Late-glacial and postglacial vegetational history of the Berkshires, western Massachusetts

QUATERNARY

RESEARCH

Late-Glacial

12, 333-357

(1979)

and Postglacial Vegetational History Western Massachusetts DONALD Received

of the Berkshires,

R. WHITEHEAD January

30, 1975

A pollen analytical investigation of the sediments of Berry Pond, Berkshire County. Massachusetts, has demonstrated a sequence of pollen assemblage zones similar to those detected elsewhere in New England. From about 13.000 to 12,000 yr B.P. the vegetation of the region was treeless, probably tundra. By 11,500 yr tundra had been replaced by open boreal forest. Closed boreal forest became dominant by 10,500 yr. Boreal forests were replaced by mixed coniferous and deciduous forests with much white pine about 9600 yr ago. A “northern hardwoods” complex with much hemlock, beech, and sugar maple succeeded the mixed forests 8600 yr ago. Hemlock declined very rapidly approximately 4800 yr ago and was replaced by birch. oak, beech, ash, and red maple. This decline may have been biologically rather than climatically induced. There is a slight maximum of pine (much of it pitch pine) from 4100 to 2600 yr ago, perhaps indicative of warmer and/or drier conditions. There were slight changes in the forests about 1600 yr ago as chestnut immigrated and spruce and larch increased slightly. European land clearance and subsequent land abandonment are detectable in the uppermost levels.

now familiar pollen assemblage zones detectable in most complete New England diagrams. More recently similar techniques have been applied to sites in northern New England (Davis et al. 1975). The sequence of pollen zones (herb zone, spruce zone, pine zone, and deciduous zones) is indicative of an essentially unidirectional sequence of vegetational changes from time of deglaciation to at least the midpostglacial. The vegetation was initially treeless, probably tundra; this was probably replaced, in sequence, by open boreal forests, closed boreal forests, mixed coniferous and deciduous forests (with much white pine), and ultimately by deciduous complexes with varying amounts of conifers. The changes within the deciduous zones in southern New England (zones C 1, C2, and C3; e.g., Deevey, 1939; Davis, 1969, 1976) have been variously interpreted, but it has been traditional to suggest that the change from an oak-hemlock assemblage (Cl) to oak-hickory (C2) was a function of warmer and/or drier conditions during the hypsithermal. The change to oak-chestnut (with some spruce) (C3) ap-

INTRODUCTION

Over the past several decades pollen analysis has been utilized in the investigation of a number of lake and bog sites in the Northeast (see reviews in Davis, 1975, 1976: Ogden, 1965; Sirkin, 1967; Davis et al., 1975; Bernabo and Webb, 1977). This work has permitted a reconstruction of the vegetational changes occurring during the late glacial and postglacial. Although sites are scattered throughout the region (Davis, 1965, Fig. l), the most comprehensive knowledge is available from southern New England and adjacent Long Island. This is a function of the number of localities that have been investigated and of the techniques employed. The use of correction factors for differential pollen representation (Davis and Goodlett, 1960; Davis, 1965), comparison of modern and fossil pollen assemblages (Davis, 1967), studies of pollen sedimentation rates (Davis and Deevey, 1964; Davis, 1969), and use of isochrone maps (Davis, 1976; Bernabo and Webb, 1977) have permitted less equivocal speculations concerning the character of the vegetational assemblages which produced the 333

0033-5894/791060333-25$02.00/O Copyright All rights

0 1979 by the University of Washington. of reproductmn in any form reserved.

334

42’

DONALD

R. WHITEHEAD

30’N-

BERRY

POND

PONTOOSUC 0 ‘

0.5 1

I *

SCALE

FIG.

1. Index

map of Berry

proximately 2000 yr ago is thought to indicate a return to cooler and moister conditions. In the uppermost portions of most profiles European land clearance can be detected by a dramatic rise in ragweed pollen (and pollen of other weedy species) and decline of tree pollen. Higher in most profiles land abandonment can be discerned by a sharp increase in pine pollen. Although this general framework seems reasonable, it is clear that many interpretational problems remain. Detailed studies at Moulton Pond in Maine have indicated that previous interpretations of some of the late-glacial pollen zones (most notably the spruce-dominated zone) may be incorrect and that pollen influx data must be used

Pond

and surrounding

LAKE 2 I

(KM)

area.

with caution, as significant sources of error remain (Davis et al., 1975). Clearly additional studies are necessary (1) to fill the many existing geographic gaps in our knowledge, (2) to provide more accurate dating for vegetational events, and (3) to permit more careful evaluation of pollen influx data. The Berkshire region of western Massachusetts, an area of topographic and vegetational diversity, is one region from which no paleoecological information is currently available. Hence this study was initiated some years ago with the primary objective of providing information on the late-glacial and postglacial vegetational and climatic history of the area. Since the initial

VEGETATION

HISTORY

pollen work was done it has become apparent that Berry Pond, the site here reported on, is of further interest because of its limnological history (Whitehead er al., 1973). Hence the project has evolved into an attempt to reconstruct (1) the vegetational history of the region and of the Berry Pond watershed, (2) the trophic history of Berry Pond itself, and (3) the character of interactions between the terrestrial and aquatic ecosystems. The present paper deals with the pollen analytical portion of the study. SITE DESCRIPTION

Berry Pond is a small lake (surface area 3.9 hectares, maximum water depth 2.8 m) located on a saddle of the Taconic ridge crest (elevation 600 m) in the Pittsfield State Forest, Berkshire County, Massachusetts (Fig. 1). It is situated in a forested watershed of 28 hectares. The pond has only one outlet, a stream which flows over a rocky ledge to the northwest; and there are several rivulets entering it, including a generalized flow through a boggy area in the southeastern arm (Fig. 2). The bedrock of the ridge is a chloritoid schist (Rowe schist) of presumed lower Cambrian age (Prindle and Knopf, 1932), the common bedrock type of much of the Taconic range. The soils of the watershed are weakly de-

FIG. 2. Bathymetry B, and C indicate. work.

of Berry respectively,

Pond. Dots indicate the pollen core,

OF

335

BERKSHIRES

veloped podzols formed in the mantle of till (Marbut, 1935; Egler, 1940). The pond is of further interest as it is the highest natural pond in the state and one of the few ponds in the area lying above the highest shorelines of the late-glacial lakes (Lakes Bascom and Housatonic) which once filled the Berkshire lowlands. CLIMATE

AND VEGETATION

Weather data for the Berkshires are available from stations in both Williamstown to the north and Pittsfield to the southeast. The data are quite comparable and indicate an average annual precipitation of between 96 and 117 cm evenly distributed throughout the year. The mean January temperature is about -4.X, the mean July temperature 21.6”C (Egler, 1940). As Berry Pond is at a higher elevation than either Pittsfield or Williamstown, one would expect the temperatures at the site to be lower by between 2.5” and 4.2”C, depending upon atmospheric moisture. Furthermore, given the location of the pond on an exposed saddle of the Taconic range, the watershed should be subjected to higher wind velocities. The Berkshire area lies within the Hemlock- White Pine-Northern Hardwoods Region as described by Braun (1950). How-

points at which core probes were taken. Letters radiocarbon core, and core for paleolimnological

A,

ever, given the highly irregular topography. the variety of bedrock types, the different glacially derived surficial sediments, and the long history of human disturbance, the region supports a variety of vegetational types. These have been well documented by Egler (1940) in his study of the Berkshire Plateau just to the east. In late May and early June of 1974 a careful study was made of the vegetation within the Berry Pond watershed and a qualitative study was made of the vegetation in the surrounding Pittsfield State Forest. Data on trees and shrubs plus saplings and seedlings were collected using the quarter method. Ground quadrats (1 m”) were used to determine herb densities and frequencies. The transects were 150 m long with quarter points at 10-m intervals. Three to four transects were run on each slope (N, S, E, and W) of the pond.

It is clear that the vegetation of the watershed is second growth and far from equilibrium. This is partly a function of the road which transverses the western edge of the pond, a campground and picnic area on the western and southern shore, and a small spruce and pine plantation on the upper slopes on the north side of the watershed. Data on frequencies of seedlings, saplings, and adults of the trees and shrubs are presented in Table 1. Percentage basal area data are also included. From this information it is apparent that red maple (Acer tw burn; authorities for all species as in Fernald, 1950), red oak (Qurrc~~s rlrbva), American ash (Fraxitzus americ~rrtza ), and black cherry (Prumrs serotina) are more common than would be expected if the forests were reasonably mature. Beech (Fagus gratzdifolicr 1. sugar maple (Acer saccharum), yellow birch (Betrrlrr lrrteu),

TABLE DATA

Species Acer Acer Acer

penns~lvanicum rubrum saccharum

Acer spicatum Amelanchier Berula lutea Betula

lae\?s

papyrifera

ON TREES

AND

SHRUBS

1 IN BERRY

Adults (70 basal area)

Saplings (%)

Seedlings (9)

9.93 19.76 14.90 0.66

1.11 23.24 9.52 0.11

18.82 13.39 8.08 2.00 1.73 1 7-l i.--

20.26 9.39 2.34 1.00 5.51 1.40 0 0 1.00 1.24 11.66 2.10

0

11.46 3.65

0

9.45 3.18

dentata

0

0

Carpinus

caroliniana

0 0

0 0

Populus Prunus Prunus Prunus

tremuloides pennsylr~anica serotina rirginiana

Quercus uubra Rhododendron roseurn Sambu~us pubens Sorbus Spirara Viburnum Viburnum Vihumum

americana 1atijXa acerij&um alnifolium recognitum

WATERSHED

Adults (96)

Castanea

Coqlus rostratu Fagus grandifolia Fraxinus americana Hamamelis rsirginiana

POND

21.50 3.40

15.96 5.68

0 0.40 1.36 3.45 34.42 2.80

0

0

2.14

0.700

0.33

0.10

0

0

0

0

0.90

6.91

0

0

0.34 1.00 0.44 0.84

0 3.18 1.34 6.10 2.23 0.330 0.40

7.02 0 0 0

24.67 0 0

0 0 0

0 0 0 0

0.44

0.22

0 0 0 0

1.03 4.06

1.00

2.36 4.00

13.66 6.96

VEGETATION

HISTORY

and white birch (Bet& pupyrifera) are also common overstory trees. The seedling and sapling data suggest that many of the more species are continuing to “opportunistic” reproduce. Although white pine (Pinus strobus) and hemlock (Tsuga canudensis) were not tabulated in the actual counts, there are a few isolated white pines in the watershed and a number of hemlocks along the shore. There are also scattered sweet birches (Betulu lentu) and a number of large hornbeams (Carpinus caroliniana) on the north shore. At lowest elevations in the State Forest and particularly along stream valleys, the vegetation appears to be more typical of the “northern hardwoods” forest of the region. Hemlock, sugar maple, and yellow and white birch are more common and ash, oak, red maple, and cherry less so. There is also a large stand of red pine (Pinus resinosa) near the forest headquarters. The shrub layer of the watershed is typical of northern hardwoods forests. Striped maple (Acer pennsylvunicum), mountain maple (Acer spicutum), beaked hazel (Coryfus rostruru), hobblebush (Viburnum ulnifolium), witch hazel (Humumelis virginiunu), shadbush (Amelunchier sp.), hornbeam, and hop hornbeam (Ostryya virginianu; present but not recorded in the transects) are common. In more open spots azalea (Rhododendron sp.), choke cherry (Prunus virginiana), and pin cherry (P. perkylvunicu) are frequent. Along the lake shore and in wetter spots arrowwood (Viburnum recognitum) and mountain holly (Nemoputhus mucronutu; not recorded on the transects) are common. There are several patches of mountain laurel (Kafmiu lutifoliu) on the west shore and a single patch of yew (Tuxus cunudensis) just out of the watershed on the west side of the pond. The other shrubby species encountered are indicated in Table 1. The boggy area in the eastern arm of the pond (Fig. 2) has a shrub community dominated by alder (Afnus rugosu), arrowwood, willows (Sulk sp.), and saplings of yellow

OF

337

BERKSHIRES

birch, gray birch (Bet& populifoliu), red maple, and mountain maple. Steeplebush (Spirueu tomentosu) and leatherleaf (Chumueduphne culycufutu) occur near the edge of the pond. There are many herbs characteristic of wet habitats. The aquatic macrophytes of the pond itself have been sampled on several occasions. Apparently much of the production in the pond is now bound to this community, as the entire bottom is carpeted by a dense mat of water milfoil (mostly Myriophyllum furwellii) and Nitellu. Spatterdock (Nuphur udvenu), water lily (Nymphueu odorutu), pondweeds (Potumogeton spp.), Sugitturiu subulutu, and Spurgunium fluctuuns also occur. FIELD TECHNIQUES

The pollen core (Core A) was obtained in October 1965 with a Livingstone sampler. The radiocarbon core (Core B) was taken by the same means in November 1968 (Fig. 2). The latter core also was used for preliminary chlorophyll extractions and pollen work. Present and initial bathymetry was determined from 30 cores and soundings taken in the summer of 1971 and in January 1972. Cores were extruded and described in the field. They were then wrapped in Saran and aluminum foil. All cores have been stored in a cold room at approximately 4°C. LABORATORY

TECHNIQUES

Sampling was initiated by cutting a disk 1 cm thick from the desired level of the core. This was accomplished by utilizing a device with two fine, parallel, stainless-steel wires located precisely 1 cm apart. Samples for various types of analysis could then be obtained from the disk. Subsamples were obtained with a punch designed to remove a cylinder having a volume of exactly 1 cm3 from the disk. Pollen samples were prepared by a KOH, HCl, HF acetolysis sequence. The residue was transferred to a small flask in 25 ml of tertiary butyl alcohol. The flask was then placed on a magnetic stirrer and the pollen

338

DONALD

HERB

Species Aralia nudicaulis Arisaema triphyllum Aster acuminatus Aster divaricatus Aster sp. Athyrium filix-femina Carex sp. Clintonia borealis Coptis groenlandica Cornus canadensis Cyperaceae (?) Dennstaedtia punctilobula Dentaria diphyila Dryopteris noveboracensis Dryopteris spinulosa Epigaea repens Erythronium americanum Gaultheria procumbens Gramineae (?) Impatiens sp.

No.lm’ 0.31 0.74 3.75 1.08 0.04 0.17 5.02 2.60 14.95 0.56 0.506 1.51 0.04 2.83 0.39 0.09 7.50 0.42 0.23 0.01

DATA

R.

WHITEHEAD

TABLE

2

FOR BERRY

Percentage 0.11 0.44 3.43 1.24 0.02 0.11 2.95 1.83 8.78 1.51 0.24 0.91 0.02 1.67 0.29 0.09 4.41 0.25 0.14 0.008

suspended by gentle stirring. Aliquots (0.1 or 0.2 ml) were transferred to silicone oil (12,500 cSt) mounting medium on slides using an Eppendorf micropipet. Slides were counted using a Leitz-Orthoplan microscope at a magnification of 400 diameters. Critical or difficult grains were studied at 1000 diameters and with phase contrast. In each case the entire slide was counted and all pollen, spores, algal remains, and other recognizable microfossils were recorded. Grains that could not be identified because of corrosion, crumpling, or obscuring detritus were classified as “unidentifiable.” Grains that were in good condition but which could not be identified were classified as “unknown.” If possible 500 grains were counted for each level (exclusive of spores, pollen of aquatics, algae, etc.). The extremely low pollen density of the lower levels made this impractical. Forty-two levels were counted. For each level, pollen data were expressed in two ways, as percentages and as accumulation rates. All pollen and spore percentages were based on a sum of pollen of terrestrial trees, shrubs, and herbs. Un-

POND

WATERSHED

Species

No./m’

Lycopodium lucidulum Lycopodium obscurum Maianthemum canadense Medeola virginiana Mitchella repens Onoclea sensibilis Osmunda claytoniana Osmunda cinnamonea Panicum sp. Prenanthes sp. Pyrola sp. Rubus sp. Smilacina racemosa Solidago sp. Trientalis borealis Trillium erectum Trillium undulatum Uvularia sessilifolia Vaccinium angustifolium Viola sp.

Percentage

16.44 0.67 60.93 0.30 1.32 0.33 0.23 0.06 11.71 1.68 0.01 0.37 0.39 0.014 3.076 0.288 0.22 7.174 2.64 0.32

6.91 0.19 37.71 0.61 1.65 0.19 0.13 0.14 7.14 2.10 0.008 0.22 0.22 0.008 1.72 0.17 0.29 4.08 2.50 0.88

knowns and unidentifiable grains, plus spores of pteridophytes and pollen of aquatics, were excluded from the pollen sum. Accumulation rates were determined by first calculating the pollen concentration per cubic centimeter of sediment and then correcting this with a sedimentation rate factor based on the radiocarbon dates from the profile. Pine pollen was recorded as Pinus strobus, non-Pinus strobus (for wellpreserved pine grains that were clearly not white pines), or unknown pines. Size-frequency studies were also made on 100 intact pine grains from selected levels (measurements as in Whitehead, 1964). RADIOCARBON

DATES

Samples for radiocarbon dating were selected from Core B. Pollen preparations were made from levels immediately above and below each of the levels submitted for radiocarbon dating so that the stratigraphy could be checked and the dates then extrapolated to the pollen core. Eight levels were selected and from each two samples were extracted for dating (Table 3; Fig. 3).

VEGETATION

HISTORY

OF

TABLE RADIOCARBON Depth (m) “C core 1.50-1.53 1.53-1.58 2.50-2.53 2.53-2.57 3.50-3.53 3.53-3.57 4.50-4.53 4.53-4.57 5.50-5.53 5.53-5.57 6.46-6.50 6.50-6.53 7.16-7.20 7.20-7.23 7.50-7.55 7.55-7.60

IU-101 owu-474 IU-100 owu-475 IU-99 OWU-476 IU-98 owu-477 IU-97 OWU-478 owu-479 IU-96 owu-480 IU-95 OWU-481 IU-94

B.P

BERRY

“C date 1,720 955 3,000 2,720 3,710 2,665 4,050 4.801 5,070 5,399 7,825 8,320 9,237 9,890 12,679 12,400

Note that both the table and the figure include equivalent depth in the pollen core. The equivalent depth was determined in two ways: by assuming a uniformly lower sedimentation rate for the pollen core and second, by checking with a rough pollen stratigraphy (Table 4). Sedimentation rate calculations are based on the pollen core alone.

YEARS

3

DATES FROM

Sample no.

(X 10’)

y(cm)=-7.40+(ll.27X162)x-(4.65X166Jx2

FIG. 3. Radiocarbon dates from Berry Pond. Triangles indicate dates run by Indiana University (IU) laboratory: dots signify those run by Ohio Wesleyan University (OWU) laboratory. Depth scale on right indicates the radiocarbon core (Core B): scale on right refers to the equivalent depth in the pollen core (Core A).

339

BERKSHIRES

k + k 2 2 k 2 f + 2 k + 2 2 f -r-

POND Equivalent pollen

150 135 170 150 170 115 190 201 190 154 294 310 230 390 480 260

depth core

(m)

1.36 1.39 2.26 2.28 3.15 3.18 4.06 4.08 4.95 4.98 5.81 5.84 6.43 6.47 6.74 6.79

Although no radiocarbon dates are available from the mud-water interface, the slope of the age vs depth curve (the curve is based on a second-order polynomial regression) suggests that the radiocarbon age of the surface sediments would be close to zero. For this reason no correction has been applied to the dates. As the bedrock type of the basin and surrounding hillsides is schist, I would expect there to be less ancient carbonate in the groundwater than in situations such as Rogers Lake in southern Connecticut (Davis, 1969). This is corroborated by surface dates from North Pond (also in Berkshire County and in the same bedrock type). Matrix accumulation rate has been calculated from the slope of the regression line (line and equation in Fig. 3). Although there is no radiocarbon control below 7.55 m (6.79 m in the pollen core), I have tentatively extrapolated the regression line beyond this point. Clearly this assumption needs verification, especially since there is a sharp change in sediment character at that point. Accordingly, the matrix accumulation rates for the lower levels must be viewed with caution. The regression line suggests a smooth change in rate from 0.010 cmyr at 12,700 yr ago to 0.111 cmiyr at the

DONALD

340 PINE

R.

WHITEHEAD

MICRONS

CURVE zk

30 I

ij

0

2

X IO3

BziPINUS

4

35 I

40 I

47 I

5p I

30

6

GRAINS/CM2/YR

STROBUS

@j NON-PINUS

STROBUS

[7 UNIDENTIFIABLE 4. Pine data for Berry Pond. Note that pine-influx curve is not identical to the pine curve on the accumulation-rate diagram (Fig. 7) because drafting was done before radiocarbon dates were available: hence. not all the correction factors for rate of matrix accumulation were correct. FIG.

top of the profile. Other interpretations cannot be excluded, however. Possibly there were transient increases in sedimentation rates at about 8000 yr B.P. (as at Roger’s Lake) and 2200 yr (Fig. 3). Dating at closer intervals would be required to determine this. Such changes in accumulation rate would not, however, cause major alterations in the general pattern of pollen influx. IDENTIFICATION

OF PINE POLLEN

Clearly environmental reconstructions would be more accurate if all pollen types could be identified to the species level, par-

titularly the dominant forest trees. Unfortunately this appears to be difficult, if not impossible, for a few common genera (oaks, pines, birches). However, apparently there are some significant pollen-size differences among the eastern species of pine (e.g., Whitehead, 1964) as well as sculpturing differences which distinguish white pine (e.g., McAndrews et al., 1973). Thus, I have attempted to determine which species of pine have contributed pollen to the Berry Pond profile (Fig. 4). Size-frequency curves have been constructed from each of the levels studied and the proportion of each sculptural type noted within the

H -J

%

.4 0

CII b

.

‘\ ,I ‘4’

P 0

‘2 4

0

LIQUIDAMBAR

A b

___-J.,- - _____-- -.--------I’ P g ELAEAGNUS C&MJTA~A

P, 0

0 ‘VI

b

l ./

---__ _ ,

-

LlRlObENDRON

N b

.*-

6 b

(METERS)

POLLEN

ZONES

STRATIGRAPHY

DEPTH

FIBROUS GYTTJA

i SYTTJA

/ OTTED

CURVES=

5X

.-.::,.. $j$. CLAY El

q;A;

TILL

EXAGGERATION FIG.

5. Percentage pollen diagrm

ISHRUB

POLLEN

HERB I

I for Berry Pond.

3 POLLEN : i I ----

VEGETATION

HISTORY

TABLE POLLEN

DATA (PERCENTAGES)

OF

343

BERKSHIRES

4 FROM

RADIOCARBON

CORE

Depth

Cm)

Picea

Pinus

Tsuga

1.49 1.59 2.49 2.58 3.49 3.58 4.47 4.49 4.58 5.49 5.58 6.45 6.54 7.15 7.24 7.49 7.61

2.45 3.04 0.40 0.10 0.00 0.10 0.10 0.00 0.10 0.20 0.00 0.60 1.30 30.41 38.50 18.45 12.10

4.45 6.21 8.94 11.40 12.05 8.75 5.10 4.50 5.50 6.50 4.65 16.30 20.50 26.60 22.35 29.15 32.65

12.10 13.01 3.45 4.15 3.85 4.65 6.02 14.30 16.50 19.45 23.70 17.45 11.51 1.05 0.00 0.00 0.00

Bet&a 19.01 23.02 20.10 19.45 23.50 19.65 23.20 22.35 18.40 17.15 18.40 10.50 9.35 9.45 3.45 1.25 0.85

Fagus

Quercus

Castanea

15.60 17.01 14.00 12.36 13.75 15.60 14.45 13.15 11.45 10.40 12.35 4.50 2.65 0.15 0.00 0.00 0.00

17.95 23.05 28.70 26.23 28.30 29.45 27.60 23.75 22.40 24.50 21.35 28.35 29.30 4.50 7.45 5.65 4.75

6.20 4.40 0.60 1.05 0.10 0.00 0.00 0.15 0.00 0.00 0.15 0.00 0.00 0.00 0.00 0.00 0.00

curve by cross-hatching. The pine-influx curve in this figure is slightly different from the pine curve in Figure 8. Figure 4 was drafted before radiocarbon dates were available; hence sedimentation rate was based on assumed ages for pollen-zone boundaries. As is evident, the size-frequency curve from the lower portion of the core (6.60 m) is essentially unimodal with the mode at about 34 pm. The sculptural type is “non-Pinus strobus.“ This suggests that the pines contributing pollen were almost exclusively jack or red pines. The size-frequency curves slightly higher in the profile (6.45 m, 6.30 m) become increasingly bimodal (larger mode at about 42-43 pm) with the bulk of the larger grains of the “Pinus strobus” type. Thus, as time progressed, not only was more pine pollen sedimented into the lake per unit time, but also the amount of white pine pollen contributed increased sharply. From the peak of the “pine period” (6.22 m), the curve is essentially unimodal at the larger size mode with the bulk of the pollen of the white pine type. It is evident, however, that a few larger grains of the nonPinus strobes type were deposited. Thus the dominant pine during the pine zone ap-

Alms

Cyperaceae

2.00 1.20 1.35 0.96 0.50 1.10 1.00 0.50 1.05 0.50 0.65 1.15 2.45 12.45 7.95 6.50 4.65

1.00 2.45 0.00 0.65 0.25 0.55 0.34 0.75 1.25 0.50 1.30 0.85 1.25 5.65 7.55 17.50 32.65

pears to have been white pine, although some pitch pine and jack and/or red pine pollen was also sedimented. Immediately after the “pine zone”(5.70 m) the curve remains essentially unimodal at the larger size, with much white pine pollen represented. However, evidently some pitch pine and jack and/or red pine types were also deposited. In the middle of the postglacial there is a subtle pine maximum (Figs. 5 and 6). Data from this maximum (3.20 and 2.71 m) indicate that most of the pollen grains sedimented were large and that approximately half of them were of the “non-P. strobus” type. Thus pitch pine evidently contributed as much pollen to the sediments as white pine during this time interval. Some jack and/or red pine was also recorded. THE POLLEN

DIAGRAM

The percentage pollen data are presented in Figure 5, selected accumulation rate data in Figures 7 and 8. The diagram is similar to many other diagrams from the Northeast (e.g., Davis 1958, 1965, 1967; Leopold 1956; Ogden 1959; Deevey 1939; Whitehead and Bentley 1963) and can be divided into

344

--.,

LJVNAL”

.

r

r.

-

K.

6

7"',,,,,,,, 12345676 CLUSTERING

PASSES

FIG. 6. Pollen zones. Stratigraphic column shows zones based on changes in major pollen types. Clustering program is E. J. Cushing’s OPTAGG 1, a modification of Orloci (1967).

pollen assemblage zones for ease of discussion. Pollen assemblage zones have been delineated in two ways: (1) by comparison with other New England diagrams utilizing major changes in the dominant pollen

I

2

X IO‘+GRAINS/

FIG.

Pond.

7. Total

pollen

4

3 CM’/YR

accumulation

rate

for

Berry

../...

*..*,r..

rx

types. and (2) by using a clustering program (OPTAGG 1 provided by E. J. Cushing) that represents Cushing’s modification of Orloci’s (1967) agglomerative method for the classification of plant communities. In general, there is reasonable agreement between the two approaches. (Fig. 6). Modern matches for the fossil spectra have also been sought in two ways: ( 1) by comparison with isopollen lines for the major pollen types derived from the work of Davis and Webb (1975) and Webb and McAndrews (1975), and also using data included in Davis (1967) and Ogden ( 1969); (2) a data matrix of 919 modern pollen assemblages(provided by T. Webb and based on the data presented in Davis and Webb (1975) and Webb and McAndrews ( 1975)) was used and a modification of Orloci’s (1967) agglomerative method utilized to calculate absolute distance (II) between the fossil spectrum and all samples in the data matrix. NAP-Pine assemblage zone. This assemblage zone is present from the base of the profile to about 6.70 m. The upper boundary is placed at about 13,000 yr, based primarily on the rapid changes in sedge and spruce percentages. The clustering program (Fig. 6) suggests that the zone boundary should be placed slightly higher (6.61 m) at 12,100 yr. The zone is characterized by high percentages of nonarboreal pollen (up to 46% NAP of which the bulk is Cyperaceae (up to 36%)) and pine. Size-frequency data (Fig. 4) indicate that the bulk of the pine pollen is that of jack and/or red pine. This zone is the equivalent of the “herb zone” or “T” zone described from the late glacial of a number of New England diagrams. Although pine percentages are high, the accumulation rate data (Figs. 7 and 8) clearly show that this is a statistical artifact. Total pollen sedimentation is very low suggesting an essentially treeless vegetation with pine pollen being blown in from forested regions some distance away. Total pollen accumulation rate appears to be approximately 200 grains/

7

6

5

4

3

2

I

1

0

4

4

6

16

4

8

YR

4

8. Accumulation-rate

GRAINS/CM’/

FIG.

X IO’

I2

4

6

diagram

4

12

for Berry

2

I

Pond.

I

Note

2

that only

I I

selected

I

taxa

I

have

I

been

2

plotted.

I

I

I

I

2

7

346

DONALD

R. WHITEHEAD

cm”/yr (based on extrapolation of sediment accumulation rates based on 14C dates slightly higher in the core). There are no close analogs among the available modern pollen spectra, although there are obvious similarities to samples from areas of tundra and forest -tundra (Davis, 1967; Lichti-Federovich and Ritchie, 1968; Davis and Webb, 1975; Webb and McAndrews, 1975). The high sedge percentages are comparable to many spectra from modern tundra, both east and west of Hudson Bay, but the pine percentages are considerably higher. In addition, virtually all modern tundra samples have higher birch and alder percentages than the Berry Pond samples. The agglomerative approach suggests that the best match is to be found in an area of forest-tundra at 58”48’ N Lat., 94”OO’ W Long. (D = 14.4). However, the sprucepine pollen ratios from the herb zone (about 0.50) are unlike those from forest tundra (generally > 1 .O). They match those that can be derived from areas of tundra some 60-200 km north of patchy forest-tundra (calculations from data of LichtiFederovich and Ritchie, 1968; Davis and Webb, 1975; Webb and McAndrews, 1975; Davis, 1967). The pollen sedimentation rates also seem to be indicative of tundra as they are comparable to those derived from areas of rock-desert, sedge-moss tundra, and dwarf shrub tundra in arctic and subarctic Canada (Ritchie and LichtiFederovich, 1967; Birks, 1973). The lack of exact matches could indicate that the vegetation which produced the herb zone was unlike any modern tundra community, but it must be remembered that our knowledge of patterns of pollen deposition in the modern tundra is very incomplete. The higher pine percentages in the Berry Pond samples probably indicate that forest was closer than in the case of the modern tundra samples. There are a number of excellent matches from late-glacial spectra from southern Connecticut and central Massachusetts

(Leopold, 1956; Davis. 1958. 1969). Sedge and pine percentages are comparable to those from herb zone spectra in southern Connecticut and central Massachusetts. Spruce assemblage zonk. This zone extends from 6.70 to 6.30 m; this is equivalent to a time span from about 13,000 to 9600 yr. It is characterized by a maximum of spruce (between 20 and 50%), a minimum of pine (down to IO%), and maxima for alder (lo%), Juniperus type, larch, fir. oak, and hornbeam. The lower zone boundary is defined primarily by rapidly decreasing percentages of sedge and comparable increases for spruce pollen. The upper zone boundary is delimited by the point of most rapid decline for spruce and increase for pine and birch pollen. Use of the clustering program suggeststhe lower boundary lies at 6.61 m (12,100 yr). Inspection of Figure 6 also indicates that the upper boundary of this zone could be placed lower (6.40 m, 10,200 yr). Overall pollen sedimentation rate increases smoothly from 400 grains/cm”/yr at the base of the zone to 16,000 at the top. The apparent minimum for pine is an artifact of the sharp influx maximum for spruce pollen (maximum rate of 39001 cm”/yr in the middle of the zone), as there is, in fact, a smooth increase in pine sedimentation from 90/cm2/yr at the base of the zone to 5000 at the top. The pine size-frequency curve (Fig. 4) from this zone is becoming bimodal, although the majority of grains are still small and of the “non-Pirzus strobus” type (thus jack andlor red pine). Comparison of spruce zone spectra with isopollen maps (Davis and Webb, 1975) suggests that modern samples in an area of boreal forest and forest-tundra just southeast of James Bay (50” N Lat. and between 75” and 80” W Long.) might provide the best matches. Percentages for spruce. fir, birch, larch, alder, and pine compare well: however, oak percentages are higher in the fossil spectra. The statistical approach provides similar

VEGETATION

HISTORY

results. The best match (D = 15.2) is with a sample from an area of forest-tundra 51”27’ N Lat., 78”32’ W Long. The next best comparison (D = 16.9) is with an assemblage from similar vegetation (53”08’ N Lat., 70”57’ W Long.). The spruce zone spectra are extremely similar to spruce zone (A zone) spectra from elsewhere in New England (Davis, 1958, 1969; Leopold, 1956). Although subzones have been delineated in the spruce zone elsewhere (e.g., Leopold, 1956; Davis, 1958, 1965), no attempt has been made to make such subdivisions from the Berry Pond profile, as the zone is too compressed. However, it is evident that oak and hornbeam are more common in the lower half of the zone and that alder, birch, fir, and larch are more abundant in the upper half. Pine-birch assemblage zone. The pine zone (B zone in New England diagrams) extends from 6.30 to 6.00 m; this is the equivalent of a time span from about 9600 to 8600 yr. The zone is characterized by high percentages of pine pollen (up to 42%) and a distinct maximum for birch (22%). The lower zone boundary is delineated by rapidly decreasing percentages of spruce and rising pine. The upper zone boundary is defined by decreasing pine and rapidly increasing hemlock. The zone boundaries are confirmed by the clutering program (Fig. 6), although the lower boundary could be shifted downward by about 10 cm (to 10,200 yr) and the upper boundary upward by a comparable amount (to 8250 yr). Oak increases markedly and reaches a maximum in the upper half of the zone. The pine data show (Fig. 4) that the earliest portion of the pine zone was characterized by a bimodal curve dominated by smaller grain types (jack and/or red pine), but with clearly increasing white pine in the larger size mode. By the “height” of the pine zone the size-frequency curve has become essentially unimodal at larger sizes and is obviously dominated by white pine type. A few “non-

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strobus” large grains are present suggesting the presence of pitch pine (Pinus rigida) in the region. Pollen accumulation rates range from 16,000 to 34,000 grains/ cm?yr within the zone. Pine-influx rate climbs smoothly from about 5000/cm2/yr at the lower zone boundary to a maximum of 12,300/cm2/yr, and then declines to about 5000 at the upper zone boundary. Birch behaves in a similar fashion reaching a peak influx of 4400 grains/cm2/yr. There is a sharp maximum for oak (9700/cm2/yr) and influx maxima for hornbeam, ash, hazel, sugar, maple, and elm (Fig. 7). Visual comparison of the pine-birch zone spectra with modern assemblage data (Davis, 1967; Davis and Webb, 1975; Webb and McAndrews, 1975) suggests that the closest matches might be found in an area of mixed coniferous and deciduous forests just northeast of Lake Huron at about 47” N Lat. and between 80” and 75” W Long. The agglomerative technique suggests that the closest matches occur in areas of mixed conifer- hardwood forest at 44”41’ N Lat., 88”41’ W Long. (D = 9.8), and 44”41’ N Lat., 83”24’ W Long. (D = 12.1). The pine-birch assemblage from Berry Pond is extremely similar to analogous “B zone” spectra from Vermont (Davis, 1965: Whitehead and Bentley, 1963), central Massachusetts (Davis, 1958), and Connecticut (Leopold, 1956; Davis, 1969). As this zone is compressed, no attempt has been made to differentiate subzones, although one could establish a lower pine alder subzone and an upper pine-oakhemlock subzone. Oak-birch -beech -hemlock zone. The remainder of the profile, from 6.00 m to the surface, can be characterized as an oak-birch-beech-hemlock assemblage zone. This is equivalent to the “C” pollen zones of previous workers. For the Berry Pond area it spans the time interval from 8600 (or 8250) ‘“C yr ago until the present. The zone is generally characterized by high percentages of pollen of birch (ca. 20%), oak (20-30%), beech (lo-20%). and hemPinus

348

DONALD

R.

lock (3-22%). Pollen of other deciduous taxa is well represented in contrast to the lower zones. Pine percentages are usually low with a maximum of only 11% in the middle of the zone. Pollen of other conifers is uncommon. The pollen sedimentation rate is variable, but generally above 20,000 grains/cmYyr except for subzone C3 where values are lower. Four reasonably distinct subzones can be differentiated within this pollen zone: (1) a hemlock subzone (equivalent to pollen zone Cl of previous workers); (2) an oak -pine-hickory subzone (equivalent to pollen zone C2); (3) a chestnut-spruce subzone (equivalent to pollen zone C3); and (4) a ragweed-grass-dock subzone (the uppermost portion of C3, a function of European land clearance). Hemlock subzone. This distinctive subzone extends from the boundary of the pine-birch and oak-birch-beech-hemlock zones (6.00 m) to about 4.00 m in the profile. This is equivalent to a time interval of from 8600 (or 8250) to about 4800 14C yr. The upper boundary of the zone is defined by a sharp decline in hemlock pollen percentages (from 16 to 5% between two sample points). This decline is real and not a statistical artifact, as shown by the accumulation rate data. Hemlock influx declines from 4800 to a low of 700 grains/ cm2/yr. Given the information on rates of sediment accumulation in the profile, this decline took place in less than 260 yr. Data from Mirror Lake in north-central New Hampshire (Likens and Davis, 1974) indicate that the decline took place in less than 150 yr. The clustering program (Fig. 6) suggests that the zone boundary could be placed higher in the section (at about 3.8 m; 4200 yr). However, it seems more reasonable to base the boundary on hemlock rather than postdecline successional changes. There appear to be no perfect matches among available modern spectra. Use of the isopollen maps in Davis and Webb (1975) (particularly the maps for hemlock, birch,

WHITEHEAD

beech, oak, and pine) suggest that the closest approximations should be found in an area of northern hardwood forest and transitional forest just east and southeast of Lake Ontario. The statistical program confirms this, indicating that the most similar modern assemblage (D = 18.6) derives from an area of northern hardwoods forest at 42”47’ N Lat., 76”08’ W Long. Oak -pine -hickory subzone. This subzone extends from 4.00 to 1.60 m, thus spanning the time interval from 4800 to 1600 ‘C yr. The lower boundary of this subzone is marked by the hemlock decline, the upper boundary by increasing percentages (and influxes) of spruce and chestnut. The clustering program (Fig. 6) seems to suggest that the boundary should be placed higher, but I prefer to base it on the coordinated changes in spruce and chestnut. The subzone is characterized by the distinctive minimum of hemlock, slightly higher percentages of oak and hickory, and a slight maximum of pine. This is corroborated in a general way by the influx data. The pine maximum is interesting as size-frequency and morphological data indicate that virtually all of the grains are large (thus suggesting that little jack and/or red pine was present) and about half of them are of the non-Pinus strobus type. This suggests that pitch pine was more abundant in the region during this time interval. The best match for this assemblage derives from an area of Appalachian oak forest at 39”34’ N Lat., 79”16’ W Long. (D = 16.1) (Davis and Webb, 1975). Modern spectra from this area differ in having lower percentages of beech. Pollen spectra from pollen zone C2 from southern New England, Massachusetts, and Vermont are similar (Davis, 1958, 1965, 1969; Leopold, 1956; Whitehead and Bentley, 1963). Chestnut -spruce subzone. This subzone occurs from 1.60 to 0.40 m, the equivalent of 1600 to about 200 14C yr. It is distinguished by slight maxima for spruce and chestnut pollen, decreases for pine and

VEGETATION

HISTORY

beech, and a slight increase for hemlock pollen. The hemlock increase is not corroborated by the influx data. However, the reliability of the influx data from this zone is questionable, as 14C control is less secure. Ragweed -grass -dock subzone. This assemblage subzone, a function of land clearance by European settlers, occurs in the upper 40 cm of the profile. The lower boundary is delineated by the characteristic rise of ragweed pollen and other indicators of disturbed environments. In the uppermost levels of this subzone there is a sharp increase in pine pollen, undoubtedly a function of land abandonment and “old field” growth of pine in the late 1800s and early 1900s. VEGETATIONAL AND CLIMATIC INFERENCES NAP-Pine assemblage zone.

The radiocarbon dates and pollen data indicate that the sedimentary record from Berry Pond goes back more than 12,700 yr. Extrapolation of the lowest dates and comparison with other profiles from central and southern New England suggest that the oldest spectra may be about 14,000 yr old. This is consistent with geologic data which suggest that ice retreat from the classical Wisconsin terminal moraines began approximately 17,000 yr ago (Borns, 1973; Connally and Sirkin, 1973), and that by 13,000 yr ago the ice margin of Hudson-Champlain Lake was north of Glens Falls, New York (Connally and Sirkin, 1971, 1973). By this time (about 13,000 yr) the ice in eastern New England had retreated from the Kennebunk and Pond Ridge moraines in coastal Maine (Borns, 1973). At the time that the sedimentary record in Berry Pond began to accumulate there were extensive glacial lakes in the Hudson drainage (Lake Albany), the Connecticut Valley (Lake Hitchcock), and in the Berkshire lowlands (Lake Bascom and Lake Housatonic) (Connally and Sirkin, 1973; Schafer and Hartshorn, 1965).

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Although topographic diversity of the Berkshire region is such that a variety of ecologically distinct vegetational types can exist simultaneously, indications are that the entire region was treeless during this portion of the late glacial, as suggested by low pollen accumulation rates, high herb percentages, matches among modern spectra, and spruce-pine ratios. Such an inference is further supported by the data from southern Connecticut, 300 km southeast of Berry Pond, which clearly show that treeless vegetation existed in that region between 14,300 and 12,150 yr ago (Davis, 1969; Leopold, 1956). Davis suggests that the data from Rogers Lake and other sites in southern Connecticut are consistent with a hypothesis placing the tundra/forest boundary some 100 km south. If the border of the ice sheet during this portion of the late glacial lay north of Glens Falls, New York, and St. Johnsbury, Vermont (Connally and Sirkin, 1973; Schafer and Hartshorn, 1965), then apparently there was a zone of tundra nearly 450-500 km wide. However, it has been suggested that the upper time limit for tundra in Connecticut (12,150 yr) may be too young (Davis et al., 1975) which, if true, would argue for a somewhat narrower band of tundra. Studies from the unglaciated region further south show that in the vicinity of Buckle’s Bog on the Allegheny Plateau in Maryland, an area some 700 km southwest of Berry Pond, tundra vegetation existed at least on the uplands during full-glacial and a portion of late-glacial time. Boreal forest did not replace tundra until about 12,700 yr ago (Maxwell and Davis, 1972). The spruce/ pine ratios from Buckle’s Bog suggest that boreal forest occurred within 10 to 25 km of the site. This study and the lowermost spectra from Marsh, Pennsylvania (Martin, 1958), indicate that the late-glacial forest/ tundra boundary lay in the vicinity of southern Pennsylvania. Comparable lateglacial spectra from areas further south indicate the existence of boreal forest in Vir-

350

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ginia and North Carolina (Craig, 1969: Harrison et al., 1965: Whitehead, 1973). Climatic reconstructions for this time interval are difficult, as there are no close matches among the existing modern spectra from tundra regions. However, late-glacial conditions in the Berkshires very likely were more similar to those of present tundra regions of Canada, some 200 to 400 km north of the forest/tundra boundary, than to conditions in the alpine zone of the White Mountains of New Hampshire. Additional pollen-rain investigations in Canada, particularly in tundra regions east of Hudson Bay, may permit more precise reconstructions. Spruce assemblage zone. The succession of spectra within this assemblage zone seems to record a progressive change from tundra to closed boreal forest (LGve, 1970). This is suggested by the general similarity of spectra low in the zone to modern samples close to the forest/tundra boundary and of samples high in the zone to areas of closed boreal forest in Quebec (e.g., Davis, 1967; Lichti-Federovich and Ritchie, 1968; Davis and Webb, 1975; Webb and McAndrews, 1975). Such an interpretation is substantiated by the pollen accumulation rate data (Figs. 7 and 8). The higher pollen influx in the upper half of the zone is initially a function of the peak input of spruce (up to 3900 grains/cm”/yr); later pine contributes to the sharp increase (more than 50001 cm”lyr at the boundary between spruce and pine zones). The spruce/pine pollen ratios are also consistent with the above hypothesis. The ratio is low at the base of the zone (0.81), rises to a sharp peak (between 4.6 and 3.3), then declines gradually to a low of 0.3 at the upper boundary. If one plots the spruce/ pine ratios in the transect of surface samples from James Bay southward (this transect was selected because the fossil spectra match modern assemblages from this region best; Davis, 1967) a similar trend is evident (Fig. 9). The ratio is initially low in regions of forest and tundra close to 52” N Lat..

WHITEHEAD

i

.\

.\

-. .--forest-

52”

-.__

,.cc

. 50”~ w 0 249’~

/ .’

tundra --

l

.

I

boreal

forest

:”

F Yi 40”

~~i-~~~~~~~ ;

47O L 0

~~~

@ mixed coniferous and deciduous forest ~I 2 3 4 SPRUCE/PINE

~~~

5

RATIO

FIG. 9. Spruce/pine ratio vs latitude. This figure has been derived from modern pollen assemblages in a latitudinal transect from James Bay south to the Great Lakes (Davis, 1967).

rises to a peak of between 4.0 and 5.0 in closed boreal forest, then declines smoothly to approximately 0.30 close to the border of mixed coniferous and deciduous forests at 47” N Lat. An analysis of the total data matrix derived from Davis and Webb (1975) and Webb and McAndrews (1975) demonstrates the same general trends. The ratios are highest in forest-tundra and boreal forest (0.8- 15.00) and decrease northward and southward. However, the addition of this range of samples introduces significantly greater variability. Thus there is no indication of any climatic and vegetational oscillation within this portion of the late glacial. All data are consistent with a transition from tundra to open boreal forest between 13,000 and 12,000 yr ago and a progression to more closed boreal forest by 10,500 yr ago. Although I would assume that closed boreal forests developed during this portion of the late glacial, the overall pollen accumulation rates (rather low for forest) and high pine and birch percentages might indicate a more open forest. Elsewhere in New England the spruce zone is divided into subzones. For example, Davis (1969) has differentiated the spruce zone into A-l (transition from herb to spruce zone), A-2-3 (spruce-oak zone),

VEGETATION

HISTORY

and A-4 (spruce-fir zone). As mentioned previously, such a subdivision is difficult for this profile as the zone is so compressed. Closer interval sampling would probably reveal a zonation virtually identical to that detected elsewhere in New England. In summary, it would appear that approximately 13,000 - 12,000 yr the vegetation of the ridge crests of the Berkshires was still tundra, but that patches of forest must have existed. By about 11,500 yr tundra had been replaced by open boreal forest. More closed boreal forest became dominant by 10,500 yr. The sharp spruce pollen decline near the upper boundary of the zone, combined with the maximum for alder and increases for birch and pine imply that the transition to mixed coniferous and deciduous forests may have been quite rapid. It is likely that birches, pine, and particularly alder played successional roles in gaps in the deteriorating spruce forests (Bernabo and Webb, 1977). This would be consistent with roles played by these taxa in many modern boreal forest communities (e.g., Braun, 1950; Rowe, 1959; Reiners et al., 1971). The sequence of vegetational changes inferred for the Berkshires is similar floristically to that suggested for central Massachusetts by Davis (1958). The sequence at Rogers Lake in southern Connecticut is virtually identical. Further south, the base of the spruce-pine zone from Buckle’s Bog on the Allegheny Plateau appears to be 12,700 yr. In northeastern North Carolina and southeastern Virginia, a spruce -pine zone appears to span the time interval from 22,000 to 10,200 yr (Whitehead, 1973; Harrison et al., 1965). Thus, it would appear that sprucedominated boreal forest once occurred over a broad area extending from northern New England to southern Virginia. As one might expect, the lower boundary of the pollen assemblage suggesting boreal forest is progressively older further south. For example, the data from Rockyhock Bay in north-

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eastern North Carolina indicate that while the vegetation in the Berkshires was changing from forest-tundra to closed boreal forest, the vegetation in northern North Carolina was changing from a boreal forest to a deciduous forest containing many species of the modern northern hardwoods forest (Figs. 3 and 4 in Whitehead, 1973). Pine -birch assemblage zone. The changes within this pollen assemblage zone record a gradual change from boreal forests to mixed coniferous and deciduous forests. This is suggested by decreasing percentages and accumulation rates for boreal taxa (spruce, fir, larch) and increasing values for hemlock, oak, ash, hornbeam, sugar maple, and elm. Influx peaks for birch, oak, hornbeam, hazel, ash, sugar maple, and elm indicate the mixed character of the forest. Jack pine (and red pine) and white pine appear to have contributed equally to the pollen rain about 9000 yr ago, but a few hundred years later, virtually all of the pollen sedimented was derived from white pine. Some pitch pines were also present. As mentioned previously, there are reasonable matches for these fossil spectra in a broad area of mixed coniferous and deciduous forests in the upper Great Lakes region (Davis, 1967; Davis and Webb, 1975; Webb and McAndrews, 1975). Therefore the vegetation of the Berkshires during this early portion of the postglacial probably was similar to that presently existing in the relevant portions of Wisconsin, Ontario, and Quebec. Doubtless the vegetation was patchy, reflecting the topographic diversity of the area. Thus the climate of western Massachusetts during the early postglacial may have been more continental than at present; most probably it was both cooler and drier than now. This is consistent with other interpretations of the same assemblage from elsewhere in New England (e.g., Davis, 1967). The area1 extent of the vegetation which produced the “pine zone” was obviously

352

DONALD

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WHITEHEAD

great. All profiles from New England re- Pond are virtually identical. This is not surcord this zone, as well as profiles from prising, for the two sites are separated by only 50 km. The vegetation of the BerkNova Scotia (Livingstone and Livingstone, 1958). A simiIar zone is detectable at shires also appears to have been interBuckle’s Bog on the Allegheny Plateau mediate between that of southern Connectwhere it is older (Maxwell and Davis, 1973). icut and that of northern Vermont. The Also the zone occurs at Marsh, Pennsylcomparable subzone from Rogers Lake has vania (Martin, 1958). In areas further south significantly higher percentages of oak and the transition is different, as boreal lower percentages of hemlock, birch, and spruce -pine forests were apparently re- beech (Davis, 1969), whereas that from placed directly by deciduous forests with Brownington Pond has much less oak and considerably higher percentages of birch. many components of the present northern hardwoods forests (Craig, 1969; This was probably a function of the climatic Whitehead, 1967, 1972, 1973; Frey 1953; gradient that would be evident over some Harrison et al., 1965; Watts, 1970). 420 km from Long Island Sound to northern The “deciduous” pollen zones. The re- Vermont. The three areas in question lie in mainder of the profile records the gradual different vegetational zones today (e.g., development of the present northern Braun, 1950). hardwoods forests of the Berkshires: this Davis (1969) has reported an increase in progression was characterized by a number ragweed pollen in the lower portion of this of significant changes in forest composisubzone at Rogers Lake and has suggested tion, some of which may have been oc- that it might be indicative of drier condicasioned by postglacial climatic changes, tions which resulted in the creation of some by delayed immigration of important more-open forests. This ragweed pollen trees, and others by recent disturbances maximum correlates with the period of brought about by European settlers. Tradieastward expansion of the prairie peninsula tionally the tripartite division of the “C in the upper Midwest (Wright, 1968). Alzones” of New England diagrams has been though there is no evidence of a ragweed given a climatic interpretation (e.g., Deev- maximum in the Berry Pond profile, there is ey, 1939; Davis, 1965, 1969), although it a slight decline in the pollen sedimentation is becoming apparent that there are other rate for most types of tree pollen. This same explanations for the postglacial changes. general decline was noted by Davis at RogFor the period from 8600 (8250?) to 4800 ers Lake. Closer interval sampling of the yr (hemlock subzone) the vegetation was Berry Pond core would be necessary to probably rather similar to the northern suggest unequivocally that an early posthardwoods forests that presently occur in glacial ragweed maximum is not present in areas of Ontario and New York State just western Massachusetts. east of Lake Ontario. Data of pollen repreThe upper boundary of the hemlock subsentation (Davis and Goodlett, 1960: Davis. zone is sharply delineated by the fall in 1965) can be used to suggest that the domihemlock. This occurred approximately nant forest trees of the Berkshires were 4800 14C yr B.P., and was a dramatic event hemlock, sugar maple, and beech. Oak and taking place within a very short period of birch were also common along with a time. The hemlock decline is a wellnumber of other taxa (hornbeam, hazel, documented event, as it is detectable in ash, elm, etc). virtually every pollen diagram from the It is interesting to compare data for this Northeast. Traditionally this event has subzone from other places in New England. been ascribed to the hypsithermal during The pollen profiles from the Pownal Bog which a warming andlor drying trend was (Whitehead and Bentley, 1963) and Berry thought to have stimulated the decline in

VEGETATION

HISTORY

hemlock. However, as M. B. Davis (personal communication, 1978; Likens and Davis, 1974) has pointed out, the fact that the decline was so abrupt (accomplished within 150 yr at Mirror Lake in northern New Hampshire) and that only hemlock appears to have been affected, argues instead for a biological explanation; perhaps it reflects a disease or insect that attacked hemlocks specifically. At any rate, for the Berry Pond area, a significant vegetational change apparently took place within a short time. Hemlock, once the dominant tree, became relatively uncommon. This apparently generated successional processes in which hemlock was replaced by birch, oak, beech, ash, and red maple. There is evidence that hazel and hornbeam increased also. Closer-interval sampling in the future will permit an analysis of the precise successional changes and a reconstruction of the rates at which both the hemlock decline and the successional replacements took place. There is an apparent transitory increase in overall pollen influx associated with the hemlock decline (Fig. 7). This could be explained as (1) an artifact of preparation techniques, (2) a consequence of a short-term change in matrix accumulation not detected by the radiocarbon dating, (3) the elimination of a dense hemlock stand bordering the pond (which would temporarily decrease impaction and capture of pollen being transported beneath the canopy and thus increase input to the pond (Tauber, 1967)), or (4) the replacement of hemlock (a species characterized by moderate pollen production) by species (birch, oak, etc.) with far higher pollen productivities. Although there is no completely objective way of determining which explanation is most likely, I feel that the increased influx is real, and most probably a function of an interaction of (3) and (4) above. The analyses have indicated that there were interesting watershed and pond changes associated with the vegetational change. Evidence was found of a marked

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increase in the productivity of the pond during this time interval and a sharp increase in the rate of delivery of leaf fragments of deciduous trees to the pond (Whitehead et al., 1973). I feel that there was an increase both in runoff and in the rate of nutrient delivery to the pond. The runoff could be occasioned by two factors: (1) the initial openings in the forest brought about by the apparent hemlock die-off (which would lead to an immediate loss of transpirational surface), and (2) the change in forest character from primarily coniferous to primarily deciduous (spring runoff is more compact and more intense in a deciduous forest (W. A. Reiners, personal communication, 1978). The nutrient input to the pond could have been in the form of leaf fragments (which then decomposed to release nutrients) and other particles and dissolved materials (partly a function of increased runoff, partly due to decomposition of hemlock litter). The pollen subzone above the hemlock fall (oak-pine-hickory; or C2) is generally thought to indicate warmer and drier conditions during the mid-postglacial. This was formerly defined as the hypsithermal interval (Deevey and Flint, 1957; Denton and Karlen, 1973). The evidence of this interval from Berry Pond is less secure, especially if we must ascribe a biological rather than a climatic interpretation to the hemlock fall. The maximum of oak (and the slight increase in hickory) would then become largely successional rather than climatic. However, a slight maximum of pine occurs between 4100 and 2500 yr ago and about half of the pine pollen sedimented was derived from pitch pines. At present pitch pines are not common in the Berkshires and are isolated on dry, exposed ridges. This latter evidence is certainly compatible with warmer and/or drier conditions. It is interesting that the best fit among modern assemblages is in areas south of the Berkshires (Davis and Webb, 1975), but this could be coincidental, especially if the hemlock fall was not climatically induced.

354

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The upper boundary of the oakpine-hickory subzone is defined by an increase in the influx rates for spruce and chestnut and a slight increase in the percentage of hemlock pollen. The sustained higher percentages of hemlock pollen are apparently statistical artifacts, as only a temporary increase is evident in the accumulation rate diagram. However, radiocarbon control of matrix accumulation is inadequate in these upper levels. Whether a climatic deterioration is responsible for these changes is difficult to determine. The rise in chestnut pollen has usually been interpreted as a function of delayed immigration of chestnut populations from “refuges” to the south (Davis, 1976). The increase of spruce pollen is easier to ascribe to climatic changes, but spruce does play an early successional role in disturbed sites at higher elevations in the Berkshires (Egler, 1940). A climatic interpretation is supported by the occurrence of larch and fir pollen. The increases for sedge and alder pollen and for fern spores are probably unrelated to these vegetational and/or climatic changes, but instead a function of a developing bog mat in the southeastern arm of the pond where these plants are abundant. The sharp increase for Isoetes microspores is probably due to decreasing water depth which permitted sufficient light penetration for growth of quillworts (Whitehead et al.. 1973). The changes in the uppermost portion of the profile which permit the delineation of the ragweed-grass-dock subzone are obviously a function of land clearance practices. The increases for pollen of ragweed, chenopods, grasses, composites, dock, and the presence of pollen of Plantago lanceolata are suggestive of a sharp increase in the amount of disturbed land available to be colonized by weedy species. The increase in pine pollen at the surface is attributable to land abandonment and the rapid colonir zation of such land by white pine. The decline of chestnut pollen in the uppermost level is undoubtedly due to the chestnut

WHITEHEAD

blight. Closer interval sampling of the upper 0.5 m of the core would probably permit some interesting reconstructions of successional sequences and rates of succession. A comparison of modern vegetation data (Tables 1 and 2) with the surface pollen spectra indicates that many extremely common weedy and herbaceous taxa leave virtually no pollen record. In fact the shrub and herb strata at Berry Pond are virtually unrecorded in the pollen rain. POSTGLACIAL

CHANGES INFLUX

IN POLLEN

Davis et al. (1975) have compared overall influx data from Moulton Pond and Rogers Lake (Davis, 1969). The generalized pattern of influx at Berry Pond is strikingly similar (Fig. 7). There is a pronounced maximum associated with the pine-birch assemblage zone and the early portion of the overlying hemlock subzone (influx values up to 3.0-3.7 x lo4 cn?yr-‘) and another sharp increase in influx at 4800 yr B.P. in the lower portion of the oak-pine-hickory subzone (up to 3.6 x lo4 cm-2yr-‘). Above the latter maximum there is an oscillating decline up to the present. It has been suggested that the mid- and late-postglacial influx changes cannot be explained satisfactorily in terms of vegetational changes, and hence are likely to be the result of changes in sedimentation patterns (Davis et al., 1975). I disagree with part of the assertion. As mentioned previously, the mid-postglacial peak in influx is associated with the decline of hemlock and the replacement of hemlock by birch, oak, and beech. Thus a moderate pollen producer was replaced by at least some taxa (birch and oak) characterized by high pollen productivities. Furthermore, it seems likely that hemlock was most abundant close to the lake; hence, its decline would result in the elimination of a screen (fine hemlock needles and branches) effective in capturing a fraction of the pollen transported through the trunk space of the forest (Tauber, 1967). I agree that the steady decline in apparent

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influx from this point (4800 yr) to the present cannot be explained in terms of vegetation events. Hence, it does seem likely that changes in sediment focusing caused by steady changes in basin morphometry were responsible for this decline (e.g., Lehman, 1975). This interpretation is confirmed by cladoceran-influx data (e.g., Whitehead and Crisman, 1976) which show a general decline (with superimposed maxima) from the mid-postglacial to the present. There is an influx maximum associated with the hemlock decline, but it is much less significant than that in pollen and can be interpreted more readily as representing a real increase in influx (due to increased primary production, rather than as a function of changing sedimentation rate). SUMMARY

The pollen data from Berry Pond indicate that the entire region was treeless (probably tundra) from deglaciation to between 13,000 and 12,000 yr ago. This is suggested both by high NAP percentages, comparison with modern and fossil spectra, and extremely low pollen sedimentation rates. Between 12,000 and 9600 (or 10,200?) yr ago the vegetation gradually changed from tundra to open boreal woodland to closed boreal forest. During this time interval spruce percentages and sedimentation rates increased sharply, NAP declined, and the assemblages became reasonably similar to modern ones from boreal forests. About 9600 (or 10,200?) to 8600 yr ago the boreal forest was replaced by forest similar to the modern mixed coniferous and deciduous forest. This portion of time is characterized by peak percentages and high sedimentation rates for pine pollen (most of which is pollen of white pine). About 8600 yr ago these forests were replaced by a “northern hardwoods” complex in which hemlock, beech, sugar maple, birches, and oaks were the dominant trees. These forests may have been similar to modern ones in the area just southeast of Lake Ontario. Approximately 4800 yr ago there was a very sharp decline in hemlock. This was quite possibly a

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biological rather than a climatic event. Within a very short time span (<250 yr) hemlock went from the dominant tree of the vegetation to a relatively uncommon one. Hemlock was replaced in the vegetation by birch, oak, beech, ash, and red maple. Some 1600 yr ago there was a slight increase in spruce (and larch) and chestnut began to expand. The latter species was apparently a late immigrant to the region. In the uppermost levels of the core European land clearance and subsequent land abandonment are recorded. ACKNOWLEDGMENTS The initial phases of this project were carried out while I was teaching at Williams College, Williamstown. Massachusetts. The preliminary pollen analyses were run by John Secrist and Kenneth Kurtz and incorporated in undergraduate honors theses. I am grateful to them for this work and for much assistance in the field. William T. Fox assisted in obtaining the radiocarbon core. Haydon Rochester, Jr., Mark C. Sheehan, Steven W. Rissing. and Thomas L. Crisman participated in many of the subsequent coring forays. I am indebted to Crisman and members of an advanced field biology class from Indiana University for help with limnological work and vegetational surveys in the Berry Pond area. I am particularly grateful to the staff of the Pittsfield State Forest for permission to work in the area and for advice on weather and pond conditions. This paper was completed while I was on sabbatical leave at Washington.State University. In this respect I am indebted to the Anthropology Department of Washington State University for providing space, facilities, and services and to Peter J. Mehringer, Jr., for his efforts in making it possible and for many stimulating discussions. Kenneth McEIvain provided invaluable help with computer programs and statistical procedures. Thomas L. Crisman, Haydon’Rochester, Jr., Owen Davis, and Peter J. Mehringer, Jr. have read the manuscript and provided invaluable commentary.

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