Palynology of Three Bog Cores Shows Complex European
Impact on the Forests of Central Maine
Robert E. Nelson, C. Kittinger Clark, Elizabeth F. Littlefield,
and Newton W. Krumdieck
Northeastern Naturalist, Volume 17, Issue 1 (2010): 63–76
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2010 NORTHEASTERN NATURALIST 17(1):63–76
Palynology of Three Bog Cores Shows Complex European
Impact on the Forests of Central Maine
Robert E. Nelson1,*, C. Kittinger Clark1,2, Elizabeth F. Littlefield1,3,
and Newton W. Krumdieck1,4
Abstract - Short peat cores from three sphagnum bogs in central Maine were analyzed
palynologically to determine whether recent reforestation approximates forest
composition immediately prior to European colonization and deforestation. Radiocarbon
dating and palynology show that the cores extend to 600–2000 years b.p.,
beginning well before 18th-century colonial forest disturbance. Cores from Round
Pond bog (Franklin County) and Kanokolus Bog (Waldo County) show that Tsuga
canadensis (Eastern Hemlock) was much more abundant on the local landscape at the
time of European settlement than it is today; a core from Hamilton Pond bog (Kennebec
County) records an abrupt local Eastern Hemlock decline, and accompanying
Acer spp. (maple) rise, that preceded European contact by several centuries. All three
bogs show increased heath (Ericales) abundance with deforestation, presumably a
result of augmented nutrient flux into the bog basins due to increased erosion on
surrounding slopes.
Modern forest composition around all three sites is quite different from the forests
immediately preceding European colonization and clearing. Pollen types indicative
of agricultural activities (Ambrosia, other Asteraceae, Poaceae, Brassicaceae) that
mark European deforestation and the onset of farming, have faded or disappeared
as many farms have been allowed to revert to forest in the past half-century. Pine
(mostly Pinus strobus [White Pine]) is more abundant in the modern pollen record
than in subhistoric time, as are Abies spp. (fir) and Picea spp. (spruce); dominant
hardwood taxa have responded differently to reforestation of the areas surrounding
the study sites, in part determined by local edaphic conditions.
Introduction
The nature of pre-European North American environments is becoming
a question of significance as we attempt to evaluate the impacts of global
climate change and as attempts are made to re-establish “natural” ecological
habitats or restore aquatic ecosystems (e.g., Cantor et al. 2007, Carroll 1973,
Clark et al. 2007, Fuller et al. 1998, Lorimer 1977, Myrbo 2005, Pederson et
al. 2005, Russell and Davis 2001, Russell et al. 1993, Sanderson and Brown
2007). The full impacts of European colonization are only becoming readily
apparent in Maine as we carefully re-examine data at hand and undertake
new studies.
1Department of Geology, Colby College, 5804 Mayflower Hill, Waterville, ME
04901-8858. 2Current address - Department of Geosciences, University of Nebraska,
Lincoln, NE 68588-0340. 3Current address - Department of Geological Sciences and
Engineering, MS172, University of Nevada, Reno;1664 North Virginia Street, Reno
NV 89557-0138. 4Current address - 443 Taborton Road, Sand Lake, NY 12153. *Corresponding
author - renelson@colby.edu.
64 Northeastern Naturalist Vol. 17, No. 1
Much of central Maine, heavily agricultural prior to World War II, has
been allowed to return to forest as large-scale agriculture has become noncompetitive
with areas with warmer and longer growing seasons, and a
common popular assumption is that this reforestation represents a return to
natural—i.e., “normal”—conditions. This study was undertaken to compare
the modern post-agricultural forest composition of central Maine with that
which existed at the onset of European settlement, to determine whether this
assumption is warranted, and was based on study of the pollen content from
sphagnum bog cores, as a proxy for vegetation change on land.
Russell et al. (1993) and Russell and Davis (2001) have already studied
pollen from lacustrine cores across the northeastern United States, and
documented the regional impacts of European settlement, noting that modern
forests represent a product of complex interactions between natural conditions
and human disturbance. However, humans often interact with their environments
on a more local scale, and data at this level are not readily available. The
second contribution of this study is thus to document local-scale modern conditions
in central Maine as they compare to those of two to three centuries ago.
A third contribution is to determine what local changes might be masked in
large-scale studies, and particularly to determine whether bog pollen records
may show details hidden or absent in lacustrine vegetational histories.
Study Sites
Three sphagnum bogs were chosen for coring (Table 1, Fig. 1), aligned
roughly in an east–west transect across three formerly predominantly
agricultural counties in central Maine. Kanokolus Bog lies atop a bedrockbased
drainage divide with outlet streams to the north and south; Hamilton
Pond bog and Round Pond bog lie on the outlet ends of kettle pond basins
in glacial esker/outwash complexes, from which either first-order streams
originate (Round Pondbog) or subsurface flow (Hamilton Pond bog) drains
excess waters. Hamilton Pond undoubtedly drains through adjacent esker
sediments into the adjoining (and much smaller) Stuart Pond, from which a
first-order stream originates.
Kanokolus Bog is surrounded by soils of the Monarda series (Hedstrom
and Popp 1984), characterized by poor drainage and natural vegetation that
tolerates or prefers wetter sites, including Fraxinus spp. (ash), Acer rubrum
L. (Red Maple), Betula populifolia Marsh. (Gray Birch), Tsuga canadensis
(L.) Carrière (Eastern Hemlock), Thuja occidentalis L. (Northern White
Cedar), Larix laricina (Du Roi) K. Koch (Tamarack), and Picea mariana
(Mill.) Britton, Sterns and Poggenb. (Black Spruce).
Table 1. Specific locality information for each of the sites reported in this study.
Study Site County Town Core geographic coordinates
Round Pond bog Franklin Chesterville 44°31'14"N, 70°05'22"W
Hamilton Pond bog Kennebec Belgrade 44°27'58"N, 69°50'15"W
Kanokolus Bog Waldo Unity 44°33'28"N, 69°22'22"W
2010 R.E. Nelson, C.K. Clark, E.F. Littlefield, and N.W. Krumdieck 65
Both Round Pond bog and Hamilton Pond bog occur in complex eskeroutwash
glacial systems and are underlain by much-better-drained substrates.
Upland soils near Round Pond bog are predominantly Adams loamy sand
and Colton gravelly fine sandy loam (Hedstrom 2003); Hamilton Pond bog
is surrounded by Hinckley gravelly sandy loam (Faust and LaFlamme 1978).
Adams, Colton, and Hinckley soils are all considered excessively well-drained,
and forested sites underlain by these soils today commonly support communities
dominated by Pinus strobus L. (White Pine), Quercus rubra L. (Northern
Red Oak), Fagus grandifolia Ehrh. (American Beech), Betula alleghaniensis
Britton (Yellow Birch), and Acer saccharum Marsh. (Sugar Maple).
Figure 1. Index map of Maine, showing locations of the three study sites.
66 Northeastern Naturalist Vol. 17, No. 1
Historical Records
Earliest probes into the central Maine area were by fur trappers and
explorers, followed shortly by loggers, perhaps as early as 1650. Unfortunately,
early historical records by European explorers are unreliable as
regards species composition of the forests, inasmuch as all conifers were
generally called pines (Carroll 1973). However, Carroll (1973:24) presented
a generalized map indicating that the area under study lay near the northern
margin of a hemlock-White Pine-hardwood forest in presettlement times.
The earliest documented European settlers in the area of interest were
apparently in the Unity area, where they were driven out by the onset of the
French and Indian War in 1754 (Taber 1916). Settlers returned following
the close of the war, and the first frame house was erected in 1782, and the
censused population had grown to 264 people by 1799 (Taber 1916).
The earliest forest clearing in the Belgrade area apparently occurred in
1774, and the population had grown to 159 by 1790 (Guptill et al. 1976).
Logging had begun in Chesterville by 1780, and the first clearing for a
farm took place in 1782 (York 1976). Thus, it appears that the onset of
widespread forest clearing across the area of study occurred in the latter
half of the 18th century.
Field and Laboratory Methods
Coring sites at Round Pond bog and Hamilton Pond bog were selected
in open areas away from trees and shrubby vegetation; difficulty in reaching
such a site at Kanokolus Bog resulted in coring being done in a small
sphagnum-bearing swale in a wooded portion of the bog, surrounded by
Black Spruce and Tamarack.
Cores from 0.8–1.8 m in length were extracted from each of the bog sites
using a modified Livingstone piston corer (Livingstone, 1955). The coring
device was constructed with 5-cm-diameter stainless steel coring tubes and
T6 aluminum extension rods; the principal modification of Livingstone's
original design was the use of a coring tube with sharpened, serrated teeth
for cutting through the sphagnum mat (and any roots encountered) with a
minimum of compaction.
Coring success was outstanding, with no loss noted from any core segments
obtained. Peats recovered from Hamilton Pond bog and Round Pond
bog consisted of fibrous sphagnum peat, while that from Kanokolus Bog was
less fibrous and more humified, but nonetheless sufficiently coherent to yield
continuous core when extruded.
Hamilton Pond bog and Round Pond bog were cored from the open
sphagnum mats surrounded by heath thickets and occasional Black Spruce
and Tamarack; Kanokolus Bog was cored from within a Black Spruce stand
adjacent to the main sphagnum mat. Core segments were extruded and
wrapped in plastic film and aluminum foil in the field, and refrigerated until
sampled in the laboratory.
2010 R.E. Nelson, C.K. Clark, E.F. Littlefield, and N.W. Krumdieck 67
In the lab, cores were split lengthwise in January–February, 2007; winter
sampling minimized potential for airborne pollen contamination. Samples
were taken from the interiors of the cores at 5-cm intervals, beginning with
the core top. Pollen samples were immediately placed in 15-ml polypropylene
centrifuge tubes, covered with glacial acetic acid, and sealed. Samples
from approximately mid-depth and at the base of each core were oven-dried
in glass beakers at ≈50 °C, and submitted for commercial AMS radiocarbon
dating. The sample from 33 cm deep in the core from Kanokolus Bog consisted
of a piece of wood; other radiocarbon samples were 5-mm-thick slices
of sphagnum peat from the indicated depths.
Pollen samples were processed using standard techniques (Faegri and
Iversen 1989), including 5% KOH, coarse sieving (0.250 mm), HF digestion,
acetylation, dewatering using 95% ethanol and tert-butyl alcohol, and
mounting of residues in silicone oil (2000 cs. viscosity).
Pollen counts were performed at 400x magnification, with at least
300 identifiable pollen grains being counted at each level. Counting was
continued downwards in the cores until the bottom of the core was reached
(Hamilton Pond bog, Kanokolus Bog) or it was clear that pre-European
sediments had been reached (Round Pond bog). Pollen percentages were calculated
from the basic pollen sum (Σ on diagrams) including all identifiable
pollen grains, including potentially identifiable but unknown pollen grains,
but excluding moss, fern, and fungal spores. Monolete and trilete fern spores
were also counted.
Results
Radiocarbon ages for samples from these cores are shown in Table 2.
Results of pollen analysis for Hamilton Pond bog, Round Pond bog, and
Kanokolus bog are shown in Figures 2–4, respectively.
Radiocarbon dating shows clearly that all core bases date to well before
the initial European contact period. Although some modern carbon may have
been introduced via root contamination, this would have yielded apparent
Table 2. Radiocarbon dates for samples from each of the cores utilized in this study. All dates
are AMS radiocarbon determinations on 5-mm-thick peat slices from the indicated core depths,
except that from 33 cm at Kanokolus Bog, which consisted of a piece of wood ≈15 mm in diameter.
Avg. sed. rate = average sedimentation rate.
Depth Avg. sed. rate
Core Site (cm) 14C age* Calendar age** Lab number (mm/yr)
Round Pond bog 88 480 ± 40 1400–1460 A.D. Beta 228432 1.83
Round Pond bog 175 2120 ± 40 350–300 B.C.E. Beta 228433 0.83
Hamilton Pond bog 50 1090 ± 40 880–1020 A.D. Beta 228434 0.46
Hamilton Pond bog 90 1770 ± 40 140–380 A.D. Beta 228435 0.51
Kanokolus Bog 33 330 ± 40 1450–1650 A.D. Beta 228436 1.00
Kanokolus Bog 86 1950 ± 40 40 B.C.E.–130 A.D. Beta 228437 0.44
*Conventional radiocarbon age.
**2-sigma confidence interval.
68 Northeastern Naturalist Vol. 17, No. 1
Figure 2. Percentage pollen diagram for Round Pond bog, including position of applicable radiocarbon date; all percentages based on the basic
pollen sum (Σ). Dashed line represents approximate level of European impact. Analysis by E.F. Littlefield.
2010 R.E. Nelson, C.K. Clark, E.F. Littlefield, and N.W. Krumdieck 69
Figure 3. Percentage pollen diagram for Hamilton Pond bog, including position of applicable radiocarbon dates; all percentages based on the
basic pollen sum (Σ). Dashed line represents approximate level of European impact. Analysis by C.K. Clark.
70 Northeastern Naturalist Vol. 17, No. 1
Figure 4. Percentage pollen diagram for Kanokolus Bog, including position of applicable radiocarbon dates; all percentages based on the basic
pollen sum (Σ). Dashed line represents approximate level of European impact. Analysis by N.W. Krumdieck.
2010 R.E. Nelson, C.K. Clark, E.F. Littlefield, and N.W. Krumdieck 71
ages younger than the true age. Pre-European contact ages for core bases are,
however, confirmed by the palynology: increases in Ambrosia L. (ragweed),
grass and other agricultural weed pollen, commonly associated with forest
clearing, occur well above the core bases. Average sedimentation rates vary
among basins, with Round Pond bog showing the greatest resolution with 2
mm/yr accumulation; Kanokolus Bog sediments accumulated at ≈1 mm/yr,
and Hamilton Pond bog’s average sedimentation rate was ≈0.5 mm/yr.
All three sites show a significant increase in ragweed pollen about 200
calendar years b.p., which is accompanied by a sharp and significant decline
in hemlock at both Round Pond bog and Kanokolus Bog. At Hamilton
Pond bog, Eastern Hemlock declined abruptly some 600–800 years earlier
(800–1000 b.p.), for unknown reasons, and was accompanied by a rise in
Acer (maple) pollen; lesser but significant local declines in pre-European
Eastern Hemlock pollen percentages were also seen at Round Pond bog at
about 380 b.p. and at Kanokolus Bog about 500–800 years ago. At all three
sites, a rise in pollen of heaths also accompanies the spike in ragweed. Significant (30–50%) increases in birch pollen percentages occur immediately
above the spike in ragweed in each core.
At Round Pond Bog, both pine and spruce declined significantly with
European settlement, though both taxa were relatively unaffected by forest
clearance around both Kanokolus Bog and Hamilton Pond Bog. All three
sites, however, show modern pine pollen percentages far in excess of those
that characterized pre-European landscapes.
Maple increased in post-European time at Round Pond bog and Kanokolus
Bog, but decreased at Hamilton Pond bog. Oak is constant across
the European contact at Round Pond bog and Kanokolus Bog, but declined
at Hamilton Pond bog. Beech was not abundant at any site prior to European
contact, but nonetheless declined at both Round Pond bog (from 10% to
3.5% of total pollen) and Hamilton Pond bog (from 2–3% to all but absent).
Fir and spruce have both increased in recent years at Round Pond bog and
Kanokolus Bog, but remain essentially unchanged at Hamilton Pond bog.
Discussion
Based on this study and those of previous workers (e.g., Carroll 1973,
Russell and Davis 2001, Russell et al. 1993), the virgin forests at the time
of European arrival in central Maine had more Eastern Hemlock, birch, and
beech, and less pine, fir, and spruce than those of today. Eastern Hemlock
and Northern White Cedar were particularly abundant on wetter sites, such
as the riverbanks along which early exploration proceeded, including the
lower Kennebec Valley (Pierce 1775, reported in Roberts 1942). Small, local
clearings for Native American cultivation of Zea mays L. (Corn; reported by
Smith 1616) apparently were insufficient in size and impact to show in the
pollen record.
Forest clearing at the time of European colonization in Maine was mainly
for the purpose of opening farmland and followed closely on the heels
72 Northeastern Naturalist Vol. 17, No. 1
of commercial logging. The tall, straight conifers were highly prized for
shipbuilding timbers and masts; those greater than 24" in diameter one foot
above the ground were claimed as “King’s Timber” in the Massachusetts
Charter of 1691, and officially protected for exclusive use by the English
Crown (Kawashima and Tone 1983). Hemlocks were particularly prized for
the density and durability of their wood, and were also harvested for use of
the bark by the leather-tanning industry (Russell et al. 1993).
The deforestation with European colonization resulted in different major
impacts on species composition and relative abundances in the remaining
forests, and in land that was cut over and then allowed to regenerate
naturally. At Round Pond bog, the hemlock decline was accompanied by
an abrupt rise in birch and Alnus (alder) and a minor increase in ash, and
followed shortly by a rise in maple and walnut (probably Juglans cinerea
L. [Butternut]), The cooling climatic signal of the past two centuries, the
rise in spruce and fir (Russell and Davis 2001), is accompanied by a rise
in pine and, to a lesser extent, birch, that is probably in part successional
and in part anthropogenic, as pines are being widely planted for timber and
pulpwood production. Multi-crowned “pasture pines” (due to leader-killing
by Pissodes strobi Peck [White Pine Weevil]) in old pasturelands have also
regenerated areas of pine-dominated forest as abandoned pastures have reverted
to forest stands. Current birch pollen percentage, however, remains
below where it was in even late pre-European time.
Round Pond also showed significant grass pollen percentages (up to
nearly 10% of the total) prior to European forest clearing, probably in part
derived from marsh grasses at the outlet stream, though Hamilton Pond also
showed 2–5% grass pollen prior to disturbance. Both sites are situated in
geologic settings surrounded by exceptionally well-drained sandy soils that
may also have supported grasses in small open areas in addition to those in
the bog margins.
At Hamilton Pond bog, the European impact on Eastern Hemlock appears
to have been negligible, though maple, and to a lesser extent, fir, both
declined. Corylus (hazel) pollen percentages rise at the same time as Ericales
and ragweed, perhaps in response to greater light availability in forest
margins. The pre-European drop in hemlock, too abrupt to likely be just a
product of a climatic cooling (Russell et al. 1993), was followed by a gradual
decrease in oak and beech abundances, and an increase in maple (probably
mostly Sugar Maple) and subtle increases in both birch and spruce, which
may have been driven by gradual drying, or climatic cooling as suggested
by Russell et al. (1993). The pollen record culminates with a dramatic rise
in pine, particularly in the post-European time frame, where modern relative
abundance is twice what it was in the pre-European period. Only at the
very top of the core does maple drop dramatically. There is no discernible
increase in the abundance of either spruce or fir pollen at Hamilton Pond bog
from the time of first forest clearing, though the exceptionally well-drained
substrates in this area are not particularly hospitable to either fir or spruce.
2010 R.E. Nelson, C.K. Clark, E.F. Littlefield, and N.W. Krumdieck 73
Birch pollen, though variable, shows no clear trend over the entire Hamilton
Pond bog record.
At Kanokolus Bog, perhaps the least disturbed of the three sites, grass
was essentially absent from the record prior to the rapid rise in Ragweed
pollen that marked European agricultural clearing. Grass has dropped to
lower abundances than pre-European values at both Hamilton Pond bog and
Round Pond bog in modern samples, but remains detectable at modest levels
(3–5%) at Kanokolus Bog. This last site is also the only one of the three
still surrounded by significant active agricultural activity, predominantly
hayfields supporting a local dairy industry.
The climatically controlled modern rise in spruce and fir pollen (Russell
et al. 1993) is probably most dramatic at Kanokolus Bog, though overall percentages
remain low (<15% spruce, ≈5% fir); like the other two sites, pine
pollen here has increased dramatically—to almost 40% of the total pollen
content, or about four times what it was at the time of European forest clearing.
Birch pollen at Kanokolus Bog, however, is also less important today
than it was earlier in the record, just as at Round Pond bog.
A new finding from the study of all three of these cores, however, is
an increase in the pollen percentages of heath pollen at each of the sites—
something that has not been detected, and would not be expected, in studies
of lacustrine cores. Heaths are insect-pollinated and are represented by
a number of taxa in Maine’s sphagnum bogs, including Chamaedaphne
calyculata (L.) Moench (Leatherleaf), Rhododendron canadense (L.) Torr.
(Canadian Rhododendron or Rhodora), Vaccinium oxycoccos L. (Dwarf Bog
Cranberry), Kalmia angustifolia L. (Sheep Laurel), K. polifolia Wangenh.
(Bog Laurel) and Ledum groenlandicum Oeder (Labrador Tea). Pollen of
these plants would enter a depositional basin primarily by gravity fall of
dead flowers directly below the plants, rather than widespread dissemination
in the wind. Thus, the rise in this pollen type in all three sites indicates
significant local floral change at or proximal to the actual core sites.
Maine's sphagnum bogs, including those in this study, are generally
ombrotrophic, and receive all nutritional input directly from the atmosphere
(Davis and Anderson 1991), either in dust or as nucleation centers in precipitation
(raindrops or snowflakes). Sphagnum moss is able to survive and
develop extensive mats in wet lowland settings under these conditions, but
does not do well where greater nutrient availability allows competition. The
abrupt rise in Ericales pollen in each of these basins, coincident with the
rise in ragweed and agricultural weeds, strongly suggests that deforestation
resulted in increased nutrient flux, either by windblown dust or in surface
or subsurface water flow, into the waters of the respective bogs. At both
Kanokolus Bog and particularly at Hamilton Pond bog, pollen abundance of
heaths remains higher today than at any time in the late prehistoric record;
only at Round Pond bog has the level of heath pollen dropped back to pre-
European levels.
74 Northeastern Naturalist Vol. 17, No. 1
Hamilton Pond is ringed by multiple homes with septic systems for
waste-water discharge, and the bog coring site is situated at the outflow
end, adjacent to a state highway that runs on an esker crest. Thus, it may be
receiving enhanced nutrient flux at a rate higher than the other sites, neither
of which has any human dwellings nearby, from both road runoff and subsurface
water flow into the basin.
Kanokolus Bog also shows a sharp increase in pollen of Ilex (holly) at
the very top; I. verticillata (L.) A. Gray (Winterberry) grows extensively
around the perimeter of Kanokolus Bog today and is likely the species
represented in the pollen record. This wetland shrub has also apparently
benefited from increased nutrient flux into this particular basin, although
it was also quite abundant in the earliest sample studied, which dates from
nearly 2000 years ago.
Conclusions
Study of these three sites in Maine have shown that European impacts on
local forest composition, and its response, has varied significantly by site.
Eastern Hemlock, however, was much more important in the Maine forest
prior to European colonization than it is today. Maples have benefited from
the loss of Hemlock in the mature forest, though this has likely been Red
Maple at Kanokolus Bog and similarly wet sites and Sugar Maple on drier
substrates such as that surrounding Round Pond and Hamilton Pond. Reforestation
remains a dynamic process, influenced by both climate and human
impacts, as recorded regionally by Russell et al. (1993) and Russell and Davis
(2001) and in central New England by Fuller et al. (1998). Bog-dwelling
ericaceous shrubs, however, likely benefited from increased nutrient flux
into the bogs, particularly at Hamilton Pond bog. Pine, likely predominantly
White Pine, is clearly a much more important element in the modern Maine
forests than it was at any time in the late prehistoric period. This enhanced
importance of pine is likely a product of both intentional plantation management
and natural reforestation of abandoned agricultural lands.
Acknowledgments
Funded by the Natural Sciences Division Research Fund and the Department of
Geology, Colby College. Particular thanks to David Potter of Unity College for his
guidance and advice at Kanokolus Bog. Samuel B. Reid and Bradford M. Cantor of
Colby College, and Jackie Slawson and Holli Cedarholm of Unity College, also assisted
in the field. The manuscript benefitted significantly from thoughtful reviews
by two anonymous reviewers. Radiocarbon dating by Beta Analytic of Miami, fl.
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