Jackson K. Singer
T.
Aven
Department of Botany, Nelson Building,
WY
Wyoming, 8207
Laramie,
University of
Marsh northwestern
abstract. Paleoecological studies Portage in In-
at
diana provide a Holocene record of local populations of four species disjunct
Rhynchospora macrostachya,
from the Gulf and Atlantic Coastal Plains: R.
The
populations
Fuirena pumila, and Eleocharis equisetoides.
scirpoides,
were Portage Marsh when water levels dropped owing to re-
established
at
They
drying during the mid-Holocene. persisted until the late
gional climatic
macrostachya occurs the marsh. Populations of
Holocene; only in
R. still
these and other Coastal Plain disjuncts probably were established in the south-
mid-Holocene drying and formation of
ern Lake Michigan region following
extensive shallow wetlands by coastal processes. Seed sources for these pop-
We
Lakes propose
may Great region. that
ulations have been in the eastern
Great Lakes region
development of Coastal Plain disjunctions in the central
of westward range-shifts in response to cli-
consisted of a sequential series
migration along
than a single late-glacial
mate-induced habitat changes, rather
a corridor of suitable habitat.
populations, climate
Key paleoecology, disjunct
Words: biogeography,
Lakes
change, Great
with Gulf and Atlantic
species
populations of plant
Scattered
Great Lakes region
occur the central
in
Coastal Plain affinities
have
These species typically ex-
Reznicek 1994).
1922;
(Peattie
from
ranging south-
on Coastal Plain,
the
tensive distributions
New and occasionally southern
Jersey
Texas southern
eastern to
most North
New through of the
and absent or rare
England, are
geography, ecology,
review of the
American In a recent
interior.
Reznicek
populations,
and conservation biology of the disjunct
most
lakeshores
Although concentrations of the disjunct
water
fluctuating levels.
Lakes
Great region,
central
areas in the
occur several
species in
Lake Michigan
southern
the
and diverse
most extensive is
the
Michigan (Rez-
and southwestern
Indiana
region of northwestern
have been
populations
most Indiana
Unfortunately,
nicek 1994).
101
Rhodora
102 99
[Vol.
extirpated owing to extensive wetland destruction during the past
(Wilhelm
century
1990).
The Coastal Plain disjunctions have long intrigued ecologists
and biogeographers (Peattie 1922, 1930; McLaughlin 1932; Cain
Keddy Keddy
and Reznicek Rez-
1944; 1981, 1983; 1982, 1986).
nicek (1994) reviewed hypotheses proposed to explain the dis-
which from
junctions, range long-distance dispersal to late-glacial
migration along a corridor of suitable habitat extending along the
ancestral Great Lakes and their outlets. These and other expla-
nations are difficult to test empirically, however.
The of biogeographic explanations based on
difficulty testing
(Wood Brown
past events widely recognized 1972; and Gibson
is
1983; Stuckey 1993). Paleoecological studies are a powerful tool
ma-
for testing disjunction hypotheses, because pollen and plant
crofossils provide direct records of past occurrences and
distri-
butions of species (Whitehead 1972). For example, plant macro-
New
fossil studies of late-glacial sediments in England and the
eastern Great Lakes region have been used explanations
to test
for disjunct ranges of high-arctic and cordilleran species south-
in
Canada and Thompson
eastern (Miller 1979; Miller 1987, 1989,
1993).
We
have completed Marsh
a paleoecological study of Portage
in northwestern Indiana that provides a long-term record of local
populations of four Coastal Plain Eleocharis equiseto-
disjuncts:
ides (Elliott) Ton*., Fuirena pumila (Torr.) Sprengel, Rhynchos-
pora macrostachya and Rhynchospora
scirpoides (Vahl)
Torr.,
Griseb. (Singer et 1996). That record, combined with recent
al.
advances in understanding of the Holocene climatic history of the
Webb
Great Lakes region (Baker
1992, 1996; R.S.
et al. et al.
1993; Singer et 1996), provides a framework for evaluating
al.
We
the origin of the disjunction. describe here our paleoecolog-
summarize
ical results, the postglacial geological, paleoecologi-
and
cal, paleoclimatic history of the Great Lakes region, and dis-
cuss mechanisms
potential responsible for the Coastal Plain dis-
junctions.
MATERIALS AND METHODS
Portage Marsh, a shallow, 18 hectare marsh in the towns of
Portage and Garyton in northwestern Indiana (Figure among
is
1),
the few remaining undrained or marshes northwestern
unfilled
in
—
Jackson and Singer Coastal Plain Disjuncts 103
1997]
America.
North
Marsh eastern
in
Location of Portage site
Figure
1
.
The on
Lakeshore.
Dunes National site is
Indiana
Indiana outside
C
and 13,000 l4 years
between 12,200
deposited
sediments
shore
Glenwood phase of ancestral
B.P) during the II
Before Present (yr
The marsh
Thompson
1992).
and
(Chrzastowski
Lake Michigan
century.
human during the past
by activity
has been disturbed
1950s
before the
marsh urban;
The surrounding the is
landscape
Marsh vegetation
was predominantly agricultural.
landscape
the
Rhodora
104 99
[Vol.
dominated today by Carex lasiocarpa Ehrh. and Calamagrostis
is
Typha
canadensis (Michx.) Beauv., with scattered patches of
P.
Dulichium arundinaceum and Cephal-
(L.) Britton,
latifolia L.,
m
Open
deep
anthus occidentalis L. water patches (ca. 0.6 in
summer 1994) are occupied by Proserpinaca palustris L., Pota-
A
mogeton gramineus and Utricularia vulgaris L. complete
L.,
observed marsh provided Singer
of plants in the is in et al.
list
Plant nomenclature follows Gleason and Cronquist
(1996).
Of Rhynchospora ma-
(1991). the Coastal Plain species, only
crostachya has been observed in the modern flora and seed bank
of the marsh.
We
analyzed pollen and plant macrofossils from two sediment
was
cores (Singer et 1996). Core obtained using a land-
al. 1
cm
based vibracorer diameter) and included a complete se-
(7.6
quence of Holocene and sediments. Core which
late-glacial
2,
was
included only the top meter of sediment, collected using a
cm
Both
modified Livingstone piston-corer (10.2 diameter). cores
were taken approximately 75 meters from northern edge of
the
the basin, where sediments are deepest. Sediment age estimates
were based on radiocarbon dating of both cores.
cm
Sediment samples (50 3 each) were dispersed, sieved (710
X
and 355 jim mesh), and scanned 6.5 magnification using a
at
stereomicroscope for macrofossil analysis. All well-preserved
microspo-
macrofossils (including seeds, conifer needles,
fruits,
rangia, and oospores) were identified by comparison with her-
barium-documented specimens were
reference specimens. All as-
sumed Lake
modern
to be constituents of the flora of the southern
Deam
Michigan region (Peattie 1930; 1940; Voss 1972, 1985;
Swink and Wilhelm Notes on morphological used
1979). criteria
Appendix
macrofossil provided an Sing-
in identification are in in
er et (1996).
al.
Sediment samples for pollen analysis were prepared using stan-
dard dispersion and digestion procedures, suspended silicone
in
400 X
and scanned (Singer 1996). Pollen percentages
oil, at et
al.
sum
were on
for terrestrial taxa calculated based a of arboreal,
all
shrub, and upland herb types. Cyperaceae pollen was not included
in that sum. Pollen percentages for wetland and aquatic plants,
sum
including Cyperaceae, were calculated from a of terres-
all
and
wetland, aquatic types.
trial,
—
Jackson and
1997] Singer Coastal Plain Disjuncts 105
RESULTS
and
Pollen plant macrofossils from sediment
cores provide
a
record of regional upland and
local aquatic/wetland vegetation
for the past 11,000 years (Singer The
et al. 1996). pollen per-
centages for tree taxa, Ambrosia, and Poaceae (Figure primar-
2)
ily represent vegetation on the surrounding regional uplands.
Some
Poaceae and most Cyperaceae
pollen probably derives from
wetland
Marsh
The
pollen record during (>
the late-glacial interval 10,000 yr
B.P)
indicates regional vegetation consisting of open dom-
forest
by
inated Picea
spp. (Figure together with Abies, Larix, Pop-
2),
ulus, and Pinus banksiana Lambert (Singer 1996; Jackson
et
al.
Webb
et al. 1986; et 1983). During this period, the basin was
al.
occupied by
an open, hard water
Plant macrofossils
lake. are rare
sediments
0,000 and
of mixed
Que
Fraxinus and Carya The
L., nigra Marshall, (Figure
reus,
2).
was
basin occupied by submersed
a lake containing plants [Najas
&
flexilis (Willd.) Rostk. Schmidt, Chara Figure Emergent
sp.; 31.
plants were scarce in the basin, and sediments consisted of fine-
mud
textured
algal lake
(gyttja).
Between
6000 and 5500 yr B.P., the mesic forests of the region
were replaced by Quercus savanna (Figure At the same time,
2).
water Marsh dropped
levels in the Portage basin rapidly, leading
to development of a shallow, peat-forming marsh with a diverse
Many
assemblage of emergent plants (Figure of the emergents
3).
are annuals or perennials characteristic of exposed shorelines and
drawdown The
mudflats during temporary occurrence of
events.
submersed Potamogeton and
(Najas Chara, spp.) floating-
flexilis,
drawdown
leaved emergents
plants (Brasenia) together with the
in the assemblages regime of interannual water level
indicates a
fluctuations.
Figure Pollen percentage diagram from Portage Marsh Core Only
2. 1.
taxa
am
Figure
3.
Core
1. Only selected taxa are included. Modified from Singer et al. (1996).
Rhodora
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Jackson and
1997] Singer Coastal
Plain Disjuncts 107
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Jackson and Singer Coastal Plain Disjuncts 109
1997]
The {Rhynchospora
four Coastal Plain species scirpoides, R.
macrostachya, Fuirena pumila, and Eleocharis equisetoides) col-
Of
onized the marsh between 5700 and 4500 yr B.P (Figure
3).
shallow-water submersed while
these, E. equisetoides a plant,
is
and pumila emergents of
R. scirpoides, R. macrostachya, F. are
Rhynchospora
and wet scirpoides
mudflats other exposed,
sites.
and pumila
F. are annuals.
Quercus savanna on uplands of northwestern Indiana
persisted
American 1980),
al-
and Fagus developed
though mesic of Acer, Betula, lo-
forests
Holocene
cally on with fine-textured soils during the late
sites
Futyma
3000 yr B.P; Singer 1996; 1985; Bailey 1972).
(ca. et al.
mixed
assembla
Marsh
underwent some changes
emergent
turbance, although the flora
2800 and Eleocharis equisetoides dis-
after yr B.P. (Figures 3 4).
Rhynchospora scirpoides and Fui-
appeared 2800 B.P, but
yr
ca.
American
may marsh Euro-
rena pumila have persisted in the until
disturbance (Figures 3 and The exact timing of their extirpa-
4).
spanning
owing a depositional hiatus at least
tion uncertain, to
is
Rhynchos-
the 19th and early 20th centuries (Singer et al. 1996).
have persisted in the
pora macrostachya populations evidently
and
4500 years (Figures 3 4).
basin throughout the past
DISCUSSION
The
Holocene
climate
and water
lev-
wetland vegetation,
changes
in regional vegetation,
Marsh
10,000 yr
pattern
Holocene (10,000
warm, moist climate during the early
5700
mid
J
Holocene (2800 yr B.P. to
cooler, moister conditions in the late
Marsh
from Portage
diagram
concentration
Figure macrofossil
4. Plant
spanning the past
meter of sediments,
Core Core 2 includes only the top
2.
from
Modified Sing-
included.
2800 Only taxa are
radiocarbon selected
years.
er
et (1996).
al.
110 Rhodora
[Vol.99
documented
present). This a regional climate pattern in east-
fits
ern Iowa, northern southern Wisconsin, northern Indiana,
Illinois,
(Webb
and Michigan Baker
southern 1983; 1992,
et et
al. al.
1996; Singer 1996).
et
al.
The Holocene
period of highest effective moisture pre-
(i.e.,
minus Lake Mich-
cipitation evapo-transpiration) in the southern
6000
igan region, 10,000 to yr B.P., corresponds to the Milan-
summer maximum
kovitch insolation following withdrawal of the
Webb
Laurentide ice sheet (Kutzbach and 1991). Wright (1992)
summer
proposed monsoonal
that higher insolation amplified
summer
flow into the southern Great Lakes region, increasing
Reduction monsoonal flow summer
rainfall. in as insolation de-
6000 B.R
creased after yr led to drier conditions. Continuing late
Holocene summer
reduction in insolation led to cooling and in-
creased effective moisture after 3000 yr B.P. (Wright 1992; T.
Webb
et 1993).
al.
The eastern Great Lakes, Lawrence and Hudson-
valley,
St.
Mohawk
lowlands experienced sequence of Holocene
a different
climatic changes. These regions also were cool and moist during
the late-glacial period (> 10,000 yr B.R). However, they were
warmest and Holocene 6000
driest during the early (9000 to yr
Webb Webb Webb
B.R; Gaudreau and
1986; 1990; R.
S. et
al.
Webb
summer
High were
1993; temperatures
T. et 1993). re-
al.
summer maximum.
lated to the insolation Regional lake levels
were low (Webb and upland was
1990), vegetation relatively xer-
Webb Summer may
have been
ic (R. S. et 1993). precipitation
al.
low summer
because storm tracks were shifted north (relative to
today) along the steep thermal gradient the edge of the Lau-
at
(Webb much
rentide ice sheet 1990), which occupied of eastern
Canada from 9000 to 7000 yr B.P. (Dyke and Prest 1987). Ef-
Webb
fective moisture increased after 7000 yr B.R (R. S. et
al.
and
1993), the region has undergone a cooling trend for the past
Webb Webb
5000 years (Gaudreau and
1986; 1993).
T. et al.
Climate change and
the origin of coastal plain disjunc-
Hypotheses proposed
tions. to explain the Coastal Plain dis-
junctions in the Great Lakes region into two general cate-
fall
Holocene
gories: (1) long-distance dispersal from the Coastal
and
Plain populations, (2) late-glacial migration along the ances-
Great Lakes and Lawrence and Hud-
their outlets in the
tral St.
son-Mohawk
and up
valleys the Mississippi and River
Illinois